cryabb

Proposed New Ontology Terms

holdase chaperone activity

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: cryabb: cryabb is the broadly expressed zebrafish alphaB-crystallin paralog that retained the widespread protective function of mammalian CRYAB after gene duplication (PMID:16420472). 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.

Parent term: molecular_function

Supporting Evidence:

PMID:16420472 : The chaperone-like activity of purified recombinant alphaB2 protein was assayed by measuring its ability to prevent the chemically induced aggregation of alpha-lactalbumin and lysozyme
PMID:16420472 : At 25 degrees C and 30 degrees C, zebrafish alphaB2 showed greater chaperone-like activity than human alphaB-crystallin

Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0043066 negative regulation of apoptotic process	IBA GO_REF:0000033	KEEP AS NON CORE	Summary: IBA annotation based on phylogenetic inference from mammalian alpha-crystallins (CRYAA, CRYAB, HSPB1) which have documented anti-apoptotic roles. cryabb retains the broad expression pattern and protective functions of mammalian CRYAB (PMID:16420472), making this inference more applicable than for the lens-specific cryaba paralog. However, anti-apoptosis is a downstream biological process rather than a core molecular function. Reason: Anti-apoptotic activity is a recognized function of the sHSP family and is more relevant for cryabb than cryaba given that cryabb retained the widespread protective role of mammalian CRYAB (PMID:16420472). However, this represents a downstream biological process rather than a core molecular function. Retained as non-core.
GO:0005737 cytoplasm	IBA GO_REF:0000033	ACCEPT	Summary: IBA annotation for cytoplasmic localization, inferred phylogenetically from multiple sHSP orthologs. Consistent with the known biology of alpha-crystallins as cytoplasmic proteins. Reason: Cytoplasmic localization is well-established for alpha-crystallins and sHSPs. The IBA inference is phylogenetically sound and consistent with IEA annotations. Falcon deep research independently supports a primary cytosolic site of action. Supporting Evidence: file:DANRE/cryabb/cryabb-deep-research-falcon.md crystallins are described as soluble cytoplasmic proteins in vertebrate optical tissues, supporting a primary intracellular/cytosolic localization
GO:0005634 nucleus	IBA GO_REF:0000033	KEEP AS NON CORE	Summary: IBA annotation for nuclear localization based on phylogenetic inference from mammalian sHSPs that translocate to the nucleus under stress conditions. Nuclear localization is not the primary site of action for alpha-crystallins. 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. Retained as non-core.
GO:0009408 response to heat	IBA GO_REF:0000033	ACCEPT	Summary: IBA annotation for heat stress response, inferred phylogenetically from multiple sHSP orthologs. cryabb belongs to the sHSP/HSP20 family and has robust chaperone-like activity (PMID:16420472), maintaining the widespread protective role of mammalian CRYAB. This is a well-supported annotation. Reason: cryabb is a member of the sHSP family with demonstrated chaperone-like activity (PMID:16420472). It retained the broad protective function of mammalian CRYAB after gene duplication. Response to heat is a core function for this protein. Falcon deep research adds zebrafish-specific quantitative evidence that cryabb is heat-shock inducible in a stage-dependent manner. Supporting Evidence: file:DANRE/cryabb/cryabb-deep-research-falcon.md heat shock (1 h at 37°C) produced modest, stage-dependent changes in cryabb expression file:DANRE/cryabb/cryabb-deep-research-falcon.md approximately 2.5-fold at 12 hpf, 1.7-fold at 24 hpf, decreased at 48 hpf, and minimal change by 5 dpf
GO:0042026 protein refolding	IBA GO_REF:0000033	MODIFY	Summary: IBA annotation for protein refolding, inferred primarily from Drosophila sHSP orthologs. Alpha-crystallins function as holdases rather than foldases -- they prevent aggregation of denaturing proteins but do not actively refold them. cryabb has robust chaperone-like (holdase) activity at physiological temperatures (PMID:16420472). The protein refolding term is inaccurate for a holdase. Reason: Alpha-crystallins are holdase chaperones that prevent aggregation of unfolded proteins but do not catalyze refolding. GO:0042026 implies active refolding activity, which is inaccurate for cryabb. GO:0140309 (unfolded protein carrier activity) is not appropriate because it is carrier-specific (per go-ontology#30552). The replacement is the proposed holdase chaperone activity NTR (see proposed_new_terms). Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: GRANULARITY MISMATCH FUNCTIONAL DIVERGENCE Sources checked: PANTHER:PTN000897708 · sHSP / alpha-crystallin ancestral node (PTHR45620) SUPPORTS TRANSFER Descent from this sHSP node correctly transfers chaperone involvement, but GO:0042026 (protein refolding) overstates a foldase activity that cryabb lacks; it is an ATP-independent holdase preventing aggregation without refolding. FB:FBgn0001226 · Drosophila small heat-shock protein donor SUPPORTS TRANSFER Representative Drosophila sHSP donor seeding the node; holdase-vs-foldase distinction not captured by the term. Proposed replacements: holdase chaperone activity Supporting Evidence: PMID:16420472 At 25 degrees C and 30 degrees C, zebrafish alphaB2 showed greater chaperone-like activity than human alphaB-crystallin, and at 35 degrees C and 40 degrees C, the human protein provided greater protection against aggregation. file:DANRE/cryabb/cryabb-deep-research-falcon.md the primary function is best described as an ATP-independent chaperone-like holdase that maintains proteostasis by suppressing protein aggregation
GO:0051082 unfolded protein binding	IBA GO_REF:0000033	MODIFY	Summary: IBA annotation for unfolded protein binding based on phylogenetic inference from multiple sHSP orthologs. GO:0051082 is now formally obsolete. cryabb has demonstrated chaperone-like activity (PMID:16420472). The holdase function should be captured by GO:0140309. Reason: GO:0051082 is now formally obsolete. The holdase activity of cryabb has been demonstrated by in vitro chaperone assays showing robust prevention of substrate aggregation (PMID:16420472). GO:0140309 (unfolded protein carrier activity) is not appropriate because it is carrier-specific (per go-ontology#30552). The replacement is the proposed holdase chaperone activity NTR (see proposed_new_terms). Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: GRANULARITY MISMATCH Sources checked: PANTHER:PTN000897708 · sHSP / alpha-crystallin ancestral node (PTHR45620) SUPPORTS TRANSFER The node is well supported for unfolded-protein binding across sHSP orthologs, so the transfer itself is sound. The issue is term scoping: GO:0051082 is proposed for obsoletion, so the term (not the propagation) needs updating. UniProtKB:P02511 · Human alphaB-crystallin (CRYAB) SUPPORTS TRANSFER Experimentally characterized alphaB-crystallin ortholog donor supporting holdase / unfolded-protein binding. Proposed replacements: holdase chaperone activity Supporting Evidence: PMID:16420472 At 25 degrees C and 30 degrees C, zebrafish alphaB2 showed greater chaperone-like activity than human alphaB-crystallin, and at 35 degrees C and 40 degrees C, the human protein provided greater protection against aggregation. file:DANRE/cryabb/cryabb-deep-research-falcon.md cryabb is not an enzyme or transporter file:DANRE/cryabb/cryabb-deep-research-falcon.md αB-crystallins (including cryabb) are discussed as contributing to protein quality control and cytoskeletal stabilization
GO:0005198 structural molecule activity	IEA GO_REF:0000117	ACCEPT	Summary: IEA annotation based on ARBA machine learning models. cryabb has the more specific annotation GO:0005212 (structural constituent of eye lens) from IEA, and its primary molecular function is holdase chaperone activity rather than a generic structural role. However, cryabb does have expression in the lens and the UniProt keyword KW-0273 (Eye lens protein) is annotated. Reason: While GO:0005198 is general, it is not incorrect -- cryabb contributes to structural integrity in multiple tissues including lens and muscle. The more specific term GO:0005212 is also annotated. Acceptable as an IEA inference.
GO:0005212 structural constituent of eye lens	IEA GO_REF:0000120	KEEP AS NON CORE	Summary: IEA annotation based on InterPro domain match (IPR003090 Alpha-crystallin_N) and UniProt keyword (KW-0273 Eye lens protein). cryabb is expressed in the lens and contributes to lens transparency (PMID:38705506), though its primary role is in broad tissue protection rather than lens structure. Reason: cryabb does contribute to lens transparency (PMID:38705506), but unlike cryaba, it retained the broad expression and protective function of mammalian CRYAB (PMID:16420472). The structural lens role is secondary to its widespread chaperone function. Falcon deep research reinforces that cryabb is best annotated as an intracellular stress-response chaperone rather than a structural refractive crystallin, with its early lens contribution being limited and context-dependent. Retained as non-core. Supporting Evidence: file:DANRE/cryabb/cryabb-deep-research-falcon.md cryabb is best annotated as an intracellular, ATP-independent sHSP chaperone supporting proteostasis and stress tolerance rather than a structural refractive crystallin essential for early lens development file:DANRE/cryabb/cryabb-deep-research-falcon.md its lens contribution in early development is limited compared with cryaa
