hsp-12.6

Existing Annotations Review

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. Consistent with direct IDA evidence for cytoplasmic localization from immunohistochemistry (PMID:11001875). Reason: Cytoplasmic localization is well-established for sHSP family proteins and directly confirmed for HSP-12.6 by IDA evidence (PMID:11001875). The IBA inference is phylogenetically sound and experimentally validated.
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 (CRYAA, CRYAB, HSP27/HSPB1) that have been reported to translocate to the nucleus under stress conditions. Nuclear localization has not been specifically demonstrated for C. elegans HSP-12.6. 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 HSP-12.6 function. Retained as non-core.
GO:0009408 response to heat	IBA GO_REF:0000033	MARK AS OVER ANNOTATED	Summary: IBA annotation for involvement in heat stress response, inferred phylogenetically from multiple sHSP orthologs. HSP-12.6 is a member of the sHSP/HSP20 family. However, Leroux et al. 1997 (PMID:9139746) reported that HSP-12.6 expression is not significantly upregulated by a wide range of stressors, which calls into question a strong role in heat stress response for this particular sHSP. Nevertheless, the IBA inference from the broader sHSP family is phylogenetically sound and the protein retains an alpha-crystallin domain characteristic of heat stress responders. Reason: This "response to heat" annotation over-represents an acute heat-stress role that HSP-12.6 does not have. Unlike canonical heat-inducible sHSPs (e.g. the hsp-16 genes), HSP-12.6 is constitutively expressed and is not heat-inducible: its expression is not significantly upregulated by a wide range of stressors (PMID:9139746), and the falcon deep research notes it is often described as constitutively expressed and not strongly heat-inducible. Far from being induced by heat, a 2023 study found hsp-12.6 mRNA was actually downregulated (~49.4% decrease under 35C heat stress) rather than induced. Its in vivo regulation and function are better described through DAF-16/HSF-1 longevity signaling than through an acute heat-shock response. The IBA inference is a phylogenetic carry-over from the broader sHSP family that does not hold for this atypical member, so "response to heat" is an over-annotation. Supporting Evidence: PMID:9139746 Expression of HSP12.6 is limited to the first larval stage of C. elegans and is not significantly up-regulated by a wide range of stressors. file:worm/hsp-12.6/hsp-12.6-deep-research-falcon.md hsp-12.6 is often described as constitutively expressed and not strongly heat-inducible file:worm/hsp-12.6/hsp-12.6-deep-research-falcon.md A 49.4% decrease under 35°C heat stress (p < 0.01)
GO:0042026 protein refolding	IBA GO_REF:0000033	REMOVE	Summary: IBA annotation for protein refolding, inferred phylogenetically primarily from Drosophila sHSP orthologs. However, HSP-12.6 has been experimentally demonstrated to lack chaperone activity in vitro (PMID:9139746). Leroux et al. showed that HSP-12.6 does not function as a molecular chaperone in vitro, being unable to prevent thermally induced aggregation of test substrates. There is also an explicit NOT annotation for GO:0051082 (unfolded protein binding) from the same publication. This annotation is therefore incorrect for HSP-12.6. Reason: HSP-12.6 has been directly demonstrated to lack chaperone activity in vitro (PMID:9139746). It is monomeric rather than forming the large oligomeric complexes required for holdase function. The IBA inference from Drosophila sHSP orthologs does not apply because HSP-12.6 has divergent structural properties (shortest N- and C-terminal regions of any known sHSP, monomeric) that preclude chaperone activity. The NOT annotation for GO:0051082 from the same publication confirms this. The falcon deep research independently corroborates the absence of canonical holdase activity: recombinant HSP-12.6 failed to prevent thermally induced citrate synthase aggregation (reported at 45C), and the monomeric behaviour plus truncated terminal regions are discussed as the mechanistic reason it does not form the higher-order assemblies associated with classical in vitro sHSP holdase activity. Note that falcon also flags reproducible in vivo protective roles (proteostasis/longevity) that are not captured by this in vitro refolding assay; these are addressed under the heat/longevity annotations rather than via a protein refolding (GO:0042026) term. Supporting Evidence: PMID:9139746 HSP12.6 does not function as a molecular chaperone in vitro, since it is unable to prevent the thermally induced aggregation of a test substrate. file:worm/hsp-12.6/hsp-12.6-deep-research-falcon.md did not prevent thermally induced citrate synthase aggregation (reported at 45°C) file:worm/hsp-12.6/hsp-12.6-deep-research-falcon.md the monomeric behavior and truncation of terminal regions are discussed as plausible reasons that HSP-12.6 does not form the higher-order assemblies often associated with classical in vitro sHSP holdase activity
