id: P02511
gene_symbol: CRYAB
product_type: PROTEIN
status: IN_PROGRESS
taxon:
  id: NCBITaxon:9606
  label: Homo sapiens
description: >-
  CRYAB (alpha-crystallin B chain, also known as HSPB5) is a small heat shock protein
  that functions as a molecular chaperone with holdase activity. It binds partially denatured
  or destabilized proteins in an ATP-independent manner to prevent their aggregation, but
  unlike HSP70-family foldase chaperones, it does NOT actively refold substrates. CRYAB
  forms large polydisperse oligomeric complexes, typically of 10-40 subunits, and can
  hetero-oligomerize with CRYAA (HSPB4). The canonical sHSP architecture comprises a
  central alpha-crystallin domain (ACD) flanked by a variable N-terminal domain (NTD) and
  a short C-terminal domain (CTD); chaperone activity is tightly coupled to oligomeric
  assembly and dynamic subunit exchange (DOI:10.1038/s41467-024-54647-7). A conserved
  N-terminal IXI-like motif (NT-IXI) engages the ACD hydrophobic groove, and perturbation
  of this motif transforms native assemblies into reversible elongated helical fibrils, as
  resolved by cryo-EM (DOI:10.1038/s41467-024-54647-7). Stress-activated phosphorylation
  at Ser19/Ser45/Ser59 by p38 MAPK modulates oligomeric state; the p38-CRYAB(pS59) cascade
  is a stress-response module that can shift CRYAB condensates toward less dynamic,
  aggregate-prone states under pathological conditions (DOI:10.1016/j.isci.2024.109510,
  DOI:10.1172/jci163730). In the eye lens, CRYAB serves dual roles as a structural protein
  contributing to transparency and refractive index, and as a chaperone preventing aggregation
  of damaged crystallins. Outside the lens, it is highly expressed in cardiac and skeletal
  muscle where it associates with cytoskeletal elements including desmin intermediate
  filaments and titin at Z-bands and intercalated disks. CRYAB also functions as a
  mitochondrial chaperone and anti-apoptotic protein, binding pro-apoptotic factors Bax,
  Bcl-X(S), cytochrome c, and VDAC; the E105K mutation causing hereditary optic atrophy
  reduces these interactions and impairs mitochondrial OXPHOS assembly
  (DOI:10.1172/jci.insight.182209). CRYAB is secreted via extracellular vesicles and exerts
  paracrine effects including promotion of angiogenesis in cardiac contexts
  (DOI:10.1186/s13287-023-03468-4, DOI:10.1038/s42003-022-04402-9). Mutations in CRYAB
  cause myofibrillar myopathy, cataracts, dilated cardiomyopathy, restrictive cardiomyopathy,
  and hereditary optic atrophy.
existing_annotations:
- term:
    id: GO:0043066
    label: negative regulation of apoptotic process
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      IBA annotation for negative regulation of apoptotic process, phylogenetically
      propagated across small heat shock protein family members (CRYAA, CRYAB, HSPB1).
      CRYAB has well-documented anti-apoptotic activity. It binds pro-apoptotic Bax
      and Bcl-X(S) to prevent their translocation from cytosol to mitochondria during
      staurosporine-induced apoptosis (PMID:14752512). This preserves mitochondrial
      integrity and blocks caspase-3 activation and PARP degradation.
    action: ACCEPT
    reason: >-
      CRYAB is a bona fide anti-apoptotic protein. PMID:14752512 demonstrates that
      alpha-crystallins bind Bax and Bcl-X(S) both in vitro and in vivo, preventing
      their translocation to mitochondria. The IBA annotation is phylogenetically
      appropriate and reflects a well-established function of CRYAB beyond its lens
      chaperone role. This is a core function of CRYAB, particularly in cardiac and
      muscle contexts.
    supported_by:
      - reference_id: PMID:14752512
        supporting_text: >-
          alphaA- and alphaB-crystallins prevent staurosporine-induced apoptosis
          through interactions with members of the Bcl-2 family. Using GST pulldown
          assays and coimmunoprecipitations, we demonstrated that alpha-crystallins
          bind to Bax and Bcl-X(S) both in vitro and in vivo.
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      IBA annotation for cytoplasm localization, phylogenetically propagated across
      sHSP family. CRYAB is a predominantly cytoplasmic protein. Multiple IDA
      annotations from different studies (PMID:19464326, PMID:20587334, PMID:14752512)
      confirm cytoplasmic localization. UniProt lists cytoplasm as a primary
      subcellular location.
    action: ACCEPT
    reason: >-
      Cytoplasm is the primary localization of CRYAB. This is confirmed by multiple
      independent IDA studies (PMID:19464326, PMID:20587334, PMID:14752512) and is
      consistent with its role as a cytoplasmic holdase chaperone. The IBA annotation
      is appropriate and well-supported.
    supported_by:
      - reference_id: PMID:19464326
        supporting_text: >-
          Online databases did not accurately predict the sub-cellular
          distribution of all the HSPB members.
- term:
    id: GO:0005634
    label: nucleus
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      IBA annotation for nuclear localization. CRYAB has been shown to translocate
      to the nucleus during heat shock, where it resides in SC35 speckles (nuclear
      splicing speckles) (PMID:19464326). It can also accumulate in the nucleus when
      co-expressed with LBH (PMID:20587334). Multiple IDA annotations support this.
    action: ACCEPT
    reason: >-
      Nuclear localization is confirmed by IDA evidence from PMID:19464326 and
      PMID:20587334. CRYAB translocates to the nucleus during heat stress and
      resides in SC35 speckles. This is a conditional/stress-dependent localization
      but is well-documented. The IBA annotation is appropriate.
    supported_by:
      - reference_id: PMID:19464326
        supporting_text: >-
          Some members also show a dynamic, stress-induced translocation to
          SC35 splicing speckles.
- term:
    id: GO:0009408
    label: response to heat
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      IBA annotation for response to heat. CRYAB is a small heat shock protein
      (HSPB5) that is upregulated during heat stress and translocates to the nucleus
      (PMID:19464326). Its chaperone activity in preventing protein aggregation is
      central to its role in the heat shock response. The IBA is propagated from
      multiple Drosophila and C. elegans HSP orthologs.
    action: ACCEPT
    reason: >-
      Response to heat is a core function of CRYAB as a member of the small heat
      shock protein family. It is upregulated during heat stress and shows
      stress-induced nuclear translocation (PMID:19464326). The IBA annotation is
      phylogenetically appropriate and reflects the conserved heat stress response
      function of sHSPs.
    supported_by:
      - reference_id: PMID:19464326
        supporting_text: >-
          Unlike HSPB1 and HSPB5, that chaperoned heat unfolded substrates and
          kept them folding competent, HSPB7 did not support refolding.
- term:
    id: GO:0042026
    label: protein refolding
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: >-
      IBA annotation for protein refolding, propagated from Drosophila sHSP
      orthologs. This is problematic for CRYAB specifically. While some sHSPs in
      other organisms may participate in protein refolding pathways (by passing
      substrates to foldase chaperones like HSP70), CRYAB itself is a holdase -- it
      prevents aggregation of denatured proteins but does NOT actively refold them.
      PMID:19464326 explicitly tested refolding activity: HSPB1 and HSPB5 chaperoned
      heat unfolded substrates and kept them folding competent, but the refolding
      itself depends on downstream HSP70/HSP40 machinery. The term protein refolding
      implies direct refolding activity which CRYAB does not have.
    action: MODIFY
    reason: >-
      CRYAB is a holdase chaperone that prevents aggregation but does NOT perform
      protein refolding. The IBA may be appropriate at the broader sHSP family level
      where some members participate in refolding pathways, but for CRYAB
      specifically, protein refolding is misleading. CRYAB keeps substrates in a
      folding-competent state for downstream foldases (PMID:19464326), which is
      better captured by GO:0050821 protein stabilization (already annotated via
      IMP from PMID:12235146). The annotation should be modified to better reflect
      holdase/protein stabilization activity rather than direct refolding.
    proposed_replacement_terms:
      - id: GO:0050821
        label: protein stabilization
    supported_by:
      - reference_id: PMID:19464326
        supporting_text: >-
          HSPB1 and HSPB5, that chaperoned heat unfolded substrates and kept them
          folding competent, HSPB7 did not support refolding.
      - reference_id: PMID:16303126
        supporting_text: >-
          the major lenticular protein chaperones, alpha A- and alpha B-crystallin,
          increased the solubility of the T5P gamma C-crystallin both in vitro and
          in transfected cells.
- 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 being obsoleted (go-ontology#30962).
      CRYAB/HSPB5 does bind partially denatured or destabilized proteins, but the term
      "unfolded protein binding" is problematic because it implies a simple binding function
      rather than the chaperone holdase activity that CRYAB performs. CRYAB acts as a
      molecular chaperone that suppresses aggregation of destabilized proteins in an
      ATP-independent manner (PMID:16303126), but unlike HSP70-family foldase chaperones,
      it does NOT actively refold substrates. The IBA annotation is phylogenetically
      propagated from sHSP family members, which is appropriate at the family level since
      small heat shock proteins share this holdase chaperone function. However, the term
      itself needs replacement. GO:0044183 "protein folding chaperone" (defined as "Binding
      to a protein or a protein-containing complex to assist the protein folding process")
      is the closest available MF term. This is an imperfect replacement because CRYAB
      specifically does NOT assist in protein folding -- it prevents aggregation (holdase
      activity). A dedicated holdase-specific GO term does not yet exist and should be
      requested. UniProt describes CRYAB as having "chaperone-like activity, preventing
      aggregation of various proteins under a wide range of stress conditions."
    action: MODIFY
    reason: >-
      GO:0051082 is being obsoleted. CRYAB has well-documented chaperone-like holdase
      activity: alpha-crystallins (including CRYAB) increase the solubility of destabilized
      T5P gamma C-crystallin and reduce the size of its aggregates both in vitro and in
      transfected cells (PMID:16303126). However, CRYAB does NOT refold proteins -- it is a
      holdase, not a foldase. The best available interim MF replacement is GO:0044183
      "protein folding chaperone," though this term is not ideal because its definition
      references "protein folding process" which is not what CRYAB does. A new
      holdase-specific term should be requested. GO:0050821 "protein stabilization" is
      appropriate as a BP term and is already annotated for CRYAB via PMID:12235146.
    proposed_replacement_terms:
      - id: GO:0044183
        label: protein folding chaperone
    additional_reference_ids:
      - PMID:16303126
      - PMID:12235146
    supported_by:
      - reference_id: PMID:16303126
        supporting_text: >-
          the major lenticular protein chaperones, alpha A- and alpha B-crystallin,
          increased the solubility of the T5P gamma C-crystallin both in vitro and in
          transfected cells. More importantly, the size of the T5P gamma C-crystallin
          aggregates were also significantly reduced in the presence of the lenticular
          chaperones.
- term:
    id: GO:0005198
    label: structural molecule activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  review:
    summary: >-
      IEA annotation from ARBA machine learning for structural molecule activity.
