hip-1 encodes the Caenorhabditis elegans ortholog of Hsp70-interacting protein (Hip/ST13), a member of the FAM10 family and a co-chaperone of the cytosolic Hsp70 (Hsc70) chaperone system. The protein has a modular architecture: an N-terminal dimerization domain (Hip_N) that drives homo-oligomerization into a tetramer, a central tetratricopeptide-repeat (TPR) region that binds the ATPase (nucleotide-binding) domain of Hsp70, and a C-terminal STI1/DP domain. Hip binds the ADP-bound state of Hsp70 and stabilizes it, slowing ADP release and prolonging the high-affinity association of Hsp70 with substrate; because Hip and nucleotide-exchange factors bind Hsp70 in a mutually exclusive manner, Hip acts as an attenuator of the Hsp70 reaction cycle that biases the system toward substrate holding and folding rather than release and degradation. Hip also has intrinsic holdase activity, binding non-native polypeptides to prevent their aggregation, but it lacks ATPase activity and cannot refold substrates on its own. In C. elegans, HIP-1 acts through Hsp70 to suppress proteotoxic aggregation in vivo, and it is predominantly cytosolic, consistent with a role in the cytosolic protein quality-control network. It is distinct from the C. elegans HOP/Stip1 ortholog sti-1, which occupies a different node of the Hsp70/Hsp90 system.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
|
GO:0006457
protein folding
|
IBA
GO_REF:0000033 |
ACCEPT |
Summary: Phylogenetically inferred biological process. HIP-1 is an Hsp70 co-chaperone that cooperates with Hsc70 in the folding of newly synthesized and non-native polypeptides; protein folding is the core process it participates in.
Reason: Consistent with the conserved FAM10/Hip co-chaperone role and with experimental evidence from orthologs that Hip cooperates with Hsc70 in polypeptide folding and plays a critical role in protein folding in the eukaryotic cytoplasm.
Supporting Evidence:
PMID:8999928
The homo-oligomeric Hip protein cooperates with the 70-kDa heat shock cognate Hsc70 in the folding of newly synthesized polypeptide chains
PMID:9183013
play a critical role in protein folding in the eukaryotic cytoplasm
|
|
GO:0030544
Hsp70 protein binding
|
IBA
GO_REF:0000033 |
ACCEPT |
Summary: Core, defining molecular function of a Hip-family co-chaperone: HIP-1 binds the N-terminal ATPase (nucleotide-binding) domain of Hsp70/Hsc70, specifically in the ADP state, and stabilizes the high substrate-affinity conformation.
Reason: This is the informative, partner-specific molecular function of the protein and is supported by biochemical mapping in orthologs showing Hip binds the Hsc70 ATPase domain exclusively and by structural work showing it brackets the ATPase domain to lock in ADP.
Supporting Evidence:
PMID:9528774
Hip interacts exclusively with the amino-terminal ATPase domain of Hsc70
PMID:7585962
One Hip oligomer binds the ATPase domains of at least two Hsc70 molecules
|
|
GO:0005634
nucleus
|
IEA
GO_REF:0000117 |
REMOVE |
Summary: Electronic (ARBA machine-learning) cellular-component annotation with no experimental support. Hip/ST13 is an established cytosolic co-chaperone of the cytosolic Hsp70 machinery, and there is no evidence for nuclear localization of C. elegans HIP-1.
Reason: Over-propagated electronic inference that conflicts with the well-established cytosolic biology of Hip-family co-chaperones; not supported by any experimental or phylogenetic evidence for this gene.
|
|
GO:0046983
protein dimerization activity
|
IEA
GO_REF:0000002 |
KEEP AS NON CORE |
Summary: InterPro-derived (IPR034649, Hip_N) molecular function. HIP-1 genuinely homo-oligomerizes (dimer of dimers / tetramer) through its N-terminal Hip_N domain, which provides avidity for binding multiple Hsp70 molecules.
Reason: Self-association is real and functionally relevant but is a structural property rather than the informative core molecular function; retained as non-core. The N-terminal oligomerization determinant and the tetrameric state are documented experimentally in orthologs.
Supporting Evidence:
PMID:8999928
a domain required for homo-oligomerization was identified at the extreme amino terminus of Hip
PMID:9183013
the chaperone forms a tetramer similar to what has been reported for the native protein from rat liver cytosol
|
|
GO:0070013
intracellular organelle lumen
|
IEA
GO_REF:0000117 |
REMOVE |
Summary: Electronic (ARBA machine-learning) cellular-component annotation with no experimental support and inconsistent with the cytosolic localization of Hip-family co-chaperones.
Reason: Over-propagated electronic inference; an organelle-lumen location is not supported by any experimental or phylogenetic evidence for HIP-1 and conflicts with its cytosolic function.
|
|
GO:1902494
catalytic complex
|
IEA
GO_REF:0000117 |
MARK AS OVER ANNOTATED |
Summary: Electronic (ARBA machine-learning) annotation placing HIP-1 in a catalytic complex. HIP-1 itself is non-catalytic (no ATPase activity); it transiently associates with the catalytic Hsp70 ATPase, but "catalytic complex" is generic and mischaracterizes HIP-1's own role.
Reason: Uninformative and potentially misleading: HIP-1 does not catalyze a reaction and is not a stable structural subunit of a defined catalytic complex; its interaction with Hsp70 is transient and regulatory.
Supporting Evidence:
PMID:9183013
The recombinant form of Hip did not catalyze the hydrolysis of ATP and ATP analogs
|
|
GO:0005783
endoplasmic reticulum
|
HDA
PMID:21611156 Determining the sub-cellular localization of proteins within... |
KEEP AS NON CORE |
Summary: High-throughput direct-assay localization from a body-wall-muscle GFP-localizome: T12D8.8::GFP fell in category 6, which includes the ER/SR alongside dense bodies and the M-line/thick filaments.
Reason: Experimental (HDA) but from muscle-specific overexpression of a C-terminally GFP-tagged protein, which the authors explicitly caution may perturb localization; retained as a non-core, muscle-context localization rather than the core cytosolic site of action.
Supporting Evidence:
PMID:21611156
They appear to be in the dense bodies, M-line and/or thick filaments, as well as the ER or SR
PMID:21611156
the presence or perhaps over expression of the GFP-tagged protein may be disruptive
|
|
GO:0030017
sarcomere
|
HDA
PMID:21611156 Determining the sub-cellular localization of proteins within... |
KEEP AS NON CORE |
Summary: High-throughput GFP-localizome placing T12D8.8::GFP at sarcomeric structures (M-line/thick filaments) in body-wall muscle (category 6).
Reason: Experimental (HDA) but from muscle overexpression of a GFP fusion with acknowledged tagging/overexpression caveats; a genuine sarcomeric quality-control role is biologically plausible for a chaperone but unconfirmed for HIP-1, so kept as non-core.
Supporting Evidence:
PMID:21611156
They appear to be in the dense bodies, M-line and/or thick filaments, as well as the ER or SR
|
|
GO:0055120
striated muscle dense body
|
HDA
PMID:21611156 Determining the sub-cellular localization of proteins within... |
KEEP AS NON CORE |
Summary: High-throughput GFP-localizome placing T12D8.8::GFP at the dense body (Z-disk analog) in body-wall muscle (category 6).
Reason: Experimental (HDA) but from muscle overexpression of a GFP fusion with acknowledged tagging/overexpression caveats; retained as a non-core, muscle-context localization rather than the core cytosolic site of action.
Supporting Evidence:
PMID:21611156
They appear to be in the dense bodies, M-line and/or thick filaments, as well as the ER or SR
|
|
GO:0005829
cytosol
|
ISS
PMID:9183013 Characterization of the molecular-chaperone function of the ... |
NEW |
Summary: Proposed core localization. Hip/ST13 orthologs are predominantly cytosolic co-chaperones of the cytosolic Hsp70 machinery, and worm HIP-1 acts through Hsp70 in the cytosol; the cytosol is inferred as the primary site of action (the muscle GFP-overexpression pattern notwithstanding).
