id: P21953
gene_symbol: BCKDHB
product_type: PROTEIN
status: INITIALIZED
taxon:
  id: NCBITaxon:9606
  label: Homo sapiens
description: >-
  BCKDHB encodes the beta subunit (E1-beta / BCKDE1B) of the E1 component of the
  mitochondrial branched-chain alpha-ketoacid dehydrogenase (BCKDH) complex. Together
  with the E1-alpha subunit (BCKDHA) it forms an alpha2-beta2 heterotetrameric,
  thiamine diphosphate (ThDP)-dependent decarboxylase (2-oxoisovalerate dehydrogenase,
  EC 1.2.4.4). This E1 decarboxylase catalyses the first, committed and rate-limiting
  step of branched-chain amino acid (BCAA) catabolism: the oxidative decarboxylation
  of the branched-chain 2-oxo (alpha-keto) acids derived from valine, leucine and
  isoleucine (2-oxoisovalerate/KIV, 4-methyl-2-oxopentanoate/KIC, and
  (S)-3-methyl-2-oxopentanoate/KMV), producing CO2 and a branched-chain acyl group
  that is reductively transferred to the lipoyl cofactor of the E2 transacylase. The
  active site lies at the alpha-beta' interface, and the beta subunit contributes
  residues for ThDP binding, structural K+ coordination, and heterotetramer/E2
  assembly. The full BCKDH multienzyme complex is organized around a 24-meric E2
  (DBT) cubic core, to which multiple E1 (BCKDHA/BCKDHB) tetramers and E3 (DLD)
  dimers associate; complex activity is regulated by reversible phosphorylation of
  E1-alpha (by BCKDK) and dephosphorylation (by PPM1K/PP2Cm). BCKDHB acts in the
  mitochondrial matrix. Biallelic loss-of-function variants in BCKDHB cause maple
  syrup urine disease type Ib (MSUD 1B), in which loss of the beta subunit also
  destabilizes the alpha subunit and abolishes complex activity.
alternative_products:
- name: '1'
  id: P21953-1
- name: '2'
  id: P21953-2
  sequence_note: VSP_056370, VSP_056371
existing_annotations:
- term:
    id: GO:0009083
    label: branched-chain amino acid catabolic process
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: involved_in
  review:
    summary: >-
      Phylogenetic (IBA) propagation of the core biological process. As the E1-beta
      subunit of the BCKDH complex, BCKDHB is directly required for the committed,
      rate-limiting oxidative decarboxylation step of BCAA (valine/leucine/isoleucine)
      catabolism.
    action: ACCEPT
    reason: >-
      Correct and central to the gene's function; well supported by direct experimental
      evidence in human and orthologs. This is a core biological process for BCKDHB.
    supported_by:
    - reference_id: UniProtKB:P21953
      supporting_text: >-
        Together with BCKDHA forms the heterotetrameric E1 subunit of the mitochondrial
        branched-chain alpha-ketoacid dehydrogenase (BCKD) complex. The BCKD complex
        catalyzes the multi-step oxidative decarboxylation of alpha-ketoacids derived
        from the branched-chain amino-acids valine, leucine and isoleucine producing
        CO2 and acyl-CoA
- term:
    id: GO:0160157
    label: branched-chain alpha-ketoacid dehydrogenase complex
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: part_of
  review:
    summary: >-
      Phylogenetic (IBA) assignment of the cellular component. BCKDHB is an integral,
      constitutive subunit of the BCKDH complex, forming (with BCKDHA) the E1
      alpha2-beta2 decarboxylase that associates with the E2 (DBT) core and E3 (DLD).
    action: ACCEPT
    reason: >-
      Correct core localization to the multienzyme complex; supported by structural,
      biochemical and disease genetics evidence (heterotetrameric E1 component).
    supported_by:
    - reference_id: UniProtKB:P21953
      supporting_text: >-
        Heterotetramer of 2 alpha/BCKDHA and 2 beta chains/BCKDHB that
        forms the branched-chain alpha-keto acid decarboxylase (E1) component
        of the BCKD complex
- term:
    id: GO:0007584
    label: response to nutrient
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: involved_in
  review:
    summary: >-
      Phylogenetic (IBA) annotation reflecting that BCAA catabolic flux through BCKDH
      is nutritionally regulated. This is a broad, downstream physiological process
      rather than the molecular role of the beta subunit.
    action: KEEP_AS_NON_CORE
    reason: >-
      Not wrong at the pathway level (BCKDH activity is modulated by nutrient status
      via BCKDK/PPM1K), but this is a peripheral, non-core physiological association
      for the E1-beta subunit, not its direct molecular function.