      CRYAB does indeed serve as a structural protein in the eye lens, contributing to
      transparency and refractive index. There is also an IDA annotation for this term
      from PMID:16303126. However, the more specific term GO:0005212 structural
      constituent of eye lens is also annotated and is more informative. This broader
      IEA annotation is acceptable as it also reflects the structural role in muscle
      (association with sarcomeric Z-discs and desmin filaments).
    action: ACCEPT
    reason: >-
      CRYAB has structural roles both in the lens (where it contributes to
      transparency) and in muscle (where it associates with desmin intermediate
      filaments and sarcomeric structures). The broader term structural molecule
      activity captures both contexts. The IDA annotation from PMID:16303126 provides
      independent experimental support.
- term:
    id: GO:0005212
    label: structural constituent of eye lens
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  review:
    summary: >-
      IEA annotation from combined automated methods for structural constituent of
      eye lens. CRYAB is one of the major structural proteins of the eye lens. It
      contributes to lens transparency and refractive index. This is well-established
      from decades of crystallin research and is supported by the InterPro
      alpha-crystallin N-terminal domain annotation (IPR003090) and the UniProt eye
      lens protein keyword.
    action: ACCEPT
    reason: >-
      CRYAB is a major structural protein of the vertebrate eye lens. This is a
      core function. The annotation is appropriate and well-supported by the
      established biology of alpha-crystallins as both structural lens proteins and
      molecular chaperones.
- term:
    id: GO:0005576
    label: extracellular region
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  review:
    summary: >-
      IEA annotation from UniProt subcellular location mapping. UniProt annotates
      CRYAB as Secreted based on PMID:32272059, which showed CRYAB can be secreted
      via an unconventional TMED10-dependent pathway involving translocation to the
      ERGIC. Additionally, CRYAB is found in extracellular exosomes (PMID:23533145,
      PMID:19056867). The extracellular region annotation is therefore justified.
    action: ACCEPT
    reason: >-
      CRYAB has been shown to be secreted via an unconventional protein secretion
      pathway involving TMED10 (PMID:32272059) and is found in extracellular
      exosomes (PMID:23533145). The IEA annotation correctly reflects the UniProt
      subcellular location annotation for Secreted.
- term:
    id: GO:0005634
    label: nucleus
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  review:
    summary: >-
      IEA annotation from UniProt subcellular location mapping for nucleus. This is
      a duplicate of the IBA annotation for nucleus, and is also supported by
      multiple IDA annotations (PMID:19464326, PMID:20587334). Nuclear localization
      is stress-dependent.
    action: ACCEPT
    reason: >-
      This IEA annotation is consistent with the IBA and IDA evidence. CRYAB
      translocates to the nucleus during heat stress (PMID:19464326). The IEA
      correctly maps the UniProt subcellular location annotation.
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  review:
    summary: >-
      IEA annotation from combined automated methods for cytoplasm localization.
      CRYAB is primarily a cytoplasmic protein, confirmed by multiple IDA annotations
      (PMID:19464326, PMID:20587334, PMID:14752512) and the IBA annotation.
    action: ACCEPT
    reason: >-
      This is redundant with the IBA and IDA annotations but is a correct broader
      IEA annotation. Cytoplasm is the primary localization of CRYAB.
- term:
    id: GO:0005764
    label: lysosome
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  review:
    summary: >-
      IEA annotation from UniProt subcellular location mapping. UniProt annotates
      CRYAB as localizing to the lysosome based on similarity to the mouse ortholog
      P23927 (ECO:0000250). This is supported by PMID:31786107, which shows that
      CRYAB forms a complex with ATP6V1A and mTOR and regulates lysosome activity
      in lens epithelial cells.
    action: ACCEPT
    reason: >-
      Lysosome localization is annotated by similarity to the mouse ortholog and is
      supported by the functional interaction between CRYAB, ATP6V1A (a lysosomal
      V-ATPase subunit) and mTOR (PMID:31786107). The IEA annotation is reasonable.
- term:
    id: GO:0009892
    label: negative regulation of metabolic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  review:
    summary: >-
      IEA annotation from ARBA machine learning for negative regulation of
      metabolic process. This is an extremely broad BP term. CRYAB does negatively
      regulate some metabolic processes (e.g., negative regulation of apoptosis,
      negative regulation of protein aggregation), but this term is too general to
      be informative. More specific terms are already annotated.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      This is an overly broad term that does not add useful information beyond what
      is captured by more specific annotations such as GO:0043066 negative
      regulation of apoptotic process and GO:0031333 negative regulation of
      protein-containing complex assembly. The ARBA prediction likely derives from
      the general chaperone/anti-apoptotic activities but is too unspecific.
- term:
    id: GO:0046872
    label: metal ion binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000043
  review:
    summary: >-
      IEA annotation from UniProt keyword mapping for metal ion binding. CRYAB binds
      zinc ions through histidine residues (His-83, His-104, His-106, His-111,
      His-119) as documented in UniProt based on PMID:22890888. Zinc binding enhances
      oligomer stability.
    action: ACCEPT
    reason: >-
      CRYAB has documented zinc-binding sites identified by chemical modification
      and MALDI-TOF mass spectrometry (PMID:22890888). Multiple histidine residues
      coordinate zinc ions, and this inter-subunit bridging enhances structural
      stability. The IEA annotation from the UniProt metal-binding keyword is
      appropriate.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:11700327
  review:
    summary: >-
      IPI annotation for protein binding from PMID:11700327 (Fu & Liang 2002),
      which used a mammalian two-hybrid system to detect interactions among lens
      crystallins. The WITH/FROM column in GOA lists interactions with CRYAA
      (P02489), HSPB1 (P04792), CRYGC (P07315), and CRYBB2 (P43320). These are
      genuine crystallin-crystallin interactions. However, protein binding is
      uninformative; the interactions with CRYAA are better captured by identical
      protein binding or the broader chaperone complex context.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Protein binding is uninformative per GO curation guidelines. The interactions
      detected in PMID:11700327 (crystallin-crystallin interactions in mammalian
      two-hybrid assay) are real but are better captured by more specific terms
      such as identical protein binding (for self-interaction) or the chaperone
      function annotations. The binding to other crystallins reflects CRYAB's
      chaperone/structural role in the lens.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:12601044
  review:
    summary: >-
      IPI annotation from PMID:12601044 (Fu & Liang 2003), which characterized
      altered protein-protein interactions of congenital cataract crystallin mutants
      using a mammalian two-hybrid system. Interactions detected include CRYAB with
      CRYAA, HSPB1, CRYGC, and CRYBB2.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Protein binding is uninformative. The interactions described reflect
      crystallin-crystallin interactions relevant to lens function and are better
      captured by the identical protein binding and chaperone annotations.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:16049941
  review:
    summary: >-
      IPI annotation from PMID:16049941, a pilot proteomic study of amyloid
      precursor protein (APP, P05067) interactors in Alzheimer's disease. CRYAB was
      identified as an interactor of APP.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Protein binding is uninformative. The interaction with APP is more
      specifically captured by the amyloid-beta binding annotation (GO:0001540)
      from PMID:23106396.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:17046756
  review:
    summary: >-
      IPI annotation from PMID:17046756 (Narayanan et al. 2006), which showed
      CRYAB competes for amyloid-beta peptide interactions using NMR spectroscopy.
      The WITH/FROM is CRYBA1 (P05813). The study demonstrated that CRYAB
      interactions involve the hydrophobic core residues of Abeta.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Protein binding is uninformative. The interaction with amyloid-beta is better
      captured by GO:0001540 amyloid-beta binding (already annotated from
      PMID:23106396) and the negative regulation of amyloid fibril formation
      annotation.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:18330356
  review:
    summary: >-
      IPI annotation from PMID:18330356, a large-scale normalized yeast two-hybrid
      library screen. The WITH/FROM is HSPB1 (P04792). CRYAB interaction with HSPB1
      is well-established.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Protein binding is uninformative. CRYAB-HSPB1 interaction is well-documented
      and reflects sHSP hetero-oligomer formation. This is better captured by the
      protein-containing complex and identical protein binding annotations.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:19651604
  review:
    summary: >-
      IPI annotation from PMID:19651604 (Peschek et al. 2009), which showed that
      alpha-crystallin forms defined globular assemblies. The WITH/FROM is CRYAA
      (P02489), reflecting the CRYAB-CRYAA hetero-oligomerization.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Protein binding is uninformative. The CRYAB-CRYAA interaction reflects
      hetero-oligomer formation and is better captured by the identical protein
      binding and protein-containing complex annotations.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:22085609
  review:
    summary: >-
      IPI annotation from PMID:22085609, which studied the F71L mutant
      alphaA-crystallin and its effects on hetero-oligomeric complex stability. The
      WITH/FROM is CRYAA (P02489).
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Protein binding is uninformative. This reflects CRYAB-CRYAA
      hetero-oligomerization. More specific annotations are already present.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:22153508
  review:
    summary: >-
      IPI annotation from PMID:22153508 (Baldwin et al. 2011), which elucidated the
      polyhedral architecture of CRYAB oligomers. The WITH/FROM is CRYAA (P02489).
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Protein binding is uninformative. This reflects CRYAB oligomerization
      dynamics. Better captured by identical protein binding and protein-containing
      complex annotations.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:22158051
  review:
    summary: >-
      IPI annotation from PMID:22158051 (Huang et al. 2012), which showed CRYAB
      associates with the cadherin/catenin adherens junction. The WITH/FROM is
      beta-catenin (CTNNB1, P35222). CRYAB interacts with both E-cadherin and
      beta-catenin via its alpha-crystallin core domain, inhibiting E-cadherin
      internalization and NPC progression.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Protein binding is uninformative. The specific interaction with beta-catenin
      described in PMID:22158051 reflects CRYAB's role in cell adhesion regulation
      in cancer context. This is a secondary/non-core function and the term protein
      binding does not capture the functional significance.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:23188086
  review:
    summary: >-
      IPI annotation from PMID:23188086 (Delbecq et al. 2012), which studied the
      IxI motif binding determinants of CRYAB. The WITH/FROM includes CRYAA
      (P02489), HSPB1 (P04792), and HSPB2 (Q16082).
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Protein binding is uninformative. The IxI motif interactions are critical for
      sHSP oligomer assembly and are better captured by the identical protein
      binding and oligomerization-related annotations.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:23542032
  review:
    summary: >-
      IPI annotation from PMID:23542032 (Yamashita et al. 2013), which identified
      CRYAB as a binding partner of mitsugumin23 (TMEM109/MG23, mouse Q3UBX0). The
      interaction mediates a protective role against UVC-induced cell death by
      accumulating CRYAB near the ER.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Protein binding is uninformative. The CRYAB-TMEM109 interaction is
      functionally significant in the DNA damage response, but the protein binding
      term does not capture this. The functional role is partially captured by the
      regulation of programmed cell death annotation.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:24183572
  review:
    summary: >-
      IPI annotation from PMID:24183572 (Kingsley et al. 2013), which showed
      preferential and specific binding of CRYAB to the cataract-related G18V
      variant of gammaS-crystallin (CRYGS, P22914). CRYAB binds more strongly to
      the variant via a well-defined interaction surface.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Protein binding is uninformative. This interaction reflects CRYAB's chaperone
      function in the lens -- it preferentially binds destabilized crystallin
      variants. This is better captured by the chaperone/holdase MF annotations.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:25910212
  review:
    summary: >-
      IPI annotation from PMID:25910212, a large-scale study of macromolecular
      interaction perturbations in human genetic disorders. The WITH/FROM is CRYAA
      (P02489).
