id: O00330
gene_symbol: PDHX
product_type: PROTEIN
status: INITIALIZED
taxon:
  id: NCBITaxon:9606
  label: Homo sapiens
description: >-
  PDHX (component X / E3-binding protein, E3BP) is a structural, non-catalytic
  subunit of the mitochondrial pyruvate dehydrogenase complex (PDC), which
  catalyses the oxidative decarboxylation of pyruvate to acetyl-CoA linking
  glycolysis to the TCA cycle. PDHX has a segmented multidomain architecture
  analogous to the E2 component (DLAT): an N-terminal lipoyl domain (lipoylated at
  Lys97), a peripheral subunit-binding / E3-binding domain, and a C-terminal
  E2-like inner-core (I') domain that packs into the dodecahedral E2 (DLAT) core.
  Its established function is to bind and anchor the E3 dihydrolipoyl dehydrogenase
  (DLD) to the E2 core, positioning E3 to reoxidise the reduced lipoyl arms; this
  tethering is essential for a functional PDC. Unlike E2, the catalytic-site
  histidine of the inner-core acyltransferase fold is replaced by serine in human
  E3BP, so PDHX does not itself catalyse acetyl-CoA formation. PDHX resides in the
  mitochondrial matrix. Its lipoyl-Lys97 is a substrate of the SIRT4 lipoamidase,
  providing a regulatory input to PDC activity. Loss-of-function variants cause
  pyruvate dehydrogenase E3-binding protein deficiency (a form of PDC deficiency
  with congenital lactic acidosis, hypotonia and psychomotor retardation).
alternative_products:
- name: '1'
  id: O00330-1
- name: '2'
  id: O00330-2
  sequence_note: VSP_045271
- name: '3'
  id: O00330-3
  sequence_note: VSP_053817
existing_annotations:
- term:
    id: GO:0005739
    label: mitochondrion
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: is_active_in
  review:
    summary: >-
      PDHX is a mitochondrial matrix protein and subunit of the mitochondrial PDC.
      Phylogenetic (IBA) placement in the mitochondrion is correct, though less
      specific than mitochondrial matrix.
    action: ACCEPT
    reason: >-
      UniProt records subcellular location "Mitochondrion matrix" and a
      cleavable mitochondrial transit peptide (residues 1-53). The term is
      correct; the more specific GO:0005759 (mitochondrial matrix) annotation is
      also present.
    supported_by:
    - reference_id: file:human/PDHX/PDHX-uniprot.txt
      supporting_text: "SUBCELLULAR LOCATION: Mitochondrion matrix."
- term:
    id: GO:0045254
    label: pyruvate dehydrogenase complex
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: part_of
  review:
    summary: >-
      PDHX is a bona fide subunit of the pyruvate dehydrogenase complex,
      constituting part of the E2/E3BP inner core. Correct and core.
    action: ACCEPT
    reason: >-
      Direct experimental and structural evidence establishes PDHX as part of the
      PDC inner core; the IBA phylogenetic annotation is consistent with this.
    supported_by:
    - reference_id: PMID:19240034
      supporting_text: >-
        a noncatalytic component, E3-binding protein (E3BP), which specifically
        tethers E3 dimers to the PDC.
- term:
    id: GO:0004742
    label: dihydrolipoyllysine-residue acetyltransferase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  qualifier: enables
  review:
    summary: >-
      This is a homology/family-based electronic annotation propagated from the
      E2 (acetyltransferase) fold that PDHX shares. However, human E3BP is not a
      functional acetyltransferase: the catalytic-site histidine of the inner-core
      acyltransferase domain is replaced by a serine, so CoA acetylation by this
      protein is unlikely.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      PDHX retains the E2-like inner-core fold (hence the ARBA family mapping) but
      lacks the catalytic histidine required for transacetylase activity; it is a
      structural/E3-anchoring subunit, not a catalytic acyltransferase. The
      annotation reflects fold similarity, not true molecular function.
    supported_by:
    - reference_id: PMID:9242632
      supporting_text: >-
        The putative catalytic site histidine residue present in the inner core
        domains of all dihydrolipoamide acyltransferases is replaced by a serine
        residue in human E3BP; thus, catalysis of coenzyme A acetylation by this
        protein is unlikely.
