Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0005829 cytosol	IBA GO_REF:0000033	ACCEPT	Summary: Phylogenetic inference of cytosol localization is well-supported. IRSp53 is detected throughout the cytoplasm in the absence of specific binding partners and shows cytosolic distribution when not membrane-recruited. Reason: Consistent with UniProt subcellular location data and IDA evidence from HPA immunofluorescence (GO_REF:0000052). The protein shuttles between cytosol and membrane in a curvature/GTPase-dependent manner.
GO:0005654 nucleoplasm	IBA GO_REF:0000033	KEEP AS NON CORE	Summary: Nucleoplasm localization is questionable for IRSp53. The protein is primarily a cytoplasmic/membrane-associated adaptor with no well-established nuclear function. Reason: While IBA annotation is present, IRSp53's core functions are at the plasma membrane and cytoplasm. Nuclear localization is not supported by deep research or UniProt annotations. May represent low-level detection or isoform-specific behavior.
GO:0030838 positive regulation of actin filament polymerization	IBA GO_REF:0000033	ACCEPT	Summary: IRSp53 promotes actin polymerization by recruiting nucleation-promoting factors via its SH3 domain to sites of membrane curvature. This is a well-established core function. Reason: Deep research confirms IRSp53 recruits WAVE/Arp2/3 and triggers actin polymerization bursts at sites of membrane curvature. The SH3 domain binds proline-rich regions of actin effectors. Supporting Evidence: DOI:10.7554/eLife.72316 IRSp53 recognizes ~100 nm PM evaginations produced by stretch/compression, triggering a rapid Rac1/Arp2/3 actin polymerization burst
GO:0051017 actin filament bundle assembly	IBA GO_REF:0000033	ACCEPT	Summary: IRSp53's I-BAR domain can directly bundle actin filaments, contributing to filopodial structure. This is a core molecular function. Reason: UniProt function notes that the isolated IMD domain can induce actin bundling and filopodia formation. Participates in actin bundling when associated with EPS8. Supporting Evidence: PMID:14752106 A novel actin bundling/filopodium-forming domain conserved in insulin receptor tyrosine kinase substrate p53
GO:0051764 actin crosslink formation	IBA GO_REF:0000033	ACCEPT	Summary: Actin crosslink formation is closely related to bundling activity. IRSp53-EPS8 complex promotes actin bundling and crosslinking. Reason: Supported by experimental evidence showing IRSp53 works with EPS8 in synergistic actin bundling activity that promotes filopodial protrusions. Supporting Evidence: PMID:17115031 Regulation of cell shape by Cdc42 is mediated by the synergic actin-bundling activity of the Eps8-IRSp53 complex
GO:0001726 ruffle	IEA GO_REF:0000044	ACCEPT	Summary: Ruffle localization is well-supported. IRSp53 is detected close to membrane ruffles and is essential for Rac1-mediated membrane ruffling. Reason: UniProt subcellular location explicitly states detection in filopodia and close to membrane ruffles. IRSp53 is necessary for RAC1-mediated membrane ruffling. Supporting Evidence: PMID:11130076 IRSp53 is an essential intermediate between Rac and WAVE in the regulation of membrane ruffling
GO:0005737 cytoplasm	IEA GO_REF:0000044	ACCEPT	Summary: Cytoplasm localization is well-established and broader than cytosol. Reason: Consistent with cytosol annotation and UniProt subcellular location. IRSp53 localizes throughout the cytoplasm and at membrane-associated structures.
GO:0005856 cytoskeleton	IEA GO_REF:0000044	ACCEPT	Summary: Cytoskeleton localization supported by IDA evidence showing colocalization with actin cytoskeleton. Reason: IRSp53 colocalizes with actin cytoskeleton (IDA from PMID:19366662). This is expected given its role as an actin-membrane adaptor.
GO:0007009 plasma membrane organization	IEA GO_REF:0000002	ACCEPT	Summary: IRSp53 is directly involved in plasma membrane organization through its I-BAR domain which senses and induces membrane curvature. Reason: Core function. Deep research shows IRSp53 plays a central role in membrane shape homeostasis at the nanoscale, detecting curvature and coordinating membrane remodeling. Supporting Evidence: DOI:10.7554/eLife.72316 A mechanosensing mechanism controls plasma membrane shape homeostasis at the nanoscale
GO:0008093 cytoskeletal anchor activity	IEA GO_REF:0000002	ACCEPT	Summary: IRSp53 anchors actin cytoskeleton to the plasma membrane through its I-BAR domain. This is a core molecular function. Reason: The I-BAR domain binds membranes while the SH3 domain recruits actin effectors, creating a molecular bridge. Supported by TAS evidence from PMID:10343108. Supporting Evidence: PMID:10343108 Identification of BAIAP2 (BAI-associated protein 2), a novel human homologue of hamster IRSp53, whose SH3 domain interacts with the cytoplasmic domain of BAI1
GO:0016020 membrane	IEA GO_REF:0000044	ACCEPT	Summary: Membrane localization is well-established but generic. Reason: UniProt indicates peripheral membrane protein. More specific term (plasma membrane) is also annotated with better evidence.
GO:0030175 filopodium	IEA GO_REF:0000044	ACCEPT	Summary: Filopodium localization is a core aspect of IRSp53 function. The protein is essential for CDC42-mediated filopodia formation. Reason: UniProt explicitly lists filopodium as a subcellular location. IRSp53 acts synergistically with ENAH and EPS8 to promote filopodia formation. Supporting Evidence: PMID:11696321 Cdc42 induces filopodia by promoting the formation of an IRSp53:Mena complex
GO:0032956 regulation of actin cytoskeleton organization	IEA GO_REF:0000002	ACCEPT	Summary: This is a core biological process for IRSp53. The protein coordinates actin organization downstream of Rho GTPases. Reason: Supported by IMP evidence (PMID:19366662). IRSp53 is necessary for CDC42-mediated and RAC1-mediated reorganization of actin cytoskeleton. Supporting Evidence: PMID:19366662 Insulin receptor tyrosine kinase substrate links the E. coli O157:H7 actin assembly effectors Tir and EspF(U) during pedestal formation
GO:0070064 proline-rich region binding	IEA GO_REF:0000117	ACCEPT	Summary: The SH3 domain of IRSp53 binds proline-rich regions of effector proteins. This is experimentally validated. Reason: Supported by IDA evidence (PMID:19366662). The SH3 domain mediates interactions with WAVE, N-WASP, Eps8, Mena/VASP through proline-rich motifs. Supporting Evidence: PMID:11130076 carboxy-terminal Src-homology-3 domain of IRSp53 binds to WAVE
GO:0098609 cell-cell adhesion	IEA GO_REF:0000108	KEEP AS NON CORE	Summary: Inferred from cadherin binding annotation. IRSp53 is found at adherens junctions and binds cadherin. Reason: While IRSp53 localizes to adherens junctions (HDA PMID:25468996), cell-cell adhesion is not a primary function. The protein's core role is membrane-actin coupling, not adhesion per se.
GO:0005515 protein binding	IPI PMID:10332026 Dentatorubral-pallidoluysian atrophy protein interacts throu...	REMOVE	Summary: Non-informative molecular function term. The interaction with ATN1 should be represented by more specific terms. Reason: GO curation guidelines discourage generic "protein binding" annotations. IRSp53 has adaptor activity that should be captured with more specific terms like protein-macromolecule adaptor activity. Proposed replacements: protein-macromolecule adaptor activity Supporting Evidence: PMID:10332026 Dentatorubral-pallidoluysian atrophy protein interacts through a proline-rich region near polyglutamine with the SH3 domain of an insulin receptor tyrosine kinase substrate.
GO:0005515 protein binding	IPI PMID:11130076 IRSp53 is an essential intermediate between Rac and WAVE in ...	REMOVE	Summary: Interaction with WAVE complex members (WASF1, WASF2). This should be captured as adaptor activity or WAVE complex binding. Reason: Generic protein binding does not convey the functional significance. IRSp53 functions as an adapter linking Rac to WAVE in membrane ruffling. Proposed replacements: protein-macromolecule adaptor activity Supporting Evidence: PMID:11130076 IRSp53 is an essential intermediate between Rac and WAVE in the regulation of membrane ruffling.
GO:0005515 protein binding	IPI PMID:11157984 Cdc42Hs facilitates cytoskeletal reorganization and neurite ...	REMOVE	Summary: Interaction with CDC42. Should be annotated as small GTPase binding. Reason: The interaction with CDC42 is functionally significant for activation of IRSp53. More informative to use small GTPase binding. Proposed replacements: small GTPase binding Supporting Evidence: PMID:11157984 Cdc42Hs facilitates cytoskeletal reorganization and neurite outgrowth by localizing the 58-kD insulin receptor substrate to filamentous actin.
GO:0005515 protein binding	IPI PMID:11696321 Cdc42 induces filopodia by promoting the formation of an IRS...	REMOVE	Summary: Interactions with RAC1 and ENAH (Mena). These represent core functional interactions that should use specific terms. Reason: RAC1 binding should be small GTPase binding; ENAH interaction relates to filopodia formation via adaptor function. Proposed replacements: small GTPase binding protein-macromolecule adaptor activity Supporting Evidence: PMID:11696321 Cdc42 induces filopodia by promoting the formation of an IRSp53:Mena complex.
GO:0005515 protein binding	IPI PMID:12598619 Novel espin actin-bundling proteins are localized to Purkinj...	REMOVE	Summary: Interaction with espin proteins in dendritic spines. Non-informative term. Reason: Should use adaptor activity terms to capture functional significance. Proposed replacements: protein-macromolecule adaptor activity Supporting Evidence: PMID:12598619 Novel espin actin-bundling proteins are localized to Purkinje cell dendritic spines and bind the Src homology 3 adapter protein insulin receptor substrate p53.
GO:0005515 protein binding	IPI PMID:15289329 IRSp53/Eps8 complex is important for positive regulation of ...	REMOVE	Summary: Interactions with EPS8 and ABI1. These are functionally important for Rac regulation and cancer cell motility. Reason: EPS8-IRSp53 complex has specific actin bundling function. Should be captured with more specific MF terms. Proposed replacements: protein-macromolecule adaptor activity Supporting Evidence: PMID:15289329 IRSp53/Eps8 complex is important for positive regulation of Rac and cancer cell motility/invasiveness.
GO:0005515 protein binding	IPI PMID:15324660 Proteomic, functional, and domain-based analysis of in vivo ...	REMOVE	Summary: 14-3-3 protein binding. Non-informative generic term. Reason: 14-3-3 binding regulates IRSp53 localization and activity. Should be captured with specific 14-3-3 binding or scaffold binding terms. Proposed replacements: scaffold protein binding Supporting Evidence: PMID:15324660 Proteomic, functional, and domain-based analysis of in vivo 14-3-3 binding proteins involved in cytoskeletal regulation and cellular organization.
GO:0005515 protein binding	IPI PMID:16189514 Towards a proteome-scale map of the human protein-protein in...	REMOVE	Summary: Large-scale proteome mapping. Generic annotation from HTP study. Reason: Non-informative generic term from high-throughput study. Proposed replacements: protein-macromolecule adaptor activity Supporting Evidence: PMID:16189514 Towards a proteome-scale map of the human protein-protein interaction network.
GO:0005515 protein binding	IPI PMID:16713569 A protein-protein interaction network for human inherited at...	REMOVE	Summary: Interaction network for Purkinje cell degeneration disorders. Reason: Non-informative generic term. Proposed replacements: protein-macromolecule adaptor activity Supporting Evidence: PMID:16713569 A protein-protein interaction network for human inherited ataxias and disorders of Purkinje cell degeneration.
GO:0005515 protein binding	IPI PMID:17003044 The RAC binding domain/IRSp53-MIM homology domain of IRSp53 ...	REMOVE	Summary: RAC1 binding via RCB/IMD domain. Important for membrane deformation. Reason: Should use small GTPase binding to capture this interaction. Proposed replacements: small GTPase binding Supporting Evidence: PMID:17003044 2006 Sep 25. The RAC binding domain/IRSp53-MIM homology domain of IRSp53 induces RAC-dependent membrane deformation.
GO:0005515 protein binding	IPI PMID:17353931 Large-scale mapping of human protein-protein interactions by...	REMOVE	Summary: Large-scale mass spectrometry protein-protein interaction mapping. Reason: Non-informative generic term from HTP study. Proposed replacements: protein-macromolecule adaptor activity Supporting Evidence: PMID:17353931 Large-scale mapping of human protein-protein interactions by mass spectrometry.
GO:0005515 protein binding	IPI PMID:18448434 The Cdc42 effector IRSp53 generates filopodia by coupling me...	REMOVE	Summary: CDC42 effector function. IRSp53 generates filopodia by coupling membrane protrusion with actin dynamics. Reason: Should use small GTPase binding and adaptor activity. Proposed replacements: small GTPase binding Supporting Evidence: PMID:18448434 2008 Apr 29. The Cdc42 effector IRSp53 generates filopodia by coupling membrane protrusion with actin dynamics.
GO:0005515 protein binding	IPI PMID:19171758 Kank attenuates actin remodeling by preventing interaction b...	REMOVE	Summary: Interactions with ACTB, RAC1, KANK1. KANK attenuates IRSp53-Rac1 interaction. Reason: Specific interactions should use more informative terms. Proposed replacements: actin binding small GTPase binding Supporting Evidence: PMID:19171758 Kank attenuates actin remodeling by preventing interaction between IRSp53 and Rac1.
GO:0005515 protein binding	IPI PMID:19460367 SPIN90-IRSp53 complex participates in Rac-induced membrane r...	REMOVE	Summary: SPIN90-IRSp53 complex in Rac-induced membrane ruffling. Reason: Non-informative generic term. Proposed replacements: protein-macromolecule adaptor activity Supporting Evidence: PMID:19460367 Epub 2009 May 19. SPIN90-IRSp53 complex participates in Rac-induced membrane ruffling.
GO:0005515 protein binding	IPI PMID:19564905 Eps8 regulates axonal filopodia in hippocampal neurons in re...	REMOVE	Summary: EPS8 interaction in axonal filopodia. Reason: Non-informative generic term. Proposed replacements: protein-macromolecule adaptor activity Supporting Evidence: PMID:19564905 2009 Jun 30. Eps8 regulates axonal filopodia in hippocampal neurons in response to brain-derived neurotrophic factor (BDNF).
GO:0005515 protein binding	IPI PMID:19933840 Regulation of IRSp53-dependent filopodial dynamics by antago...	REMOVE	Summary: 14-3-3 (YWHAZ) binding regulates IRSp53 filopodial dynamics. Reason: Non-informative generic term. 14-3-3 binding is regulatory. Proposed replacements: scaffold protein binding Supporting Evidence: PMID:19933840 Regulation of IRSp53-dependent filopodial dynamics by antagonism between 14-3-3 binding and SH3-mediated localization.
GO:0005515 protein binding	IPI PMID:20936779 A human MAP kinase interactome.	REMOVE	Summary: CDC42 interaction from MAP kinase interactome study. Reason: Should use small GTPase binding. Proposed replacements: small GTPase binding Supporting Evidence: PMID:20936779 A human MAP kinase interactome.
GO:0005515 protein binding	IPI PMID:21311754 Rho GTPase Cdc42 is a direct interacting partner of Adenomat...	REMOVE	Summary: CDC42 interaction related to APC localization. Reason: Should use small GTPase binding. Proposed replacements: small GTPase binding Supporting Evidence: PMID:21311754 Rho GTPase Cdc42 is a direct interacting partner of Adenomatous Polyposis Coli protein and can alter its cellular localization.
GO:0005515 protein binding	IPI PMID:24189400 Perturbation of the mutated EGFR interactome identifies vuln...	REMOVE	Summary: EGFR interactome perturbation study. Reason: Non-informative generic term from HTP study. Proposed replacements: protein-macromolecule adaptor activity Supporting Evidence: PMID:24189400 Perturbation of the mutated EGFR interactome identifies vulnerabilities and resistance mechanisms.
GO:0005515 protein binding	IPI PMID:24658140 The mammalian-membrane two-hybrid assay (MaMTH) for probing ...	REMOVE	Summary: EGFR interaction from MaMTH assay. Reason: Non-informative generic term. Proposed replacements: protein-macromolecule adaptor activity Supporting Evidence: PMID:24658140 The mammalian-membrane two-hybrid assay (MaMTH) for probing membrane-protein interactions in human cells.
GO:0005515 protein binding	IPI PMID:25416956 A proteome-scale map of the human interactome network.	REMOVE	Summary: Multiple interactions from proteome-scale interactome study. Reason: Non-informative generic term from HTP study. Proposed replacements: protein-macromolecule adaptor activity Supporting Evidence: PMID:25416956 A proteome-scale map of the human interactome network.
GO:0005515 protein binding	IPI PMID:25519916 The EHEC-host interactome reveals novel targets for the tran...	REMOVE	Summary: Interaction with E.coli Tir protein (EHEC host-pathogen interaction). Reason: While functionally significant for bacterial pathogenesis, protein binding is too generic. This represents adaptor activity hijacked by pathogen. Proposed replacements: protein-macromolecule adaptor activity Supporting Evidence: PMID:25519916 The EHEC-host interactome reveals novel targets for the translocated intimin receptor.
GO:0005515 protein binding	IPI PMID:25814554 Phospho-tyrosine dependent protein-protein interaction netwo...	REMOVE	Summary: Phospho-tyrosine dependent interaction network. Reason: Non-informative generic term. Proposed replacements: protein-macromolecule adaptor activity Supporting Evidence: PMID:25814554 Phospho-tyrosine dependent protein-protein interaction network.
GO:0005515 protein binding	IPI PMID:26496610 A human interactome in three quantitative dimensions organiz...	REMOVE	Summary: Interaction with BAIAP2L1 from quantitative interactome study. Reason: Non-informative generic term. Proposed replacements: protein-macromolecule adaptor activity Supporting Evidence: PMID:26496610 Oct 22. A human interactome in three quantitative dimensions organized by stoichiometries and abundances.
GO:0005515 protein binding	IPI PMID:28514442 Architecture of the human interactome defines protein commun...	REMOVE	Summary: 14-3-3 protein interactions. Reason: Non-informative generic term. Proposed replacements: scaffold protein binding Supporting Evidence: PMID:28514442 Architecture of the human interactome defines protein communities and disease networks.
GO:0005515 protein binding	IPI PMID:31980649 Extensive rewiring of the EGFR network in colorectal cancer ...	REMOVE	Summary: EGFR network in KRAS-mutant colorectal cancer. Reason: Non-informative generic term from HTP study. Proposed replacements: protein-macromolecule adaptor activity Supporting Evidence: PMID:31980649 Extensive rewiring of the EGFR network in colorectal cancer cells expressing transforming levels of KRAS(G13D).
GO:0005515 protein binding	IPI PMID:33961781 Dual proteome-scale networks reveal cell-specific remodeling...	REMOVE	Summary: Dual proteome-scale interactome study. Reason: Non-informative generic term from HTP study. Proposed replacements: protein-macromolecule adaptor activity Supporting Evidence: PMID:33961781 2021 May 6. Dual proteome-scale networks reveal cell-specific remodeling of the human interactome.
GO:0005515 protein binding	IPI PMID:35271311 OpenCell: Endogenous tagging for the cartography of human ce...	REMOVE	Summary: OpenCell endogenous tagging study. Reason: Non-informative generic term from HTP study. Proposed replacements: protein-macromolecule adaptor activity Supporting Evidence: PMID:35271311 2022 Mar 11. OpenCell: Endogenous tagging for the cartography of human cellular organization.
GO:0005515 protein binding	IPI PMID:35384245 Physical and functional interactome atlas of human receptor ...	REMOVE	Summary: RTK interactome study. Reason: Non-informative generic term from HTP study. Proposed replacements: protein-macromolecule adaptor activity Supporting Evidence: PMID:35384245 Physical and functional interactome atlas of human receptor tyrosine kinases.
GO:0005515 protein binding	IPI PMID:36931259 A central chaperone-like role for 14-3-3 proteins in human c...	REMOVE	Summary: 14-3-3 protein chaperone-like role study. Reason: Non-informative generic term. Proposed replacements: scaffold protein binding Supporting Evidence: PMID:36931259 A central chaperone-like role for 14-3-3 proteins in human cells.
GO:0005515 protein binding	IPI PMID:39251607 Systematic identification of post-transcriptional regulatory...	REMOVE	Summary: Post-transcriptional regulatory module study. Reason: Non-informative generic term from HTP study. Proposed replacements: protein-macromolecule adaptor activity Supporting Evidence: PMID:39251607 Systematic identification of post-transcriptional regulatory modules.
GO:0042802 identical protein binding	IPI PMID:11696321 Cdc42 induces filopodia by promoting the formation of an IRS...	MODIFY	Summary: IRSp53 forms homodimers via its I-BAR domain. This is functionally important for membrane binding and actin bundling. Reason: While identical protein binding is accurate, protein homodimerization activity is more specific and captures the functional importance. Proposed replacements: protein homodimerization activity Supporting Evidence: PMID:11696321 Cdc42 induces filopodia by promoting the formation of an IRSp53:Mena complex.
GO:0042802 identical protein binding	IPI PMID:14752106 A novel actin bundling/filopodium-forming domain conserved i...	MODIFY	Summary: Homodimer formation via IMD domain, important for actin bundling. Reason: Same as above - homodimerization activity is more informative. Proposed replacements: protein homodimerization activity Supporting Evidence: PMID:14752106 2004 Jan 29. A novel actin bundling/filopodium-forming domain conserved in insulin receptor tyrosine kinase substrate p53 and missing in metastasis protein.
