HSP-6 is the C. elegans mitochondrial HSP70 chaperone (mtHSP70/mortalin ortholog) that functions as the primary ATP-dependent chaperone in the mitochondrial matrix. It is essential for mitochondrial protein import, serving as the import motor that drives translocation of precursor proteins across the inner membrane. HSP-6 also participates in protein folding within the matrix and is involved in iron-sulfur cluster biogenesis. The hsp-6 gene is a canonical marker of the mitochondrial unfolded protein response (UPR-mt), with hsp-6p::GFP being the standard reporter for UPR-mt activation. Expression is strongly induced by mitochondrial proteotoxic stress in an ATFS-1-dependent manner. Knockdown of HSP-6 causes reduced ATP levels, abnormal mitochondrial morphology, and progeria-like phenotypes including shortened lifespan.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005737 cytoplasm | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: IBA annotation indicating cytoplasmic localization based on phylogenetic inference. While some HSP70 family members have cytoplasmic pools, HSP-6 is specifically the mitochondrial HSP70 with a mitochondrial transit peptide (residues 1-27) and is experimentally localized to mitochondria. Reason: HSP-6 has an N-terminal mitochondrial transit peptide (UniProt FT TRANSIT 1..27) and is characterized as the mitochondrial matrix HSP70. While precursor protein may transiently exist in cytoplasm before import, the functional protein is mitochondrial. The IBA annotation likely reflects the broader HSP70 family distribution rather than HSP-6 specifically. However, this annotation is not incorrect as the precursor does exist in the cytoplasm before mitochondrial import. Supporting Evidence: PMID:17189267 HSP-6 (hsp70F) is a nematode orthologue of mthsp70. |
| GO:0005739 mitochondrion | IBA GO_REF:0000033 | ACCEPT | Summary: IBA annotation for mitochondrial localization based on phylogenetic inference from HSP70 family orthologs. This is strongly supported by experimental evidence. Reason: HSP-6 is the C. elegans mitochondrial HSP70 (mtHSP70). UniProt annotation indicates subcellular location as mitochondrion and the protein has an N-terminal mitochondrial transit peptide. This is further confirmed by IDA evidence from PMID:17189267. Supporting Evidence: PMID:17189267 Mitochondrial heat shock protein 70 (mthsp70) functions as a mitochondrial import motor and is essential in mitochondrial biogenesis and energy generation in eukaryotic cells. |
| GO:0016887 ATP hydrolysis activity | IBA GO_REF:0000033 | ACCEPT | Summary: IBA annotation for ATPase activity based on phylogenetic inference. HSP70 family chaperones universally require ATP hydrolysis for their chaperone function, driving conformational changes that mediate substrate binding and release. Reason: HSP-6 contains the canonical HSP70 ATPase nucleotide-binding domain (IPR043129, Pfam HSP70). ATP hydrolysis is essential for HSP70 chaperone function, driving the conformational changes that allow substrate binding and release. For mtHSP70 specifically, ATP hydrolysis powers the import motor function. UniProt lists ATP-binding as a keyword. Supporting Evidence: file:worm/hsp-6/hsp-6-deep-research-falcon.md HSP-6/mtHSP70 functions as an ATP-dependent mitochondrial chaperone supporting protein import and folding in the matrix [editorial summary of deep research] |
| GO:0031072 heat shock protein binding | IBA GO_REF:0000033 | ACCEPT | Summary: IBA annotation indicating HSP-6 binds other heat shock proteins. This is consistent with HSP70 family function, as mtHSP70 works in concert with HSP60/HSP10 chaperonin system and co-chaperones. Reason: HSP70 family members functionally interact with co-chaperones and other chaperones. In the mitochondrial matrix, mtHSP70 cooperates with HSP-60 (GroEL homolog) and DNJ-type co-chaperones. The IBA annotation is phylogenetically sound. Supporting Evidence: PMID:17189267 Knockdown of HSP-6 by RNA interference in young adult nematodes caused a reduction in the levels of ATP-2, HSP-60 and CLK-1, leading to abnormal mitochondrial morphology and lower ATP levels. |