Reason: Not present in GOA but strongly supported by ortholog localization (native Hip purifies from cytosol) and by the cytosolic Hsp70-dependent proteostasis role demonstrated in the worm.
Supporting Evidence:
PMID:9183013
the native protein from rat liver cytosol
|
|
GO:0051082
unfolded protein binding
|
ISS
PMID:9183013 Characterization of the molecular-chaperone function of the ... |
NEW |
Summary: Proposed molecular function. HIP-1 has intrinsic holdase activity, binding non-native/unfolded polypeptides to prevent aggregation, independent of the Hsp70 ATP cycle, as shown for the ortholog.
Reason: Not present in GOA but experimentally demonstrated for the ortholog (specific binding to reduced, carboxymethylated alpha-lactalbumin but not the native form); an informative MF complementing the Hsp70-binding activity.
Supporting Evidence:
PMID:9183013
The role of Hip as a molecular chaperone has been confirmed by its ability to strongly bind to the reduced, carboxymethylated form of alpha-lactalbumin
|
|
GO:1903334
positive regulation of protein folding
|
ISS
PMID:23812373 Structure and function of Hip, an attenuator of the Hsp70 ch... |
NEW |
Summary: Proposed biological process. By stabilizing the ADP-bound state and attenuating the Hsp70 cycle, HIP-1 biases the chaperone system toward productive substrate holding and folding and enhances aggregation prevention by Hsp70.
Reason: Not present in GOA but follows directly from the attenuator mechanism and the in vivo anti-aggregation phenotype; captures the regulatory direction of HIP-1's effect on folding.
Supporting Evidence:
PMID:23812373
This mechanism explains how Hip enhances aggregation prevention by Hsp70
|
Q: Which endogenous C. elegans proteins are obligate HIP-1 clients, and does HIP-1 loss produce a phenotype (development, lifespan, proteotoxic-stress resistance, muscle maintenance) under normal conditions?
Q: Does endogenous HIP-1 localize to the cytosol in most tissues, and is the muscle sarcomeric/ER pattern seen on overexpression a genuine site of function?
Experiment: Generate a hip-1 loss-of-function allele (deletion or auxin-inducible degron) and phenotype development, brood size, lifespan, thermotolerance, and heat/proteotoxic stress resistance, with and without sti-1/HOP and hsp-90 co-depletion to test redundancy in the chaperone network.
Hypothesis: HIP-1 buffers proteotoxic stress by stabilizing Hsp70-substrate complexes on endogenous clients.
Type: genetics / phenotyping
Experiment: Immunoprecipitate CRISPR-tagged endogenous HIP-1 (and its Hsp70 partner HSP-1) from staged worms and identify co-purifying substrates by mass spectrometry, comparing basal and heat-stressed conditions.
Hypothesis: HIP-1 has a defined set of endogenous folding clients in the worm.
Type: interaction proteomics
What is not known — curated, literature-grounded statements of the open unknowns (the inverse of core functions).
Gap: The endogenous physiological clients/substrates of C. elegans HIP-1, and the loss-of-function phenotype of hip-1 under normal (non-transgenic) conditions, are undefined. The only direct in vivo worm evidence uses an overexpressed heterologous aggregation reporter (human alpha-synuclein), so it does not reveal which native worm proteins depend on HIP-1 or what its loss does to development, lifespan, or stress resistance.
OPEN BIOLOGY RESIDUAL_SUBGAP
What is known: The conserved molecular mechanism is solid (HIP-1 binds the Hsp70 ADP state, attenuates the chaperone cycle, and has holdase activity) and genetic epistasis in the worm shows HIP-1 acts through Hsp70. What is unknown is the native client set and the organismal phenotype of HIP-1 loss.
Significance: Without native clients or a described phenotype, HIP-1's dedicated biological role in the worm cannot be separated from redundant, buffered co-chaperone functions (the sti-1/HOP and Hsp90 arms), leaving its importance for proteostasis in the intact animal unquantified.
What would resolve it: Phenotype a hip-1 deletion/RNAi allele across development, lifespan, and proteotoxic-stress paradigms, and identify endogenous clients by immunoprecipitation-mass spectrometry of tagged endogenous HIP-1.
Provenance (the field's own admissions):
Gap: Where endogenous HIP-1 acts in the C. elegans cell is not directly measured. Cytosolic localization is inferred from mammalian orthologs, and the only worm localization data come from muscle-specific GFP overexpression that placed the protein at dense bodies, the M-line/thick filaments, and the ER/SR; whether HIP-1 has a genuine sarcomeric/muscle quality-control role is unconfirmed.
OPEN BIOLOGY CC_DARK
What is known: Mammalian Hip/ST13 is firmly cytosolic. The worm GFP-overexpression screen reported a muscle sarcomeric/ER pattern for T12D8.8, but with explicit tagging/overexpression caveats and no endogenous-localization confirmation.
Significance: Distinguishing a general cytosolic role from a dedicated sarcomeric/muscle quality-control function would clarify whether HIP-1 contributes to muscle protein maintenance, a tissue where chaperone machinery is known to service the contractile apparatus.
What would resolve it: CRISPR endogenous tagging of hip-1 followed by in vivo imaging across tissues, and tissue-specific rescue/depletion to test a muscle-autonomous requirement.
Provenance (the field's own admissions):
The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.
You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.
We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.
We are interested in where in or outside the cell the gene product carries out its function.
We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.
Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.
The C. elegans gene hip-1 (systematic name T12D8.8; UniProt accession G5EE04) encodes an STI1 domain-containing protein that is the nematode ortholog of mammalian Hip (Hsp70-interacting protein), also known as ST13 (Suppressor of Tumorigenicity 13) or p48 (shi2007whatweknow pages 1-2). It is important to distinguish this protein from the C. elegans sti-1 gene, which encodes the ortholog of HOP (Hsp70–Hsp90 organizing protein) — a related but functionally distinct co-chaperone (song2009c.eleganssti1 pages 8-9). While both Hip and Hop share STI1-type domains, they occupy different positions in the Hsp70 chaperone network. HIP-1 belongs to the FAM10 protein family, which is the gene family designation for ST13/Hip orthologs across eukaryotes (shi2007whatweknow pages 1-2). The protein is conserved across animals, plants, and protozoa, though notably absent from Saccharomyces cerevisiae and other fungi (li2013structureandfunction pages 31-35).
HIP-1 functions as a co-chaperone of the Hsp70 family of molecular chaperones. Its primary biochemical activity is to stabilize the ADP-bound state of Hsp70, thereby prolonging Hsp70–substrate complexes and preventing premature substrate release (leak2014heatshockproteins pages 4-5, shi2007whatweknow pages 2-4). In mammalian systems, Hip binds to the nucleotide-binding domain (NBD/ATPase domain) of Hsp70 specifically when Hsp70 is in the ADP-bound conformation, with a dissociation constant (K_D) of approximately 8–10 µM (li2013structureandfunction pages 82-86, li2013structureandfunction pages 121-125). One Hip dimer binds two Hsp70 molecules (li2013structureandfunction pages 82-86).
Structurally, Hip's TPR domain forms a "bracket" over the nucleotide-binding cleft of Hsp70, dampening dynamic movement of subdomain IIB and slowing ADP dissociation (li2013structureandfunction pages 121-125, karunanayake2021cytosolicproteinquality pages 8-10). This mechanism locks Hsp70 in its high-affinity substrate-binding state (the "closed lid" state), effectively attenuating the Hsp70 chaperone cycle and extending the dwell time of substrates on the chaperone (li2013structureandfunction pages 31-35, li2013structureandfunction pages 125-129).
Hip also possesses intrinsic holdase activity: it can bind unfolded proteins and prevent their aggregation independently of Hsp70, though it cannot fold substrates on its own and has no ATPase activity (li2013structureandfunction pages 31-35, velten2002domainstructureof pages 7-7, velten2002domainstructureof pages 5-7).
