id: Q16082
gene_symbol: HSPB2
product_type: PROTEIN
status: COMPLETE
taxon:
  id: NCBITaxon:9606
  label: Homo sapiens
description: HSPB2 (heat shock protein beta-2; also MKBP, "DMPK-binding protein") is an ATP-independent small heat-shock protein (sHSP) of the alpha-crystallin/HSP20 family, expressed preferentially in skeletal and cardiac muscle. Like other sHSPs it acts as a holdase chaperone, binding non-native/destabilized client proteins through its alpha-crystallin domain to prevent their aggregation under stress, holding them for downstream ATP-dependent refolding. HSPB2 forms its own oligomeric complex in muscle cytosol, distinct from the alphaB-crystallin (CRYAB)/HSP27 complex, and is notable for binding and activating the myotonic dystrophy protein kinase (DMPK), enhancing its kinase activity and protecting it from heat-induced inactivation. It localizes to the cytoplasm (Z-membrane of myofibrils and the neuromuscular junction) and to nuclear foci. HSPB2 is not strongly heat-inducible but participates in the muscle stress response and is cardioprotective during ischemia, helping maintain ATP levels.
existing_annotations:
- term:
    id: GO:0005634
    label: nucleus
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: is_active_in
  review:
    summary: Phylogenetic (IBA) nuclear localization, corroborated by direct experimental evidence that HSPB2 localizes to nuclear foci.
    action: ACCEPT
    reason: Nuclear localization is directly supported (PMID:19464326, HPA nucleoplasm IDA) in addition to the IBA transfer.
    supported_by:
    - reference_id: file:human/HSPB2/HSPB2-uniprot.txt
      supporting_text: Note=Localizes to nuclear foci.
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: is_active_in
  review:
    summary: Phylogenetic (IBA) cytoplasmic localization, corroborated by direct evidence; HSPB2 is a cytosolic muscle sHSP localizing to the myofibrillar Z-membrane.
    action: ACCEPT
    reason: Cytoplasmic localization is directly supported (PMID:19464326 IDA; TAS cytosol) and is a principal site of HSPB2 chaperone action.
    supported_by:
    - reference_id: file:human/HSPB2/HSPB2-uniprot.txt
      supporting_text: 'SUBCELLULAR LOCATION: Cytoplasm'
- term:
    id: GO:0043066
    label: negative regulation of apoptotic process
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: involved_in
  review:
    summary: Phylogenetic transfer of the cytoprotective/anti-apoptotic role common to small HSPs. Consistent with HSPB2's cardioprotective (anti-ischemic) phenotype, but a downstream consequence of its chaperone activity rather than a direct molecular function.
    action: KEEP_AS_NON_CORE
    reason: A plausible downstream cytoprotective effect supported by the cardioprotection phenotype, but secondary to HSPB2's core holdase/kinase-activator functions.
    supported_by:
    - reference_id: PMID:26465331
      supporting_text: transgenic overexpressing mice including reduced infarct size and maintenance of
- term:
    id: GO:0009408
    label: response to heat
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: involved_in
  review:
    summary: Phylogenetic transfer of "response to heat" from the heat-shock protein family. Notably HSPB2/MKBP is NOT induced by heat shock, though it participates in the muscle stress response and protects clients from heat-induced damage.
    action: KEEP_AS_NON_CORE
    reason: HSPB2 expression is not heat-inducible, so the term applies only loosely via its stress-protective chaperone activity; retained as non-core.
    supported_by:
    - reference_id: file:human/HSPB2/HSPB2-uniprot.txt
      supporting_text: The expression of MKBP is not induced by heat shock
- term:
    id: GO:0042026
    label: protein refolding
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: involved_in
  review:
    summary: IBA transfer of "protein refolding". Small HSPs are ATP-independent holdases that bind and sequester non-native proteins; they do not autonomously refold clients, which requires downstream ATP-dependent chaperones (HSP70/HSP100).
    action: KEEP_AS_NON_CORE
    reason: Mechanistically HSPB2 is a holdase, not a foldase; refolding is a downstream outcome of the wider chaperone system, so this is non-core. The holdase activity is better captured by unfolded protein binding.
    supported_by:
    - reference_id: PMID:26465331
      supporting_text: validated as a potential client protein of HspB2 through chaperone assays
- term:
    id: GO:0005212
    label: structural constituent of eye lens
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: enables
  review:
    summary: InterPro2GO transfer of the lens structural role from the alpha-crystallin domain signature. HSPB2 is explicitly not expressed in the lens, so this is an erroneous family-level over-annotation.
    action: REMOVE
    reason: HSPB2 is not a lens crystallin and is expressly absent from the lens; the term is incorrectly transferred from the broader alpha-crystallin/sHSP family.
    supported_by:
    - reference_id: file:human/HSPB2/HSPB2-uniprot.txt
      supporting_text: Expressed preferentially in skeletal muscle and heart but not in the lens.