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Protein binding is uninformative. Large-scale interaction studies do not
      provide functional specificity beyond what is already captured by more
      specific annotations.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:26465331
  review:
    summary: >-
      IPI annotation from PMID:26465331 (Grose et al. 2015), which characterized
      the cardiac HSPB2 interactome. The WITH/FROM is HSPB2 (Q16082). CRYAB
      interacts with HSPB2, consistent with sHSP hetero-oligomerization.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Protein binding is uninformative. The CRYAB-HSPB2 interaction is part of the
      sHSP oligomeric network and is better captured by more specific annotations.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:28514442
  review:
    summary: >-
      IPI annotation from PMID:28514442, a large-scale interactome mapping study.
      The WITH/FROM is HSPB1 (P04792).
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Protein binding is uninformative. Large-scale interactome studies confirm
      known sHSP interactions but do not add functional specificity.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:32296183
  review:
    summary: >-
      IPI annotation from PMID:32296183, a reference map of the human binary
      protein interactome. The WITH/FROM includes CRYAA (P02489), KRTAP6-1
      (Q3LI64), and GORASP2 (Q9H8Y8).
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Protein binding is uninformative. Large-scale binary interactome studies do
      not provide functional specificity.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:32814053
  review:
    summary: >-
      IPI annotation from PMID:32814053, an interactome mapping study focused on
      neurodegenerative disease proteins. The WITH/FROM includes multiple proteins
      (APP/P05067, CTNNB1/P35222, EXOC5/O00471, ANXA4/P09525, PRPS1/P60891,
      CRMP1/Q14194, CORO6/Q6QEF8, ADAMTSL4/Q6UY14, PRUNE2/Q8WUY3, HSFY2/Q96LI6).
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Protein binding is uninformative. This large-scale interactome study
      identifies many interactors but the term does not capture the functional
      significance of any of these interactions.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:33961781
  review:
    summary: >-
      IPI annotation from PMID:33961781, a dual proteome-scale network study. The
      WITH/FROM is HSPB1 (P04792).
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Protein binding is uninformative. Confirms CRYAB-HSPB1 interaction from
      large-scale proteomics.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:40205054
  review:
    summary: >-
      IPI annotation from PMID:40205054, multimodal cell maps study. The WITH/FROM
      is HSPB1 (P04792).
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Protein binding is uninformative per GO curation guidelines.
- term:
    id: GO:0042802
    label: identical protein binding
  evidence_type: IPI
  original_reference_id: PMID:12601044
  review:
    summary: >-
      IPI annotation for identical protein binding (CRYAB self-interaction) from
      PMID:12601044 (Fu & Liang 2003). The study used mammalian two-hybrid to show
      CRYAB-CRYAB interaction, and that the R120G mutation decreases self-interaction.
      CRYAB forms large homo-oligomeric complexes.
    action: ACCEPT
    reason: >-
      CRYAB self-association to form large homo-oligomeric complexes (typically
      24-32 subunits) is a core feature of its biology. This is confirmed by
      multiple structural studies. The identical protein binding annotation is
      appropriate and more informative than generic protein binding.
    supported_by:
      - reference_id: PMID:12601044
        supporting_text: >-
          for the R120G alphaB-crystallin, the interactions with alphaA- and
          alphaB-crystallin decreased, but those with betaB2- and
          gammaC-crystallin increased slightly.
- term:
    id: GO:0042802
    label: identical protein binding
  evidence_type: IPI
  original_reference_id: PMID:18330356
  review:
    summary: >-
      IPI annotation for identical protein binding from PMID:18330356 (normalized
      yeast two-hybrid library). Confirms CRYAB self-interaction.
    action: ACCEPT
    reason: >-
      Confirms CRYAB homo-oligomerization by an independent method. Core property
      of CRYAB.
- term:
    id: GO:0042802
    label: identical protein binding
  evidence_type: IPI
  original_reference_id: PMID:19651604
  review:
    summary: >-
      IPI annotation from PMID:19651604 (Peschek et al. 2009), which demonstrated
      that alpha-crystallin forms defined globular assemblies. CRYAB self-interaction
      is central to its oligomeric architecture.
    action: ACCEPT
    reason: >-
      CRYAB homo-oligomerization is a core structural property documented by
      multiple biophysical approaches.
- term:
    id: GO:0042802
    label: identical protein binding
  evidence_type: IPI
  original_reference_id: PMID:20802487
  review:
    summary: >-
      IPI annotation from PMID:20802487, which used solid-state NMR and SAXS to
      study CRYAB oligomer activation. Self-interaction confirmed by structural
      methods.
    action: ACCEPT
    reason: >-
      Confirms CRYAB self-association by biophysical methods. Core property.
- term:
    id: GO:0042802
    label: identical protein binding
  evidence_type: IPI
  original_reference_id: PMID:21464278
  review:
    summary: >-
      IPI annotation from PMID:21464278, which showed that the N-terminal domain
      of CRYAB provides a conformational switch for multimerization and structural
      heterogeneity.
    action: ACCEPT
    reason: >-
      Confirms CRYAB homo-oligomeric assembly, specifically identifying the
      N-terminal domain role. Core property.
- term:
    id: GO:0042802
    label: identical protein binding
  evidence_type: IPI
  original_reference_id: PMID:22143763
  review:
    summary: >-
      IPI annotation from PMID:22143763, which elucidated multiple molecular
      architectures of CRYAB oligomers using a triple hybrid approach.
    action: ACCEPT
    reason: >-
      Confirms CRYAB polydisperse homo-oligomeric assembly by multiple structural
      methods.
- term:
    id: GO:0042802
    label: identical protein binding
  evidence_type: IPI
  original_reference_id: PMID:22153508
  review:
    summary: >-
      IPI annotation from PMID:22153508 (Baldwin et al. 2011), which demonstrated
      the interconverting polyhedral architecture of CRYAB oligomers using NMR,
      mass spectrometry, and electron microscopy.
    action: ACCEPT
    reason: >-
      Provides structural basis for CRYAB polydisperse oligomeric assembly. Core
      property.
    supported_by:
      - reference_id: PMID:22153508
        supporting_text: >-
          We report structural models for the most abundant oligomers populated by
          the polydisperse molecular chaperone alphaB-crystallin.
- term:
    id: GO:0042802
    label: identical protein binding
  evidence_type: IPI
  original_reference_id: PMID:23188086
  review:
    summary: >-
      IPI annotation from PMID:23188086 (Delbecq et al. 2012), which characterized
      the IxI motif binding to the alpha-crystallin domain groove. This inter-subunit
      interaction is critical for oligomer formation.
    action: ACCEPT
    reason: >-
      The IxI motif interaction is a key determinant of sHSP oligomer assembly
      and client binding. This study provides molecular detail on CRYAB
      self-interaction. Core property.
    supported_by:
      - reference_id: PMID:23188086
        supporting_text: >-
          The most commonly observed inter-subunit interaction involves a highly
          conserved C-terminal 'IxI/V' motif and a groove in the ACD that is also
          implicated in client binding.
- term:
    id: GO:0042802
    label: identical protein binding
  evidence_type: IPI
  original_reference_id: PMID:24183572
  review:
    summary: >-
      IPI annotation from PMID:24183572 (Kingsley et al. 2013). The WITH/FROM is
      CRYAB itself (P02511), reflecting self-interaction in the context of studying
      CRYAB binding to gammaS-crystallin variants.
    action: ACCEPT
    reason: >-
      Confirms CRYAB self-interaction. Core property.
- term:
    id: GO:0042802
    label: identical protein binding
  evidence_type: IPI
  original_reference_id: PMID:26465331
  review:
    summary: >-
      IPI annotation from PMID:26465331 (Grose et al. 2015), cardiac HSPB2
      interactome study. The WITH/FROM is CRYAB itself (P02511).
    action: ACCEPT
    reason: >-
      Confirms CRYAB self-interaction in cardiac context.
- term:
    id: GO:0042802
    label: identical protein binding
  evidence_type: IPI
  original_reference_id: PMID:27226619
  review:
    summary: >-
      IPI annotation from PMID:27226619, which studied the 343delT HSPB5 mutation
      associated with early-onset skeletal myopathy and its defects in protein
      solubility. Confirms CRYAB self-interaction.
    action: ACCEPT
    reason: >-
      Confirms CRYAB self-interaction. Disease mutations affect oligomeric assembly,
      underscoring the functional importance of self-interaction.
- term:
    id: GO:0005739
    label: mitochondrion
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IEA annotation from Ensembl Compara ortholog transfer, based on mouse CRYAB
      (P23927). CRYAB has been reported to translocate to mitochondria in some
      contexts, particularly related to its anti-apoptotic function (sequestering
      Bax and Bcl-X(S) to prevent mitochondrial translocation, PMID:14752512). The
      anti-apoptotic mechanism involves preventing Bax translocation TO mitochondria
      rather than CRYAB being a mitochondrial resident protein.
    action: KEEP_AS_NON_CORE
    reason: >-
      Mitochondrial localization may occur transiently or in specific contexts
      (e.g., during apoptosis regulation), but CRYAB is not a constitutive
      mitochondrial protein. The annotation from Ensembl Compara mouse ortholog
      transfer is acceptable but represents a non-core, context-dependent
      localization.
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IEA annotation from Ensembl Compara ortholog transfer for cytosol. CRYAB is
      primarily a cytosolic protein, supported by IDA evidence from GO_REF:0000052
      (HPA immunofluorescence). Cytosol is consistent with the cytoplasm annotations.
    action: ACCEPT
    reason: >-
      Cytosol is the more specific subcellular compartment within cytoplasm where
      CRYAB resides. Supported by IDA from HPA data and consistent with CRYAB's
      known biology as a soluble cytoplasmic chaperone.
- term:
    id: GO:0005886
    label: plasma membrane
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IEA annotation from Ensembl Compara ortholog transfer for plasma membrane.
      Also supported by IDA from HPA immunofluorescence (GO_REF:0000052). CRYAB
      has been reported at the plasma membrane in some contexts (e.g., association
      with cadherin/catenin complexes at the cell membrane, PMID:22158051).
    action: KEEP_AS_NON_CORE
    reason: >-
      Plasma membrane localization may occur in specific contexts (e.g., cell
      adhesion junctions) but is not a core localization of CRYAB. The HPA IDA
      data and mouse ortholog transfer provide some support, but cytoplasm/cytosol
      are the primary locations.
- term:
    id: GO:0006457
    label: protein folding
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IEA annotation from Ensembl Compara ortholog transfer (from rat) for protein
      folding. CRYAB is a holdase chaperone that prevents protein aggregation but
      does NOT actively fold proteins. It keeps substrates in a folding-competent
      state that can then be refolded by ATP-dependent foldase chaperones like HSP70.
