PFDN4

Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0005737 cytoplasm	IBA GO_REF:0000033	ACCEPT	Summary: GO:0005737 "cytoplasm" is an appropriate cellular component annotation for PFDN4. This IBA annotation was inferred from phylogenetic analysis (PANTHER) with evidence from yeast (SGD:S000005097), Arabidopsis (TAIR:locus:2025655), and human PFDN4 itself. The prefoldin complex is a cytoplasmic chaperone that operates in the cytosol to capture unfolded nascent polypeptides and deliver them to the cytosolic chaperonin TRiC/CCT (PMID:9630229). The deep research review describes prefoldin as a predominantly cytosolic complex for the canonical chaperone role. This is also supported by the IDA annotation from PMID:17936702 for the same term. The term "cytoplasm" is appropriately broad, as a more specific CC annotation to "prefoldin complex" (GO:0016272) is already present in this annotation set. Reason: PFDN4 operates as part of the cytoplasmic prefoldin complex. The cytoplasm annotation is well-supported phylogenetically and consistent with direct experimental data (PMID:17936702, PMID:9630229). The IBA is sound and complements the more specific prefoldin complex (GO:0016272) annotation. Supporting Evidence: PMID:9630229 Prefoldin binds specifically to cytosolic chaperonin (c-cpn) and transfers target proteins to it.
GO:0006457 protein folding	IBA GO_REF:0000033	ACCEPT	Summary: GO:0006457 "protein folding" is a well-supported core function of PFDN4. This IBA annotation was inferred from phylogenetic analysis (PANTHER) with evidence from Arabidopsis (TAIR:locus:2025655) and human PFDN4 itself. The prefoldin complex is a bona fide co-chaperone that captures unfolded nascent polypeptides (primarily actin and tubulin) and delivers them to TRiC/CCT for ATP-dependent folding (PMID:9630229). Gestaut et al. 2019 (PMID:30955883) showed that PFD enhances the rate and yield of TRiC-mediated folding, directly demonstrating involvement in protein folding. The deep research review (PFDN4-deep-research-falcon.md) confirms this as the primary function: "Non-enzymatic co-chaperone; assists folding of cytoskeletal proteins by handing off clients to TRiC/CCT." This is the central biological process for PFDN4. Reason: Protein folding is the core biological process for all prefoldin subunits. The IBA annotation is phylogenetically well-supported and consistent with extensive experimental literature demonstrating prefoldin's role in delivering substrates to TRiC/CCT for folding (PMID:9630229, PMID:30955883). Supporting Evidence: PMID:9630229 We describe the discovery of a heterohexameric chaperone protein, prefoldin, based on its ability to capture unfolded actin. Prefoldin binds specifically to cytosolic chaperonin (c-cpn) and transfers target proteins to it. PMID:30955883 PFD can act after TRiC bound its substrates to enhance the rate and yield of the folding reaction, suppressing non-productive reaction cycles. file:human/PFDN4/PFDN4-deep-research-falcon.md Primary function: Non-enzymatic co-chaperone; assists folding of cytoskeletal proteins by handing off clients to TRiC/CCT. Substrate specificity centers on actin and tubulin.
GO:0051082 unfolded protein binding	IBA GO_REF:0000033	MODIFY	Summary: GO:0051082 "unfolded protein binding" is now formally obsolete (go-ontology#30962). This IBA annotation was inferred from phylogenetic analysis (PANTHER) with evidence from human PFDN4 itself. While prefoldin does indeed bind unfolded proteins, the term "unfolded protein binding" is a pure binding term that fails to capture the functional significance of this interaction. Prefoldin acts as a holdase/transfer chaperone: it captures unfolded substrates (primarily actin and tubulin) and delivers them to the TRiC/CCT chaperonin for folding. As described in Vainberg et al. 1998 (PMID:9630229), "Prefoldin binds specifically to cytosolic chaperonin (c-cpn) and transfers target proteins to it." The more appropriate term is GO:0044183 "protein folding chaperone" which captures the functional chaperone activity rather than just substrate binding. Note that unlike PFDN1, PFDN4 does not have an existing IBA annotation to GO:0044183, so a NEW annotation for that term is proposed separately. Reason: GO:0051082 is now formally obsolete. The term describes only a binding activity and does not capture the chaperone function of prefoldin. Prefoldin is a molecular chaperone that binds unfolded substrates and delivers them to TRiC/CCT for folding (PMID:9630229, PMID:30955883). GO:0044183 "protein folding chaperone" (defined as "Binding to a protein or a protein-containing complex to assist the protein folding process") is the recommended replacement. Proposed replacements: protein folding chaperone Supporting Evidence: PMID:9630229 Prefoldin binds specifically to cytosolic chaperonin (c-cpn) and transfers target proteins to it. PMID:30955883 PFD alternates between an open "latched" conformation and a closed "engaged" conformation that aligns the PFD-TRiC substrate binding chambers.