Hip functions as a pro-folding co-chaperone that biases the Hsp70 system toward protein refolding rather than degradation. It competes with the nucleotide exchange factor BAG-1 for binding to the Hsp70 ATPase domain (shi2007whatweknow pages 2-4, leak2014heatshockproteins pages 4-5, li2013structureandfunction pages 31-35). While Hip stabilizes Hsp70–substrate complexes to promote refolding, BAG-1 stimulates ADP release and substrate dissociation, which can route substrates toward proteasomal degradation. Under normal cellular conditions, Hip is typically 5–10 times more abundant than BAG-1 or BAG-2, favoring the folding pathway (arndt2007tobeor pages 6-8). Importantly, Hip is not found in complexes with CHIP (the E3 ubiquitin ligase that links Hsp70 to the proteasome), suggesting steric incompatibility between the pro-folding (Hip) and pro-degradation (CHIP) co-chaperone pathways on Hsp70 (arndt2007tobeor pages 6-8).
The conserved domain architecture of HIP-1 inferred from the UniProt annotation and detailed structural studies of mammalian Hip is summarized below:
| Domain name | InterPro ID | Approximate residue positions in mammalian Hip/ST13 | Known function |
|---|---|---|---|
| Hip_N | IPR034649 | 1–44 | N-terminal dimerization domain; forms a stable Hip dimer that supports avid Hsp70 binding and co-chaperone function (li2013structureandfunction pages 31-35, li2013structureandfunction pages 35-39) |
| STI1_HS-bd | IPR006636 | ~113–214 | TPR-containing Hsp70-binding module; binds the Hsp70 nucleotide-binding/ATPase domain preferentially in the ADP-bound state and stabilizes Hsp70-substrate complexes by slowing ADP release (li2013structureandfunction pages 31-35, li2013structureandfunction pages 121-125, shi2007whatweknow pages 1-2) |
| TPR repeat | IPR019734 | within ~113–214 | Repeated tetratricopeptide motifs that build the Hsp70-binding scaffold; mediate protein–protein interaction with Hsp70 and contribute to attenuation of the Hsp70 chaperone cycle (li2013structureandfunction pages 35-39, li2013structureandfunction pages 121-125) |
| TPR-like helical domain superfamily | IPR011990 | within ~113–214 | Helical superstructure underlying the TPR region; provides the structural scaffold for docking onto Hsp70’s nucleotide-binding domain and forming the “bracket” that stabilizes the ADP-bound conformation (li2013structureandfunction pages 121-125, karunanayake2021cytosolicproteinquality pages 8-10) |
| GGMP repeat region | — | ~278–311 | Flexible repeat-rich region with seven imperfect GGMP tetrapeptide repeats; precise role remains unresolved, but it is part of the conserved C-terminal region associated with Hip function in substrate/chaperone complexes (li2013structureandfunction pages 35-39, velten2002domainstructureof pages 5-7) |
| STI1/HOP_DP | IPR041243 | ~312–368 | C-terminal DP domain; contains hydrophobic grooves implicated in binding non-native substrate segments and is important for substrate/client handling and conformational maturation in vivo (li2013structureandfunction pages 31-35, li2013structureandfunction pages 35-39, li2013structureandfunction pages 121-125) |
Table: This table summarizes the conserved domain architecture of C. elegans HIP-1/T12D8.8 inferred from UniProt domain calls and mechanistic studies of mammalian Hip/ST13. It is useful for mapping sequence features to likely co-chaperone functions in Hsp70-dependent proteostasis.
The multi-domain organization is connected by long, negatively charged, disordered linkers that provide conformational flexibility, allowing Hip to recognize diverse Hsp70–substrate complexes (li2013structureandfunction pages 121-125). The N-terminal dimerization domain forms a compact α-helical dimer with slow subunit exchange (half-time ~6 hours), which is essential for avidity-based binding to multiple Hsp70 molecules simultaneously (li2013structureandfunction pages 35-39, li2013structureandfunction pages 125-129). The two-domain structural organization (an elongated N-terminal dimeric domain and a globular C-terminal domain) was also confirmed by limited proteolysis and biophysical characterization (velten2002domainstructureof pages 7-7, velten2002domainstructureof pages 5-7).
Hip/ST13 is predominantly a cytosolic protein. Studies in mammalian cells demonstrate that Hip shows a uniform distribution throughout the cytoplasm, with an estimated concentration in reticulocyte lysate of approximately 1 µM (shi2007whatweknow pages 1-2, wu2019acytosolicchaperone pages 2-3, li2013structureandfunction pages 31-35). Immunostaining confirms cytosolic localization distinct from ER-associated punctate patterns (wu2019acytosolicchaperone pages 2-3). This cytoplasmic localization is consistent with its function as a co-chaperone of the cytosolic Hsp70 machinery. By inference, C. elegans HIP-1 is predicted to similarly function in the cytosol, where it can engage the nematode Hsp70 homologs (such as HSP-1) in their chaperone cycles.
The most direct experimental evidence for C. elegans HIP-1 function comes from a landmark study by Roodveldt et al. (2009) using a transgenic worm model expressing α-synuclein-YFP in body wall muscle cells. Key findings include:
RNAi knockdown of hip-1 (T12D8.8) significantly increased the number of α-synuclein inclusions by 2.3-fold (P < 0.0001), demonstrating that HIP-1 is required for suppression of α-synuclein aggregation in vivo (roodveldt2009chaperoneproteostasisin pages 6-8, roodveldt2009chaperoneproteostasisin pages 8-10).
Double knockdown of hsp-70 (C12C8.1) and hip-1 reduced inclusions by approximately 60% compared to single hip-1 knockdown, reaching a level similar to hsp-70 knockdown alone (roodveldt2009chaperoneproteostasisin pages 8-10, roodveldt2009chaperoneproteostasisin pages 10-10). This provides strong genetic evidence that HIP-1 acts through and with Hsp70 in an epistatic relationship, functioning upstream of Hsp70 to modulate its anti-aggregation activity.
In vitro reconstitution showed that addition of Hip to Hsp70 in the presence of ATP completely suppressed the conversion of α-synuclein into amyloid species, maintaining both Hsp70 and α-synuclein in solution (roodveldt2009chaperoneproteostasisin pages 6-8). Hip alone did not inhibit fibril formation, confirming that its anti-amyloidogenic activity is mediated through Hsp70 (roodveldt2009chaperoneproteostasisin pages 6-8).
The mechanistic model posits that without Hip, the ADP-bound Hsp70/α-synuclein complex can co-aggregate, depleting functional Hsp70 from solution and allowing rapid α-synuclein fibril formation. Hip stabilizes the ADP-Hsp70 complex and maintains Hsp70 in solution, thereby sustaining chaperone-mediated inhibition of amyloid pathways (roodveldt2009chaperoneproteostasisin pages 8-10, roodveldt2009chaperoneproteostasisin pages 10-10).
The C. elegans chaperone network includes a separate co-chaperone, STI-1, which is the ortholog of mammalian HOP/Stip1 and mediates client transfer from Hsp70 to Hsp90 (song2009c.eleganssti1 pages 8-9). CeSTI-1 is involved in aging and thermotolerance, with loss of function shortening lifespan by 68–77% at different temperatures (song2009c.eleganssti1 pages 8-9). HIP-1 and STI-1 thus occupy complementary roles in the nematode proteostasis network: HIP-1 stabilizes Hsp70–substrate complexes to promote the holding/folding function, while STI-1 facilitates substrate transfer between the Hsp70 and Hsp90 systems.
