C. elegans HSP-12.3 is a 12.3 kDa member of the small heat shock protein (sHSP/HSP20) family. It contains an alpha-crystallin domain (SHSP domain) but has an unusually short N-terminal region and lacks a C-terminal tail, making it one of the smallest known sHSPs. Recombinant HSP-12.3 forms tetramers rather than the large oligomeric complexes typical of other sHSPs, and critically, it lacks detectable in vitro chaperone-like activity (PMID:9744800). This distinguishes it from canonical sHSPs that function as holdase chaperones. HSP-12.3 physically interacts with HSP-12.2 (PMID:9744800). The protein is associated with reproductive tissues including vulva and spermatheca (PMID:11001875). Despite lacking chaperone activity in vitro, C. elegans 12 kDa sHSPs play roles in dauer formation, longevity, and reproduction in vivo. The PMID:9744800 study concludes that tetramers are the building blocks of sHSP complexes and that higher multimer formation, mediated through the N-terminal domains, is a prerequisite for chaperone-like activity. Consistent with this atypical profile, an evolutionary survey of sHSP-mediated sequestration classified HSP-12.3 as sequestrase-negative, arguing against a major role in inclusion-forming sequestration. Rather than acting as a canonical holdase, hsp-12.3 behaves as a stress-response/longevity effector gene: it is regulated by insulin/IGF-1 signaling via DAF-16/FOXO (upregulated when daf-2/IIS is reduced, downregulated when daf-16 activity is reduced), reduced in hpk-1 loss-of-function animals, and listed among HIF-1-positively-regulated stress-response genes under short-term hypoxia. Its protein abundance increases with age and rises further in long-lived daf-2 mutants. hsp-12.3(RNAi) has not been shown to alter lifespan, but this is inconclusive given unverified RNAi specificity and potential redundancy/heterotetramerization with HSP-12.2.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005737 cytoplasm | IBA GO_REF:0000033 | ACCEPT | Summary: IBA annotation for cytoplasmic localization, inferred phylogenetically from a large set of sHSP orthologs across fly, worm, mouse, rat, human, and zebrafish species. The inference is phylogenetically well-supported. sHSPs are generally cytoplasmic proteins, and immunohistochemical data in C. elegans shows HSP12 proteins in vulva and spermatheca tissue (PMID:11001875). Reason: Cytoplasmic localization is well-established for sHSP family proteins. The IBA inference from multiple orthologs is phylogenetically sound and consistent with immunohistochemical localization data in C. elegans (PMID:11001875). Falcon deep research concurs that, in the absence of gene-specific reporter data, the most defensible statement is that HSP-12.3 is a small cytosolic sHSP-family protein. Supporting Evidence: file:worm/hsp-12.3/hsp-12.3-deep-research-falcon.md the most defensible current statement is that **Hsp-12.3 is a small cytosolic sHSP-family protein**, but its precise subcellular compartment(s) and tissue specificity require confirmation with gene-specific reporters or specific antibodies. |
| GO:0005634 nucleus | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: IBA annotation for nuclear localization based on phylogenetic inference from mammalian sHSP orthologs including CRYAA, CRYAB, HSP27/HSPB1 that have been reported to translocate to the nucleus under stress conditions. Nuclear localization is not the primary compartment for sHSPs and has not been specifically demonstrated for C. elegans HSP-12.3. Reason: Nuclear localization has been reported for some mammalian sHSP orthologs. The IBA inference is phylogenetically supported but represents a secondary or stress-dependent localization. Not the primary compartment for sHSP function. Retained as non-core. |
| GO:0009408 response to heat | IBA GO_REF:0000033 | ACCEPT | Summary: IBA annotation for involvement in heat stress response, inferred phylogenetically from a large set of sHSP orthologs across fly, worm, and zebrafish. HSP-12.3 is classified as a heat shock protein (HSP20 family), and while its in vivo response to heat has not been specifically characterized, its classification as an sHSP and the IBA inference from well-characterized orthologs support this annotation. Reason: HSP-12.3 is a member of the sHSP/HSP20 family which is fundamentally involved in heat stress response. The IBA inference from multiple well-characterized sHSP orthologs is phylogenetically well-supported, and this inference alone is sufficient to ACCEPT "response to heat" as a core sHSP-family function (even though the mechanism likely differs from canonical chaperone activity and is probably partner-dependent rather than canonical holdase activity). Note: the falcon deep research evidence on hsp-12.3 regulation (DAF-16/FOXO insulin-signaling targeting, reduced expression in hpk-1 loss-of-function animals, HIF-1-positive regulation under short-term hypoxia, and increased protein abundance with age and in long-lived daf-2 mutants) demonstrates general stress-pathway/longevity regulation, NOT heat-specific induction. No heat-specific induction data (e.g. heat-shock fold-change values) for hsp-12.3 were available in that report, so those general-stress entries were not anchored here as heat-specific evidence; the ACCEPT rests on the IBA inference. |