    - reference_id: PMID:19240034
      supporting_text: >-
        a noncatalytic component, E3-binding protein (E3BP), which specifically
        tethers E3 dimers to the PDC.
- term:
    id: GO:0005759
    label: mitochondrial matrix
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  qualifier: located_in
  review:
    summary: >-
      Correct and the most specific localization for PDHX; matches the UniProt
      subcellular location.
    action: ACCEPT
    reason: >-
      UniProt SubCell mapping (SL-0170) to mitochondrial matrix is consistent with
      the curated UniProt location and with PDHX being an assembled subunit of the
      matrix-resident PDC.
    supported_by:
    - reference_id: file:human/PDHX/PDHX-uniprot.txt
      supporting_text: "SUBCELLULAR LOCATION: Mitochondrion matrix."
- term:
    id: GO:0006086
    label: pyruvate decarboxylation to acetyl-CoA
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: involved_in
  review:
    summary: >-
      PDHX is a required structural subunit of the PDC, which performs the
      oxidative decarboxylation of pyruvate to acetyl-CoA. As part_of the complex
      it is legitimately "involved_in" this process even though it is not itself
      catalytic.
    action: ACCEPT
    reason: >-
      Anchoring E3 to the E2 core is essential for a functional PDC; loss of PDHX
      causes PDC deficiency. The BP annotation captures the pathway role of the
      subunit and is corroborated by the ComplexPortal IDA (PMID:24534072) and the
      IC annotation (PMID:9242632).
    supported_by:
    - reference_id: PMID:9242632
      supporting_text: >-
        Protein X, recently renamed dihydrolipoamide dehydrogenase-binding protein
        (E3BP), is required for anchoring dihydrolipoamide dehydrogenase (E3) to
        the dihydrolipoamide transacetylase (E2) core of the pyruvate dehydrogenase
        complexes of eukaryotes.
- term:
    id: GO:0016746
    label: acyltransferase activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: enables
  review:
    summary: >-
      Broad acyltransferase MF mapped from InterPro domains of the shared E2-like
      fold. As with the more specific GO:0004742, PDHX does not catalyse acyl
      transfer (catalytic His->Ser), so this is a fold-based over-annotation.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      The InterPro signatures (2-oxoacid_DH acyltransferase, E2/Pdx1) reflect the
      E2-like inner-core fold that PDHX possesses structurally; the catalytic
      residue is absent and no acyltransferase activity has been demonstrated.
    supported_by:
    - reference_id: PMID:9242632
      supporting_text: >-
        The putative catalytic site histidine residue present in the inner core
        domains of all dihydrolipoamide acyltransferases is replaced by a serine
        residue in human E3BP; thus, catalysis of coenzyme A acetylation by this
        protein is unlikely.
- term:
    id: GO:0045254
    label: pyruvate dehydrogenase complex
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  qualifier: part_of
  review:
    summary: >-
      Electronic (IEA) part_of PDC annotation, duplicating the well-supported
      experimental/IBA annotations. Correct and core.
    action: ACCEPT
    reason: >-
      Consistent with all other evidence that PDHX is a subunit of the PDC inner
      core.
    supported_by:
    - reference_id: PMID:16263718
      supporting_text: >-
        The dihydrolipoamide dehydrogenase-binding protein (E3BP) and the
        dihydrolipoamide acetyltransferase (E2) component enzyme form the
        structural core of the human pyruvate dehydrogenase complex
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:16263718
  qualifier: enables
  review:
    summary: >-
      IPI interaction with DLD (E3, P09622) from the crystal structure of the
      E3BP E3-binding domain in complex with E3. This is the key biological
      interaction of PDHX, but the bare "protein binding" term is uninformative;
      the specific E3-anchoring/adaptor role is captured in core_functions.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Per curation guidelines, bare GO:0005515 "protein binding" adds no functional
      information. The underlying DLD interaction is real and central, but is
      better represented by the E3-anchoring adaptor function (GO:0030674) in
      core_functions rather than by this generic term.
