id: P27420
gene_symbol: hsp-3
product_type: PROTEIN
status: COMPLETE
taxon:
  id: NCBITaxon:6239
  label: Caenorhabditis elegans
description: >-
  HSP-3 is one of the two endoplasmic reticulum (ER)-resident HSP70/BiP (GRP78/KAR2)
  chaperones of Caenorhabditis elegans; the other is its close paralog HSP-4. HSP-3 is
  a soluble ER-lumen protein bearing an N-terminal signal peptide and a C-terminal
  KDEL-type ER-retention motif, with the canonical HSP70 nucleotide-binding and
  substrate-binding domain architecture. It acts as an ATP-dependent molecular chaperone
  that assists folding, refolding and assembly of nascent secretory and membrane proteins
  in the ER lumen. Like other BiP orthologs, HSP-3 also participates in the ER unfolded
  protein response (UPR): it (with HSP-4) associates with the three UPR stress sensors
  IRE-1, ATF-6 and PEK-1 to hold them inactive, and its own transcription is modestly
  induced by ER stress in an ire-1/xbp-1-dependent manner. HSP-3 is generally the more
  constitutively expressed of the two worm BiP paralogs, whereas HSP-4 is the strongly
  stress-inducible one. HSP-3 is a direct substrate of the FIC-1 AMPylase and contributes
  to tolerance of chronic ER stress and to innate immunity.
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: PMID:11779465
    title: Complementary signaling pathways regulate the unfolded protein response and
      are required for C. elegans development.
    findings:
      - statement: Foundational study establishing that C. elegans uses ire-1-mediated
          splicing of xbp-1 mRNA for UPR gene transcription and survival upon ER stress.
        supporting_text: C. elegans requires ire-1-mediated splicing of xbp-1 mRNA for
          UPR gene transcription and survival upon ER stress
    reference_review:
      relevance: MEDIUM
      correctness: UNVERIFIED
      review_notes: >-
        PubMed-verified as the foundational C. elegans UPR paper (Shen et al., Cell 2001)
        and the source of the WormBase IEP UPR annotations for hsp-3. Only the abstract is
        cached locally, so the hsp-3-specific expression data underlying the IEP call could
        not be independently re-verified here; the experimental annotation is deferred to
        the WormBase curator who read the full text.
  - id: PMID:12186849
    title: A survival pathway for Caenorhabditis elegans with a blocked unfolded protein
      response.
    findings:
      - statement: Genome-wide microarray of the C. elegans ER-stress response; hsp-3
          (cosmid C15H9.6) is among the tunicamycin-induced genes whose induction is
          attenuated in xbp-1 mutants (Table I), establishing hsp-3 as an xbp-1-dependent
          UPR target.
        supporting_text: in C. elegans, the ire-1 and xbp-1 pathway has retained its
          essential role in upregulating expression of many UPR target genes that are
          similarly upregulated by the homologous pathway in yeast
    reference_review:
      relevance: HIGH
      correctness: VERIFIED
      review_notes: >-
        PubMed-verified (Urano et al., J Cell Biol 2002). hsp-3 is unambiguously cosmid
        C15H9.6 (UniProt/WormBase ORFName); C15H9.6 appears in Table I of tunicamycin-
        induced, xbp-1-dependent genes (N2 log2 1.32 +/- 0.06, reduced to 0.68 +/- 0.05 in
        xbp-1), directly supporting the HEP UPR annotation on hsp-3.
  - id: PMID:2225768
    title: The HSP70 multigene family of Caenorhabditis elegans.
    findings:
      - statement: Reviews the C. elegans HSP70 multigene family, including the
          ER-resident BiP-type members; used as the ISS source for ATP hydrolysis activity.
    reference_review:
      relevance: LOW
      correctness: UNVERIFIED
      review_notes: >-
        Review article (Heschl & Baillie 1990); abstract-only in the local cache. Cited by
        WormBase as the ISS basis (by similarity to yeast KAR2, UniProtKB:P16474) for the
        HSP70 ATPase activity of hsp-3. Family-level context rather than direct hsp-3
        functional data.