| GO:0042026 protein refolding | IBA GO_REF:0000033 | REMOVE | Summary: IBA annotation for protein refolding, inferred phylogenetically primarily from Drosophila sHSP orthologs. However, HSP-12.3 has been experimentally demonstrated to lack chaperone-like activity in vitro (PMID:9744800). Kokke et al. showed that recombinant HSP-12.3 forms tetramers and is devoid of in vitro chaperone-like abilities. The authors concluded that higher multimer formation, mediated through the N-terminal domains that HSP-12.3 lacks, is a prerequisite for chaperone-like activity. This annotation is therefore incorrect for HSP-12.3. Reason: HSP-12.3 has been directly demonstrated to lack chaperone-like activity in vitro (PMID:9744800). It forms tetramers rather than the large oligomeric complexes required for chaperone function. The IBA inference from Drosophila sHSP orthologs does not apply because HSP-12.3 has divergent structural properties (very short N-terminal region, no C-terminal tail) that preclude holdase/chaperone activity. There is also a NOT annotation for GO:0051082 (unfolded protein binding) from the same publication confirming this. Supporting Evidence: PMID:9744800 both appear devoid of in vitro chaperone-like abilities. This supports the notion that tetramers are the building blocks of sHSP complexes, and that higher multimer formation, mediated through the N-terminal domains, is a prerequisite for chaperone-like activity. file:worm/hsp-12.3/hsp-12.3-deep-research-falcon.md Recombinant **HSP-12.3 did not prevent citrate synthase aggregation** in a thermal unfolding assay, indicating **no detectable classical holdase activity under those conditions**. file:worm/hsp-12.3/hsp-12.3-deep-research-falcon.md HSP-12.3 was classified as sequestrase-negative and lacked sequence features associated with sequestrase-positive sHSPs, arguing against a major role in inclusion-forming sequestration. |
| GO:0031072 heat shock protein binding | IPI PMID:9744800 Caenorhabditis elegans small heat-shock proteins Hsp12.2 and... | ACCEPT | Summary: IPI annotation for heat shock protein binding based on Kokke et al. 1998 (PMID:9744800). The study demonstrated physical interaction between HSP-12.3 and HSP-12.2 (WB:WBGene00002011), both of which are 12 kDa sHSPs that form tetramers. This represents homotypic interaction within the sHSP family. Reason: The physical interaction between HSP-12.3 and HSP-12.2 is directly demonstrated by experimental evidence (PMID:9744800). Heat shock protein binding accurately captures this interaction between sHSP family members. This is a core molecular function for HSP-12.3. Supporting Evidence: PMID:9744800 they are the first sHSPs shown to occur as tetramers, rather than forming the usual large multimeric complexes file:worm/hsp-12.3/hsp-12.3-deep-research-falcon.md Unlike many sHSPs that form larger multimeric assemblies, HSP-12.3 is reported to assemble as a **tetramer**, and is additionally reported to form **heterotetramers with HSP-12.2**. |
| GO:0051082 unfolded protein binding | IDA NOT PMID:9744800 Caenorhabditis elegans small heat-shock proteins Hsp12.2 and... | ACCEPT | Summary: NOT annotation (negated IDA) for unfolded protein binding based on Kokke et al. 1998 (PMID:9744800). The study directly tested recombinant HSP-12.3 for chaperone-like activity and found it devoid of the ability to prevent aggregation of denaturing substrate proteins. This negative result is consistent with the structural analysis showing that HSP-12.3 forms tetramers rather than the large oligomeric complexes required for chaperone function. GO:0051082 is now formally obsolete, but the negation is still informative as it indicates this protein does not have holdase activity. Reason: This NOT annotation is an important negative result directly demonstrated by experimental evidence (PMID:9744800). HSP-12.3 lacks chaperone-like activity and does not bind unfolded proteins in the functional sense despite being an sHSP family member. The negation correctly documents this experimentally determined absence of function. Supporting Evidence: PMID:9744800 [Both HSP-12.2 and HSP-12.3 are] devoid of in vitro chaperone-like abilities. file:worm/hsp-12.3/hsp-12.3-deep-research-falcon.md Recombinant **HSP-12.3 did not prevent citrate synthase aggregation** in a thermal unfolding assay, indicating **no detectable classical holdase activity under those conditions**. |
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