GO:0005737 cytoplasm	IEA GO_REF:0000117	ACCEPT	Summary: IEA annotation for cytoplasmic localization based on ARBA machine learning models. Consistent with the IBA annotation for the same term. Reason: Cytoplasmic localization is well-established. This IEA annotation is consistent with the IBA annotation. Acceptable as automated confirmation.
GO:0009892 negative regulation of metabolic process	IEA GO_REF:0000117	MARK AS OVER ANNOTATED	Summary: IEA annotation based on ARBA machine learning models. This is a very broad biological process term. Alpha-crystallins can regulate metabolic processes through their chaperone activity, but GO:0009892 is too general to be informative. Reason: GO:0009892 (negative regulation of metabolic process) is excessively broad and uninformative. While sHSPs can influence metabolic processes indirectly through their chaperone activity, this IEA annotation does not capture any specific function of cryabb. The annotation likely reflects a generic ARBA prediction from sequence features shared by many proteins.
GO:0043066 negative regulation of apoptotic process	IEA GO_REF:0000117	KEEP AS NON CORE	Summary: IEA annotation for negative regulation of apoptotic process based on ARBA machine learning models. Consistent with the IBA annotation for the same term and the known anti-apoptotic function of mammalian CRYAB. Reason: This IEA annotation is consistent with the IBA annotation for the same term. The anti-apoptotic function is well-established for mammalian CRYAB and likely conserved in cryabb. However, this is a downstream biological process rather than a core molecular function. Retained as non-core consistent with the IBA.
GO:0046872 metal ion binding	IEA GO_REF:0000043	MODIFY	Summary: IEA annotation based on UniProt keyword mapping (KW-0479 Metal-binding). The UniProt entry has keywords for zinc and metal-binding based on ARBA evidence. While the annotation is technically correct, it is very general. The more specific term GO:0008270 (zinc ion binding) would be more informative. Reason: The annotation is too general. UniProt keywords indicate zinc binding for this protein. A more specific term would be more informative. Proposed replacements: zinc ion binding
GO:0036438 maintenance of lens transparency	IMP PMID:38705506 Loss of αBa-crystallin, but not αA-crystallin, increases age...	KEEP AS NON CORE	Summary: IMP annotation for maintenance of lens transparency based on Posner et al. 2024 (PMID:38705506). The study examined individual mutant zebrafish lines for all three alpha-crystallin genes. While the primary finding was that cryaba loss led to the greatest increase in cataract, the study also evaluated cryabb mutants for lens transparency. cryabb contributes to lens maintenance but its primary role is in broad tissue protection. Reason: The experimental evidence from PMID:38705506 supports a role for cryabb in lens transparency maintenance. However, cryabb's primary function is as a broadly expressed protective chaperone (PMID:16420472), and its lens role is secondary compared to cryaba. Retained as non-core. Supporting Evidence: PMID:38705506 zebrafish express one lens-specific alphaA-crystallin gene (cryaa), they express two alphaB-crystallin genes, with one evolving lens specificity (cryaba) and the other retaining the broad expression of its mammalian ortholog (cryabb). file:DANRE/cryabb/cryabb-deep-research-falcon.md about ~30% of cryabb−/− embryos having lens defects at 4 dpf file:DANRE/cryabb/cryabb-deep-research-falcon.md This should be reflected in annotation as “context-dependent lens clarity support,” not as an absolute developmental requirement
GO:0007519 skeletal muscle tissue development	IMP PMID:25866181 In vivo characterization of human myofibrillar myopathy gene...	ACCEPT	Summary: IMP annotation for skeletal muscle tissue development based on Buhrdel et al. 2015 (PMID:25866181). Morpholino knockdown of MFM disease genes including cryabb led to compromised skeletal muscle function due to myofibrillar degeneration. This is more relevant for cryabb than cryaba because cryabb retains the broad muscle expression of mammalian CRYAB (PMID:16420472). Reason: cryabb retains the widespread expression including muscle tissue that is characteristic of mammalian CRYAB (PMID:16420472). The morpholino knockdown evidence (PMID:25866181) supports a direct role in skeletal muscle tissue development/maintenance. This is a core function for cryabb. Supporting Evidence: PMID:25866181 targeted ablation of MFM genes in zebrafish led to compromised skeletal muscle function mostly due to myofibrillar degeneration as well as severe heart failure. file:DANRE/cryabb/cryabb-deep-research-falcon.md cryabb (αBb) is described as more widely expressed than cryaba, including lens, muscle, and brain