  - id: PMID:27138431
    title: The Caenorhabditis elegans Protein FIC-1 Is an AMPylase That Covalently
      Modifies Heat-Shock 70 Family Proteins, Translation Elongation Factors and Histones.
    findings:
      - statement: HSP-3 is directly retained within the ER lumen (contrasted with the
          cytosolic HSP-1), confirming its ER-lumenal localization by direct study.
        supporting_text: HSP-1 is predominantly cytosolic, whereas HSP-3 is retained
          within the ER lumen.
      - statement: HSP-3 is a direct in vivo AMPylation substrate of FIC-1, identified by
          mass spectrometry among the AMPylated protein fraction.
        supporting_text: 'two classes of proteins over-represented amongst the AMPylated
          fraction of proteins: HSP 70 proteins (HSP-1, HSP-3)'
      - statement: HSP-3, with HSP-4, forms a complex with the three UPR sensors IRE-1,
          ATF-6 and PEK-1 to keep them inactive (the classical BiP brake on UPR signaling).
        supporting_text: form a complex with IRE-1, ATF-6 and PEK-1, to preclude
          activation of UPR-related signaling events
      - statement: HSP-3 contributes to tolerance of chronic ER stress and to innate
          immunity, based on hypersensitivity of hsp-3 animals to Pseudomonas aeruginosa.
        supporting_text: highlighting a role for HSP-3 in the tolerance of chronic ER
          stress and innate immunity.
      - statement: The two worm BiP paralogs hsp-3 and hsp-4 are assumed to
          cross-compensate as ER-resident chaperones, framing their functional redundancy.
        supporting_text: elegans encodes two Grp78/BiP homologues, hsp-3 and hsp-4,
          assumed to cross-compensate for each other in their roles as ER-residing protein
          chaperones
    reference_review:
      relevance: HIGH
      correctness: VERIFIED
      review_notes: >-
        PubMed-verified (Truttmann et al., PLoS Genet 2016); full text cached. Provides the
        strongest hsp-3-specific experimental data available: ER-lumen localization,
        FIC-1 AMPylation, membership in the BiP-UPR-sensor repressive complex, and a role
        in chronic ER-stress tolerance / innate immunity. Cited by UniProt P27420 for the
        AMPylation PTM.
existing_annotations:
  - term:
      id: GO:0005737
      label: cytoplasm
    evidence_type: IBA
    original_reference_id: GO_REF:0000033
    qualifier: is_active_in
    review:
      summary: >-
        IBA annotation propagated across the broad HSP70 phylogenetic tree, which contains
        cytosolic and nuclear members. HSP-3 is a dedicated ER-lumenal BiP with a cleaved
        signal peptide and a C-terminal KDEL ER-retention motif; its functional
        compartment is the ER lumen, not the cytoplasm.
      action: MARK_AS_OVER_ANNOTATED
      reason: >-
        Over-propagation from the pan-HSP70 family tree. HSP-3 is directly reported to be
        retained within the ER lumen and carries a signal peptide plus ER-retention motif,
        so a general cytoplasm annotation does not represent its site of action.
      supported_by:
        - reference_id: PMID:27138431
          supporting_text: HSP-1 is predominantly cytosolic, whereas HSP-3 is retained
            within the ER lumen.
        - reference_id: UniProt:P27420
          supporting_text: 'SUBCELLULAR LOCATION: Endoplasmic reticulum lumen'
      propagation_review:
        root_cause: PROPAGATION_BAD
        failure_modes:
          - COMPARTMENT_OR_COMPLEX_MISMATCH
        source_entities:
          - source_id: PANTHER:PTN002321897
            source_status: SUPPORTS_SOURCE_BUT_NOT_TARGET
            comment: >-
              GO_Central IBA propagated across the broad HSP70 tree, which contains
              cytosolic/nuclear members; HSP-3 is a signal-peptide-bearing, KDEL-retained
              ER-lumenal BiP, so the cytosolic localization does not transfer to it.