GO:0016272 prefoldin complex	IBA GO_REF:0000033	ACCEPT	Summary: GO:0016272 "prefoldin complex" is a well-supported core annotation for PFDN4. This IBA annotation was inferred from phylogenetic analysis (PANTHER) with evidence from yeast (SGD:S000005097) and human PFDN4 itself. PFDN4 is one of the four beta subunits (PFDN1, PFDN2, PFDN4, PFDN6) of the heterohexameric prefoldin complex (PMID:9630229). The complex is registered in ComplexPortal as CPX-6149 ("Prefoldin co-chaperone complex"). Structural data from cryo-EM (PMID:30955883) includes PFDN4 as chain 4 in PDB structures 6NR8/6NR9/6NRB/6NRC/6NRD and 7WU7. Reason: PFDN4 is a core structural subunit of the prefoldin complex. The IBA phylogenetic inference is strongly supported and consistent with multiple experimental studies (PMID:9630229, PMID:30955883, PMID:23614719). Supporting Evidence: PMID:9630229 We describe the discovery of a heterohexameric chaperone protein, prefoldin, based on its ability to capture unfolded actin. PMID:30955883 Maintaining proteostasis in eukaryotic protein folding involves cooperation of distinct chaperone systems. To understand how the essential ring-shaped chaperonin TRiC/CCT cooperates with the chaperone prefoldin/GIMc (PFD), we integrate cryoelectron microscopy (cryo-EM), crosslinking-mass-spectrometry and biochemical and cellular approaches to elucidate the structural and functional interplay between TRiC/CCT and PFD.
GO:0005634 nucleus	IEA GO_REF:0000044	KEEP AS NON CORE	Summary: GO:0005634 "nucleus" inferred electronically from UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping (GO_REF:0000044). The UniProt record for PFDN4 reports nuclear localization based on PMID:17936702. Djouder et al. 2007 studied URI1 (a prefoldin-like protein) interactions and found PFDN4 co-purified with URI1 in various subcellular compartments. The deep research review (PFDN4-deep-research-falcon.md) notes "nuclear functions are suggested for certain prefoldin subunits and for PFDN4/Protein C-1 as a transcriptional cofactor." However, the nuclear localization likely reflects a secondary, non-canonical role distinct from the primary cytoplasmic chaperone function. This IEA is consistent with the IDA annotation from the same publication. Reason: The IEA mapping from UniProt subcellular location is correct and reflects the experimental observation from PMID:17936702. However, nuclear localization represents a non-canonical localization for PFDN4. The primary site of prefoldin chaperone function is the cytoplasm. Keeping as non-core consistent with the IDA annotation for the same term.
GO:0005737 cytoplasm	IEA GO_REF:0000120	ACCEPT	Summary: GO:0005737 "cytoplasm" inferred electronically by combined automated annotation methods (ARBA:ARBA00026971 and UniProtKB-SubCell:SL-0086). This IEA annotation is consistent with the IBA annotation to the same term and with the IDA annotation from PMID:17936702. The prefoldin complex primarily operates in the cytoplasm (PMID:9630229). Reason: The IEA annotation to cytoplasm is correct and consistent with higher-confidence IBA and IDA annotations. The prefoldin complex is a cytoplasmic chaperone (PMID:9630229, PMID:17936702).
GO:0005739 mitochondrion	IEA GO_REF:0000044	KEEP AS NON CORE	Summary: GO:0005739 "mitochondrion" inferred electronically from UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping (GO_REF:0000044). The UniProt record for PFDN4 reports mitochondrial localization based on PMID:17936702. Djouder et al. 2007 showed that the prefoldin-like protein URI1 forms complexes with PP1gamma at mitochondria, and PFDN4 was identified as an interactor of URI1. The mitochondrial localization of PFDN4 appears to be related to the URI1/PAQosome axis rather than canonical prefoldin chaperone function. This IEA is consistent with the IDA annotation from the same publication. Reason: The IEA mapping from UniProt subcellular location is correct and reflects the experimental observation from PMID:17936702. However, mitochondrial localization represents a non-canonical localization related to the URI1 interaction. The primary site of prefoldin chaperone function is the cytoplasm. Keeping as non-core consistent with the IDA annotation for the same term.