- term:
    id: GO:0003863
    label: branched-chain 2-oxo acid dehydrogenase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: enables
  review:
    summary: >-
      Electronic (IEA) assignment of the E1 decarboxylase molecular function
      (EC 1.2.4.4), mapped via ortholog, RHEA reactions (RHEA:13457/84639/84643) and
      EC. This is the core catalytic activity of the BCKDH E1 component.
    action: ACCEPT
    reason: >-
      The mapping is correct and matches the UniProt catalytic activity and the
      experimental IDA/IMP annotations of the same term. The IEA uses 'enables' whereas
      the manual annotations use 'contributes_to'; contributes_to is technically more
      precise for a subunit of a shared active site, but the IEA is not wrong at this
      level and captures the correct enzymatic function.
    supported_by:
    - reference_id: UniProtKB:P21953
      supporting_text: >-
        Reaction=N(6)-[(R)-lipoyl]-L-lysyl-[protein] + 3-methyl-2-oxobutanoate
    - reference_id: file:human/BCKDHB/BCKDHB-deep-research-falcon.md
      supporting_text: thiamine diphosphate (ThDP)-dependent decarboxylase
- term:
    id: GO:0005759
    label: mitochondrial matrix
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: located_in
  review:
    summary: >-
      Electronic (IEA) assignment of mitochondrial matrix localization via ortholog and
      UniProt subcellular location keyword. BCKDH is a soluble matrix multienzyme complex.
    action: ACCEPT
    reason: >-
      Correct and consistent with the UniProt subcellular location and with NAS/ISS/TAS
      annotations of the same term.
    supported_by:
    - reference_id: UniProtKB:P21953
      supporting_text: 'SUBCELLULAR LOCATION: Mitochondrion matrix'
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:12902323
  qualifier: enables
  review:
    summary: >-
      IPI 'protein binding' annotation whose WITH/FROM is UniProtKB:P12694 (BCKDHA),
      i.e. the direct E1-alpha partner with which BCKDHB forms the alpha2-beta2
      heterotetramer. This paper dissects the catalytic mechanism (His-alpha/His-beta'
      in reductive acylation) of the assembled E1.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      The interaction is real (BCKDHB obligately binds BCKDHA), but the bare
      'protein binding' term is uninformative. The biologically meaningful capture of
      this interaction is already provided by the E1 heterotetramer / BCKDH complex
      annotations (GO:0160157) and the E1 decarboxylase molecular function (GO:0003863).
    supported_by:
    - reference_id: UniProtKB:P21953
      supporting_text: 'P21953; P12694: BCKDHA; NbExp=15; IntAct=EBI-1029067, EBI-1029053;'
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:15166214
  qualifier: enables
  review:
    summary: >-
      IPI 'protein binding' annotation, WITH/FROM UniProtKB:P12694 (BCKDHA). This study
      addresses ThDP-binding / phosphorylation-loop cross-talk in the assembled E1
      decarboxylase, again reflecting the BCKDHB-BCKDHA E1 heterotetramer.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Real interaction but uninformative bare 'protein binding'. The E1 heterotetramer
      is better captured by the BCKDH complex (GO:0160157) and E1 activity (GO:0003863)
      annotations.
    supported_by:
    - reference_id: UniProtKB:P21953
      supporting_text: 'P21953; P12694: BCKDHA; NbExp=15; IntAct=EBI-1029067, EBI-1029053;'
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:15576032
  qualifier: enables
  review:
    summary: >-
      IPI 'protein binding' annotation, WITH/FROM UniProtKB:P12694 (BCKDHA). This paper
      concerns regulation of the assembled BCKDH complex by phosphorylation of E1-alpha,
      again reflecting the E1 heterotetramer interaction.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Real interaction but uninformative bare 'protein binding'; the meaningful content
      is captured by the complex (GO:0160157) and MF (GO:0003863) annotations.
    supported_by:
    - reference_id: UniProtKB:P21953
      supporting_text: 'P21953; P12694: BCKDHA; NbExp=15; IntAct=EBI-1029067, EBI-1029053;'
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:28514442
  qualifier: enables
  review:
    summary: >-
      Large-scale interactome (BioPlex) IPI, WITH/FROM UniProtKB:P12694 (BCKDHA),
      recovering the BCKDHB-BCKDHA interaction that constitutes the E1 heterotetramer.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      High-throughput detection of the genuine E1-alpha/E1-beta interaction, but the
      generic 'protein binding' term is uninformative and the interaction is already
      captured by the BCKDH complex annotation (GO:0160157).
    supported_by:
    - reference_id: UniProtKB:P21953
      supporting_text: 'P21953; P12694: BCKDHA; NbExp=15; IntAct=EBI-1029067, EBI-1029053;'
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:33961781
  qualifier: enables
  review:
    summary: >-
      Large-scale interactome (BioPlex 3.0) IPI, WITH/FROM UniProtKB:P12694 (BCKDHA),
      again capturing the BCKDHB-BCKDHA E1 heterotetramer interaction.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Genuine but uninformative bare 'protein binding'; the meaningful E1-alpha
      interaction is captured by the BCKDH complex (GO:0160157) and E1 MF (GO:0003863).
    supported_by:
    - reference_id: UniProtKB:P21953
      supporting_text: 'P21953; P12694: BCKDHA; NbExp=15; IntAct=EBI-1029067, EBI-1029053;'
- term:
    id: GO:0006550
    label: L-isoleucine catabolic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Electronic (Ensembl Compara ortholog) transfer of a more granular BCAA subprocess.
