Islet cell autoantigen 1-like protein (ICA1L), paralog of ICA1/ICA69, containing N-terminal arfaptin/BAR domain (amino acids 46-248). BAR domains are curvature-sensing and membrane-binding modules that form dimeric banana-shaped scaffolds, enabling detection and induction of membrane curvature during vesicle trafficking. Functions as cytosolic membrane scaffolding/adaptor protein involved in secretory pathway and vesicle biogenesis. BAR domain mediates membrane interactions, dimerization, and membrane tubulation. Binds PICK1 (protein interacting with C kinase-1) via BAR-BAR domain interactions. Like ICA69, functions in dense-core secretory granule biogenesis and maturation. Predicted to participate in Golgi-to-vesicle trafficking, acting as effector for small GTPases (Rab/ARF family). May regulate AMPA receptor trafficking in neurons by forming complexes with PICK1. Expression tissue-enriched in brain and also in testis. In spermatids, predicted to localize to acrosomal vesicle, contributing to acrosome formation. Proteomic studies link ICA1L to cerebral small vessel disease - reduced ICA1L in brain cortex associated with lacunar stroke and intracerebral hemorrhage risk. Enriched in cortical glutamatergic neurons. Immunofluorescence unexpectedly shows mitochondrial localization in some cell lines, suggesting potential dual roles. C-terminal region may confer tissue-specific interactions. Functions primarily in secretory pathway through membrane scaffolding and protein complex assembly at Golgi and secretory vesicles.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0030667 secretory granule membrane | IBA GO_REF:0000033 | ACCEPT | Summary: IBA annotation based on phylogenetic inference from ICA1/ICA69 paralogs that localize to secretory granule membranes in neuroendocrine cells. ICA69 is well-established to function at immature secretory granules in pancreatic beta cells and neurons, where it regulates dense-core vesicle biogenesis and maturation. Reason: This annotation accurately reflects ICA1L's predicted core function at secretory vesicle membranes. The paralog ICA69 localizes to Golgi and immature secretory granules where it controls insulin granule formation via interaction with PICK1. ICA1L shares the BAR domain architecture and PICK1-binding capacity, suggesting conserved localization. While direct experimental evidence for ICA1L at secretory granule membranes is limited, the phylogenetic inference is well-supported by structural homology and known function of the ICA69/PICK1 complex in dense-core vesicle biogenesis. Supporting Evidence: file:human/ICA1L/ICA1L-deep-research-openai.md ICA69 (ICA1) localizes both to cytosol and to membranes of the Golgi and immature secretory granules, and loss of ICA69 disrupts insulin granule formation. By extension, ICA1L likely serves a similar function: acting as a scaffold for vesicle budding and maturation at the trans-Golgi network or other organelles. |
| GO:0051046 regulation of secretion | IBA GO_REF:0000033 | ACCEPT | Summary: IBA annotation indicating involvement in regulation of secretion, inferred from ICA69 function. ICA69/PICK1 complex controls insulin granule trafficking and maturation in pancreatic beta cells, and PICK1 knockout mice show impaired insulin granule maturation. Similar role predicted for ICA1L in regulating secretory processes in neurons and other cell types. Reason: This is a core biological process for ICA1L. The protein functions as a membrane scaffolding adapter at the trans-Golgi network and secretory vesicles, where it regulates dense-core vesicle biogenesis and maturation. Evidence from paralog ICA69 demonstrates that the ICA69/PICK1 heterodimer is required for proper insulin secretory granule formation, and mice lacking either protein show defects in granule maturation and secretion. ICA1L's structural similarity, PICK1-binding capacity, and expression pattern support conserved function in secretion regulation, particularly in brain neurons and potentially in testis during acrosome formation. Supporting Evidence: file:human/ICA1L/ICA1L-deep-research-openai.md PICK1 and ICA69 form a BAR domain heterodimer that regulates the synaptic targeting and surface expression of AMPA receptors (AMPARs). This complex retains AMPARs in the endosomal/Golgi compartment, preventing premature synaptic insertion. Mice lacking PICK1 resemble ICA69 knockouts in showing impaired insulin granule maturation and male infertility due to failed acrosome formation. |