GO:0042802 identical protein binding	IPI PMID:25416956 A proteome-scale map of the human interactome network.	MODIFY	Summary: Self-interaction from large-scale interactome study. Reason: Should use homodimerization activity. Proposed replacements: protein homodimerization activity Supporting Evidence: PMID:25416956 A proteome-scale map of the human interactome network.
GO:0001221 transcription coregulator binding	IEA GO_REF:0000107	MARK AS OVER ANNOTATED	Summary: Transcription coregulator binding is not well-supported for IRSp53. The protein functions primarily in cytoskeletal regulation, not transcription. Reason: Not supported by deep research or UniProt annotations. IRSp53's primary functions are at the plasma membrane and cytoskeleton.
GO:0005874 microtubule	IEA GO_REF:0000107	MARK AS OVER ANNOTATED	Summary: Microtubule localization is not well-established for IRSp53. The protein is primarily associated with actin cytoskeleton. Reason: IRSp53 is an I-BAR protein that functions with actin, not microtubules. This may be transferred from an ortholog with different localization.
GO:0005886 plasma membrane	IEA GO_REF:0000107	ACCEPT	Summary: Plasma membrane localization is a core feature of IRSp53 function. The I-BAR domain binds PI(4,5)P2-rich membranes. Reason: Well-supported by IDA evidence (HPA), TAS evidence, and deep research. IRSp53 localizes to plasma membrane nanodomains of negative curvature. Supporting Evidence: DOI:10.7554/eLife.72316 Sites of action: IRSp53 concentrates at the plasma membrane at regions of negative curvature
GO:0008360 regulation of cell shape	IEA GO_REF:0000107	ACCEPT	Summary: IRSp53 regulates cell shape through its effects on membrane curvature and actin organization. Reason: Core function. Deep research shows IRSp53 controls plasma membrane shape homeostasis at the nanoscale and drives protrusion formation. Supporting Evidence: DOI:10.7554/eLife.72316 A mechanosensing mechanism controls plasma membrane shape homeostasis at the nanoscale
GO:0010976 positive regulation of neuron projection development	IEA GO_REF:0000107	ACCEPT	Summary: IRSp53 promotes neurite outgrowth and dendritic spine formation. Reason: Supported by literature. UniProt notes a role in neurite growth. IRSp53 is enriched at dendritic spines. Supporting Evidence: PMID:11157984 Cdc42Hs facilitates cytoskeletal reorganization and neurite outgrowth by localizing the 58-kD insulin receptor substrate to filamentous actin
GO:0014069 postsynaptic density	IEA GO_REF:0000107	ACCEPT	Summary: IRSp53 localizes to postsynaptic density and interacts with SHANK scaffold proteins. Reason: UniProt documents interactions with SHANK1, SHANK2, SHANK3 at postsynaptic sites. Supporting Evidence: PMID:12504591 The insulin receptor substrate IRSp53 links postsynaptic shank1 to the small G-protein cdc42
GO:0030027 lamellipodium	IEA GO_REF:0000107	ACCEPT	Summary: IRSp53 is involved in lamellipodium formation through Rac1-WAVE signaling. Reason: Deep research confirms IRSp53 functions at lamellipodial edges. Supporting Evidence: PMID:11130076 IRSp53 is an essential intermediate between Rac and WAVE in the regulation of membrane ruffling
GO:0030141 secretory granule	IEA GO_REF:0000107	MARK AS OVER ANNOTATED	Summary: Secretory granule localization is not well-documented for IRSp53. Reason: Not supported by deep research or UniProt. May be transferred from ortholog data.
GO:0030165 PDZ domain binding	IEA GO_REF:0000107	ACCEPT	Summary: PDZ domain binding is supported by SHANK protein interactions which contain PDZ domains. Reason: IRSp53 interacts with SHANK1, SHANK2, SHANK3 which are PDZ domain-containing scaffold proteins.
GO:0030182 neuron differentiation	IEA GO_REF:0000120	KEEP AS NON CORE	Summary: IRSp53 plays a role in neuronal development, particularly in dendritic spine morphogenesis. Reason: While supported, this is a broad developmental process. Core function is actin-membrane coupling, which contributes to neuronal morphology.
GO:0030674 protein-macromolecule adaptor activity	IEA GO_REF:0000107	ACCEPT	Summary: This is the CORE molecular function of IRSp53. The protein links membrane-bound GTPases (Rac1, Cdc42) to cytoplasmic actin effectors. Reason: Perfectly captures IRSp53's primary function as an adapter between small GTPases, membranes, and actin regulatory proteins. Supporting Evidence: DOI:10.1242/jcs.262064 IRSp53 is a curvature-sensitive membrane-cytoskeleton adaptor that couples plasma membrane shape to actin remodeling
GO:0035418 protein localization to synapse	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: IRSp53 localizes to synapses and may help recruit other proteins. Reason: Synaptic function is established but is not the primary function of IRSp53, which operates in multiple cell types.
GO:0042803 protein homodimerization activity	IEA GO_REF:0000107	ACCEPT	Summary: IRSp53 forms functional homodimers through its I-BAR domain, essential for membrane binding and curvature sensing. Reason: Homodimerization is structurally and functionally important for IRSp53. The dimeric I-BAR domain creates the curvature-sensing interface. Supporting Evidence: PMID:15635447 Structural basis of filopodia formation induced by the IRSp53/MIM homology domain of human IRSp53
GO:0043005 neuron projection	IEA GO_REF:0000107	ACCEPT	Summary: IRSp53 localizes to and promotes formation of neuronal projections. Reason: Consistent with role in filopodia and neurite outgrowth. UniProt notes role in neurite growth.
GO:0043025 neuronal cell body	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Neuronal cell body localization is expected given cytoplasmic distribution in neurons. Reason: Not a site of primary function - IRSp53 acts at membrane protrusions.
GO:0043197 dendritic spine	IEA GO_REF:0000107	ACCEPT	Summary: Dendritic spine localization is well-documented for IRSp53. Reason: Deep research confirms IRSp53 is enriched at dendritic spine structures. Interacts with SHANK proteins at this location. Supporting Evidence: DOI:10.7554/eLife.72316 In neurons, it is enriched at dendritic spine structures
GO:0043198 dendritic shaft	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Dendritic shaft localization is consistent with neuronal expression. Reason: Less specific than dendritic spine. IRSp53 is more functionally important at spine heads.
GO:0044306 neuron projection terminus	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Localization at neuron projection terminus is consistent with role in growth cone dynamics. Reason: Consistent with filopodial function but relatively specific neuronal term.
GO:0046847 filopodium assembly	IEA GO_REF:0000107	ACCEPT	Summary: Filopodium assembly is a CORE biological process for IRSp53. Reason: Well-documented by multiple studies. IRSp53 is essential for CDC42- mediated filopodia formation, working with Mena/VASP and EPS8. Supporting Evidence: PMID:11696321 Cdc42 induces filopodia by promoting the formation of an IRSp53:Mena complex
GO:0050804 modulation of chemical synaptic transmission	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: IRSp53's role at synapses may affect synaptic transmission through effects on spine morphology. Reason: This is a downstream effect of IRSp53's structural role at synapses rather than a direct function.
GO:0051017 actin filament bundle assembly	IEA GO_REF:0000107	ACCEPT	Summary: Duplicate of IBA annotation. Actin bundling is a core function. Reason: Same as IBA annotation review. Well-supported core function.
GO:0051764 actin crosslink formation	IEA GO_REF:0000107	ACCEPT	Summary: Duplicate of IBA annotation. Actin crosslinking is a core function. Reason: Same as IBA annotation review. Well-supported core function.
GO:0060076 excitatory synapse	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: IRSp53 localizes to excitatory synapses (glutamatergic). Reason: Synaptic localization is established but is context-specific (neuronal).
GO:0061003 positive regulation of dendritic spine morphogenesis	IEA GO_REF:0000107	ACCEPT	Summary: IRSp53 promotes dendritic spine formation and morphology. Reason: Well-supported neuronal function. IRSp53 at spines regulates actin dynamics affecting spine shape. Supporting Evidence: DOI:10.7554/eLife.72316 IRSp53 has established roles in dendritic spine morphogenesis and synaptic plasticity
GO:0061845 neuron projection branch point	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Localization at branch points is consistent with membrane curvature sensing function. Reason: Plausible but not a primary site of function for this protein.
GO:0061846 dendritic spine cytoplasm	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Cytoplasmic localization within dendritic spines. Reason: Overly specific sublocalization term.
GO:0071364 cellular response to epidermal growth factor stimulus	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: EGF response involves IRSp53 through its interaction with EGFR and downstream signaling. Reason: While IRSp53 interacts with EGFR (documented in IPI studies), this is not a core function of the protein.
GO:0097060 synaptic membrane	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Synaptic membrane localization is consistent with postsynaptic function. Reason: Neuronal-specific term; plasma membrane is more general core annotation.
GO:0097110 scaffold protein binding	IEA GO_REF:0000107	ACCEPT	Summary: IRSp53 binds SHANK scaffold proteins at postsynaptic sites. Reason: Well-documented interaction with SHANK1/2/3 scaffold proteins. Supporting Evidence: PMID:12504591 The insulin receptor substrate IRSp53 links postsynaptic shank1 to the small G-protein cdc42
GO:0098685 Schaffer collateral - CA1 synapse	IEA GO_REF:0000107	MARK AS OVER ANNOTATED	Summary: Very specific hippocampal synapse localization. Reason: While IRSp53 is expressed in hippocampus, this very specific synapse type annotation may be over-annotation from mouse data.
GO:0098793 presynapse	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Presynaptic localization is documented but IRSp53 is predominantly postsynaptic. Reason: Less prominent than postsynaptic localization.
GO:0098794 postsynapse	IEA GO_REF:0000107	ACCEPT	Summary: Postsynaptic localization is well-established. Reason: Consistent with postsynaptic density annotation and SHANK interactions.
GO:0098978 glutamatergic synapse	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Glutamatergic synapse localization is consistent with excitatory synapse function. Reason: Neuronal-specific term.
GO:0099092 postsynaptic density, intracellular component	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: More specific than postsynaptic density term. Reason: Redundant with postsynaptic density annotation.
GO:0099175 regulation of postsynapse organization	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: IRSp53 regulates postsynaptic structure through effects on actin and spine morphology. Reason: Neuronal-specific process; core function is actin-membrane coupling.
GO:0099523 presynaptic cytosol	IEA GO_REF:0000107	MARK AS OVER ANNOTATED	Summary: Very specific subcompartment term. Reason: Overly specific; cytosol annotation is sufficient.
GO:0099524 postsynaptic cytosol	IEA GO_REF:0000107	MARK AS OVER ANNOTATED	Summary: Very specific subcompartment term. Reason: Overly specific; cytosol annotation is sufficient.
GO:1905232 cellular response to L-glutamate	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Glutamate response at synapses. Reason: May be a downstream effect rather than direct function.
GO:1905274 regulation of modification of postsynaptic actin cytoskeleton	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Specific term for postsynaptic actin regulation. Reason: Very specific neuronal term; general actin regulation is core function.
GO:2000463 positive regulation of excitatory postsynaptic potential	IEA GO_REF:0000107	KEEP AS NON CORE	Summary: Electrophysiological effect of IRSp53 at synapses. Reason: Downstream effect of structural role; not a direct function.
GO:0005829 cytosol	IDA GO_REF:0000052	ACCEPT	Summary: IDA from HPA immunofluorescence confirms cytosol localization. Reason: Direct experimental evidence for cytosol localization.
GO:0005886 plasma membrane	IDA GO_REF:0000052	ACCEPT	Summary: IDA from HPA immunofluorescence confirms plasma membrane localization. Reason: Direct experimental evidence for plasma membrane localization.
GO:0032956 regulation of actin cytoskeleton organization	IMP PMID:19366662 Insulin receptor tyrosine kinase substrate links the E. coli...	ACCEPT	Summary: IMP evidence from bacterial pedestal formation study. Reason: Direct experimental evidence showing IRSp53 is required for actin cytoskeleton reorganization during E. coli infection. Supporting Evidence: PMID:19366662 Insulin receptor tyrosine kinase substrate links the E. coli O157:H7 actin assembly effectors Tir and EspF(U) during pedestal formation
GO:0005912 adherens junction	HDA PMID:25468996 E-cadherin interactome complexity and robustness resolved by...	KEEP AS NON CORE	Summary: High-throughput proteomics of E-cadherin interactome identifies IRSp53 at adherens junctions. Reason: While IRSp53 is found at adherens junctions, this is not its primary site of function. Supporting Evidence: PMID:25468996 E-cadherin interactome complexity and robustness resolved by quantitative proteomics.
GO:0098641 cadherin binding involved in cell-cell adhesion	HDA PMID:25468996 E-cadherin interactome complexity and robustness resolved by...	KEEP AS NON CORE	Summary: Cadherin binding identified from E-cadherin interactome proteomics. Reason: While documented, this is not a primary molecular function of IRSp53. The protein's core MF is adaptor activity. Supporting Evidence: PMID:25468996 E-cadherin interactome complexity and robustness resolved by quantitative proteomics.
GO:0070062 extracellular exosome	HDA PMID:23533145 In-depth proteomic analyses of exosomes isolated from expres...	KEEP AS NON CORE	Summary: Found in prostatic extracellular exosomes by proteomics. Reason: Exosomal presence may reflect its membrane association but is not a core localization. Supporting Evidence: PMID:23533145 2013 Apr 23. In-depth proteomic analyses of exosomes isolated from expressed prostatic secretions in urine.
GO:0070062 extracellular exosome	HDA PMID:19056867 Large-scale proteomics and phosphoproteomics of urinary exos...	KEEP AS NON CORE	Summary: Found in urinary exosomes by proteomics. Reason: Exosomal presence is not a core localization. Supporting Evidence: PMID:19056867 2008 Dec 3. Large-scale proteomics and phosphoproteomics of urinary exosomes.
GO:0005829 cytosol	TAS Reactome:R-HSA-2029465	ACCEPT	Summary: Reactome pathway: RAC1:GTP and PIP3 bind WAVE Regulatory Complex. Reason: Consistent with cytosol localization and WAVE complex interaction.
GO:0005829 cytosol	TAS Reactome:R-HSA-2029466	ACCEPT	Summary: Reactome pathway: (WASPs, WAVE):G-actin:ARP2/3 binds F-actin. Reason: Consistent with cytosolic function in WAVE-Arp2/3 pathway.
GO:0005829 cytosol	TAS Reactome:R-HSA-2029469	ACCEPT	Summary: Reactome pathway: p-ERK phosphorylates WAVEs and ABI. Reason: Consistent with cytosol localization.
GO:0005829 cytosol	TAS Reactome:R-HSA-2130194	ACCEPT	Summary: Reactome pathway: ABL phosphorylates WAVEs. Reason: Consistent with cytosol localization.
GO:0005829 cytosol	TAS Reactome:R-HSA-2197690	ACCEPT	Summary: Reactome pathway: Detachment of WASP/WAVE. Reason: Consistent with cytosol localization.
GO:0005829 cytosol	TAS Reactome:R-HSA-9013145	ACCEPT	Summary: Reactome pathway: RAC1 binds effectors at the plasma membrane. Reason: Consistent with cytosol localization.
GO:0005829 cytosol	TAS Reactome:R-HSA-9013157	ACCEPT	Summary: Reactome pathway: CDC42 binds effectors at the plasma membrane. Reason: Consistent with cytosol localization and CDC42 interaction.
GO:0008360 regulation of cell shape	ISS GO_REF:0000024	ACCEPT	Summary: ISS from mouse ortholog Q8BKX1. Reason: Well-supported by IEA annotation and deep research.
GO:0051017 actin filament bundle assembly	ISS GO_REF:0000024	ACCEPT	Summary: ISS from mouse ortholog Q8BKX1. Reason: Well-supported by IBA annotation and deep research.
GO:0051764 actin crosslink formation	ISS GO_REF:0000024	ACCEPT	Summary: ISS from mouse ortholog Q8BKX1. Reason: Well-supported by IBA annotation and deep research.
GO:0005829 cytosol	IDA PMID:19366662 Insulin receptor tyrosine kinase substrate links the E. coli...	ACCEPT	Summary: IDA from pedestal formation study. Reason: Direct experimental evidence. Supporting Evidence: PMID:19366662 Insulin receptor tyrosine kinase substrate links the E.
GO:0015629 actin cytoskeleton	IDA PMID:19366662 Insulin receptor tyrosine kinase substrate links the E. coli...	ACCEPT	Summary: IDA showing colocalization with actin cytoskeleton. Reason: Direct experimental evidence. Core localization for this protein. Supporting Evidence: PMID:19366662 recruiting IRTKS to sites of bacterial attachment
GO:0070064 proline-rich region binding	IDA PMID:19366662 Insulin receptor tyrosine kinase substrate links the E. coli...	ACCEPT	Summary: IDA demonstrating SH3 domain binding to proline-rich regions. Reason: Direct experimental evidence for this molecular function. Supporting Evidence: PMID:19366662 the ability to bind EspF(U) identified the SH3 domain of insulin receptor tyrosine kinase substrate (IRTKS)
GO:0005515 protein binding	TAS PMID:10343108 Identification of BAIAP2 (BAI-associated protein 2), a novel...	REMOVE	Summary: TAS annotation from original BAIAP2 identification paper. Reason: Non-informative generic term. Should use adaptor activity. Proposed replacements: protein-macromolecule adaptor activity Supporting Evidence: PMID:10343108 Identification of BAIAP2 (BAI-associated protein 2), a novel human homologue of hamster IRSp53, whose SH3 domain interacts with the cytoplasmic domain of BAI1.
GO:0005737 cytoplasm	TAS PMID:10343108 Identification of BAIAP2 (BAI-associated protein 2), a novel...	ACCEPT	Summary: TAS for cytoplasm localization from original identification paper. Reason: Well-supported by multiple evidence types. Supporting Evidence: PMID:10343108 Identification of BAIAP2 (BAI-associated protein 2), a novel human homologue of hamster IRSp53, whose SH3 domain interacts with the cytoplasmic domain of BAI1.
GO:0005886 plasma membrane	TAS PMID:10343108 Identification of BAIAP2 (BAI-associated protein 2), a novel...	ACCEPT	Summary: TAS for plasma membrane localization. Reason: Well-supported core localization. Supporting Evidence: PMID:10343108 Identification of BAIAP2 (BAI-associated protein 2), a novel human homologue of hamster IRSp53, whose SH3 domain interacts with the cytoplasmic domain of BAI1.
GO:0007409 axonogenesis	TAS PMID:10343108 Identification of BAIAP2 (BAI-associated protein 2), a novel...	KEEP AS NON CORE	Summary: Role in axonal development from original identification paper. Reason: Neuronal developmental process; core function is actin-membrane coupling. Supporting Evidence: PMID:10343108 Identification of BAIAP2 (BAI-associated protein 2), a novel human homologue of hamster IRSp53, whose SH3 domain interacts with the cytoplasmic domain of BAI1.
GO:0008093 cytoskeletal anchor activity	TAS PMID:10343108 Identification of BAIAP2 (BAI-associated protein 2), a novel...	ACCEPT	Summary: TAS for cytoskeletal anchor activity. Reason: Core molecular function. Also supported by IEA from InterPro. Supporting Evidence: PMID:10343108 Identification of BAIAP2 (BAI-associated protein 2), a novel human homologue of hamster IRSp53, whose SH3 domain interacts with the cytoplasmic domain of BAI1.
GO:0008286 insulin receptor signaling pathway	TAS PMID:10343108 Identification of BAIAP2 (BAI-associated protein 2), a novel...	KEEP AS NON CORE	Summary: IRSp53 was originally named for its identification as an insulin receptor tyrosine kinase substrate. Reason: Historical name association; insulin signaling is not the core function of IRSp53. Modern research shows its primary role is in actin-membrane coupling independent of insulin signaling. Supporting Evidence: PMID:10343108 Identification of BAIAP2 (BAI-associated protein 2), a novel human homologue of hamster IRSp53, whose SH3 domain interacts with the cytoplasmic domain of BAI1.
GO:0140090 membrane curvature sensor activity	IDA file:human/BAIAP2/BAIAP2-deep-research-falcon.md	NEW	Summary: IRSp53's I-BAR domain is a curvature sensor that preferentially binds negatively curved membranes. This is a key molecular function not currently annotated. Reason: Deep research (eLife 2023) provides quantitative evidence that IRSp53 I-BAR domain senses membrane curvature with peak sorting at ~0.05 nm^-1 (~100 nm diameter evaginations) with ~2x enrichment. This is a defining molecular function of the I-BAR domain family. Supporting Evidence: file:human/BAIAP2/BAIAP2-deep-research-falcon.md IRSp53 shows maximal sorting to membrane evaginations at curvature ≈0.05 nm−1 with ~2× enrichment over control; evaginations are ~100 nm scale
GO:0005546 phosphatidylinositol-4,5-bisphosphate binding	IDA file:human/BAIAP2/BAIAP2-deep-research-falcon.md	NEW	Summary: IRSp53 I-BAR domain binds PI(4,5)P2-rich membranes. This lipid specificity is important for membrane targeting. Reason: Deep research shows IRSp53 binds PI(4,5)P2-rich membranes and induces membrane deformation on PI(4,5)P2 GUVs. This lipid binding specificity is a key aspect of its membrane targeting. Supporting Evidence: file:human/BAIAP2/BAIAP2-deep-research-falcon.md full-length IRSp53 induces inward membrane indentations/tubules on PI(4,5)P2 GUVs that recruit BIN1
GO:0031267 small GTPase binding	IPI PMID:11130076 IRSp53 is an essential intermediate between Rac and WAVE in ...	NEW	Summary: IRSp53 directly binds active Rac1 and Cdc42 through its CRIB/IMD region. This is a core molecular function currently represented only by generic protein binding annotations. Reason: UniProt and deep research document binding to RAC1 and CDC42 as central to IRSp53 function. The protein acts as an effector of these GTPases. Supporting Evidence: PMID:11130076 Activated Rac binds to the amino terminus of IRSp53