A recent study (Juszkiewicz et al., 2025) has identified a previously unappreciated function for St13/Hip in mitochondrial precursor protein import. St13 directly engages mitochondrial targeting signals (MTS) through the hydrophobic groove of its STI1 domain, accommodating the hydrophobic face of amphipathic MTS helices (juszkiewicz2025mechanismofchaperone pages 9-10). Upon emergence of the precursor polypeptide from the ribosome, St13 recruits and facilitates loading of Hsc70 onto the precursor, stabilizing Hsc70's ADP-bound state and maintaining the precursor in an unfolded, import-competent state (juszkiewicz2025mechanismofchaperone pages 9-10, juszkiewicz2025mechanismofchaperone pages 7-9). St13 also facilitates recruitment of the Stip1-Hsp90 system to these precursors (juszkiewicz2025mechanismofchaperone pages 7-9). The authors propose that St13 is the long-sought "presequence binding factor" (PBF), a ~50 kDa protein previously identified in early studies as interacting with mitochondrial presequences (juszkiewicz2025mechanismofchaperone pages 9-10). During mitochondrial import stress, this interaction becomes particularly important for buffering precursor degradation and preserving import competence (juszkiewicz2025mechanismofchaperone pages 1-2). This finding suggests that C. elegans HIP-1, by domain conservation, may similarly participate in mitochondrial protein biogenesis.
| Study/Reference | Experimental approach | Key finding | Functional implication |
|---|---|---|---|
| Roodveldt et al., 2009, EMBO Journal | RNAi knockdown of hip-1/T12D8.8 in a transgenic C. elegans α-synuclein-YFP inclusion model; confocal quantification of inclusions in young adults | hip-1 RNAi increased α-synuclein inclusions 2.3-fold relative to control (P<0.0001) (roodveldt2009chaperoneproteostasisin pages 6-8, roodveldt2009chaperoneproteostasisin pages 8-10) | hip-1 is required in vivo to suppress proteotoxic α-synuclein aggregation and supports proteostasis in the worm cytosol (roodveldt2009chaperoneproteostasisin pages 6-8, roodveldt2009chaperoneproteostasisin pages 10-10) |
| Roodveldt et al., 2009, EMBO Journal | Double RNAi knockdown of hsp70 (C12C8.1) + hip-1 (T12D8.8) in the same C. elegans α-synuclein model | Double knockdown reduced inclusions by ~60% compared with hip-1 knockdown alone, approaching the hsp70-knockdown phenotype (roodveldt2009chaperoneproteostasisin pages 8-10, roodveldt2009chaperoneproteostasisin pages 10-10) | Provides genetic evidence that hip-1 acts through/with Hsp70, functioning upstream to modulate Hsp70-dependent anti-aggregation activity (roodveldt2009chaperoneproteostasisin pages 8-10) |
| Roodveldt et al., 2009, EMBO Journal | In vitro α-synuclein aggregation assay with purified proteins; ThT fluorescence, TEM, and solubility analysis in the presence of Hip + Hsp70 + ATP | Addition of Hip to Hsp70 in the presence of ATP completely suppressed conversion of α-synuclein into amyloid species and maintained Hsp70 and α-synuclein in soluble form (roodveldt2009chaperoneproteostasisin pages 6-8, roodveldt2009chaperoneproteostasisin pages 1-2) | hip-1/Hip is an Hsp70 co-chaperone that prevents Hsp70 co-aggregation and stabilizes anti-amyloid chaperone function under ATP-turnover conditions (roodveldt2009chaperoneproteostasisin pages 6-8, roodveldt2009chaperoneproteostasisin pages 8-10) |
| Li et al., 2013, Nature Structural & Molecular Biology | Structural and biochemical characterization of mammalian Hip/ST13, including domain mapping and Hsp70-binding analysis | Hip’s TPR domain binds the Hsp70 nucleotide-binding domain (NBD) and forms a bracket over the nucleotide-binding cleft, stabilizing the ADP-bound state; Hip preferentially binds ADP-Hsp70 (KD ~8–10 µM) (li2013structureandfunction pages 121-125, li2013structureandfunction pages 82-86) | Explains the likely molecular mechanism of worm hip-1: a conserved Hip-family co-chaperone that slows ADP release, prolongs substrate holding, and prevents premature substrate release (li2013structureandfunction pages 31-35, li2013structureandfunction pages 121-125) |
| Juszkiewicz et al., 2025, Molecular Biology of the Cell | Biochemical and mechanistic analysis of St13 on mitochondrial precursor proteins and mitochondrial targeting signals (MTSs) | St13 directly engages mitochondrial targeting signals via its STI1 domain hydrophobic groove and recruits/retains Hsc70/Hsp90 on precursors to maintain import competence (juszkiewicz2025mechanismofchaperone pages 9-10, juszkiewicz2025mechanismofchaperone pages 7-9, juszkiewicz2025mechanismofchaperone pages 1-2) | Expands Hip-family function beyond generic proteostasis: hip-1-like proteins can act in mitochondrial precursor triage/import competence, suggesting additional conserved roles for worm hip-1 inferred from domain architecture (juszkiewicz2025mechanismofchaperone pages 9-10, juszkiewicz2025mechanismofchaperone pages 1-2) |
Table: This table summarizes the main experimental findings supporting functional annotation of C. elegans hip-1 and its orthologous Hip/ST13 mechanism. It links worm genetic evidence to conserved biochemical and structural studies that explain how HIP-1 acts as an Hsp70 co-chaperone.
C. elegans hip-1 (T12D8.8, UniProt G5EE04) encodes a cytosolic co-chaperone of the Hip/ST13/FAM10 family that functions as a critical regulator of Hsp70 chaperone activity. Its primary molecular function is to stabilize the ADP-bound state of Hsp70, prolonging substrate engagement and promoting protein folding over degradation. The protein achieves this through a conserved multi-domain architecture comprising an N-terminal dimerization domain (Hip_N), a central TPR domain that binds the Hsp70 ATPase domain, and a C-terminal DP domain involved in substrate interactions. Direct experimental evidence in C. elegans demonstrates that HIP-1 is essential for suppressing α-synuclein aggregation in an Hsp70-dependent manner (roodveldt2009chaperoneproteostasisin pages 6-8, roodveldt2009chaperoneproteostasisin pages 8-10). The protein functions in the cytosol where it participates in general proteostasis and, based on recent evidence from the conserved mammalian ortholog, may also play a role in maintaining mitochondrial precursor import competence (juszkiewicz2025mechanismofchaperone pages 9-10, juszkiewicz2025mechanismofchaperone pages 7-9). HIP-1 represents a key node in the C. elegans cytosolic protein quality control network, operating alongside but distinct from other co-chaperones such as STI-1/HOP and CHIP in directing client protein fate decisions.
References
(shi2007whatweknow pages 1-2): Zheng-zheng Shi, Jia-wei Zhang, and Shu Zheng. What we know about st13, a co-factor of heat shock protein, or a tumor suppressor? Journal of Zhejiang University SCIENCE B, 8:170-176, Mar 2007. URL: https://doi.org/10.1631/jzus.2007.b0170, doi:10.1631/jzus.2007.b0170. This article has 59 citations.
(song2009c.eleganssti1 pages 8-9): Hyun-Ok Song, Wonhae Lee, Kiyoung An, Hye-suk Lee, Jeong Hoon Cho, Zee-Yong Park, and Joohong Ahnn. C. elegans sti-1, the homolog of sti1/hop, is involved in aging and stress response. Journal of molecular biology, 390 4:604-17, Jul 2009. URL: https://doi.org/10.1016/j.jmb.2009.05.035, doi:10.1016/j.jmb.2009.05.035. This article has 68 citations and is from a domain leading peer-reviewed journal.
(li2013structureandfunction pages 31-35): Zhuo Li, F Ulrich Hartl, and Andreas Bracher. Structure and function of hip, an attenuator of the hsp70 chaperone cycle. Nature Structural &Molecular Biology, 20:929-935, Jun 2013. URL: https://doi.org/10.1038/nsmb.2608, doi:10.1038/nsmb.2608. This article has 97 citations.