| GO:0097753 membrane bending | IBA GO_REF:0000033 | ACCEPT | Summary: IBA annotation based on BAR domain structure. BAR (Bin/Amphiphysin/Rvs) domains form dimeric banana-shaped scaffolds that bind to membrane surfaces and induce membrane curvature, essential for vesicle budding and tubulation. ICA1L contains an arfaptin/BAR domain (amino acids 46-248) that mediates this membrane deformation activity. Reason: This is a core molecular function directly attributable to ICA1L's BAR domain. The arfaptin homology domain present in ICA1L (and ICA69) is a well-characterized membrane curvature-inducing module. BAR domains are known to detect and drive membrane curvature through their dimeric crescent-shaped structure that scaffolds lipid bilayers. This membrane bending activity is fundamental to ICA1L's role in secretory vesicle biogenesis, where membrane deformation is required for budding nascent vesicles from the Golgi or other organelles. The annotation accurately reflects the biochemical activity conferred by the protein's domain architecture. Supporting Evidence: file:human/ICA1L/ICA1L-deep-research-openai.md BAR domains are dimerization and lipid-binding modules known to sense and induce membrane curvature. This domain architecture suggests that ICA1L can detect and drive membrane curvature, similar to other BAR domain proteins that deform lipid bilayers during vesicle budding and fusion. BAR domains form dimers that can detect and drive membrane curvature, and may also be involved in protein-protein interactions. |
| GO:0140090 membrane curvature sensor activity | IBA GO_REF:0000033 | ACCEPT | Summary: IBA annotation for membrane curvature sensing, a key molecular function of BAR domain proteins. This term captures the ability to recognize curved membrane surfaces, which is mechanistically distinct but functionally coupled to membrane bending (GO:0097753). BAR domains both sense existing curvature and induce additional curvature. Reason: This is the primary molecular function term for ICA1L and accurately describes the BAR domain's activity. Membrane curvature sensor activity is fundamental to how ICA1L operates at organelle membranes - the protein recognizes regions of membrane curvature (such as budding vesicles at the Golgi) and stabilizes or amplifies that curvature through its banana-shaped dimeric structure. This sensing function enables ICA1L to localize specifically to sites of vesicle formation and coordinate with other trafficking machinery. The dual capacity to sense and induce curvature is a hallmark of BAR domain proteins and central to their role in membrane remodeling during secretory vesicle biogenesis. Supporting Evidence: file:human/ICA1L/ICA1L-deep-research-openai.md The BAR (arfaptin) domain of ICA1L is a curvature-sensing module that allows the protein to form dimers and bind to membrane surfaces. This domain architecture suggests that ICA1L can detect and drive membrane curvature. BAR domains form dimers that can detect and drive membrane curvature, contributing to vesicle formation. |
| GO:0005737 cytoplasm | IEA GO_REF:0000117 | ACCEPT | Summary: IEA annotation from ARBA machine learning models indicating cytoplasmic localization. Human Protein Atlas immunohistochemistry shows ICA1L with cytoplasmic and granular expression pattern across all tissues examined. The protein is not secreted and has no signal peptide or transmembrane domains. Reason: Correct broad localization term. ICA1L is a cytosolic/peripheral membrane protein that associates with organelle membranes (Golgi, secretory vesicles, and reportedly mitochondria in some cell lines) but is not an integral membrane protein. The cytoplasm annotation is appropriately general and accurate. While more specific subcellular localizations (secretory granule membrane, Golgi) are also annotated and represent the functional sites, cytoplasm remains valid as the broader compartment where ICA1L operates. This term does not contradict the more specific membrane-associated annotations. Supporting Evidence: file:human/ICA1L/ICA1L-deep-research-openai.md ICA1L is an intracellular protein with a predominantly cytosolic distribution that punctates on specific organelles. Human Protein Atlas immunohistochemistry data describe ICA1L protein expression as cytoplasmic and granular in virtually all tissues examined. This punctate cytoplasmic pattern is typical of proteins associated with organelle membranes or vesicle clusters. |
| GO:0012505 endomembrane system | IEA GO_REF:0000117 | ACCEPT | Summary: IEA annotation from ARBA models for endomembrane system localization. This broad term encompasses Golgi apparatus, endoplasmic reticulum, secretory vesicles, and endosomes - organelles connected by vesicular trafficking. ICA1L functions at trans-Golgi network and secretory granule membranes, both components of the endomembrane system. Reason: Accurate general localization term that appropriately captures ICA1L's association with the secretory pathway. The protein operates at endomembrane compartments involved in vesicle trafficking, specifically at the Golgi-to-granule transport interface. This term is complementary to the more specific annotations for secretory granule membrane and provides useful context that ICA1L functions within the interconnected membrane network of the secretory pathway. The annotation is well-supported by evidence that ICA1L (like ICA69) localizes to Golgi membranes and immature secretory vesicles budding from the trans-Golgi network. Supporting Evidence: file:human/ICA1L/ICA1L-deep-research-openai.md ICA1L is predicted to function as a membrane scaffolding/adaptor protein involved in intracellular trafficking and organelle biogenesis. Early bioinformatic annotations and homology-based predictions placed ICA1L in Golgi-associated membranes and secretory vesicles, reflecting its putative role in Golgi-to-granule transport. |