GO:0006457 protein folding	IEA GO_REF:0000002	ACCEPT	Summary: GO:0006457 "protein folding" inferred electronically from InterPro domain mapping (IPR002777, the prefoldin beta-like domain, and IPR016661, the PFDN4-specific domain). This IEA annotation is consistent with the IBA and IDA annotations to the same term, and with the well-established role of the prefoldin complex in protein folding (PMID:9630229). Reason: The IEA annotation to protein folding via InterPro is correct and consistent with the higher-confidence IBA and IDA annotations. The prefoldin beta-like domain (IPR002777) is specifically associated with the protein folding function of the prefoldin complex (PMID:9630229, PMID:30955883).
GO:0016272 prefoldin complex	IEA GO_REF:0000002	ACCEPT	Summary: GO:0016272 "prefoldin complex" inferred electronically from InterPro domain mapping (IPR002777, the prefoldin beta-like domain, and IPR016661, the PFDN4-specific domain). PFDN4 is one of the four beta subunits of the heterohexameric prefoldin complex (PMID:9630229). The complex is registered in ComplexPortal as CPX-6149. This IEA annotation is consistent with the IDA annotations to the same term from PMID:30955883 and PMID:23614719 and the IBA annotation. Reason: PFDN4 is a core structural subunit of the prefoldin complex. The IEA mapping from the prefoldin beta-like domain (IPR002777) to prefoldin complex membership is appropriate and consistent with experimental evidence (PMID:9630229, PMID:30955883).
GO:0032991 protein-containing complex	IEA GO_REF:0000117	MARK AS OVER ANNOTATED	Summary: GO:0032991 "protein-containing complex" was inferred electronically by the ARBA machine learning model (ARBA:ARBA00028902). While technically correct -- PFDN4 is part of the prefoldin complex, which is indeed a protein-containing complex -- this annotation is redundant and overly general given the more specific GO:0016272 "prefoldin complex" annotation that is already present from IBA, IEA (InterPro), and IDA (PMID:30955883, PMID:23614719) evidence. The term "protein-containing complex" adds no informational value beyond what is already captured. Reason: This is an overly general annotation. PFDN4 is part of the prefoldin complex (GO:0016272), which is a child term of protein-containing complex. The more specific term is already annotated with IBA, IEA, and IDA evidence. The generic "protein-containing complex" adds no useful information.
GO:0051082 unfolded protein binding	IEA GO_REF:0000002	MODIFY	Summary: GO:0051082 "unfolded protein binding" is now formally obsolete (go-ontology#30962). This IEA annotation was inferred electronically from InterPro domain mapping (IPR002777, the prefoldin beta-like domain). The InterPro-to-GO mapping associates the prefoldin domain with unfolded protein binding, which is functionally accurate in that prefoldin subunits do contact unfolded substrates. However, since the term is now formally obsolete, the annotation should be replaced with GO:0044183 "protein folding chaperone" which better describes the functional role of the prefoldin complex as a holdase/transfer chaperone that delivers substrates to TRiC/CCT. Reason: GO:0051082 is now formally obsolete. While the InterPro mapping correctly identifies that the prefoldin domain binds unfolded proteins, the replacement term GO:0044183 "protein folding chaperone" better captures the functional role of prefoldin as a chaperone that assists in protein folding by delivering unfolded substrates to the TRiC/CCT chaperonin (PMID:9630229, PMID:30955883). Proposed replacements: protein folding chaperone Supporting Evidence: PMID:9630229 Prefoldin binds specifically to cytosolic chaperonin (c-cpn) and transfers target proteins to it.
GO:0005515 protein binding	IPI PMID:25416956 A proteome-scale map of the human interactome network.	MARK AS OVER ANNOTATED	Summary: GO:0005515 "protein binding" (IPI with UniProtKB:P61758/VBP1) from Rolland et al. 2014 (PMID:25416956), a proteome-scale map of the human interactome network. P61758 is VBP1 (von Hippel-Lindau binding protein 1), which is also known as prefoldin subunit 3 (PFDN3), an alpha-type subunit of the prefoldin complex. The PFDN4-VBP1/PFDN3 interaction reflects intra-complex subunit assembly within the prefoldin hexamer. UniProt confirms this interaction (NbExp=10 for the VBP1 interaction). While the interaction is real and well-supported, the "protein binding" term is uninformative -- this interaction is already captured by the GO:0016272 "prefoldin complex" annotation. Reason: "Protein binding" is uninformative. The PFDN4-VBP1/PFDN3 interaction reflects co-membership in the prefoldin complex, already captured by GO:0016272 "prefoldin complex." This high-throughput interactome study provides no additional functional insight. Supporting Evidence: PMID:25416956 Here, we describe a systematic map of ...high-quality human binary protein-protein interactions.
