id: P13804
gene_symbol: ETFA
product_type: PROTEIN
status: INITIALIZED
taxon:
  id: NCBITaxon:9606
  label: Homo sapiens
description: >-
  ETFA is the alpha subunit of the electron-transfer flavoprotein (ETF), a soluble
  FAD-containing heterodimer of ETFA and ETFB that resides in the mitochondrial matrix (on
  the matrix face of the inner membrane). ETF is the common electron acceptor for at least a
  dozen mitochondrial FAD-dependent primary dehydrogenases, including the chain-length-specific
  acyl-CoA dehydrogenases of fatty-acid beta-oxidation (e.g. ACADM/MCAD, ACADVL) and
  dehydrogenases of amino-acid catabolism (IVD, glutaryl-CoA dehydrogenase GCDH) as well as
  sarcosine/dimethylglycine dehydrogenases of choline degradation. ETF accepts reducing
  equivalents from these dehydrogenases, storing them transiently on its single bound FAD, and
  passes the electrons to ETF-ubiquinone oxidoreductase (ETFDH / ETF-QO), which reduces the
  ubiquinone pool and thereby funnels the electrons into the mitochondrial respiratory chain.
  The heterodimer binds one FAD and one AMP per dimer; most of the FAD is coordinated by the
  C-terminal domain of the alpha subunit. ETF is thus the third major electron feeder to the
  respiratory chain after complexes I and II, and is required for normal mitochondrial fatty
  acid oxidation and amino acid metabolism. Biallelic loss-of-function of ETFA (or ETFB or
  ETFDH) causes multiple acyl-CoA dehydrogenase deficiency (MADD) / glutaric acidemia type II.
alternative_products:
- name: '1'
  id: P13804-1
- name: '2'
  id: P13804-2
  sequence_note: VSP_043246
existing_annotations:
- term:
    id: GO:0005739
    label: mitochondrion
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: is_active_in
  review:
    summary: >-
      Phylogenetic (IBA) localization of ETFA to the mitochondrion. Correct but general; ETF
      acts specifically in the mitochondrial matrix, which is separately and more precisely
      annotated (GO:0005759).
    action: KEEP_AS_NON_CORE
    reason: >-
      The compartment is correct, but "mitochondrion" is the broad parent of the more specific
      and better-supported "mitochondrial matrix" location. Retained as non-core context; the
      matrix annotation is preferred as the core localization.
    supported_by:
    - reference_id: PMID:8617498
      supporting_text: >-
        obligatory electron acceptor for several dehydrogenases and is located in the
- term:
    id: GO:0009055
    label: electron transfer activity
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: enables
  review:
    summary: >-
      Phylogenetic (IBA) assignment of electron transfer activity, the core molecular function
      of ETF: it accepts electrons from primary flavoprotein dehydrogenases and passes them to
      ETFDH. Well supported experimentally and by the phylogeny of the ETF alpha/FixB family.
    action: ACCEPT
    reason: >-
      This is the central, defining molecular function of the ETF alpha subunit and is
      concordant with the direct experimental annotations (PMID:9334218, PMID:10423253) and the
      UniProt FUNCTION statement.
    supported_by:
    - reference_id: PMID:10423253
      supporting_text: >-
        serves as an intermediate electron carrier
- term:
    id: GO:0033539
    label: fatty acid beta-oxidation using acyl-CoA dehydrogenase
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: involved_in
  review:
    summary: >-
      Phylogenetic (IBA) assignment linking ETF to fatty-acid beta-oxidation. ETF is the
      obligate electron acceptor for the chain-length-specific acyl-CoA dehydrogenases of the
      beta-oxidation spiral, so its activity is required for flux through this pathway.
    action: ACCEPT
    reason: >-
      Strongly supported: ETF accepts electrons from the beta-oxidation acyl-CoA dehydrogenases,
      and this term is also directly annotated (IDA, PMID:25416781). Loss of ETFA causes a
      functional block in fatty-acid beta-oxidation (MADD).
    supported_by:
    - reference_id: PMID:9334218
      supporting_text: >-
        Among these dehydrogenases are the four chain
    - reference_id: PMID:25416781
      supporting_text: >-
        Some of these dehydrogenases, e.g. medium chain acyl-CoA dehydrogenase (MCAD), are
        involved in β-oxidation of fatty acids
- term:
    id: GO:0050660
    label: flavin adenine dinucleotide binding
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: enables
  review:
    summary: >-
      Phylogenetic (IBA) assignment of FAD binding. ETF carries a single FAD per heterodimer,
      most of which is coordinated by the alpha subunit; FAD is the redox cofactor that
      transiently stores the transferred electrons.