      The BCKDH E1 decarboxylates KMV (the isoleucine-derived 2-oxo acid), so this is a
      correct, more specific descendant of BCAA catabolism.
    action: ACCEPT
    reason: >-
      Biochemically correct - the E1 decarboxylase acts on the isoleucine-derived
      branched-chain 2-oxo acid (S)-3-methyl-2-oxopentanoate (KMV). More granular than,
      and consistent with, the core GO:0009083 annotation; retain as non-core detail.
    supported_by:
    - reference_id: UniProtKB:P21953
      supporting_text: >-
        Reaction=N(6)-[(R)-lipoyl]-L-lysyl-[protein] + (S)-3-methyl-2-
    - reference_id: PMID:3593587
      supporting_text: The BCKADH effectively oxidized all of KIV, KIC, and KMV
- term:
    id: GO:0006552
    label: L-leucine catabolic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Electronic (Ensembl Compara ortholog) transfer. The BCKDH E1 decarboxylates KIC
      (4-methyl-2-oxopentanoate), the leucine-derived 2-oxo acid, so this granular BCAA
      subprocess is correct.
    action: ACCEPT
    reason: >-
      Biochemically correct (E1 acts on the leucine-derived branched-chain 2-oxo acid,
      4-methyl-2-oxopentanoate/KIC). More specific than, and consistent with, the core
      GO:0009083 annotation; retain as non-core detail.
    supported_by:
    - reference_id: UniProtKB:P21953
      supporting_text: >-
        Reaction=N(6)-[(R)-lipoyl]-L-lysyl-[protein] + 4-methyl-2-oxopentanoate
    - reference_id: PMID:3593587
      supporting_text: The BCKADH effectively oxidized all of KIV, KIC, and KMV
- term:
    id: GO:0006574
    label: L-valine catabolic process
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: involved_in
  review:
    summary: >-
      Electronic (Ensembl Compara ortholog) transfer. The BCKDH E1 decarboxylates KIV
      (3-methyl-2-oxobutanoate), the valine-derived 2-oxo acid, so this granular BCAA
      subprocess is correct.
    action: ACCEPT
    reason: >-
      Biochemically correct (E1 acts on the valine-derived branched-chain 2-oxo acid,
      3-methyl-2-oxobutanoate/KIV; RHEA:13457 is the experimentally verified human
      reaction). More specific than, and consistent with, the core GO:0009083
      annotation; retain as non-core detail.
    supported_by:
    - reference_id: UniProtKB:P21953
      supporting_text: >-
        Reaction=N(6)-[(R)-lipoyl]-L-lysyl-[protein] + 3-methyl-2-oxobutanoate
    - reference_id: PMID:3593587
      supporting_text: The BCKADH effectively oxidized all of KIV, KIC, and KMV
- term:
    id: GO:0032991
    label: protein-containing complex
  evidence_type: IEA
  original_reference_id: GO_REF:0000107
  qualifier: part_of
  review:
    summary: >-
      Electronic (Ensembl Compara ortholog) transfer of the generic 'protein-containing
      complex' term. BCKDHB is a subunit of the specific, well-defined BCKDH complex.
    action: MODIFY
    reason: >-
      Correct but far too general: BCKDHB is part of the specific branched-chain
      alpha-ketoacid dehydrogenase complex, which is already directly annotated
      (GO:0160157) with stronger evidence. Replace the generic term with the specific one.
    proposed_replacement_terms:
    - id: GO:0160157
      label: branched-chain alpha-ketoacid dehydrogenase complex
    supported_by:
    - reference_id: UniProtKB:P21953
      supporting_text: >-
        Heterotetramer of 2 alpha/BCKDHA and 2 beta chains/BCKDHB that
        forms the branched-chain alpha-keto acid decarboxylase (E1) component
        of the BCKD complex
- term:
    id: GO:0005759
    label: mitochondrial matrix
  evidence_type: NAS
  original_reference_id: PMID:3593587
  qualifier: located_in
  review:
    summary: >-
      Non-traceable author statement (ComplexPortal-assigned) of matrix localization,
      supported by purification of the intact human liver BCKDH complex, a soluble
      matrix multienzyme complex.
    action: ACCEPT
    reason: >-
      Consistent with all other matrix annotations and with UniProt subcellular location.
      Correct core localization.
    supported_by:
    - reference_id: PMID:3593587
      supporting_text: >-
        Purification and characterization of human liver branched-chain alpha-keto acid
        dehydrogenase complex.