(leak2014heatshockproteins pages 4-5): Rehana K. Leak. Heat shock proteins in neurodegenerative disorders and aging. Journal of Cell Communication and Signaling, 8:293-310, Sep 2014. URL: https://doi.org/10.1007/s12079-014-0243-9, doi:10.1007/s12079-014-0243-9. This article has 226 citations and is from a peer-reviewed journal.
(shi2007whatweknow pages 2-4): Zheng-zheng Shi, Jia-wei Zhang, and Shu Zheng. What we know about st13, a co-factor of heat shock protein, or a tumor suppressor? Journal of Zhejiang University SCIENCE B, 8:170-176, Mar 2007. URL: https://doi.org/10.1631/jzus.2007.b0170, doi:10.1631/jzus.2007.b0170. This article has 59 citations.
(li2013structureandfunction pages 82-86): Zhuo Li, F Ulrich Hartl, and Andreas Bracher. Structure and function of hip, an attenuator of the hsp70 chaperone cycle. Nature Structural &Molecular Biology, 20:929-935, Jun 2013. URL: https://doi.org/10.1038/nsmb.2608, doi:10.1038/nsmb.2608. This article has 97 citations.
(li2013structureandfunction pages 121-125): Zhuo Li, F Ulrich Hartl, and Andreas Bracher. Structure and function of hip, an attenuator of the hsp70 chaperone cycle. Nature Structural &Molecular Biology, 20:929-935, Jun 2013. URL: https://doi.org/10.1038/nsmb.2608, doi:10.1038/nsmb.2608. This article has 97 citations.
(karunanayake2021cytosolicproteinquality pages 8-10): Chamithi Karunanayake and Richard C Page. Cytosolic protein quality control machinery: interactions of hsp70 with a network of co-chaperones and substrates. Experimental Biology and Medicine, 246:1419-1434, Mar 2021. URL: https://doi.org/10.1177/1535370221999812, doi:10.1177/1535370221999812. This article has 21 citations and is from a peer-reviewed journal.
(li2013structureandfunction pages 125-129): Zhuo Li, F Ulrich Hartl, and Andreas Bracher. Structure and function of hip, an attenuator of the hsp70 chaperone cycle. Nature Structural &Molecular Biology, 20:929-935, Jun 2013. URL: https://doi.org/10.1038/nsmb.2608, doi:10.1038/nsmb.2608. This article has 97 citations.
(velten2002domainstructureof pages 7-7): Marion Velten, Nathalie Gomez-Vrielynck, Alain Chaffotte, and Moncef M. Ladjimi. Domain structure of the hsc70 cochaperone, hip*. The Journal of Biological Chemistry, 277:259-266, Jan 2002. URL: https://doi.org/10.1074/jbc.m106881200, doi:10.1074/jbc.m106881200. This article has 30 citations.
(velten2002domainstructureof pages 5-7): Marion Velten, Nathalie Gomez-Vrielynck, Alain Chaffotte, and Moncef M. Ladjimi. Domain structure of the hsc70 cochaperone, hip*. The Journal of Biological Chemistry, 277:259-266, Jan 2002. URL: https://doi.org/10.1074/jbc.m106881200, doi:10.1074/jbc.m106881200. This article has 30 citations.
(arndt2007tobeor pages 6-8): V. Arndt, Christian Rogon, and J. Höhfeld. To be, or not to be — molecular chaperones in protein degradation. Cellular and Molecular Life Sciences, 64:2525-2541, Jun 2007. URL: https://doi.org/10.1007/s00018-007-7188-6, doi:10.1007/s00018-007-7188-6. This article has 248 citations and is from a domain leading peer-reviewed journal.
(li2013structureandfunction pages 35-39): Zhuo Li, F Ulrich Hartl, and Andreas Bracher. Structure and function of hip, an attenuator of the hsp70 chaperone cycle. Nature Structural &Molecular Biology, 20:929-935, Jun 2013. URL: https://doi.org/10.1038/nsmb.2608, doi:10.1038/nsmb.2608. This article has 97 citations.
(wu2019acytosolicchaperone pages 2-3): Yang Wu, Jingzi Zhang, Lei Fang, Hon Cheung Lee, and Yong Juan Zhao. A cytosolic chaperone complex controls folding and degradation of type iii cd38. Journal of Biological Chemistry, 294:4247-4258, Mar 2019. URL: https://doi.org/10.1074/jbc.ra118.005844, doi:10.1074/jbc.ra118.005844. This article has 15 citations and is from a domain leading peer-reviewed journal.
(roodveldt2009chaperoneproteostasisin pages 6-8): Cintia Roodveldt, Carlos W Bertoncini, August Andersson, Annemieke T van der Goot, Shang-Te Hsu, Rafael Fernández-Montesinos, Jannie de Jong, Tjakko J van Ham, Ellen A Nollen, David Pozo, John Christodoulou, and Christopher M Dobson. Chaperone proteostasis in parkinson's disease: stabilization of the hsp70/α‐synuclein complex by hip. The EMBO Journal, 28:3758-3770, Dec 2009. URL: https://doi.org/10.1038/emboj.2009.298, doi:10.1038/emboj.2009.298. This article has 151 citations.
(roodveldt2009chaperoneproteostasisin pages 8-10): Cintia Roodveldt, Carlos W Bertoncini, August Andersson, Annemieke T van der Goot, Shang-Te Hsu, Rafael Fernández-Montesinos, Jannie de Jong, Tjakko J van Ham, Ellen A Nollen, David Pozo, John Christodoulou, and Christopher M Dobson. Chaperone proteostasis in parkinson's disease: stabilization of the hsp70/α‐synuclein complex by hip. The EMBO Journal, 28:3758-3770, Dec 2009. URL: https://doi.org/10.1038/emboj.2009.298, doi:10.1038/emboj.2009.298. This article has 151 citations.
(roodveldt2009chaperoneproteostasisin pages 10-10): Cintia Roodveldt, Carlos W Bertoncini, August Andersson, Annemieke T van der Goot, Shang-Te Hsu, Rafael Fernández-Montesinos, Jannie de Jong, Tjakko J van Ham, Ellen A Nollen, David Pozo, John Christodoulou, and Christopher M Dobson. Chaperone proteostasis in parkinson's disease: stabilization of the hsp70/α‐synuclein complex by hip. The EMBO Journal, 28:3758-3770, Dec 2009. URL: https://doi.org/10.1038/emboj.2009.298, doi:10.1038/emboj.2009.298. This article has 151 citations.
(juszkiewicz2025mechanismofchaperone pages 9-10): Szymon Juszkiewicz, Sew-Yeu Peak-Chew, and Ramanujan S. Hegde. Mechanism of chaperone recruitment and retention on mitochondrial precursors. Molecular Biology of the Cell, Jan 2025. URL: https://doi.org/10.1091/mbc.e25-01-0035, doi:10.1091/mbc.e25-01-0035. This article has 21 citations and is from a domain leading peer-reviewed journal.
(juszkiewicz2025mechanismofchaperone pages 7-9): Szymon Juszkiewicz, Sew-Yeu Peak-Chew, and Ramanujan S. Hegde. Mechanism of chaperone recruitment and retention on mitochondrial precursors. Molecular Biology of the Cell, Jan 2025. URL: https://doi.org/10.1091/mbc.e25-01-0035, doi:10.1091/mbc.e25-01-0035. This article has 21 citations and is from a domain leading peer-reviewed journal.
(juszkiewicz2025mechanismofchaperone pages 1-2): Szymon Juszkiewicz, Sew-Yeu Peak-Chew, and Ramanujan S. Hegde. Mechanism of chaperone recruitment and retention on mitochondrial precursors. Molecular Biology of the Cell, Jan 2025. URL: https://doi.org/10.1091/mbc.e25-01-0035, doi:10.1091/mbc.e25-01-0035. This article has 21 citations and is from a domain leading peer-reviewed journal.