Core Functions

IRSp53 is fundamentally an adaptor protein that links membrane-bound small GTPases (Rac1, Cdc42) to cytoplasmic actin effectors (WAVE, N-WASP, Eps8, Mena/VASP). This is its primary molecular function.

Molecular Function:

protein-macromolecule adaptor activity

Directly Involved In:

filopodium assembly regulation of actin cytoskeleton organization

Cellular Locations:

plasma membrane

The I-BAR domain preferentially binds to negatively curved membranes, showing maximal sorting at curvatures of ~0.05 nm^-1 with ~2x enrichment (eLife 2023). This curvature sensing triggers downstream actin assembly.

Molecular Function:

membrane curvature sensor activity

Directly Involved In:

plasma membrane organization

Cellular Locations:

plasma membrane

References

GO_REF:0000002

Gene Ontology annotation through association of InterPro records with GO terms

GO_REF:0000024

Manual transfer of experimentally-verified manual GO annotation data to orthologs by curator judgment of sequence similarity

GO_REF:0000033

Annotation inferences using phylogenetic trees

GO_REF:0000044

Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping

GO_REF:0000052

Gene Ontology annotation based on curation of immunofluorescence data

GO_REF:0000107

Automatic transfer of experimentally verified manual GO annotation data to orthologs using Ensembl Compara

GO_REF:0000108

Automatic assignment of GO terms using logical inference, based on inter-ontology links

GO_REF:0000117

Electronic Gene Ontology annotations created by ARBA machine learning models

GO_REF:0000120

Combined Automated Annotation using Multiple IEA Methods

PMID:10332026

Dentatorubral-pallidoluysian atrophy protein interacts through a proline-rich region near polyglutamine with the SH3 domain of an insulin receptor tyrosine kinase substrate

PMID:10343108

Identification of BAIAP2 (BAI-associated protein 2), a novel human homologue of hamster IRSp53, whose SH3 domain interacts with the cytoplasmic domain of BAI1

Original identification and characterization of human BAIAP2/IRSp53

PMID:11130076

IRSp53 is an essential intermediate between Rac and WAVE in the regulation of membrane ruffling

IRSp53 links Rac to WAVE complex for membrane ruffling

PMID:11157984

Cdc42Hs facilitates cytoskeletal reorganization and neurite outgrowth by localizing the 58-kD insulin receptor substrate to filamentous actin

CDC42 binding and neurite outgrowth function

PMID:11696321

Cdc42 induces filopodia by promoting the formation of an IRSp53:Mena complex

Key paper demonstrating filopodia formation mechanism

PMID:12504591

The insulin receptor substrate IRSp53 links postsynaptic shank1 to the small G-protein cdc42

SHANK interaction and postsynaptic function

PMID:14752106

A novel actin bundling/filopodium-forming domain conserved in insulin receptor tyrosine kinase substrate p53 and missing in metastasis protein

Characterization of I-BAR/IMD domain actin bundling activity

PMID:15635447

Structural basis of filopodia formation induced by the IRSp53/MIM homology domain of human IRSp53

Crystal structure of I-BAR domain

PMID:17115031

Regulation of cell shape by Cdc42 is mediated by the synergic actin-bundling activity of the Eps8-IRSp53 complex

EPS8-IRSp53 complex function

PMID:19366662

Insulin receptor tyrosine kinase substrate links the E. coli O157:H7 actin assembly effectors Tir and EspF(U) during pedestal formation

Bacterial hijacking of IRSp53 for pedestal formation

PMID:25468996

E-cadherin interactome complexity and robustness resolved by quantitative proteomics

Adherens junction proteomics

PMID:12598619

Novel espin actin-bundling proteins are localized to Purkinje cell dendritic spines and bind the Src homology 3 adapter protein insulin receptor substrate p53.

PMID:15289329

IRSp53/Eps8 complex is important for positive regulation of Rac and cancer cell motility/invasiveness.

PMID:15324660

Proteomic, functional, and domain-based analysis of in vivo 14-3-3 binding proteins involved in cytoskeletal regulation and cellular organization.

PMID:16189514

Towards a proteome-scale map of the human protein-protein interaction network.

PMID:16713569

A protein-protein interaction network for human inherited ataxias and disorders of Purkinje cell degeneration.

PMID:17003044

The RAC binding domain/IRSp53-MIM homology domain of IRSp53 induces RAC-dependent membrane deformation.

PMID:17353931

Large-scale mapping of human protein-protein interactions by mass spectrometry.

PMID:18448434

The Cdc42 effector IRSp53 generates filopodia by coupling membrane protrusion with actin dynamics.

PMID:19171758

Kank attenuates actin remodeling by preventing interaction between IRSp53 and Rac1.

PMID:19460367

SPIN90-IRSp53 complex participates in Rac-induced membrane ruffling.

PMID:19564905

Eps8 regulates axonal filopodia in hippocampal neurons in response to brain-derived neurotrophic factor (BDNF).

PMID:19933840

Regulation of IRSp53-dependent filopodial dynamics by antagonism between 14-3-3 binding and SH3-mediated localization.

PMID:20936779

A human MAP kinase interactome.

PMID:21311754

Rho GTPase Cdc42 is a direct interacting partner of Adenomatous Polyposis Coli protein and can alter its cellular localization.

PMID:24189400

Perturbation of the mutated EGFR interactome identifies vulnerabilities and resistance mechanisms.

PMID:24658140

The mammalian-membrane two-hybrid assay (MaMTH) for probing membrane-protein interactions in human cells.

PMID:25416956

A proteome-scale map of the human interactome network.

PMID:25519916

The EHEC-host interactome reveals novel targets for the translocated intimin receptor.

PMID:25814554

Phospho-tyrosine dependent protein-protein interaction network.

PMID:26496610

A human interactome in three quantitative dimensions organized by stoichiometries and abundances.

PMID:28514442

Architecture of the human interactome defines protein communities and disease networks.

PMID:31980649

Extensive rewiring of the EGFR network in colorectal cancer cells expressing transforming levels of KRAS(G13D).

PMID:33961781

Dual proteome-scale networks reveal cell-specific remodeling of the human interactome.

PMID:35271311

OpenCell: Endogenous tagging for the cartography of human cellular organization.

PMID:35384245

Physical and functional interactome atlas of human receptor tyrosine kinases.

PMID:36931259

A central chaperone-like role for 14-3-3 proteins in human cells.

PMID:39251607

Systematic identification of post-transcriptional regulatory modules.

PMID:23533145

In-depth proteomic analyses of exosomes isolated from expressed prostatic secretions in urine.

PMID:19056867

Large-scale proteomics and phosphoproteomics of urinary exosomes.

Reactome:R-HSA-2029465

RAC1:GTP and PIP3 bind WAVE Regulatory Complex

Reactome:R-HSA-2029466

(WASPs, WAVE):G-actin:ARP2/3 binds F-actin

Reactome:R-HSA-2029469

p-ERK phosphorylates WAVEs and ABI

Reactome:R-HSA-2130194

ABL phosphorylates WAVEs

Reactome:R-HSA-2197690

Detachment of WASP/WAVE

Reactome:R-HSA-9013145

RAC1 binds effectors at the plasma membrane

Reactome:R-HSA-9013157

CDC42 binds effectors at the plasma membrane

file:human/BAIAP2/BAIAP2-deep-research-falcon.md

Deep research review of BAIAP2/IRSp53

Key 2023 paper on membrane curvature sensing mechanism
Quantitative curvature sensing data
IRSp53-BIN1 cooperation in filopodia
PI(4,5)P2 binding evidence
Review of I-BAR biology and membrane curvature

Suggested Experiments

Experiment: Liposome binding assays with defined curvatures and lipid compositions to quantify PI(4,5)P2 vs other PIP binding specificity. This would clarify lipid binding specificity of the I-BAR domain.

Deep Research

Falcon

(BAIAP2-deep-research-falcon.md)

this with annotations you find in gene/protein databases, but these can be outdated or inaccurate. Falcon Edison Scientific Literature 15 citations 2025-12-27T01:56:26.022883

The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.

You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.

We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.

We are interested in where in or outside the cell the gene product carries out its function.

We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.

Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.

Plan and verification
- Identity and symbol verification: The target is human BAIAP2 (UniProt Q9UQB8), also known as IRSp53 (insulin receptor substrate of 53 kDa) and BAI1-associated protein 2. Literature consistently uses these aliases for the human I-BAR/IMD family adaptor IRSp53/BAIAP2, confirming symbol, organism, and domain architecture alignment (I-BAR/IMD N-terminus and C-terminal SH3, with CRIB/PR region and additional motifs) (https://doi.org/10.1242/jcs.262064; 2024; https://doi.org/10.3892/mmr.2025.13437; 2025; https://doi.org/10.7554/eLife.72316; 2023) (lacouture2024hiv1assembly–whenvirology pages 6-7, zhang2025insulinreceptortyrosine pages 2-3, quiroga2023amechanosensingmechanism pages 6-8).

Domain family: BAIAP2/IRSp53 is a member of the BAR superfamily’s I-BAR/IMD subgroup, with an N-terminal I-BAR/IMD that binds phosphoinositide-rich membranes, senses/generates negative curvature, and a C-terminal SH3 domain that recruits actin-regulatory partners. CRIB/PR motifs mediate small GTPase coupling. This matches the UniProt-listed domain composition (https://doi.org/10.1242/jcs.262064; 2024; https://doi.org/10.3892/mmr.2025.13437; 2025; https://doi.org/10.7554/eLife.72316; 2023) (lacouture2024hiv1assembly–whenvirology pages 6-7, zhang2025insulinreceptortyrosine pages 2-3, quiroga2023amechanosensingmechanism pages 6-8).

Key concepts and definitions (current understanding)
- Primary molecular role: IRSp53 is a curvature-sensitive membrane-cytoskeleton adaptor that couples plasma membrane shape to actin remodeling. Its I-BAR/IMD domain binds and sorts to negatively curved membrane topologies; its SH3 domain recruits actin effectors (e.g., WAVE/Scar complexes, N-WASP, Eps8, Mena/VASP) to modulate branched versus bundled actin assembly, integrating small GTPase signals (Rac1, Cdc42) (eLife, Sep 2023, https://doi.org/10.7554/eLife.72316; J Cell Sci, 2024, https://doi.org/10.1242/jcs.262064; Mol Med Rep, 2025, https://doi.org/10.3892/mmr.2025.13437) (quiroga2023amechanosensingmechanism pages 6-8, lacouture2024hiv1assembly–whenvirology pages 6-7, zhang2025insulinreceptortyrosine pages 2-3).
- Distinct from enzymes/transporters: IRSp53 is a scaffold/adaptor, not catalytic; it tunes actin architecture and membrane curvature rather than catalyzing chemical reactions or transporting substrates (https://doi.org/10.7554/eLife.72316; 2023; https://doi.org/10.1242/jcs.262064; 2024) (quiroga2023amechanosensingmechanism pages 6-8, lacouture2024hiv1assembly–whenvirology pages 6-7).

Molecular mechanism and pathway integration
- Curvature sensing/generation: IRSp53’s I-BAR displays curvature-dependent membrane sorting with a peak near 0.05 nm−1 (∼100 nm-diameter evaginations) and roughly twofold enrichment over control, linking membrane topography to actin assembly. In vitro, full-length IRSp53 deforms PI(4,5)P2-rich membranes, induces indentations/tubules, and can seed co-recruitment of partner BAR proteins (e.g., BIN1) (eLife 2023; Communications Biology 2024) (https://doi.org/10.7554/eLife.72316; https://doi.org/10.1038/s42003-024-06168-8) (quiroga2023amechanosensingmechanism pages 6-8, picas2024bin1regulatesactinmembrane pages 3-5).
- Small GTPase coupling: A central CRIB/PR region and overall architecture place IRSp53 at the intersection of Rac1- and Cdc42-mediated signaling. Rac1 pathways bias toward WAVE–Arp2/3-dependent lamellipodia/ruffles, whereas Cdc42 influences filopodia; IRSp53 integrates these via its membrane-binding I-BAR and SH3-recruited effectors (J Cell Sci 2024; Mol Med Rep 2025) (https://doi.org/10.1242/jcs.262064; https://doi.org/10.3892/mmr.2025.13437) (lacouture2024hiv1assembly–whenvirology pages 6-7, zhang2025insulinreceptortyrosine pages 2-3).
- SH3-mediated effectors: Through SH3, IRSp53 binds proline-rich partners, including components of the WAVE/Scar complex, N-WASP, Eps8, and Ena/VASP proteins, controlling actin nucleation and bundling to produce filopodia and lamellipodial edge dynamics (eLife 2023; Mol Med Rep 2025) (https://doi.org/10.7554/eLife.72316; https://doi.org/10.3892/mmr.2025.13437) (quiroga2023amechanosensingmechanism pages 6-8, zhang2025insulinreceptortyrosine pages 2-3).
- Cooperative BAR networks: IRSp53 and the N-BAR protein BIN1 cooperate in filopodia biogenesis; IRSp53-generated curvature recruits BIN1, and BIN1 requires IRSp53 to drive filopodia in cells, highlighting BAR–BAR crosstalk (Communications Biology, May 2024, https://doi.org/10.1038/s42003-024-06168-8) (picas2024bin1regulatesactinmembrane pages 3-5).

Subcellular localization and structures
- Sites of action: IRSp53 concentrates at the plasma membrane at regions of negative curvature, including nanoscale evaginations (~100 nm), and at protrusive structures like filopodia and lamellipodial edges. In neurons, it is enriched at dendritic spine structures. Full-length IRSp53 is required for curvature-enrichment and mechanochemical coupling to actin (eLife 2023; J Cell Sci 2024) (https://doi.org/10.7554/eLife.72316; https://doi.org/10.1242/jcs.262064) (quiroga2023amechanosensingmechanism pages 6-8, lacouture2024hiv1assembly–whenvirology pages 6-7).

Recent developments and latest research (emphasis 2023–2024)
- Nanoscale mechanosensing of membrane shape homeostasis (eLife 2023): Mechanical stretch/compression generates ∼100 nm plasma membrane evaginations that are rapidly recognized by IRSp53. This triggers a transient Rac1/Arp2/3-driven actin burst that re-flattens the membrane (feedback timescale on the order of seconds; Ezrin recruitment lags actin by ∼10 s), establishing a membrane shape homeostasis mechanism (https://doi.org/10.7554/eLife.72316; Sep 2023) (quiroga2023amechanosensingmechanism pages 6-8).
- BIN1–IRSp53 cooperation in filopodia (Communications Biology 2024): BIN1 is necessary and sufficient to promote filopodia in myoblasts, but requires IRSp53; >75% of IRSp53-positive filopodia co-localize with BIN1. IRSp53 forms membrane indentations on PI(4,5)P2 GUVs that recruit BIN1; IRSp53 knockdown reduces BIN1-driven filopodia. This defines a cooperative actin–membrane platform for protrusion (https://doi.org/10.1038/s42003-024-06168-8; May 2024) (picas2024bin1regulatesactinmembrane pages 3-5).
- Updated reviews of I-BAR/IRSp53 biology and virology interface (J Cell Sci 2024): IRSp53 is presented as the founding I-BAR family member with dual curvature sensing/generating capacity, PI(4,5)P2 binding, and SH3-mediated effector recruitment at the Rac1/Cdc42 signaling crossroads. Potential roles are discussed in EV release and viral assembly contexts (https://doi.org/10.1242/jcs.262064; 2024) (lacouture2024hiv1assembly–whenvirology pages 6-7).
- Family-level synthesis (Mol Med Rep 2025, accepted Dec 2024): While centered on IRTKS, this review contextualizes IRSp53 within the I-BAR family, emphasizing membrane curvature control, SH3-mediated recruitment of Eps8/WAVE/Ena-VASP, and Rac/Cdc42 interplay. It supports a conserved scaffold mechanism across family members (https://doi.org/10.3892/mmr.2025.13437; Jan 2025; accepted Dec 19, 2024) (zhang2025insulinreceptortyrosine pages 2-3).

Current applications and real-world implementations
- Mechanobiology and cell migration: The eLife 2023 work operationalizes IRSp53 as a mechanosensor that restores membrane shape at the nanoscale, providing a framework for how cells maintain plasma membrane topography during migration and force adaptation—a concept applicable to immune cell navigation and epithelial dynamics (https://doi.org/10.7554/eLife.72316; 2023) (quiroga2023amechanosensingmechanism pages 6-8).
- Filopodia engineering and muscle/cytoskeletal pathology: The BIN1–IRSp53 partnership offers a route to modulate filopodial dynamics and membrane–actin coupling in muscle and other cells, relevant to BIN1-linked myopathies and to protrusion-dependent processes such as neurite outgrowth and cell–cell contacts (https://doi.org/10.1038/s42003-024-06168-8; 2024) (picas2024bin1regulatesactinmembrane pages 3-5).
- Virology/EV biology: Reviews highlight IRSp53’s potential role in viral assembly interfaces and EV biogenesis at curved membrane microdomains, suggesting biophysical targets in pathogen–host interactions and intercellular cargo transfer (https://doi.org/10.1242/jcs.262064; 2024) (lacouture2024hiv1assembly–whenvirology pages 6-7).

Expert opinions and authoritative analyses
- Integrative perspective (J Cell Sci 2024): IRSp53 is framed as a central node connecting the plasma membrane’s lipid/curvature code with actin effectors downstream of Rac1/Cdc42. The review emphasizes how I-BAR electrostatics, PI(4,5)P2 nanodomains, and SH3-driven partner selection tune protrusion types (https://doi.org/10.1242/jcs.262064; 2024) (lacouture2024hiv1assembly–whenvirology pages 6-7).
- Mechanochemical control (eLife 2023): The study proposes a generalizable membrane homeostasis module in which I-BAR proteins (IRSp53) detect nanoscale curvature and recruit actin machinery to restore shape, prioritizing curvature sensing over curvature creation per se in the tested context (https://doi.org/10.7554/eLife.72316; 2023) (quiroga2023amechanosensingmechanism pages 6-8).
- Family-level convergence (Mol Med Rep 2025): Cross-family comparisons (IRSp53/IRTKS) support a modular scaffold logic: I-BAR for curvature, CRIB/PR for small GTPase inputs, SH3 for NPF recruitment and actin bundling/nucleation output (https://doi.org/10.3892/mmr.2025.13437; 2025) (zhang2025insulinreceptortyrosine pages 2-3).

Relevant statistics and quantitative data (recent)
- Curvature sorting and enrichment: IRSp53 shows maximal sorting to membrane evaginations at curvature ≈0.05 nm−1 with ~2× enrichment over control; evaginations are ~100 nm scale; Ezrin follows IRSp53/actin with a ~10 s delay (eLife 2023, https://doi.org/10.7554/eLife.72316; Sep 2023) (quiroga2023amechanosensingmechanism pages 6-8).
- Filopodia co-localization and dependency: In myoblasts, >75% of IRSp53-positive filopodia co-localize with BIN1; IRSp53 knockdown significantly reduces filopodia density; in vitro, full-length IRSp53 induces inward membrane indentations/tubules on PI(4,5)P2 GUVs that recruit BIN1 (Communications Biology 2024, https://doi.org/10.1038/s42003-024-06168-8; May 2024) (picas2024bin1regulatesactinmembrane pages 3-5).
- Mechanistic models and recruitment: Work compiling I-BAR behavior shows IRSp53 recruitment to negatively curved membranes and coupling to Arp2/3-mediated actin network assembly in protrusions in cell-based systems (2023 synthesis) (sahnine2023molecularmechanismsregulating pages 125-131).

Pathways and compartmental context
- Pathways: IRSp53 integrates Rho-family GTPase signaling (Rac1, Cdc42) with actin nucleation/bundling via SH3 partners (WAVE, N-WASP, Ena/VASP, Eps8) to drive lamellipodial ruffles, filopodial protrusions, and endocytic/EV-associated actin dynamics (https://doi.org/10.1242/jcs.262064; 2024; https://doi.org/10.3892/mmr.2025.13437; 2025; https://doi.org/10.7554/eLife.72316; 2023) (lacouture2024hiv1assembly–whenvirology pages 6-7, zhang2025insulinreceptortyrosine pages 2-3, quiroga2023amechanosensingmechanism pages 6-8).
- Compartments: Plasma membrane protrusions (filopodia/lamellipodia), nanoscale membrane evaginations, dendritic spine compartments; endocytic and extracellular vesicle biogenesis sites are implicated by curvature-sensitive recruitment (https://doi.org/10.7554/eLife.72316; 2023; https://doi.org/10.1242/jcs.262064; 2024) (quiroga2023amechanosensingmechanism pages 6-8, lacouture2024hiv1assembly–whenvirology pages 6-7).

Disease and pathogen relevance (focused to available evidence)
- Neuronal/synaptic function: IRSp53 has established roles in dendritic spine morphogenesis and synaptic plasticity (supported by primary work cited within the 2023 eLife mechanistic paper), positioning BAIAP2 as a synaptic scaffold impacting plasticity phenotypes (https://doi.org/10.7554/eLife.72316; 2023) (quiroga2023amechanosensingmechanism pages 30-31).
- Pathogen/virology interfaces: Reviews highlight the plausibility of IRSp53 in viral assembly and EV release due to its ability to sense/organize PI(4,5)P2-rich curved microdomains and recruit actin effectors, a concept consistent with broader I-BAR biology (J Cell Sci 2024, https://doi.org/10.1242/jcs.262064) (lacouture2024hiv1assembly–whenvirology pages 6-7).

Concise summary of primary function, location, and pathways
- Function: Curvature-sensitive membrane–actin adaptor that biases actin network architecture by recruiting NPFs/bundlers via SH3 in response to local membrane shape and small GTPase inputs (Rac1/Cdc42) (https://doi.org/10.7554/eLife.72316; https://doi.org/10.1242/jcs.262064) (quiroga2023amechanosensingmechanism pages 6-8, lacouture2024hiv1assembly–whenvirology pages 6-7).
- Location: Plasma membrane nanodomains of negative curvature, filopodia, lamellipodia, and neuronal dendritic spines; also implicated at endocytic/EV sites (https://doi.org/10.7554/eLife.72316; 2023; https://doi.org/10.1242/jcs.262064; 2024) (quiroga2023amechanosensingmechanism pages 6-8, lacouture2024hiv1assembly–whenvirology pages 6-7).
- Pathways: Rho GTPase–actin regulatory networks (Rac1/Cdc42) with downstream Arp2/3 and Ena/VASP/Eps8/WAVE via SH3 interactions, and cooperation with other BAR proteins (e.g., BIN1) (https://doi.org/10.1038/s42003-024-06168-8; 2024; https://doi.org/10.3892/mmr.2025.13437; 2025) (picas2024bin1regulatesactinmembrane pages 3-5, zhang2025insulinreceptortyrosine pages 2-3).

