cryaa encodes zebrafish alpha-crystallin A chain, a 173-residue member of the small heat shock protein (HSP20) family built around a central alpha-crystallin domain. It is a soluble cytoplasmic protein expressed at high level in the lens and only marginally elsewhere, where it accumulates to the very high concentrations that make crystallins the bulk structural protein of the lens and set its refractive properties. It also acts as an ATP-independent holdase chaperone: it binds proteins that are beginning to unfold and holds them in a soluble state, preventing their aggregation, an activity whose strength depends on exposed hydrophobic surface and on temperature. In the lens these two roles are the same role, since keeping gamma-crystallins soluble is what preserves transparency; loss of alphaA-crystallin in zebrafish gives abnormal, more reflective lenses and impaired fibre-cell differentiation, and restoring it rescues both.
Definition: Binding to an unfolded or misfolded protein to prevent its aggregation without actively catalyzing refolding. The holdase maintains the client protein in a soluble, folding-competent state. This is mechanistically distinct from foldase activity (GO:0044183) and from carrier-holdase activity (GO:0140309).
Justification: cryaa is the lens-dominant zebrafish alphaA-crystallin, whose recombinant protein suppresses aggregation of model client proteins without ATP or refolding. Obsolete GO:0051082 captured binding only; GO:0044183 requires assisting folding, and GO:0140309 (relabelled 'unfolded protein holdase activity') keeps a carrier-specific definition requiring escort to an acceptor molecule or location, which is not demonstrated here. See go-ontology#30552. The same request is made for the paralogs cryaba and cryabb.
Parent term: molecular_function
Supporting Evidence:
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0042026 protein refolding | IBA GO_REF:0000033 | MARK AS OVER ANNOTATED | Summary: Protein refolding, propagated from the broad small heat shock protein node PTN000897708 (Drosophila Hsp22/23/26/27 and related members). Alpha-crystallins bind denaturing proteins and hold them soluble; restoring activity to the client is done by ATP-dependent chaperone systems, not by the sHSP itself. Reason: Every assay of zebrafish alphaA-crystallin measures prevention of aggregation, not recovery of client activity, and the protein is ATP-independent. Holding an unfolded client in a soluble state contributes to refolding by other chaperones but is not itself the refolding step; GO:0140309 unfolded protein holdase activity, annotated here by IDA, is the term that names what this gene product does. Not wrong at the family level but an over-reach for a lens crystallin. Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: ROLE CONFLATION GRANULARITY MISMATCH Sources checked: PANTHER:PTN000897708 SUPPORTS SOURCE BUT NOT TARGET Ancestral sHSP node placement is sound for chaperone-like function, but the refolding process term ascribes to the sHSP a step performed by the ATP-dependent chaperones it hands clients to. Supporting Evidence: PMID:15692462 The chaperone-like activities of zebrafish and human alpha-crystallins were compared by assaying their ability to prevent the chemically induced aggregation of several target proteins at temperatures between 25 degrees C and 40 degrees C PMID:22479631 ability to prevent the chemically induced aggregation of insulin and/or lactalbumin PMID:22479631 Small heat shock proteins (sHsps) maintain cellular homeostasis by preventing stress and disease-induced protein aggregation |
| GO:0005634 nucleus | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Nucleus: reported for mammalian alpha-crystallins under stress and inherited here by propagation and by the UniProt location mapping; no zebrafish data address nuclear localization. Node PTN000897708. Reason: Nuclear pools of alpha-crystallins are documented in mammalian cell culture, and zebrafish cryaa is inside the clade the node covers, so the annotation is not unfounded. But the gene product is overwhelmingly a lens cytoplasmic protein in this species, with expression essentially confined to the lens, so a nuclear role is not core. Supporting Evidence: file:DANRE/cryaa/cryaa-uniprot.txt SUBCELLULAR LOCATION: Cytoplasm {ECO:0000256|ARBA:ARBA00004496}. Nucleus PMID:11925526 We detected high expression of zebrafish alphaA-crystallin in the lens and very low expression in liver and spleen PMID:11925526 These data suggest that zebrafish alphaA-crystallin plays a physiologically limited role outside of the zebrafish lens, similar to its mammalian orthologues file:DANRE/cryaa/cryaa-deep-research-falcon.md I did **not** find direct experimental evidence specifying Cryaaβs **subcellular localization** (e.g., cytosolic vs membraneβbound fractions, nuclear association) in zebrafish lens cells |