- term:
    id: GO:0005634
    label: nucleus
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  qualifier: located_in
  review:
    summary: Electronic (UniProt SubCell) nuclear localization, redundant with the experimental IDA nuclear annotation.
    action: ACCEPT
    reason: Correct, supported by direct experimental evidence for nuclear foci.
    supported_by:
    - reference_id: file:human/HSPB2/HSPB2-uniprot.txt
      supporting_text: Note=Localizes to nuclear foci.
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  qualifier: located_in
  review:
    summary: Electronic (UniProt SubCell) cytoplasmic localization, redundant with the experimental IDA cytoplasm annotation.
    action: ACCEPT
    reason: Correct, supported by direct experimental evidence.
    supported_by:
    - reference_id: file:human/HSPB2/HSPB2-uniprot.txt
      supporting_text: 'SUBCELLULAR LOCATION: Cytoplasm'
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:14594798
  qualifier: enables
  review:
    summary: Interaction with the small heat-shock protein HSPB8/HSP22 (Q9UJY1). This sHSP-sHSP interaction is more informatively captured as heat shock protein binding than bare protein binding.
    action: MODIFY
    reason: The partner is another heat-shock protein (HSPB8), so heat shock protein binding is the appropriate specific molecular function.
    proposed_replacement_terms:
    - id: GO:0031072
      label: heat shock protein binding
    supported_by:
    - reference_id: file:human/HSPB2/HSPB2-uniprot.txt
      supporting_text: 'Q16082; Q9UJY1: HSPB8; NbExp=3; IntAct=EBI-739395, EBI-739074'
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:23188086
  qualifier: enables
  review:
    summary: Interaction with the small heat-shock protein alphaB-crystallin/CRYAB (P02511), reflecting sHSP hetero-oligomer recognition via the IxI motif.
    action: MODIFY
    reason: The partner is another heat-shock protein (CRYAB), so heat shock protein binding is the appropriate specific molecular function.
    proposed_replacement_terms:
    - id: GO:0031072
      label: heat shock protein binding
    supported_by:
    - reference_id: file:human/HSPB2/HSPB2-uniprot.txt
      supporting_text: 'Q16082; P02511: CRYAB; NbExp=3; IntAct=EBI-739395, EBI-739060'
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:26465331
  qualifier: enables
  review:
    summary: Cardiac yeast two-hybrid interactome again capturing the HSPB2-CRYAB interaction (and broader myofibrillar/mitochondrial clients). The sHSP-sHSP interaction is better captured as heat shock protein binding.
    action: MODIFY
    reason: Partner is the heat-shock protein CRYAB; heat shock protein binding is the specific molecular function. The wider client-binding role is captured by unfolded protein binding in core functions.
    proposed_replacement_terms:
    - id: GO:0031072
      label: heat shock protein binding
    supported_by:
    - reference_id: file:human/HSPB2/HSPB2-uniprot.txt
      supporting_text: 'Q16082; P02511: CRYAB; NbExp=3; IntAct=EBI-739395, EBI-739060'
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:32296183
  qualifier: enables
  review:
    summary: Large binary HuRI interactome screen capturing many heterogeneous partners (BAG3, A1CF, CEP19, POGZ, VEZF1 and others). Bare protein binding is uninformative.
    action: KEEP_AS_NON_CORE
    reason: High-throughput binary interactions; bare protein binding is not elevated to core and the partners are mostly unrelated to HSPB2's chaperone function.
    supported_by:
    - reference_id: file:human/HSPB2/HSPB2-uniprot.txt
      supporting_text: 'Q16082; O95817: BAG3; NbExp=5; IntAct=EBI-739395, EBI-747185'
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:32814053
  qualifier: enables
  review:
    summary: Neurodegeneration interactome screen capturing an HSPB2-APP (amyloid precursor protein) interaction. Bare protein binding from a single high-throughput screen.
    action: KEEP_AS_NON_CORE
    reason: An isolated high-throughput interaction; uninformative bare protein binding, not part of the core muscle/chaperone function.
    supported_by:
    - reference_id: file:human/HSPB2/HSPB2-uniprot.txt
      supporting_text: 'Q16082; P05067: APP; NbExp=3; IntAct=EBI-739395, EBI-77613'
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:33961781
  qualifier: enables
  review:
    summary: BioPlex affinity-purification interactome capturing an HSPB2-BAG3 interaction. BAG3 is a co-chaperone that cooperates with small HSPs; nonetheless this is a bare protein binding annotation.
    action: KEEP_AS_NON_CORE
    reason: Records a real interaction with the sHSP co-chaperone BAG3 but as an uninformative bare-binding annotation; retained as non-core.