GO:0005515 protein binding	IPI PMID:28514442 Architecture of the human interactome defines protein commun...	MARK AS OVER ANNOTATED	Summary: GO:0005515 "protein binding" (IPI with UniProtKB:P61758/VBP1) from Huttlin et al. 2017 (PMID:28514442), the BioPlex human interactome study (architecture of the human interactome). This is another detection of the PFDN4-VBP1/PFDN3 interaction, expected for subunits of the same hexameric prefoldin complex. The "protein binding" term is uninformative and the interaction is already captured by the prefoldin complex membership annotation (GO:0016272). Reason: "Protein binding" is uninformative. The PFDN4-VBP1/PFDN3 interaction reflects co-membership in the prefoldin complex, already captured by GO:0016272. This high-throughput interactome study provides no additional functional insight beyond complex membership.
GO:0005515 protein binding	IPI PMID:32296183 A reference map of the human binary protein interactome.	MARK AS OVER ANNOTATED	Summary: GO:0005515 "protein binding" (IPI with UniProtKB:O75679/RFPL3 and UniProtKB:P61758/VBP1) from Luck et al. 2020 (PMID:32296183), a reference map of the human binary protein interactome (HuRI). The VBP1/PFDN3 interaction again reflects intra-complex assembly. The RFPL3 (Ret finger protein-like 3) interaction is also confirmed in the UniProt record (NbExp=3). RFPL3 is involved in protein ubiquitination, and its biological significance for PFDN4 function is unclear. In either case, the "protein binding" term is uninformative. Reason: "Protein binding" is uninformative. The PFDN4-VBP1/PFDN3 interaction is captured by GO:0016272. The RFPL3 interaction, while replicated (NbExp=3 in IntAct), does not clarify PFDN4 function. The core molecular function is better captured by GO:0044183 "protein folding chaperone."
GO:0005515 protein binding	IPI PMID:33961781 Dual proteome-scale networks reveal cell-specific remodeling...	MARK AS OVER ANNOTATED	Summary: GO:0005515 "protein binding" (IPI with UniProtKB:P61758/VBP1) from Huttlin et al. 2021 (PMID:33961781), a dual proteome-scale network study of the human interactome. This is yet another independent detection of the PFDN4-VBP1/PFDN3 intra-complex interaction. The "protein binding" term is uninformative. Reason: "Protein binding" is uninformative. This is a replication of the PFDN4-VBP1 interaction (intra-complex) that does not add functional insight beyond what is captured by GO:0016272 (prefoldin complex).
GO:0005515 protein binding	IPI PMID:40205054 Multimodal cell maps as a foundation for structural and func...	MARK AS OVER ANNOTATED	Summary: GO:0005515 "protein binding" (IPI with UniProtKB:P61758/VBP1) from multimodal cell maps study (PMID:40205054). This is yet another replication of the PFDN4-VBP1/PFDN3 interaction, expected for co-members of the prefoldin complex. The "protein binding" term is uninformative. Reason: "Protein binding" is uninformative. This is a further replication of the known PFDN4-VBP1/PFDN3 intra-complex interaction from a large-scale study. The relevant functions are already captured by more specific annotations (GO:0016272 for complex membership).
GO:0006457 protein folding	NAS PMID:32699605 The functions and mechanisms of prefoldin complex and prefol...	ACCEPT	Summary: GO:0006457 "protein folding" (NAS) from ComplexPortal, citing Liang et al. 2020 (PMID:32699605), a comprehensive review of prefoldin complex functions and mechanisms. The review describes how the prefoldin complex helps protein fold correctly by providing the TRiC/CCT chaperonin with unfolded substrates. This NAS annotation is consistent with the IBA and IDA annotations to the same term. Reason: Protein folding is the core biological process for PFDN4. This NAS annotation from ComplexPortal cites a well-sourced review (PMID:32699605) that accurately describes the protein folding function of the prefoldin complex. Consistent with IBA and IDA evidence to the same term. Supporting Evidence: PMID:32699605 The correct folding is a key process for a protein to acquire its functional structure and conformation. Prefoldin is a well-known chaperone protein that regulates the correct folding of proteins.