- term:
    id: GO:0009083
    label: branched-chain amino acid catabolic process
  evidence_type: IDA
  original_reference_id: PMID:3593587
  qualifier: involved_in
  review:
    summary: >-
      Direct experimental (IDA) annotation of the core BCAA catabolic process. The
      purified human liver BCKDH complex oxidized all three branched-chain 2-oxo acids
      (KIV, KIC, KMV), demonstrating its role in BCAA (valine/leucine/isoleucine)
      catabolism.
    action: ACCEPT
    reason: >-
      Direct biochemical evidence for the complex's role in BCAA catabolism; this is a
      core process for BCKDHB.
    supported_by:
    - reference_id: PMID:3593587
      supporting_text: >-
        The BCKADH effectively oxidized all of KIV, KIC, and KMV, yielding apparent Km
        values in the range of 14-17 microM for those alpha-keto acids.
- term:
    id: GO:0160157
    label: branched-chain alpha-ketoacid dehydrogenase complex
  evidence_type: IPI
  original_reference_id: PMID:3593587
  qualifier: part_of
  review:
    summary: >-
      ComplexPortal (CPX-2216) IPI annotation of BCKDHB as a subunit of the BCKDH
      complex, based on co-purification of the intact human liver complex.
    action: ACCEPT
    reason: >-
      Correct core complex membership, supported by biochemical purification showing the
      subunit composition of the human liver BCKDH complex.
    supported_by:
    - reference_id: PMID:3593587
      supporting_text: >-
        the purified enzyme complex gave three major bands having
        molecular weights of 51,000, 46,000, and 36,000
- term:
    id: GO:0005739
    label: mitochondrion
  evidence_type: IDA
  original_reference_id: GO_REF:0000052
  qualifier: located_in
  review:
    summary: >-
      Human Protein Atlas immunofluorescence (IDA) localization of BCKDHB to
      mitochondria. Less granular than the matrix annotations but consistent.
    action: ACCEPT
    reason: >-
      Correct localization; mitochondrion is a valid parent of the more specific
      mitochondrial matrix localization also annotated. Directly supported by
      immunofluorescence.
- term:
    id: GO:0005759
    label: mitochondrial matrix
  evidence_type: NAS
  original_reference_id: PMID:10745006
  qualifier: located_in
  review:
    summary: >-
      Author statement (NAS, UniProt) of mitochondrial matrix localization, associated
      with the crystal structure paper of the human E1b heterotetramer.
    action: ACCEPT
    reason: >-
      Consistent with the UniProt subcellular location and all other matrix annotations;
      correct core localization.
    supported_by:
    - reference_id: UniProtKB:P21953
      supporting_text: 'SUBCELLULAR LOCATION: Mitochondrion matrix'
- term:
    id: GO:0005759
    label: mitochondrial matrix
  evidence_type: ISS
  original_reference_id: GO_REF:0000024
  qualifier: is_active_in
  review:
    summary: >-
      Sequence-similarity (ISS) transfer from ortholog (UniProtKB:P21839, rat E1-beta)
      asserting BCKDHB is active in the mitochondrial matrix, where the BCKDH complex
      functions.
    action: ACCEPT
    reason: >-
      Correct: the E1 decarboxylase acts within the mitochondrial matrix as part of the
      BCKDH complex. The 'is_active_in' qualifier appropriately links localization to
      the site of catalytic function.
    supported_by:
    - reference_id: UniProtKB:P21953
      supporting_text: 'SUBCELLULAR LOCATION: Mitochondrion matrix'
- term:
    id: GO:0120552
    label: branched-chain alpha-keto acid decarboxylation to branched-chain acyl-CoA
  evidence_type: IMP
  original_reference_id: PMID:10745006
  qualifier: involved_in
  review:
    summary: >-
      Mutant-phenotype (IMP) annotation to the specific process of branched-chain
      alpha-keto acid decarboxylation. The crystal structure of human E1b rationalizes
      how MSUD mutations in the beta subunit impair this decarboxylation step.
    action: ACCEPT
    reason: >-
      Accurate, appropriately specific description of the E1 decarboxylase step in which
      BCKDHB participates. Supported by structural/mutational analysis of MSUD variants.
    supported_by:
    - reference_id: PMID:10745006
      supporting_text: >-
        The known
        MSUD mutations affect the functioning of E1b by interfering with the cofactor
        and K(+) sites, the packing of hydrophobic cores, and the precise arrangement of
        residues at or near several subunit interfaces.