Concept	Mechanistic / evidence summary	Principal interactors / effectors	Subcellular site / structure	Source (year, DOI/URL, context ID)
Key concepts & definitions	IRSp53 (BAIAP2) is an I-BAR/IMD family scaffold that senses and/or generates negative membrane curvature and couples membrane shape to actin remodeling via SH3-mediated recruitment of actin regulators.	Rac1, Cdc42, Arp2/3, WAVE complex, N-WASP, Eps8, Mena/VASP, Ezrin, Arc	Plasma membrane evaginations, filopodia, lamellipodia, dendritic spines, endocytic/EV sites	Quiroga et al., eLife 2023 (doi:10.7554/eLife.72316) (quiroga2023amechanosensingmechanism pages 6-8); Zhang & Zhang, Mol Med Rep 2025 (doi:10.3892/mmr.2025.13437) (zhang2025insulinreceptortyrosine pages 2-3); Lacouture et al. J Cell Sci 2024 (jcs262064) (lacouture2024hiv1assembly–whenvirology pages 6-7)
Domain architecture & partners	N-terminal I-BAR/IMD domain (membrane curvature binding/induction) — central CRIB/PR region for small GTPase input — C-terminal SH3 (recruits proline-rich NPFs/actin modulators); WW/PDZ motifs reported.	BIN1, Dynamin, WAVE, N-WASP, Eps8, Mena/VASP, Ezrin	Co-localizes to filopodia base/shaft; forms membrane tubules on PI(4,5)P2 GUVs in vitro	Picas et al., Commun Biol 2024 (doi:10.1038/s42003-024-06168-8) (picas2024bin1regulatesactinmembrane pages 3-5); Zhang & Zhang 2025 (zhang2025insulinreceptortyrosine pages 2-3); Lacouture 2024 (lacouture2024hiv1assembly–whenvirology pages 6-7)
Core molecular mechanisms	I-BAR domain preferentially sorts to negative curvature (peak at ~0.05 nm^-1) with ~2-fold enrichment; links curvature sensing to actin polymerization via Rac1/Cdc42 → Arp2/3 (branched) or filopodial (Cdc42/formin) outputs; SH3 recruits NPFs/bundlers to modulate protrusion type.	Rac1, Cdc42, Arp2/3, WAVE complex, N-WASP, Formins, Eps8, Mena/VASP	Membrane evaginations (nanoscale ~100 nm), filopodial tips, leading edge	Quiroga et al., eLife 2023 (doi:10.7554/eLife.72316) (quiroga2023amechanosensingmechanism pages 6-8); Sahnine 2023 (sahnine2023molecularmechanismsregulating pages 125-131); Zhang & Zhang 2025 (zhang2025insulinreceptortyrosine pages 2-3)
Cellular localization & structures	Enriched at dendritic spines and filopodia; recruited to mechanically induced nanoscale evaginations; full-length protein required for enrichment at evaginations; forms membrane indentations/tubules in vitro.	Ezrin, BIN1 (co-recruitment), Arc (EV biogenesis contexts)	Dendritic spines, filopodia, lamellipodia, nanoscale PM evaginations, EV biogenesis sites	Quiroga et al., eLife 2023 (doi:10.7554/eLife.72316) (quiroga2023amechanosensingmechanism pages 6-8); Picas et al., Commun Biol 2024 (doi:10.1038/s42003-024-06168-8) (picas2024bin1regulatesactinmembrane pages 3-5); Lacouture 2024 (lacouture2024hiv1assembly–whenvirology pages 6-7)
Mechanosensing & membrane homeostasis	IRSp53 recognizes ~100 nm PM evaginations produced by stretch/compression, triggering a rapid Rac1→Arp2/3 actin polymerization burst that re-flattens evaginations (mechanochemical feedback). Quantified curvature sorting: peak at ~0.05 nm^-1 with ~2× enrichment.	Rac1, Arp2/3, Ezrin	Nanoscale plasma membrane evaginations (mechanosensing sites)	Quiroga et al., eLife 2023 (doi:10.7554/eLife.72316) (quiroga2023amechanosensingmechanism pages 6-8); Sahnine 2023 (sahnine2023molecularmechanismsregulating pages 125-131)
Cooperative factors (example: BIN1)	BIN1 (N-BAR) bundles actin and requires IRSp53 for BIN1-driven filopodia; BIN1 localizes at filopodia base and along filopodia and is recruited to IRSp53-induced membrane indentations; BIN1–IRSp53 association is SH3-mediated. Quant: >75% of IRSp53-positive filopodia show BIN1 colocalization.	BIN1, Dynamin, Ezrin	Filopodia base and shaft; GUV membrane tubules in vitro	Picas et al., Commun Biol 2024 (doi:10.1038/s42003-024-06168-8) (picas2024bin1regulatesactinmembrane pages 3-5)
Disease & pathogen contexts	IRSp53 implicated in neuronal development/plasticity and neuropsychiatric phenotypes (mouse social deficits, synaptic roles), cancer/tissue fluidity (tumor spheroid wetting), and pathogen exploitation (host protrusions, EV-mediated cargo like Arc/tau; reported roles in bacterial cell-to-cell spread and proposed involvement in virus assembly).	Afadin (junctional partner in tissue mechanics), Arc (EV biogenesis), factors in migration/invasion pathways	Brain (dendritic spines, circuits affecting social behavior), tumor spheroids (tissue fluidity), infection-related protrusions/EV release	Lacouture 2024 (lacouture2024hiv1assembly–whenvirology pages 6-7); Quiroga et al. 2023 (quiroga2023amechanosensingmechanism pages 6-8); Picas et al. 2024 (picas2024bin1regulatesactinmembrane pages 3-5); Zhang & Zhang 2025 (zhang2025insulinreceptortyrosine pages 2-3)

Table: Compact reference table summarizing IRSp53/BAIAP2 key concepts, mechanisms, partners, cellular sites, mechanosensing functions, cooperative factors (e.g., BIN1), and disease/pathogen contexts with primary source citations for rapid lookup.

Limitations and open questions
- Human genetic associations and detailed clinical statistics for BAIAP2 in neuropsychiatric disorders, cancer, and pathogen exploitation require additional targeted studies; the present synthesis emphasizes mechanistic and cell-biophysical work (2023–2024) and authoritative reviews that frame hypotheses for those disease contexts (https://doi.org/10.1242/jcs.262064; 2024; https://doi.org/10.3892/mmr.2025.13437; 2025) (lacouture2024hiv1assembly–whenvirology pages 6-7, zhang2025insulinreceptortyrosine pages 2-3).

Citations with URLs and dates
- Quiroga X et al. A mechanosensing mechanism controls plasma membrane shape homeostasis at the nanoscale. eLife. Sep 2023. https://doi.org/10.7554/eLife.72316 (quiroga2023amechanosensingmechanism pages 6-8, quiroga2023amechanosensingmechanism pages 30-31).
- Picas L et al. BIN1 regulates actin-membrane interactions during IRSp53-dependent filopodia formation. Communications Biology. May 2024. https://doi.org/10.1038/s42003-024-06168-8 (picas2024bin1regulatesactinmembrane pages 3-5).
- Lacouture C et al. HIV-1 assembly—when virology meets biophysics. Journal of Cell Science. 2024. https://doi.org/10.1242/jcs.262064 (lacouture2024hiv1assembly–whenvirology pages 6-7).
- Zhang X, Zhang Z. Insulin receptor tyrosine kinase substrate in health and disease (Review). Molecular Medicine Reports. Jan 2025 (accepted Dec 2024). https://doi.org/10.3892/mmr.2025.13437 (zhang2025insulinreceptortyrosine pages 2-3).
- Sahnine M. Molecular mechanisms regulating actin cytoskeleton remodeling within membrane protrusions induced by one-dimensional wetting. 2023. (context describing IRSp53 recruitment to negative curvature and Arp2/3 coupling) (sahnine2023molecularmechanismsregulating pages 125-131).

References

(lacouture2024hiv1assembly–whenvirology pages 6-7): C Lacouture, B Carrio, and C Favard. Hiv-1 assembly–when virology meets biophysics. Unknown journal, 2024.
(zhang2025insulinreceptortyrosine pages 2-3): Xueyan Zhang and Zhewen Zhang. Insulin receptor tyrosine kinase substrate in health and disease (review). Molecular Medicine Reports, Jan 2025. URL: https://doi.org/10.3892/mmr.2025.13437, doi:10.3892/mmr.2025.13437. This article has 0 citations and is from a peer-reviewed journal.
(quiroga2023amechanosensingmechanism pages 6-8): Xarxa Quiroga, Nikhil Walani, Andrea Disanza, Albert Chavero, Alexandra Mittens, Francesc Tebar, Xavier Trepat, Robert G Parton, María Isabel Geli, Giorgio Scita, Marino Arroyo, Anabel-Lise Le Roux, and Pere Roca-Cusachs. A mechanosensing mechanism controls plasma membrane shape homeostasis at the nanoscale. eLife, Sep 2023. URL: https://doi.org/10.7554/elife.72316, doi:10.7554/elife.72316. This article has 17 citations and is from a domain leading peer-reviewed journal.
(picas2024bin1regulatesactinmembrane pages 3-5): Laura Picas, Charlotte André-Arpin, Franck Comunale, Hugo Bousquet, Feng-Ching Tsai, Félix Rico, Paolo Maiuri, Julien Pernier, Stéphane Bodin, Anne-Sophie Nicot, Jocelyn Laporte, Patricia Bassereau, Bruno Goud, Cécile Gauthier-Rouvière, and Stéphanie Miserey. Bin1 regulates actin-membrane interactions during irsp53-dependent filopodia formation. Communications Biology, May 2024. URL: https://doi.org/10.1038/s42003-024-06168-8, doi:10.1038/s42003-024-06168-8. This article has 10 citations and is from a peer-reviewed journal.
(sahnine2023molecularmechanismsregulating pages 125-131): M Sahnine. Molecular mechanisms regulating actin cytoskeleton remodeling within membrane protrusions induced by one-dimensional wetting. Unknown journal, 2023.
(quiroga2023amechanosensingmechanism pages 30-31): Xarxa Quiroga, Nikhil Walani, Andrea Disanza, Albert Chavero, Alexandra Mittens, Francesc Tebar, Xavier Trepat, Robert G Parton, María Isabel Geli, Giorgio Scita, Marino Arroyo, Anabel-Lise Le Roux, and Pere Roca-Cusachs. A mechanosensing mechanism controls plasma membrane shape homeostasis at the nanoscale. eLife, Sep 2023. URL: https://doi.org/10.7554/elife.72316, doi:10.7554/elife.72316. This article has 17 citations and is from a domain leading peer-reviewed journal.

Citations

quiroga2023amechanosensingmechanism pages 6-8
zhang2025insulinreceptortyrosine pages 2-3
sahnine2023molecularmechanismsregulating pages 125-131
quiroga2023amechanosensingmechanism pages 30-31
https://doi.org/10.1242/jcs.262064;
https://doi.org/10.3892/mmr.2025.13437;
https://doi.org/10.7554/eLife.72316;
https://doi.org/10.3892/mmr.2025.13437
https://doi.org/10.1038/s42003-024-06168-8
https://doi.org/10.1242/jcs.262064
https://doi.org/10.1038/s42003-024-06168-8;
https://doi.org/10.7554/eLife.72316
https://doi.org/10.3892/mmr.2025.13437,
https://doi.org/10.7554/elife.72316,
https://doi.org/10.1038/s42003-024-06168-8,

Perplexity

(BAIAP2-deep-research-perplexity.md)

Comprehensive Functional Annotation of BAIAP2 (Brain-Specific Angiogenesis Inhibitor 1-Associated Protein 2) Perplexity sonar-deep-research 47 citations 2025-12-27T16:12:12.347361

The user is asking for a comprehensive research report on the gene BAIAP2 (also known as IRSp53), UniProt accession Q9UQB8, from Homo sapiens (human).

Let me first verify that I have the correct gene/protein based on the search results provided:
- UniProt Q9UQB8 matches the protein described: BAR/IMD domain-containing adapter protein 2
- Gene symbol BAIAP2 is correct
- Also known as IRSp53 (Insulin Receptor Substrate protein of 53 kDa)
- This is a human protein
- Key domains: BAR domain, I-BAR domain, SH3 domain

Looking at the search results, I have extensive literature on BAIAP2/IRSp53. The search results include:
1. Multiple research papers on molecular and cellular functions
2. Structural information
3. Information about its role in synaptic development
4. Information about psychiatric disorders
5. Information about filopodia formation
6. Information about dendritic spine development
7. Information about its protein-protein interactions
8. Recent findings on developmental epileptic encephalopathies

This is clearly the correct gene, and there's plenty of literature to work with.

Now let me plan a comprehensive 10000+ word report:

Title and Key Findings Summary
Molecular Structure and Architecture - discussing the domain organization
Cellular Localization and Protein Interaction Partners - where it's found and what it binds to
Primary Molecular Functions - what does it actually do at the molecular level
Regulation and Activation Mechanisms - how is BAIAP2/IRSp53 regulated
Role in Synaptic Development and Dendritic Spine Morphogenesis - one of its major functions
Involvement in Cell Motility and Filopodia Formation - membrane protrusion dynamics
Pathological Associations and Disease Implications - neuropsychiatric disorders and epilepsy
Evolutionary Conservation and Related Family Members
Conclusions and Future Directions

This structure will provide a thorough examination of the protein's molecular architecture, cellular roles, regulatory mechanisms, and clinical significance across multiple biological contexts.

Comprehensive Functional Annotation of BAIAP2 (Brain-Specific Angiogenesis Inhibitor 1-Associated Protein 2)

BAIAP2, commonly known by its alternative name IRSp53 (insulin receptor substrate protein of 53 kDa), is a multidomain adaptor and scaffolding protein that functions as a central integrator of signaling pathways regulating actin cytoskeleton dynamics, membrane morphology, and synaptic organization[1][2][5]. This protein serves as a critical molecular hub that couples membrane-bound small GTPase signaling—particularly through Rho family members such as Cdc42 and Rac1—with diverse downstream effectors that control actin polymerization and membrane remodeling[2][10][13]. The functional importance of BAIAP2 is underscored by its abundant expression in the brain, particularly within the postsynaptic density of excitatory synapses, and by its implication in multiple neuropsychiatric and neurological disorders including autism spectrum disorders, schizophrenia, attention-deficit/hyperactivity disorder, developmental epileptic encephalopathies, and depression[5][21][43]. Through its unique multidomain architecture and its ability to transduce signals across different cellular compartments, BAIAP2 orchestrates fundamental processes ranging from the initiation and elongation of cellular protrusions such as filopodia and lamellipodia to the formation and refinement of dendritic spines during brain development.

Molecular Architecture and Structural Organization

Domain Composition and Structural Features

BAIAP2 is a 552-amino acid protein comprising three major functional domains that collaborate to enable its diverse cellular roles[3][4]. The N-terminal inverse-BAR (I-BAR) domain, also referred to as the IRSp53/MIM homology domain (IMD), spans approximately the first 231 amino acids and forms a distinctive crescent-shaped homodimer structure that is critical for membrane sensing and deformation[3][10][14]. This I-BAR domain belongs to the larger family of Bin-Amphiphysin-Rvs (BAR) domains and possesses the remarkable ability to recognize and bind to highly curved, negatively charged membrane surfaces, particularly those enriched in phosphatidylserine (PS) and phosphatidylinositol 4,5-bisphosphate (PIP₂)[14][47]. The I-BAR domain serves not merely as a passive membrane-binding module but as an active membrane-deforming element that can induce both the sensing of negative membrane curvature and the generation of membrane protrusions[17][14]. This property makes it essential for initiating the formation of cellular protrusions like filopodia and lamellipodia.

Following the I-BAR domain, BAIAP2 contains a Cdc42/Rac interactive binding-proline-rich (CRIB-PR) domain located at residues 260-291[10][37]. This domain serves as the primary recognition site for activated small GTPases, particularly Cdc42, though it can also interact with Rac1 with lower affinity[10]. The CRIB domain itself provides the direct binding interface for the GTPases, while the adjacent proline-rich sequence that interrupts this motif creates an extended recognition surface that permits more complex interactions with regulatory molecules[10][37]. Notably, in the inactive state of the protein, the CRIB-PR domain can engage in intramolecular interactions with the downstream SH3 domain, resulting in a compact, closed conformation that constrains the protein's activity[10][37].

The C-terminal Src homology 3 (SH3) domain, positioned at residues 375-437, represents one of the most versatile functional elements of BAIAP2[10][50]. The SH3 domain mediates interactions with numerous downstream cytoskeletal regulatory proteins by recognizing proline-rich motifs present in target proteins[2][10][13]. These interaction partners include vasodilator-stimulated phosphoprotein (VASP), enabled/VASP-like protein (Ena/VASP), Eps8, N-WASP, and members of the WAVE2 complex, among others[10][20][52]. The specificity and regulatory capacity of these SH3-mediated interactions allow BAIAP2 to functionally integrate signals from multiple upstream activators and to coordinate the recruitment of distinct sets of actin regulatory machinery depending on cellular context[2][10][13].

Between the CRIB-PR and SH3 domains lies a flexible linker region (approximately residues 292-374) that is particularly rich in serine, threonine, and proline residues[10][37]. This linker region contains multiple phosphorylation sites that serve as a regulatory hub for post-translational modification of the protein[10][37][51]. Phosphorylation of two or more sites within this linker region, particularly at positions corresponding to T360 and S366, triggers the binding of 14-3-3 regulatory proteins, which locks BAIAP2 in its autoinhibited, closed conformation and prevents activation by either Cdc42 or downstream cytoskeletal effectors[10][37]. Additionally, this linker region contains a PDZ-binding motif (PBM) at its C-terminus that mediates critical interactions with postsynaptic density scaffold proteins like PSD-95 and Shank3[7][9].

Structural Basis of Dimeric Organization and Membrane Coupling

The I-BAR domain of BAIAP2 naturally assembles into homodimers with an extensive dimer interface, forming a symmetric, crescent-shaped structure that spans roughly 150 amino acids[3]. This dimeric organization is not merely an incidental feature but is functionally essential for the protein's ability to sense membrane curvature and to organize local molecular events at the membrane[3][14][20]. Structural studies have demonstrated that the I-BAR domain dimer can stabilize and induce specific membrane geometries, with the crescent-shaped dimer fitting into negatively curved membranes in a manner analogous to how a wedge fits into a gap[14][17]. Recent investigations have revealed that BAIAP2 does not function as isolated dimers but rather self-assembles into higher-order clusters on membranes in a PIP₂-dependent manner[14][20]. These clusters form preferentially on PIP₂-enriched membrane domains and create a positive feedback mechanism whereby I-BAR domain clustering induces the local enrichment of PIP₂ lipids, which in turn promotes further recruitment and clustering of additional BAIAP2 molecules[14][20].

Cellular Localization and Subcellular Compartmentalization

Postsynaptic Density Localization and Synaptic Enrichment

BAIAP2 is exceptionally abundant at the postsynaptic density (PSD) of excitatory synapses, a specialized electron-dense region located immediately opposite presynaptic terminals that serves as a hub for organizing synaptic signaling and structural proteins[5][7][9][22]. Biochemical fractionation studies have demonstrated that BAIAP2 is enriched in crude synaptosomal preparations (P2 fraction) and synaptic membrane fractions (LP1), and it accumulates in purified PSD fractions prepared from brain tissue[9][22]. Within the PSD, BAIAP2 is distributed throughout both the core and peripheral regions, consistent with its simultaneous binding to both core scaffold proteins (PSD-95, Shank3) and to F-actin located in the more peripheral compartments[7][12]. Immunogold electron microscopy in situ has revealed that BAIAP2 molecules are dispersed throughout the PSD architecture rather than forming discrete punctate clusters, though accumulation is greater in the PSD pallium under excitatory conditions[26].

The synaptic localization of BAIAP2 depends critically on its PDZ-binding motif (PBM) at its C-terminus and on its interactions with major PSD scaffolding proteins[9][12]. BAIAP2 directly binds to PSD-95 through specific interactions between its PBM and the PDZ domains of PSD-95, and it also binds to Shank3 through its SH3 domain engaging with proline-rich sequences in Shank3[7][9][12]. Functional experiments using cultured neurons have demonstrated that deletion of the PBM eliminates the synaptic localization of BAIAP2 and causes the protein to remain diffusely distributed throughout the cytoplasm[9]. Similarly, mutations in the SH3 domain that disrupt Shank3 binding significantly reduce synaptic enrichment of BAIAP2[9]. These findings collectively establish that BAIAP2's synaptic targeting depends on multivalent interactions with PSD scaffold proteins.

Double immunofluorescence staining of cultured hippocampal neurons reveals that BAIAP2 colocalizes extensively with PSD-95 at dendritic spines and at sites closely apposed to the presynaptic marker synaptophysin, confirming its concentration at functional synapses[9][22]. Beyond its abundant synaptic localization, BAIAP2 is also detected at lower levels in dendritic shafts and in other cellular compartments including the soma and growth cones, reflecting its roles in multiple cellular contexts[9].

Extra-Synaptic and Growth Cone Functions

Although BAIAP2 is most prominently associated with the postsynaptic density, significant populations of the protein function outside the synapse at different cellular locations depending on developmental stage and cellular context[9][10]. During neuronal development, BAIAP2 is particularly enriched in growth cones at the tips of extending neurites[8]. Growth cones are dynamic, motile structures that probe the extracellular environment and guide axonal and dendritic growth to appropriate target sites[8]. The presence of BAIAP2 in growth cones suggests roles in the actin-based motility and morphological dynamics required for effective growth cone navigation[8][12].

BAIAP2 also localizes to lamellipodia and filopodia, which are actin-rich cellular protrusions that initiate motile responses in many cell types[2][10]. In cells undergoing migration or morphological remodeling, BAIAP2 accumulates at the leading edges and at sites of membrane protrusion formation, consistent with its functions in regulating these actin-dependent structures[10][14][20].