    action: ACCEPT
    reason: >-
      Core cofactor-binding function of ETFA, corroborated by direct experimental annotations
      (IDA, PMID:9334218, PMID:10423253) and by the crystallographically defined FAD-binding
      residues on the alpha subunit in UniProt.
    supported_by:
    - reference_id: PMID:8962055
      supporting_text: >-
        most of the FAD molecule residing in the
- term:
    id: GO:0005739
    label: mitochondrion
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  qualifier: located_in
  review:
    summary: >-
      Electronic (ARBA) localization to the mitochondrion. Correct but general relative to the
      experimentally supported mitochondrial matrix location.
    action: KEEP_AS_NON_CORE
    reason: >-
      Compartment is correct; broader than the specific matrix annotation. Retained as
      non-core.
- term:
    id: GO:0005759
    label: mitochondrial matrix
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  qualifier: located_in
  review:
    summary: >-
      Electronic annotation (UniProt Subcellular Location keyword mapping) placing ETFA in the
      mitochondrial matrix, the compartment where ETF operates.
    action: ACCEPT
    reason: >-
      Consistent with the experimentally determined subcellular location (IDA, PMID:3760196;
      NAS, PMID:8504797) and with the biology of ETF as a matrix electron shuttle.
    supported_by:
    - reference_id: PMID:8617498
      supporting_text: >-
        obligatory electron acceptor for several dehydrogenases and is located in the
- term:
    id: GO:0009055
    label: electron transfer activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: enables
  review:
    summary: >-
      Electronic (InterPro2GO, IPR001308 ETF alpha/FixB) assignment of electron transfer
      activity, the core molecular function of the ETF alpha subunit.
    action: ACCEPT
    reason: >-
      The InterPro family (ETF alpha/FixB) maps correctly to electron transfer activity, in
      agreement with the direct experimental and phylogenetic annotations.
    supported_by:
    - reference_id: PMID:10423253
      supporting_text: >-
        serves as an intermediate electron carrier
- term:
    id: GO:0050660
    label: flavin adenine dinucleotide binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: enables
  review:
    summary: >-
      Electronic (InterPro2GO, IPR001308) assignment of FAD binding, the redox cofactor carried
      by the alpha subunit.
    action: ACCEPT
    reason: >-
      Correct InterPro-to-GO mapping for the ETF alpha/FixB family; concordant with direct
      experimental FAD-binding annotations and the crystallographic FAD-binding residues.
    supported_by:
    - reference_id: PMID:8962055
      supporting_text: >-
        most of the FAD molecule residing in the
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:24606901
  qualifier: enables
  review:
    summary: >-
      IntAct-curated binary interaction (with HSCB, Q8IWL3) captured as the uninformative term
      "protein binding". Derived from a study of the Fe-S cluster cochaperone HSC20/HSCB.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      "protein binding" (GO:0005515) is not an informative molecular function and does not
      document ETFA's role. The interaction is not further pursued in this HSC20-focused study;
      per curation policy this bare IPI is marked as over-annotated rather than removed.
    supported_by:
    - reference_id: PMID:24606901
      supporting_text: >-
        LYR motifs
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:26618866
  qualifier: enables
  review:
    summary: >-
      IntAct-curated binary interaction (with CFTR, P13569) from a large-scale CFTR-interactome
      remodelling study, captured as the uninformative term "protein binding".
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Bare "protein binding" from a high-throughput interactome dataset; not an informative
      molecular function for ETFA and no dedicated functional follow-up. Marked as
      over-annotated per policy.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:27499296
  qualifier: enables
  review:
    summary: >-
      IntAct-curated interaction (with ETFB, P38117) from the mitochondrial protein interaction
      map that identified LYRM5/ETFRF1 as a "deflavinase" directly regulating ETF. Captured only
      as the generic term "protein binding".