- term:
    id: GO:0120552
    label: branched-chain alpha-keto acid decarboxylation to branched-chain acyl-CoA
  evidence_type: IDA
  original_reference_id: PMID:3593587
  qualifier: involved_in
  review:
    summary: >-
      Direct experimental (IDA) annotation to the branched-chain alpha-keto acid
      decarboxylation process, supported by the purified human liver BCKDH complex
      oxidizing all three branched-chain 2-oxo acids.
    action: ACCEPT
    reason: >-
      Correct, appropriately specific process describing the reaction the E1 component
      (including BCKDHB) initiates. Directly supported by biochemical characterization.
    supported_by:
    - reference_id: PMID:3593587
      supporting_text: >-
        The BCKADH effectively oxidized all of KIV, KIC, and KMV, yielding apparent Km
        values in the range of 14-17 microM for those alpha-keto acids.
- term:
    id: GO:0005759
    label: mitochondrial matrix
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-9865121
  qualifier: located_in
  review:
    summary: >-
      Reactome (TAS) matrix localization annotation from a curated pathway reaction
      involving the BCKDH complex.
    action: ACCEPT
    reason: >-
      Consistent with the UniProt subcellular location and the other matrix annotations;
      correct core localization from a curated pathway source.
- term:
    id: GO:0005739
    label: mitochondrion
  evidence_type: HTP
  original_reference_id: PMID:34800366
  qualifier: located_in
  review:
    summary: >-
      High-throughput (HTP) mitochondrial proteomics localization of BCKDHB to
      mitochondria (Morgenstern et al. high-confidence human mitochondrial proteome).
    action: ACCEPT
    reason: >-
      Consistent with all other localization evidence; a valid (if less specific) parent
      of the mitochondrial matrix localization. Correct.
    supported_by:
    - reference_id: PMID:34800366
      supporting_text: >-
        Quantitative high-confidence human mitochondrial proteome and its dynamics
        in cellular context.
- term:
    id: GO:0160157
    label: branched-chain alpha-ketoacid dehydrogenase complex
  evidence_type: IMP
  original_reference_id: PMID:2022752
  qualifier: part_of
  review:
    summary: >-
      Mutant-phenotype (IMP) evidence that BCKDHB is part of the BCKDH complex: an
      11-bp deletion abolishing the beta subunit destabilizes E1-alpha and reduces
      complex activity to ~6% of normal, demonstrating BCKDHB is a required structural
      subunit.
    action: ACCEPT
    reason: >-
      Strong genetic/biochemical evidence that BCKDHB is an integral subunit of the
      BCKDH complex whose absence disassembles/inactivates the enzyme. Core complex
      membership.
    supported_by:
    - reference_id: PMID:2022752
      supporting_text: The absence of the E1 beta subunit results in instability of the E1 alpha subunit.
- term:
    id: GO:0160157
    label: branched-chain alpha-ketoacid dehydrogenase complex
  evidence_type: IDA
  original_reference_id: PMID:9582350
  qualifier: part_of
  review:
    summary: >-
      Direct experimental (IDA) evidence that BCKDHB is a subunit of the E1 component:
      reconstitution/assembly studies show wild-type E1 exists as alpha2-beta2 tetramers
      of E1-alpha and E1-beta.
    action: ACCEPT
    reason: >-
      Directly demonstrates BCKDHB as part of the E1 decarboxylase of the BCKDH complex
      (alpha2-beta2 tetramer). Core complex membership.
    supported_by:
    - reference_id: PMID:9582350
      supporting_text: >-
        The E1 decarboxylase component of the human branched-chain ketoacid
        dehydrogenase complex comprises two E1alpha (45.5 kDa) and two E1beta (37.5 kDa)
        subunits forming an alpha2 beta2 tetramer.
- term:
    id: GO:0160157
    label: branched-chain alpha-ketoacid dehydrogenase complex
  evidence_type: IDA
  original_reference_id: PMID:10745006
  qualifier: part_of
  review:
    summary: >-
      Direct experimental (IDA) evidence from the crystal structure of the human E1b
      component (170 kDa alpha2-beta2 heterotetramer), establishing BCKDHB as an
      integral subunit of the BCKDH complex.
    action: ACCEPT
    reason: >-
      Structural determination of the E1b heterotetramer directly demonstrates BCKDHB as
      part of the complex. Core complex membership.
    supported_by:
    - reference_id: PMID:10745006
      supporting_text: >-
        the 170 kDa
        alpha(2)beta(2) heterotetrameric E1b component of the
        branched-chain alpha-ketoacid dehydrogenase multienzyme complex.
- term:
    id: GO:0003863
    label: branched-chain 2-oxo acid dehydrogenase activity
  evidence_type: IDA
  original_reference_id: PMID:10745006
  qualifier: contributes_to
  review:
    summary: >-
      Direct experimental (IDA) annotation with the appropriate 'contributes_to'
      qualifier: BCKDHB contributes to the E1 decarboxylase molecular function. The
      crystal structure shows the active site at the alpha-beta' interface, with beta
      subunit residues involved in cofactor and K+ binding.
    action: ACCEPT
    reason: >-
      Core molecular function. 'contributes_to' correctly reflects that catalysis
      requires both subunits (active site at alpha-beta' interface); BCKDHB alone does
      not carry the full activity but is essential to it.
    supported_by:
    - reference_id: PMID:10745006
      supporting_text: >-
        The position of two important potassium (K(+)) ions was
        determined.