Primary Molecular Functions

Actin Binding and F-Actin Bundling

One of the fundamental enzymatic activities of BAIAP2 is direct binding to and bundling of actin filaments, properties mediated primarily by the I-BAR domain[3][7][12][26]. Purified BAIAP2 or its isolated I-BAR domain can bind to filamentous actin (F-actin) in vitro and induce the formation of tightly bundled arrays of parallel actin filaments[3][7]. This actin bundling activity requires specific positively charged residues in the I-BAR domain, and mutation of these residues abolishes both the in vitro bundling capacity and the ability of BAIAP2 to induce filopodia formation in cells[3][7]. The molecular mechanism of BAIAP2-mediated actin bundling differs from that of other known actin-bundling proteins; rather than directly crosslinking adjacent filaments as does the protein fascin, BAIAP2's I-BAR domain appears to stabilize bundles by binding along the length of actin filaments and organizing them into regular, parallel arrays[3][7][12].

Recent studies employing biochemical reconstitution on supported lipid bilayers have demonstrated that BAIAP2-mediated actin bundling is dramatically enhanced when the protein undergoes phase separation through its interactions with PSD-95 and other scaffold proteins[7][12][26]. When BAIAP2 and PSD-95 form phase-separated condensates—liquid-like droplets that concentrate proteins and promote protein-protein interactions—the local concentration of BAIAP2 increases substantially, thereby lowering the threshold concentration required for efficient actin bundling[7][12][26]. These reconstituted PSD condensates can nucleate and organize bundled actin filament arrays both in solution and when tethered to lipid bilayers, suggesting that the layered organization of the postsynaptic density promotes efficient actin organization at synapses[7][12][26].

Membrane Binding and Curvature Sensing

The I-BAR domain of BAIAP2 functions as a specialized lipid-binding and membrane-sensing module that recognizes both specific lipid species and membrane geometric properties[14][17][47]. The dimeric crescent shape of the I-BAR domain creates a positively charged inner surface that electrostatically attracts negatively charged phospholipids such as PS and PIP₂[14][47]. In addition to lipid-specific recognition, the I-BAR domain can selectively stabilize regions of the membrane that exhibit negative curvature—inward-directed bending of the lipid bilayer[14][17][47]. This curvature-sensing capability enables BAIAP2 to selectively localize to and accumulate at sites of dynamic membrane remodeling[14][20].

Recent investigations employing the innovative technique of pulling membrane nanotubes from live cells have revealed that BAIAP2 localizes preferentially to regions of the plasma membrane that undergo rapid and substantial shape changes rather to flatter, more static membrane regions[14][47]. This dynamic localization pattern suggests that BAIAP2 is regulated to become active only at sites where cellular processes such as filopodium initiation or synapse remodeling are occurring, thus providing spatial and temporal specificity to its functions[14][47]. The curvature-sensing property of BAIAP2 appears to rely on a combination of membrane composition (particularly PIP₂ concentration) and dynamic membrane movements, indicating that BAIAP2 integrates multiple types of cellular information to regulate its activation state[14][47].

GTPase Binding and Cdc42/Rac1 Signal Transduction

The CRIB-PR domain of BAIAP2 serves as a direct effector binding site for activated Cdc42 and Rac1, allowing these small GTPases to regulate BAIAP2 activity and localization[10][35][37]. Binding of GTP-Cdc42 to the CRIB-PR domain triggers a conformational transition of BAIAP2 from its autoinhibited closed state to an active, open state in which the SH3 domain becomes exposed and accessible to downstream binding partners[10][37][52]. This conformational change is monitored through fluorescence resonance energy transfer (FRET) assays that measure the distance between the CRIB-PR and SH3 domains in response to GTPase binding[10][37].

The interaction between BAIAP2 and Cdc42 is kinetically rapid and has important functional consequences for cell morphology[10][52]. Cells expressing constitutively active Cdc42 or those stimulated with agents that activate Cdc42 exhibit pronounced formation of filopodia-like protrusions that depend critically on BAIAP2 and its interaction with Cdc42[10][52]. Conversely, disruption of Cdc42 binding through mutation of the CRIB motif impairs filopodia formation, indicating that Cdc42 activation of BAIAP2 is both necessary and sufficient for this morphological response[10][52].

Recruitment and Clustering of Actin Regulatory Proteins

A principal function of the BAIAP2 SH3 domain is to recruit and spatially organize diverse actin regulatory proteins at sites of membrane protrusion and synaptic activity[2][10][13][23][52]. The SH3 domain of BAIAP2 has particularly high affinity for VASP (vasodilator-stimulated phosphoprotein), an actin polymerase that catalyzes the processive addition of actin monomers to the barbed ends of actin filaments[10][52]. Through its SH3 domain, BAIAP2 can capture VASP from the cytoplasm and organize it into high-density clusters on membranes, particularly at sites enriched in PIP₂[14][20][52]. This clustering function is essential for VASP's ability to overcome the inhibitory effects of capping proteins that normally prevent actin elongation[52].

The recruitment and clustering of VASP by BAIAP2 represents a critical step in filopodium initiation[14][20][52]. In vitro reconstitution experiments demonstrate that when BAIAP2 clusters are present on PIP₂-enriched lipid bilayers, they efficiently recruit VASP tetramers and stimulate VASP-mediated actin polymerization, leading to the assembly of actin filaments directly on the membrane surface[14][20][52]. These membrane-proximal actin filaments can then be organized into bundles by the actin-bundling protein fascin, ultimately driving the formation of filopodium-like membrane protrusions[14][20].

Beyond VASP, BAIAP2's SH3 domain interacts with multiple other actin regulators including Eps8, Ena/VASP family members, and components of the WAVE2/Arp2/3 complex[10][13][23]. The relative recruitment and clustering of different SH3 domain partners is regulated by competitive binding and by differential activation of upstream GTPases, allowing BAIAP2 to coordinate distinct actin assembly programs depending on the cellular context[23][52].

Regulation of BAIAP2 Activity and Function

Conformational Regulation and Autoinhibition

BAIAP2 exists in an autoinhibited conformational state under resting conditions in which the SH3 domain makes intramolecular contacts with the CRIB-PR domain, limiting access of downstream effector proteins to the SH3 domain[10][37][52]. This autoinhibited conformation can be disrupted by either of two types of activating inputs: binding of GTP-Cdc42 or GTP-Rac1 to the CRIB-PR domain, or direct binding of SH3 domain partners such as VASP or Eps8 to the SH3 domain itself[10][37][52]. These two activation mechanisms are not redundant but rather appear to activate distinct downstream effector programs[10][37][52].

The conformational changes associated with activation have been directly visualized using FRET-based biosensors that measure the distance between the CRIB-PR and SH3 domains[10][37]. When BAIAP2 binds to activated Cdc42, the protein undergoes a transition toward a more open conformation in which the SH3 domain moves away from the CRIB-PR region, increasing the accessibility of the SH3 domain to binding partners[10][37]. Similarly, when downstream effectors directly engage the SH3 domain, they also promote the open conformation[10][37].

Phosphorylation-Dependent Inhibition by 14-3-3 Proteins

Phosphorylation of the linker region between the CRIB-PR and SH3 domains represents a major mechanism for negatively regulating BAIAP2 activity[10][37][51]. The linker region contains multiple potential phosphorylation sites, and phosphorylation at two or more specific sites (particularly T360 and S366) within this region triggers the binding of 14-3-3 regulatory proteins[10][37][51]. When 14-3-3 proteins bind to phosphorylated BAIAP2, they lock the protein into its closed, autoinhibited conformation, effectively blocking both the binding of Cdc42 to the CRIB-PR domain and the recruitment of downstream SH3 domain binding partners[10][37].

This phosphorylation-dependent inhibition occurs particularly under conditions of serum deprivation or metabolic stress[10][37]. Mechanistically, the phosphorylation sites that mediate 14-3-3 binding include AMPK consensus motifs, indicating that the AMP-activated protein kinase (AMPK) directly phosphorylates BAIAP2 under conditions of low cellular energy[10][51]. Pharmacological activation of AMPK increases phosphorylation of BAIAP2 and promotes 14-3-3 binding, whereas inhibition of AMPK reduces phosphorylation and promotes BAIAP2 activation[10][51]. This metabolic regulation allows cells to suppress filopodium formation and restrict actin-based motility during periods of energy stress, redirecting metabolic resources toward energy generation rather than biosynthetic and motility processes[10][51].

Regulated Assembly into Membrane Clusters

BAIAP2 self-assembles into discrete clusters on PIP₂-containing membranes, and this clustering is essential for multiple aspects of its function[14][20]. The clustering process itself is regulated by PIP₂ concentration and membrane composition, with higher PIP₂ levels promoting more extensive clustering[14][20]. Notably, BAIAP2 clustering enriches PIP₂ lipids locally, creating a positive feedback loop in which I-BAR domain clusters further concentrate PIP₂, thereby promoting additional BAIAP2 recruitment[14][20].

The clustering of BAIAP2 also represents a form of functional regulation in that high-density BAIAP2 arrays can recruit VASP and other actin regulators more efficiently than can individual monomeric or dimeric BAIAP2 molecules[14][20][52]. In cells, BAIAP2 clustering appears to be dynamically regulated in response to cell signals; accumulation of BAIAP2 into clusters at the plasma membrane typically precedes the initiation of filopodium formation by seconds to minutes[14][20]. This temporal coordination suggests that cluster formation is an active regulatory process that gates filopodium initiation.

Role in Dendritic Spine Development and Synaptic Plasticity

Mechanisms of Spine Morphogenesis

Dendritic spines are small, actin-filled protrusions that emerge from the main dendritic shaft and serve as the primary sites of excitatory synaptic contact in the brain[9][12][50]. The formation, maturation, and dynamic remodeling of dendritic spines depend critically on the regulated control of actin cytoskeleton dynamics within spine heads[9][12][50]. BAIAP2 is one of the most abundant proteins in the postsynaptic density, where it performs essential functions in controlling actin organization within spine heads and in regulating spine morphology[9][12][50].

Overexpression of wild-type BAIAP2 in cultured neurons increases the density of dendritic spines and promotes spine maturation, whereas loss of BAIAP2 through genetic deletion or knockdown dramatically reduces spine density and impairs dendritic spine morphogenesis[9][12][50]. Experiments in which cultured cortical neurons from BAIAP2 knockout mice are rescued with exogenous BAIAP2 expression demonstrate that BAIAP2 is both necessary and sufficient for proper dendritic spine development[12][26]. Critically, mutants of BAIAP2 that cannot interact with PSD-95 (lacking the PDZ-binding motif) fail to rescue the spine deficits observed in knockout neurons, indicating that the PSD-95 interaction is essential for BAIAP2's role in spine development[12][26].

At the mechanistic level, BAIAP2 regulates spine morphogenesis through its dual abilities to bundle actin filaments and to organize these bundles at the spine membrane[7][12]. Within dendritic spines, BAIAP2 organizes robust bundles of actin filaments that reinforce the spine structure and resist deformation[7][12]. When BAIAP2 is absent or when mutations disrupt its actin-binding capacity, spines fail to develop proper actin bundle organization and consequently fail to mature properly[7][12]. The phase separation-mediated organization of BAIAP2 within PSD condensates further enhances actin bundling efficiency, suggesting that PSD assembly itself promotes spine development by creating an environment conducive to BAIAP2-mediated actin organization[7][12][26].

Interaction with Glutamate Receptor Signaling

BAIAP2 functions as a critical link between postsynaptic glutamate receptor signaling and actin cytoskeleton reorganization[5][50][55]. The protein binds directly to multiple components of the PSD, including the NMDA receptor-associated scaffold proteins PSD-95 and Shank, creating a molecular bridge between the machinery that responds to synaptic glutamate and the actin-regulating machinery[5][9][50]. This physical linkage positions BAIAP2 to transduce glutamate-evoked calcium signals and kinase cascades into rapid changes in actin organization[5][50].

Experiments employing electrophysiological recording from neurons with conditional deletion of BAIAP2 specifically in glutamatergic neurons have revealed that loss of BAIAP2 disrupts the balance between excitatory and inhibitory synaptic transmission[5][55]. In male mice, glutamatergic BAIAP2 deletion leads to an increased ratio of evoked excitatory to inhibitory postsynaptic currents (E/I ratio) in the medial prefrontal cortex, particularly in layer V pyramidal neurons[5][55]. This E/I imbalance is associated with behavioral manifestations including social deficits and hyperactivity[5][55]. Notably, the effects of BAIAP2 deletion differ between sexes, with female mice showing more modest E/I ratio alterations and behavioral effects, indicating that BAIAP2's role in synaptic regulation interacts with sex-specific signaling mechanisms[5][55].

Filopodia Formation and Cell Motility

Filopodium Initiation and Assembly

Filopodia are thin, actin-filled cellular protrusions typically 0.1-0.2 micrometers in diameter and up to several micrometers in length[14][20][52]. These structures are essential for neuronal growth cone guidance, cell migration, and cell-cell communication[10][14][20]. BAIAP2 is recognized as one of the most critical regulators of filopodium formation, functioning to initiate their assembly through its coordinated action of membrane sensing, actin bundling, and recruitment of actin polymerases[10][14][20][52].

The molecular mechanism of filopodium initiation appears to involve a coordinated sequence of events in which BAIAP2 accumulates at sites of dynamic membrane curvature, self-assembles into clusters, recruits VASP, and organizes actin polymerization at the membrane[14][20]. Recent live-cell imaging studies using advanced fluorescence microscopy have documented that BAIAP2 begins to accumulate at developing filopodia sites several seconds to minutes before visible actin assembly begins, indicating that BAIAP2 clustering represents an initiating event[14][20]. Once BAIAP2 clusters form, they recruit VASP tetramers, which catalyze the processive addition of actin monomers to the barbed ends of actin filaments[20][52]. The actin filaments thus nucleated are subsequently organized into parallel bundles by the bundling protein fascin, creating the characteristic bundle of parallel filaments that forms the core of the filopodium[14][20].

The importance of this sequence is underscored by observations that disrupting any single step—whether BAIAP2 clustering, VASP recruitment, VASP polymerase activity, or fascin-mediated bundling—substantially impairs filopodium formation[14][20][52]. Conversely, when all components are present and properly activated, filopodia form spontaneously even in cell-free reconstitution systems containing only purified proteins and lipid bilayers, demonstrating that BAIAP2 and its associated machinery are essentially sufficient for filopodium formation[14][20].

Coupling to Rho GTPase Signaling

The Rho family of small GTPases—particularly Cdc42 and Rac1—functions as upstream regulators that activate BAIAP2 and thereby initiate filopodium formation in response to extracellular signals[10][52]. Growth factors, adhesion molecules, and other extracellular stimuli activate guanine nucleotide exchange factors (GEFs) that catalyze the release of GDP and loading of GTP onto Cdc42 and Rac1[10]. GTP-loaded Cdc42 then binds to the CRIB-PR domain of BAIAP2, triggering its conformational activation and promoting filopodia formation[10][52].

The relationship between Cdc42 and BAIAP2 is not merely one of Cdc42 activating a downstream target; rather, BAIAP2 functions as a crucial effector that translates Cdc42 activation into the physical reorganization of the actin cytoskeleton[10][52]. Cells lacking BAIAP2 fail to form filopodia in response to Cdc42 activation, even though other Cdc42 effectors remain intact, demonstrating that BAIAP2 occupies a unique position in Cdc42 signaling networks[10][52]. Rac1 also activates filopodia formation, though less potently than Cdc42; BAIAP2 can bind to GTP-Rac1, though with reduced affinity compared to Cdc42[10].

Disease Associations and Pathological Implications

Psychiatric and Neuropsychiatric Disorders

BAIAP2 has been identified as a genetic risk factor in multiple neuropsychiatric disorders through genome-wide association studies, whole exome sequencing, and targeted mutation screening[5][21][33][43][50][55]. Genetic variations in BAIAP2 have been associated with autism spectrum disorders (ASD), schizophrenia, attention-deficit/hyperactivity disorder (ADHD), and major depression[5][21][33][43][50][55].

Autism Spectrum Disorders: Multiple studies have documented genetic alterations in BAIAP2 in individuals with autism, including rare, coding mutations and common polymorphisms[5][33][50]. The biological significance of these associations is supported by animal model studies: mice with global deletion of BAIAP2 display strong social deficits and hyperactivity that resemble behavioral features of autism[5][55]. When BAIAP2 deletion is restricted to glutamatergic neurons using conditional knockout approaches, social deficits emerge in male mice, though with less severity than in global knockouts, indicating that BAIAP2 function in glutamatergic neurons is particularly important for social behavior[5][55]. The social deficits in BAIAP2-deficient mice are accompanied by specific defects in the development and function of cortical circuits involved in social information processing[58]. Neuronal recordings from the medial prefrontal cortex of BAIAP2-knockout mice reveal reduced firing variability and reduced burst firing in excitatory neurons, coupled with a reduced proportion of neurons that selectively respond to social stimuli[58]. These circuit-level abnormalities appear to contribute directly to the social behavioral deficits[58].

Schizophrenia: Whole exome sequencing studies in schizophrenia cohorts have identified rare loss-of-function variants in BAIAP2, and genome-wide association studies have detected common polymorphisms associated with schizophrenia risk[33][50]. The mechanism by which BAIAP2 dysfunction contributes to schizophrenia remains incompletely understood, but given the critical role of BAIAP2 in glutamatergic synapse development and function, altered BAIAP2 activity could disrupt the balance of excitatory and inhibitory neurotransmission implicated in schizophrenia pathogenesis[33][50].

Depression: Recent investigations have demonstrated that hippocampal BAIAP2 expression is significantly reduced in mice exposed to chronic mild stress (CMS), a well-validated animal model of depression[21]. Importantly, viral-mediated overexpression of BAIAP2 in the hippocampus of CMS-exposed mice significantly prevented depression-like behaviors, suggesting that restoration of BAIAP2 levels can have antidepressant effects[21]. The protective mechanism appears to involve maintenance of hippocampal synaptic plasticity; BAIAP2 overexpression prevented CMS-induced decreases in dendritic spine density and sustained expression of synaptic plasticity-related proteins including GluA1 and synaptophysin[21].

Developmental and Epileptic Encephalopathies

Very recent investigations have established de novo missense variants in BAIAP2 as a novel genetic cause of developmental and epileptic encephalopathies (DEEs), a severe category of childhood-onset epilepsy associated with developmental delay and cognitive impairment[43][46]. Six unrelated patients with de novo BAIAP2 missense variants were identified through whole exome or genome sequencing, and all exhibited severe infantile or early childhood-onset epilepsy, with four of the six displaying refractory seizures resistant to multiple antiepileptic drugs[43][46]. All patients showed language and motor developmental delays, and most showed degrees of intellectual disability[43][46].

Notably, the mutations identified in DEE patients were clustered in the linker region between the CRIB-PR and SH3 domains—the same region that contains phosphorylation sites critical for 14-3-3 binding and autoinhibition[43][46]. Molecular and cellular studies demonstrated that these DEE-associated BAIAP2 variants disrupt the autoinhibited conformation and induce a gain-of-function state in which the protein is constitutively active, leading to enhanced filopodia-lamellipodia formation and elevated neuronal excitability[43][46]. Neurons expressing DEE-associated BAIAP2 variants displayed increased excitatory synaptogenesis and elevated spontaneous firing rates[43][46]. Transgenic zebrafish expressing mutant BAIAP2 showed developmental defects, abnormal neurite growth, and enhanced sensitivity to seizure-inducing agents[43][46]. These findings indicate that pathological excess of BAIAP2 function, not merely loss of function, can cause severe neurological disease, establishing BAIAP2 as a dosage-sensitive regulator of neuronal development and excitability[43][46].

Family Members and Evolutionary Conservation

BAIAP2 belongs to a small family of related proteins that share conserved I-BAR and SH3 domains[44]. The family includes BAIAP2L1 (also known as IRTKS or IRSp53-related Trk-binding protein), BAIAP2L2, and more distantly related proteins like Missing-in-Metastasis (MIM)[44]. These family members share the characteristic I-BAR/IMD domain and SH3 domain architecture and possess overlapping but not identical functions[44]. BAIAP2L1 is particularly well-characterized and shares many functions with BAIAP2, including roles in cell migration and actin organization, though it also has specialized functions in particular cell types[44].

BAIAP2 sequences are highly conserved across mammalian species, with the human protein sharing greater than 95 percent sequence identity with the mouse ortholog[3]. The conservation extends to the domain architecture, suggesting that the multidomain functional organization has been maintained throughout mammalian evolution[3]. Outside of mammals, BAIAP2 orthologs are present in lower vertebrates such as zebrafish, and more distantly related I-BAR domain-containing proteins are found in invertebrates and even in protozoa, indicating that this protein family represents an ancient mechanism for coupling membrane organization to actin dynamics[3][14].

Conclusion and Future Perspectives

BAIAP2 has emerged as one of the most central and multifunctional adapter proteins in the mammalian brain, serving as a critical integrator of signaling pathways that regulate actin cytoskeleton organization, membrane morphology, and synaptic development. Through its unique multidomain architecture—comprising an N-terminal I-BAR domain that senses membrane curvature and bundles actin, a CRIB-PR domain that binds small GTPases, and an SH3 domain that recruits diverse downstream effectors—BAIAP2 coordinates the initiation, maturation, and plasticity of dendritic spines and other cellular structures essential for brain function[1][2][5][10][12][50].

The localization of BAIAP2 to the postsynaptic density positions it to directly couple synaptic signaling to cytoskeletal reorganization, enabling rapid changes in spine morphology in response to neural activity[7][9][12][26]. Its role as a molecular hub for integrating Rho GTPase signaling with downstream effector recruitment and its regulation through phosphorylation-dependent 14-3-3 binding provide multiple layers of functional control[10][37][51]. The discovery that gain-of-function BAIAP2 variants cause developmental epileptic encephalopathies, while loss-of-function alterations are associated with autism, schizophrenia, and ADHD, underscores the exquisite dosage-sensitivity of BAIAP2-dependent processes and suggests that precise quantitative control of BAIAP2 expression and activity is essential for normal brain development and function[5][21][33][43][46][50][55].