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      The underlying interaction is biologically real and meaningful (ETF is directly regulated
      by LYRM5/ETFRF1, and ETFA obligately partners ETFB), but the GO term "protein binding" is
      uninformative. The functional relationships are better captured by the ETF-complex
      (GO:0045251) and electron-transfer annotations; the bare IPI is over-annotated.
    supported_by:
    - reference_id: PMID:27499296
      supporting_text: >-
        We also establish LYRM5 as a “deflavinase” that directly regulates the electron
        transferring flavoprotein (ETF)
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:28380382
  qualifier: enables
  review:
    summary: >-
      IntAct-curated interaction (with HSCB, Q8IWL3) from a study of the HSC20 cochaperone-
      scaffold Fe-S delivery complex; captured as the generic term "protein binding".
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Bare "protein binding" from a study centred on respiratory-chain Fe-S cluster delivery,
      not on ETFA function. Uninformative molecular function; marked over-annotated per policy.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:33961781
  qualifier: enables
  review:
    summary: >-
      IntAct-curated interaction (with ETFB, P38117) from a proteome-scale (BioPlex) interactome
      network, captured as the uninformative term "protein binding".
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Bare "protein binding" from a high-throughput interactome; the ETFA-ETFB partnership is
      informatively captured by the ETF complex annotation (GO:0045251). Marked over-annotated.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:35156780
  qualifier: enables
  review:
    summary: >-
      IntAct-curated interaction (with CFTR, P13569) from a CFTR mammalian membrane two-hybrid
      screen, captured as the uninformative term "protein binding".
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Bare "protein binding" from a high-throughput CFTR screen; not an informative ETFA
      molecular function. Marked over-annotated per policy.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:36012204
  qualifier: enables
  review:
    summary: >-
      IntAct-curated interaction (with CFTR, P13569) from a CFTR proximity-labeling interactome
      study, captured as the uninformative term "protein binding".
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Bare "protein binding" from a high-throughput proximity-labeling dataset; uninformative
      for ETFA function. Marked over-annotated per policy.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:40205054
  qualifier: enables
  review:
    summary: >-
      IntAct-curated interaction (with ETFB, P38117) from a multimodal cell-map / structural and
      functional genomics study, captured as the uninformative term "protein binding".
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Bare "protein binding" from a large-scale cell-mapping dataset; the ETFA-ETFB relationship
      is better captured by the ETF complex annotation. Marked over-annotated per policy.
- term:
    id: GO:0005759
    label: mitochondrial matrix
  evidence_type: IDA
  original_reference_id: PMID:3760196
  qualifier: located_in
  review:
    summary: >-
      Direct experimental (IDA) evidence that alpha-ETF is synthesized in the cytosol as a
      larger precursor, imported into mitochondria, and processed to the mature form in the
      matrix. This is the core, experimentally defined localization of ETFA.
    action: ACCEPT
    reason: >-
      Biosynthesis/import study demonstrating mitochondrial (matrix) localization of the
      processed alpha subunit; it is the basis for the UniProt Subcellular Location and matches
      the biology of ETF as a matrix electron shuttle.
    supported_by:
    - reference_id: PMID:3760196
      supporting_text: >-
        translocated into the
- term:
    id: GO:0009055
    label: electron transfer activity
  evidence_type: IDA
  original_reference_id: PMID:9334218
  qualifier: enables
  review:
    summary: >-
      Direct experimental (IDA) demonstration of ETF electron transfer activity: recombinant
      wild-type and pathogenic-mutant ETF were assayed for electron transfer from primary
      dehydrogenases and onward to ETF-QO, with mutations impairing this activity.
    action: ACCEPT
    reason: >-
      Direct biochemical characterization of the core electron-transfer function of ETF,
      including the effect of GA2A mutations on activity. This is a defining core function.
    supported_by:
    - reference_id: PMID:9334218
      supporting_text: >-
        electron transfer from nine primary flavoprotein dehydrogenases to the main
- term:
    id: GO:0005759
    label: mitochondrial matrix
  evidence_type: NAS
  original_reference_id: PMID:8504797
  qualifier: located_in
  review:
    summary: >-
      Non-traceable author statement (ComplexPortal) supporting mitochondrial matrix
      localization; the cited work shows the ETF beta subunit is imported to the mitochondrial
      matrix, consistent with the matrix location of the ETF heterodimer.
    action: ACCEPT
    reason: >-
      Concordant with the direct experimental IDA matrix annotation (PMID:3760196) and the
      established matrix location of ETF. Retained as supporting the core localization.
