id: Q9NQP4
gene_symbol: PFDN4
product_type: PROTEIN
status: IN_PROGRESS
taxon:
  id: NCBITaxon:9606
  label: Homo sapiens
description: >-
  PFDN4 (Prefoldin subunit 4) encodes a beta-type subunit of the heterohexameric
  prefoldin complex (also known as GimC). The prefoldin complex is a jellyfish-shaped
  molecular chaperone composed of two alpha subunits (PFDN3/VBP1, PFDN5) and four beta
  subunits (PFDN1, PFDN2, PFDN4, PFDN6). Prefoldin functions as a co-chaperone/holdase
  that captures unfolded nascent polypeptides -- primarily actin and tubulin -- and
  delivers them to the group II chaperonin TRiC/CCT for ATP-dependent folding. The
  prefoldin-TRiC interaction is mediated through a conserved electrostatic interface
  (PMID:30955883). Beyond cytoskeletal protein folding, the prefoldin complex has been
  shown to inhibit amyloid-beta fibrillation (PMID:23614719), suggesting roles in
  neuroprotection. PFDN4 (also known as Protein C-1) interacts with URI1 at
  mitochondria in a phosphorylation- and growth-dependent manner (PMID:17936702).
  PFDN4 is ubiquitously expressed and located on chromosome 20q13.2. Structural
  data from cryo-EM places PFDN4 within the PFD-TRiC supra-chaperone complex
  (PDB: 6NR8, 6NR9, 6NRB, 6NRC, 6NRD, 7WU7).
existing_annotations:
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    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.
    action: ACCEPT
    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.
    supported_by:
    - reference_id: PMID:9630229
      supporting_text: >-
        Prefoldin binds specifically to cytosolic chaperonin (c-cpn) and transfers
        target proteins to it.
- term:
    id: GO:0006457
    label: protein folding
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    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.
    action: ACCEPT
    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).
    supported_by:
    - reference_id: PMID:9630229
      supporting_text: >-
        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.
    - reference_id: PMID:30955883
      supporting_text: >-
        PFD can act after TRiC bound its substrates to enhance the rate and yield
        of the folding reaction, suppressing non-productive reaction cycles.
    - reference_id: file:human/PFDN4/PFDN4-deep-research-falcon.md
      supporting_text: >-
        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.
- term:
    id: GO:0051082
    label: unfolded protein binding
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      GO:0051082 "unfolded protein binding" is being obsoleted (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.
    action: MODIFY
    reason: >-
      GO:0051082 is being obsoleted. 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_replacement_terms:
    - id: GO:0044183
      label: protein folding chaperone
    additional_reference_ids:
    - PMID:9630229
    - PMID:30955883
    supported_by:
    - reference_id: PMID:9630229
      supporting_text: >-
        Prefoldin binds specifically to cytosolic chaperonin (c-cpn) and transfers
        target proteins to it.
    - reference_id: PMID:30955883
      supporting_text: >-
        PFD alternates between an open "latched" conformation and a closed "engaged"
        conformation that aligns the PFD-TRiC substrate binding chambers.
- term:
    id: GO:0016272
    label: prefoldin complex
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    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.
    action: ACCEPT
    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).
    supported_by:
    - reference_id: PMID:9630229
      supporting_text: >-
        We describe the discovery of a heterohexameric chaperone protein, prefoldin,
        based on its ability to capture unfolded actin.
    - reference_id: PMID:30955883
      supporting_text: >-
        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.
- term:
    id: GO:0005634
    label: nucleus
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  review:
    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.
    action: KEEP_AS_NON_CORE
    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.
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  review:
    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).
    action: ACCEPT
    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).
- term:
    id: GO:0005739
    label: mitochondrion
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  review:
    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.
    action: KEEP_AS_NON_CORE
    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.
- term:
    id: GO:0006457
    label: protein folding
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  review:
    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).
    action: ACCEPT
    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).
- term:
    id: GO:0016272
    label: prefoldin complex
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  review:
    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.
    action: ACCEPT
    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).
- term:
    id: GO:0032991
    label: protein-containing complex
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  review:
    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.
    action: MARK_AS_OVER_ANNOTATED
    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.
- term:
    id: GO:0051082
    label: unfolded protein binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  review:
    summary: >-
      GO:0051082 "unfolded protein binding" is being obsoleted (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 being obsoleted, 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.
    action: MODIFY
    reason: >-
      GO:0051082 is being obsoleted. 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_replacement_terms:
    - id: GO:0044183
      label: protein folding chaperone
    additional_reference_ids:
    - PMID:9630229
    - PMID:30955883
    supported_by:
    - reference_id: PMID:9630229
      supporting_text: >-
        Prefoldin binds specifically to cytosolic chaperonin (c-cpn) and transfers
        target proteins to it.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:25416956
  review:
    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.
    action: MARK_AS_OVER_ANNOTATED
    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.
    supported_by:
    - reference_id: PMID:25416956
      supporting_text: >-
        Here, we describe a systematic map of ...high-quality human
        binary protein-protein interactions.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:28514442
  review:
    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).
    action: MARK_AS_OVER_ANNOTATED
    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.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:32296183
  review:
    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.
    action: MARK_AS_OVER_ANNOTATED
    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."