Future research directions that warrant investigation include further characterization of how BAIAP2 integrates multiple upstream signals to coordinate distinct actin assembly programs in different cellular contexts; delineation of the molecular determinants that specify which downstream effectors are recruited to BAIAP2 under different signaling conditions; and determination of how postsynaptic density phase separation and BAIAP2-mediated actin organization mechanistically promote dendritic spine maturation and synaptic strength. Additionally, understanding the therapeutic implications of BAIAP2 modulation for neuropsychiatric and neurological disorders represents an important direction for future clinical investigation. The emerging picture of BAIAP2 as a central node in synaptic development and function and as a key determinant of brain circuit function positions this protein as a promising target for therapeutic intervention in multiple neurological and psychiatric conditions.

Citations

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https://mfib.pbrg.hu/almanach.php?id=MF7000957
https://www.uniprot.org/uniprotkb/I3L4C2/entry
https://www.frontiersin.org/journals/cellular-neuroscience/articles/10.3389/fncel.2020.00023/full
https://platform.opentargets.org/target/ENSG00000175866
https://pubmed.ncbi.nlm.nih.gov/35819332/
https://pubmed.ncbi.nlm.nih.gov/10343108/
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https://www.molbiolcell.org/doi/10.1091/mbc.E18-09-0600
https://www.uniprot.org/uniprotkb/Q8BKX1/entry
https://rupress.org/jcb/article/221/8/e202105035/213346/IRSp53-promotes-postsynaptic-density-formation-and
https://maayanlab.cloud/Harmonizome/gene/BAIAP2
https://www.science.org/doi/10.1126/sciadv.abp8677
https://www.genecards.org/cgi-bin/carddisp.pl?gene=BAIAP2
https://pmc.ncbi.nlm.nih.gov/articles/PMC4621619/
https://www.usbio.net/antibodies/243711/BAIAP2/data-sheet
https://pmc.ncbi.nlm.nih.gov/articles/PMC5746258/
https://pmc.ncbi.nlm.nih.gov/articles/PMC9565809/
https://www.frontiersin.org/journals/psychiatry/articles/10.3389/fpsyt.2023.1192379/full
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https://pmc.ncbi.nlm.nih.gov/articles/PMC6779427/
https://rupress.org/jgp/article/157/6/e202413574/278242/Exploring-a-peripheral-PIP2-binding-site-and-its
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📄 View Raw YAML

id: Q9UQB8
gene_symbol: BAIAP2
product_type: PROTEIN
status: COMPLETE
taxon:
  id: NCBITaxon:9606
  label: Homo sapiens
description: >-
  BAR/IMD domain-containing adapter protein 2 (IRSp53) is a curvature-sensitive
  membrane-cytoskeleton adaptor that couples plasma membrane shape to actin
  remodeling. The protein contains an N-terminal I-BAR/IMD domain that senses
  and generates negative membrane curvature by binding PI(4,5)P2-rich membranes,
  a central CRIB/proline-rich region for small GTPase (Rac1/Cdc42) coupling, and
  a C-terminal SH3 domain that recruits actin nucleation-promoting factors
  (WAVE, N-WASP, Eps8, Mena/VASP). IRSp53 integrates Rho-family GTPase signaling
  with actin network assembly to drive filopodia, lamellipodia, and membrane
  ruffles. The protein is enriched at plasma membrane protrusions, dendritic
  spines, and sites of negative membrane curvature.
existing_annotations:
# ============================================
# IBA ANNOTATIONS (phylogenetic inference)
# ============================================
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      Phylogenetic inference of cytosol localization is well-supported.
      IRSp53 is detected throughout the cytoplasm in the absence of specific
      binding partners and shows cytosolic distribution when not membrane-recruited.
    action: ACCEPT
    reason: >-
      Consistent with UniProt subcellular location data and IDA evidence from
      HPA immunofluorescence (GO_REF:0000052). The protein shuttles between
      cytosol and membrane in a curvature/GTPase-dependent manner.
- term:
    id: GO:0005654
    label: nucleoplasm
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      Nucleoplasm localization is questionable for IRSp53. The protein is
      primarily a cytoplasmic/membrane-associated adaptor with no well-established
      nuclear function.
    action: KEEP_AS_NON_CORE
    reason: >-
      While IBA annotation is present, IRSp53's core functions are at the plasma
      membrane and cytoplasm. Nuclear localization is not supported by deep
      research or UniProt annotations. May represent low-level detection or
      isoform-specific behavior.
- term:
    id: GO:0030838
    label: positive regulation of actin filament polymerization
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      IRSp53 promotes actin polymerization by recruiting nucleation-promoting
      factors via its SH3 domain to sites of membrane curvature. This is a
      well-established core function.
    action: ACCEPT
    reason: >-
      Deep research confirms IRSp53 recruits WAVE/Arp2/3 and triggers actin
      polymerization bursts at sites of membrane curvature. The SH3 domain
      binds proline-rich regions of actin effectors.
    supported_by:
    - reference_id: DOI:10.7554/eLife.72316
      supporting_text: IRSp53 recognizes ~100 nm PM evaginations produced by 
        stretch/compression, triggering a rapid Rac1/Arp2/3 actin polymerization
        burst
      full_text_unavailable: true
- term:
    id: GO:0051017
    label: actin filament bundle assembly
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      IRSp53's I-BAR domain can directly bundle actin filaments, contributing
      to filopodial structure. This is a core molecular function.
    action: ACCEPT
    reason: >-
      UniProt function notes that the isolated IMD domain can induce actin
      bundling and filopodia formation. Participates in actin bundling when
      associated with EPS8.
    supported_by:
    - reference_id: PMID:14752106
      supporting_text: A novel actin bundling/filopodium-forming domain 
        conserved in insulin receptor tyrosine kinase substrate p53
- term:
    id: GO:0051764
    label: actin crosslink formation
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      Actin crosslink formation is closely related to bundling activity.
      IRSp53-EPS8 complex promotes actin bundling and crosslinking.
    action: ACCEPT
    reason: >-
      Supported by experimental evidence showing IRSp53 works with EPS8 in
      synergistic actin bundling activity that promotes filopodial protrusions.
    supported_by:
    - reference_id: PMID:17115031
      supporting_text: Regulation of cell shape by Cdc42 is mediated by the 
        synergic actin-bundling activity of the Eps8-IRSp53 complex

# ============================================
# IEA ANNOTATIONS (electronic annotation)
# ============================================
- term:
    id: GO:0001726
    label: ruffle
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  review:
    summary: >-
      Ruffle localization is well-supported. IRSp53 is detected close to
      membrane ruffles and is essential for Rac1-mediated membrane ruffling.
    action: ACCEPT
    reason: >-
      UniProt subcellular location explicitly states detection in filopodia
      and close to membrane ruffles. IRSp53 is necessary for RAC1-mediated
      membrane ruffling.
    supported_by:
    - reference_id: PMID:11130076
      supporting_text: IRSp53 is an essential intermediate between Rac and WAVE 
        in the regulation of membrane ruffling
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  review:
    summary: >-
      Cytoplasm localization is well-established and broader than cytosol.
    action: ACCEPT
    reason: >-
      Consistent with cytosol annotation and UniProt subcellular location.
      IRSp53 localizes throughout the cytoplasm and at membrane-associated
      structures.
- term:
    id: GO:0005856
    label: cytoskeleton
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  review:
    summary: >-
      Cytoskeleton localization supported by IDA evidence showing
      colocalization with actin cytoskeleton.
    action: ACCEPT
    reason: >-
      IRSp53 colocalizes with actin cytoskeleton (IDA from PMID:19366662).
      This is expected given its role as an actin-membrane adaptor.
- term:
    id: GO:0007009
    label: plasma membrane organization
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  review:
    summary: >-
      IRSp53 is directly involved in plasma membrane organization through its
      I-BAR domain which senses and induces membrane curvature.
    action: ACCEPT
    reason: >-
      Core function. Deep research shows IRSp53 plays a central role in
      membrane shape homeostasis at the nanoscale, detecting curvature and
      coordinating membrane remodeling.
    supported_by:
    - reference_id: DOI:10.7554/eLife.72316
      supporting_text: A mechanosensing mechanism controls plasma membrane shape
        homeostasis at the nanoscale
      full_text_unavailable: true
- term:
    id: GO:0008093
    label: cytoskeletal anchor activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  review:
    summary: >-
      IRSp53 anchors actin cytoskeleton to the plasma membrane through its
      I-BAR domain. This is a core molecular function.
    action: ACCEPT
    reason: >-
      The I-BAR domain binds membranes while the SH3 domain recruits actin
      effectors, creating a molecular bridge. Supported by TAS evidence from
      PMID:10343108.
    supported_by:
    - reference_id: PMID:10343108
      supporting_text: Identification of BAIAP2 (BAI-associated protein 2), a 
        novel human homologue of hamster IRSp53, whose SH3 domain interacts with
        the cytoplasmic domain of BAI1
- term:
    id: GO:0016020
    label: membrane
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  review:
    summary: >-
      Membrane localization is well-established but generic.
    action: ACCEPT
    reason: >-
      UniProt indicates peripheral membrane protein. More specific term
      (plasma membrane) is also annotated with better evidence.
- term:
    id: GO:0030175
    label: filopodium
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  review:
    summary: >-
      Filopodium localization is a core aspect of IRSp53 function. The protein
      is essential for CDC42-mediated filopodia formation.
    action: ACCEPT
    reason: >-
      UniProt explicitly lists filopodium as a subcellular location. IRSp53
      acts synergistically with ENAH and EPS8 to promote filopodia formation.
    supported_by:
    - reference_id: PMID:11696321
      supporting_text: Cdc42 induces filopodia by promoting the formation of an 
        IRSp53:Mena complex
- term:
    id: GO:0032956
    label: regulation of actin cytoskeleton organization
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  review:
    summary: >-
      This is a core biological process for IRSp53. The protein coordinates
      actin organization downstream of Rho GTPases.
    action: ACCEPT
    reason: >-
      Supported by IMP evidence (PMID:19366662). IRSp53 is necessary for
      CDC42-mediated and RAC1-mediated reorganization of actin cytoskeleton.
    supported_by:
    - reference_id: PMID:19366662
      supporting_text: Insulin receptor tyrosine kinase substrate links the E. 
        coli O157:H7 actin assembly effectors Tir and EspF(U) during pedestal 
        formation
- term:
    id: GO:0070064
    label: proline-rich region binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  review:
    summary: >-
      The SH3 domain of IRSp53 binds proline-rich regions of effector proteins.
      This is experimentally validated.
    action: ACCEPT
    reason: >-
      Supported by IDA evidence (PMID:19366662). The SH3 domain mediates
      interactions with WAVE, N-WASP, Eps8, Mena/VASP through proline-rich
      motifs.
    supported_by:
    - reference_id: PMID:11130076
      supporting_text: carboxy-terminal Src-homology-3 domain of IRSp53 binds to
        WAVE
- term:
    id: GO:0098609
    label: cell-cell adhesion
  evidence_type: IEA
  original_reference_id: GO_REF:0000108
  review:
    summary: >-
      Inferred from cadherin binding annotation. IRSp53 is found at adherens
      junctions and binds cadherin.
    action: KEEP_AS_NON_CORE
    reason: >-
      While IRSp53 localizes to adherens junctions (HDA PMID:25468996), cell-cell
      adhesion is not a primary function. The protein's core role is membrane-actin
      coupling, not adhesion per se.

# ============================================
# GO:0005515 PROTEIN BINDING - REMOVE ALL
# ============================================
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:10332026
  review:
    summary: >-
      Non-informative molecular function term. The interaction with ATN1
      should be represented by more specific terms.
    action: REMOVE
    reason: >-
      GO curation guidelines discourage generic "protein binding" annotations.
      IRSp53 has adaptor activity that should be captured with more specific
      terms like protein-macromolecule adaptor activity.
    proposed_replacement_terms:
    - id: GO:0030674
      label: protein-macromolecule adaptor activity
    supported_by:
    - reference_id: PMID:10332026
      supporting_text: Dentatorubral-pallidoluysian atrophy protein interacts 
        through a proline-rich region near polyglutamine with the SH3 domain of 
        an insulin receptor tyrosine kinase substrate.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:11130076
  review:
    summary: >-
      Interaction with WAVE complex members (WASF1, WASF2). This should be
      captured as adaptor activity or WAVE complex binding.
    action: REMOVE
    reason: >-
      Generic protein binding does not convey the functional significance.
      IRSp53 functions as an adapter linking Rac to WAVE in membrane ruffling.
    proposed_replacement_terms:
    - id: GO:0030674
      label: protein-macromolecule adaptor activity
    supported_by:
    - reference_id: PMID:11130076
      supporting_text: IRSp53 is an essential intermediate between Rac and WAVE 
        in the regulation of membrane ruffling.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:11157984
  review:
    summary: >-
      Interaction with CDC42. Should be annotated as small GTPase binding.
    action: REMOVE
    reason: >-
      The interaction with CDC42 is functionally significant for activation
      of IRSp53. More informative to use small GTPase binding.
    proposed_replacement_terms:
    - id: GO:0031267
      label: small GTPase binding
    supported_by:
    - reference_id: PMID:11157984
      supporting_text: Cdc42Hs facilitates cytoskeletal reorganization and 
        neurite outgrowth by localizing the 58-kD insulin receptor substrate to 
        filamentous actin.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:11696321
  review:
    summary: >-
      Interactions with RAC1 and ENAH (Mena). These represent core functional
      interactions that should use specific terms.
    action: REMOVE
    reason: >-
      RAC1 binding should be small GTPase binding; ENAH interaction relates to
      filopodia formation via adaptor function.
    proposed_replacement_terms:
    - id: GO:0031267
      label: small GTPase binding
    - id: GO:0030674
      label: protein-macromolecule adaptor activity
    supported_by:
    - reference_id: PMID:11696321
      supporting_text: Cdc42 induces filopodia by promoting the formation of an 
        IRSp53:Mena complex.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:12598619
  review:
    summary: >-
      Interaction with espin proteins in dendritic spines. Non-informative term.
    action: REMOVE
    reason: >-
      Should use adaptor activity terms to capture functional significance.
    proposed_replacement_terms:
    - id: GO:0030674
      label: protein-macromolecule adaptor activity
    supported_by:
    - reference_id: PMID:12598619
      supporting_text: Novel espin actin-bundling proteins are localized to 
        Purkinje cell dendritic spines and bind the Src homology 3 adapter 
        protein insulin receptor substrate p53.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:15289329
  review:
    summary: >-
      Interactions with EPS8 and ABI1. These are functionally important for
      Rac regulation and cancer cell motility.
    action: REMOVE
    reason: >-
      EPS8-IRSp53 complex has specific actin bundling function. Should be
      captured with more specific MF terms.
    proposed_replacement_terms:
    - id: GO:0030674
      label: protein-macromolecule adaptor activity
    supported_by:
    - reference_id: PMID:15289329
      supporting_text: IRSp53/Eps8 complex is important for positive regulation 
        of Rac and cancer cell motility/invasiveness.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:15324660
  review:
    summary: >-
      14-3-3 protein binding. Non-informative generic term.
    action: REMOVE
    reason: >-
      14-3-3 binding regulates IRSp53 localization and activity. Should be
      captured with specific 14-3-3 binding or scaffold binding terms.
    proposed_replacement_terms:
    - id: GO:0097110
      label: scaffold protein binding
    supported_by:
    - reference_id: PMID:15324660
      supporting_text: Proteomic, functional, and domain-based analysis of in 
        vivo 14-3-3 binding proteins involved in cytoskeletal regulation and 
        cellular organization.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:16189514
  review:
    summary: >-
      Large-scale proteome mapping. Generic annotation from HTP study.
    action: REMOVE
    reason: >-
      Non-informative generic term from high-throughput study.
    proposed_replacement_terms:
    - id: GO:0030674
      label: protein-macromolecule adaptor activity
    supported_by:
    - reference_id: PMID:16189514
      supporting_text: Towards a proteome-scale map of the human protein-protein
        interaction network.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:16713569
  review:
    summary: >-
      Interaction network for Purkinje cell degeneration disorders.
    action: REMOVE
    reason: >-
      Non-informative generic term.
    proposed_replacement_terms:
    - id: GO:0030674
      label: protein-macromolecule adaptor activity
    supported_by:
    - reference_id: PMID:16713569
      supporting_text: A protein-protein interaction network for human inherited
        ataxias and disorders of Purkinje cell degeneration.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:17003044
  review:
    summary: >-
      RAC1 binding via RCB/IMD domain. Important for membrane deformation.
    action: REMOVE
    reason: >-
      Should use small GTPase binding to capture this interaction.
    proposed_replacement_terms:
    - id: GO:0031267
      label: small GTPase binding
    supported_by:
    - reference_id: PMID:17003044
      supporting_text: 2006 Sep 25. The RAC binding domain/IRSp53-MIM homology 
        domain of IRSp53 induces RAC-dependent membrane deformation.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:17353931
  review:
    summary: >-
      Large-scale mass spectrometry protein-protein interaction mapping.
    action: REMOVE
    reason: >-
      Non-informative generic term from HTP study.
    proposed_replacement_terms:
    - id: GO:0030674
      label: protein-macromolecule adaptor activity
    supported_by:
    - reference_id: PMID:17353931
      supporting_text: Large-scale mapping of human protein-protein interactions
        by mass spectrometry.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:18448434
  review:
    summary: >-
      CDC42 effector function. IRSp53 generates filopodia by coupling membrane
      protrusion with actin dynamics.
    action: REMOVE
    reason: >-
      Should use small GTPase binding and adaptor activity.
    proposed_replacement_terms:
    - id: GO:0031267
      label: small GTPase binding
    supported_by:
    - reference_id: PMID:18448434
      supporting_text: 2008 Apr 29. The Cdc42 effector IRSp53 generates 
        filopodia by coupling membrane protrusion with actin dynamics.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:19171758
  review:
    summary: >-
      Interactions with ACTB, RAC1, KANK1. KANK attenuates IRSp53-Rac1 interaction.
    action: REMOVE
    reason: >-
      Specific interactions should use more informative terms.
    proposed_replacement_terms:
    - id: GO:0003779
      label: actin binding
    - id: GO:0031267
      label: small GTPase binding
    supported_by:
    - reference_id: PMID:19171758
      supporting_text: Kank attenuates actin remodeling by preventing 
        interaction between IRSp53 and Rac1.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:19460367
  review:
    summary: >-
      SPIN90-IRSp53 complex in Rac-induced membrane ruffling.
    action: REMOVE
    reason: >-
      Non-informative generic term.
    proposed_replacement_terms:
    - id: GO:0030674
      label: protein-macromolecule adaptor activity
    supported_by:
    - reference_id: PMID:19460367
      supporting_text: Epub 2009 May 19. SPIN90-IRSp53 complex participates in 
        Rac-induced membrane ruffling.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:19564905
  review:
    summary: >-
      EPS8 interaction in axonal filopodia.
    action: REMOVE
    reason: >-
      Non-informative generic term.
    proposed_replacement_terms:
    - id: GO:0030674
      label: protein-macromolecule adaptor activity
    supported_by:
    - reference_id: PMID:19564905
      supporting_text: 2009 Jun 30. Eps8 regulates axonal filopodia in 
        hippocampal neurons in response to brain-derived neurotrophic factor 
        (BDNF).
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:19933840
  review:
    summary: >-
      14-3-3 (YWHAZ) binding regulates IRSp53 filopodial dynamics.
    action: REMOVE
    reason: >-
      Non-informative generic term. 14-3-3 binding is regulatory.
    proposed_replacement_terms:
    - id: GO:0097110
      label: scaffold protein binding
    supported_by:
    - reference_id: PMID:19933840
      supporting_text: Regulation of IRSp53-dependent filopodial dynamics by 
        antagonism between 14-3-3 binding and SH3-mediated localization.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:20936779
  review:
    summary: >-
      CDC42 interaction from MAP kinase interactome study.
    action: REMOVE
    reason: >-
      Should use small GTPase binding.
    proposed_replacement_terms:
    - id: GO:0031267
      label: small GTPase binding
    supported_by:
    - reference_id: PMID:20936779
      supporting_text: A human MAP kinase interactome.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:21311754
  review:
    summary: >-
      CDC42 interaction related to APC localization.
    action: REMOVE
    reason: >-
      Should use small GTPase binding.
    proposed_replacement_terms:
    - id: GO:0031267
      label: small GTPase binding
    supported_by:
    - reference_id: PMID:21311754
      supporting_text: Rho GTPase Cdc42 is a direct interacting partner of 
        Adenomatous Polyposis Coli protein and can alter its cellular 
        localization.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:24189400
  review:
    summary: >-
      EGFR interactome perturbation study.
    action: REMOVE
    reason: >-
      Non-informative generic term from HTP study.
    proposed_replacement_terms:
    - id: GO:0030674
      label: protein-macromolecule adaptor activity
    supported_by:
    - reference_id: PMID:24189400
      supporting_text: Perturbation of the mutated EGFR interactome identifies 
        vulnerabilities and resistance mechanisms.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:24658140
  review:
    summary: >-
      EGFR interaction from MaMTH assay.
    action: REMOVE
    reason: >-
      Non-informative generic term.
    proposed_replacement_terms:
    - id: GO:0030674
      label: protein-macromolecule adaptor activity
    supported_by:
    - reference_id: PMID:24658140
      supporting_text: The mammalian-membrane two-hybrid assay (MaMTH) for 
        probing membrane-protein interactions in human cells.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:25416956
  review:
    summary: >-
      Multiple interactions from proteome-scale interactome study.
    action: REMOVE
    reason: >-
      Non-informative generic term from HTP study.
    proposed_replacement_terms:
    - id: GO:0030674
      label: protein-macromolecule adaptor activity
    supported_by:
    - reference_id: PMID:25416956
      supporting_text: A proteome-scale map of the human interactome network.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:25519916
  review:
    summary: >-
      Interaction with E.coli Tir protein (EHEC host-pathogen interaction).
    action: REMOVE
    reason: >-
      While functionally significant for bacterial pathogenesis, protein binding
      is too generic. This represents adaptor activity hijacked by pathogen.
    proposed_replacement_terms:
    - id: GO:0030674
      label: protein-macromolecule adaptor activity
    supported_by:
    - reference_id: PMID:25519916
      supporting_text: The EHEC-host interactome reveals novel targets for the 
        translocated intimin receptor.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:25814554
  review:
    summary: >-
      Phospho-tyrosine dependent interaction network.
    action: REMOVE
    reason: >-
      Non-informative generic term.
    proposed_replacement_terms:
    - id: GO:0030674
      label: protein-macromolecule adaptor activity
    supported_by:
    - reference_id: PMID:25814554
      supporting_text: Phospho-tyrosine dependent protein-protein interaction 
        network.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:26496610
  review:
    summary: >-
      Interaction with BAIAP2L1 from quantitative interactome study.
    action: REMOVE
    reason: >-
      Non-informative generic term.
    proposed_replacement_terms:
    - id: GO:0030674
      label: protein-macromolecule adaptor activity
    supported_by:
    - reference_id: PMID:26496610
      supporting_text: Oct 22. A human interactome in three quantitative 
        dimensions organized by stoichiometries and abundances.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:28514442
  review:
    summary: >-
      14-3-3 protein interactions.
    action: REMOVE
    reason: >-
      Non-informative generic term.
    proposed_replacement_terms:
    - id: GO:0097110
      label: scaffold protein binding
    supported_by:
    - reference_id: PMID:28514442
      supporting_text: Architecture of the human interactome defines protein 
        communities and disease networks.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:31980649
  review:
    summary: >-
      EGFR network in KRAS-mutant colorectal cancer.
    action: REMOVE
    reason: >-
      Non-informative generic term from HTP study.
    proposed_replacement_terms:
    - id: GO:0030674
      label: protein-macromolecule adaptor activity
    supported_by:
    - reference_id: PMID:31980649
      supporting_text: Extensive rewiring of the EGFR network in colorectal 
        cancer cells expressing transforming levels of KRAS(G13D).
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:33961781
  review:
    summary: >-
      Dual proteome-scale interactome study.
    action: REMOVE
    reason: >-
      Non-informative generic term from HTP study.
    proposed_replacement_terms:
    - id: GO:0030674
      label: protein-macromolecule adaptor activity
    supported_by:
    - reference_id: PMID:33961781
      supporting_text: 2021 May 6. Dual proteome-scale networks reveal 
        cell-specific remodeling of the human interactome.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:35271311
  review:
    summary: >-
      OpenCell endogenous tagging study.
    action: REMOVE
    reason: >-
      Non-informative generic term from HTP study.
    proposed_replacement_terms:
    - id: GO:0030674
      label: protein-macromolecule adaptor activity
    supported_by:
    - reference_id: PMID:35271311
      supporting_text: '2022 Mar 11. OpenCell: Endogenous tagging for the cartography
        of human cellular organization.'
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:35384245
  review:
    summary: >-
      RTK interactome study.
    action: REMOVE
    reason: >-
      Non-informative generic term from HTP study.
    proposed_replacement_terms:
    - id: GO:0030674
      label: protein-macromolecule adaptor activity
    supported_by:
    - reference_id: PMID:35384245
      supporting_text: Physical and functional interactome atlas of human 
        receptor tyrosine kinases.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:36931259
  review:
    summary: >-
      14-3-3 protein chaperone-like role study.
    action: REMOVE
    reason: >-
      Non-informative generic term.
    proposed_replacement_terms:
    - id: GO:0097110
      label: scaffold protein binding
    supported_by:
    - reference_id: PMID:36931259
      supporting_text: A central chaperone-like role for 14-3-3 proteins in 
        human cells.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:39251607
  review:
    summary: >-
      Post-transcriptional regulatory module study.
    action: REMOVE
    reason: >-
      Non-informative generic term from HTP study.
    proposed_replacement_terms:
    - id: GO:0030674
      label: protein-macromolecule adaptor activity