      The term protein folding implies direct participation in the folding process,
      which is misleading for a holdase.
    action: MODIFY
    reason: >-
      CRYAB is a holdase chaperone, not a foldase. It prevents aggregation and
      maintains substrates in a folding-competent state (PMID:19464326,
      PMID:16303126) but does not perform protein folding per se. GO:0050821
      protein stabilization is more appropriate as a BP term. The annotation should
      be modified to reflect holdase activity rather than folding activity.
    proposed_replacement_terms:
      - id: GO:0050821
        label: protein stabilization
    supported_by:
      - reference_id: PMID:19464326
        supporting_text: >-
          HSPB1 and HSPB5, that chaperoned heat unfolded substrates and kept them
          folding competent, HSPB7 did not support refolding.
- term:
    id: GO:0008017
    label: microtubule binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IEA annotation from Ensembl Compara ortholog transfer (from rat CRYAB) for
      microtubule binding. There is limited direct evidence for CRYAB binding
      microtubules in human. CRYAB is better known for binding intermediate filaments
      (desmin) and actin filaments. The rat data may reflect CRYAB's broader
      cytoskeletal interactions.
    action: KEEP_AS_NON_CORE
    reason: >-
      Microtubule binding is plausible given CRYAB's known interactions with
      cytoskeletal elements (desmin intermediate filaments, actin), but the primary
      cytoskeletal interaction is with intermediate filaments (PMID:28470624). The
      broader cytoskeletal protein binding annotation (GO:0008092) is also present
      and may be more appropriate. This is a non-core function.
- term:
    id: GO:0008092
    label: cytoskeletal protein binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IEA annotation from Ensembl Compara ortholog transfer for cytoskeletal protein
      binding. CRYAB interacts with desmin intermediate filaments (PMID:28470624),
      titin (PMID:14676215), and associates with the sarcomeric cytoskeleton. This
      is well-supported.
    action: ACCEPT
    reason: >-
      CRYAB has well-documented interactions with cytoskeletal proteins including
      desmin (PMID:28470624) and titin (UniProt, PMID:14676215). Mutations in CRYAB
      cause desmin-related myopathy (PMID:9731540), underscoring the functional
      importance of this interaction. The IEA annotation is appropriate.
    supported_by:
      - reference_id: PMID:28470624
        supporting_text: >-
          the binding of CRYAB to desmin is subject to its assembly status, to the
          subunit organization within filaments formed and to the integrity of the
          C-terminal tail domain of desmin.
- term:
    id: GO:0009986
    label: cell surface
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IEA annotation from Ensembl Compara ortholog transfer for cell surface.
      CRYAB is primarily an intracellular protein. Some evidence suggests it can
      be secreted (PMID:32272059) and found in exosomes, but cell surface
      localization is not well-established for human CRYAB.
    action: KEEP_AS_NON_CORE
    reason: >-
      Cell surface localization is not well-documented for human CRYAB. It may
      be transiently present at the cell surface during unconventional secretion.
      This is a non-core, context-dependent localization transferred from rat
      ortholog.
- term:
    id: GO:0030018
    label: Z disc
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IEA annotation from Ensembl Compara ortholog transfer for Z disc localization.
      UniProt notes that CRYAB localizes at Z-bands and the intercalated disk in
      cardiomyocytes (PMID:28493373). This is consistent with its role in muscle
      and its interaction with desmin and titin.
    action: ACCEPT
    reason: >-
      Z disc localization is documented for human CRYAB in cardiomyocytes
      (PMID:28493373) and is consistent with its interaction with sarcomeric
      proteins desmin and titin. This is a core localization in muscle tissue.
- term:
    id: GO:0030308
    label: negative regulation of cell growth
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IEA annotation from Ensembl Compara ortholog transfer for negative regulation
      of cell growth. CRYAB has been implicated in tumor suppression in some
      contexts (PMID:22158051 in NPC) and its overexpression can suppress tumor
      formation. However, this is not a core function.
    action: KEEP_AS_NON_CORE
    reason: >-
      Negative regulation of cell growth is a secondary function of CRYAB,
      observed in certain cancer contexts (PMID:22158051). It is not a core
      function and likely reflects downstream consequences of its anti-apoptotic
      and chaperone activities rather than a direct growth regulatory function.
- term:
    id: GO:0030424
    label: axon
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IEA annotation from Ensembl Compara ortholog transfer for axon localization.
      CRYAB is expressed in the nervous system and accumulates in Alexander's disease
      brain. Axonal localization is plausible but represents a tissue-specific
      localization rather than core biology.
    action: KEEP_AS_NON_CORE
    reason: >-
      Axon localization is transferred from rat ortholog. CRYAB is expressed in
      neural tissues and accumulates in neurological disease contexts, but axonal
      localization is not a core feature. Non-core tissue-specific localization.
- term:
    id: GO:0031109
    label: microtubule polymerization or depolymerization
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IEA annotation from Ensembl Compara ortholog transfer for microtubule
      polymerization or depolymerization. There is limited direct evidence for CRYAB
      regulating microtubule dynamics in human. This may be an over-annotation from
      the rat ortholog.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      There is insufficient evidence that CRYAB directly regulates microtubule
      polymerization or depolymerization in human. CRYAB's primary cytoskeletal
      interactions are with intermediate filaments (desmin) rather than
      microtubules. This annotation likely represents an over-annotation from
      ortholog transfer.
- term:
    id: GO:0031430
    label: M band
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IEA annotation from Ensembl Compara ortholog transfer for M band localization.
      CRYAB interacts with titin, which spans from Z disc to M band. M band
      localization is plausible in the context of sarcomeric association.
    action: KEEP_AS_NON_CORE
    reason: >-
      M band localization is consistent with CRYAB's interaction with titin and
      its sarcomeric association. However, the primary sarcomeric localization
      documented for human CRYAB is at Z-bands (PMID:28493373). M band is a
      secondary localization from rat ortholog transfer.
- term:
    id: GO:0031674
    label: I band
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IEA annotation from Ensembl Compara ortholog transfer for I band localization.
      I band localization is consistent with CRYAB's association with sarcomeric
      structures and its interaction with titin (which spans the I band).
    action: KEEP_AS_NON_CORE
    reason: >-
      I band localization is plausible given CRYAB's interaction with titin and
      sarcomeric structures, but is transferred from rat ortholog. Non-core but
      reasonable for muscle tissue context.
- term:
    id: GO:0032355
    label: response to estradiol
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IEA annotation from Ensembl Compara ortholog transfer for response to
      estradiol. CRYAB expression may be regulated by estradiol in certain tissues,
      but this is not a core function.
    action: KEEP_AS_NON_CORE
    reason: >-
      Response to estradiol is a secondary, context-dependent process for CRYAB.
      Many stress-responsive genes show altered expression in response to various
      stimuli including hormones. This is not a core function and is transferred
      from rat ortholog.
- term:
    id: GO:0032432
    label: actin filament bundle
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IEA annotation from Ensembl Compara ortholog transfer for actin filament
      bundle localization. CRYAB has been reported to associate with actin
      cytoskeletal structures in addition to its well-known intermediate filament
      interactions.
    action: KEEP_AS_NON_CORE
    reason: >-
      Actin filament bundle localization is a secondary cytoskeletal association
      for CRYAB. Its primary cytoskeletal interaction is with desmin intermediate
      filaments. Transferred from rat ortholog.
- term:
    id: GO:0042542
    label: response to hydrogen peroxide
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IEA annotation from Ensembl Compara ortholog transfer for response to hydrogen
      peroxide. As a stress-responsive chaperone, CRYAB is likely upregulated during
      oxidative stress including H2O2 exposure. UniProt notes susceptibility to
      oxidation at Met-48, Met-60, and Trp-68.
    action: KEEP_AS_NON_CORE
    reason: >-
      Response to hydrogen peroxide is consistent with CRYAB's role as a
      stress-responsive chaperone. It is a non-core, general stress response
      function rather than a specific core activity. Transferred from rat ortholog.
- term:
    id: GO:0043066
    label: negative regulation of apoptotic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  review:
    summary: >-
      IEA annotation from combined automated methods for negative regulation of
      apoptotic process. This duplicates the IBA annotation and is also supported
      by IDA evidence from PMID:14752512. CRYAB's anti-apoptotic activity through
      binding Bax and Bcl-X(S) is well-established.
    action: ACCEPT
    reason: >-
      This IEA annotation is consistent with the IBA and IDA evidence for CRYAB's
      anti-apoptotic function. PMID:14752512 provides direct experimental evidence.
- term:
    id: GO:0043197
    label: dendritic spine
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IEA annotation from Ensembl Compara ortholog transfer for dendritic spine
      localization. CRYAB is expressed in the nervous system and has been found
      in neural structures. Dendritic spine localization is plausible but
      represents a tissue-specific neural localization.
    action: KEEP_AS_NON_CORE
    reason: >-
      Dendritic spine localization is a neural tissue-specific localization
      transferred from rat ortholog. CRYAB is expressed in the brain and
      accumulates in neurological disease contexts. Non-core, tissue-specific.
- term:
    id: GO:0043204
    label: perikaryon
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IEA annotation from Ensembl Compara ortholog transfer for perikaryon (cell
      body of neuron) localization. CRYAB is expressed in neural tissues.
    action: KEEP_AS_NON_CORE
    reason: >-
      Perikaryon localization is a neural tissue-specific localization transferred
      from rat ortholog. Non-core.
- term:
    id: GO:0043292
    label: contractile muscle fiber
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IEA annotation from Ensembl Compara ortholog transfer for contractile muscle
      fiber localization. CRYAB is highly expressed in cardiac and skeletal muscle
      (HPA: tissue enhanced in heart muscle, skeletal muscle, tongue) and associates
      with sarcomeric structures.
    action: ACCEPT
    reason: >-
      CRYAB is highly expressed in muscle tissue and localizes to sarcomeric
      structures (Z-bands, intercalated disks) as documented by PMID:28493373.
      Contractile muscle fiber localization is consistent with CRYAB's role in
      muscle and its association with desmin and titin.
- term:
    id: GO:0051403
    label: stress-activated MAPK cascade
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IEA annotation from Ensembl Compara ortholog transfer for stress-activated
      MAPK cascade. CRYAB has been reported to modulate MAPK signaling in some
      stress contexts, but this is not a core function.
    action: KEEP_AS_NON_CORE
    reason: >-
      Stress-activated MAPK cascade involvement is a secondary consequence of
      CRYAB's stress-protective functions rather than a direct core activity.
      Transferred from rat ortholog. Non-core.
- term:
    id: GO:0097060
    label: synaptic membrane
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IEA annotation from Ensembl Compara ortholog transfer for synaptic membrane
      localization. CRYAB is expressed in neural tissues. Synaptic membrane
      localization is a tissue-specific neural localization.
    action: KEEP_AS_NON_CORE
    reason: >-
      Synaptic membrane localization is a neural tissue-specific localization
      transferred from rat ortholog. Non-core.
- term:
    id: GO:0097512
    label: cardiac myofibril
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IEA annotation from Ensembl Compara ortholog transfer for cardiac myofibril
      localization. CRYAB is highly expressed in cardiac muscle and localizes to
      sarcomeric structures including Z-bands and intercalated disks
      (PMID:28493373).
    action: ACCEPT
    reason: >-
      Cardiac myofibril localization is well-supported by CRYAB's high expression
      in cardiac muscle (HPA, UniProt) and its documented localization at Z-bands
      and intercalated disks (PMID:28493373). CRYAB mutations cause
      cardiomyopathies, underscoring its cardiac muscle function.