GO:0006457 protein folding	IDA PMID:30955883 The Chaperonin TRiC/CCT Associates with Prefoldin through a ...	ACCEPT	Summary: GO:0006457 "protein folding" (IDA) from Gestaut et al. 2019 (PMID:30955883), which used cryo-EM, crosslinking mass spectrometry, and biochemical reconstitution to characterize the structural and functional interplay between the prefoldin (PFD) complex and TRiC/CCT chaperonin. The study demonstrates that "PFD can act after TRiC bound its substrates to enhance the rate and yield of the folding reaction, suppressing non-productive reaction cycles," directly showing involvement in protein folding. The reconstituted human prefoldin complex includes PFDN4 as a structural component. Reason: This IDA annotation is supported by strong direct experimental evidence from Gestaut et al. 2019 (PMID:30955883), which demonstrated through cryo-EM and biochemical approaches that the PFD-TRiC supra-chaperone assembly enhances protein folding rates. Protein folding is the core biological process for PFDN4. Supporting Evidence: PMID:30955883 PFD can act after TRiC bound its substrates to enhance the rate and yield of the folding reaction, suppressing non-productive reaction cycles. PMID:30955883 The supra-chaperone assembly formed by PFD and TRiC is essential to prevent toxic conformations and ensure effective cellular proteostasis.
GO:0016272 prefoldin complex	IDA PMID:30955883 The Chaperonin TRiC/CCT Associates with Prefoldin through a ...	ACCEPT	Summary: GO:0016272 "prefoldin complex" (IDA) from Gestaut et al. 2019 (PMID:30955883). This study used reconstituted human prefoldin complex (containing all six subunits including PFDN4) and characterized its structure and function through cryo-EM, crosslinking mass spectrometry, and biochemical assays. The cryo-EM structures (PDB: 6NR8, 6NR9, 6NRB, 6NRC, 6NRD) include PFDN4 as chain 4, directly demonstrating that PFDN4 is a component of the prefoldin complex. Reason: PFDN4 is a core structural subunit of the prefoldin complex. This IDA annotation is supported by high-resolution cryo-EM structural data from Gestaut et al. 2019 (PMID:30955883) that directly demonstrates PFDN4 as a component of the human prefoldin complex. Supporting Evidence: PMID:30955883 Maintaining proteostasis in eukaryotic protein folding involves cooperation of distinct chaperone systems. To understand how the essential ring-shaped chaperonin TRiC/CCT cooperates with the chaperone prefoldin/GIMc (PFD), we integrate cryoelectron microscopy (cryo-EM), crosslinking-mass-spectrometry and biochemical and cellular approaches to elucidate the structural and functional interplay between TRiC/CCT and PFD.
GO:0051082 unfolded protein binding	IDA PMID:30955883 The Chaperonin TRiC/CCT Associates with Prefoldin through a ...	MODIFY	Summary: GO:0051082 "unfolded protein binding" is now formally obsolete (go-ontology#30962). This IDA annotation cites Gestaut et al. 2019 (PMID:30955883), which demonstrated that prefoldin associates with TRiC through a conserved electrostatic interface and undergoes conformational cycling during substrate transfer. Critically, the paper shows that PFD functions not merely as a passive binder of unfolded substrates but as an active co-chaperone that enhances the rate and yield of TRiC-mediated folding. GO:0044183 "protein folding chaperone" is the appropriate replacement, capturing the functional role of prefoldin in the chaperone-assisted folding pathway. Reason: GO:0051082 is now formally obsolete. Gestaut et al. 2019 (PMID:30955883) demonstrates that prefoldin functions as a co-chaperone/holdase that cooperates with TRiC/CCT in substrate folding, not merely as an unfolded protein binder. GO:0044183 "protein folding chaperone" accurately describes this co-chaperone activity. The GO:0044183 definition ("Binding to a protein or a protein-containing complex to assist the protein folding process") appropriately encompasses the holdase/transfer function. Proposed replacements: protein folding chaperone Supporting Evidence: PMID:30955883 PFD can act after TRiC bound its substrates to enhance the rate and yield of the folding reaction, suppressing non-productive reaction cycles. PMID:30955883 Disrupting the TRiC-PFD interaction in vivo is strongly deleterious, leading to accumulation of amyloid aggregates. PMID:9630229 Prefoldin binds specifically to cytosolic chaperonin (c-cpn) and transfers target proteins to it.