  - term:
      id: GO:0005788
      label: endoplasmic reticulum lumen
    evidence_type: IBA
    original_reference_id: GO_REF:0000033
    qualifier: is_active_in
    review:
      summary: >-
        The ER lumen is the primary functional location of HSP-3, consistent with its
        signal peptide, KDEL retention motif, and direct experimental localization.
      action: ACCEPT
      reason: >-
        Core localization of HSP-3/BiP. UniProt records ER lumen localization and the
        FIC-1 study directly reports HSP-3 retention in the ER lumen.
      supported_by:
        - reference_id: UniProt:P27420
          supporting_text: 'SUBCELLULAR LOCATION: Endoplasmic reticulum lumen'
        - reference_id: PMID:27138431
          supporting_text: HSP-1 is predominantly cytosolic, whereas HSP-3 is retained
            within the ER lumen.
  - term:
      id: GO:0016887
      label: ATP hydrolysis activity
    evidence_type: IBA
    original_reference_id: GO_REF:0000033
    qualifier: enables
    review:
      summary: >-
        HSP-3/BiP is an ATPase; ATP hydrolysis drives the allosteric chaperone cycle of
        substrate binding and release. This is a conserved core molecular function of the
        HSP70 family.
      action: ACCEPT
      reason: >-
        ATP hydrolysis is essential to the HSP70/BiP chaperone cycle. UniProt annotates
        this activity (ISS to yeast KAR2), and it is a defining feature of the family.
      supported_by:
        - reference_id: UniProt:P27420
          supporting_text: GO:0016887; F:ATP hydrolysis activity; ISS:WormBase
        - reference_id: UniProt:P27420
          supporting_text: Belongs to the heat shock protein 70 family
  - term:
      id: GO:0044183
      label: protein folding chaperone
    evidence_type: IBA
    original_reference_id: GO_REF:0000033
    qualifier: enables
    review:
      summary: >-
        HSP-3 is an ER-resident molecular chaperone that assists folding and assembly of
        client proteins in the ER lumen, the core molecular function of BiP orthologs.
      action: ACCEPT
      reason: >-
        This is the core molecular function of HSP-3. UniProt describes a role in
        facilitating assembly of multimeric protein complexes in the ER, and the FIC-1
        study frames HSP-3 and HSP-4 as cross-compensating ER-resident chaperones.
      supported_by:
        - reference_id: UniProt:P27420
          supporting_text: Probably plays a role in facilitating the assembly of
        - reference_id: PMID:27138431
          supporting_text: elegans encodes two Grp78/BiP homologues, hsp-3 and hsp-4,
            assumed to cross-compensate for each other in their roles as ER-residing
            protein chaperones
        - reference_id: file:worm/hsp-3/hsp-3-deep-research-falcon.md
          supporting_text: primarily responsible for de novo protein folding and the
            refolding of misfolded proteins within the ER lumen
  - term:
      id: GO:0005634
      label: nucleus
    evidence_type: IBA
    original_reference_id: GO_REF:0000033
    qualifier: is_active_in
    review:
      summary: >-
        IBA annotation propagated from nuclear/cytosolic HSP70 family members. HSP-3 is an
        ER-lumenal BiP and is not a nuclear protein.
      action: MARK_AS_OVER_ANNOTATED
      reason: >-
        Over-propagation from the broad HSP70 tree. HSP-3 has a signal peptide and a KDEL
        ER-retention motif and is directly reported to reside in the ER lumen; nuclear
        localization does not represent its function.
      supported_by:
        - reference_id: PMID:27138431
          supporting_text: HSP-1 is predominantly cytosolic, whereas HSP-3 is retained
            within the ER lumen.
        - reference_id: UniProt:P27420
          supporting_text: 'SUBCELLULAR LOCATION: Endoplasmic reticulum lumen'
      propagation_review:
        root_cause: PROPAGATION_BAD
        failure_modes:
          - COMPARTMENT_OR_COMPLEX_MISMATCH
        source_entities:
          - source_id: PANTHER:PTN001834223
            source_status: SUPPORTS_SOURCE_BUT_NOT_TARGET
            comment: >-
              Nuclear localization is contributed by nuclear/cytosolic HSP70 members of the
              family tree; it does not transfer to the ER-lumenal BiP HSP-3.