- term:
    id: GO:2000378
    label: negative regulation of reactive oxygen species metabolic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  review:
    summary: >-
      IEA annotation from Ensembl Compara ortholog transfer for negative regulation
      of reactive oxygen species metabolic process. CRYAB has been implicated in
      oxidative stress protection, but this is a secondary function.
    action: KEEP_AS_NON_CORE
    reason: >-
      Negative regulation of ROS is a downstream protective effect of CRYAB's
      chaperone activity rather than a direct core function. Transferred from rat
      ortholog. Non-core.
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: IDA
  original_reference_id: GO_REF:0000052
  review:
    summary: >-
      IDA annotation from HPA immunofluorescence curation for cytosol localization.
      CRYAB is a soluble cytoplasmic chaperone that resides in the cytosol under
      normal conditions.
    action: ACCEPT
    reason: >-
      Cytosol localization is the primary subcellular localization of CRYAB under
      normal conditions. Supported by HPA immunofluorescence data and consistent
      with its role as a soluble chaperone.
- term:
    id: GO:0005886
    label: plasma membrane
  evidence_type: IDA
  original_reference_id: GO_REF:0000052
  review:
    summary: >-
      IDA annotation from HPA immunofluorescence curation for plasma membrane.
      Some plasma membrane signal may be detected by immunofluorescence but CRYAB
      is primarily cytosolic.
    action: KEEP_AS_NON_CORE
    reason: >-
      Plasma membrane localization from HPA immunofluorescence is a secondary
      localization. CRYAB may associate with membrane-proximal structures in some
      contexts (e.g., cadherin/catenin complexes, PMID:22158051) but is primarily
      a cytosolic protein. Non-core.
- term:
    id: GO:0043067
    label: regulation of programmed cell death
  evidence_type: IMP
  original_reference_id: PMID:23542032
  review:
    summary: >-
      IMP annotation from PMID:23542032 (Yamashita et al. 2013) for regulation of
      programmed cell death. The study showed that knockdown of CRYAB facilitates
      death of UVC-exposed cells, and that CRYAB expressed as an ER-anchored form
      lowered UVC sensitivity. CRYAB binding to MG23/TMEM109 mediates protection
      against UVC-induced cell death.
    action: ACCEPT
    reason: >-
      CRYAB's role in regulating programmed cell death is well-established. This
      annotation from PMID:23542032 specifically documents the protective role
      against UVC-induced cell death via interaction with TMEM109. This is
      consistent with CRYAB's broader anti-apoptotic function (PMID:14752512). The
      parent term regulation of programmed cell death is appropriate here since
      the paper demonstrates both protection and sensitization depending on CRYAB
      expression levels.
    supported_by:
      - reference_id: PMID:23542032
        supporting_text: >-
          The small heat shock protein αB-crystallin (αBC) is identified as a
          MG23 binding molecule and its knockdown facilitates death of UVC-exposed
          cells.
- term:
    id: GO:0005198
    label: structural molecule activity
  evidence_type: IDA
  original_reference_id: PMID:16303126
  review:
    summary: >-
      IDA annotation for structural molecule activity from PMID:16303126 (Pigaga &
      Quinlan 2006). This paper primarily demonstrates chaperone-like activity of
      alpha-crystallins in suppressing aggregation of T5P gamma C-crystallin. The
      structural molecule activity annotation may reflect CRYAB's dual role in the
      lens as both a structural protein and a chaperone.
    action: ACCEPT
    reason: >-
      CRYAB has a dual role in the lens as both a structural protein (contributing
      to lens transparency and refractive index) and a molecular chaperone
      (preventing aggregation of damaged crystallins). PMID:16303126 demonstrates
      both roles. The structural molecule activity annotation is appropriate for
      the structural lens function.
    supported_by:
      - reference_id: PMID:16303126
        supporting_text: >-
          These data therefore suggest a dual role for these chaperones in
          maintaining transparency in the lens.
- term:
    id: GO:0032991
    label: protein-containing complex
  evidence_type: IDA
  original_reference_id: PMID:16303126
  review:
    summary: >-
      IDA annotation for protein-containing complex from PMID:16303126. CRYAB forms
      large oligomeric complexes, typically of 24-32 subunits. This is a fundamental
      feature of its biology as a small heat shock protein.
    action: ACCEPT
    reason: >-
      CRYAB forms large polydisperse homo-oligomeric and hetero-oligomeric
      complexes. This is a core structural feature well-documented by multiple
      biophysical studies (PMID:16303126, PMID:22153508, PMID:19651604).
- term:
    id: GO:0042802
    label: identical protein binding
  evidence_type: IPI
  original_reference_id: PMID:16303126
  review:
    summary: >-
      IPI annotation for identical protein binding from PMID:16303126, reflecting
      CRYAB self-association in the context of alpha-crystallin oligomeric
      complexes.
    action: ACCEPT
    reason: >-
      Confirms CRYAB self-interaction, which is central to its oligomeric
      assembly. Core property.
- term:
    id: GO:0031333
    label: negative regulation of protein-containing complex assembly
  evidence_type: IDA
  original_reference_id: PMID:23106396
  review:
    summary: >-
      IDA annotation from PMID:23106396 (Narayan et al. 2012) for negative
      regulation of protein-containing complex assembly. The study demonstrated
      that CRYAB binds to misfolded amyloid-beta oligomeric species, forming
      long-lived complexes that prevent further growth into fibrils and prevent
      their dissociation. This is a manifestation of CRYAB's holdase chaperone
      activity applied to amyloid aggregation.
    action: ACCEPT
    reason: >-
      This annotation captures an important aspect of CRYAB's chaperone function
      -- it prevents further assembly of amyloid-beta oligomers into fibrils.
      PMID:23106396 provides direct experimental evidence using single-molecule
      fluorescence techniques.
    supported_by:
      - reference_id: PMID:23106396
        supporting_text: >-
          both chaperones bind to misfolded oligomeric species and form long-lived
          complexes, thereby preventing both their further growth into fibrils and
          their dissociation.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:20587334
  review:
    summary: >-
      IPI annotation from PMID:20587334 (Deng et al. 2010), which identified LBH
      (Q53QV2) as a CRYAB-interacting partner by yeast two-hybrid and confirmed by
      co-immunoprecipitation and GST pull-down. The interaction leads to synergistic
      repression of p53 and p21 transcriptional activities.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Protein binding is uninformative. The CRYAB-LBH interaction is interesting
      but the term does not capture the functional significance. The downstream
      functional consequence is captured by the negative regulation of
      DNA-templated transcription annotation from the same paper.
- term:
    id: GO:0005634
    label: nucleus
  evidence_type: IDA
  original_reference_id: PMID:20587334
  review:
    summary: >-
      IDA annotation for nucleus localization from PMID:20587334. The study showed
      that CRYAB, which is normally cytoplasmic, accumulates partially in the
      nucleus when co-transfected with LBH in COS-7 cells.
    action: ACCEPT
    reason: >-
      Nuclear localization of CRYAB is confirmed by direct observation in
      PMID:20587334, consistent with other IDA evidence from PMID:19464326.
      CRYAB translocates to the nucleus under specific conditions.
    supported_by:
      - reference_id: PMID:20587334
        supporting_text: >-
          alphaB-crystallin that is cytoplasmic alone, accumulates partialy in
          the nucleus when co-transfected with LBH.
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IDA
  original_reference_id: PMID:20587334
  review:
    summary: >-
      IDA annotation for cytoplasm localization from PMID:20587334. CRYAB is
      cytoplasmic when expressed alone in COS-7 cells.
    action: ACCEPT
    reason: >-
      Cytoplasm is the primary localization of CRYAB, confirmed by direct
      observation in PMID:20587334.
- term:
    id: GO:0032991
    label: protein-containing complex
  evidence_type: IDA
  original_reference_id: PMID:20587334
  review:
    summary: >-
      IDA annotation for protein-containing complex from PMID:20587334. CRYAB forms
      a complex with LBH as shown by co-immunoprecipitation and GST pull-down.
    action: ACCEPT
    reason: >-
      CRYAB forms complexes with multiple partners. The complex with LBH is
      documented by co-immunoprecipitation in PMID:20587334.
- term:
    id: GO:0045892
    label: negative regulation of DNA-templated transcription
  evidence_type: IDA
  original_reference_id: PMID:20587334
  review:
    summary: >-
      IDA annotation from PMID:20587334 for negative regulation of DNA-templated
      transcription. Overexpression of CRYAB reduced the transcriptional activities
      of p53 and p21 promoters, and co-expression with LBH resulted in stronger
      repression. This is a secondary/non-core function of CRYAB.
    action: KEEP_AS_NON_CORE
    reason: >-
      While the experimental evidence from PMID:20587334 supports that CRYAB can
      repress transcription from p53 and p21 promoters, this is likely a secondary
      consequence of CRYAB's interaction with LBH and its general protein-binding
      chaperone activity rather than a core transcriptional regulatory function.
      CRYAB is not a transcription factor. This function is non-core.
    supported_by:
      - reference_id: PMID:20587334
        supporting_text: >-
          Transient transfection assays indicated that overexpression of LBH or
          alphaB-crystallin reduced the transcriptional activities of p53 and p21,
          respectively, Overexpression of both alphaB-crystallin and LBH together
          resulted in a stronger repression of the transcriptional activities of
          p21 and p53.
- term:
    id: GO:0001540
    label: amyloid-beta binding
  evidence_type: IPI
  original_reference_id: PMID:23106396
  review:
    summary: >-
      IPI annotation from PMID:23106396 (Narayan et al. 2012) for amyloid-beta
      binding. Using single-molecule fluorescence techniques, the study demonstrated
      that CRYAB binds to amyloid-beta oligomeric species, forming long-lived
      complexes. The WITH/FROM is APP processed to amyloid-beta
      (P05067-PRO_0000000093).
    action: ACCEPT
    reason: >-
      CRYAB binding to amyloid-beta oligomers is well-documented (PMID:23106396,
      PMID:17046756). This is a specific manifestation of CRYAB's holdase chaperone
      activity -- it sequesters misfolded amyloid-beta species. CRYAB is found
      co-localized with amyloid-beta in senile plaques of Alzheimer's disease
      patients. This is a meaningful specific MF annotation.
    supported_by:
      - reference_id: PMID:23106396
        supporting_text: >-
          both chaperones bind to misfolded oligomeric species and form long-lived
          complexes, thereby preventing both their further growth into fibrils and
          their dissociation.
      - reference_id: PMID:17046756
        supporting_text: >-
          Interactions between Abeta and alphaB-crystallin involve the hydrophobic
          core residues 17-21 as well as residues 31-32 of Abeta, and thus the same
          chemical groups which are important for Abeta aggregation.
- term:
    id: GO:0044877
    label: protein-containing complex binding
  evidence_type: IPI
  original_reference_id: PMID:23106396
  review:
    summary: >-
      IPI annotation from PMID:23106396 for protein-containing complex binding.
      The WITH/FROM is ComplexPortal:CPX-1180, which refers to the amyloid-beta
      oligomeric complex. CRYAB binds to these oligomeric complexes as shown by
      single-molecule fluorescence.
    action: ACCEPT
    reason: >-
      CRYAB binds to amyloid-beta oligomeric complexes (PMID:23106396). This
      annotation specifically captures the binding to a protein-containing complex
      (the amyloid-beta oligomer) as opposed to individual amyloid-beta monomers.