    supported_by:
    - reference_id: PMID:8504797
      supporting_text: >-
        reach the mitochondrial matrix
- term:
    id: GO:0009063
    label: amino acid catabolic process
  evidence_type: IDA
  original_reference_id: PMID:25416781
  qualifier: involved_in
  review:
    summary: >-
      Direct experimental (IDA, ComplexPortal) evidence that ETF participates in amino-acid
      catabolism: the ETF alpha/beta heterodimer receives electrons from amino-acid-oxidation
      dehydrogenases such as glutaryl-CoA dehydrogenase (GCDH) and isovaleryl-CoA dehydrogenase.
    action: ACCEPT
    reason: >-
      ETF is the obligate electron acceptor for amino-acid catabolic dehydrogenases; loss of
      ETFA impairs amino-acid metabolism (a component of the MADD phenotype). Supported by the
      cited study characterizing ETF electron transfer from GCDH.
    supported_by:
    - reference_id: PMID:25416781
      supporting_text: >-
        others, including glutaryl-CoA dehydrogenase (GCDH) and isovaleryl-CoA dehydrogenase,
        are involved in the oxidation of amino acids
- term:
    id: GO:0022904
    label: respiratory electron transport chain
  evidence_type: IDA
  original_reference_id: PMID:25416781
  qualifier: involved_in
  review:
    summary: >-
      Direct experimental (IDA, ComplexPortal) evidence linking ETF to the respiratory electron
      transport chain: ETF shuttles electrons from matrix dehydrogenases to ETF:quinone
      oxidoreductase and thence to the ubiquinone pool, acting as the third major electron
      provider to the respiratory chain after complexes I and II.
    action: ACCEPT
    reason: >-
      ETF feeds electrons into the respiratory chain via ETFDH/ubiquinone; this is a core
      physiological role of ETFA, well documented in the cited study.
    supported_by:
    - reference_id: PMID:25416781
      supporting_text: >-
        it is the third major provider of electrons to the ubiquinone
- term:
    id: GO:0033539
    label: fatty acid beta-oxidation using acyl-CoA dehydrogenase
  evidence_type: IDA
  original_reference_id: PMID:25416781
  qualifier: involved_in
  review:
    summary: >-
      Direct experimental (IDA, ComplexPortal) evidence that ETF participates in acyl-CoA-
      dehydrogenase-dependent fatty-acid beta-oxidation: the heterodimer receives electrons from
      dehydrogenases such as medium-chain acyl-CoA dehydrogenase (MCAD) involved in beta-oxidation.
    action: ACCEPT
    reason: >-
      Core physiological role: ETF is the obligate electron acceptor for the beta-oxidation
      acyl-CoA dehydrogenases. Duplicate of the IBA annotation to the same term; both accepted.
    supported_by:
    - reference_id: PMID:25416781
      supporting_text: >-
        Some of these dehydrogenases, e.g. medium chain acyl-CoA dehydrogenase (MCAD), are
        involved in β-oxidation of fatty acids
- term:
    id: GO:0045251
    label: electron transfer flavoprotein complex
  evidence_type: IPI
  original_reference_id: PMID:8962055
  qualifier: part_of
  review:
    summary: >-
      ETFA is a subunit of the electron transfer flavoprotein complex, the FAD-containing
      alpha/beta heterodimer whose crystal structure was solved to 2.1 A. ETFA contributes two
      of the three structural domains and coordinates most of the FAD.
    action: ACCEPT
    reason: >-
      Directly demonstrated by the X-ray structure of the human ETF heterodimer (also captured
      as ComplexPortal CPX-2731). This is the defining cellular complex for ETFA and a core
      annotation.
    supported_by:
    - reference_id: PMID:8962055
      supporting_text: >-
        Mammalian electron transfer flavoproteins (ETF) are heterodimers containing a
- term:
    id: GO:0005739
    label: mitochondrion
  evidence_type: IDA
  original_reference_id: GO_REF:0000052
  qualifier: located_in
  review:
    summary: >-
      Immunofluorescence-based (HPA, IDA) localization of ETFA to the mitochondrion. Correct but
      general relative to the specific matrix location.
    action: KEEP_AS_NON_CORE
    reason: >-
      Compartment is correct and independently corroborated (HPA imaging); broader than the
      specific mitochondrial matrix annotation. Retained as non-core.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:35362222
  qualifier: enables
  review:
    summary: >-
      IntAct-curated interaction (with MBTPS1/S1P, Q14703, and ETFB, P38117) demonstrated by
      Co-IP and GST pull-down; S1P forms a trimeric complex with ETFA/ETFB, stabilizing the
      heterodimer and promoting FAD incorporation. Captured only as the generic term "protein
      binding".
