HSP17.7

id: O81822
gene_symbol: HSP17.7
product_type: PROTEIN
status: DRAFT
taxon:
  id: NCBITaxon:3702
  label: Arabidopsis thaliana
description: >-
  HSP17.7 (also known as At-HSP17.6A in older literature; locus At5g12030) is a 17.7 kDa
  cytosolic class II small heat shock protein (sHSP) in Arabidopsis thaliana. Like other sHSPs,
  it belongs to the HSP20/alpha-crystallin family characterized by a conserved alpha-crystallin
  domain (ACD). sHSPs function as ATP-independent holdase chaperones: they bind unfolding or
  denaturing substrate proteins to prevent irreversible aggregation, maintaining them in a
  soluble, refoldable state, but they do not actively refold substrates. Refolding requires
  subsequent transfer to ATP-dependent chaperone systems such as HSP70/DnaK. HSP17.7 forms
  oligomeric structures typical of sHSPs. Its expression is induced by heat stress and osmotic
  stress, and overexpression confers enhanced salt and drought tolerance. The chaperone
  (holdase) activity has been demonstrated in vitro (PMID:11576425).
existing_annotations:
- term:
    id: GO:0009408
    label: response to heat
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      HSP17.7 is a small heat shock protein whose expression is induced by heat stress
      (PMID:11576425). The IBA annotation is well-supported by phylogenetic inference across
      the HSP20 family, with extensive evidence from multiple plant sHSP orthologs. Response
      to heat is a core biological process for all sHSPs.
    action: ACCEPT
    reason: >-
      Heat shock response is a defining characteristic of sHSPs. The annotation is supported
      by phylogenetic inference (IBA) and corroborated by direct experimental evidence from
      PMID:11576425, which demonstrated heat-inducible expression of this gene.
    supported_by:
      - reference_id: PMID:11576425
        supporting_text: "The At-HSP17.6A expression was induced by heat and osmotic stress, as well as during seed development."

- term:
    id: GO:0051082
    label: unfolded protein binding
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      GO:0051082 (unfolded protein binding) is proposed for obsoletion (go-ontology#30962).
      HSP17.7 is a classic sHSP holdase that binds unfolding proteins to prevent aggregation
      but does not actively refold them (PMID:11576425). Per UPB project decision rules, sHSPs
      should be reannotated to a holdase chaperone activity NTR when created. GO:0140309
      (unfolded protein carrier activity) does not fit because it was created for carrier-holdases
      (TIM chaperones) that escort substrates between compartments, whereas sHSPs are in-situ
      holdases. Retain GO:0051082 until the holdase NTR is available.
    action: MODIFY
    reason: >-
      sHSPs like HSP17.7 are ATP-independent holdases: they bind denaturing proteins to prevent
      aggregation in situ but do not actively refold them. GO:0044183 (protein folding chaperone)
      is inappropriate because sHSPs do not catalyze folding. GO:0140309 does not fit because it
      is carrier-specific (created for TIM chaperones per go-ontology#30552). A general holdase
      chaperone activity NTR is needed. Retain GO:0051082 until this NTR exists.
    proposed_replacement_terms:
      - id: NTR
        label: holdase chaperone activity (NTR needed; GO:0140309 does not fit -- carrier-specific)
    additional_reference_ids:
      - go-ontology#30962
      - go-ontology#30552
    supported_by:
      - reference_id: PMID:11576425
        supporting_text: "The chaperone activity of At-HSP17.6A was demonstrated in vitro."

- term:
    id: GO:0006457
    label: protein folding
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      The annotation of HSP17.7 to GO:0006457 (protein folding) via IBA is phylogenetically
      inferred. sHSPs participate in the broader protein folding pathway by preventing
      aggregation and maintaining substrates in a refoldable state, but they do not themselves
      catalyze folding (that is done by downstream ATP-dependent chaperones like HSP70). The
      involved_in relationship captures the broader pathway participation appropriately,
      though it should be understood that the sHSP contribution is specifically holdase/
      aggregation-prevention rather than active folding.
    action: ACCEPT
    reason: >-
      While sHSPs do not actively fold proteins, they participate in the protein folding process
      by preventing irreversible aggregation and maintaining substrates in a folding-competent
      state. The BP annotation (involved_in protein folding) is acceptable at the process level
      -- the sHSP step is part of the broader protein quality control/folding pathway. The IBA
      annotation is phylogenetically sound for the HSP20 family.