  - term:
      id: GO:0031072
      label: heat shock protein binding
    evidence_type: IBA
    original_reference_id: GO_REF:0000033
    qualifier: enables
    review:
      summary: >-
        HSP70/BiP chaperones cooperate with co-chaperones (J-domain/Hsp40 proteins and
        nucleotide-exchange factors) that regulate the ATPase cycle and substrate
        handling; this is captured by heat shock protein binding.
      action: ACCEPT
      reason: >-
        A defensible family-level function that is more informative than generic protein
        binding: it reflects the co-chaperone interactions central to the HSP70 mechanism.
        Retained as a supporting (non-defining) molecular function.
      supported_by:
        - reference_id: UniProt:P27420
          supporting_text: Belongs to the heat shock protein 70 family
  - term:
      id: GO:0036503
      label: ERAD pathway
    evidence_type: IBA
    original_reference_id: GO_REF:0000033
    qualifier: involved_in
    review:
      summary: >-
        BiP orthologs recognize and retain misfolded ER proteins destined for
        ER-associated degradation. This is a genuine BiP-family role, but there is no
        hsp-3-specific experimental evidence in C. elegans and it is peripheral to the
        constitutive folding role.
      action: KEEP_AS_NON_CORE
      reason: >-
        Plausible by orthology (BiP participates in ERAD substrate recognition) but not the
        primary, directly demonstrated function of HSP-3; retained as a non-core role
        pending worm-specific evidence.
      supported_by:
        - reference_id: UniProt:P27420
          supporting_text: Belongs to the heat shock protein 70 family
  - term:
      id: GO:0016020
      label: membrane
    evidence_type: IBA
    original_reference_id: GO_REF:0000033
    qualifier: is_active_in
    review:
      summary: >-
        HSP-3 is a soluble ER-lumen protein, not a membrane-embedded protein. It may
        transiently associate with membrane-bound clients or the translocon, but is not an
        integral membrane protein.
      action: MARK_AS_OVER_ANNOTATED
      reason: >-
        Overly broad and imprecise for a soluble ER-lumenal BiP with a KDEL retention
        motif. The specific location endoplasmic reticulum lumen (GO:0005788) is more
        appropriate.
      proposed_replacement_terms:
        - id: GO:0005788
          label: endoplasmic reticulum lumen
      supported_by:
        - reference_id: UniProt:P27420
          supporting_text: 'SUBCELLULAR LOCATION: Endoplasmic reticulum lumen'
      propagation_review:
        root_cause: TERM_SCOPING_PROBLEM
        failure_modes:
          - GRANULARITY_MISMATCH
          - COMPARTMENT_OR_COMPLEX_MISMATCH
        source_entities:
          - source_id: PANTHER:PTN001834223
            source_status: SUPPORTS_SOURCE_BUT_NOT_TARGET
            comment: >-
              The generic membrane term reflects membrane-associated HSP70 family members;
              HSP-3 is a soluble ER-lumen protein, so ER lumen (GO:0005788) is the correct
              scoped location.
  - term:
      id: GO:0042026
      label: protein refolding
    evidence_type: IBA
    original_reference_id: GO_REF:0000033
    qualifier: involved_in
    review:
      summary: >-
        HSP70/BiP chaperones iteratively bind and release substrates through the
        ATP-driven cycle to promote (re)folding of unfolded or misfolded ER clients.
      action: ACCEPT
      reason: >-
        Refolding/folding of ER clients is a core activity of HSP-3/BiP, driven by its
        ATPase cycle. Consistent with UniProt and the family-level chaperone role.
      supported_by:
        - reference_id: UniProt:P27420
          supporting_text: Probably plays a role in facilitating the assembly of
        - reference_id: UniProt:P27420
          supporting_text: Belongs to the heat shock protein 70 family
  - term:
      id: GO:0034663
      label: endoplasmic reticulum chaperone complex
    evidence_type: IBA
    original_reference_id: GO_REF:0000033
    qualifier: part_of
    review:
      summary: >-
        HSP-3 functions within the ER chaperone machinery, cooperating with co-chaperones
        and other ER quality-control factors, and it physically associates with the UPR
        stress sensors in the ER membrane.
      action: ACCEPT
      reason: >-
        HSP-3/BiP is a component of the ER chaperone complex. This is supported both by
        phylogenetic inference and by the direct demonstration that HSP-3 forms a complex
        with IRE-1, ATF-6 and PEK-1.