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      The interaction is biologically meaningful and ETFA-specific (direct GST-ETFA pull-down,
      docking of specific ETFA residues), but "protein binding" is an uninformative molecular
      function. The functional consequence (heterodimer stabilization / FAD binding) is better
      captured by the FAD-binding and ETF-complex annotations; the bare IPI is over-annotated.
    supported_by:
    - reference_id: PMID:35362222
      supporting_text: >-
        S1P forms a trimeric complex with ETFA and ETFB proteins
- term:
    id: GO:0005739
    label: mitochondrion
  evidence_type: HTP
  original_reference_id: PMID:34800366
  qualifier: located_in
  review:
    summary: >-
      High-throughput (HTP) mitochondrial-proteome localization of ETFA to the mitochondrion,
      consistent with its established matrix location.
    action: KEEP_AS_NON_CORE
    reason: >-
      Correct compartment from a high-confidence mitochondrial proteome; broader than the
      specific matrix annotation. Retained as non-core.
- term:
    id: GO:0009055
    label: electron transfer activity
  evidence_type: IDA
  original_reference_id: PMID:25416781
  qualifier: enables
  review:
    summary: >-
      Direct experimental (IDA, ComplexPortal) evidence of ETF electron transfer activity: the
      ETF alpha/beta heterodimer mediates electron transfer from acyl-CoA dehydrogenases (MCAD,
      GCDH) to an electron acceptor, an activity modulated by ETFB methylation.
    action: ACCEPT
    reason: >-
      Direct assay of the core electron-transfer function of the ETF heterodimer. Duplicate of
      other electron-transfer-activity annotations; accepted as core.
    supported_by:
    - reference_id: PMID:25416781
      supporting_text: >-
        ETF acts as a mobile electron carrier that shuttles electrons between several
        FAD-containing dehydrogenases
- term:
    id: GO:0005739
    label: mitochondrion
  evidence_type: HDA
  original_reference_id: PMID:20833797
  qualifier: located_in
  review:
    summary: >-
      High-throughput direct assay (HDA) placing ETFA in the mitochondrion, from a
      phosphoproteome of mitochondria isolated from human muscle.
    action: KEEP_AS_NON_CORE
    reason: >-
      Correct compartment from isolated-mitochondria mass spectrometry; broader than the
      specific matrix annotation. Retained as non-core.
    supported_by:
    - reference_id: PMID:20833797
      supporting_text: >-
        mitochondria isolated from human muscle
- term:
    id: GO:0005759
    label: mitochondrial matrix
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-169260
  qualifier: located_in
  review:
    summary: >-
      Traceable author statement (Reactome) placing ETF in the mitochondrial matrix, where it
      accepts reducing equivalents from fatty-acyl-CoA beta-oxidation.
    action: ACCEPT
    reason: >-
      Concordant with the experimentally supported matrix localization and the reaction context
      (ETF residing on the matrix face of the inner membrane).
- term:
    id: GO:0005759
    label: mitochondrial matrix
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-169270
  qualifier: located_in
  review:
    summary: >-
      Traceable author statement (Reactome) placing ETF in the mitochondrial matrix in the
      reaction where ETFDH re-oxidizes reduced ETF and reduces CoQ.
    action: ACCEPT
    reason: >-
      Concordant with the experimentally supported matrix localization and the ETF -> ETFDH ->
      ubiquinone electron-transfer reaction.
- term:
    id: GO:0009055
    label: electron transfer activity
  evidence_type: IDA
  original_reference_id: PMID:10423253
  qualifier: enables
  review:
    summary: >-
      Direct experimental (IDA) study of ETF as an intermediate electron carrier: substitution
      of the FAD analog 4'-deoxy-FAD altered redox potentials and abolished electron transfer to
      and from ETF-QO, dissecting the electron-transfer mechanism of ETF.
    action: ACCEPT
    reason: >-
      Directly probes the core electron-transfer function of ETF and its dependence on the FAD
      cofactor. Duplicate of other electron-transfer-activity annotations; accepted as core.