| GO:0005737 cytoplasm | IBA GO_REF:0000033 | ACCEPT | Summary: Cytoplasm: alphaA-crystallin is a soluble cytoplasmic protein that accumulates to very high concentration in the cytoplasm of lens fibre cells. Node PTN000897708, with zebrafish cryaa itself among the descendants seeding it. Reason: All chaperone assays use the soluble recombinant protein, the lens function requires it to be dispersed in fibre cell cytoplasm, and UniProt assigns cytoplasm. This is the location where the holdase and lens structural roles are executed. Supporting Evidence: file:DANRE/cryaa/cryaa-uniprot.txt SUBCELLULAR LOCATION: Cytoplasm {ECO:0000256|ARBA:ARBA00004496}. Nucleus PMID:11925526 We detected high expression of zebrafish alphaA-crystallin in the lens and very low expression in liver and spleen PMID:16728471 Crystallins are the major structural proteins in mouse, human and zebrafish lens |
| GO:0043066 negative regulation of apoptotic process | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Negative regulation of apoptotic process, propagated from node PTN002264124 (mouse Cryab/Cryaa, rat and human alphaA/alphaB-crystallins). Anti-apoptotic activity of alpha-crystallins is documented in mammalian cells; no zebrafish evidence exists. Reason: The node placement is defensible - the anti-apoptotic behaviour is reported for several mammalian donors - and it plausibly follows from the same substrate-holding activity applied to apoptotic regulators. But for zebrafish cryaa, whose expression is essentially lens-restricted, this is a peripheral consequence of chaperone function rather than a core process. Supporting Evidence: PMID:11925526 These data suggest that zebrafish alphaA-crystallin plays a physiologically limited role outside of the zebrafish lens, similar to its mammalian orthologues PMID:22479631 Small heat shock proteins (sHsps) maintain cellular homeostasis by preventing stress and disease-induced protein aggregation PMID:16728471 AlphaA-crystallin is a chaperone that protects proteins from misfolding and becoming insoluble |
| GO:0009408 response to heat | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Response to heat, propagated from node PTN000897708, whose donors are largely inducible small heat shock proteins of Drosophila and C. elegans. Zebrafish alphaA-crystallin is a constitutive lens protein; what the literature shows is that its chaperone-like activity and thermal stability track physiological temperature, not that the gene responds to heat stimulus. Reason: The family relationship is real and the protein does function as a stress chaperone, so the term is not wrong at family level. But the evidence in this lineage is about temperature adaptation of an always-expressed lens protein - zebrafish crystallins denature at lower temperatures than mammalian ones, and substituting cold-adapted residues changes activity - rather than about heat induction. Kept as non-core. Propagation Review Root cause: NO FAILURE NON CORE Failure modes: CONTEXT OR TISSUE MISMATCH Sources checked: PANTHER:PTN000897708 SUPPORTS SOURCE BUT NOT TARGET Node is seeded mainly by heat-inducible invertebrate sHSPs; the vertebrate lens alphaA-crystallin branch is constitutively expressed, so the heat-response framing fits the donors better than the target. Supporting Evidence: PMID:15692462 The denaturation temperatures of zebrafish crystallins were lower than those of mammals. PMID:22479631 Altering hydrophobicity of specific zebrafish PMID:22479631 Small heat shock proteins (sHsps) maintain cellular homeostasis by preventing stress and disease-induced protein aggregation |