    - reference_id: UniProtKB:P21953
      supporting_text: >-
        The E1 subunit
        catalyzes the first step with the decarboxylation of the alpha-ketoacid
- term:
    id: GO:0003863
    label: branched-chain 2-oxo acid dehydrogenase activity
  evidence_type: IDA
  original_reference_id: PMID:9582350
  qualifier: contributes_to
  review:
    summary: >-
      Direct experimental (IDA) annotation of the E1 decarboxylase activity with
      'contributes_to'. E1-alpha missense mutations abolish E1 and BCKDH catalytic
      activity, and BCKDHB is a required subunit of the catalytically competent
      alpha2-beta2 E1.
    action: ACCEPT
    reason: >-
      Core molecular function; 'contributes_to' is correct for a shared active site
      formed by the alpha2-beta2 heterotetramer.
    supported_by:
    - reference_id: PMID:9582350
      supporting_text: >-
        the E1alpha subunit is
        affected, resulting in the loss of E1 and
        branched-chain ketoacid dehydrogenase catalytic activities.
- term:
    id: GO:0005759
    label: mitochondrial matrix
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-5693148
  qualifier: located_in
  review:
    summary: >-
      Reactome (TAS) mitochondrial matrix localization from a curated pathway reaction
      involving the BCKDH complex.
    action: ACCEPT
    reason: >-
      Consistent with all other matrix localization evidence; correct core localization.
- term:
    id: GO:0005759
    label: mitochondrial matrix
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-5693153
  qualifier: located_in
  review:
    summary: >-
      Reactome (TAS) mitochondrial matrix localization from a curated pathway reaction
      involving the BCKDH complex.
    action: ACCEPT
    reason: >-
      Consistent with all other matrix localization evidence; correct core localization.
- term:
    id: GO:0005759
    label: mitochondrial matrix
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-9912527
  qualifier: located_in
  review:
    summary: >-
      Reactome (TAS) mitochondrial matrix localization from a curated pathway reaction
      (BCKDH dephosphorylation by PPM1K) involving the BCKDH complex.
    action: ACCEPT
    reason: >-
      Consistent with all other matrix localization evidence; correct core localization.
- term:
    id: GO:0003863
    label: branched-chain 2-oxo acid dehydrogenase activity
  evidence_type: IMP
  original_reference_id: PMID:2022752
  qualifier: contributes_to
  review:
    summary: >-
      Mutant-phenotype (IMP) evidence for the E1 decarboxylase activity: loss of the
      beta subunit reduces BCKDH activity to ~6% of normal, demonstrating BCKDHB is
      required for the complex's dehydrogenase activity. Annotated with 'contributes_to'.
    action: ACCEPT
    reason: >-
      Core molecular function supported by loss-of-function genetics; 'contributes_to'
      is appropriate for a subunit of the shared active site.
    supported_by:
    - reference_id: PMID:2022752
      supporting_text: The BCKDH activity in the proband with MSUD was approximately 6% of the normal control level.
- term:
    id: GO:0005759
    label: mitochondrial matrix
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-9859148
  qualifier: located_in
  review:
    summary: >-
      Reactome (TAS) mitochondrial matrix localization from the curated reaction in
      which the BCKDHA:BCKDHB E1 tetramer decarboxylates KIC, KMV and KIV.
    action: ACCEPT
    reason: >-
      Consistent with all other matrix localization evidence and directly describes the
      E1 catalytic reaction. Correct core localization.
- term:
    id: GO:0005759
    label: mitochondrial matrix
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-9859163
  qualifier: located_in
  review:
    summary: >-
      Reactome (TAS) mitochondrial matrix localization from a curated pathway reaction
      involving the BCKDH complex.
    action: ACCEPT
    reason: >-
      Consistent with all other matrix localization evidence; correct core localization.
- term:
    id: GO:0005759
    label: mitochondrial matrix
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-9859172
  qualifier: located_in
  review:
    summary: >-
      Reactome (TAS) mitochondrial matrix localization from the curated reaction in
      which the DLD (E3) dimer dehydrogenates dihydrolipoyl, part of the BCKDH complex
      cycle.
    action: ACCEPT
    reason: >-
      Consistent with all other matrix localization evidence; correct core localization.
- term:
    id: GO:0005759
    label: mitochondrial matrix
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-9865115
  qualifier: located_in
  review:
    summary: >-
      Reactome (TAS) mitochondrial matrix localization from a curated reaction involving
      DBT (E2) loss-of-function within the BCKDH pathway.
    action: ACCEPT
    reason: >-
      Consistent with all other matrix localization evidence; correct core localization.