    supported_by:
    - reference_id: PMID:16263718
      supporting_text: >-
        How dihydrolipoamide dehydrogenase-binding protein binds dihydrolipoamide
        dehydrogenase in the human pyruvate dehydrogenase complex.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:16442803
  qualifier: enables
  review:
    summary: >-
      IPI interaction with DLD (E3, P09622) from a second crystal structure of the
      E3-binding domain in complex with E3, including hot-spot mutagenesis. Real
      but bare/uninformative.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Meaningful DLD interaction but recorded as generic protein binding; the
      specific anchoring/adaptor function is captured in core_functions.
    supported_by:
    - reference_id: PMID:16442803
      supporting_text: >-
        utilizes the specific dihydrolipoamide dehydrogenase (E3) binding protein
        (E3BP) to tether the essential E3 component to the 60-meric core of the
        complex
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:21516116
  qualifier: enables
  review:
    summary: >-
      Interaction with AGTRAP (Q6RW13) from a high-throughput next-generation
      sequencing interactome (Y2H) screen. No established biological role of PDHX
      involves AGTRAP; a bare, high-throughput protein-binding hit.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Generic protein-binding annotation from a proteome-scale screen with no
      functional context for PDHX; uninformative for the gene's function.
    supported_by:
    - reference_id: PMID:21516116
      supporting_text: Next-generation sequencing to generate interactome datasets.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:25416956
  qualifier: enables
  review:
    summary: >-
      Interaction with AGTRAP (Q6RW13) from a proteome-scale binary interactome
      map. High-throughput, bare protein-binding hit with no functional context.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Uninformative generic protein-binding from a large-scale interactome screen.
    supported_by:
    - reference_id: PMID:25416956
      supporting_text: A proteome-scale map of the human interactome network.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:25525879
  qualifier: enables
  review:
    summary: >-
      IPI interaction with SIRT4 (Q9Y6E7). SIRT4 is a lipoamidase that removes the
      lipoyl modification from PDHX (Lys97) and DLAT to regulate PDC activity, so
      this is a biologically meaningful interaction, but bare "protein binding" is
      uninformative.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      The SIRT4 interaction is functionally relevant (regulatory delipoylation),
      but as recorded it is a generic protein-binding term; the regulatory
      relationship is better captured as PTM/regulation, not as a core MF.
    supported_by:
    - reference_id: PMID:25525879
      supporting_text: >-
        SIRT4 removed lipoamide from DLAT and PDHX peptides
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:28514442
  qualifier: enables
  review:
    summary: >-
      Interaction with DLD (P09622) captured in a large-scale AP-MS interactome
      (BioPlex). Consistent with the biological E3(DLD) interaction, but a bare,
      uninformative protein-binding term.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      High-throughput DLD interaction; real but generic. Anchoring function is in
      core_functions.
    supported_by:
    - reference_id: PMID:28514442
      supporting_text: >-
        Architecture of the human interactome defines protein communities and
        disease networks.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:31515488
  qualifier: enables
  review:
    summary: >-
      Interaction with AGTRAP (Q6RW13) from a variant/interaction disruption study.
      High-throughput, bare protein-binding hit with no functional role for PDHX.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Generic protein-binding from a large-scale interaction screen; uninformative.
    supported_by:
    - reference_id: PMID:31515488
      supporting_text: >-
        Extensive disruption of protein interactions by genetic variants across
        the allele frequency spectrum in human populations.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:32296183
  qualifier: enables
  review:
    summary: >-
      Interactions with DLD (P09622) and CIDEB (Q9UHD4) from a reference binary
      interactome map (HuRI). The DLD hit is consistent with biology; CIDEB has no
      established role with PDHX. Bare protein-binding term.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Mixed high-throughput hits recorded as generic protein binding; the DLD
      interaction is real (anchoring, in core_functions) and CIDEB is an
      uncharacterized screen hit.
    supported_by:
    - reference_id: PMID:32296183
      supporting_text: A reference map of the human binary protein interactome.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:33961781
  qualifier: enables
  review:
    summary: >-
      Interaction with DLD (P09622) from a cell-specific AP-MS interactome
      (BioPlex 3.0). Consistent with the biological E3(DLD) interaction, but bare.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      High-throughput DLD interaction; real but recorded as generic protein
      binding.
    supported_by:
    - reference_id: PMID:33961781
      supporting_text: >-
        Dual proteome-scale networks reveal cell-specific remodeling of the human
        interactome.