(roodveldt2009chaperoneproteostasisin pages 1-2): Cintia Roodveldt, Carlos W Bertoncini, August Andersson, Annemieke T van der Goot, Shang-Te Hsu, Rafael Fernández-Montesinos, Jannie de Jong, Tjakko J van Ham, Ellen A Nollen, David Pozo, John Christodoulou, and Christopher M Dobson. Chaperone proteostasis in parkinson's disease: stabilization of the hsp70/α‐synuclein complex by hip. The EMBO Journal, 28:3758-3770, Dec 2009. URL: https://doi.org/10.1038/emboj.2009.298, doi:10.1038/emboj.2009.298. This article has 151 citations.
UniProt: G5EE04 (G5EE04_CAEEL). WormBase: WBGene00011735 / T12D8.8. Chromosome III.
Gene symbol: hip-1. Product: STI1 domain-containing protein = Hsc70-interacting protein (HIP),
ortholog of mammalian Hip/ST13 (FAM10 family). Evidence at protein level (PE1; PeptideAtlas).
The UniProt record IS the HSP70-interacting co-chaperone, not an unrelated gene:
- UniProt FUNCTION (ARBA): "One HIP oligomer binds the ATPase domains of at least two HSC70
molecules dependent on activation of the HSC70 ATPase by HSP40. Stabilizes the ADP state of
HSC70 that has a high affinity for substrate protein."
- Domain architecture matches Hip/ST13: Hip_N (IPR034649, N-terminal dimerization), STI1/HOP_DP
(IPR041243, C-terminal DP domain), STI1_HS-bd (IPR006636), TPR repeats (IPR019734), TPR-like
helical superfamily (IPR011990); Pfam HipN (PF18253), STI1-HOP_DP (PF17830), TPR_16 (PF13432);
SMART STI1 + 3×TPR.
- PANTHER PTHR45883 "HSC70-INTERACTING PROTEIN" (subfamily SF2). "Belongs to the FAM10 family."
- NOTE: distinct from C. elegans sti-1 (the HOP/Stip1 ortholog); both carry STI1-type domains
but occupy different positions in the Hsp70/Hsp90 network
[file:worm/hip-1/hip-1-deep-research-falcon.md "It is important to distinguish this protein from
the C. elegans sti-1 gene, which encodes the ortholog of HOP"].
Core MF = GO:0030544 Hsp70 protein binding; core BP = GO:0006457 protein folding + GO:1903334
positive regulation of protein folding; core CC = GO:0005829 cytosol.
All 9 GOA annotations resolved; 3 NEW proposed annotations added. Every supporting_text
was grep/normalization-verified as a verbatim substring of the cached publication.
Knowledge gaps recorded (top-level): (1) endogenous worm clients + LoF phenotype are
undefined (only a heterologous overexpressed αSyn reporter was assayed in vivo)
[RESIDUAL_SUBGAP]; (2) native subcellular localization of endogenous HIP-1 unmeasured;
worm data are muscle GFP-overexpression only [CC_DARK].
Note: the "no annotation references the deep research file" validation WARNING is left
unresolved because the pre-edit hook resolves file: references against a temp-dir copy
and cannot see the (real, present) falcon file; this is a non-blocking warning only.
id: G5EE04
gene_symbol: hip-1
product_type: PROTEIN
status: DRAFT
taxon:
id: NCBITaxon:6239
label: Caenorhabditis elegans
description: >-
hip-1 encodes the Caenorhabditis elegans ortholog of Hsp70-interacting protein
(Hip/ST13), a member of the FAM10 family and a co-chaperone of the cytosolic
Hsp70 (Hsc70) chaperone system. The protein has a modular architecture: an
N-terminal dimerization domain (Hip_N) that drives homo-oligomerization into a
tetramer, a central tetratricopeptide-repeat (TPR) region that binds the ATPase
(nucleotide-binding) domain of Hsp70, and a C-terminal STI1/DP domain. Hip binds
the ADP-bound state of Hsp70 and stabilizes it, slowing ADP release and prolonging
the high-affinity association of Hsp70 with substrate; because Hip and
nucleotide-exchange factors bind Hsp70 in a mutually exclusive manner, Hip acts as
an attenuator of the Hsp70 reaction cycle that biases the system toward substrate
holding and folding rather than release and degradation. Hip also has intrinsic
holdase activity, binding non-native polypeptides to prevent their aggregation, but
it lacks ATPase activity and cannot refold substrates on its own. In C. elegans,
HIP-1 acts through Hsp70 to suppress proteotoxic aggregation in vivo, and it is
predominantly cytosolic, consistent with a role in the cytosolic protein
quality-control network. It is distinct from the C. elegans HOP/Stip1 ortholog
sti-1, which occupies a different node of the Hsp70/Hsp90 system.
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:0000117
title: Electronic Gene Ontology annotations created by ARBA machine learning models
findings: []
- id: PMID:7585962
title: Hip, a novel cochaperone involved in the eukaryotic Hsc70/Hsp40 reaction cycle.
findings: []
reference_review:
relevance: HIGH
correctness: VERIFIED
review_notes: >-
Original characterization of Hip. PubMed-verified. Establishes that one Hip
oligomer binds the ATPase domains of Hsc70 and stabilizes the ADP (high
substrate-affinity) state. Mechanism is on the mammalian ortholog; conserved
in the FAM10 family to which C. elegans HIP-1 belongs. Abstract-only in cache.
- id: PMID:8999928
title: Characterization of functional domains of the eukaryotic co-chaperone Hip.
findings: []
reference_review:
relevance: HIGH
correctness: VERIFIED
review_notes: >-
PubMed-verified. Maps the Hsc70-binding site to the TPR domain and the
homo-oligomerization determinant to the extreme N terminus; supports the
folding/co-chaperone role. Mammalian ortholog; abstract-only in cache.
- id: PMID:9528774
title: The carboxy-terminal domain of Hsc70 provides binding sites for a distinct
set of chaperone cofactors.
findings: []
reference_review:
relevance: HIGH
correctness: VERIFIED
review_notes: >-
PubMed-verified. Shows Hip binds exclusively the amino-terminal ATPase domain
of Hsc70 and that Hsc70 has separate nonoverlapping sites for Hsp40, Hip and
Hop, and that Hip and BAG-1 compete. Directly supports the Hsp70-binding MF.
- id: PMID:9183013
title: Characterization of the molecular-chaperone function of the heat-shock-cognate-70-interacting
protein.
findings: []
reference_review:
relevance: HIGH
correctness: VERIFIED
review_notes: >-
PubMed-verified. Recombinant Hip forms a tetramer, has intrinsic holdase
activity (binds reduced carboxymethylated alpha-lactalbumin), does not
hydrolyze ATP, and cannot refold substrates on its own. Anchors the holdase MF
and the non-catalytic character.
- id: PMID:23812373
title: Structure and function of Hip, an attenuator of the Hsp70 chaperone cycle.
findings: []
reference_review:
relevance: HIGH
correctness: VERIFIED
review_notes: >-
PubMed-verified. Crystal structures show the TPR core forms a bracket over the
Hsp70 ATPase domain that locks ADP in the cleft, and that Hip and NEF binding
are mutually exclusive, so Hip attenuates the cycle. Defines the mechanism of
the Hsp70-binding MF.
- id: PMID:19875982
title: "Chaperone proteostasis in Parkinson's disease: stabilization of the Hsp70/alpha-synuclein
complex by Hip."
findings: []
reference_review:
relevance: HIGH
correctness: VERIFIED
review_notes: >-
PubMed-verified; full text available. The only study with direct in vivo
C. elegans evidence: hip-1 (T12D8.8) RNAi increases alpha-synuclein inclusions
and epistasis shows HIP-1 acts through Hsp70. Uses a heterologous overexpressed
alpha-synuclein reporter, so it does not identify endogenous worm clients.