      supported_by:
        - reference_id: PMID:27138431
          supporting_text: form a complex with IRE-1, ATF-6 and PEK-1, to preclude
            activation of UPR-related signaling events
  - term:
      id: GO:0030968
      label: endoplasmic reticulum unfolded protein response
    evidence_type: IBA
    original_reference_id: GO_REF:0000033
    qualifier: involved_in
    review:
      summary: >-
        HSP-3/BiP is both a UPR effector and a target. It binds the UPR sensors to keep
        them inactive under basal conditions, and its transcription is induced by ER
        stress in an ire-1/xbp-1-dependent manner.
      action: ACCEPT
      reason: >-
        Involvement in the ER UPR is a core BiP function. HSP-3 directly participates in
        the sensor-repressive complex and is a modestly xbp-1-dependent UPR target gene.
      supported_by:
        - reference_id: PMID:27138431
          supporting_text: form a complex with IRE-1, ATF-6 and PEK-1, to preclude
            activation of UPR-related signaling events
        - reference_id: PMID:12186849
          supporting_text: in C. elegans, the ire-1 and xbp-1 pathway has retained its
            essential role in upregulating expression of many UPR target genes that are
            similarly upregulated by the homologous pathway in yeast
  - term:
      id: GO:0005524
      label: ATP binding
    evidence_type: IEA
    original_reference_id: GO_REF:0000002
    qualifier: enables
    review:
      summary: >-
        HSP-3 binds ATP through its nucleotide-binding domain; ATP binding and its
        allosteric coupling to the substrate-binding domain drive the chaperone cycle.
      action: ACCEPT
      reason: >-
        Core molecular function of HSP-3/BiP, supported by the conserved HSP70
        nucleotide-binding domain and UniProt keyword annotation.
      supported_by:
        - reference_id: UniProt:P27420
          supporting_text: GO:0005524; F:ATP binding; IEA:UniProtKB-KW
  - term:
      id: GO:0005788
      label: endoplasmic reticulum lumen
    evidence_type: IEA
    original_reference_id: GO_REF:0000044
    qualifier: located_in
    review:
      summary: >-
        IEA localization from UniProt subcellular-location mapping, duplicating the IBA
        call from a different source. ER lumen is the established location of HSP-3.
      action: ACCEPT
      reason: >-
        Correct and well-supported localization; multiple independent evidence sources for
        the ER lumen are appropriate.
      supported_by:
        - reference_id: UniProt:P27420
          supporting_text: 'SUBCELLULAR LOCATION: Endoplasmic reticulum lumen'
  - term:
      id: GO:0016887
      label: ATP hydrolysis activity
    evidence_type: IEA
    original_reference_id: GO_REF:0000002
    qualifier: enables
    review:
      summary: >-
        IEA annotation from InterPro-to-GO mapping, duplicating the IBA ATP hydrolysis
        call. HSP-3 is an ATPase.
      action: ACCEPT
      reason: >-
        ATP hydrolysis is a core function of HSP-3/BiP; multiple evidence sources are
        appropriate.
      supported_by:
        - reference_id: UniProt:P27420
          supporting_text: GO:0016887; F:ATP hydrolysis activity; ISS:WormBase
  - term:
      id: GO:0030968
      label: endoplasmic reticulum unfolded protein response
    evidence_type: IEA
    original_reference_id: GO_REF:0000117
    qualifier: involved_in
    review:
      summary: >-
        IEA annotation from ARBA machine-learning models, duplicating the UPR involvement
        supported by direct and expression evidence.
      action: ACCEPT
      reason: >-
        HSP-3 involvement in the ER UPR is well-supported by direct interaction with the
        UPR sensors and by its xbp-1-dependent induction.
      supported_by:
        - reference_id: PMID:27138431
          supporting_text: form a complex with IRE-1, ATF-6 and PEK-1, to preclude
            activation of UPR-related signaling events
  - term:
      id: GO:0036498
      label: IRE1-mediated unfolded protein response
    evidence_type: IEP
    original_reference_id: PMID:11779465
    qualifier: involved_in
    review:
      summary: >-
        IEP annotation based on expression pattern. Shen et al. (2001) established the
        ire-1/xbp-1 UPR pathway in C. elegans, which controls UPR target-gene transcription
        including the BiP genes.