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:33961781
  review:
    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.
    action: MARK_AS_OVER_ANNOTATED
    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).
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:40205054
  review:
    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.
    action: MARK_AS_OVER_ANNOTATED
    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).
- term:
    id: GO:0006457
    label: protein folding
  evidence_type: NAS
  original_reference_id: PMID:32699605
  review:
    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.
    action: ACCEPT
    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.
    supported_by:
    - reference_id: PMID:32699605
      supporting_text: >-
        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.
- term:
    id: GO:0006457
    label: protein folding
  evidence_type: IDA
  original_reference_id: PMID:30955883
  review:
    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.
    action: ACCEPT
    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.
    supported_by:
    - reference_id: PMID:30955883
      supporting_text: >-
        PFD can act after TRiC bound its substrates to enhance the rate and yield
        of the folding reaction, suppressing non-productive reaction cycles.
    - reference_id: PMID:30955883
      supporting_text: >-
        The supra-chaperone assembly formed by PFD and TRiC is essential to
        prevent toxic conformations and ensure effective cellular proteostasis.
- term:
    id: GO:0016272
    label: prefoldin complex
  evidence_type: IDA
  original_reference_id: PMID:30955883
  review:
    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.
    action: ACCEPT
    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.
    supported_by:
    - reference_id: PMID:30955883
      supporting_text: >-
        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.
- term:
    id: GO:0051082
    label: unfolded protein binding
  evidence_type: IDA
  original_reference_id: PMID:30955883
  review:
    summary: >-
      GO:0051082 "unfolded protein binding" is being obsoleted (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.
    action: MODIFY
    reason: >-
      GO:0051082 is being obsoleted. 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_replacement_terms:
    - id: GO:0044183
      label: protein folding chaperone
    additional_reference_ids:
    - PMID:9630229
    supported_by:
    - reference_id: PMID:30955883
      supporting_text: >-
        PFD can act after TRiC bound its substrates to enhance the rate and yield
        of the folding reaction, suppressing non-productive reaction cycles.
    - reference_id: PMID:30955883
      supporting_text: >-
        Disrupting the TRiC-PFD interaction in vivo is strongly deleterious,
        leading to accumulation of amyloid aggregates.
    - reference_id: PMID:9630229
      supporting_text: >-
        Prefoldin binds specifically to cytosolic chaperonin (c-cpn) and transfers
        target proteins to it.
- term:
    id: GO:0001540
    label: amyloid-beta binding
  evidence_type: IDA
  original_reference_id: PMID:23614719
  review:
    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.
    action: KEEP_AS_NON_CORE
    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.
    supported_by:
    - reference_id: PMID:23614719
      supporting_text: >-
        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.
- term:
    id: GO:0016272
    label: prefoldin complex
  evidence_type: IDA
  original_reference_id: PMID:23614719
  review:
    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.
    action: ACCEPT
    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.
    supported_by:
    - reference_id: PMID:23614719
      supporting_text: >-
        Prefoldin (PFD) is a molecular chaperone that prevents aggregation of
        misfolded proteins.
- term:
    id: GO:1905907
    label: negative regulation of amyloid fibril formation
  evidence_type: IDA
  original_reference_id: PMID:23614719
  review:
    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.
    action: KEEP_AS_NON_CORE
    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.
    supported_by:
    - reference_id: PMID:23614719
      supporting_text: >-
        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.
    - reference_id: PMID:23614719
      supporting_text: >-
        Our findings show a relation between cytotoxicity of Abeta oligomers and
        structure and suggest a possible protective role of PFD in AD.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:17936702
  review:
    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.
    action: MARK_AS_OVER_ANNOTATED
    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."
    supported_by:
    - reference_id: PMID:17936702
      supporting_text: >-
        the prefoldin chaperone URI represents a mitochondrial substrate
        of S6K1.
- term:
    id: GO:0005634
    label: nucleus
  evidence_type: IDA
  original_reference_id: PMID:17936702
  review:
    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.
    action: KEEP_AS_NON_CORE
    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.
    supported_by:
    - reference_id: PMID:17936702
      supporting_text: >-
        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
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IDA
  original_reference_id: PMID:17936702
  review:
    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).
    action: ACCEPT
    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.
    supported_by:
    - reference_id: PMID:9630229
      supporting_text: >-
        Prefoldin binds specifically to cytosolic chaperonin (c-cpn) and transfers
        target proteins to it.