- term:
    id: GO:0005739
    label: mitochondrion
  evidence_type: NAS
  original_reference_id: PMID:24534072
  qualifier: located_in
  review:
    summary: >-
      Non-traceable statement of mitochondrial localization (ComplexPortal),
      consistent with the well-established matrix localization. Correct but less
      specific than mitochondrial matrix.
    action: ACCEPT
    reason: >-
      PDHX is a matrix-resident PDC subunit; the mitochondrion annotation is
      correct.
    supported_by:
    - reference_id: file:human/PDHX/PDHX-uniprot.txt
      supporting_text: "SUBCELLULAR LOCATION: Mitochondrion matrix."
- term:
    id: GO:0006086
    label: pyruvate decarboxylation to acetyl-CoA
  evidence_type: IDA
  original_reference_id: PMID:24534072
  qualifier: involved_in
  review:
    summary: >-
      ComplexPortal IDA: reconstituted recombinant human PDC (including E3BP) was
      shown to be functional in producing acetyl-CoA. PDHX participates as a
      required structural subunit. Correct as involved_in.
    action: ACCEPT
    reason: >-
      A well-defined recombinant human PDC containing PDHX was assembled and shown
      catalytically competent, supporting the subunit's involvement in pyruvate
      decarboxylation to acetyl-CoA (as part of the complex, not as a catalyst).
    supported_by:
    - reference_id: PMID:24534072
      supporting_text: >-
        The mammalian pyruvate dehydrogenase complex (PDC) is a multi-component
        mitochondrial enzyme that plays a key role in the conversion of pyruvate to
        acetyl-CoA connecting glycolysis to the citric acid cycle.
- term:
    id: GO:0045254
    label: pyruvate dehydrogenase complex
  evidence_type: IPI
  original_reference_id: PMID:19240034
  qualifier: part_of
  review:
    summary: >-
      Experimental (IPI) part_of PDC from stoichiometry/reconstitution work
      establishing PDHX as ~20 copies (40/20 model) within the E2/E3BP core.
      Correct and core.
    action: ACCEPT
    reason: >-
      Direct biophysical characterization places E3BP within the PDC core and shows
      it tethers E3 to the complex.
    supported_by:
    - reference_id: PMID:19240034
      supporting_text: >-
        The human PDC is organized around a 60-meric dodecahedral core comprising
        the C-terminal domains of E2p and a noncatalytic component, E3-binding
        protein (E3BP), which specifically tethers E3 dimers to the PDC.
- term:
    id: GO:0005739
    label: mitochondrion
  evidence_type: IDA
  original_reference_id: GO_REF:0000052
  qualifier: located_in
  review:
    summary: >-
      Immunofluorescence (HPA) localization to mitochondrion. Consistent with the
      established matrix localization.
    action: ACCEPT
    reason: >-
      Direct imaging evidence of mitochondrial localization; correct though less
      specific than mitochondrial matrix.
    supported_by:
    - reference_id: file:human/PDHX/PDHX-uniprot.txt
      supporting_text: "SUBCELLULAR LOCATION: Mitochondrion matrix."