      action: ACCEPT
      reason: >-
        hsp-3 is induced by ER stress in an ire-1/xbp-1-dependent manner (see the Urano
        microarray, cosmid C15H9.6). The IEP call from the foundational UPR paper is
        defensible; the full text (read by the WormBase curator) is not cached, so the
        specific hsp-3 expression evidence is deferred to the curator.
      supported_by:
        - reference_id: PMID:11779465
          supporting_text: C. elegans requires ire-1-mediated splicing of xbp-1 mRNA for
            UPR gene transcription and survival upon ER stress
  - term:
      id: GO:0036498
      label: IRE1-mediated unfolded protein response
    evidence_type: HEP
    original_reference_id: PMID:12186849
    qualifier: involved_in
    review:
      summary: >-
        HEP annotation from the genome-wide ER-stress microarray. hsp-3 (cosmid C15H9.6)
        is among the tunicamycin-induced genes whose induction is attenuated in xbp-1
        mutants, placing it downstream of the ire-1/xbp-1 (IRE1-mediated) UPR branch.
      action: ACCEPT
      reason: >-
        Directly supported: C15H9.6 (= hsp-3) appears in Table I of xbp-1-dependent,
        tunicamycin-induced genes (N2 log2 1.32, reduced to 0.68 in xbp-1), a modest but
        genuine IRE1/xbp-1-dependent induction.
      supported_by:
        - reference_id: PMID:12186849
          supporting_text: in C. elegans, the ire-1 and xbp-1 pathway has retained its
            essential role in upregulating expression of many UPR target genes that are
            similarly upregulated by the homologous pathway in yeast
  - term:
      id: GO:0030968
      label: endoplasmic reticulum unfolded protein response
    evidence_type: IEP
    original_reference_id: PMID:11779465
    qualifier: involved_in
    review:
      summary: >-
        IEP annotation from the foundational C. elegans UPR study, based on the ER-stress
        expression program controlled by ire-1/xbp-1.
      action: ACCEPT
      reason: >-
        hsp-3 is an ER-stress-responsive gene within the ire-1/xbp-1-controlled UPR program
        (see Urano microarray). Deferred to the WormBase curator for the specific full-text
        expression evidence.
      supported_by:
        - reference_id: PMID:11779465
          supporting_text: C. elegans requires ire-1-mediated splicing of xbp-1 mRNA for
            UPR gene transcription and survival upon ER stress
  - term:
      id: GO:0030968
      label: endoplasmic reticulum unfolded protein response
    evidence_type: HEP
    original_reference_id: PMID:12186849
    qualifier: involved_in
    review:
      summary: >-
        HEP annotation from the ER-stress microarray. hsp-3 (C15H9.6) is a tunicamycin-
        induced, xbp-1-dependent gene, marking it as part of the ER UPR transcriptional
        program.
      action: ACCEPT
      reason: >-
        Supported by Table I of Urano et al., where C15H9.6 (= hsp-3) is induced by ER
        stress and attenuated in xbp-1 mutants. Consistent with BiP being a canonical UPR
        target.
      supported_by:
        - reference_id: PMID:12186849
          supporting_text: in C. elegans, the ire-1 and xbp-1 pathway has retained its
            essential role in upregulating expression of many UPR target genes that are
            similarly upregulated by the homologous pathway in yeast
  - term:
      id: GO:0034663
      label: endoplasmic reticulum chaperone complex
    evidence_type: ISS
    original_reference_id: PMID:11779465
    qualifier: part_of
    review:
      summary: >-
        ISS annotation (by similarity to human BiP, UniProtKB:P11021) placing HSP-3 in the
        ER chaperone complex. Corroborated by its physical association with the ER UPR
        sensors.
      action: ACCEPT
      reason: >-
        HSP-3 is orthologous to mammalian BiP, a component of the ER chaperone machinery,
        and directly forms a complex with IRE-1/ATF-6/PEK-1 in the ER.