    supported_by:
    - reference_id: file:human/HSPB2/HSPB2-uniprot.txt
      supporting_text: 'Q16082; O95817: BAG3; NbExp=5; IntAct=EBI-739395, EBI-747185'
- term:
    id: GO:0005654
    label: nucleoplasm
  evidence_type: IDA
  original_reference_id: GO_REF:0000052
  qualifier: located_in
  review:
    summary: HPA immunofluorescence localization to the nucleoplasm, consistent with the reported nuclear foci.
    action: ACCEPT
    reason: Direct antibody-based localization consistent with the documented nuclear pool.
    supported_by:
    - reference_id: file:human/HSPB2/HSPB2-uniprot.txt
      supporting_text: Note=Localizes to nuclear foci.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:25556234
  qualifier: enables
  review:
    summary: AgBase-curated interaction (with P0DOE7) reported in a respiratory syncytial virus host-factor screen. Bare protein binding, unrelated to HSPB2's core function.
    action: KEEP_AS_NON_CORE
    reason: Isolated screen-derived interaction; uninformative bare protein binding.
    supported_by:
    - reference_id: file:human/HSPB2/HSPB2-goa.tsv
      supporting_text: UniProtKB:P0DOE7
- term:
    id: GO:0005634
    label: nucleus
  evidence_type: IDA
  original_reference_id: PMID:19464326
  qualifier: located_in
  review:
    summary: Direct experimental demonstration that HSPB2 localizes to the nucleus (nuclear foci).
    action: ACCEPT
    reason: Strongest-evidence nuclear localization.
    supported_by:
    - reference_id: file:human/HSPB2/HSPB2-uniprot.txt
      supporting_text: Note=Localizes to nuclear foci.
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IDA
  original_reference_id: PMID:19464326
  qualifier: located_in
  review:
    summary: Direct experimental demonstration that HSPB2 localizes to the cytoplasm.
    action: ACCEPT
    reason: Strongest-evidence cytoplasmic localization; principal site of HSPB2 action.
    supported_by:
    - reference_id: file:human/HSPB2/HSPB2-uniprot.txt
      supporting_text: 'SUBCELLULAR LOCATION: Cytoplasm'
- term:
    id: GO:0006986
    label: response to unfolded protein
  evidence_type: NAS
  original_reference_id: PMID:9344664
  qualifier: involved_in
  review:
    summary: HSPB2 is an alpha-crystallin/small-HSP family member implicated in the stress response to unfolded proteins. Consistent with its holdase chaperone activity.
    action: KEEP_AS_NON_CORE
    reason: A reasonable stress-response process annotation; the underlying molecular activity (binding non-native proteins) is the core feature captured by unfolded protein binding.
    supported_by:
    - reference_id: file:human/HSPB2/HSPB2-uniprot.txt
      supporting_text: Belongs to the small heat shock protein (HSP20) family.
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: TAS
  original_reference_id: PMID:9490724
  qualifier: located_in
  review:
    summary: Author-stated cytosolic localization; in muscle cytosol HSPB2/MKBP exists as an oligomeric complex distinct from the CRYAB/HSP27 complex.
    action: ACCEPT
    reason: Supported by the original MKBP characterization; cytosol is a principal site of HSPB2 oligomers.
    supported_by:
    - reference_id: PMID:9490724
      supporting_text: MKBP exists as an oligomeric complex separate from the complex
- term:
    id: GO:0008047
    label: enzyme activator activity
  evidence_type: TAS
  original_reference_id: PMID:9490724
  qualifier: enables
  review:
    summary: HSPB2/MKBP binds the myotonic dystrophy protein kinase (DMPK), enhances its kinase activity and protects it from heat-induced inactivation, acting as a kinase activator. This is a distinctive, well-documented HSPB2 function.
    action: ACCEPT
    reason: Directly demonstrated in vitro; HSPB2 enhances DMPK kinase activity, a genuine and specific enzyme-activator (kinase-activator) function.
    supported_by:
    - reference_id: PMID:9490724
      supporting_text: enhances the kinase activity of DMPK and protects it from heat-induced
references:
- id: GO_REF:0000002
  title: Gene Ontology annotation through association of InterPro records with GO terms
  findings: []
- id: GO_REF:0000033
  title: Annotation inferences using phylogenetic trees
  findings: []
- id: GO_REF:0000044
  title: Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping, accompanied by conservation of the subcellular location
  findings: []
- id: GO_REF:0000052
  title: Gene Ontology annotation based on curation of immunofluorescence data
  findings: []
- id: PMID:9344664
  title: Identification and characterization of the gene encoding a new member of the alpha-crystallin/small hsp family, closely linked to the alphaB-crystallin gene in a head-to-head manner.
  findings: []
- id: PMID:9490724
  title: MKBP, a novel member of the small heat shock protein family, binds and activates the myotonic dystrophy protein kinase.