- term:
    id: GO:0009651
    label: response to salt stress
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      The IBA annotation for response to salt stress is supported by phylogenetic inference.
      PMID:11576425 demonstrated that overproduction of At-HSP17.6A (=HSP17.7) increases
      salt tolerance in Arabidopsis, providing direct experimental support for this annotation
      in this specific gene. However, salt stress response is secondary to the core chaperone
      function and represents a stress-responsive phenotype rather than the primary molecular role.
    action: KEEP_AS_NON_CORE
    reason: >-
      Salt stress response is a downstream phenotypic consequence of the holdase chaperone
      function rather than a core molecular activity. The gene is induced under osmotic stress
      and overexpression confers salt tolerance (PMID:11576425), but this reflects the
      protective role of the holdase rather than a salt-specific function. Kept as non-core.
    supported_by:
      - reference_id: PMID:11576425
        supporting_text: "Overproduction of At-HSP17.6A could increase salt and drought tolerance in Arabidopsis."

- term:
    id: GO:0042542
    label: response to hydrogen peroxide
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      The IBA annotation for response to hydrogen peroxide is phylogenetically inferred from
      other plant sHSP orthologs. Oxidative stress can induce sHSP expression and sHSP
      holdase activity can protect against oxidative damage. However, there is no direct
      experimental evidence for HSP17.7 specifically in hydrogen peroxide response. This is
      a plausible but peripheral function.
    action: KEEP_AS_NON_CORE
    reason: >-
      Hydrogen peroxide response is likely a secondary stress-responsive role. The IBA inference
      is phylogenetically reasonable for the sHSP family, but it represents a peripheral stress
      response rather than the core holdase chaperone function. No direct experimental evidence
      for HSP17.7/O81822 specifically.

- term:
    id: GO:0051259
    label: protein complex oligomerization
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      sHSPs characteristically form large oligomeric complexes (typically 12-40mers) that
      dynamically dissociate and reassociate in response to stress. Oligomerization is
      fundamental to sHSP function: substrate binding occurs when the oligomer dissociates
      under stress. UniProt notes for HSP17.7 that it "may form oligomeric structures."
      The IBA annotation is well-supported across the sHSP family.
    action: ACCEPT
    reason: >-
      Oligomerization is a core structural and functional property of sHSPs. The IBA annotation
      is phylogenetically sound and consistent with UniProt annotation. This is integral to
      chaperone mechanism, not a peripheral function.

- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  review:
    summary: >-
      Cytoplasmic localization is inferred from UniProt subcellular location annotation.
      HSP17.7 is described as a cytosolic class II sHSP in the literature (PMID:11576425),
      and UniProt annotates it as cytoplasmic. The more specific cytosol annotation (GO:0005829)
      also exists via TAS. This broader cytoplasm annotation is acceptable and consistent.
    action: ACCEPT
    reason: >-
      Cytoplasmic localization is well-established for this cytosolic class II sHSP. The IEA
      annotation is consistent with the TAS annotation for cytosol and with the published
      characterization of this protein as a cytosolic sHSP (PMID:11576425).

- term:
    id: GO:0006950
    label: response to stress
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  review:
    summary: >-
      This IEA annotation to the general term GO:0006950 (response to stress) is computed
      by ARBA machine learning models. It is a very broad term, and more specific stress
      response terms (response to heat GO:0009408, response to salt stress GO:0009651) are
      already annotated. While not wrong, this general term adds little information beyond
      the more specific annotations.
    action: ACCEPT
    reason: >-
      The broad IEA annotation is correct -- HSP17.7 is a stress-responsive protein. While
      more specific stress annotations exist, the general term from an automated pipeline is
      acceptable and not misleading. IEA annotations at broader levels than what is determined
      by IBA or literature are acceptable.

- term:
    id: GO:0071456
    label: cellular response to hypoxia
  evidence_type: HEP
  original_reference_id: PMID:31519798
  review:
    summary: >-
      This HEP (high-throughput expression pattern) annotation is based on PMID:31519798,
      a multi-omic study of Arabidopsis seedlings under hypoxia. The paper found that hypoxia
      promoted "a progressive upregulation of heat stress transcripts, as evidenced by RNAPII
      binding and increased nuclear RNA." HSP17.7 is a heat stress transcript that was
      progressively upregulated under hypoxia. This is an expression-based annotation with
      the weaker "acts_upstream_of_or_within" qualifier, reflecting that the gene is
      transcriptionally responsive to hypoxia rather than having a demonstrated functional
      role in hypoxia response.
    action: KEEP_AS_NON_CORE
    reason: >-
      The HEP annotation reflects transcriptional upregulation during hypoxia rather than
      a demonstrated functional role. The paper describes progressive upregulation of heat
      stress genes during hypoxia (PMID:31519798), which is a secondary stress cross-talk
      phenomenon. This is a peripheral annotation, not a core function.
    supported_by:
      - reference_id: PMID:31519798
        supporting_text: "Hypoxia promoted a progressive upregulation of heat stress transcripts, as evidenced by RNAPII binding and increased nuclear RNA, with polyadenylated RNA levels only elevated after prolonged stress or reoxygenation."

- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: ISM
  original_reference_id: GO_REF:0000122
  review:
    summary: >-
      This ISM annotation is based on AtSubP (Arabidopsis Subcellular Proteome Prediction)
      computational analysis. Cytoplasmic localization is well-established for this cytosolic
      class II sHSP and is consistent with the IEA and TAS annotations. Duplicate of the
      IEA cytoplasm annotation but from a different computational method.
    action: ACCEPT
    reason: >-
      Consistent with multiple other lines of evidence for cytoplasmic localization. The
      ISM prediction agrees with UniProt subcellular annotation, the TAS cytosol annotation,
      and the characterization as a cytosolic sHSP (PMID:11576425).

- term:
    id: GO:0006457
    label: protein folding
  evidence_type: IDA
  original_reference_id: PMID:11576425
  review:
    summary: >-
      The IDA annotation to protein folding is based on the in vitro chaperone activity
      demonstrated in PMID:11576425. The paper showed that At-HSP17.6A (=HSP17.7, O81822)
      possesses chaperone activity in vitro. However, the sHSP mechanism is holdase-type:
      it prevents aggregation of denaturing substrates but does not actively refold them.
      The "acts_upstream_of_or_within" qualifier used in the GOA is appropriate, as the sHSP
      participates in the protein folding pathway upstream of the actual folding step.
    action: ACCEPT
    reason: >-
      The BP annotation with "acts_upstream_of_or_within" qualifier is appropriate. sHSPs
      participate in the protein quality control and folding pathway by preventing aggregation
      and maintaining substrates for subsequent refolding by HSP70-type foldases. The in vitro
      chaperone assay in PMID:11576425 demonstrated this activity. While sHSPs do not
      themselves fold proteins, involvement in the folding process at the BP level is accurate.
    supported_by:
      - reference_id: PMID:11576425
        supporting_text: "The chaperone activity of At-HSP17.6A was demonstrated in vitro."

- term:
    id: GO:0051082
    label: unfolded protein binding
  evidence_type: IDA
  original_reference_id: PMID:11576425
  review:
    summary: >-
      The IDA annotation to GO:0051082 (unfolded protein binding) is based on the in vitro
      chaperone assay in PMID:11576425, which demonstrated that At-HSP17.6A (=HSP17.7)
      binds denaturing substrate proteins and prevents their aggregation. This is holdase
      activity -- the sHSP binds unfolding proteins without actively refolding them. Per UPB
      project rules, GO:0051082 is proposed for obsoletion and should be replaced with a
      holdase chaperone activity NTR when available. GO:0044183 (protein folding chaperone)
      is NOT appropriate for pure holdases. GO:0140309 is carrier-specific and does not fit
      in-situ holdases.
    action: MODIFY
    reason: >-
      GO:0051082 is being obsoleted (go-ontology#30962). HSP17.7 is a classic sHSP holdase:
      it prevents aggregation of denaturing proteins in situ without active refolding. Per UPB
      project decision rules for sHSPs/holdases, retain GO:0051082 until a holdase chaperone
      activity NTR is created. GO:0044183 is not appropriate (sHSPs do not actively fold).
      GO:0140309 does not fit (carrier-specific, created for TIM chaperones per go-ontology#30552).
    proposed_replacement_terms:
      - id: NTR
        label: holdase chaperone activity (NTR needed; GO:0140309 does not fit -- carrier-specific)
    additional_reference_ids:
      - go-ontology#30962
      - go-ontology#30552
    supported_by:
      - reference_id: PMID:11576425
        supporting_text: "The chaperone activity of At-HSP17.6A was demonstrated in vitro."