# ============================================
# IDENTICAL PROTEIN BINDING
# ============================================
    supported_by:
    - reference_id: PMID:39251607
      supporting_text: Systematic identification of post-transcriptional 
        regulatory modules.
- term:
    id: GO:0042802
    label: identical protein binding
  evidence_type: IPI
  original_reference_id: PMID:11696321
  review:
    summary: >-
      IRSp53 forms homodimers via its I-BAR domain. This is functionally
      important for membrane binding and actin bundling.
    action: MODIFY
    reason: >-
      While identical protein binding is accurate, protein homodimerization
      activity is more specific and captures the functional importance.
    proposed_replacement_terms:
    - id: GO:0042803
      label: protein homodimerization activity
    supported_by:
    - reference_id: PMID:11696321
      supporting_text: Cdc42 induces filopodia by promoting the formation of an 
        IRSp53:Mena complex.
- term:
    id: GO:0042802
    label: identical protein binding
  evidence_type: IPI
  original_reference_id: PMID:14752106
  review:
    summary: >-
      Homodimer formation via IMD domain, important for actin bundling.
    action: MODIFY
    reason: >-
      Same as above - homodimerization activity is more informative.
    proposed_replacement_terms:
    - id: GO:0042803
      label: protein homodimerization activity
    supported_by:
    - reference_id: PMID:14752106
      supporting_text: 2004 Jan 29. A novel actin bundling/filopodium-forming 
        domain conserved in insulin receptor tyrosine kinase substrate p53 and 
        missing in metastasis protein.
- term:
    id: GO:0042802
    label: identical protein binding
  evidence_type: IPI
  original_reference_id: PMID:25416956
  review:
    summary: >-
      Self-interaction from large-scale interactome study.
    action: MODIFY
    reason: >-
      Should use homodimerization activity.
    proposed_replacement_terms:
    - id: GO:0042803
      label: protein homodimerization activity

# ============================================
# IEA ANNOTATIONS FROM ENSEMBL COMPARA
# ============================================
    supported_by:
    - reference_id: PMID:25416956
      supporting_text: A proteome-scale map of the human interactome network.
- term:
    id: GO:0001221
    label: transcription coregulator binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      Transcription coregulator binding is not well-supported for IRSp53.
      The protein functions primarily in cytoskeletal regulation, not
      transcription.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Not supported by deep research or UniProt annotations. IRSp53's
      primary functions are at the plasma membrane and cytoskeleton.
- term:
    id: GO:0005874
    label: microtubule
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      Microtubule localization is not well-established for IRSp53. The protein
      is primarily associated with actin cytoskeleton.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      IRSp53 is an I-BAR protein that functions with actin, not microtubules.
      This may be transferred from an ortholog with different localization.
- term:
    id: GO:0005886
    label: plasma membrane
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      Plasma membrane localization is a core feature of IRSp53 function.
      The I-BAR domain binds PI(4,5)P2-rich membranes.
    action: ACCEPT
    reason: >-
      Well-supported by IDA evidence (HPA), TAS evidence, and deep research.
      IRSp53 localizes to plasma membrane nanodomains of negative curvature.
    supported_by:
    - reference_id: DOI:10.7554/eLife.72316
      supporting_text: 'Sites of action: IRSp53 concentrates at the plasma membrane
        at regions of negative curvature'
      full_text_unavailable: true
- term:
    id: GO:0008360
    label: regulation of cell shape
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IRSp53 regulates cell shape through its effects on membrane curvature
      and actin organization.
    action: ACCEPT
    reason: >-
      Core function. Deep research shows IRSp53 controls plasma membrane
      shape homeostasis at the nanoscale and drives protrusion formation.
    supported_by:
    - reference_id: DOI:10.7554/eLife.72316
      supporting_text: A mechanosensing mechanism controls plasma membrane shape
        homeostasis at the nanoscale
      full_text_unavailable: true
- term:
    id: GO:0010976
    label: positive regulation of neuron projection development
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IRSp53 promotes neurite outgrowth and dendritic spine formation.
    action: ACCEPT
    reason: >-
      Supported by literature. UniProt notes a role in neurite growth.
      IRSp53 is enriched at dendritic spines.
    supported_by:
    - reference_id: PMID:11157984
      supporting_text: Cdc42Hs facilitates cytoskeletal reorganization and 
        neurite outgrowth by localizing the 58-kD insulin receptor substrate to 
        filamentous actin
- term:
    id: GO:0014069
    label: postsynaptic density
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IRSp53 localizes to postsynaptic density and interacts with SHANK
      scaffold proteins.
    action: ACCEPT
    reason: >-
      UniProt documents interactions with SHANK1, SHANK2, SHANK3 at
      postsynaptic sites.
    supported_by:
    - reference_id: PMID:12504591
      supporting_text: The insulin receptor substrate IRSp53 links postsynaptic 
        shank1 to the small G-protein cdc42
- term:
    id: GO:0030027
    label: lamellipodium
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IRSp53 is involved in lamellipodium formation through Rac1-WAVE
      signaling.
    action: ACCEPT
    reason: >-
      Deep research confirms IRSp53 functions at lamellipodial edges.
    supported_by:
    - reference_id: PMID:11130076
      supporting_text: IRSp53 is an essential intermediate between Rac and WAVE 
        in the regulation of membrane ruffling
- term:
    id: GO:0030141
    label: secretory granule
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      Secretory granule localization is not well-documented for IRSp53.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Not supported by deep research or UniProt. May be transferred from
      ortholog data.
- term:
    id: GO:0030165
    label: PDZ domain binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      PDZ domain binding is supported by SHANK protein interactions which
      contain PDZ domains.
    action: ACCEPT
    reason: >-
      IRSp53 interacts with SHANK1, SHANK2, SHANK3 which are PDZ
      domain-containing scaffold proteins.
- term:
    id: GO:0030182
    label: neuron differentiation
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  review:
    summary: >-
      IRSp53 plays a role in neuronal development, particularly in
      dendritic spine morphogenesis.
    action: KEEP_AS_NON_CORE
    reason: >-
      While supported, this is a broad developmental process. Core function
      is actin-membrane coupling, which contributes to neuronal morphology.
- term:
    id: GO:0030674
    label: protein-macromolecule adaptor activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      This is the CORE molecular function of IRSp53. The protein links
      membrane-bound GTPases (Rac1, Cdc42) to cytoplasmic actin effectors.
    action: ACCEPT
    reason: >-
      Perfectly captures IRSp53's primary function as an adapter between
      small GTPases, membranes, and actin regulatory proteins.
    supported_by:
    - reference_id: DOI:10.1242/jcs.262064
      supporting_text: IRSp53 is a curvature-sensitive membrane-cytoskeleton 
        adaptor that couples plasma membrane shape to actin remodeling
      full_text_unavailable: true
- term:
    id: GO:0035418
    label: protein localization to synapse
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IRSp53 localizes to synapses and may help recruit other proteins.
    action: KEEP_AS_NON_CORE
    reason: >-
      Synaptic function is established but is not the primary function of
      IRSp53, which operates in multiple cell types.
- term:
    id: GO:0042803
    label: protein homodimerization activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IRSp53 forms functional homodimers through its I-BAR domain, essential
      for membrane binding and curvature sensing.
    action: ACCEPT
    reason: >-
      Homodimerization is structurally and functionally important for IRSp53.
      The dimeric I-BAR domain creates the curvature-sensing interface.
    supported_by:
    - reference_id: PMID:15635447
      supporting_text: Structural basis of filopodia formation induced by the 
        IRSp53/MIM homology domain of human IRSp53
- term:
    id: GO:0043005
    label: neuron projection
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IRSp53 localizes to and promotes formation of neuronal projections.
    action: ACCEPT
    reason: >-
      Consistent with role in filopodia and neurite outgrowth. UniProt notes
      role in neurite growth.
- term:
    id: GO:0043025
    label: neuronal cell body
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      Neuronal cell body localization is expected given cytoplasmic
      distribution in neurons.
    action: KEEP_AS_NON_CORE
    reason: >-
      Not a site of primary function - IRSp53 acts at membrane protrusions.
- term:
    id: GO:0043197
    label: dendritic spine
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      Dendritic spine localization is well-documented for IRSp53.
    action: ACCEPT
    reason: >-
      Deep research confirms IRSp53 is enriched at dendritic spine structures.
      Interacts with SHANK proteins at this location.
    supported_by:
    - reference_id: DOI:10.7554/eLife.72316
      supporting_text: In neurons, it is enriched at dendritic spine structures
      full_text_unavailable: true
- term:
    id: GO:0043198
    label: dendritic shaft
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      Dendritic shaft localization is consistent with neuronal expression.
    action: KEEP_AS_NON_CORE
    reason: >-
      Less specific than dendritic spine. IRSp53 is more functionally
      important at spine heads.
- term:
    id: GO:0044306
    label: neuron projection terminus
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      Localization at neuron projection terminus is consistent with role
      in growth cone dynamics.
    action: KEEP_AS_NON_CORE
    reason: >-
      Consistent with filopodial function but relatively specific neuronal term.
- term:
    id: GO:0046847
    label: filopodium assembly
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      Filopodium assembly is a CORE biological process for IRSp53.
    action: ACCEPT
    reason: >-
      Well-documented by multiple studies. IRSp53 is essential for CDC42-
      mediated filopodia formation, working with Mena/VASP and EPS8.
    supported_by:
    - reference_id: PMID:11696321
      supporting_text: Cdc42 induces filopodia by promoting the formation of an 
        IRSp53:Mena complex
- term:
    id: GO:0050804
    label: modulation of chemical synaptic transmission
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IRSp53's role at synapses may affect synaptic transmission through
      effects on spine morphology.
    action: KEEP_AS_NON_CORE
    reason: >-
      This is a downstream effect of IRSp53's structural role at synapses
      rather than a direct function.
- term:
    id: GO:0051017
    label: actin filament bundle assembly
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      Duplicate of IBA annotation. Actin bundling is a core function.
    action: ACCEPT
    reason: >-
      Same as IBA annotation review. Well-supported core function.
- term:
    id: GO:0051764
    label: actin crosslink formation
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      Duplicate of IBA annotation. Actin crosslinking is a core function.
    action: ACCEPT
    reason: >-
      Same as IBA annotation review. Well-supported core function.
- term:
    id: GO:0060076
    label: excitatory synapse
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IRSp53 localizes to excitatory synapses (glutamatergic).
    action: KEEP_AS_NON_CORE
    reason: >-
      Synaptic localization is established but is context-specific (neuronal).
- term:
    id: GO:0061003
    label: positive regulation of dendritic spine morphogenesis
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IRSp53 promotes dendritic spine formation and morphology.
    action: ACCEPT
    reason: >-
      Well-supported neuronal function. IRSp53 at spines regulates actin
      dynamics affecting spine shape.
    supported_by:
    - reference_id: DOI:10.7554/eLife.72316
      supporting_text: IRSp53 has established roles in dendritic spine 
        morphogenesis and synaptic plasticity
      full_text_unavailable: true
- term:
    id: GO:0061845
    label: neuron projection branch point
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      Localization at branch points is consistent with membrane curvature
      sensing function.
    action: KEEP_AS_NON_CORE
    reason: >-
      Plausible but not a primary site of function for this protein.
- term:
    id: GO:0061846
    label: dendritic spine cytoplasm
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      Cytoplasmic localization within dendritic spines.
    action: KEEP_AS_NON_CORE
    reason: >-
      Overly specific sublocalization term.
- term:
    id: GO:0071364
    label: cellular response to epidermal growth factor stimulus
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      EGF response involves IRSp53 through its interaction with EGFR and
      downstream signaling.
    action: KEEP_AS_NON_CORE
    reason: >-
      While IRSp53 interacts with EGFR (documented in IPI studies), this
      is not a core function of the protein.
- term:
    id: GO:0097060
    label: synaptic membrane
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      Synaptic membrane localization is consistent with postsynaptic function.
    action: KEEP_AS_NON_CORE
    reason: >-
      Neuronal-specific term; plasma membrane is more general core annotation.
- term:
    id: GO:0097110
    label: scaffold protein binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IRSp53 binds SHANK scaffold proteins at postsynaptic sites.
    action: ACCEPT
    reason: >-
      Well-documented interaction with SHANK1/2/3 scaffold proteins.
    supported_by:
    - reference_id: PMID:12504591
      supporting_text: The insulin receptor substrate IRSp53 links postsynaptic 
        shank1 to the small G-protein cdc42
- term:
    id: GO:0098685
    label: Schaffer collateral - CA1 synapse
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      Very specific hippocampal synapse localization.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      While IRSp53 is expressed in hippocampus, this very specific synapse
      type annotation may be over-annotation from mouse data.
- term:
    id: GO:0098793
    label: presynapse
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      Presynaptic localization is documented but IRSp53 is predominantly
      postsynaptic.
    action: KEEP_AS_NON_CORE
    reason: >-
      Less prominent than postsynaptic localization.
- term:
    id: GO:0098794
    label: postsynapse
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      Postsynaptic localization is well-established.
    action: ACCEPT
    reason: >-
      Consistent with postsynaptic density annotation and SHANK interactions.
- term:
    id: GO:0098978
    label: glutamatergic synapse
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      Glutamatergic synapse localization is consistent with excitatory
      synapse function.
    action: KEEP_AS_NON_CORE
    reason: >-
      Neuronal-specific term.
- term:
    id: GO:0099092
    label: postsynaptic density, intracellular component
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      More specific than postsynaptic density term.
    action: KEEP_AS_NON_CORE
    reason: >-
      Redundant with postsynaptic density annotation.
- term:
    id: GO:0099175
    label: regulation of postsynapse organization
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IRSp53 regulates postsynaptic structure through effects on actin
      and spine morphology.
    action: KEEP_AS_NON_CORE
    reason: >-
      Neuronal-specific process; core function is actin-membrane coupling.
- term:
    id: GO:0099523
    label: presynaptic cytosol
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      Very specific subcompartment term.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Overly specific; cytosol annotation is sufficient.
- term:
    id: GO:0099524
    label: postsynaptic cytosol
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      Very specific subcompartment term.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Overly specific; cytosol annotation is sufficient.
- term:
    id: GO:1905232
    label: cellular response to L-glutamate
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      Glutamate response at synapses.
    action: KEEP_AS_NON_CORE
    reason: >-
      May be a downstream effect rather than direct function.
- term:
    id: GO:1905274
    label: regulation of modification of postsynaptic actin cytoskeleton
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      Specific term for postsynaptic actin regulation.
    action: KEEP_AS_NON_CORE
    reason: >-
      Very specific neuronal term; general actin regulation is core function.
- term:
    id: GO:2000463
    label: positive regulation of excitatory postsynaptic potential
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      Electrophysiological effect of IRSp53 at synapses.
    action: KEEP_AS_NON_CORE
    reason: >-
      Downstream effect of structural role; not a direct function.

# ============================================
# IDA AND OTHER EXPERIMENTAL ANNOTATIONS
# ============================================
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: IDA
  original_reference_id: GO_REF:0000052
  review:
    summary: >-
      IDA from HPA immunofluorescence confirms cytosol localization.
    action: ACCEPT
    reason: >-
      Direct experimental evidence for cytosol localization.
- term:
    id: GO:0005886
    label: plasma membrane
  evidence_type: IDA
  original_reference_id: GO_REF:0000052
  review:
    summary: >-
      IDA from HPA immunofluorescence confirms plasma membrane localization.
    action: ACCEPT
    reason: >-
      Direct experimental evidence for plasma membrane localization.
- term:
    id: GO:0032956
    label: regulation of actin cytoskeleton organization
  evidence_type: IMP
  original_reference_id: PMID:19366662
  review:
    summary: >-
      IMP evidence from bacterial pedestal formation study.
    action: ACCEPT
    reason: >-
      Direct experimental evidence showing IRSp53 is required for actin
      cytoskeleton reorganization during E. coli infection.
    supported_by:
    - reference_id: PMID:19366662
      supporting_text: Insulin receptor tyrosine kinase substrate links the E. 
        coli O157:H7 actin assembly effectors Tir and EspF(U) during pedestal 
        formation
- term:
    id: GO:0005912
    label: adherens junction
  evidence_type: HDA
  original_reference_id: PMID:25468996
  review:
    summary: >-
      High-throughput proteomics of E-cadherin interactome identifies IRSp53
      at adherens junctions.
    action: KEEP_AS_NON_CORE
    reason: >-
      While IRSp53 is found at adherens junctions, this is not its primary
      site of function.
    supported_by:
    - reference_id: PMID:25468996
      supporting_text: E-cadherin interactome complexity and robustness resolved
        by quantitative proteomics.
- term:
    id: GO:0098641
    label: cadherin binding involved in cell-cell adhesion
  evidence_type: HDA
  original_reference_id: PMID:25468996
  review:
    summary: >-
      Cadherin binding identified from E-cadherin interactome proteomics.
    action: KEEP_AS_NON_CORE
    reason: >-
      While documented, this is not a primary molecular function of IRSp53.
      The protein's core MF is adaptor activity.
    supported_by:
    - reference_id: PMID:25468996
      supporting_text: E-cadherin interactome complexity and robustness resolved
        by quantitative proteomics.
- term:
    id: GO:0070062
    label: extracellular exosome
  evidence_type: HDA
  original_reference_id: PMID:23533145
  review:
    summary: >-
      Found in prostatic extracellular exosomes by proteomics.
    action: KEEP_AS_NON_CORE
    reason: >-
      Exosomal presence may reflect its membrane association but is not
      a core localization.
    supported_by:
    - reference_id: PMID:23533145
      supporting_text: 2013 Apr 23. In-depth proteomic analyses of exosomes 
        isolated from expressed prostatic secretions in urine.
- term:
    id: GO:0070062
    label: extracellular exosome
  evidence_type: HDA
  original_reference_id: PMID:19056867
  review:
    summary: >-
      Found in urinary exosomes by proteomics.
    action: KEEP_AS_NON_CORE
    reason: >-
      Exosomal presence is not a core localization.