- term:
    id: GO:0005739
    label: mitochondrion
  evidence_type: IDA
  original_reference_id: PMID:17936702
  review:
    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.
    action: KEEP_AS_NON_CORE
    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.
    supported_by:
    - reference_id: PMID:17936702
      supporting_text: >-
        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
- term:
    id: GO:0006457
    label: protein folding
  evidence_type: TAS
  original_reference_id: PMID:9630229
  review:
    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.
    action: ACCEPT
    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.
    supported_by:
    - reference_id: PMID:9630229
      supporting_text: >-
        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.
- term:
    id: GO:0051087
    label: protein-folding chaperone binding
  evidence_type: TAS
  original_reference_id: PMID:9630229
  review:
    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.
    action: ACCEPT
    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).
    supported_by:
    - reference_id: PMID:9630229
      supporting_text: >-
        Prefoldin binds specifically to cytosolic chaperonin (c-cpn) and transfers
        target proteins to it.
    - reference_id: PMID:30955883
      supporting_text: >-
        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.
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: NAS
  original_reference_id: PMID:9630229
  review:
    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.
    action: ACCEPT
    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.
    supported_by:
    - reference_id: PMID:9630229
      supporting_text: >-
        Prefoldin binds specifically to cytosolic chaperonin (c-cpn) and transfers
        target proteins to it.
- term:
    id: GO:0044183
    label: protein folding chaperone
  evidence_type: IDA
  original_reference_id: PMID:30955883
  review:
    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.
    action: NEW
    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 being obsoleted. This term is the recommended replacement and accurately
      captures the holdase/transfer chaperone activity of PFDN4 demonstrated by
      PMID:30955883 and PMID:9630229.
    additional_reference_ids:
    - PMID:30955883
    - PMID:9630229
    supported_by:
    - reference_id: PMID:9630229
      supporting_text: >-
        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.
    - reference_id: PMID:30955883
      supporting_text: >-
        PFD can act after TRiC bound its substrates to enhance the rate and yield
        of the folding reaction, suppressing non-productive reaction cycles.
core_functions:
- description: >-
    PFDN4 is a beta-type subunit of the heterohexameric prefoldin co-chaperone complex
    that captures unfolded nascent polypeptides (primarily actin and tubulin) and delivers
    them to the TRiC/CCT chaperonin for ATP-dependent folding. Cryo-EM structural data
    show PFDN4 as chain 4 in the PFD-TRiC supra-chaperone complex. The prefoldin complex
    alternates between an open "latched" conformation and a closed "engaged" conformation
    that aligns the PFD-TRiC substrate binding chambers, and this conformational cycling
    enhances the rate and yield of TRiC-mediated protein folding. Disrupting the TRiC-PFD
    interaction in vivo leads to accumulation of amyloid aggregates.
  molecular_function:
    id: GO:0044183
    label: protein folding chaperone
  directly_involved_in:
    - id: GO:0006457
      label: protein folding
  locations:
    - id: GO:0005829
      label: cytosol
  in_complex:
    id: GO:0016272
    label: prefoldin complex
  supported_by:
    - reference_id: PMID:9630229
      supporting_text: >-
        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.
    - reference_id: PMID:30955883
      supporting_text: >-
        PFD can act after TRiC bound its substrates to enhance the rate and yield
        of the folding reaction, suppressing non-productive reaction cycles.
    - reference_id: PMID:30955883
      supporting_text: >-
        Disrupting the TRiC-PFD interaction in vivo is strongly deleterious,
        leading to accumulation of amyloid aggregates.
references:
- id: GO_REF:0000002
  title: Gene Ontology annotation through association of InterPro records with GO
    terms
  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, accompanied by conservative changes to GO terms applied by
    UniProt
  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:17936702
  title: S6K1-mediated disassembly of mitochondrial URI/PP1gamma complexes activates
    a negative feedback program that counters S6K1 survival signaling.
  findings: []
- id: PMID:23614719
  title: "Human prefoldin inhibits amyloid-\u03B2 (A\u03B2) fibrillation and contributes\
    \ to formation of nontoxic A\u03B2 aggregates."
  findings: []
- id: PMID:25416956
  title: A proteome-scale map of the human interactome network.
  findings: []
- id: PMID:28514442
  title: Architecture of the human interactome defines protein communities and disease
    networks.
  findings: []
- id: PMID:30955883
  title: The Chaperonin TRiC/CCT Associates with Prefoldin through a Conserved Electrostatic
    Interface Essential for Cellular Proteostasis.
  findings: []
- id: PMID:32296183
  title: A reference map of the human binary protein interactome.
  findings: []
- id: PMID:32699605
  title: The functions and mechanisms of prefoldin complex and prefoldin-subunits.
  findings: []
- id: PMID:33961781
  title: Dual proteome-scale networks reveal cell-specific remodeling of the human
    interactome.
  findings: []
- id: PMID:40205054
  title: Multimodal cell maps as a foundation for structural and functional genomics.
  findings: []
- id: PMID:9630229
  title: 'Prefoldin, a chaperone that delivers unfolded proteins to cytosolic chaperonin.'
  findings: []