- term:
    id: GO:0005759
    label: mitochondrial matrix
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-9907572
  qualifier: located_in
  review:
    summary: >-
      Reactome (TAS) mitochondrial matrix localization from a curated pathway reaction
      involving the BCKDH complex.
    action: ACCEPT
    reason: >-
      Consistent with all other matrix localization evidence; correct core localization.
- term:
    id: GO:0005759
    label: mitochondrial matrix
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-9912480
  qualifier: located_in
  review:
    summary: >-
      Reactome (TAS) mitochondrial matrix localization from the curated reaction in
      which BCKDK loss-of-function mutations fail to phosphorylate BCKDH.
    action: ACCEPT
    reason: >-
      Consistent with all other matrix localization evidence; correct core localization.
- term:
    id: GO:0005739
    label: mitochondrion
  evidence_type: IMP
  original_reference_id: PMID:2022752
  qualifier: located_in
  review:
    summary: >-
      Mutant-phenotype (IMP) mitochondrial localization inference. The disease allele
      deletes part of the E1-beta mitochondrial targeting leader peptide, consistent
      with normal mitochondrial localization of the wild-type protein.
    action: ACCEPT
    reason: >-
      Correct localization; a valid parent of the mitochondrial matrix annotations.
      The mutation disrupts the mitochondrial targeting peptide, underscoring the
      protein's mitochondrial destination.
    supported_by:
    - reference_id: PMID:2022752
      supporting_text: >-
        An 11-bp deletion was identified in the region that encoded the
        mitochondrial targeting leader peptide in the E1 beta cDNA.
- term:
    id: GO:0009083
    label: branched-chain amino acid catabolic process
  evidence_type: IMP
  original_reference_id: PMID:2022752
  qualifier: involved_in
  review:
    summary: >-
      Mutant-phenotype (IMP) evidence for the core BCAA catabolic process: complete loss
      of the beta subunit causes MSUD (BCAA/BCKA accumulation) and reduces BCKDH activity
      to ~6% of normal, demonstrating BCKDHB's requirement for BCAA catabolism.
    action: ACCEPT
    reason: >-
      Strong loss-of-function evidence for a core biological process; MSUD 1B is the
      pathological consequence of impaired BCAA catabolism due to E1-beta deficiency.
    supported_by:
    - reference_id: PMID:2022752
      supporting_text: >-
        These observations show the biological importance of the E1 beta
        subunit of BCKDH to maintain normal function of the enzyme activity.
core_functions:
- description: >-
    E1-beta subunit of the BCKDH E1 decarboxylase; contributes (with BCKDHA) to the
    thiamine diphosphate-dependent oxidative decarboxylation of branched-chain 2-oxo
    (alpha-keto) acids, the committed and rate-limiting step of branched-chain amino
    acid catabolism.
  molecular_function:
    id: GO:0003863
    label: branched-chain 2-oxo acid dehydrogenase activity
  directly_involved_in:
  - id: GO:0009083
    label: branched-chain amino acid catabolic process
  locations:
  - id: GO:0005759
    label: mitochondrial matrix
  in_complex:
    id: GO:0160157
    label: branched-chain alpha-ketoacid dehydrogenase complex
  supported_by:
  - reference_id: UniProtKB:P21953
    supporting_text: >-
      Together with BCKDHA forms the heterotetrameric E1 subunit of
      the mitochondrial branched-chain alpha-ketoacid dehydrogenase (BCKD)
      complex.
  - reference_id: PMID:10745006
    supporting_text: >-
      the 170 kDa
      alpha(2)beta(2) heterotetrameric E1b component of the
      branched-chain alpha-ketoacid dehydrogenase multienzyme complex.
references:
- id: file:human/BCKDHB/BCKDHB-deep-research-falcon.md
  title: BCKDHB (P21953) deep research report (falcon / Edison Scientific Literature)
  findings: []
- id: GO_REF:0000024
  title: Manual transfer of experimentally-verified manual GO annotation data to orthologs
    by curator judgment of sequence similarity
  findings: []
- id: GO_REF:0000033
  title: Annotation inferences using phylogenetic trees
  findings: []
- id: GO_REF:0000052
  title: Gene Ontology annotation based on curation of immunofluorescence data
  findings: []
- id: GO_REF:0000107
  title: Automatic transfer of experimentally verified manual GO annotation data to
    orthologs using Ensembl Compara
  findings: []
- id: GO_REF:0000120
  title: Combined Automated Annotation using Multiple IEA Methods
  findings: []
- id: PMID:10745006
  title: Crystal structure of human branched-chain alpha-ketoacid dehydrogenase and
    the molecular basis of multienzyme complex deficiency in maple syrup urine disease.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      PubMed-verified. Crystal structure of the human E1b alpha2-beta2 heterotetramer;
      directly establishes BCKDHB as a subunit of the E1 decarboxylase and its role in
      cofactor/K+ binding. Cached abstract only (full_text_available: false), but the
      catalytic-activity and structural claims are also anchored in UniProt.