    supported_by:
    - reference_id: PMID:10423253
      supporting_text: >-
        serves as an intermediate electron carrier
- term:
    id: GO:0050660
    label: flavin adenine dinucleotide binding
  evidence_type: IDA
  original_reference_id: PMID:10423253
  qualifier: enables
  review:
    summary: >-
      Direct experimental (IDA) evidence of FAD binding: binding constants for FAD (and the
      4'-deoxy-FAD analog) with the ETF apoprotein were measured, and the intra-cofactor
      4'-hydroxyl-N1 hydrogen bond of the bound FAD was characterized.
    action: ACCEPT
    reason: >-
      Direct biochemical characterization of the FAD-binding function of ETF, a core cofactor-
      binding function of the alpha subunit.
    supported_by:
    - reference_id: PMID:10423253
      supporting_text: >-
        the 4'-hydroxyl of the ribityl side chain of FAD is hydrogen bonded to N(1)
- term:
    id: GO:0050660
    label: flavin adenine dinucleotide binding
  evidence_type: IDA
  original_reference_id: PMID:9334218
  qualifier: enables
  review:
    summary: >-
      Direct experimental (IDA) evidence of FAD binding: the flavin environment and kinetics of
      flavin release from oxidized and reduced ETF were characterized for wild-type and the
      pathogenic alphaT266M mutant, which perturbs the FAD-binding site.
    action: ACCEPT
    reason: >-
      Direct biochemical characterization of ETFA FAD binding, including the effect of a GA2A
      mutation on the flavin environment. Core cofactor-binding function. Duplicate of the other
      FAD-binding annotations; accepted.
    supported_by:
    - reference_id: PMID:9334218
      supporting_text: >-
        Among these dehydrogenases are the four chain
- term:
    id: GO:0005739
    label: mitochondrion
  evidence_type: TAS
  original_reference_id: PMID:3170610
  qualifier: located_in
  review:
    summary: >-
      Traceable author statement (PINC) placing alpha-ETF in the mitochondrion, from the
      molecular cloning of the alpha subunit precursor, whose identity was confirmed by
      mitochondrial processing of the translated protein.
    action: KEEP_AS_NON_CORE
    reason: >-
      Correct compartment; broader than the specific matrix annotation. Retained as non-core.
    supported_by:
    - reference_id: PMID:3170610
      supporting_text: >-
        mitochondrial processing of the
- term:
    id: GO:0005759
    label: mitochondrial matrix
  evidence_type: TAS
  original_reference_id: PMID:8617498
  qualifier: located_in
  review:
    summary: >-
      Traceable author statement (PINC) placing ETF in the mitochondrial matrix, from the
      chromosomal-assignment study which states ETF is an obligatory electron acceptor located
      in the mitochondrial matrix.
    action: ACCEPT
    reason: >-
      Concordant with the direct experimental matrix localization; supports the core location of
      ETFA.
    supported_by:
    - reference_id: PMID:8617498
      supporting_text: >-
        obligatory electron acceptor for several dehydrogenases and is located in the
core_functions:
- description: >-
    Electron transfer (electron-carrier) activity: the ETFA/ETFB heterodimer accepts electrons
    from multiple mitochondrial matrix FAD-dependent primary dehydrogenases and passes them to
    ETF-ubiquinone oxidoreductase (ETFDH), feeding the respiratory chain.
  molecular_function:
    id: GO:0009055
    label: electron transfer activity
  directly_involved_in:
  - id: GO:0022904
    label: respiratory electron transport chain
  in_complex:
    id: GO:0045251
    label: electron transfer flavoprotein complex
  locations:
  - id: GO:0005759
    label: mitochondrial matrix
  supported_by:
  - reference_id: PMID:9334218
    supporting_text: >-
      electron transfer from nine primary flavoprotein dehydrogenases to the main
  - reference_id: PMID:10423253
    supporting_text: >-
      serves as an intermediate electron carrier
- description: >-
    FAD binding: ETFA coordinates most of the single FAD cofactor of the ETF heterodimer, which
    transiently stores the electrons transferred between dehydrogenases and ETFDH.
  molecular_function:
    id: GO:0050660
    label: flavin adenine dinucleotide binding
  in_complex:
    id: GO:0045251
    label: electron transfer flavoprotein complex
  locations:
  - id: GO:0005759
    label: mitochondrial matrix
  supported_by:
  - reference_id: PMID:8962055
    supporting_text: >-
      most of the FAD molecule residing in the
  - reference_id: PMID:10423253
    supporting_text: >-
      the 4'-hydroxyl of the ribityl side chain of FAD is hydrogen bonded to N(1)
- description: >-
    As the common electron acceptor for the beta-oxidation acyl-CoA dehydrogenases, ETF is
    required for mitochondrial fatty-acid beta-oxidation flux; its loss produces a functional
    block in this pathway (MADD).