GO:0001540 amyloid-beta binding	IDA PMID:23614719 Human prefoldin inhibits amyloid-β (Aβ) fibrillation and con...	KEEP AS NON CORE	Summary: GO:0001540 "amyloid-beta binding" (IDA) from Sorgjerd et al. 2013 (PMID:23614719). This study demonstrated that recombinant human prefoldin (hPFD) inhibits amyloid-beta (Abeta 1-42) fibrillation in vitro and induces formation of soluble Abeta oligomers with reduced toxicity. The study used thioflavin T measurements and immunoblotting to show that hPFD directly interacts with Abeta peptides and modifies their aggregation pathway. While this demonstrates that the prefoldin complex can bind Abeta, this is not the core function of PFDN4 -- it reflects the general chaperone/holdase property of prefoldin applied to an amyloidogenic substrate. The annotation was made on the intact prefoldin complex, not PFDN4 individually. Reason: Amyloid-beta binding is a secondary, non-core function that reflects the general holdase/chaperone activity of the prefoldin complex applied to an amyloidogenic substrate. The study (PMID:23614719) used the intact hexameric complex rather than individual PFDN4. While the data are solid, this represents a peripheral function compared to the core role in actin/tubulin folding via TRiC/CCT delivery. Supporting Evidence: PMID:23614719 we investigated the effect of recombinant human PFD (hPFD) on Abeta(1-42) aggregation in vitro and found that hPFD inhibited Abeta fibrillation and induced formation of soluble Abeta oligomers.
GO:0016272 prefoldin complex	IDA PMID:23614719 Human prefoldin inhibits amyloid-β (Aβ) fibrillation and con...	ACCEPT	Summary: GO:0016272 "prefoldin complex" (IDA) from Sorgjerd et al. 2013 (PMID:23614719). This study expressed and purified recombinant human prefoldin complex (hPFD) to investigate its effect on amyloid-beta aggregation. The successful reconstitution and purification of the hexameric complex provides direct evidence for PFDN4 membership in the prefoldin complex, consistent with the IDA annotation from PMID:30955883 and the IBA and IEA annotations. Reason: PFDN4 is a core structural subunit of the prefoldin complex. This IDA annotation from PMID:23614719 provides independent experimental evidence through reconstitution of the human prefoldin hexamer, consistent with the structural data from PMID:30955883. Supporting Evidence: PMID:23614719 Prefoldin (PFD) is a molecular chaperone that prevents aggregation of misfolded proteins.
GO:1905907 negative regulation of amyloid fibril formation	IDA PMID:23614719 Human prefoldin inhibits amyloid-β (Aβ) fibrillation and con...	KEEP AS NON CORE	Summary: GO:1905907 "negative regulation of amyloid fibril formation" (IDA) from Sorgjerd et al. 2013 (PMID:23614719). The study demonstrated that recombinant human prefoldin "inhibited Abeta fibrillation and induced formation of soluble Abeta oligomers" that were 30-40% less toxic than Abeta fibrils. Thioflavin T measurements confirmed reduced fibril formation. While the experimental evidence is sound, this represents a non-core function of the prefoldin complex -- an extension of its general holdase/chaperone properties to amyloidogenic substrates rather than its primary role in actin/tubulin folding. The study was performed on the intact hexameric complex, not PFDN4 individually. Reason: The experimental evidence from PMID:23614719 is solid, but this is a secondary function reflecting the general anti-aggregation properties of the prefoldin complex rather than its core role in delivering unfolded actin/tubulin to TRiC/CCT. The study was performed in vitro on the intact hexameric complex, and the relevance to PFDN4 specifically (as opposed to the complex as a whole) is indirect. Supporting Evidence: PMID:23614719 we investigated the effect of recombinant human PFD (hPFD) on Abeta(1-42) aggregation in vitro and found that hPFD inhibited Abeta fibrillation and induced formation of soluble Abeta oligomers. PMID:23614719 Our findings show a relation between cytotoxicity of Abeta oligomers and structure and suggest a possible protective role of PFD in AD.
GO:0005515 protein binding	IPI PMID:17936702 S6K1-mediated disassembly of mitochondrial URI/PP1gamma comp...	MARK AS OVER ANNOTATED	Summary: GO:0005515 "protein binding" (IPI with UniProtKB:O94763/URI1) from Djouder et al. 2007 (PMID:17936702). This study identified PFDN4 as an interactor of URI1 (unconventional prefoldin RPB5 interactor 1) in a growth-dependent and phosphorylation-dependent manner. The UniProt record for PFDN4 confirms the interaction: "Interacts with URI1; the interaction is phosphorylation- dependent and occurs in a growth-dependent manner." URI1 is a component of the PAQosome/R2TP-prefoldin-like complex involved in macromolecular assembly. While the interaction is genuine and biologically interesting (linking PFDN4 to the URI1/PAQosome pathway), the "protein binding" term is uninformative. Reason: "Protein binding" is uninformative. The PFDN4-URI1 interaction was demonstrated by focused biochemistry (PMID:17936702) and is biologically interesting, but the GO term provides no functional insight. The specific interaction with URI1 is noted in the UniProt record. The core molecular function of PFDN4 is better captured by GO:0044183 "protein folding chaperone." Supporting Evidence: PMID:17936702 the prefoldin chaperone URI represents a mitochondrial substrate of S6K1.