- id: PMID:12902323
  title: 'Roles of His291-alpha and His146-beta'' in the reductive acylation reaction
    catalyzed by human branched-chain alpha-ketoacid dehydrogenase: refined phosphorylation
    loop structure in the active site.'
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: >-
      Mechanistic study of the assembled E1; basis for an IPI 'protein binding'
      annotation (WITH/FROM BCKDHA). Cached abstract only.
- id: PMID:15166214
  title: Cross-talk between thiamin diphosphate binding and phosphorylation loop conformation
    in human branched-chain alpha-keto acid decarboxylase/dehydrogenase.
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: >-
      Basis for an IPI 'protein binding' annotation (WITH/FROM BCKDHA), reflecting the
      E1 heterotetramer. Cached abstract only.
- id: PMID:15576032
  title: Molecular mechanism for regulation of the human mitochondrial branched-chain
    alpha-ketoacid dehydrogenase complex by phosphorylation.
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: >-
      Regulation of the assembled complex by E1-alpha phosphorylation; basis for an
      IPI 'protein binding' annotation (WITH/FROM BCKDHA). Cached abstract only.
- id: PMID:2022752
  title: Maple syrup urine disease. Complete defect of the E1 beta subunit of the
    branched chain alpha-ketoacid dehydrogenase complex due to a deletion of an 11-bp
    repeat sequence which encodes a mitochondrial targeting leader peptide in a family
    with the disease.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      PubMed-verified. Directly on BCKDHB (E1-beta): 11-bp deletion in the
      mitochondrial targeting peptide; loss of E1-beta destabilizes E1-alpha and reduces
      BCKDH activity to ~6% of normal. Supports complex membership, BCAA catabolism, and
      mitochondrial localization annotations. Full text (JCI, PMC295312) available.
- id: PMID:28514442
  title: Architecture of the human interactome defines protein communities and disease
    networks.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: >-
      Large-scale BioPlex interactome; basis for a high-throughput IPI 'protein binding'
      annotation with BCKDHA (E1 heterotetramer). Recovers the genuine interaction but
      uninformative at the bare protein-binding level.
- id: PMID:33961781
  title: Dual proteome-scale networks reveal cell-specific remodeling of the human
    interactome.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: >-
      Large-scale BioPlex 3.0 interactome; basis for a high-throughput IPI 'protein
      binding' annotation with BCKDHA. Genuine but uninformative bare protein binding.
- id: PMID:34800366
  title: Quantitative high-confidence human mitochondrial proteome and its dynamics
    in cellular context.
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: >-
      High-confidence human mitochondrial proteome (HTP); supports mitochondrial
      localization of BCKDHB.
- id: PMID:3593587
  title: Purification and characterization of human liver branched-chain alpha-keto
    acid dehydrogenase complex.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      PubMed-verified. Purification of the intact human liver BCKDH complex; shows the
      complex oxidizes all three branched-chain 2-oxo acids (KIV, KIC, KMV). Supports the
      MF, BCAA catabolism, decarboxylation and complex-membership annotations. Cached
      abstract only.
- id: PMID:9582350
  title: Impaired assembly of E1 decarboxylase of the branched-chain alpha-ketoacid
    dehydrogenase complex in type IA maple syrup urine disease.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      PubMed-verified. Establishes the E1 decarboxylase as an alpha2-beta2 tetramer of
      E1-alpha and E1-beta; supports BCKDHB complex membership and its contribution to
      E1 catalytic activity. Cached abstract only.
- id: Reactome:R-HSA-5693148
  title: "BCKDK phosphorylates BCKDH"
  findings: []
- id: Reactome:R-HSA-5693153
  title: "PPM1K dephosphorylates p-BCKDH"
  findings: []
- id: Reactome:R-HSA-9859148
  title: "BCKDHA:BCKDHB tetramer decarboxylates KIC, KMVA, KIV"
  findings: []
- id: Reactome:R-HSA-9859163
  title: "DBT transfers BCAA to CoA"
  findings: []
- id: Reactome:R-HSA-9859172
  title: "DLD dimer dehydrogenates dihydrolipoyl"
  findings: []
- id: Reactome:R-HSA-9865115
  title: "DBT loss-of-function mutants don't synthesize BCAA-CoA"
  findings: []
- id: Reactome:R-HSA-9865121
  title: "BCKDHA or BCKDHB loss-of-function mutants don't synthesize BCAA-CoA"
  findings: []
- id: Reactome:R-HSA-9907572
  title: "Loss-of-function DLD mutants don't dehydrogenate dihydrolipoyl DBT"
  findings: []
- id: Reactome:R-HSA-9912480
  title: "BCKDK loss-of-function mutations do not phosphorylate BCKDH"
  findings: []
- id: Reactome:R-HSA-9912527
  title: "H139Hfs13* PPM1K does not dephosphorylate BCKDH"
  findings: []