| GO:0002088 lens development in camera-type eye | IBA GO_REF:0000033 | ACCEPT | Summary: Lens development in camera-type eye: loss of zebrafish alphaA-crystallin produces lens abnormalities, and the knockout line shows a more severe and consistent phenotype than morphants. Node PTN002900910, with zebrafish cryaa among the seeding descendants. Reason: The gene product does work in the process rather than merely being required for it: it is one of the major structural proteins of the lens and keeps gamma-crystallins soluble, and restoring it rescues lens transparency and fibre-cell differentiation. Core process for this gene. Supporting Evidence: PMID:26149094 A more consistent and severe lens phenotype was evident in maternal/zygotic PMID:26149094 These findings demonstrate that the role of PMID:16728471 these results indicate that alphaA-crystallin expression is required for normal lens development |
| GO:0005212 structural constituent of eye lens | IEA GO_REF:0000002 | ACCEPT | Summary: Structural constituent of eye lens: alphaA-crystallin is one of the major structural proteins of the zebrafish lens, expressed there at high level and almost nowhere else. Mapped from InterPro IPR003090 (alpha-crystallin). Reason: Crystallins are the bulk protein of the vertebrate lens and set its refractive properties; zebrafish alphaA-crystallin is high in lens and very low elsewhere, and its loss makes the lens abnormal. Core molecular function alongside the holdase activity. Supporting Evidence: PMID:16728471 Crystallins are the major structural proteins in mouse, human and zebrafish lens PMID:11925526 We detected high expression of zebrafish alphaA-crystallin in the lens and very low expression in liver and spleen PMID:26149094 A more consistent and severe lens phenotype was evident in maternal/zygotic |
| GO:0005634 nucleus | IEA GO_REF:0000044 | KEEP AS NON CORE | Summary: Nucleus: reported for mammalian alpha-crystallins under stress and inherited here by propagation and by the UniProt location mapping; no zebrafish data address nuclear localization. UniProtKB-SubCell mapping of the same UniProt line. Reason: Nuclear pools of alpha-crystallins are documented in mammalian cell culture, and zebrafish cryaa is inside the clade the node covers, so the annotation is not unfounded. But the gene product is overwhelmingly a lens cytoplasmic protein in this species, with expression essentially confined to the lens, so a nuclear role is not core. Supporting Evidence: file:DANRE/cryaa/cryaa-uniprot.txt SUBCELLULAR LOCATION: Cytoplasm {ECO:0000256|ARBA:ARBA00004496}. Nucleus PMID:11925526 We detected high expression of zebrafish alphaA-crystallin in the lens and very low expression in liver and spleen PMID:11925526 These data suggest that zebrafish alphaA-crystallin plays a physiologically limited role outside of the zebrafish lens, similar to its mammalian orthologues file:DANRE/cryaa/cryaa-deep-research-falcon.md I did **not** find direct experimental evidence specifying Cryaaβs **subcellular localization** (e.g., cytosolic vs membraneβbound fractions, nuclear association) in zebrafish lens cells |
| GO:0005737 cytoplasm | IEA GO_REF:0000120 | ACCEPT | Summary: Cytoplasm: alphaA-crystallin is a soluble cytoplasmic protein that accumulates to very high concentration in the cytoplasm of lens fibre cells. ARBA and UniProt subcellular-location mapping. Reason: All chaperone assays use the soluble recombinant protein, the lens function requires it to be dispersed in fibre cell cytoplasm, and UniProt assigns cytoplasm. This is the location where the holdase and lens structural roles are executed. Supporting Evidence: file:DANRE/cryaa/cryaa-uniprot.txt SUBCELLULAR LOCATION: Cytoplasm {ECO:0000256|ARBA:ARBA00004496}. Nucleus PMID:11925526 We detected high expression of zebrafish alphaA-crystallin in the lens and very low expression in liver and spleen PMID:16728471 Crystallins are the major structural proteins in mouse, human and zebrafish lens |
| GO:0002088 lens development in camera-type eye | IMP PMID:26149094 A conserved role of Ξ±A-crystallin in the development of the ... | ACCEPT | Summary: Lens development in camera-type eye: loss of zebrafish alphaA-crystallin produces lens abnormalities, and the knockout line shows a more severe and consistent phenotype than morphants. Morpholino knockdown of alphaA-, alphaBa- and alphaBb-crystallin plus a maternal/zygotic alphaA-crystallin knockout line. Reason: The gene product does work in the process rather than merely being required for it: it is one of the major structural proteins of the lens and keeps gamma-crystallins soluble, and restoring it rescues lens transparency and fibre-cell differentiation. Core process for this gene. Supporting Evidence: PMID:26149094 we have carried out morpholino-mediated knockdown of PMID:26149094 A more consistent and severe lens phenotype was evident in maternal/zygotic PMID:26149094 These findings demonstrate that the role of |