      supported_by:
        - reference_id: PMID:27138431
          supporting_text: form a complex with IRE-1, ATF-6 and PEK-1, to preclude
            activation of UPR-related signaling events
        - reference_id: UniProt:P27420
          supporting_text: Belongs to the heat shock protein 70 family
  - term:
      id: GO:0016887
      label: ATP hydrolysis activity
    evidence_type: ISS
    original_reference_id: PMID:2225768
    qualifier: enables
    review:
      summary: >-
        ISS annotation (by similarity to yeast KAR2/BiP, UniProtKB:P16474) for the HSP70
        ATPase activity. HSP-3 is an ER-resident HSP70 with conserved ATPase machinery.
      action: ACCEPT
      reason: >-
        ATP hydrolysis is a conserved core function of ER HSP70/BiP proteins. The ISS to
        yeast KAR2 is appropriate given the strong sequence conservation of the HSP70
        nucleotide-binding domain.
      supported_by:
        - reference_id: UniProt:P27420
          supporting_text: GO:0016887; F:ATP hydrolysis activity; ISS:WormBase
        - reference_id: UniProt:P27420
          supporting_text: Belongs to the heat shock protein 70 family
  - term:
      id: GO:0006457
      label: protein folding
    evidence_type: NAS
    review:
      summary: >-
        Added to align core_functions with existing_annotations. Protein folding is the
        biological process served by the HSP-3 chaperone/ATPase activities in the ER lumen.
      action: NEW
      reason: >-
        Core process term not present among the GOA existing annotations; HSP-3/BiP is an
        ATP-dependent chaperone whose primary role is folding of ER client proteins.
      supported_by:
        - reference_id: UniProt:P27420
          supporting_text: Probably plays a role in facilitating the assembly of
core_functions:
  - description: >-
      HSP-3 is an ER-lumen-resident HSP70/BiP molecular chaperone that assists folding,
      refolding and assembly of nascent secretory and membrane client proteins in the ER
      lumen, using ATP-dependent cycles of substrate binding and release. It also
      participates in the ER unfolded protein response, both as a sensor-repressing
      chaperone and as a stress-inducible effector.
    molecular_function:
      id: GO:0044183
      label: protein folding chaperone
    directly_involved_in:
      - id: GO:0006457
        label: protein folding
      - id: GO:0030968
        label: endoplasmic reticulum unfolded protein response
    locations:
      - id: GO:0005788
        label: endoplasmic reticulum lumen
    supported_by:
      - reference_id: UniProt:P27420
        supporting_text: Probably plays a role in facilitating the assembly of
      - reference_id: PMID:27138431
        supporting_text: HSP-1 is predominantly cytosolic, whereas HSP-3 is retained
          within the ER lumen.
  - description: >-
      ATP hydrolysis drives the HSP-3 chaperone cycle. Allosteric coupling between the
      nucleotide-binding and substrate-binding domains converts ATP turnover into
      regulated binding and release of client polypeptides.
    molecular_function:
      id: GO:0016887
      label: ATP hydrolysis activity
    directly_involved_in:
      - id: GO:0006457
        label: protein folding
    locations:
      - id: GO:0005788
        label: endoplasmic reticulum lumen
    supported_by:
      - reference_id: UniProt:P27420
        supporting_text: GO:0016887; F:ATP hydrolysis activity; ISS:WormBase
  - description: >-
      HSP-3 binds ATP through its conserved HSP70 nucleotide-binding domain; nucleotide
      state allosterically controls substrate-binding affinity during the chaperone cycle.
    molecular_function:
      id: GO:0005524
      label: ATP binding
    locations:
      - id: GO:0005788
        label: endoplasmic reticulum lumen
    supported_by:
      - reference_id: UniProt:P27420
        supporting_text: GO:0005524; F:ATP binding; IEA:UniProtKB-KW
proposed_new_terms: []
knowledge_gaps:
  - gap_statement: >-
      The molecular basis of the division of labor between the two C. elegans BiP paralogs
      HSP-3 and HSP-4 is undetermined: which client proteins specifically require HSP-3
      (versus HSP-4), and which tissue programs and signaling interfaces each paralog
      serves, are not established.
    boundary: >-
      Both are ER-lumen HSP70/BiP orthologs with canonical nucleotide- and substrate-
      binding domains that share >70% sequence similarity, and recent paralog-resolved
      work indicates they are functionally diversified rather than strictly interchangeable
      (HSP-3 canonical folding; HSP-4 specialized for stress/ER-phagy signaling). What is
      undetermined is the paralog-specific clientele and mechanism.
