Caenorhabditis elegans HSP-3 is an ER-resident BiP/HSP70-family chaperone with an N-terminal targeting sequence and C-terminal KDEL retention motif. Its conserved ATP-dependent chaperone mechanism supports folding and quality control of secretory-pathway proteins, and its expression responds to the IRE-1/XBP-1 unfolded-protein-response pathway. HSP-3 and its paralog HSP-4 share essential proteostasis functions but differ in developmental expression, stress responses and signaling phenotypes. HSP-3 is particularly abundant during larval development and contributes to infection-associated antimicrobial gene induction. Purified HSP-3 is AMPylated by FIC-1 at Thr176 in vitro; the site-specific physiological effect remains incompletely resolved.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005737 cytoplasm | IBA GO_REF:0000033 | ACCEPT | Summary: Cytoplasm includes the ER compartment in which HSP-3 acts. Reason: GO cytoplasm includes organelles; it is not synonymous with soluble cytosol. ER residence therefore supports this broad inherited location. The actual cytoplasm IBD PTN002321897 lies on the target path. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN002321897 SUPPORTS TRANSFER Actual ancestral node verified. ER localization is compatible with cytoplasm. |
| GO:0005788 endoplasmic reticulum lumen | IBA GO_REF:0000033 | ACCEPT | Summary: The ER lumen is the primary functional location of HSP-3, consistent with its signal peptide, KDEL retention motif, and direct experimental localization. Reason: Retain the canonical BiP-family ER folding function, consistent with targeting/retention sequence, conserved ancestry and target proteostasis phenotypes. The 2025 comparative study supports the model of a prominent HSP-3 folding role but does not directly measure purified HSP-3 refolding kinetics; the 2016 ER-location statement is biological background rather than a new localization assay. Supporting Evidence: UniProt:P27420 SUBCELLULAR LOCATION: Endoplasmic reticulum lumen PMID:27138431 HSP-1 is predominantly cytosolic, whereas HSP-3 is retained within the ER lumen. |
| GO:0016887 ATP hydrolysis activity | IBA GO_REF:0000033 | ACCEPT | 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. 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. Supporting Evidence: UniProt:P27420 GO:0016887; F:ATP hydrolysis activity; ISS:WormBase UniProt:P27420 Belongs to the heat shock protein 70 family |
| GO:0044183 protein folding chaperone | IBA GO_REF:0000033 | ACCEPT | 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. Reason: Retain the canonical BiP-family ER folding function, consistent with targeting/retention sequence, conserved ancestry and target proteostasis phenotypes. The 2025 comparative study supports the model of a prominent HSP-3 folding role but does not directly measure purified HSP-3 refolding kinetics; the 2016 ER-location statement is biological background rather than a new localization assay. Supporting Evidence: UniProt:P27420 Probably plays a role in facilitating the assembly of PMID:27138431 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 file:worm/hsp-3/hsp-3-deep-research-falcon.md primarily responsible for de novo protein folding and the refolding of misfolded proteins within the ER lumen |
| GO:0005634 nucleus | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: The inherited nuclear category is compatible with BiP at the nuclear envelope. Reason: Actual BiP IBD PTN001834223 is ancestral to HSP-3, with BiP-family rather than arbitrary cytosolic-HSP70 grounding. Fission-yeast donor BiP has direct nuclear-envelope immunofluorescence in PMID:1373379. GO nucleus includes its envelope and perinuclear space, so ER-lumen retention is not a refutation. Retain a contextual family-level location; this is not a claim of an independently demonstrated HSP-3 nucleoplasmic pool. Propagation Review Root cause: NO FAILURE NON CORE Sources checked: PANTHER:PTN001834223 SUPPORTS TRANSFER BiP-specific nuclear IBD and exact target path verified with no target loss. The donor nuclear-envelope observation is compatible with lumenal topology. Supporting Evidence: PMID:1373379 Immunofluorescence of cells expressing an epitope-tagged BiP protein show it to be localized to the nuclear envelope, around the cell periphery and in a reticular structure through the cytoplasm. |
| GO:0031072 heat shock protein binding | IBA GO_REF:0000033 | ACCEPT | 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. 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. Supporting Evidence: UniProt:P27420 Belongs to the heat shock protein 70 family |
