Hsp22

Summary: Cytoplasm is consistent with the conserved small heat shock protein function.

Reason: Cytoplasm includes mitochondria and other cytoplasmic organelles; the mitochondrial matrix assignment is compatible with this broad location.

Summary: An additional heat-dependent nuclear pool remains unresolved.

Reason: Actual PTHR45640 topology places Hsp22 below nucleus IBD PTN000897708, with no recovered nuclear-loss event on the target path. Full PMID:10896659 establishes specific mitochondrial colocalization in S2 cells after heat shock/recovery and matrix residence using heterologous fractionation, but does not exhaust other stress/time conditions. The publisher abstract of PMID:6772504 explicitly reports 22-kDa heat-shock protein in nuclear/chromatin/nucleolar preparations; its full band-identity and purity controls remain unavailable. Historical fractionation could reflect true transient localization or contamination. Neither predominant mitochondrial targeting nor lack of a modern nuclear assay alone settles the inherited claim. Focused adjudication is queued.

Summary: Response to heat is consistent with the conserved small heat shock protein function.

Reason: Heat induction and experimentally demonstrated client protection support the conserved heat-response function. Transcript induction alone is not the whole evidence: purified-client protection and stress phenotypes establish active chaperone work.

Summary: Protein refolding is consistent with the conserved small heat shock protein function.

Reason: Hsp22 and Hsp23 bind heat-damaged clients, prevent aggregation and preserve a pool that the ATP-supplemented reticulocyte chaperone machinery can reactivate (full PMID:16572729). This is direct participation in the refolding process even though the small chaperone does not itself drive the later folding reaction. Actual target ancestry agrees with this inference.

Summary: Use the active holdase activity term for the demonstrated client-binding mechanism.

Reason: Live QuickGO confirms that GO:0051082 is obsolete and GO:0140309 is active, named unfolded protein holdase activity. Its definition allows delivery to an acceptor molecule OR a specific location; it does not require transport between compartments. Full PMID:16572729 directly demonstrates client holding and later recovery by the reticulocyte chaperone machinery, with different efficiencies for each small Hsp. The active holdase term captures that activity; replacing the obsolete term with itself or awaiting a new term is unnecessary.

Proposed replacements: unfolded protein holdase activity

Summary: IEA annotation from ARBA for response to heat. Consistent with the IBA and IDA annotations for the same term. Redundant with better-evidenced annotations but not incorrect.

Reason: This IEA annotation is broader but consistent with the IDA and IBA annotations for the same term. Acceptable as redundant support.

Summary: IDA annotation for protein folding based on the Morrow et al. 2006 study demonstrating chaperone-like activity. All four Drosophila sHSPs prevent heat-induced protein aggregation and maintain proteins in a refoldable state (PMID:16572729). This is the parent process term for the more specific protein refolding.

Reason: Hsp22 has demonstrated chaperone-like activity in preventing heat-induced protein aggregation and maintaining substrates in a refoldable state (PMID:16572729). Protein folding is an appropriate broad process annotation for a chaperone.

Summary: Holdase activity is the more precise description of the source experiment.

Reason: GO:0044183 does not define chaperones as necessarily ATP dependent. Its current comment distinguishes folding a client from holding it unfolded. Full PMID:16572729 demonstrates protection during heat treatment followed by reactivation by other chaperones in reticulocyte lysate plus ATP. GO:0140309 captures the small Hsp contribution specifically. Full PMID:26705243 excluded Hsp22 from cellular refolding assays and tested HSP70 knockdown for Hsp27 and CG14207, so those knockdown data should not be described as a direct Hsp22/Hsp23 requirement.

Proposed replacements: unfolded protein holdase activity

Summary: Hsp22 has a well-supported mitochondrial-matrix pool.