- term:
    id: GO:0004742
    label: dihydrolipoyllysine-residue acetyltransferase activity
  evidence_type: IDA
  original_reference_id: PMID:9242632
  qualifier: enables
  review:
    summary: >-
      Legacy IDA (MGI) assigning transacetylase activity, but the same primary
      paper explicitly concludes that CoA acetylation by human E3BP is unlikely
      because the catalytic-site histidine is replaced by serine. This MF should
      not be treated as a genuine catalytic function of PDHX.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      The cited paper reconstituted a functional PDC using E3BP but attributes the
      acetyltransferase catalysis to E2; it states the E3BP inner-core domain lacks
      the catalytic histidine and is unlikely to catalyse acetylation. PDHX is a
      structural (E3-anchoring) subunit, so this catalytic MF is an over-annotation
      of the fold rather than a demonstrated activity.
    supported_by:
    - reference_id: PMID:9242632
      supporting_text: >-
        The putative catalytic site histidine residue present in the inner core
        domains of all dihydrolipoamide acyltransferases is replaced by a serine
        residue in human E3BP; thus, catalysis of coenzyme A acetylation by this
        protein is unlikely.
- term:
    id: GO:0006086
    label: pyruvate decarboxylation to acetyl-CoA
  evidence_type: IC
  original_reference_id: PMID:9242632
  qualifier: acts_upstream_of_or_within
  review:
    summary: >-
      Curator inference (IC) that PDHX participates in pyruvate decarboxylation to
      acetyl-CoA, based on its role in reconstituting a functional PDC. Consistent
      with the subunit's essential contribution to the pathway.
    action: ACCEPT
    reason: >-
      PDHX is required for a functional PDC; its involvement in the
      pyruvate->acetyl-CoA conversion is a reasonable curator inference and is
      supported by reconstitution of the complex.
    supported_by:
    - reference_id: PMID:9242632
      supporting_text: >-
        Coexpression of cDNAs for E3BP and E2 resulted in the formation of an
        E2.E3BP subcomplex that spontaneously reconstituted the pyruvate
        dehydrogenase complex in the presence of native E3 and recombinant pyruvate
        decarboxylase (E1).
- term:
    id: GO:0005739
    label: mitochondrion
  evidence_type: HTP
  original_reference_id: PMID:34800366
  qualifier: located_in
  review:
    summary: >-
      High-throughput mitochondrial proteome localization. Consistent with the
      established matrix localization of PDHX.
    action: ACCEPT
    reason: >-
      Corroborates mitochondrial localization; less specific than mitochondrial
      matrix but correct.
    supported_by:
    - reference_id: PMID:34800366
      supporting_text: >-
        Quantitative high-confidence human mitochondrial proteome and its dynamics
        in cellular context.
- term:
    id: GO:0045254
    label: pyruvate dehydrogenase complex
  evidence_type: IDA
  original_reference_id: PMID:9242632
  qualifier: part_of
  review:
    summary: >-
      Direct experimental (IDA) part_of PDC from reconstitution of the E2.E3BP
      subcomplex and functional PDC. Correct and core.
    action: ACCEPT
    reason: >-
      PDHX (E3BP) was shown to assemble into the PDC core with E2 and reconstitute
      a functional complex, directly demonstrating it is part of the PDC.
    supported_by:
    - reference_id: PMID:9242632
      supporting_text: >-
        Coexpression of cDNAs for E3BP and E2 resulted in the formation of an
        E2.E3BP subcomplex that spontaneously reconstituted the pyruvate
        dehydrogenase complex in the presence of native E3 and recombinant pyruvate
        decarboxylase (E1).
- term:
    id: GO:0045254
    label: pyruvate dehydrogenase complex
  evidence_type: IDA
  original_reference_id: PMID:25525879
  qualifier: part_of
  review:
    summary: >-
      IDA part_of PDC (UniProt), consistent with PDHX being a structural subunit of
      the PDH complex characterized in the SIRT4 study. Correct and core.
    action: ACCEPT
    reason: >-
      The study describes PDHX as a structural subunit of the PDH complex and
      immuno-isolates it as part of the complex.
    supported_by:
    - reference_id: PMID:25525879
      supporting_text: a structural subunit (PDH-binding component X, PDHX)
- term:
    id: GO:0005759
    label: mitochondrial matrix
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-203946
  qualifier: located_in
  review:
    summary: >-
      Reactome TAS localization to mitochondrial matrix (PDH regulation reaction
      context). Correct and matches the UniProt subcellular location.
    action: ACCEPT
    reason: >-
      Consistent with the curated matrix localization of PDHX as a PDC subunit.
    supported_by:
    - reference_id: file:human/PDHX/PDHX-uniprot.txt
      supporting_text: "SUBCELLULAR LOCATION: Mitochondrion matrix."