GO:0007626 locomotory behavior	IMP PMID:25866181 In vivo characterization of human myofibrillar myopathy gene...	KEEP AS NON CORE	Summary: IMP annotation for locomotory behavior based on Buhrdel et al. 2015 (PMID:25866181). Morpholino knockdown of cryabb led to compromised skeletal muscle function affecting locomotion. Reason: The locomotory behavior phenotype from cryabb knockdown (PMID:25866181) is a downstream consequence of myofibrillar degeneration rather than a direct role in locomotion. Retained as non-core.
GO:0030239 myofibril assembly	IMP PMID:25866181 In vivo characterization of human myofibrillar myopathy gene...	ACCEPT	Summary: IMP annotation for myofibril assembly based on Buhrdel et al. 2015 (PMID:25866181). Morpholino knockdown of cryabb led to myofibrillar degeneration. This is consistent with the known role of mammalian CRYAB in maintaining myofibrillar integrity, and cryabb retains the broad muscle expression of its mammalian ortholog (PMID:16420472). Reason: cryabb retains the broad muscle expression of mammalian CRYAB (PMID:16420472) and morpholino knockdown causes myofibrillar degeneration (PMID:25866181). Myofibril assembly/maintenance is a core function for cryabb, consistent with the known role of mammalian CRYAB as a major myofibrillar myopathy gene.
GO:0060047 heart contraction	IMP PMID:25866181 In vivo characterization of human myofibrillar myopathy gene...	ACCEPT	Summary: IMP annotation for heart contraction based on Buhrdel et al. 2015 (PMID:25866181). Morpholino knockdown of MFM genes including cryabb led to severe heart failure. cryabb retains the cardiac expression of mammalian CRYAB (PMID:16420472). Reason: cryabb retains the broad expression including heart tissue characteristic of mammalian CRYAB (PMID:16420472). The heart failure phenotype from knockdown (PMID:25866181) supports a direct role in cardiac function. This is a core function for cryabb, consistent with human CRYAB being a cardiomyopathy gene. Falcon deep research adds independent zebrafish evidence linking alphaB-crystallin loss to an embryonic cardiac edema phenotype. Supporting Evidence: file:DANRE/cryabb/cryabb-deep-research-falcon.md The study reports an embryonic cardiac edema phenotype characteristic of αB-crystallin knockout lines
GO:0051082 unfolded protein binding	IDA PMID:16420472 Gene duplication and separation of functions in alphaB-cryst...	MODIFY	Summary: IDA annotation based on Smith et al. 2006 (PMID:16420472), which characterized the chaperone-like activity of alphaB2-crystallin (cryabb). The study measured the ability of recombinant cryabb to prevent chemically induced aggregation of alpha-lactalbumin and lysozyme at temperatures from 25 to 40 degrees C. cryabb showed greater chaperone-like activity than human CRYAB at 25-30 degrees C. GO:0051082 is now formally obsolete; the holdase function is not captured by the carrier-specific GO:0140309; a holdase chaperone activity NTR is proposed instead. Reason: GO:0051082 is now formally obsolete. The chaperone-like activity assays in PMID:16420472 directly demonstrate holdase function for cryabb -- prevention of chemically induced aggregation of substrate proteins. GO:0140309 does not fit: despite its 'unfolded protein holdase activity' label its definition still requires escort to an acceptor molecule or location, which crystallins do not do (issue #2222, go-ontology#30552). The replacement is the proposed 'holdase chaperone activity' NTR (see proposed_new_terms). Proposed replacements: holdase chaperone activity Supporting Evidence: PMID:16420472 At 25 degrees C and 30 degrees C, zebrafish alphaB2 showed greater chaperone-like activity than human alphaB-crystallin, and at 35 degrees C and 40 degrees C, the human protein provided greater protection against aggregation. PMID:16420472 zebrafish alphaB2 maintained the widespread protective role also found in mammalian alphaB-crystallin, while zebrafish alphaB1 adopted a more restricted, nonchaperone role in the lens. file:DANRE/cryabb/cryabb-deep-research-falcon.md an ATP-independent molecular chaperone (“holdase”) supporting proteostasis by suppressing aggregation of destabilized proteins
GO:0005575 cellular_component	ND GO_REF:0000015	ACCEPT	Summary: ND (no data) annotation indicating that no specific cellular component has been experimentally determined for cryabb. This is a placeholder annotation. However, IBA evidence supports cytoplasmic and nuclear localization, and IEA evidence supports cytoplasmic localization. Reason: ND annotations are standard placeholders indicating no experimental data is available for a particular aspect. While there are IBA and IEA annotations for specific compartments, no direct experimental localization data exists for cryabb. This ND annotation is valid as a factual statement.