# ============================================
# TAS ANNOTATIONS (Reactome and literature)
# ============================================
    supported_by:
    - reference_id: PMID:19056867
      supporting_text: 2008 Dec 3. Large-scale proteomics and phosphoproteomics 
        of urinary exosomes.
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-2029465
  review:
    summary: >-
      Reactome pathway: RAC1:GTP and PIP3 bind WAVE Regulatory Complex.
    action: ACCEPT
    reason: >-
      Consistent with cytosol localization and WAVE complex interaction.
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-2029466
  review:
    summary: >-
      Reactome pathway: (WASPs, WAVE):G-actin:ARP2/3 binds F-actin.
    action: ACCEPT
    reason: >-
      Consistent with cytosolic function in WAVE-Arp2/3 pathway.
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-2029469
  review:
    summary: >-
      Reactome pathway: p-ERK phosphorylates WAVEs and ABI.
    action: ACCEPT
    reason: >-
      Consistent with cytosol localization.
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-2130194
  review:
    summary: >-
      Reactome pathway: ABL phosphorylates WAVEs.
    action: ACCEPT
    reason: >-
      Consistent with cytosol localization.
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-2197690
  review:
    summary: >-
      Reactome pathway: Detachment of WASP/WAVE.
    action: ACCEPT
    reason: >-
      Consistent with cytosol localization.
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-9013145
  review:
    summary: >-
      Reactome pathway: RAC1 binds effectors at the plasma membrane.
    action: ACCEPT
    reason: >-
      Consistent with cytosol localization.
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-9013157
  review:
    summary: >-
      Reactome pathway: CDC42 binds effectors at the plasma membrane.
    action: ACCEPT
    reason: >-
      Consistent with cytosol localization and CDC42 interaction.
- term:
    id: GO:0008360
    label: regulation of cell shape
  evidence_type: ISS
  original_reference_id: GO_REF:0000024
  review:
    summary: >-
      ISS from mouse ortholog Q8BKX1.
    action: ACCEPT
    reason: >-
      Well-supported by IEA annotation and deep research.
- term:
    id: GO:0051017
    label: actin filament bundle assembly
  evidence_type: ISS
  original_reference_id: GO_REF:0000024
  review:
    summary: >-
      ISS from mouse ortholog Q8BKX1.
    action: ACCEPT
    reason: >-
      Well-supported by IBA annotation and deep research.
- term:
    id: GO:0051764
    label: actin crosslink formation
  evidence_type: ISS
  original_reference_id: GO_REF:0000024
  review:
    summary: >-
      ISS from mouse ortholog Q8BKX1.
    action: ACCEPT
    reason: >-
      Well-supported by IBA annotation and deep research.
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: IDA
  original_reference_id: PMID:19366662
  review:
    summary: >-
      IDA from pedestal formation study.
    action: ACCEPT
    reason: >-
      Direct experimental evidence.
    supported_by:
    - reference_id: PMID:19366662
      supporting_text: Insulin receptor tyrosine kinase substrate links the E.
- term:
    id: GO:0015629
    label: actin cytoskeleton
  evidence_type: IDA
  original_reference_id: PMID:19366662
  review:
    summary: >-
      IDA showing colocalization with actin cytoskeleton.
    action: ACCEPT
    reason: >-
      Direct experimental evidence. Core localization for this protein.
    supported_by:
    - reference_id: PMID:19366662
      supporting_text: recruiting IRTKS to sites of bacterial attachment
- term:
    id: GO:0070064
    label: proline-rich region binding
  evidence_type: IDA
  original_reference_id: PMID:19366662
  review:
    summary: >-
      IDA demonstrating SH3 domain binding to proline-rich regions.
    action: ACCEPT
    reason: >-
      Direct experimental evidence for this molecular function.
    supported_by:
    - reference_id: PMID:19366662
      supporting_text: the ability to bind EspF(U) identified the SH3 domain of 
        insulin receptor tyrosine kinase substrate (IRTKS)
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: TAS
  original_reference_id: PMID:10343108
  review:
    summary: >-
      TAS annotation from original BAIAP2 identification paper.
    action: REMOVE
    reason: >-
      Non-informative generic term. Should use adaptor activity.
    proposed_replacement_terms:
    - id: GO:0030674
      label: protein-macromolecule adaptor activity
    supported_by:
    - reference_id: PMID:10343108
      supporting_text: Identification of BAIAP2 (BAI-associated protein 2), a 
        novel human homologue of hamster IRSp53, whose SH3 domain interacts with
        the cytoplasmic domain of BAI1.
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: TAS
  original_reference_id: PMID:10343108
  review:
    summary: >-
      TAS for cytoplasm localization from original identification paper.
    action: ACCEPT
    reason: >-
      Well-supported by multiple evidence types.
    supported_by:
    - reference_id: PMID:10343108
      supporting_text: Identification of BAIAP2 (BAI-associated protein 2), a 
        novel human homologue of hamster IRSp53, whose SH3 domain interacts with
        the cytoplasmic domain of BAI1.
- term:
    id: GO:0005886
    label: plasma membrane
  evidence_type: TAS
  original_reference_id: PMID:10343108
  review:
    summary: >-
      TAS for plasma membrane localization.
    action: ACCEPT
    reason: >-
      Well-supported core localization.
    supported_by:
    - reference_id: PMID:10343108
      supporting_text: Identification of BAIAP2 (BAI-associated protein 2), a 
        novel human homologue of hamster IRSp53, whose SH3 domain interacts with
        the cytoplasmic domain of BAI1.
- term:
    id: GO:0007409
    label: axonogenesis
  evidence_type: TAS
  original_reference_id: PMID:10343108
  review:
    summary: >-
      Role in axonal development from original identification paper.
    action: KEEP_AS_NON_CORE
    reason: >-
      Neuronal developmental process; core function is actin-membrane coupling.
    supported_by:
    - reference_id: PMID:10343108
      supporting_text: Identification of BAIAP2 (BAI-associated protein 2), a 
        novel human homologue of hamster IRSp53, whose SH3 domain interacts with
        the cytoplasmic domain of BAI1.
- term:
    id: GO:0008093
    label: cytoskeletal anchor activity
  evidence_type: TAS
  original_reference_id: PMID:10343108
  review:
    summary: >-
      TAS for cytoskeletal anchor activity.
    action: ACCEPT
    reason: >-
      Core molecular function. Also supported by IEA from InterPro.
    supported_by:
    - reference_id: PMID:10343108
      supporting_text: Identification of BAIAP2 (BAI-associated protein 2), a 
        novel human homologue of hamster IRSp53, whose SH3 domain interacts with
        the cytoplasmic domain of BAI1.
- term:
    id: GO:0008286
    label: insulin receptor signaling pathway
  evidence_type: TAS
  original_reference_id: PMID:10343108
  review:
    summary: >-
      IRSp53 was originally named for its identification as an insulin
      receptor tyrosine kinase substrate.
    action: KEEP_AS_NON_CORE
    reason: >-
      Historical name association; insulin signaling is not the core function
      of IRSp53. Modern research shows its primary role is in actin-membrane
      coupling independent of insulin signaling.

# ============================================
# SUGGESTED NEW ANNOTATIONS
# ============================================
    supported_by:
    - reference_id: PMID:10343108
      supporting_text: Identification of BAIAP2 (BAI-associated protein 2), a 
        novel human homologue of hamster IRSp53, whose SH3 domain interacts with
        the cytoplasmic domain of BAI1.
- term:
    id: GO:0140090
    label: membrane curvature sensor activity
  evidence_type: IDA
  original_reference_id: file:human/BAIAP2/BAIAP2-deep-research-falcon.md
  review:
    summary: >-
      IRSp53's I-BAR domain is a curvature sensor that preferentially binds
      negatively curved membranes. This is a key molecular function not
      currently annotated.
    action: NEW
    reason: >-
      Deep research (eLife 2023) provides quantitative evidence that IRSp53
      I-BAR domain senses membrane curvature with peak sorting at ~0.05 nm^-1
      (~100 nm diameter evaginations) with ~2x enrichment. This is a defining
      molecular function of the I-BAR domain family.
    supported_by:
    - reference_id: file:human/BAIAP2/BAIAP2-deep-research-falcon.md
      supporting_text: IRSp53 shows maximal sorting to membrane evaginations at 
        curvature ≈0.05 nm−1 with ~2× enrichment over control; evaginations are 
        ~100 nm scale
- term:
    id: GO:0005546
    label: phosphatidylinositol-4,5-bisphosphate binding
  evidence_type: IDA
  original_reference_id: file:human/BAIAP2/BAIAP2-deep-research-falcon.md
  review:
    summary: >-
      IRSp53 I-BAR domain binds PI(4,5)P2-rich membranes. This lipid
      specificity is important for membrane targeting.
    action: NEW
    reason: >-
      Deep research shows IRSp53 binds PI(4,5)P2-rich membranes and induces
      membrane deformation on PI(4,5)P2 GUVs. This lipid binding specificity
      is a key aspect of its membrane targeting.
    supported_by:
    - reference_id: file:human/BAIAP2/BAIAP2-deep-research-falcon.md
      supporting_text: full-length IRSp53 induces inward membrane 
        indentations/tubules on PI(4,5)P2 GUVs that recruit BIN1
- term:
    id: GO:0031267
    label: small GTPase binding
  evidence_type: IPI
  original_reference_id: PMID:11130076
  review:
    summary: >-
      IRSp53 directly binds active Rac1 and Cdc42 through its CRIB/IMD region.
      This is a core molecular function currently represented only by generic
      protein binding annotations.
    action: NEW
    reason: >-
      UniProt and deep research document binding to RAC1 and CDC42 as central
      to IRSp53 function. The protein acts as an effector of these GTPases.
    supported_by:
    - reference_id: PMID:11130076
      supporting_text: Activated Rac binds to the amino terminus of IRSp53
references:
- id: GO_REF:0000002
  title: Gene Ontology annotation through association of InterPro records with 
    GO terms
  findings: []
- id: GO_REF:0000024
  title: Manual transfer of experimentally-verified manual GO annotation data to
    orthologs by curator judgment of sequence similarity
  findings: []
- id: GO_REF:0000033
  title: Annotation inferences using phylogenetic trees
  findings: []
- id: GO_REF:0000044
  title: Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular 
    Location vocabulary mapping
  findings: []
- id: GO_REF:0000052
  title: Gene Ontology annotation based on curation of immunofluorescence data
  findings: []
- id: GO_REF:0000107
  title: Automatic transfer of experimentally verified manual GO annotation data
    to orthologs using Ensembl Compara
  findings: []
- id: GO_REF:0000108
  title: Automatic assignment of GO terms using logical inference, based on 
    inter-ontology links
  findings: []
- id: GO_REF:0000117
  title: Electronic Gene Ontology annotations created by ARBA machine learning 
    models
  findings: []
- id: GO_REF:0000120
  title: Combined Automated Annotation using Multiple IEA Methods
  findings: []
- id: PMID:10332026
  title: Dentatorubral-pallidoluysian atrophy protein interacts through a 
    proline-rich region near polyglutamine with the SH3 domain of an insulin 
    receptor tyrosine kinase substrate
  findings: []
- id: PMID:10343108
  title: Identification of BAIAP2 (BAI-associated protein 2), a novel human 
    homologue of hamster IRSp53, whose SH3 domain interacts with the cytoplasmic
    domain of BAI1
  findings:
  - statement: Original identification and characterization of human 
      BAIAP2/IRSp53
- id: PMID:11130076
  title: IRSp53 is an essential intermediate between Rac and WAVE in the 
    regulation of membrane ruffling
  findings:
  - statement: IRSp53 links Rac to WAVE complex for membrane ruffling
- id: PMID:11157984
  title: Cdc42Hs facilitates cytoskeletal reorganization and neurite outgrowth 
    by localizing the 58-kD insulin receptor substrate to filamentous actin
  findings:
  - statement: CDC42 binding and neurite outgrowth function
- id: PMID:11696321
  title: Cdc42 induces filopodia by promoting the formation of an IRSp53:Mena 
    complex
  findings:
  - statement: Key paper demonstrating filopodia formation mechanism
- id: PMID:12504591
  title: The insulin receptor substrate IRSp53 links postsynaptic shank1 to the 
    small G-protein cdc42
  findings:
  - statement: SHANK interaction and postsynaptic function
- id: PMID:14752106
  title: A novel actin bundling/filopodium-forming domain conserved in insulin 
    receptor tyrosine kinase substrate p53 and missing in metastasis protein
  findings:
  - statement: Characterization of I-BAR/IMD domain actin bundling activity
- id: PMID:15635447
  title: Structural basis of filopodia formation induced by the IRSp53/MIM 
    homology domain of human IRSp53
  findings:
  - statement: Crystal structure of I-BAR domain
- id: PMID:17115031
  title: Regulation of cell shape by Cdc42 is mediated by the synergic 
    actin-bundling activity of the Eps8-IRSp53 complex
  findings:
  - statement: EPS8-IRSp53 complex function
- id: PMID:19366662
  title: Insulin receptor tyrosine kinase substrate links the E. coli O157:H7 
    actin assembly effectors Tir and EspF(U) during pedestal formation
  findings:
  - statement: Bacterial hijacking of IRSp53 for pedestal formation
- id: PMID:25468996
  title: E-cadherin interactome complexity and robustness resolved by 
    quantitative proteomics
  findings:
  - statement: Adherens junction proteomics
- id: PMID:12598619
  title: Novel espin actin-bundling proteins are localized to Purkinje cell 
    dendritic spines and bind the Src homology 3 adapter protein insulin 
    receptor substrate p53.
  findings: []
- id: PMID:15289329
  title: IRSp53/Eps8 complex is important for positive regulation of Rac and 
    cancer cell motility/invasiveness.
  findings: []
- id: PMID:15324660
  title: Proteomic, functional, and domain-based analysis of in vivo 14-3-3 
    binding proteins involved in cytoskeletal regulation and cellular 
    organization.
  findings: []
- id: PMID:16189514
  title: Towards a proteome-scale map of the human protein-protein interaction 
    network.
  findings: []
- id: PMID:16713569
  title: A protein-protein interaction network for human inherited ataxias and 
    disorders of Purkinje cell degeneration.
  findings: []
- id: PMID:17003044
  title: The RAC binding domain/IRSp53-MIM homology domain of IRSp53 induces 
    RAC-dependent membrane deformation.
  findings: []
- id: PMID:17353931
  title: Large-scale mapping of human protein-protein interactions by mass 
    spectrometry.
  findings: []
- id: PMID:18448434
  title: The Cdc42 effector IRSp53 generates filopodia by coupling membrane 
    protrusion with actin dynamics.
  findings: []
- id: PMID:19171758
  title: Kank attenuates actin remodeling by preventing interaction between 
    IRSp53 and Rac1.
  findings: []
- id: PMID:19460367
  title: SPIN90-IRSp53 complex participates in Rac-induced membrane ruffling.
  findings: []
- id: PMID:19564905
  title: Eps8 regulates axonal filopodia in hippocampal neurons in response to 
    brain-derived neurotrophic factor (BDNF).
  findings: []
- id: PMID:19933840
  title: Regulation of IRSp53-dependent filopodial dynamics by antagonism 
    between 14-3-3 binding and SH3-mediated localization.
  findings: []
- id: PMID:20936779
  title: A human MAP kinase interactome.
  findings: []
- id: PMID:21311754
  title: Rho GTPase Cdc42 is a direct interacting partner of Adenomatous 
    Polyposis Coli protein and can alter its cellular localization.
  findings: []
- id: PMID:24189400
  title: Perturbation of the mutated EGFR interactome identifies vulnerabilities
    and resistance mechanisms.
  findings: []
- id: PMID:24658140
  title: The mammalian-membrane two-hybrid assay (MaMTH) for probing 
    membrane-protein interactions in human cells.
  findings: []
- id: PMID:25416956
  title: A proteome-scale map of the human interactome network.
  findings: []
- id: PMID:25519916
  title: The EHEC-host interactome reveals novel targets for the translocated 
    intimin receptor.
  findings: []
- id: PMID:25814554
  title: Phospho-tyrosine dependent protein-protein interaction network.
  findings: []
- id: PMID:26496610
  title: A human interactome in three quantitative dimensions organized by 
    stoichiometries and abundances.
  findings: []
- id: PMID:28514442
  title: Architecture of the human interactome defines protein communities and 
    disease networks.
  findings: []
- id: PMID:31980649
  title: Extensive rewiring of the EGFR network in colorectal cancer cells 
    expressing transforming levels of KRAS(G13D).
  findings: []
- id: PMID:33961781
  title: Dual proteome-scale networks reveal cell-specific remodeling of the 
    human interactome.
  findings: []
- id: PMID:35271311
  title: 'OpenCell: Endogenous tagging for the cartography of human cellular organization.'
  findings: []
- id: PMID:35384245
  title: Physical and functional interactome atlas of human receptor tyrosine 
    kinases.
  findings: []
- id: PMID:36931259
  title: A central chaperone-like role for 14-3-3 proteins in human cells.
  findings: []
- id: PMID:39251607
  title: Systematic identification of post-transcriptional regulatory modules.
  findings: []
- id: PMID:23533145
  title: In-depth proteomic analyses of exosomes isolated from expressed 
    prostatic secretions in urine.
  findings: []
- id: PMID:19056867
  title: Large-scale proteomics and phosphoproteomics of urinary exosomes.
  findings: []
- id: Reactome:R-HSA-2029465
  title: RAC1:GTP and PIP3 bind WAVE Regulatory Complex
  findings: []
- id: Reactome:R-HSA-2029466
  title: (WASPs, WAVE):G-actin:ARP2/3 binds F-actin
  findings: []
- id: Reactome:R-HSA-2029469
  title: p-ERK phosphorylates WAVEs and ABI
  findings: []
- id: Reactome:R-HSA-2130194
  title: ABL phosphorylates WAVEs
  findings: []
- id: Reactome:R-HSA-2197690
  title: Detachment of WASP/WAVE
  findings: []
- id: Reactome:R-HSA-9013145
  title: RAC1 binds effectors at the plasma membrane
  findings: []
- id: Reactome:R-HSA-9013157
  title: CDC42 binds effectors at the plasma membrane
  findings: []
- id: file:human/BAIAP2/BAIAP2-deep-research-falcon.md
  title: Deep research review of BAIAP2/IRSp53
  findings:
  - statement: Key 2023 paper on membrane curvature sensing mechanism
  - statement: Quantitative curvature sensing data
  - statement: IRSp53-BIN1 cooperation in filopodia
  - statement: PI(4,5)P2 binding evidence
  - statement: Review of I-BAR biology and membrane curvature
core_functions:
- molecular_function:
    id: GO:0030674
    label: protein-macromolecule adaptor activity
  description: >-
    IRSp53 is fundamentally an adaptor protein that links membrane-bound small
    GTPases (Rac1, Cdc42) to cytoplasmic actin effectors (WAVE, N-WASP, Eps8,
    Mena/VASP). This is its primary molecular function.
  directly_involved_in:
  - id: GO:0046847
    label: filopodium assembly
  - id: GO:0032956
    label: regulation of actin cytoskeleton organization
  locations:
  - id: GO:0005886
    label: plasma membrane
- molecular_function:
    id: GO:0140090
    label: membrane curvature sensor activity
  description: >-
    The I-BAR domain preferentially binds to negatively curved membranes,
    showing maximal sorting at curvatures of ~0.05 nm^-1 with ~2x enrichment
    (eLife 2023). This curvature sensing triggers downstream actin assembly.
  directly_involved_in:
  - id: GO:0007009
    label: plasma membrane organization
  locations:
  - id: GO:0005886
    label: plasma membrane
proposed_new_terms: []
suggested_questions:
- question: >-
    Does IRSp53 have preference for specific phosphoinositide species beyond
    PI(4,5)P2? The I-BAR domain binds PI(4,5)P2-rich membranes, but specificity
    for other PIP species is not fully characterized.
- question: >-
    What is the quantitative relationship between membrane curvature and
    IRSp53 recruitment in human cells? eLife 2023 provides quantitative data
    but further studies on curvature thresholds and residence times would be
    valuable.
suggested_experiments:
- description: >-
    Liposome binding assays with defined curvatures and lipid compositions
    to quantify PI(4,5)P2 vs other PIP binding specificity. This would clarify
    lipid binding specificity of the I-BAR domain.

BAIAP2

Gene Description

Existing Annotations Review

Core Functions

IRSp53 is fundamentally an adaptor protein that links membrane-bound small GTPases (Rac1, Cdc42) to cytoplasmic actin effectors (WAVE, N-WASP, Eps8, Mena/VASP). This is its primary molecular function.

The I-BAR domain preferentially binds to negatively curved membranes, showing maximal sorting at curvatures of ~0.05 nm^-1 with ~2x enrichment (eLife 2023). This curvature sensing triggers downstream actin assembly.

References

Suggested Questions for Experts

Suggested Experiments

Deep Research

Falcon

Citations

Perplexity

Comprehensive Functional Annotation of BAIAP2 (Brain-Specific Angiogenesis Inhibitor 1-Associated Protein 2)

Molecular Architecture and Structural Organization

Domain Composition and Structural Features

Structural Basis of Dimeric Organization and Membrane Coupling

Cellular Localization and Subcellular Compartmentalization

Postsynaptic Density Localization and Synaptic Enrichment

Extra-Synaptic and Growth Cone Functions

Primary Molecular Functions

Actin Binding and F-Actin Bundling

Membrane Binding and Curvature Sensing

GTPase Binding and Cdc42/Rac1 Signal Transduction

Recruitment and Clustering of Actin Regulatory Proteins

Regulation of BAIAP2 Activity and Function

Conformational Regulation and Autoinhibition

Phosphorylation-Dependent Inhibition by 14-3-3 Proteins

Regulated Assembly into Membrane Clusters

Role in Dendritic Spine Development and Synaptic Plasticity

Mechanisms of Spine Morphogenesis

Interaction with Glutamate Receptor Signaling

Filopodia Formation and Cell Motility

Filopodium Initiation and Assembly

Coupling to Rho GTPase Signaling

Disease Associations and Pathological Implications

Psychiatric and Neuropsychiatric Disorders

Developmental and Epileptic Encephalopathies

Family Members and Evolutionary Conservation

Conclusion and Future Perspectives

Citations

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