- term:
    id: GO:0005759
    label: mitochondrial matrix
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-204169
  qualifier: located_in
  review:
    summary: >-
      Reactome TAS localization to mitochondrial matrix. Correct.
    action: ACCEPT
    reason: >-
      Consistent with the curated matrix localization of PDHX.
    supported_by:
    - reference_id: file:human/PDHX/PDHX-uniprot.txt
      supporting_text: "SUBCELLULAR LOCATION: Mitochondrion matrix."
- term:
    id: GO:0005759
    label: mitochondrial matrix
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-9861616
  qualifier: located_in
  review:
    summary: >-
      Reactome TAS localization to mitochondrial matrix (DLD dehydrogenation
      reaction context). Correct.
    action: ACCEPT
    reason: >-
      Consistent with the curated matrix localization of PDHX.
    supported_by:
    - reference_id: file:human/PDHX/PDHX-uniprot.txt
      supporting_text: "SUBCELLULAR LOCATION: Mitochondrion matrix."
- term:
    id: GO:0005759
    label: mitochondrial matrix
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-9861667
  qualifier: located_in
  review:
    summary: >-
      Reactome TAS localization to mitochondrial matrix (DLAT acetyl transfer
      reaction context). Correct.
    action: ACCEPT
    reason: >-
      Consistent with the curated matrix localization of PDHX.
    supported_by:
    - reference_id: file:human/PDHX/PDHX-uniprot.txt
      supporting_text: "SUBCELLULAR LOCATION: Mitochondrion matrix."
- term:
    id: GO:0005759
    label: mitochondrial matrix
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-9861734
  qualifier: located_in
  review:
    summary: >-
      Reactome TAS localization to mitochondrial matrix (E1 decarboxylation
      reaction context). Correct.
    action: ACCEPT
    reason: >-
      Consistent with the curated matrix localization of PDHX.
    supported_by:
    - reference_id: file:human/PDHX/PDHX-uniprot.txt
      supporting_text: "SUBCELLULAR LOCATION: Mitochondrion matrix."
- term:
    id: GO:0030674
    label: protein-macromolecule adaptor activity
  evidence_type: IDA
  original_reference_id: PMID:16263718
  qualifier: enables
  review:
    summary: >-
      Proposed molecular function capturing PDHX's established E3-anchoring role:
      PDHX acts as an adaptor that tethers the E3 (DLD) dimer to the E2 (DLAT)
      core of the PDC. Supported by two crystal structures of the E3BP E3-binding
      domain bound to E3 and by mutagenesis of the interface hot-spot residues.
    action: NEW
    reason: >-
      The bare GO:0005515 protein-binding IPIs and the mis-attributed catalytic MF
      terms fail to capture what PDHX actually does molecularly. Its function is a
      protein-macromolecule adaptor/anchoring activity tethering E3 to the E2 core.
    supported_by:
    - reference_id: PMID:16263718
      supporting_text: >-
        The dihydrolipoamide dehydrogenase-binding protein (E3BP) and the
        dihydrolipoamide acetyltransferase (E2) component enzyme form the
        structural core of the human pyruvate dehydrogenase complex
    - reference_id: PMID:9242632
      supporting_text: >-
        Protein X, recently renamed dihydrolipoamide dehydrogenase-binding protein
        (E3BP), is required for anchoring dihydrolipoamide dehydrogenase (E3) to
        the dihydrolipoamide transacetylase (E2) core of the pyruvate dehydrogenase
        complexes of eukaryotes.