GO:0005737 cytoplasm	IDA PMID:11001875 Association of several small heat-shock proteins with reprod...	ACCEPT	Summary: IDA annotation for cytoplasmic localization based on Ding and Candido 2000 (PMID:11001875). Immunohistochemical analysis showed HSP-12.6 expression in reproductive tissues including spermatheca. This provides direct experimental evidence for cytoplasmic localization. Reason: Direct experimental evidence from immunohistochemistry in C. elegans (PMID:11001875) confirms cytoplasmic localization of HSP-12.6. This is a well-supported cellular component annotation. The falcon deep research adds independent reporter-based support: a phsp-12.6::HSP-12.6::DSRED2 translational fusion shows a punctate pattern in body muscle that does NOT co-localize with a mitochondrial GFP reporter, leading the authors to conclude HSP-12.6 is not mitochondrial (consistent with cytoplasmic localization). Supporting Evidence: PMID:11001875 the tissues expressing the greatest number of smHSPs are vulva (HSP12s, HSP43 and, under stress, HSP16s) and spermatheca (HSP12s, HSP25, HSP43 and, under stress, HSP16s). file:worm/hsp-12.6/hsp-12.6-deep-research-falcon.md is not mitochondrial in muscle cells file:worm/hsp-12.6/hsp-12.6-deep-research-falcon.md more consistent with non-mitochondrial/cytoplasmic localization in that context
GO:0042802 identical protein binding	IPI PMID:9139746 Unique structural features of a novel class of small heat sh...	ACCEPT	Summary: IPI annotation for identical protein binding based on Leroux et al. 1997 (PMID:9139746). The with/from field indicates WB:WBGene00002013, which is hsp-12.6 itself, indicating self-association. Cross-linking and sedimentation velocity analyses from the same study characterized the oligomeric state of HSP-12.6, finding it to be monomeric in solution, though self-interaction may occur transiently. Reason: The IPI annotation with the protein itself as the interacting partner indicates experimentally demonstrated self-association (PMID:9139746). While HSP-12.6 is predominantly monomeric, the cross-linking experiments would detect transient self-interactions. This is a valid molecular function annotation. The falcon deep research corroborates the unusual monomeric state: within the 12-kDa sHSP family, HSP-12.6 is reported as monomeric by sedimentation velocity and cross-linking, contrasting with the common oligomeric nature of many sHSPs. This means any identical protein binding is weak/transient rather than the stable higher-order oligomerization typical of chaperone-active sHSPs. Supporting Evidence: PMID:9139746 Cross-linking and sedimentation velocity analyses indicate that the recombinant HSP12.6 is monomeric file:worm/hsp-12.6/hsp-12.6-deep-research-falcon.md HSP-12.6 is reported as monomeric** by sedimentation velocity and cross-linking, contrasting with the common oligomeric nature of many sHSPs
GO:0051082 unfolded protein binding	IDA NOT PMID:9139746 Unique structural features of a novel class of small heat sh...	ACCEPT	Summary: NOT annotation (negated IDA) for unfolded protein binding based on Leroux et al. 1997 (PMID:9139746). The study directly tested recombinant HSP-12.6 for chaperone activity and found it unable to prevent thermally induced aggregation of test substrates. This negative result is consistent with the structural analysis showing HSP-12.6 is monomeric. GO:0051082 is now formally obsolete, but the negation is still informative as it documents the absence of holdase activity. Reason: This NOT annotation is an important negative result directly demonstrated by experimental evidence (PMID:9139746). HSP-12.6 lacks chaperone activity and does not bind unfolded proteins in a functional sense despite being an sHSP family member. The negation correctly documents this experimentally determined absence of function. The falcon deep research independently summarizes the same negative result (no detectable canonical in vitro chaperone/holdase activity in the standard citrate synthase aggregation assay), supporting retention of this NOT annotation. Supporting Evidence: PMID:9139746 HSP12.6 does not function as a molecular chaperone in vitro, since it is unable to prevent the thermally induced aggregation of a test substrate. file:worm/hsp-12.6/hsp-12.6-deep-research-falcon.md lack detectable chaperone/holdase activity in a standard citrate synthase aggregation assay