- id: PMID:21611156
title: Determining the sub-cellular localization of proteins within Caenorhabditis
elegans body wall muscle.
findings: []
reference_review:
relevance: MEDIUM
correctness: VERIFIED
review_notes: >-
PubMed-verified. High-throughput body-wall-muscle GFP-localizome; T12D8.8::GFP
is in category 6 (dense bodies, M-line/thick filaments, ER/SR). Source of the
three HDA muscle CC annotations. Authors explicitly caution that C-terminal GFP
tagging and overexpression may perturb localization, so these are non-core.
existing_annotations:
- term:
id: GO:0006457
label: protein folding
evidence_type: IBA
original_reference_id: GO_REF:0000033
qualifier: involved_in
review:
summary: >-
Phylogenetically inferred biological process. HIP-1 is an Hsp70 co-chaperone
that cooperates with Hsc70 in the folding of newly synthesized and non-native
polypeptides; protein folding is the core process it participates in.
action: ACCEPT
reason: >-
Consistent with the conserved FAM10/Hip co-chaperone role and with experimental
evidence from orthologs that Hip cooperates with Hsc70 in polypeptide folding
and plays a critical role in protein folding in the eukaryotic cytoplasm.
supported_by:
- reference_id: PMID:8999928
supporting_text: >-
The homo-oligomeric Hip protein cooperates with the 70-kDa heat shock cognate
Hsc70 in the folding of newly synthesized polypeptide chains
- reference_id: PMID:9183013
supporting_text: play a critical role in protein folding in the eukaryotic cytoplasm
- term:
id: GO:0030544
label: Hsp70 protein binding
evidence_type: IBA
original_reference_id: GO_REF:0000033
qualifier: enables
review:
summary: >-
Core, defining molecular function of a Hip-family co-chaperone: HIP-1 binds the
N-terminal ATPase (nucleotide-binding) domain of Hsp70/Hsc70, specifically in
the ADP state, and stabilizes the high substrate-affinity conformation.
action: ACCEPT
reason: >-
This is the informative, partner-specific molecular function of the protein and
is supported by biochemical mapping in orthologs showing Hip binds the Hsc70
ATPase domain exclusively and by structural work showing it brackets the ATPase
domain to lock in ADP.
supported_by:
- reference_id: PMID:9528774
supporting_text: Hip interacts exclusively with the amino-terminal ATPase domain of Hsc70
- reference_id: PMID:7585962
supporting_text: >-
One Hip oligomer binds the ATPase domains of at least two Hsc70 molecules
- term:
id: GO:0005634
label: nucleus
evidence_type: IEA
original_reference_id: GO_REF:0000117
qualifier: located_in
review:
summary: >-
Electronic (ARBA machine-learning) cellular-component annotation with no
experimental support. Hip/ST13 is an established cytosolic co-chaperone of the
cytosolic Hsp70 machinery, and there is no evidence for nuclear localization of
C. elegans HIP-1.
action: REMOVE
reason: >-
Over-propagated electronic inference that conflicts with the well-established
cytosolic biology of Hip-family co-chaperones; not supported by any experimental
or phylogenetic evidence for this gene.
- term:
id: GO:0046983
label: protein dimerization activity
evidence_type: IEA
original_reference_id: GO_REF:0000002
qualifier: enables
review:
summary: >-
InterPro-derived (IPR034649, Hip_N) molecular function. HIP-1 genuinely
homo-oligomerizes (dimer of dimers / tetramer) through its N-terminal Hip_N
domain, which provides avidity for binding multiple Hsp70 molecules.
action: KEEP_AS_NON_CORE
reason: >-
Self-association is real and functionally relevant but is a structural property
rather than the informative core molecular function; retained as non-core. The
N-terminal oligomerization determinant and the tetrameric state are documented
experimentally in orthologs.
supported_by:
- reference_id: PMID:8999928
supporting_text: >-
a domain required for homo-oligomerization was identified at the extreme amino
terminus of Hip
- reference_id: PMID:9183013
supporting_text: >-
the chaperone forms a tetramer similar to what has been reported for the native
protein from rat liver cytosol
- term:
id: GO:0070013
label: intracellular organelle lumen
evidence_type: IEA
original_reference_id: GO_REF:0000117
qualifier: located_in
review:
summary: >-
Electronic (ARBA machine-learning) cellular-component annotation with no
experimental support and inconsistent with the cytosolic localization of
Hip-family co-chaperones.
action: REMOVE
reason: >-
Over-propagated electronic inference; an organelle-lumen location is not
supported by any experimental or phylogenetic evidence for HIP-1 and conflicts
with its cytosolic function.
- term:
id: GO:1902494
label: catalytic complex
evidence_type: IEA
original_reference_id: GO_REF:0000117
qualifier: part_of
review:
summary: >-
Electronic (ARBA machine-learning) annotation placing HIP-1 in a catalytic
complex. HIP-1 itself is non-catalytic (no ATPase activity); it transiently
associates with the catalytic Hsp70 ATPase, but "catalytic complex" is generic
and mischaracterizes HIP-1's own role.
action: MARK_AS_OVER_ANNOTATED
reason: >-
Uninformative and potentially misleading: HIP-1 does not catalyze a reaction and
is not a stable structural subunit of a defined catalytic complex; its
interaction with Hsp70 is transient and regulatory.
supported_by:
- reference_id: PMID:9183013
supporting_text: >-
The recombinant form of Hip did not catalyze the hydrolysis of ATP and ATP
analogs
- term:
id: GO:0005783
label: endoplasmic reticulum
evidence_type: HDA
original_reference_id: PMID:21611156
qualifier: located_in
review:
summary: >-
High-throughput direct-assay localization from a body-wall-muscle GFP-localizome:
T12D8.8::GFP fell in category 6, which includes the ER/SR alongside dense bodies
and the M-line/thick filaments.
action: KEEP_AS_NON_CORE
reason: >-
Experimental (HDA) but from muscle-specific overexpression of a C-terminally
GFP-tagged protein, which the authors explicitly caution may perturb
localization; retained as a non-core, muscle-context localization rather than the
core cytosolic site of action.
supported_by:
- reference_id: PMID:21611156
supporting_text: >-
They appear to be in the dense bodies, M-line and/or thick filaments, as well
as the ER or SR
- reference_id: PMID:21611156
supporting_text: the presence or perhaps over expression of the GFP-tagged protein may be disruptive
- term:
id: GO:0030017
label: sarcomere
evidence_type: HDA
original_reference_id: PMID:21611156
qualifier: located_in
review:
summary: >-
High-throughput GFP-localizome placing T12D8.8::GFP at sarcomeric structures
(M-line/thick filaments) in body-wall muscle (category 6).
action: KEEP_AS_NON_CORE
reason: >-
Experimental (HDA) but from muscle overexpression of a GFP fusion with
acknowledged tagging/overexpression caveats; a genuine sarcomeric
quality-control role is biologically plausible for a chaperone but unconfirmed
for HIP-1, so kept as non-core.
supported_by:
- reference_id: PMID:21611156
supporting_text: >-
They appear to be in the dense bodies, M-line and/or thick filaments, as well
as the ER or SR
- term:
id: GO:0055120
label: striated muscle dense body
evidence_type: HDA
original_reference_id: PMID:21611156
qualifier: located_in
review:
summary: >-
High-throughput GFP-localizome placing T12D8.8::GFP at the dense body (Z-disk
analog) in body-wall muscle (category 6).
action: KEEP_AS_NON_CORE
reason: >-
Experimental (HDA) but from muscle overexpression of a GFP fusion with
acknowledged tagging/overexpression caveats; retained as a non-core,
muscle-context localization rather than the core cytosolic site of action.
supported_by:
- reference_id: PMID:21611156
supporting_text: >-
They appear to be in the dense bodies, M-line and/or thick filaments, as well
as the ER or SR
- term:
id: GO:0005829
label: cytosol
evidence_type: ISS
original_reference_id: PMID:9183013
qualifier: located_in
review:
summary: >-
Proposed core localization. Hip/ST13 orthologs are predominantly cytosolic
co-chaperones of the cytosolic Hsp70 machinery, and worm HIP-1 acts through
Hsp70 in the cytosol; the cytosol is inferred as the primary site of action
(the muscle GFP-overexpression pattern notwithstanding).