- term:
    id: GO:0005198
    label: structural molecule activity
  evidence_type: IDA
  original_reference_id: PMID:16263718
  qualifier: enables
  review:
    summary: >-
      Proposed molecular function reflecting PDHX's role as a structural
      constituent of the PDC inner core: together with E2 (DLAT) it forms the
      dodecahedral scaffold that binds the peripheral E1 and E3 catalytic
      components. PDHX itself is non-catalytic.
    action: NEW
    reason: >-
      Captures the structural/scaffolding contribution of PDHX to the PDC core,
      complementing the adaptor (E3-anchoring) function and replacing the
      fold-based catalytic over-annotations.
    supported_by:
    - reference_id: PMID:16263718
      supporting_text: >-
        The dihydrolipoamide dehydrogenase-binding protein (E3BP) and the
        dihydrolipoamide acetyltransferase (E2) component enzyme form the
        structural core of the human pyruvate dehydrogenase complex
core_functions:
- description: >-
    Anchors the E3 dihydrolipoyl dehydrogenase (DLD) dimer to the E2 (DLAT) core
    of the pyruvate dehydrogenase complex via its E3-binding (peripheral
    subunit-binding) domain, acting as a molecular adaptor that tethers the
    catalytic E3 to the assembled complex; this structural role is essential for a
    functional PDC.
  molecular_function:
    id: GO:0030674
    label: protein-macromolecule adaptor activity
  in_complex:
    id: GO:0045254
    label: pyruvate dehydrogenase complex
  locations:
  - id: GO:0005759
    label: mitochondrial matrix
  supported_by:
  - reference_id: PMID:19240034
    supporting_text: >-
      a noncatalytic component, E3-binding protein (E3BP), which specifically
      tethers E3 dimers to the PDC.
  - reference_id: PMID:9242632
    supporting_text: >-
      Protein X, recently renamed dihydrolipoamide dehydrogenase-binding protein
      (E3BP), is required for anchoring dihydrolipoamide dehydrogenase (E3) to the
      dihydrolipoamide transacetylase (E2) core of the pyruvate dehydrogenase
      complexes of eukaryotes.
- description: >-
    Serves as a structural constituent of the pyruvate dehydrogenase complex
    inner core, integrating (together with E2/DLAT) into the dodecahedral core
    that provides the scaffold binding the peripheral E1 and E3 catalytic
    components; PDHX itself is non-catalytic (its E2-like inner-core fold lacks the
    catalytic histidine).
  molecular_function:
    id: GO:0005198
    label: structural molecule activity
  in_complex:
    id: GO:0045254
    label: pyruvate dehydrogenase complex
  locations:
  - id: GO:0005759
    label: mitochondrial matrix
  supported_by:
  - reference_id: PMID:16263718
    supporting_text: >-
      The dihydrolipoamide dehydrogenase-binding protein (E3BP) and the
      dihydrolipoamide acetyltransferase (E2) component enzyme form the structural
      core of the human pyruvate dehydrogenase complex
  - reference_id: PMID:9242632
    supporting_text: >-
      The putative catalytic site histidine residue present in the inner core
      domains of all dihydrolipoamide acyltransferases is replaced by a serine
      residue in human E3BP; thus, catalysis of coenzyme A acetylation by this
      protein is unlikely.
proposed_new_terms: []
suggested_questions:
- question: >-
    Beyond its structural E3-anchoring role, does the lipoyl domain of PDHX
    (lipoylated at Lys97) participate directly in the reductive acetylation /
    lipoyl-arm shuttling cycle of the PDC, or is it functionally redundant with
    the DLAT lipoyl domains?
- question: >-
    What is the physiological significance of SIRT4-mediated delipoylation of PDHX
    Lys97 relative to delipoylation of DLAT for regulating PDC flux?
suggested_experiments:
- hypothesis: >-
    The PDHX lipoyl group is dispensable for PDC catalysis, consistent with a
    purely structural/anchoring role.
  description: >-
    Reconstitute human PDC with lipoyl-null (K97) PDHX to test whether the PDHX
    lipoyl group is catalytically required or purely structural.
- hypothesis: >-
    The PDHX inner-core domain has no detectable dihydrolipoyllysine-residue
    acetyltransferase activity because it lacks the catalytic histidine.
  description: >-
    Assay purified human E3BP/PDHX inner-core domain for any residual
    transacetylase activity to confirm the loss of acyltransferase function
    implied by the His->Ser substitution.
