hsp-12.6

id: G5EE36
gene_symbol: hsp-12.6
product_type: PROTEIN
status: IN_PROGRESS
taxon:
  id: NCBITaxon:6239
  label: Caenorhabditis elegans
description: >-
  C. elegans HSP-12.6 is a 12.6 kDa member of the small heat shock protein (sHSP/HSP20)
  family. It contains a conserved alpha-crystallin domain but has the shortest N- and
  C-terminal regions of any known sHSP (PMID:9139746). Unlike typical sHSPs, HSP-12.6
  does not form large oligomeric complexes and behaves as a monomer in solution
  (PMID:9139746). Critically, HSP-12.6 does not function as a molecular chaperone in
  vitro, being unable to prevent thermally induced aggregation of test substrates
  (PMID:9139746). Expression is limited to the first larval stage and is not
  significantly upregulated by a wide range of stressors (PMID:9139746). HSP-12.6
  self-associates (identical protein binding) as demonstrated by physical interaction
  with itself (PMID:9139746). Immunohistochemical studies show HSP-12.6 is cytoplasmic
  and associated with reproductive tissues including spermatheca (PMID:11001875).
  Despite lacking in vitro chaperone activity, C. elegans 12 kDa sHSPs play in vivo
  roles in dauer formation, longevity, and reproduction.
existing_annotations:
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    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).
    action: ACCEPT
    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.
- term:
    id: GO:0005634
    label: nucleus
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    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.
    action: KEEP_AS_NON_CORE
    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.
- term:
    id: GO:0009408
    label: response to heat
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    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.
    action: KEEP_AS_NON_CORE
    reason: >-
      While HSP-12.6 is a member of the sHSP family, its expression is not
      significantly upregulated by stress (PMID:9139746), suggesting a reduced role
      in heat stress response compared to canonical sHSPs. The IBA inference is
      phylogenetically supported but the stress-response function may be attenuated
      for this particular family member. Retained as non-core.
    supported_by:
      - reference_id: PMID:9139746
        supporting_text: >-
          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.
- term:
    id: GO:0042026
    label: protein refolding
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    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.
    action: REMOVE
    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.
    supported_by:
      - reference_id: PMID:9139746
        supporting_text: >-
          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.
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IDA
  original_reference_id: PMID:11001875
  review:
    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.
    action: ACCEPT
    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.
    supported_by:
      - reference_id: PMID:11001875
        supporting_text: >-
          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).
- term:
    id: GO:0042802
    label: identical protein binding
  evidence_type: IPI
  original_reference_id: PMID:9139746
  review:
    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.
    action: ACCEPT
    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.
    supported_by:
      - reference_id: PMID:9139746
        supporting_text: >-
          Cross-linking and sedimentation velocity analyses indicate that the
          recombinant HSP12.6 is monomeric
- term:
    id: GO:0051082
    label: unfolded protein binding
  evidence_type: IDA
  original_reference_id: PMID:9139746
  negated: true
  review:
    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
      proposed for obsoletion, but the negation is still informative as it
      documents the absence of holdase activity.
    action: ACCEPT
    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.
    supported_by:
      - reference_id: PMID:9139746
        supporting_text: >-
          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.
references:
- id: GO_REF:0000033
  title: Annotation inferences using phylogenetic trees
  findings: []
- id: PMID:11001875
  title: Association of several small heat-shock proteins with reproductive tissues
    in the nematode Caenorhabditis elegans.
  findings:
    - statement: >-
        Immunohistochemical analysis shows that HSP12 proteins including HSP-12.6
        are expressed in reproductive tissues of C. elegans, particularly vulva
        and spermatheca.
      supporting_text: >-
        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).
- id: PMID:9139746
  title: Unique structural features of a novel class of small heat shock proteins.
  findings:
    - statement: >-
        HSP-12.6 has the shortest N- and C-terminal regions of any known sHSP,
        is monomeric in solution, its expression is limited to the first larval
        stage and is not significantly stress-induced, and it does not function
        as a molecular chaperone in vitro.
      supporting_text: >-
        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.
core_functions:
  - molecular_function:
      id: GO:0042802
      label: identical protein binding
    locations:
      - id: GO:0005737
        label: cytoplasm
    description: >-
      HSP-12.6 is an atypical sHSP that is monomeric in solution and lacks
      chaperone-like activity in vitro (PMID:9139746). It has the shortest
      N- and C-terminal regions of any known sHSP and its expression is limited
      to the first larval stage. Unlike canonical sHSPs, HSP-12.6 does not
      prevent protein aggregation. Its in vivo function may involve
      protein-protein interactions rather than holdase activity. It is expressed
      in reproductive tissues (PMID:11001875).