action: NEW
reason: >-
Not present in GOA but strongly supported by ortholog localization (native Hip
purifies from cytosol) and by the cytosolic Hsp70-dependent proteostasis role
demonstrated in the worm.
supported_by:
- reference_id: PMID:9183013
supporting_text: the native protein from rat liver cytosol
- term:
id: GO:0051082
label: unfolded protein binding
evidence_type: ISS
original_reference_id: PMID:9183013
qualifier: enables
review:
summary: >-
Proposed molecular function. HIP-1 has intrinsic holdase activity, binding
non-native/unfolded polypeptides to prevent aggregation, independent of the
Hsp70 ATP cycle, as shown for the ortholog.
action: NEW
reason: >-
Not present in GOA but experimentally demonstrated for the ortholog (specific
binding to reduced, carboxymethylated alpha-lactalbumin but not the native
form); an informative MF complementing the Hsp70-binding activity.
supported_by:
- reference_id: PMID:9183013
supporting_text: >-
The role of Hip as a molecular chaperone has been confirmed by its ability to
strongly bind to the reduced, carboxymethylated form of alpha-lactalbumin
- term:
id: GO:1903334
label: positive regulation of protein folding
evidence_type: ISS
original_reference_id: PMID:23812373
qualifier: involved_in
review:
summary: >-
Proposed biological process. By stabilizing the ADP-bound state and attenuating
the Hsp70 cycle, HIP-1 biases the chaperone system toward productive substrate
holding and folding and enhances aggregation prevention by Hsp70.
action: NEW
reason: >-
Not present in GOA but follows directly from the attenuator mechanism and the
in vivo anti-aggregation phenotype; captures the regulatory direction of HIP-1's
effect on folding.
supported_by:
- reference_id: PMID:23812373
supporting_text: This mechanism explains how Hip enhances aggregation prevention by Hsp70
core_functions:
- description: >-
HIP-1 is a co-chaperone of the cytosolic Hsp70 (Hsc70) system. It binds the
ATPase/nucleotide-binding domain of Hsp70 and stabilizes the ADP-bound, high
substrate-affinity state, forming a bracket that locks ADP in the cleft and,
because it is mutually exclusive with nucleotide-exchange factors, attenuates the
Hsp70 reaction cycle so that substrates are held and folded rather than
prematurely released. In C. elegans this activity suppresses proteotoxic
aggregation in an Hsp70-dependent manner.
supported_by:
- reference_id: PMID:23812373
supporting_text: to form a bracket that locks ADP in the binding cleft
- reference_id: PMID:19875982
supporting_text: >-
the hypothesis that it might do so also in vivo is supported by studies of a
Caenorhabditis elegans model of alphaSyn aggregation
molecular_function:
id: GO:0030544
label: Hsp70 protein binding
directly_involved_in:
- id: GO:0006457
label: protein folding
- id: GO:1903334
label: positive regulation of protein folding
locations:
- id: GO:0005829
label: cytosol
- description: >-
Independent of the Hsp70 cycle, HIP-1 has intrinsic holdase (chaperone) activity:
it binds non-native/unfolded polypeptides to prevent their aggregation. It has no
ATPase activity and cannot refold substrates on its own, and it homo-oligomerizes
via its N-terminal Hip_N domain into a tetramer, giving avidity for multiple Hsp70
molecules.
supported_by:
- reference_id: PMID:9183013
supporting_text: >-
The role of Hip as a molecular chaperone has been confirmed by its ability to
strongly bind to the reduced, carboxymethylated form of alpha-lactalbumin
molecular_function:
id: GO:0051082
label: unfolded protein binding
locations:
- id: GO:0005829
label: cytosol
knowledge_gaps:
- gap_statement: >-
The endogenous physiological clients/substrates of C. elegans HIP-1, and the
loss-of-function phenotype of hip-1 under normal (non-transgenic) conditions, are
undefined. The only direct in vivo worm evidence uses an overexpressed
heterologous aggregation reporter (human alpha-synuclein), so it does not reveal
which native worm proteins depend on HIP-1 or what its loss does to development,
lifespan, or stress resistance.
boundary: >-
The conserved molecular mechanism is solid (HIP-1 binds the Hsp70 ADP state,
attenuates the chaperone cycle, and has holdase activity) and genetic epistasis in
the worm shows HIP-1 acts through Hsp70. What is unknown is the native client set
and the organismal phenotype of HIP-1 loss.
gap_kind:
- BIOLOGY
dark_aspect: RESIDUAL_SUBGAP
status: OPEN
significance: >-
Without native clients or a described phenotype, HIP-1's dedicated biological role
in the worm cannot be separated from redundant, buffered co-chaperone functions
(the sti-1/HOP and Hsp90 arms), leaving its importance for proteostasis in the
intact animal unquantified.
resolution: >-
Phenotype a hip-1 deletion/RNAi allele across development, lifespan, and
proteotoxic-stress paradigms, and identify endogenous clients by
immunoprecipitation-mass spectrometry of tagged endogenous HIP-1.
provenance:
- reference_id: PMID:19875982
supporting_text: >-
the hypothesis that it might do so also in vivo is supported by studies of a
Caenorhabditis elegans model of alphaSyn aggregation
- gap_statement: >-
Where endogenous HIP-1 acts in the C. elegans cell is not directly measured.
Cytosolic localization is inferred from mammalian orthologs, and the only worm
localization data come from muscle-specific GFP overexpression that placed the
protein at dense bodies, the M-line/thick filaments, and the ER/SR; whether HIP-1
has a genuine sarcomeric/muscle quality-control role is unconfirmed.
boundary: >-
Mammalian Hip/ST13 is firmly cytosolic. The worm GFP-overexpression screen
reported a muscle sarcomeric/ER pattern for T12D8.8, but with explicit
tagging/overexpression caveats and no endogenous-localization confirmation.
gap_kind:
- BIOLOGY
dark_aspect: CC_DARK
status: OPEN
significance: >-
Distinguishing a general cytosolic role from a dedicated sarcomeric/muscle
quality-control function would clarify whether HIP-1 contributes to muscle protein
maintenance, a tissue where chaperone machinery is known to service the
contractile apparatus.
resolution: >-
CRISPR endogenous tagging of hip-1 followed by in vivo imaging across tissues, and
tissue-specific rescue/depletion to test a muscle-autonomous requirement.
provenance:
- reference_id: PMID:21611156
supporting_text: the presence or perhaps over expression of the GFP-tagged protein may be disruptive
proposed_new_terms: []
suggested_questions:
- question: >-
Which endogenous C. elegans proteins are obligate HIP-1 clients, and does HIP-1
loss produce a phenotype (development, lifespan, proteotoxic-stress resistance,
muscle maintenance) under normal conditions?
experts: []
- question: >-
Does endogenous HIP-1 localize to the cytosol in most tissues, and is the muscle
sarcomeric/ER pattern seen on overexpression a genuine site of function?
experts: []
suggested_experiments:
- hypothesis: >-
HIP-1 buffers proteotoxic stress by stabilizing Hsp70-substrate complexes on
endogenous clients.
description: >-
Generate a hip-1 loss-of-function allele (deletion or auxin-inducible degron) and
phenotype development, brood size, lifespan, thermotolerance, and heat/proteotoxic
stress resistance, with and without sti-1/HOP and hsp-90 co-depletion to test
redundancy in the chaperone network.
experiment_type: genetics / phenotyping
- hypothesis: >-
HIP-1 has a defined set of endogenous folding clients in the worm.
description: >-
Immunoprecipitate CRISPR-tagged endogenous HIP-1 (and its Hsp70 partner HSP-1)
from staged worms and identify co-purifying substrates by mass spectrometry,
comparing basal and heat-stressed conditions.
experiment_type: interaction proteomics