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 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: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:16263718
  title: How dihydrolipoamide dehydrogenase-binding protein binds dihydrolipoamide
    dehydrogenase in the human pyruvate dehydrogenase complex.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Crystal structure of the E3BP E3-binding domain with DLD (E3); directly
      establishes the E3-anchoring/structural-core function. PubMed-verified.
- id: PMID:16442803
  title: Structural insight into interactions between dihydrolipoamide dehydrogenase
    (E3) and E3 binding protein of human pyruvate dehydrogenase complex.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Second crystal structure + hot-spot mutagenesis of the E3BP/E3 interface;
      supports the tethering function. PubMed-verified.
- id: PMID:19240034
  title: Subunit and catalytic component stoichiometries of an in vitro reconstituted
    human pyruvate dehydrogenase complex.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Explicitly describes E3BP as a "noncatalytic component" that tethers E3
      dimers to the PDC; key evidence for the non-catalytic structural role.
- id: PMID:21516116
  title: Next-generation sequencing to generate interactome datasets.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: >-
      Methods paper for a high-throughput Y2H interactome; source of an
      uninformative AGTRAP protein-binding hit.
- id: PMID:24534072
  title: Component co-expression and purification of recombinant human pyruvate dehydrogenase
    complex from baculovirus infected SF9 cells.
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: >-
      Recombinant reconstitution of functional human PDC (including E3BP);
      supports involvement in pyruvate decarboxylation as a complex subunit.
- id: PMID:25416956
  title: A proteome-scale map of the human interactome network.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: >-
      Proteome-scale binary interactome; source of an uninformative AGTRAP hit.
- id: PMID:25525879
  title: Sirtuin 4 is a lipoamidase regulating pyruvate dehydrogenase complex activity.
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: >-
      Establishes PDHX as a lipoylated structural subunit and SIRT4 lipoamidase
      substrate (Lys97); relevant to regulation, not to a catalytic MF.
- id: PMID:28514442
  title: Architecture of the human interactome defines protein communities and disease
    networks.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: >-
      BioPlex AP-MS interactome; captures the DLD interaction as a generic hit.
- id: PMID:31515488
  title: Extensive disruption of protein interactions by genetic variants across the
    allele frequency spectrum in human populations.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: >-
      Variant/interaction-disruption screen; source of an uninformative AGTRAP hit.
- id: PMID:32296183
  title: A reference map of the human binary protein interactome.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: >-
      HuRI reference interactome; DLD hit consistent with biology, CIDEB
      uncharacterized.
- 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: >-
      BioPlex 3.0 interactome; captures the DLD interaction as a generic hit.
- 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 mitochondrial proteome; corroborates mitochondrial
      localization.
- id: PMID:9242632
  title: Dihydrolipoamide dehydrogenase-binding protein of the human pyruvate dehydrogenase
    complex. DNA-derived amino acid sequence, expression, and reconstitution of the
    pyruvate dehydrogenase complex.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Primary characterization: E3BP anchors E3 to the E2 core; catalytic His
      replaced by Ser so acetyltransferase catalysis is unlikely. Foundational.
- id: Reactome:R-HSA-203946
  title: PDK isozymes phosphorylate PDHC subunit E1
  findings: []
- id: Reactome:R-HSA-204169
  title: PDP1,2 dephosphorylate p-lipo-PDH
  findings: []
- id: Reactome:R-HSA-9861616
  title: DLD dimer dehydrogenates dihydrolipoyl
  findings: []
- id: Reactome:R-HSA-9861667
  title: DLAT trimer transfers acetyl to CoA
  findings: []
- id: Reactome:R-HSA-9861734
  title: PDH E1 decarboxylates PYR, transferring acetyl to DLAT
  findings: []
- id: file:human/PDHX/PDHX-uniprot.txt
  title: UniProtKB entry O00330 (ODPX_HUMAN), Pyruvate dehydrogenase protein X component,
    mitochondrial
  findings: []