    gap_kind:
      - BIOLOGY
    dark_aspect: RESIDUAL_SUBGAP
    status: NARROWING
    significance: >-
      Distinguishing HSP-3- from HSP-4-dependent clients is required to interpret loss-of-
      function phenotypes, to model human BiP (single-gene) biology in the two-paralog worm
      system, and to know which paralog controls a given secretory or stress phenotype.
    resolution: >-
      Paralog-resolved interactome/client proteomics (e.g. proximity labeling of tagged
      endogenous HSP-3 vs HSP-4) under basal and ER-stress conditions, with reciprocal
      rescue and paralog-swap experiments.
    provenance:
      - reference_id: PMID:27138431
        supporting_text: elegans encodes two Grp78/BiP homologues, hsp-3 and hsp-4,
          assumed to cross-compensate for each other in their roles as ER-residing protein
          chaperones
  - gap_statement: >-
      The functional consequence of HSP-3 AMPylation by FIC-1 is unknown: whether, where,
      and under what conditions this modification alters HSP-3 ATPase or chaperone activity
      in vivo has not been determined.
    boundary: >-
      HSP-3 is a confirmed in vivo AMPylation substrate of the sole C. elegans Fic protein
      FIC-1 (identified by mass spectrometry), and AMPylation is a reversible
      post-translational modification, but its regulatory effect on HSP-3 activity is not
      characterized.
    gap_kind:
      - BIOLOGY
    dark_aspect: RESIDUAL_SUBGAP
    status: OPEN
    significance: >-
      AMPylation of BiP-family chaperones is a candidate mechanism for tuning ER chaperone
      capacity during stress and recovery; knowing its effect on HSP-3 would clarify how
      chaperone activity is post-translationally regulated in the worm ER.
    resolution: >-
      Measure the ATPase/chaperone activity of AMPylated versus unmodified HSP-3 and
      phenotype non-AMPylatable HSP-3 knock-in animals under ER stress and pathogen
      challenge.
    provenance:
      - reference_id: PMID:27138431
        supporting_text: results in diverse changes of their activities remains to be
          studied.
      - reference_id: PMID:27138431
        supporting_text: two classes of proteins over-represented amongst the AMPylated
          fraction of proteins
suggested_questions:
  - question: >-
      Which secretory/membrane client proteins specifically depend on HSP-3 (rather than
      HSP-4) for folding in the C. elegans ER, and in which tissues?
    experts: []
  - question: >-
      Does FIC-1-mediated AMPylation inhibit or otherwise tune HSP-3 chaperone activity in
      vivo, and is it dynamically regulated during ER-stress recovery?
    experts: []
  - question: >-
      Is the BiP-mediated repression of the IRE-1/ATF-6/PEK-1 sensors exerted specifically
      by HSP-3, by HSP-4, or does it require both paralogs?
    experts: []
suggested_experiments:
  - description: >-
      Proximity labeling (TurboID/BioID) of endogenously tagged HSP-3 and HSP-4 under basal
      and tunicamycin/pathogen-induced ER stress, to define paralog-specific client and
      interactor repertoires.
    experiment_type: proteomics
    hypothesis: HSP-3 and HSP-4 have overlapping but distinct client and interactor sets.
  - description: >-
      Generate non-AMPylatable HSP-3 knock-in alleles (mutating the FIC-1 target residue)
      and assay ER-stress tolerance, innate-immune resistance to P. aeruginosa, and
      chaperone-dependent folding reporters.
    experiment_type: genetics / phenotyping
    hypothesis: AMPylation of HSP-3 modulates its chaperone activity and stress tolerance.
  - description: >-
      Paralog-specific depletion (hsp-3 vs hsp-4) combined with a UPR reporter and sensor
      activation assays to test which paralog restrains IRE-1/ATF-6/PEK-1 under basal
      conditions.
    experiment_type: genetics / reporter assay
    hypothesis: HSP-3 and HSP-4 differ in their contribution to UPR-sensor repression.
tags:
  - caeel-proteostasis
  - caeel-upr-stress