- term:
    id: GO:0006972
    label: hyperosmotic response
  evidence_type: IMP
  original_reference_id: PMID:11576425
  review:
    summary: >-
      The IMP annotation is based on PMID:11576425, which demonstrated that overexpression
      of At-HSP17.6A (=HSP17.7) enhanced salt and drought tolerance in Arabidopsis. The gene
      expression is induced by osmotic stress at the mRNA level, though protein accumulation
      was not detected under osmotic stress alone (only under heat). Overexpression conferred
      increased tolerance to hyperosmotic conditions, supporting the IMP evidence. The
      "acts_upstream_of_or_within" qualifier is appropriate.
    action: KEEP_AS_NON_CORE
    reason: >-
      The hyperosmotic response represents a stress-protective phenotype mediated by the
      holdase chaperone activity rather than a core molecular function. The gene is
      transcriptionally induced by osmotic stress, and overexpression confers osmotolerance
      (PMID:11576425), but this is a downstream consequence of the general proteostasis
      function. Kept as non-core.
    supported_by:
      - reference_id: PMID:11576425
        supporting_text: "Overproduction of At-HSP17.6A could increase salt and drought tolerance in Arabidopsis."
      - reference_id: PMID:11576425
        supporting_text: "The At-HSP17.6A expression was induced by heat and osmotic stress, as well as during seed development. Accumulation of At-HSP17.6A proteins could be detected with heat and at a late stage of seed development, but not with osmotic stress"

- term:
    id: GO:0005829
    label: cytosol
  evidence_type: TAS
  original_reference_id: PMID:11576425
  review:
    summary: >-
      The TAS annotation to cytosol is based on the characterization of At-HSP17.6A (=HSP17.7)
      as a "cytosolic class II smHSP" in PMID:11576425. The literature consistently describes
      class II plant sHSPs as cytosolic proteins. This is a more specific localization than
      the broader cytoplasm annotations (IEA, ISM) and is well-supported.
    action: ACCEPT
    reason: >-
      Cytosolic localization is a core feature of this class II sHSP. The TAS evidence from
      PMID:11576425 is consistent with the classification of At-HSP17.6A as a cytosolic
      class II small heat shock protein, and with the broader cytoplasm annotations from
      UniProt and AtSubP prediction.
    supported_by:
      - reference_id: PMID:11576425
        supporting_text: "the gene that encoded the cytosolic class II smHSP in Arabidopsis thaliana (At-HSP17.6A) was characterized."

references:
- id: GO_REF:0000033
  title: Annotation inferences using phylogenetic trees
  findings: []
- id: GO_REF:0000044
  title: Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location
    vocabulary mapping, accompanied by conservative changes to GO terms applied by
    UniProt
  findings: []
- id: GO_REF:0000117
  title: Electronic Gene Ontology annotations created by ARBA machine learning models
  findings: []
- id: GO_REF:0000122
  title: AtSubP analysis
  findings: []
- id: PMID:11576425
  title: At-HSP17.6A, encoding a small heat-shock protein in Arabidopsis, can enhance
    osmotolerance upon overexpression.
  findings: []
- id: PMID:31519798
  title: Integrative Analysis from the Epigenome to Translatome Uncovers Patterns
    of Dominant Nuclear Regulation during Transient Stress.
  findings: []

core_functions:
- description: >-
    HSP17.7 is an ATP-independent holdase chaperone that binds unfolding/denaturing proteins
    to prevent irreversible aggregation, maintaining them in a soluble, refoldable state for
    downstream ATP-dependent chaperones. This is the core molecular function. GO:0051082 is
    used as interim until a holdase NTR is created; GO:0140309 does not fit (carrier-specific).
    GO:0044183 does not fit (sHSPs do not actively refold). Demonstrated by in vitro chaperone
    assay (PMID:11576425).
  molecular_function:
    id: GO:0051082
    label: unfolded protein binding
  directly_involved_in:
  - id: GO:0009408
    label: response to heat
  - id: GO:0006457
    label: protein folding
  locations:
  - id: GO:0005829
    label: cytosol
  supported_by:
  - reference_id: PMID:11576425
    supporting_text: "The chaperone activity of At-HSP17.6A was demonstrated in vitro."
  - reference_id: PMID:11576425
    supporting_text: "the gene that encoded the cytosolic class II smHSP in Arabidopsis thaliana (At-HSP17.6A) was characterized."
- description: >-
    HSP17.7 forms oligomeric complexes characteristic of sHSPs. Oligomerization is essential
    for sHSP chaperone function: the oligomeric storage form dynamically dissociates under
    stress to produce active holdase species that bind denaturing substrates.
  molecular_function:
    id: GO:0051082
    label: unfolded protein binding
  directly_involved_in:
  - id: GO:0051259
    label: protein complex oligomerization
  locations:
  - id: GO:0005829
    label: cytosol
  supported_by:
  - reference_id: PMID:11576425
    supporting_text: "The chaperone activity of At-HSP17.6A was demonstrated in vitro."