Reason: Full PMID:10896659 uses antibody specificity and mitochondrial-marker colocalization in heat-shocked/recovering fly S2 cells. Trypsin protection and complementary NP40/digitonin fractionation of transfected hamster mitochondria place Hsp22 in matrix; import constructs identify essential N-terminal residues. Thus matrix localization is strongly supported, with the native-cell and heterologous assay roles distinguished. This does not imply that all other locations are impossible.

Summary: ISM annotation for protein folding based on sequence model analysis. Li et al. (2009) performed comparative analysis of sHSP genes across insects, identifying conserved alpha-crystallin domains characteristic of chaperone function.

Reason: The ISM evidence from comparative genomic analysis is consistent with experimental evidence (PMID:16572729) demonstrating chaperone activity. The conserved alpha-crystallin domain is the hallmark of sHSP chaperone function.

Summary: Hsp22 forms oligomeric assemblies.

Reason: Full PMID:10896659 sedimentation, gel filtration and cross-linking support Hsp22 self-association. Two antibodies precipitate Hsp22 without the other classical small Hsps under the tested conditions. Self-association is consistent with chaperone assembly, although this study alone does not prove that every observed oligomeric state is essential for activity.

Summary: Use the active holdase activity term for the demonstrated client-binding mechanism.

Reason: Live QuickGO confirms that GO:0051082 is obsolete and GO:0140309 is active, named unfolded protein holdase activity. Its definition allows delivery to an acceptor molecule OR a specific location; it does not require transport between compartments. Full PMID:16572729 directly demonstrates client holding and later recovery by the reticulocyte chaperone machinery, with different efficiencies for each small Hsp. The active holdase term captures that activity; replacing the obsolete term with itself or awaiting a new term is unnecessary.

Proposed replacements: unfolded protein holdase activity

Summary: Use the active holdase activity term for the demonstrated client-binding mechanism.

Reason: Live QuickGO confirms that GO:0051082 is obsolete and GO:0140309 is active, named unfolded protein holdase activity. Its definition allows delivery to an acceptor molecule OR a specific location; it does not require transport between compartments. Full PMID:16572729 directly demonstrates client holding and later recovery by the reticulocyte chaperone machinery, with different efficiencies for each small Hsp. The active holdase term captures that activity; replacing the obsolete term with itself or awaiting a new term is unnecessary.

Proposed replacements: unfolded protein holdase activity

Summary: IDA annotation for response to heat from Vos et al. (2016). This study confirmed that the four classical sHSPs are all highly heat-inducible and compared the entire Drosophila sHSP family for chaperone activities.

Reason: Strongly supported by experimental evidence. Hsp22 is one of the most heat-inducible genes in Drosophila (PMID:26705243, PMID:16572729).

Summary: Hsp22 contributes to protection against oxidative stress.

Reason: Source PMID:14734639 reports increased paraquat resistance after motor-neuron Hsp22 expression. Together with direct protein-protection activity, this supports the stress-response function. Mitochondrial localization alone would only suggest the role; no specific endogenous oxidized client is identified by this experiment.

Summary: IMP annotation for determination of adult lifespan. Overexpression of Hsp22 extends lifespan in Drosophila, as demonstrated by multiple studies (PMID:14734639, PMID:15331597).

Reason: Lifespan extension upon overexpression is well-documented but represents a pleiotropic phenotypic outcome of enhanced proteostasis rather than a core molecular function. This is a non-core biological process annotation.

Summary: IMP annotation for response to heat based on mutant phenotype evidence. Overexpression of Hsp22 confers thermotolerance.

Reason: Consistent with the core function of Hsp22 as a heat-inducible sHSP. Redundant with IDA and IBA annotations for the same term but represents independent evidence.

Summary: Reduced Hsp22 expression shortens adult lifespan in the source model.

Reason: PMID:15331597 reports a loss-of-expression phenotype, rather than another overexpression experiment. Retain lifespan as a contextual organismal consequence of Hsp22-dependent protection; the assay does not identify a distinct lifespan-control molecular activity.