| GO:0140309 unfolded protein holdase activity | IDA PMID:22479631 Functional validation of hydrophobic adaptation to physiolog... | MODIFY | Summary: Unfolded protein holdase activity: recombinant zebrafish alphaA-crystallin prevents the chemically induced aggregation of denaturing target proteins in vitro, the defining ATP-independent small heat shock protein activity. Insulin and alpha-lactalbumin aggregation assays across a temperature range, with point mutants showing that specific hydrophobic residues set the activity level. Reason: Directly demonstrated with the zebrafish protein in both cited studies, and it is the activity that explains the lens phenotype, since alphaA-crystallin keeps gamma-crystallin soluble in vivo. Core molecular function. The term itself is the problem rather than the evidence: GO:0140309 retains a carrier definition requiring escort of the client to an acceptor molecule or location (go-ontology#30552), which was not measured. The replacement is the proposed holdase chaperone activity term listed under proposed_new_terms, the same request carried by the paralogs cryaba and cryabb; when GO creates it this row should move to it. Proposed replacements: holdase chaperone activity Supporting Evidence: PMID:15692462 The chaperone-like activities of zebrafish and human alpha-crystallins were compared by assaying their ability to prevent the chemically induced aggregation of several target proteins at temperatures between 25 degrees C and 40 degrees C PMID:22479631 ability to prevent the chemically induced aggregation of insulin and/or lactalbumin PMID:16728471 AlphaA-crystallin is a chaperone that protects proteins from misfolding and becoming insoluble |
| GO:0001654 eye development | IDA PMID:16728471 AlphaA-crystallin expression prevents gamma-crystallin insol... | MODIFY | Summary: Eye development (acts_upstream_of_or_within) from the cloche cataract study, in which the lens is deficient in alphaA-crystallin and overexpression of alphaA-crystallin rescues the lens phenotype. The evidence is specifically about the lens, not the eye as a whole. Reason: The experiment measures lens reflectance, gamma-crystallin solubility and fibre-cell differentiation - all lens - and the same paper concludes that alphaA-crystallin expression is required for normal lens development. The more precise lens development term, already annotated by IMP and IBA, is the right level; the general eye development term over-generalizes a lens-specific result. Proposed replacements: lens development in camera-type eye Supporting Evidence: PMID:16728471 Overexpression of exogenous alphaA-crystallin rescued the cloche lens phenotype, including solubilization of gamma-crystallin, increased lens transparency and induction of lens fiber cell differentiation PMID:16728471 these results indicate that alphaA-crystallin expression is required for normal lens development PMID:16728471 Crystallins are the major structural proteins in mouse, human and zebrafish lens |
| GO:0140309 unfolded protein holdase activity | IDA PMID:15692462 Zebrafish alpha-crystallins: protein structure and chaperone... | MODIFY | Summary: Unfolded protein holdase activity: recombinant zebrafish alphaA-crystallin prevents the chemically induced aggregation of denaturing target proteins in vitro, the defining ATP-independent small heat shock protein activity. Insulin and other chemically denatured targets, assayed between 25 and 40 degrees C; alphaA-crystallin was far more active than zebrafish alphaB-crystallin. Reason: Directly demonstrated with the zebrafish protein in both cited studies, and it is the activity that explains the lens phenotype, since alphaA-crystallin keeps gamma-crystallin soluble in vivo. Core molecular function. The term itself is the problem rather than the evidence: GO:0140309 retains a carrier definition requiring escort of the client to an acceptor molecule or location (go-ontology#30552), which was not measured. The replacement is the proposed holdase chaperone activity term listed under proposed_new_terms, the same request carried by the paralogs cryaba and cryabb; when GO creates it this row should move to it. Proposed replacements: holdase chaperone activity Supporting Evidence: PMID:15692462 The chaperone-like activities of zebrafish and human alpha-crystallins were compared by assaying their ability to prevent the chemically induced aggregation of several target proteins at temperatures between 25 degrees C and 40 degrees C PMID:22479631 ability to prevent the chemically induced aggregation of insulin and/or lactalbumin PMID:16728471 AlphaA-crystallin is a chaperone that protects proteins from misfolding and becoming insoluble |
| GO:0005212 structural constituent of eye lens | NAS PMID:11925526 Sequence and spatial expression of zebrafish (Danio rerio) a... | ACCEPT | Summary: Structural constituent of eye lens: alphaA-crystallin is one of the major structural proteins of the zebrafish lens, expressed there at high level and almost nowhere else. Asserted in the zebrafish cloning and expression paper, which measured the lens-restricted expression pattern. Reason: Crystallins are the bulk protein of the vertebrate lens and set its refractive properties; zebrafish alphaA-crystallin is high in lens and very low elsewhere, and its loss makes the lens abnormal. Core molecular function alongside the holdase activity. Supporting Evidence: PMID:16728471 Crystallins are the major structural proteins in mouse, human and zebrafish lens PMID:11925526 We detected high expression of zebrafish alphaA-crystallin in the lens and very low expression in liver and spleen PMID:26149094 A more consistent and severe lens phenotype was evident in maternal/zygotic |
| GO:0007601 visual perception | NAS PMID:11925526 Sequence and spatial expression of zebrafish (Danio rerio) a... | MARK AS OVER ANNOTATED | Summary: Visual perception, asserted without stated experimental support in the cloning paper. Cryaa is required for a transparent lens, which light must pass through, but it does no work in phototransduction or in the neural processing of a visual stimulus. Reason: Failing the participation test: the term covers receiving a visual stimulus, converting it to a molecular signal and recognizing it, none of which cryaa performs. Its contribution is upstream and structural, and is already captured by the structural constituent of eye lens and lens development annotations. Not wrong as a statement about consequences, but an over-annotation of the gene product. Supporting Evidence: PMID:11925526 We detected high expression of zebrafish alphaA-crystallin in the lens and very low expression in liver and spleen PMID:16728471 Crystallins are the major structural proteins in mouse, human and zebrafish lens PMID:11925526 These data suggest that zebrafish alphaA-crystallin plays a physiologically limited role outside of the zebrafish lens, similar to its mammalian orthologues |
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Download this section (compressed HTML)Q: Does GO:0140309 unfolded protein holdase activity, whose definition describes a carrier that escorts an unfolded client to an acceptor or location, correctly describe a small heat shock protein that simply retains clients in a soluble state? The term is what GOA now uses for cryaa after GO:0051082 was obsoleted, but the escort clause does not match the sHSP mechanism (see go-ontology issue 30552).
Q: Is any function of zebrafish cryaa exercised outside the lens? Expression is high in lens and very low in liver and spleen, which leaves the inherited anti-apoptotic and heat-response annotations without a tissue context in this species.
Experiment: Quantify gamma- and beta-crystallin solubility and lens transparency in the maternal/zygotic cryaa knockout across development, to test directly whether the lens phenotype follows from loss of holdase activity rather than from loss of bulk structural protein.
Experiment: Introduce point mutations that reduce holdase activity without altering expression level (using the hydrophobicity variants already characterized in vitro) into the endogenous locus, separating the chaperone and structural contributions of cryaa in vivo.
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