GO:0005634 nucleus	IDA PMID:17936702 S6K1-mediated disassembly of mitochondrial URI/PP1gamma comp...	KEEP AS NON CORE	Summary: GO:0005634 "nucleus" (IDA) from Djouder et al. 2007 (PMID:17936702). This study investigated URI1-mediated signaling pathways and identified PFDN4 among URI1 interactors. The subcellular localization data for PFDN4 comes from this study, where PFDN4 was detected in the nucleus. The UniProt record cites this reference for nuclear localization. The deep research review (PFDN4-deep-research-falcon.md) notes "nuclear functions are suggested for certain prefoldin subunits and for PFDN4/Protein C-1 as a transcriptional cofactor, indicating potential nucleocytoplasmic distribution depending on context." While the canonical prefoldin chaperone function is cytoplasmic, nuclear presence is documented and may relate to non-canonical transcriptional or chromatin-related functions reported for prefoldin family members. Reason: Nuclear localization is documented by IDA evidence from PMID:17936702, but this represents a non-canonical localization. The primary site of prefoldin chaperone function is the cytoplasm. The nuclear presence may relate to non-canonical transcriptional cofactor roles suggested for PFDN4/Protein C-1. Supporting Evidence: PMID:17936702 S6 kinase 1 (S6K1) acts to integrate nutrient and growth factor signals to promote cell growth but also cell survival as a mitochondria-tethered protein kinase
GO:0005737 cytoplasm	IDA PMID:17936702 S6K1-mediated disassembly of mitochondrial URI/PP1gamma comp...	ACCEPT	Summary: GO:0005737 "cytoplasm" (IDA) from Djouder et al. 2007 (PMID:17936702). This study detected PFDN4 in the cytoplasm, consistent with its role as a subunit of the cytoplasmic prefoldin complex. The UniProt record confirms cytoplasmic localization citing this reference. This is the primary location for prefoldin chaperone function (PMID:9630229). Reason: Cytoplasmic localization is the primary site of prefoldin chaperone function. This IDA annotation from PMID:17936702 is consistent with the established cytoplasmic role of the prefoldin complex and with the IBA annotation to the same term. Supporting Evidence: PMID:9630229 Prefoldin binds specifically to cytosolic chaperonin (c-cpn) and transfers target proteins to it.
GO:0005739 mitochondrion	IDA PMID:17936702 S6K1-mediated disassembly of mitochondrial URI/PP1gamma comp...	KEEP AS NON CORE	Summary: GO:0005739 "mitochondrion" (IDA) from Djouder et al. 2007 (PMID:17936702). This study demonstrated that URI1 forms complexes with PP1gamma at mitochondria, and PFDN4 was identified as an interactor of URI1. The UniProt record reports mitochondrial localization based on this study. The mitochondrial localization of PFDN4 appears to be related to its interaction with URI1 and the PAQosome axis, rather than canonical prefoldin chaperone function. Reason: Mitochondrial localization is documented by IDA evidence from PMID:17936702, but this represents a non-canonical localization related to the URI1 interaction pathway. The primary site of prefoldin chaperone function is the cytoplasm. Supporting Evidence: PMID:17936702 the prefoldin chaperone URI represents a mitochondrial substrate of S6K1. In growth factor-deprived or rapamycin-treated cells, URI forms stable complexes with protein phosphatase (PP)1gamma at mitochondria
GO:0006457 protein folding	TAS PMID:9630229 Prefoldin, a chaperone that delivers unfolded proteins to cy...	ACCEPT	Summary: GO:0006457 "protein folding" (TAS) citing the landmark Vainberg et al. 1998 paper (PMID:9630229) that first described the discovery of the prefoldin complex and its role in capturing unfolded proteins and delivering them to cytosolic chaperonin for folding. This is the original paper establishing the protein folding function of the prefoldin complex. Reason: Protein folding is the core biological process for PFDN4. This TAS annotation cites the foundational paper (PMID:9630229) establishing prefoldin as a chaperone that delivers unfolded proteins to cytosolic chaperonin for folding. Consistent with IBA, IDA, and NAS evidence to the same term. Supporting Evidence: PMID:9630229 We describe the discovery of a heterohexameric chaperone protein, prefoldin, based on its ability to capture unfolded actin. Prefoldin binds specifically to cytosolic chaperonin (c-cpn) and transfers target proteins to it.