      This reflects CRYAB's holdase function of sequestering aggregation-prone
      complexes.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:28470624
  review:
    summary: >-
      IPI annotation from PMID:28470624 (Sharma et al. 2017), which showed CRYAB
      is a sensor for assembly intermediates and subunit topology of desmin
      intermediate filaments. The WITH/FROM is desmin (DES, P17661). CRYAB binds
      rapidly during early stages of desmin filament assembly.
    action: MODIFY
    reason: >-
      Protein binding is uninformative. The CRYAB-desmin interaction is a
      functionally significant interaction that reflects CRYAB's role as a
      chaperone for cytoskeletal assembly. This should be annotated as
      cytoskeletal protein binding (GO:0008092) which is already present as an
      IEA annotation, providing experimental support for that more specific term.
    proposed_replacement_terms:
      - id: GO:0008092
        label: cytoskeletal protein binding
    supported_by:
      - reference_id: PMID:28470624
        supporting_text: >-
          the binding of CRYAB to desmin is subject to its assembly status, to the
          subunit organization within filaments formed and to the integrity of the
          C-terminal tail domain of desmin.
- term:
    id: GO:1905907
    label: negative regulation of amyloid fibril formation
  evidence_type: IDA
  original_reference_id: PMID:23106396
  review:
    summary: >-
      IDA annotation from PMID:23106396 for negative regulation of amyloid fibril
      formation. CRYAB sequesters amyloid-beta oligomers, preventing their further
      growth into fibrils. This is a specific application of CRYAB's holdase
      chaperone function to amyloid aggregation.
    action: ACCEPT
    reason: >-
      PMID:23106396 directly demonstrates that CRYAB prevents amyloid-beta
      oligomers from growing into fibrils using single-molecule fluorescence
      techniques. This is a well-supported annotation that captures a specific
      biological consequence of CRYAB's holdase activity.
    supported_by:
      - reference_id: PMID:23106396
        supporting_text: >-
          both chaperones bind to misfolded oligomeric species and form long-lived
          complexes, thereby preventing both their further growth into fibrils and
          their dissociation.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:12235146
  review:
    summary: >-
      IPI annotation from PMID:12235146 (Pasta et al. 2002), which studied C-terminal
      extension swapping between alphaA- and alphaB-crystallins. The WITH/FROM includes
      aldolase (P00883) and rhodanese (P11415), which are substrate proteins used in
      chaperone activity assays. CRYAB binding to these substrates reflects its holdase
      chaperone activity.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Protein binding is uninformative. The interactions with aldolase and rhodanese
      are chaperone-substrate interactions used as in vitro assay substrates. This
      is better captured by the chaperone function annotations (GO:0044183 or
      GO:0050821).
- term:
    id: GO:0050821
    label: protein stabilization
  evidence_type: IMP
  original_reference_id: PMID:12235146
  review:
    summary: >-
      IMP annotation from PMID:12235146 (Pasta et al. 2002) for protein
      stabilization. The study demonstrated that CRYAB (and chimeric variants)
      prevent aggregation of various substrate proteins (thermal and non-thermal
      models), demonstrating chaperone-like activity. The C-terminal extension
      plays a crucial role in structure and chaperone activity.
    action: ACCEPT
    reason: >-
      Protein stabilization is an excellent BP term for CRYAB's holdase chaperone
      activity. CRYAB prevents aggregation of denatured proteins and maintains
      them in a soluble, folding-competent state. This is a core function of
      CRYAB. PMID:12235146 provides direct evidence for chaperone-like activity
      using multiple protein substrates.
    supported_by:
      - reference_id: PMID:12235146
        supporting_text: >-
          We have used thermal and non-thermal models of protein aggregation and
          found that the chimeric alphaB with the C-terminal extension of
          alphaA-crystallin, alphaBAc, exhibits dramatically enhanced
          chaperone-like activity.
- term:
    id: GO:0005654
    label: nucleoplasm
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-5082356
  review:
    summary: >-
      TAS annotation from Reactome pathway R-HSA-5082356 (HSF1-mediated gene
      expression) for nucleoplasm localization. CRYAB translocates to the nucleus
      during heat stress (PMID:19464326) and specifically resides in SC35 speckles
      within the nucleoplasm.
    action: ACCEPT
    reason: >-
      Nucleoplasm localization is consistent with CRYAB's documented nuclear
      translocation during heat stress (PMID:19464326). SC35 speckles are
      nucleoplasmic structures. The Reactome annotation for HSF1-mediated gene
      expression context is appropriate.
- term:
    id: GO:0070062
    label: extracellular exosome
  evidence_type: HDA
  original_reference_id: PMID:23533145
  review:
    summary: >-
      HDA annotation from PMID:23533145, an in-depth proteomic study of exosomes
      isolated from expressed prostatic secretions in urine. CRYAB was identified
      in exosome fractions by mass spectrometry.
    action: ACCEPT
    reason: >-
      CRYAB has been identified in extracellular exosomes by proteomic studies
      (PMID:23533145). This is consistent with the unconventional secretion pathway
      described in PMID:32272059.
- term:
    id: GO:0070062
    label: extracellular exosome
  evidence_type: HDA
  original_reference_id: PMID:19056867
  review:
    summary: >-
      HDA annotation from PMID:19056867, a large-scale proteomics and
      phosphoproteomics study of urinary exosomes. CRYAB was identified in exosome
      fractions.
    action: ACCEPT
    reason: >-
      Independent confirmation of CRYAB in extracellular exosomes by urinary
      exosome proteomics.
- term:
    id: GO:0071480
    label: cellular response to gamma radiation
  evidence_type: IMP
  original_reference_id: PMID:23542032
  review:
    summary: >-
      IMP annotation from PMID:23542032 for cellular response to gamma radiation.
      The paper actually studies UVC-induced cell death, not gamma radiation
      specifically. It shows CRYAB knockdown facilitates death of UVC-exposed
      cells. This annotation may reflect broader DNA damage response involvement.
    action: KEEP_AS_NON_CORE
    reason: >-
      PMID:23542032 specifically demonstrates CRYAB's protective role against
      UVC-induced cell death, not gamma radiation per se. The annotation was made
      by MGI, suggesting it may be based on mouse data related to radiation
      response. CRYAB's role in DNA damage response is secondary to its core
      chaperone and anti-apoptotic functions. Non-core.
    supported_by:
      - reference_id: PMID:23542032
        supporting_text: >-
          knockdown of the ER protein mitsugumin23 (MG23) enhances cell death
          induced by ultraviolet C (UVC), which causes DNA damage.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:14752512
  review:
    summary: >-
      IPI annotation from PMID:14752512 (Mao et al. 2004). The WITH/FROM includes
      Bax (Q07812) and Bcl-X(S) (Q07817). CRYAB binds pro-apoptotic Bax and
      Bcl-X(S) to sequester their translocation during apoptosis.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Protein binding is uninformative. The functionally significant interaction
      with Bax and Bcl-X(S) is better captured by the negative regulation of
      apoptotic process annotations. The specific anti-apoptotic mechanism
      involves sequestering these pro-apoptotic factors in the cytoplasm.
- term:
    id: GO:0005634
    label: nucleus
  evidence_type: IDA
  original_reference_id: PMID:19464326
  review:
    summary: >-
      IDA annotation from PMID:19464326 (Vos et al. 2009) for nucleus localization.
      The study used confocal microscopy to show CRYAB (HSPB5) translocates to the
      nucleus during heat shock, where it resides in SC35 speckles. This is a
      well-documented stress-dependent nuclear localization.
    action: ACCEPT
    reason: >-
      Direct microscopy evidence for CRYAB nuclear translocation during heat
      stress. PMID:19464326 is the key study documenting stress-dependent nuclear
      localization and SC35 speckle residence for CRYAB.
    supported_by:
      - reference_id: PMID:19464326
        supporting_text: >-
          Some members also show a dynamic, stress-induced translocation to
          SC35 splicing speckles.
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IDA
  original_reference_id: PMID:19464326
  review:
    summary: >-
      IDA annotation from PMID:19464326 for cytoplasm localization. CRYAB localizes
      to the cytoplasm under normal (unstressed) conditions.
    action: ACCEPT
    reason: >-
      Direct microscopy evidence for cytoplasmic localization under normal
      conditions (PMID:19464326).
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IDA
  original_reference_id: GO_REF:0000054
  review:
    summary: >-
      IDA annotation from GO_REF:0000054, based on curation of intracellular
      localizations of expressed fusion proteins in living cells (LIFEdb). Confirms
      cytoplasmic localization.
    action: ACCEPT
    reason: >-
      Independent confirmation of cytoplasmic localization from expressed fusion
      protein imaging.
- term:
    id: GO:0042803
    label: protein homodimerization activity
  evidence_type: IPI
  original_reference_id: PMID:19646995
  review:
    summary: >-
      IPI annotation from PMID:19646995 (Bagneris et al. 2009) for protein
      homodimerization activity. The crystal structure of the alpha-crystallin
      domain dimer of CRYAB was solved at 2.63 angstroms, showing that the alpha-
      crystallin domain forms homodimers with a shared groove at the interface.
      The dimer is the basic building block for higher-order oligomeric assembly.
    action: ACCEPT
    reason: >-
      The crystal structure of CRYAB alpha-crystallin domain homodimers
      (PMID:19646995) directly demonstrates protein homodimerization activity.
      The dimer is the fundamental building block of the CRYAB oligomeric
      assembly. This is a core structural property.
    supported_by:
      - reference_id: PMID:19646995
        supporting_text: >-
          crystal structures of excised alpha-crystallin domain from rat Hsp20
          and that from human alphaB-crystallin show that they form homodimers
          with a shared groove at the interface by extending a beta sheet.
- term:
    id: GO:0051082
    label: unfolded protein binding
  evidence_type: IPI
  original_reference_id: PMID:16303126
  review:
    summary: >-
      GO:0051082 "unfolded protein binding" is being obsoleted (go-ontology#30962).
      This IPI annotation is based on PMID:16303126, which demonstrated that alpha
      B-crystallin (CRYAB) suppresses the aggregation of the cataract-causing T5P mutant
      gamma C-crystallin. In this study, CRYAB increased the solubility of T5P gamma
      C-crystallin both in vitro (by sedimentation assay and sucrose gradient
      centrifugation) and in transfected cells, and significantly reduced the size of
      T5P gamma C-crystallin aggregates. The interacting partner (WITH/FROM) is the
      destabilized T5P gamma C-crystallin. The paper describes this as "chaperone-like
      activity" with a "dual role" -- increasing soluble protein fraction and reducing
      aggregate size. This is classic holdase activity: CRYAB binds partially denatured
      proteins and prevents their aggregation, but does NOT refold them. The term
      GO:0044183 "protein folding chaperone" is the best available interim replacement
      MF term, though it is imperfect because CRYAB does not assist in protein folding
      per se -- it prevents aggregation. A holdase-specific GO term does not yet exist
      and should be requested.
    action: MODIFY
    reason: >-
      GO:0051082 is being obsoleted. The experimental evidence from PMID:16303126
      clearly demonstrates holdase chaperone activity -- CRYAB suppresses aggregation
      of the destabilized T5P mutant gamma C-crystallin and increases its solubility.