| GO:0044183 protein folding chaperone | IBA GO_REF:0000033 | MODIFY | Summary: IBA annotation for protein folding chaperone activity. This is a core function of HSP70 family proteins, though GO:0140662 (ATP-dependent protein folding chaperone) would be more specific. Reason: While GO:0044183 is correct, the more specific term GO:0140662 (ATP-dependent protein folding chaperone) better describes HSP-6 function as an ATP-dependent HSP70 chaperone. HSP70 chaperones specifically use ATP hydrolysis to drive conformational changes for substrate binding and release. Proposed replacements: ATP-dependent protein folding chaperone Supporting Evidence: PMID:15280428 Protein folding in the mitochondria is assisted by nuclear-encoded compartment-specific chaperones but regulation of the expression of their encoding genes is poorly understood. |
| GO:0016226 iron-sulfur cluster assembly | IBA GO_REF:0000033 | ACCEPT | Summary: IBA annotation for iron-sulfur cluster assembly based on phylogenetic inference. Mitochondrial HSP70 (HSPA9/mortalin in mammals) plays a documented role in Fe-S cluster biogenesis as part of the mitochondrial iron-sulfur cluster assembly machinery. Reason: Mitochondrial HSP70 proteins are established components of the Fe-S cluster assembly pathway. In the mitochondrial matrix, mtHSP70 works with scaffold proteins (like ISCU) and cochaperones to facilitate Fe-S cluster assembly and transfer. This is a conserved function across eukaryotes. |
| GO:0042026 protein refolding | IBA GO_REF:0000033 | ACCEPT | Summary: IBA annotation for protein refolding based on phylogenetic inference. HSP70 chaperones can assist in refolding of misfolded proteins, a key aspect of the stress response. Reason: HSP70 family members are capable of assisting protein refolding, particularly under stress conditions. This annotation is consistent with HSP-6's induction as part of the mitochondrial unfolded protein response (UPR-mt), where it helps restore proteostasis in the matrix. Supporting Evidence: PMID:15280428 These observations support the existence of a mitochondrial unfolded protein response that couples mitochondrial chaperone gene expression to changes in the protein handling environment in the organelle. |
| GO:0000166 nucleotide binding | IEA GO_REF:0000043 | KEEP AS NON CORE | Summary: IEA annotation based on UniProt keyword mapping for nucleotide binding. This is a parent term of ATP binding and is correct but less informative. Reason: While technically correct (HSP-6 binds ATP), this is subsumed by the more specific GO:0005524 (ATP binding) annotation. It provides no additional information beyond the ATP binding annotation. |
| GO:0005524 ATP binding | IEA GO_REF:0000120 | ACCEPT | Summary: IEA annotation for ATP binding based on automated annotation. HSP70 family proteins have a well-characterized nucleotide-binding domain that binds and hydrolyzes ATP. Reason: HSP-6 contains the canonical HSP70 nucleotide-binding domain (ATPase_NBD, IPR043129) and ATP binding is essential for its chaperone function. UniProt lists ATP-binding as a keyword for this protein. |
| GO:0005739 mitochondrion | IEA GO_REF:0000044 | ACCEPT | Summary: IEA annotation for mitochondrial localization based on UniProt subcellular location vocabulary mapping. This duplicates the IBA and IDA annotations but is independently derived. Reason: Correct annotation. HSP-6 is the mitochondrial HSP70 with experimental evidence for mitochondrial localization. UniProt explicitly states subcellular location as mitochondrion. |
| GO:0006457 protein folding | IEA GO_REF:0000002 | ACCEPT | Summary: IEA annotation for protein folding based on InterPro domain mapping. HSP70 family proteins assist protein folding as a core function. Reason: Protein folding assistance is a core function of HSP70 chaperones. In the mitochondrial matrix, HSP-6 assists in folding of newly imported proteins and maintains proteostasis under stress conditions. Supporting Evidence: PMID:15280428 Protein folding in the mitochondria is assisted by nuclear-encoded compartment-specific chaperones but regulation of the expression of their encoding genes is poorly understood. |