| GO:0019904 protein domain specific binding | IEA GO_REF:0000002 | ACCEPT | Summary: IEA annotation from InterPro domain analysis (IPR010504 - arfaptin homology domain). This term indicates ICA1L binds to other proteins through recognition of specific protein domains. The BAR domain of ICA1L mediates heterodimeric interactions with the BAR domain of PICK1, representing domain-domain binding. Reason: Accurate molecular function term that describes ICA1L's protein-protein interaction mechanism. The arfaptin/BAR domain of ICA1L recognizes and binds to the BAR-like domain of PICK1, forming heterodimers analogous to the well-characterized ICA69-PICK1 interaction. This is a clear example of protein domain-specific binding where the BAR domain serves as both the binding module and the binding target. The term is more informative than generic "protein binding" (GO:0005515) as it specifies the mechanism involves domain recognition. This function is critical for ICA1L's role in forming scaffolding complexes at vesicle membranes. Supporting Evidence: file:human/ICA1L/ICA1L-deep-research-openai.md ICA1L is predicted to enable protein domain-specific binding activity, indicating it may interact with other proteins via recognition of particular domains or motifs, as is common for scaffolding proteins. The BAR domain of ICA1L mediates heterodimerization with the protein PICK1 (Protein Interacting with C Kinase-1), suggesting that ICA1L's BAR domain could engage in BAR-BAR domain interactions. |
| GO:0005515 protein binding | IPI PMID:25416956 A proteome-scale map of the human interactome network. | ACCEPT | Summary: IPI annotation from high-throughput yeast two-hybrid interactome mapping study (Rolland et al. 2014). This proteome-scale study systematically mapped binary protein-protein interactions and identified KIFC3 as an ICA1L interactor. The study provides direct experimental evidence for protein binding activity. Reason: This annotation has direct experimental support from a systematic interactome study, though it is less informative than the more specific "protein domain specific binding" term (GO:0019904). The generic protein binding term is appropriate to retain as it is based on actual experimental evidence (IPI) rather than inference. The study identified ICA1L-KIFC3 interaction, and other databases report ICA1L interaction with PICK1. While this term is very broad and doesn't specify the mechanism or biological context, it validly captures that ICA1L has protein binding activity, which is essential for its scaffolding function. The more specific domain-specific binding term provides better functional resolution, but both can coexist as they are supported by different evidence types. Supporting Evidence: PMID:25416956 By systematically screening half of the interactome space with minimal inspection bias, we more than doubled the number of high-quality binary PPIs available from the literature. |
| GO:0001669 acrosomal vesicle | IEA GO_REF:0000107 | KEEP AS NON CORE | Summary: IEA annotation from Ensembl Compara orthology transfer, based on mouse ICA1L localization to acrosomal vesicle. The acrosome is a large secretory vesicle derived from Golgi in developing spermatids. PICK1 knockout mice show male infertility due to failed acrosome formation, and the ICA69/PICK1 complex is required for proacrosomal granule biogenesis in testis. Reason: This annotation represents a tissue-specific function in male germ cells rather than the core ubiquitous function of ICA1L. While ICA1L is expressed in testis and the orthology-based inference is mechanistically plausible (given PICK1's established role in acrosome formation and ICA1L's capacity to bind PICK1), this represents a specialized deployment of ICA1L's general vesicle trafficking function in a specific developmental context. The core function of ICA1L is membrane scaffolding in secretory vesicle biogenesis, which occurs broadly in many cell types, particularly neurons and endocrine cells. The acrosomal vesicle localization is a tissue-restricted application of this broader function. Therefore, this should be retained but marked as non-core to distinguish it from the primary neuronal and secretory cell functions. Supporting Evidence: file:human/ICA1L/ICA1L-deep-research-openai.md The acrosome is a large secretory vesicle derived from the Golgi apparatus in developing spermatids, and ICA1L is predicted to localize to the acrosomal vesicle during sperm maturation. Mice lacking PICK1 show impaired insulin granule maturation and male infertility due to failed acrosome formation. In the testis, a similar PICK1-containing complex is required for biogenesis of proacrosomal granules (which fuse to form the acrosome). |