      The paper explicitly describes "a dual role for these chaperones in maintaining
      transparency in the lens": increasing the proportion of soluble protein and
      reducing aggregate size. This is not passive "unfolded protein binding" but
      active suppression of aggregation (holdase function). The IPI evidence with
      T5P gamma C-crystallin as the interacting partner is strong. GO:0044183 "protein
      folding chaperone" is the closest current MF term, but a holdase-specific term
      is needed since CRYAB does NOT refold proteins.
    proposed_replacement_terms:
      - id: GO:0044183
        label: protein folding chaperone
    additional_reference_ids:
      - PMID:12235146
    supported_by:
      - reference_id: PMID:16303126
        supporting_text: >-
          the major lenticular protein chaperones, alpha A- and alpha B-crystallin,
          increased the solubility of the T5P gamma C-crystallin both in vitro and in
          transfected cells. More importantly, the size of the T5P gamma C-crystallin
          aggregates were also significantly reduced in the presence of the lenticular
          chaperones.
      - reference_id: PMID:16303126
        supporting_text: >-
          These data therefore suggest a dual role for these chaperones in maintaining
          transparency in the lens. The first is that these protein chaperones increase
          the proportion of the soluble T5P gamma C-crystallin and the second is that
          they also reduce light scatter by reducing the aggregate size of T5P gamma
          C-crystallin.
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IDA
  original_reference_id: PMID:14752512
  review:
    summary: >-
      IDA annotation from PMID:14752512 (Mao et al. 2004) for cytoplasm
      localization. The study demonstrated that CRYAB is cytoplasmic and prevents
      translocation of Bax and Bcl-X(S) from cytosol into mitochondria.
    action: ACCEPT
    reason: >-
      Cytoplasmic localization confirmed by direct observation in PMID:14752512.
      The anti-apoptotic mechanism requires CRYAB to be cytoplasmic to sequester
      pro-apoptotic factors.
    supported_by:
      - reference_id: PMID:14752512
        supporting_text: >-
          alpha-crystallins prevent the translocation of Bax and Bcl-X(S) from
          cytosol into mitochondria during staurosporine-induced apoptosis.
- term:
    id: GO:0032387
    label: negative regulation of intracellular transport
  evidence_type: IDA
  original_reference_id: PMID:14752512
  review:
    summary: >-
      IDA annotation from PMID:14752512 for negative regulation of intracellular
      transport. CRYAB prevents the translocation of Bax and Bcl-X(S) from the
      cytosol to mitochondria during staurosporine-induced apoptosis. This
      sequestration of pro-apoptotic factors is a specific form of negative
      regulation of intracellular transport.
    action: ACCEPT
    reason: >-
      PMID:14752512 directly demonstrates that CRYAB prevents the
      cytosol-to-mitochondria translocation of Bax and Bcl-X(S). This is a specific
      anti-apoptotic mechanism involving negative regulation of intracellular
      protein transport. The annotation is well-supported by direct experimental
      evidence.
    supported_by:
      - reference_id: PMID:14752512
        supporting_text: >-
          Through the interaction, alpha-crystallins prevent the translocation of
          Bax and Bcl-X(S) from cytosol into mitochondria during
          staurosporine-induced apoptosis.
- term:
    id: GO:0043066
    label: negative regulation of apoptotic process
  evidence_type: IDA
  original_reference_id: PMID:14752512
  review:
    summary: >-
      IDA annotation from PMID:14752512 for negative regulation of apoptotic
      process. The study demonstrates a clear anti-apoptotic mechanism: CRYAB binds
      Bax and Bcl-X(S) to prevent their mitochondrial translocation, preserves
      mitochondrial integrity, restricts cytochrome c release, represses caspase-3
      activation, and blocks PARP degradation.
    action: ACCEPT
    reason: >-
      This is one of the strongest pieces of evidence for CRYAB's anti-apoptotic
      function. PMID:14752512 provides a complete mechanistic pathway from
      initial binding (Bax/Bcl-X(S) sequestration) to downstream consequences
      (preserved mitochondrial integrity, blocked caspase-3 activation). This is
      a core function of CRYAB.
    supported_by:
      - reference_id: PMID:14752512
        supporting_text: >-
          alpha-crystallins preserve the integrity of mitochondria, restrict release
          of cytochrome c, repress activation of caspase-3 and block degradation of
          PARP. Thus, our results demonstrate a novel antiapoptotic mechanism for
          alpha-crystallins.
- term:
    id: GO:0006457
    label: protein folding
  evidence_type: NAS
  original_reference_id: PMID:9731540
  review:
    summary: >-
      NAS annotation from PMID:9731540 (Vicart et al. 1998) for protein folding.
      The paper identified the R120G mutation in CRYAB that causes desmin-related
      myopathy and describes CRYAB as possessing molecular chaperone activity.
      However, CRYAB is a holdase, not a foldase. It prevents aggregation but
      does not actively fold proteins.
    action: MODIFY
    reason: >-
      PMID:9731540 describes CRYAB as a molecular chaperone but does not
      demonstrate protein folding activity. CRYAB prevents protein aggregation
      (holdase activity) but does not refold denatured proteins. GO:0050821
      protein stabilization is more appropriate. The NAS evidence code itself
      is weak (non-traceable author statement).
    proposed_replacement_terms:
      - id: GO:0050821
        label: protein stabilization
    supported_by:
      - reference_id: PMID:9731540
        supporting_text: >-
          AlphaB-crystallin is a member of the small heat shock protein (shsp)
          family and possesses molecular chaperone activity.
- term:
    id: GO:0006936
    label: muscle contraction
  evidence_type: TAS
  original_reference_id: PMID:9731540
  review:
    summary: >-
      TAS annotation from PMID:9731540 for muscle contraction. The paper identified
      the CRYAB R120G mutation causing desmin-related myopathy. While CRYAB is
      important for muscle function (interacting with desmin and titin), it is not
      a direct participant in the muscle contraction machinery. Rather, it serves
      as a chaperone for muscle structural proteins.
    action: KEEP_AS_NON_CORE
    reason: >-
      CRYAB is not directly involved in the muscle contraction mechanism. Its role
      in muscle is as a chaperone for cytoskeletal and sarcomeric proteins (desmin,
      titin). Loss of CRYAB function leads to myopathy through aggregation of
      desmin, not through direct contractile defects. The TAS evidence is weak,
      and the association with muscle contraction is indirect. Non-core.
    supported_by:
      - reference_id: PMID:9731540
        supporting_text: >-
          We identified an R120G missense mutation in CRYAB that co-segregates
          with the disease phenotype in this family.
core_functions:
- molecular_function:
    id: GO:0044183
    label: protein folding chaperone
  description: >-
    CRYAB (HSPB5) is a small heat shock protein that functions as an ATP-independent
    holdase chaperone. It binds partially denatured or destabilized proteins to prevent
    their aggregation, maintaining clients in a refolding-competent state for downstream
    ATP-dependent chaperone systems such as HSP70, but does NOT actively refold substrates
    itself. CRYAB forms highly polydisperse oligomers (approximately 10-40 subunits)
    with rapid subunit exchange dynamics that are important for chaperone activity
    (DOI:10.1038/s41467-024-54647-7). The canonical architecture comprises a central
    alpha-crystallin domain (ACD) mediating dimerization, flanked by a variable N-terminal
    domain (NTD) and a short C-terminal domain (CTD). A conserved N-terminal IXI-like
    motif (NT-IXI) engages the ACD hydrophobic groove to govern assembly; perturbation
    of this motif transforms native assemblies into reversible elongated helical fibrils
    as resolved by cryo-EM (DOI:10.1038/s41467-024-54647-7). Stress-activated
    phosphorylation (notably p38 MAPK targeting Ser59) modulates oligomeric state and
    can shift CRYAB condensates toward protective or pathological material states
    (DOI:10.1016/j.isci.2024.109510, DOI:10.1172/jci163730). Substrates bound by CRYAB
    can subsequently be refolded by HSP70/HSP40 foldase chaperones, or routed to the
    ubiquitin-proteasome system for degradation.
  directly_involved_in:
    - id: GO:0050821
      label: protein stabilization
    - id: GO:0009408
      label: response to heat
    - id: GO:1905907
      label: negative regulation of amyloid fibril formation
  locations:
    - id: GO:0005829
      label: cytosol
  substrates:
    - id: UniProtKB:P17661
      label: desmin
    - id: UniProtKB:P05067-PRO_0000000093
      label: amyloid-beta
  supported_by:
    - reference_id: PMID:16303126
      supporting_text: >-
        the major lenticular protein chaperones, alpha A- and alpha B-crystallin,
        increased the solubility of the T5P gamma C-crystallin both in vitro and in
        transfected cells. More importantly, the size of the T5P gamma C-crystallin
        aggregates were also significantly reduced in the presence of the lenticular
        chaperones.
    - reference_id: PMID:19464326
      supporting_text: >-
        HSPB1 and HSPB5, that chaperoned heat unfolded substrates and kept them
        folding competent.
    - reference_id: PMID:23106396
      supporting_text: >-
        both chaperones bind to misfolded oligomeric species and form long-lived
        complexes, thereby preventing both their further growth into fibrils and
        their dissociation.
    - reference_id: PMID:12235146
      supporting_text: >-
        We have used thermal and non-thermal models of protein aggregation and found
        that the chimeric alphaB with the C-terminal extension of alphaA-crystallin
        exhibits dramatically enhanced chaperone-like activity.
- molecular_function:
    id: GO:0005212
    label: structural constituent of eye lens
  description: >-
    CRYAB is one of the major structural proteins of the vertebrate eye lens, contributing
    to lens transparency and refractive index. In the lens, it serves a dual role as both
    a structural protein (maintaining lens transparency through high concentration and
    ordered short-range interactions) and a chaperone (preventing aggregation of damaged
    crystallins that would cause light-scattering opacification).
  locations:
    - id: GO:0005829
      label: cytosol
  supported_by:
    - reference_id: PMID:16303126
      supporting_text: >-
        These data therefore suggest a dual role for these chaperones in maintaining
        transparency in the lens.
- molecular_function:
    id: GO:0008092
    label: cytoskeletal protein binding
  description: >-
    CRYAB binds desmin intermediate filaments in a manner dependent on desmin assembly
    status and subunit organization, acting as a sensor for assembly intermediates. In
    cardiac and skeletal muscle, CRYAB associates with sarcomeric structures including
    Z-bands and intercalated disks, and interacts with titin. Mutations in CRYAB (e.g.,
    R120G) cause desmin-related myopathy through aggregation of desmin filaments. Recent
    work shows that phosphorylation at Ser59 can shift CRYAB condensates toward less
    dynamic, aggregate-prone states that mislocalize cytoskeletal and sarcomeric client
    proteins, a pathological mechanism termed condensatopathy; the phosphomimetic S59D
    behaves similarly to the R120G cardiomyopathy mutant (DOI:10.1172/jci163730).
  directly_involved_in:
    - id: GO:0050821
      label: protein stabilization
  locations:
    - id: GO:0030018
      label: Z disc
    - id: GO:0097512
      label: cardiac myofibril
  substrates:
    - id: UniProtKB:P17661
      label: desmin
  supported_by:
    - reference_id: PMID:28470624
      supporting_text: >-
        the binding of CRYAB to desmin is subject to its assembly status, to the
        subunit organization within filaments formed and to the integrity of the
        C-terminal tail domain of desmin.