| GO:0006950 response to stress | IEA GO_REF:0000117 | KEEP AS NON CORE | Summary: IEA annotation for response to stress based on ARBA machine learning. While HSP-6 is stress-responsive, this term is very general. More specific terms exist. Reason: While HSP-6 is indeed induced by stress (mitochondrial stress specifically), this term is too general. The protein is already annotated to GO:0034514 (mitochondrial unfolded protein response) which is more specific and informative. This annotation is not wrong but adds little beyond the more specific UPR-mt annotation. Supporting Evidence: PMID:15280428 hsp-6 and hsp-60 induction was specific to perturbed mitochondrial protein handling, as neither heat-shock nor endoplasmic reticulum stress nor manipulations that impair mitochondrial steps in intermediary metabolism or ATP synthesis activated the mitochondrial chaperone genes. |
| GO:0016887 ATP hydrolysis activity | IEA GO_REF:0000002 | ACCEPT | Summary: IEA annotation for ATP hydrolysis activity based on InterPro domain mapping. Duplicates the IBA annotation but derived from domain analysis. Reason: Correct annotation. HSP70 proteins have intrinsic ATPase activity essential for their chaperone function. The ATPase_NBD domain (IPR043129) is present in HSP-6. |
| GO:0051082 unfolded protein binding | IEA GO_REF:0000002 | MODIFY | Summary: IEA annotation for unfolded protein binding based on InterPro domain mapping. HSP70 proteins bind to hydrophobic stretches in unfolded/misfolded proteins. Reason: GO:0051082 is now formally obsolete. HSP-6 is a mitochondrial HSP70 foldase chaperone that binds unfolded clients and facilitates their folding in an ATP-dependent manner. The appropriate replacement term is GO:0044183 (protein folding chaperone). Proposed replacements: protein folding chaperone Supporting Evidence: PMID:15280428 These observations support the existence of a mitochondrial unfolded protein response that couples mitochondrial chaperone gene expression to changes in the protein handling environment in the organelle. |
| GO:0005739 mitochondrion | IDA PMID:17189267 Knockdown of mitochondrial heat shock protein 70 promotes pr... | ACCEPT | Summary: IDA (direct assay) annotation for mitochondrial localization from Kimura et al. 2007. This provides experimental confirmation of mitochondrial localization. Reason: Direct experimental evidence from PMID:17189267 demonstrates HSP-6 is the C. elegans mitochondrial HSP70. The study showed that HSP-6 knockdown affects mitochondrial morphology and reduces levels of mitochondrial proteins ATP-2 and HSP-60. Supporting Evidence: PMID:17189267 Mitochondrial heat shock protein 70 (mthsp70) functions as a mitochondrial import motor and is essential in mitochondrial biogenesis and energy generation in eukaryotic cells. |
| GO:0034514 mitochondrial unfolded protein response | IEP PMID:15280428 Compartment-specific perturbation of protein handling activa... | ACCEPT | Summary: IEP (expression pattern) annotation indicating HSP-6 expression is induced during the mitochondrial unfolded protein response. This is the foundational study that established the UPR-mt concept using hsp-6 as a marker gene. Reason: PMID:15280428 (Yoneda et al. 2004) is the landmark paper that defined the mitochondrial unfolded protein response in C. elegans. The study demonstrated that hsp-6 is specifically induced by mitochondrial protein folding stress but not by heat shock or ER stress. IEP is appropriate as induction pattern evidence. Supporting Evidence: PMID:15280428 These observations support the existence of a mitochondrial unfolded protein response that couples mitochondrial chaperone gene expression to changes in the protein handling environment in the organelle. |