| GO:0036503 ERAD pathway | IBA GO_REF:0000033 | ACCEPT | Summary: Conserved BiP substrate quality control contributes to the ERAD pathway. Reason: The actual BiP node PTN001834223 carries ERAD inference from experimentally characterized BiP descendants. Client recognition/handling is mechanistic work in quality control, not merely a downstream stress phenotype, and absence of a separate worm assay does not make it noncore. The 2024 TRA-2 paper demonstrates BiP-dependent protection against ERAD but assays HSP-4 interaction directly; it is contextual corroboration rather than a direct HSP-3 ERAD-disposal assay. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN001834223 SUPPORTS TRANSFER Verified BiP ancestry supports conserved ER quality-control participation. Target client range and disposal-versus-protection contexts remain to be resolved. |
| GO:0016020 membrane | IBA GO_REF:0000033 | ACCEPT | Summary: Peripheral membrane association is compatible with a lumenal BiP chaperone. Reason: Live GO:0016020 includes proteins attached to a lipid bilayer, not only transmembrane proteins. The BiP ancestral membrane IBD PTN001834223 lies on the exact target path and is grounded by BiP-family descendants. Conserved interaction with membrane-associated folding/signaling machinery provides a coherent inferred role; a soluble lumenal domain does not exclude peripheral association. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN001834223 SUPPORTS TRANSFER Actual BiP membrane IBD is on the target lineage; no loss recovered. Absence of a transmembrane helix is not a term violation. |
| GO:0042026 protein refolding | IBA GO_REF:0000033 | ACCEPT | Summary: HSP70/BiP chaperones iteratively bind and release substrates through the ATP-driven cycle to promote (re)folding of unfolded or misfolded ER clients. Reason: Retain the canonical BiP-family ER folding function, consistent with targeting/retention sequence, conserved ancestry and target proteostasis phenotypes. The 2025 comparative study supports the model of a prominent HSP-3 folding role but does not directly measure purified HSP-3 refolding kinetics; the 2016 ER-location statement is biological background rather than a new localization assay. Supporting Evidence: UniProt:P27420 Probably plays a role in facilitating the assembly of UniProt:P27420 Belongs to the heat shock protein 70 family |
| GO:0034663 endoplasmic reticulum chaperone complex | IBA GO_REF:0000033 | ACCEPT | 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. Reason: Retain the conserved BiP chaperone-complex/UPR contribution. HSP-3 is an ER folding effector with direct stress-responsive expression and paralog-specific perturbation evidence. The 2016 source discusses the classical BiP sensor-repression model but does not directly co-immunoprecipitate HSP-3 with all three IRE-1/ATF-6/PEK-1 sensors. The 2025 mammalian co-IP uses human BiP in A549 cells. These limits qualify direct target binding claims without refuting the inherited complex or UPR role. Supporting Evidence: PMID:27138431 form a complex with IRE-1, ATF-6 and PEK-1, to preclude activation of UPR-related signaling events |
| GO:0030968 endoplasmic reticulum unfolded protein response | IBA GO_REF:0000033 | ACCEPT | 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. Reason: Retain the conserved BiP chaperone-complex/UPR contribution. HSP-3 is an ER folding effector with direct stress-responsive expression and paralog-specific perturbation evidence. The 2016 source discusses the classical BiP sensor-repression model but does not directly co-immunoprecipitate HSP-3 with all three IRE-1/ATF-6/PEK-1 sensors. The 2025 mammalian co-IP uses human BiP in A549 cells. These limits qualify direct target binding claims without refuting the inherited complex or UPR role. Supporting Evidence: PMID:27138431 form a complex with IRE-1, ATF-6 and PEK-1, to preclude activation of UPR-related signaling events PMID:12186849 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 |
| GO:0005524 ATP binding | IEA GO_REF:0000002 | ACCEPT | 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. Reason: Core molecular function of HSP-3/BiP, supported by the conserved HSP70 nucleotide-binding domain and UniProt keyword annotation. Supporting Evidence: UniProt:P27420 GO:0005524; F:ATP binding; IEA:UniProtKB-KW |
| GO:0005788 endoplasmic reticulum lumen | IEA GO_REF:0000044 | ACCEPT | 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. Reason: Correct and well-supported localization; multiple independent evidence sources for the ER lumen are appropriate. Supporting Evidence: UniProt:P27420 SUBCELLULAR LOCATION: Endoplasmic reticulum lumen |
| GO:0016887 ATP hydrolysis activity | IEA GO_REF:0000002 | ACCEPT | Summary: IEA annotation from InterPro-to-GO mapping, duplicating the IBA ATP hydrolysis call. HSP-3 is an ATPase. Reason: ATP hydrolysis is a core function of HSP-3/BiP; multiple evidence sources are appropriate. Supporting Evidence: UniProt:P27420 GO:0016887; F:ATP hydrolysis activity; ISS:WormBase |
| GO:0030968 endoplasmic reticulum unfolded protein response | IEA GO_REF:0000117 | ACCEPT | Summary: HSP-3 contributes to conserved ER chaperone machinery and the unfolded-protein response. Reason: Retain the conserved BiP chaperone-complex/UPR contribution. HSP-3 is an ER folding effector with direct stress-responsive expression and paralog-specific perturbation evidence. The 2016 source discusses the classical BiP sensor-repression model but does not directly co-immunoprecipitate HSP-3 with all three IRE-1/ATF-6/PEK-1 sensors. The 2025 mammalian co-IP uses human BiP in A549 cells. These limits qualify direct target binding claims without refuting the inherited complex or UPR role. Supporting Evidence: PMID:27138431 form a complex with IRE-1, ATF-6 and PEK-1, to preclude activation of UPR-related signaling events |