| GO:0007286 spermatid development | IEA GO_REF:0000107 | KEEP AS NON CORE | Summary: IEA annotation from Ensembl Compara orthology transfer indicating involvement in spermatid development. This process includes acrosome formation, a critical step in spermiogenesis where a large secretory vesicle is assembled from Golgi-derived proacrosomal granules. The annotation uses qualifier "acts_upstream_of_or_within" suggesting indirect or supporting role. Reason: This represents a tissue-specific developmental process rather than the core molecular/cellular function of ICA1L. While the protein may contribute to spermatid development through its role in acrosomal vesicle formation (as predicted from mouse ortholog), this is a specialized application of its general membrane trafficking function. The annotation is mechanistically reasonable given that PICK1 is essential for acrosome biogenesis and ICA1L can form complexes with PICK1, but spermatid development represents a narrow developmental context. ICA1L's primary and most broadly relevant function is in secretory vesicle biogenesis in neurons and other secretory cells, where it is highly expressed (particularly brain). The testis-specific role, while potentially valid, is peripheral to understanding the gene's main biological importance. Retain as non-core annotation. Supporting Evidence: file:human/ICA1L/ICA1L-deep-research-openai.md The Gene Ontology predictions note that ICA1L is postulated to act upstream of or within spermatid development. One biological process implicating ICA1L is spermiogenesis, where it may help organize or traffic components of the acrosome, a function analogous to ICA69's role in secretory granules. |
| GO:0005794 Golgi apparatus | IBA file:human/ICA1L/ICA1L-uniprot.txt | NEW | Summary: Golgi apparatus localization found in UniProt cross-references (IBA evidence from GO_Central). ICA69 paralog localizes to Golgi membranes where it functions in vesicle trafficking. Trans-Golgi network is the site of secretory granule budding where ICA1L/ICA69-PICK1 complexes regulate dense-core vesicle formation. Reason: This is a critical localization annotation that accurately reflects ICA1L's function at the Golgi apparatus, specifically at the trans-Golgi network where secretory vesicles bud. The annotation appears in UniProt with IBA evidence but is missing from the primary GOA annotation set. ICA69 is well-documented to localize to Golgi membranes and regulate Golgi-to-granule trafficking, and ICA69 is described as a Rab2 effector regulating ER-to-Golgi trafficking. ICA1L's structural homology and functional similarity strongly support Golgi localization. The deep research explicitly states that ICA1L functions at the trans-Golgi network for vesicle budding and maturation. This annotation should be added to provide complete coverage of ICA1L's subcellular localization, as Golgi is a primary site of function for this membrane trafficking protein. Supporting Evidence: file:human/ICA1L/ICA1L-deep-research-openai.md ICA69 (ICA1) localizes both to cytosol and to membranes of the Golgi and immature secretory granules. ICA1L likely serves a similar function: acting as a scaffold for vesicle budding and maturation at the trans-Golgi network or other organelles. Early bioinformatic annotations and homology-based predictions placed ICA1L in Golgi-associated membranes and secretory vesicles. ICA69 has been identified as an effector for the Rab2 GTPase, linking it to ER-to-Golgi vesicle transport. file:human/ICA1L/ICA1L-uniprot.txt GO:0005794; C:Golgi apparatus; IBA:GO_Central. |
| GO:0000139 Golgi membrane | NAS | NEW | Summary: Added to align core_functions with existing annotations. Reason: Core function term not present in existing_annotations. Supporting Evidence: file:human/ICA1L/ICA1L-deep-research-openai.md The BAR domain of ICA1L mediates heterodimerization with the protein PICK1 (Protein Interacting with C Kinase-1). ICA69 and PICK1 form a BAR domain heterodimer that regulates the synaptic targeting and surface expression of AMPA receptors (AMPARs). This complex retains AMPARs in the endosomal/Golgi compartment, preventing premature synaptic insertion. file:human/ICA1L/ICA1L-deep-research-openai.md ICA1L is well positioned to participate in neuronal trafficking pathways, possibly contributing to synapse development or neurotransmitter receptor localization through interactions with PICK1. ICA1L is particularly enriched in cortical glutamatergic neurons and reduced ICA1L may impair excitatory synaptic transmission. |
| GO:0016192 vesicle-mediated transport | NAS | NEW | Summary: Added to align core_functions with existing annotations. Reason: Core function term not present in existing_annotations. Supporting Evidence: file:human/ICA1L/ICA1L-deep-research-openai.md The BAR (arfaptin) domain of ICA1L is a curvature-sensing module that allows the protein to form dimers and bind to membrane surfaces. BAR domains form dimeric banana-shaped scaffolds that bind and tubulate membranes, contributing to vesicle formation. ICA1L likely serves a similar function to ICA69: acting as a scaffold for vesicle budding and maturation at the trans-Golgi network. file:human/ICA1L/ICA1L-deep-research-openai.md ICA69 (ICA1) localizes both to cytosol and to membranes of the Golgi and immature secretory granules, and loss of ICA69 disrupts insulin granule formation. ICA1L is thought to help regulate dense-core vesicle biogenesis and maturation in secretory cells. |
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