    - reference_id: PMID:9731540
      supporting_text: >-
        A missense mutation in the alphaB-crystallin chaperone gene causes a
        desmin-related myopathy.
- molecular_function:
    id: GO:0001540
    label: amyloid-beta binding
  description: >-
    CRYAB directly binds amyloid-beta oligomeric species and forms long-lived complexes,
    preventing both further growth of oligomers into fibrils and their dissociation. This
    represents a specific application of CRYAB holdase activity to amyloidogenic substrates.
    CRYAB is found co-localized with amyloid-beta in senile plaques of Alzheimer disease
    patients.
  directly_involved_in:
    - id: GO:0043066
      label: negative regulation of apoptotic process
    - id: GO:1905907
      label: negative regulation of amyloid fibril formation
    - id: GO:0031333
      label: negative regulation of protein-containing complex assembly
  locations:
    - id: GO:0005829
      label: cytosol
  supported_by:
    - reference_id: PMID:23106396
      supporting_text: >-
        both chaperones bind to misfolded oligomeric species and form long-lived
        complexes, thereby preventing both their further growth into fibrils and
        their dissociation.
    - reference_id: PMID:17046756
      supporting_text: >-
        alphaB-crystallin competes efficiently for Abeta monomer-monomer interactions.
        Interactions between Abeta and alphaB-crystallin involve the hydrophobic core
        residues 17-21 as well as residues 31-32 of Abeta.
references:
- id: GO_REF:0000033
  title: Annotation inferences using phylogenetic trees
  findings: []
- id: GO_REF:0000043
  title: Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping
  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:0000052
  title: Gene Ontology annotation based on curation of immunofluorescence data
  findings: []
- id: GO_REF:0000054
  title: Gene Ontology annotation based on curation of intracellular localizations
    of expressed fusion proteins in living cells
  findings: []
- id: GO_REF:0000107
  title: Automatic transfer of experimentally verified manual GO annotation data to
    orthologs using Ensembl Compara
  findings: []
- id: GO_REF:0000117
  title: Electronic Gene Ontology annotations created by ARBA machine learning models
  findings: []
- id: GO_REF:0000120
  title: Combined Automated Annotation using Multiple IEA Methods
  findings: []
- id: PMID:11700327
  title: Detection of protein-protein interactions among lens crystallins in a mammalian
    two-hybrid system assay.
  findings: []
- id: PMID:12235146
  title: Role of the C-terminal extensions of alpha-crystallins. Swapping the C-terminal
    extension of alpha-crystallin to alphaB-crystallin results in enhanced chaperone
    activity.
  findings: []
- id: PMID:12601044
  title: Alteration of protein-protein interactions of congenital cataract crystallin
    mutants.
  findings: []
- id: PMID:14752512
  title: Human alphaA- and alphaB-crystallins bind to Bax and Bcl-X(S) to sequester
    their translocation during staurosporine-induced apoptosis.
  findings: []
- id: PMID:16049941
  title: A pilot proteomic study of amyloid precursor interactors in Alzheimer's disease.
  findings: []
- id: PMID:16303126
  title: Lenticular chaperones suppress the aggregation of the cataract-causing mutant
    T5P gamma C-crystallin.
  findings: []
- id: PMID:17046756
  title: alphaB-crystallin competes with Alzheimer's disease beta-amyloid peptide
    for peptide-peptide interactions and induces oxidation of Abeta-Met35.
  findings: []
- id: PMID:18330356
  title: Construction and characterization of a normalized yeast two-hybrid library
    derived from a human protein-coding clone collection.
  findings: []
- id: PMID:19056867
  title: Large-scale proteomics and phosphoproteomics of urinary exosomes.
  findings: []
- id: PMID:19464326
  title: HSPB7 is a SC35 speckle resident small heat shock protein.
  findings: []
- id: PMID:19646995
  title: Crystal structures of alpha-crystallin domain dimers of alphaB-crystallin
    and Hsp20.
  findings: []
- id: PMID:19651604
  title: The eye lens chaperone alpha-crystallin forms defined globular assemblies.
  findings: []
- id: PMID:20587334
  title: Synergistic efficacy of LBH and alphaB-crystallin through inhibiting transcriptional
    activities of p53 and p21.
  findings: []
- id: PMID:20802487
  title: Solid-state NMR and SAXS studies provide a structural basis for the activation
    of alphaB-crystallin oligomers.
  findings: []
- id: PMID:21464278
  title: N-terminal domain of alphaB-crystallin provides a conformational switch for
    multimerization and structural heterogeneity.
  findings: []
- id: PMID:22085609
  title: 'Temperature-dependent structural and functional properties of a mutant (F71L)
    αA-crystallin: molecular basis for early onset of age-related cataract.'
  findings: []
- id: PMID:22143763
  title: Multiple molecular architectures of the eye lens chaperone αB-crystallin
    elucidated by a triple hybrid approach.
  findings: []
- id: PMID:22153508
  title: 'The polydispersity of αB-crystallin is rationalized by an interconverting
    polyhedral architecture.'
  findings: []
- id: PMID:22158051
  title: Tumor suppressor Alpha B-crystallin (CRYAB) associates with the cadherin/catenin
    adherens junction and impairs NPC progression-associated properties.
  findings: []
- id: PMID:23106396
  title: 'Amyloid-β oligomers are sequestered by both intracellular and extracellular
    chaperones.'
  findings: []
- id: PMID:23188086
  title: "Binding determinants of the small heat shock protein, \u03B1B-crystallin:\
    \ recognition of the 'IxI' motif."
  findings: []
- id: PMID:23533145
  title: In-depth proteomic analyses of exosomes isolated from expressed prostatic
    secretions in urine.
  findings: []
- id: PMID:23542032
  title: Protective role of the endoplasmic reticulum protein mitsugumin23 against
    ultraviolet C-induced cell death.
  findings: []
- id: PMID:24183572
  title: 'Preferential and specific binding of human αB-crystallin to a cataract-related
    variant of γS-crystallin.'
  findings: []
- id: PMID:25910212
  title: Widespread macromolecular interaction perturbations in human genetic disorders.
  findings: []
- id: PMID:26465331
  title: Characterization of the Cardiac Overexpression of HSPB2 Reveals Mitochondrial
    and Myogenic Roles Supported by a Cardiac HspB2 Interactome.
  findings: []
- id: PMID:27226619
  title: The Human 343delT HSPB5 Chaperone Associated with Early-onset Skeletal Myopathy
    Causes Defects in Protein Solubility.
  findings: []
- id: PMID:28470624
  title: 'αB-crystallin is a sensor for assembly intermediates and for the subunit
    topology of desmin intermediate filaments.'
  findings: []
- id: PMID:28493373
  title: 'The novel αB-crystallin (CRYAB) mutation p.D109G causes restrictive cardiomyopathy.'
  findings: []
- id: PMID:28514442
  title: Architecture of the human interactome defines protein communities and disease
    networks.
  findings: []
- id: PMID:32272059
  title: A Translocation Pathway for Vesicle-Mediated Unconventional Protein Secretion.
  findings: []
- id: PMID:32296183
  title: A reference map of the human binary protein interactome.
  findings: []
- id: PMID:32814053
  title: Interactome Mapping Provides a Network of Neurodegenerative Disease Proteins
    and Uncovers Widespread Protein Aggregation in Affected Brains.
  findings: []
- id: PMID:33961781
  title: Dual proteome-scale networks reveal cell-specific remodeling of the human
    interactome.
  findings: []
- id: PMID:40205054
  title: Multimodal cell maps as a foundation for structural and functional genomics.
  findings: []
- id: PMID:9731540
  title: A missense mutation in the alphaB-crystallin chaperone gene causes a desmin-related
    myopathy.
  findings: []
- id: Reactome:R-HSA-5082356
  title: HSF1-mediated gene expression
  findings: []
- id: DOI:10.1038/s41467-024-54647-7
  title: Dynamic fibrillar assembly of alphaB-crystallin induced by perturbation of
    the conserved NT-IXI motif resolved by cryo-EM
  findings:
    - statement: CRYAB exists in highly polydisperse oligomers (approximately 10-40
        subunits) with rapid subunit exchange dynamics important for chaperone activity
    - statement: The conserved N-terminal IXI-like motif (NT-IXI) engages the ACD
        hydrophobic groove, governing assembly; perturbation transforms native assemblies
        into reversible elongated helical fibrils resolved by cryo-EM
- id: DOI:10.1172/jci.insight.182209
  title: Mutation of CRYAB encoding a conserved mitochondrial chaperone and antiapoptotic
    protein causes hereditary optic atrophy
  findings:
    - statement: CRYAB E105K (within the ACD) causes autosomal dominant optic atrophy
        by reducing oligomer formation, chaperone activity, and interactions with
        cytochrome c and VDAC
    - statement: CRYAB deficiency/mutation leads to increased apoptosis, mitochondrial
        dysfunction, and impaired OXPHOS assembly in retinal ganglion cells
- id: DOI:10.1016/j.isci.2024.109510
  title: The activation of LBH-CRYAB signaling promotes cardiac protection against
    I/R injury by inhibiting apoptosis and ferroptosis
  findings:
    - statement: LBH enhances p38 phosphorylation and CRYAB Ser59 phosphorylation;
        p38 inhibitor abolishes LBH-induced CRYAB pS59
    - statement: Phosphorylated CRYAB facilitates NRF2 upregulation/nuclear translocation
        and contributes to ferroptosis resistance via GPX4 in cardiomyocytes
- id: DOI:10.1186/s13287-023-03468-4
  title: Mature human induced pluripotent stem cell-derived cardiomyocytes promote
    angiogenesis through alpha-B crystallin
  findings:
    - statement: CRYAB is upregulated in mature hiPSC-derived cardiomyocytes and is
        secreted via exosomes
    - statement: CRYAB siRNA knockdown significantly inhibits HUVEC migration and tube
        formation, demonstrating CRYAB is necessary for pro-angiogenic paracrine effects
- id: DOI:10.1038/s42003-022-04402-9
  title: Single-cell transcriptomics reveal extracellular vesicles secretion with a
    cardiomyocyte proteostasis signature during pathological remodeling
  findings:
    - statement: Stressed cardiomyocytes secrete EVs enriched in protein-quality-control
        factors including CRYAB during pathological remodeling
    - statement: CRYAB accumulates in recipient cells exposed to stressed
        cardiomyocyte-derived EVs
- id: DOI:10.1172/jci163730
  title: Phosphorylation of CRYAB induces a condensatopathy to worsen post-myocardial
    infarction left ventricular remodeling
  findings:
    - statement: Ser59 phosphorylation shifts CRYAB condensates toward less dynamic,
        more aggregate-prone states (condensatopathy), mislocalizing cytoskeletal and
        sarcomeric client proteins
    - statement: Phosphomimetic S59D behaves similarly to cardiomyopathy mutant R120G
        in condensate behavior; S59A mitigates aggregate toxicity