| GO:0036498 IRE1-mediated unfolded protein response | IEP PMID:11779465 Complementary signaling pathways regulate the unfolded prote... | ACCEPT | 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. 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. Supporting Evidence: PMID:11779465 C. elegans requires ire-1-mediated splicing of xbp-1 mRNA for UPR gene transcription and survival upon ER stress |
| GO:0036498 IRE1-mediated unfolded protein response | HEP PMID:12186849 A survival pathway for Caenorhabditis elegans with a blocked... | ACCEPT | 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. 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. Supporting Evidence: PMID:12186849 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 |
| GO:0030968 endoplasmic reticulum unfolded protein response | IEP PMID:11779465 Complementary signaling pathways regulate the unfolded prote... | ACCEPT | Summary: IEP annotation from the foundational C. elegans UPR study, based on the ER-stress expression program controlled by ire-1/xbp-1. 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. Supporting Evidence: PMID:11779465 C. elegans requires ire-1-mediated splicing of xbp-1 mRNA for UPR gene transcription and survival upon ER stress |
| GO:0030968 endoplasmic reticulum unfolded protein response | HEP PMID:12186849 A survival pathway for Caenorhabditis elegans with a blocked... | ACCEPT | 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. 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. Supporting Evidence: PMID:12186849 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 |
| GO:0034663 endoplasmic reticulum chaperone complex | ISS PMID:11779465 Complementary signaling pathways regulate the unfolded prote... | ACCEPT | 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. Reason: Retain the conserved BiP chaperone-complex/UPR contribution. HSP-3 is an ER folding effector with direct stress-responsive expression and paralog-specific perturbation evidence. The 2016 source discusses the classical BiP sensor-repression model but does not directly co-immunoprecipitate HSP-3 with all three IRE-1/ATF-6/PEK-1 sensors. The 2025 mammalian co-IP uses human BiP in A549 cells. These limits qualify direct target binding claims without refuting the inherited complex or UPR role. Supporting Evidence: PMID:27138431 form a complex with IRE-1, ATF-6 and PEK-1, to preclude activation of UPR-related signaling events UniProt:P27420 Belongs to the heat shock protein 70 family |
| GO:0016887 ATP hydrolysis activity | ISS PMID:2225768 The HSP70 multigene family of Caenorhabditis elegans. | ACCEPT | 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. 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. Supporting Evidence: UniProt:P27420 GO:0016887; F:ATP hydrolysis activity; ISS:WormBase UniProt:P27420 Belongs to the heat shock protein 70 family |
Loading supporting content…
Download this section (compressed HTML)Q: 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?
Q: Does FIC-1-mediated AMPylation inhibit or otherwise tune HSP-3 chaperone activity in vivo, and is it dynamically regulated during ER-stress recovery?
Q: 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?
Experiment: 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.
Hypothesis: HSP-3 and HSP-4 have overlapping but distinct client and interactor sets.
Type: proteomics
Experiment: 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.
Hypothesis: AMPylation of HSP-3 modulates its chaperone activity and stress tolerance.
Type: genetics / phenotyping
Experiment: 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.
Hypothesis: HSP-3 and HSP-4 differ in their contribution to UPR-sensor repression.
Type: genetics / reporter assay
What is not known — curated, literature-grounded statements of the open unknowns (the inverse of core functions).
Gap: 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.
NARROWING BIOLOGY RESIDUAL_SUBGAP
What is known: 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.
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.
What would resolve it: 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 (the field's own admissions):
Gap: 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.
OPEN BIOLOGY RESIDUAL_SUBGAP
What is known: 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.
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.
What would resolve it: 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 (the field's own admissions):
Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)Loading supporting content…
Download this section (compressed HTML)