  molecular_function:
    id: GO:0009055
    label: electron transfer activity
  directly_involved_in:
  - id: GO:0033539
    label: fatty acid beta-oxidation using acyl-CoA dehydrogenase
  locations:
  - id: GO:0005759
    label: mitochondrial matrix
  supported_by:
  - reference_id: PMID:25416781
    supporting_text: >-
      Some of these dehydrogenases, e.g. medium chain acyl-CoA dehydrogenase (MCAD), are
      involved in β-oxidation of fatty acids
  - reference_id: PMID:9334218
    supporting_text: >-
      Among these dehydrogenases are the four chain
- description: >-
    As the electron acceptor for amino-acid-catabolic dehydrogenases (e.g. glutaryl-CoA and
    isovaleryl-CoA dehydrogenases), ETF is required for normal amino-acid catabolism.
  molecular_function:
    id: GO:0009055
    label: electron transfer activity
  directly_involved_in:
  - id: GO:0009063
    label: amino acid catabolic process
  locations:
  - id: GO:0005759
    label: mitochondrial matrix
  supported_by:
  - reference_id: PMID:25416781
    supporting_text: >-
      others, including glutaryl-CoA dehydrogenase (GCDH) and isovaleryl-CoA dehydrogenase, are
      involved in the oxidation of amino acids
suggested_questions:
- question: >-
    Beyond serving all the acyl-CoA and amino-acid-catabolic dehydrogenases, how is electron
    flux through ETF regulated in vivo (e.g. by ETFRF1/LYRM5 deflavination or MBTPS1/S1P-mediated
    stabilization), and does this constitute a physiological control point for substrate
    selection?
suggested_experiments:
- description: >-
    Quantitative flux analysis (e.g. stable-isotope tracing of fatty-acid and branched-chain
    amino-acid oxidation) in ETFA-null versus rescued cells to measure the contribution of ETF
    to each catabolic pathway and to respiratory-chain electron input.
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: PMID:10423253
  title: The intraflavin hydrogen bond in human electron transfer flavoprotein modulates
    redox potentials and may participate in electron transfer.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      PubMed-verified. Directly characterizes ETF as an intermediate electron carrier and the
      role of the FAD cofactor in electron transfer; supports the electron-transfer-activity and
      FAD-binding core functions.
- id: PMID:20833797
  title: Phosphoproteome analysis of functional mitochondria isolated from resting
    human muscle reveals extensive phosphorylation of inner membrane protein complexes
    and enzymes.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: >-
      Mitochondrial phosphoproteome from human muscle; corroborates mitochondrial localization
      of ETFA (HDA) but not informative on molecular function.
- id: PMID:24606901
  title: Cochaperone binding to LYR motifs confers specificity of iron sulfur cluster
    delivery.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: >-
      HSC20/HSCB Fe-S cochaperone study; ETFA appears only as an IntAct interaction partner
      captured as bare "protein binding". Not informative for ETFA function.
- id: PMID:25416781
  title: Human METTL20 is a mitochondrial lysine methyltransferase that targets the
    β subunit of electron transfer flavoprotein (ETFβ) and modulates its activity.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Full text available; describes ETF alpha/beta heterodimer function (electron shuttle from
      ~13 dehydrogenases to ETF:QO; third major electron provider to the ubiquinone pool) and is
      the basis for the ComplexPortal IDA annotations. Directly supports the fatty-acid
      beta-oxidation, amino-acid catabolism, respiratory-electron-transport, and
      electron-transfer annotations.
- id: PMID:26618866
  title: ∆F508 CFTR interactome remodelling promotes rescue of cystic fibrosis.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: >-
      Large-scale CFTR-interactome study; ETFA appears only as an IntAct interaction partner
      captured as bare "protein binding". Not informative for ETFA function.
- id: PMID:27499296
  title: Mitochondrial Protein Interaction Mapping Identifies Regulators of Respiratory
    Chain Function.
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: >-
      Establishes LYRM5/ETFRF1 as a deflavinase that directly regulates ETF; the ETFA IntAct
      annotation is only bare "protein binding" but the study is biologically relevant to ETF
      regulation.