GO:0051087 protein-folding chaperone binding	TAS PMID:9630229 Prefoldin, a chaperone that delivers unfolded proteins to cy...	ACCEPT	Summary: GO:0051087 "protein-folding chaperone binding" (TAS) citing Vainberg et al. 1998 (PMID:9630229). This term is defined as "Binding to a chaperone protein, a class of proteins that bind to nascent or unfolded polypeptides and ensure correct folding or transport." Prefoldin binds specifically to the TRiC/CCT chaperonin to deliver unfolded substrates for folding. Vainberg et al. 1998 demonstrated that "Prefoldin binds specifically to cytosolic chaperonin (c-cpn) and transfers target proteins to it." This annotation accurately captures that PFDN4 (as part of the prefoldin complex) binds to another chaperone (TRiC/CCT). Gestaut et al. 2019 (PMID:30955883) further characterized this interface at the structural level. Reason: This term correctly describes the binding of prefoldin to TRiC/CCT, a protein-folding chaperone. The prefoldin-TRiC interaction is a well-established core function (PMID:9630229, PMID:30955883). The term complements GO:0044183 "protein folding chaperone" (which describes prefoldin's own chaperone activity) and GO:0006457 (the process). Supporting Evidence: PMID:9630229 Prefoldin binds specifically to cytosolic chaperonin (c-cpn) and transfers target proteins to it. PMID:30955883 We find these hetero-oligomeric chaperones associate in a defined architecture, through a conserved interface of electrostatic contacts that serves as a pivot point for a TRiC-PFD conformational cycle.
GO:0005829 cytosol	NAS PMID:9630229 Prefoldin, a chaperone that delivers unfolded proteins to cy...	ACCEPT	Summary: GO:0005829 "cytosol" (NAS) citing Vainberg et al. 1998 (PMID:9630229). The prefoldin complex operates in the cytosol, where it captures unfolded nascent polypeptides and delivers them to the cytosolic chaperonin TRiC/CCT. The term "cytosol" is more specific than "cytoplasm" (GO:0005737) and accurately describes the compartment where prefoldin functions. Both Vainberg et al. 1998 and Gestaut et al. 2019 (PMID:30955883) describe prefoldin as a cytosolic complex. Reason: The cytosol is the correct subcellular location for prefoldin chaperone function. This NAS annotation is consistent with the well-established role of prefoldin as a cytosolic co-chaperone (PMID:9630229, PMID:30955883). The term provides a more specific localization than the broader "cytoplasm" annotation. Supporting Evidence: PMID:9630229 Prefoldin binds specifically to cytosolic chaperonin (c-cpn) and transfers target proteins to it.
GO:0044183 protein folding chaperone	IDA PMID:30955883 The Chaperonin TRiC/CCT Associates with Prefoldin through a ...	NEW	Summary: GO:0044183 "protein folding chaperone" is proposed as a NEW annotation for PFDN4 based on strong experimental evidence. Unlike PFDN1, PFDN4 does not currently have an IBA or IDA annotation to this term. Gestaut et al. 2019 (PMID:30955883) demonstrated that the prefoldin complex (containing PFDN4) functions as a co-chaperone that binds unfolded substrates and delivers them to TRiC/CCT, enhancing the rate and yield of protein folding. Vainberg et al. 1998 (PMID:9630229) established that "Prefoldin binds specifically to cytosolic chaperonin (c-cpn) and transfers target proteins to it." The GO:0044183 definition ("Binding to a protein or a protein-containing complex to assist the protein folding process") precisely captures the prefoldin co-chaperone function. Reason: GO:0044183 "protein folding chaperone" is the core molecular function of PFDN4 as a subunit of the prefoldin complex. Unlike PFDN1, PFDN4 lacks this annotation, and the existing GO:0051082 "unfolded protein binding" annotations are now formally obsolete. This term is the recommended replacement and accurately captures the holdase/transfer chaperone activity of PFDN4 demonstrated by PMID:30955883 and PMID:9630229. Supporting Evidence: PMID:9630229 We describe the discovery of a heterohexameric chaperone protein, prefoldin, based on its ability to capture unfolded actin. Prefoldin binds specifically to cytosolic chaperonin (c-cpn) and transfers target proteins to it. PMID:30955883 PFD can act after TRiC bound its substrates to enhance the rate and yield of the folding reaction, suppressing non-productive reaction cycles.

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Falcon

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