| GO:0034514 mitochondrial unfolded protein response | IMP PMID:15280428 Compartment-specific perturbation of protein handling activa... | ACCEPT | Summary: IMP (mutant phenotype) annotation indicating HSP-6 participates in the mitochondrial unfolded protein response based on genetic evidence from Yoneda et al. 2004. Reason: The same foundational study (PMID:15280428) used genetic perturbations to establish that hsp-6 is a functional component of the UPR-mt. RNAi of mitochondrial chaperones and proteases induced hsp-6 expression, demonstrating it is part of the compensatory UPR-mt pathway. Supporting Evidence: PMID:15280428 We found that the mitochondrial matrix HSP70 and HSP60 chaperones, encoded by the Caenorhabditis elegans hsp-6 and hsp-60 genes, were selectively activated by perturbations that impair assembly of multi-subunit mitochondrial complexes or by RNAi of genes encoding mitochondrial chaperones or proteases, which lead to defective protein folding and processing in the organelle. |
| GO:0005759 mitochondrial matrix | IDA PMID:15280428 Compartment-specific perturbation of protein handling activa... | NEW | Summary: HSP-6 is specifically the mitochondrial matrix HSP70, functioning in the matrix compartment for protein import and folding. Reason: HSP-6 is explicitly described as the mitochondrial matrix HSP70 chaperone. The more specific localization term GO:0005759 (mitochondrial matrix) would be more informative than the generic GO:0005739 (mitochondrion). The protein has a mitochondrial transit peptide and functions in the matrix where it acts as the import motor and folding chaperone. Supporting Evidence: PMID:15280428 We found that the mitochondrial matrix HSP70 and HSP60 chaperones, encoded by the Caenorhabditis elegans hsp-6 and hsp-60 genes, were selectively activated by perturbations that impair assembly of multi-subunit mitochondrial complexes |
| GO:0030150 protein import into mitochondrial matrix | ISS PMID:17189267 Knockdown of mitochondrial heat shock protein 70 promotes pr... | NEW | Summary: mtHSP70 functions as the import motor that drives translocation of preproteins into the mitochondrial matrix. Reason: PMID:17189267 explicitly states that mtHSP70 functions as a mitochondrial import motor. This is a well-established function of mtHSP70 family members across eukaryotes, where they provide the driving force for protein translocation through the TIM23 complex. Knockdown of HSP-6 reduces levels of nuclear-encoded mitochondrial proteins like ATP-2 and HSP-60, consistent with impaired import. Supporting Evidence: PMID:17189267 Mitochondrial heat shock protein 70 (mthsp70) functions as a mitochondrial import motor and is essential in mitochondrial biogenesis and energy generation in eukaryotic cells. |
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Download this section (compressed HTML)Q: What specific co-chaperones (DNJ proteins) work with HSP-6 in C. elegans mitochondria?
Suggested experts: Mitochondrial proteostasis researchers, C. elegans geneticists
Q: Is HSP-6 involved in the folding of specific mitochondrial protein substrates, or is its substrate specificity broad?
Suggested experts: HSP70 chaperone biochemists, Mitochondrial protein import researchers
Q: What is the relative contribution of HSP-6 to import motor function versus post-import folding assistance?
Suggested experts: Mitochondrial protein import specialists, TIM23 complex researchers
Experiment: Immunofluorescence or GFP-tagging to confirm mitochondrial matrix localization specifically (vs. outer membrane or intermembrane space)
Hypothesis: HSP-6 localizes specifically to the mitochondrial matrix compartment
Type: Subcellular localization
Experiment: Co-immunoprecipitation to identify specific protein interaction partners and substrates
Hypothesis: HSP-6 interacts with TIM23 complex components and specific mitochondrial substrate proteins
Type: Protein interaction analysis
Experiment: Genetic epistasis experiments with TIM23 complex components to confirm import motor function
Hypothesis: HSP-6 functions downstream of TIM23 in the protein import pathway
Type: Genetic epistasis
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