- id: PMID:28380382
  title: A Single Adaptable Cochaperone-Scaffold Complex Delivers Nascent Iron-Sulfur
    Clusters to Mammalian Respiratory Chain Complexes I-III.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: >-
      HSC20 Fe-S delivery study focused on respiratory-chain complexes; ETFA appears only as an
      IntAct partner captured as bare "protein binding".
- id: PMID:3170610
  title: Molecular cloning and nucleotide sequence of cDNAs encoding the alpha-subunit
    of human electron transfer flavoprotein.
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: >-
      Original cloning of the human alpha-ETF precursor (333 aa); establishes the mitochondrially
      processed alpha subunit. Supports mitochondrial localization.
- 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: >-
      Proteome-scale (BioPlex) interactome; ETFA-ETFB captured as bare "protein binding". The
      partnership is better represented by the ETF complex annotation.
- 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 of ETFA
      (HTP).
- id: PMID:35156780
  title: CFTR interactome mapping using the mammalian membrane two-hybrid high-throughput
    screening system.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: >-
      High-throughput CFTR two-hybrid screen; ETFA appears only as an IntAct partner captured as
      bare "protein binding".
- id: PMID:35362222
  title: S1P defects cause a new entity of cataract, alopecia, oral mucosal disorder,
    and psoriasis-like syndrome.
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: >-
      Demonstrates a direct, ETFA-specific interaction of MBTPS1/S1P with the ETFA/ETFB
      heterodimer (Co-IP, GST-ETFA pull-down) that stabilizes the complex and promotes FAD
      incorporation. Biologically meaningful, though the GO annotation is only bare "protein
      binding".
- id: PMID:36012204
  title: Differential CFTR-Interactome Proximity Labeling Procedures Identify Enrichment
    in Multiple SLC Transporters.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: >-
      CFTR proximity-labeling interactome study; ETFA captured only as bare "protein binding".
- id: PMID:3760196
  title: Biosynthesis of electron transfer flavoprotein in a cell-free system and
    in cultured human fibroblasts. Defect in the alpha subunit synthesis is a primary
    lesion in glutaric aciduria type II.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Shows alpha-ETF is synthesized in the cytosol as a precursor, imported into mitochondria,
      and processed to the mature matrix form; defective alpha-ETF synthesis is a primary lesion
      in glutaric aciduria type II. Supports matrix localization and disease relevance.
- id: PMID:40205054
  title: Multimodal cell maps as a foundation for structural and functional genomics.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: >-
      Large-scale multimodal cell-mapping study; ETFA-ETFB captured as bare "protein binding".
- id: PMID:8504797
  title: cDNA cloning and mitochondrial import of the beta-subunit of the human electron-transfer
    flavoprotein.
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: >-
      Cloning/import of the ETF beta subunit, showing it reaches the mitochondrial matrix;
      supports the matrix localization of the ETF heterodimer.
- id: PMID:8617498
  title: 'Assignment of Etfdh, Etfb, and Etfa to chromosomes 3, 7, and 13: the mouse
    homologs of genes responsible for glutaric acidemia type II in human.'
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: >-
      States ETF is an obligatory electron acceptor for several dehydrogenases located in the
      mitochondrial matrix, with electrons transferred to the respiratory chain via ETFDH;
      supports matrix localization and the electron-shuttle role.
- id: PMID:8962055
  title: Three-dimensional structure of human electron transfer flavoprotein to 2.1-A
    resolution.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Crystal structure of the human ETF heterodimer; establishes the alpha/beta complex, the
      single FAD (most coordinated by the alpha C-terminal domain), and the electron-shuttle
      role. Supports the ETF-complex and FAD-binding core functions.
- id: PMID:9334218
  title: Expression and characterization of two pathogenic mutations in human electron
    transfer flavoprotein.
  findings: []
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      Biochemical characterization of ETF electron transfer from nine primary dehydrogenases to
      the respiratory chain and the effect of GA2A alpha-subunit mutations on activity and FAD
      binding. Supports the electron-transfer-activity and FAD-binding core functions.
- id: Reactome:R-HSA-169260
  title: Reducing equivalents from beta-oxidation of fatty acids transfer to ETF
  findings: []
- id: Reactome:R-HSA-169270
  title: ETFDH oxidises ETF (reduced) to ETF, reduces CoQ to CoQH2
  findings: []