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: "Cached publications/PMID_9490724.md title matches; anchored to GOA as the TAS source for GO:0008047 (enzyme activator activity) and GO:0005829 (cytosol). Directly establishes the HSPB2/MKBP DMPK-binding-and-activation core function. Cited in core_functions supported_by."
  findings:
  - statement: HSPB2/MKBP is a small HSP that binds DMPK, enhances its kinase activity and protects it from heat-induced inactivation; it forms an oligomeric muscle-cytosol complex distinct from the alphaB-crystallin/HSP27 complex and is not induced by heat shock.
    reference_section_type: ABSTRACT
- id: PMID:14594798
  title: Interaction of human HSP22 (HSPB8) with other small heat shock proteins.
  findings: []
- id: PMID:19464326
  title: HSPB7 is a SC35 speckle resident small heat shock protein.
  findings:
  - statement: HSPB2 localizes to both the cytoplasm and the nucleus (nuclear foci).
    reference_section_type: RESULTS
- id: PMID:23188086
  title: 'Binding determinants of the small heat shock protein, αB-crystallin: recognition of the ''IxI'' motif.'
  findings: []
- id: PMID:25556234
  title: New host factors important for respiratory syncytial virus (RSV) replication revealed by a novel microfluidics screen for interactors of matrix (M) protein.
  findings: []
- id: PMID:26465331
  title: Characterization of the Cardiac Overexpression of HSPB2 Reveals Mitochondrial and Myogenic Roles Supported by a Cardiac HspB2 Interactome.
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: "Cached publications/PMID_26465331.md title matches; anchored to GOA as an IPI protein-binding source. Provides the validated GAPDH client and cardiac/mitochondrial interactome supporting the holdase (GO:0051082) core function. Cited in core_functions supported_by."
  findings:
  - statement: Cardiac HSPB2 overexpression is cardioprotective in ischemia (reduced infarct, maintained ATP); HSPB2 has a myofibrillar/mitochondrial cardiac interactome and GAPDH was validated as a client protein via chaperone assays.
    reference_section_type: ABSTRACT
- 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: file:human/HSPB2/HSPB2-uniprot.txt
  title: UniProt entry Q16082 (HSPB2_HUMAN), Heat shock protein beta-2 (MKBP)
  findings:
  - statement: Small heat-shock protein (HSP20/alpha-crystallin family) expressed in skeletal muscle and heart but not lens; binds and may activate DMPK; localizes to cytoplasm and nucleus (nuclear foci).
    reference_section_type: OTHER
core_functions:
- description: ATP-independent small heat-shock protein (holdase) that binds non-native/destabilized client proteins via its alpha-crystallin domain to prevent their aggregation under stress, holding them for downstream refolding (validated client GAPDH).
  molecular_function:
    id: GO:0051082
    label: unfolded protein binding
  locations:
  - id: GO:0005737
    label: cytoplasm
  - id: GO:0005634
    label: nucleus
  supported_by:
  - reference_id: PMID:26465331
    supporting_text: validated as a potential client protein of HspB2 through chaperone assays
  - reference_id: file:human/HSPB2/HSPB2-uniprot.txt
    supporting_text: Belongs to the small heat shock protein (HSP20) family.
- description: DMPK kinase activator; HSPB2/MKBP binds the myotonic dystrophy protein kinase, enhances its kinase activity and protects it from heat-induced inactivation, constituting a muscle stress-responsive system.
  molecular_function:
    id: GO:0008047
    label: enzyme activator activity
  locations:
  - id: GO:0005737
    label: cytoplasm
  supported_by:
  - reference_id: PMID:9490724
    supporting_text: enhances the kinase activity of DMPK and protects it from heat-induced
proposed_new_terms: []
suggested_questions:
- question: Does HSPB2 form a defined hetero-oligomer with HSPB3 in muscle, and how does this complex differ functionally from HSPB2 homo-oligomers and the CRYAB/HSP27 complex?
- question: Is DMPK activation a direct allosteric effect of HSPB2 binding, and is it disrupted in myotonic dystrophy where MKBP is selectively upregulated?
suggested_experiments:
- description: In vitro aggregation-protection (holdase) assays with recombinant HSPB2 against model and physiological clients (e.g. GAPDH) to quantify chaperone activity and ATP-independence.
- description: Reconstitute DMPK with HSPB2 to map the binding interface and measure kinase-activation kinetics, testing whether disease-associated changes alter activation.
- description: Define the muscle HSPB2/HSPB3 complex stoichiometry by size-exclusion/native MS and test client specificity relative to HSPB2 alone.