id: Q8N183
gene_symbol: NDUFAF2
product_type: PROTEIN
status: INITIALIZED
taxon:
  id: NCBITaxon:9606
  label: Homo sapiens
description: >-
  NDUFAF2 (also known as NDUFA12L, B17.2L, and Mimitin) is a nuclear-encoded,
  mitochondrially targeted assembly factor for respiratory chain complex I
  (NADH:ubiquinone oxidoreductase). It is a paralog of the structural complex I
  subunit NDUFA12 (B17.2) but, unlike its paralog, it is not a stable component
  of the mature holoenzyme. Instead it acts as a molecular chaperone that binds
  transiently to a large (~830 kDa) late-stage complex I assembly intermediate
  containing subunits of both the matrix (peripheral) and membrane arms, and is
  released once assembly is complete. By stabilizing this subassembly it increases
  the efficiency of complex I biogenesis, although residual assembly can occur in
  its absence. The protein carries an N-terminal mitochondrial transit peptide and
  a C-terminal disordered region. Loss-of-function variants cause autosomal
  recessive mitochondrial complex I deficiency nuclear type 10 (MC1DN10),
  presenting as progressive encephalopathy/leukoencephalopathy and Leigh syndrome.
  A more recently reported pleiotropic role links NDUFAF2 to primary cilium
  formation through interaction with the basal-body protein ARMC9.
existing_annotations:
- term:
    id: GO:0005739
    label: mitochondrion
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: is_active_in
  review:
    summary: >-
      Mitochondrial localization is correct and well supported. NDUFAF2 has an
      N-terminal mitochondrial transit peptide and UniProt records it as
      mitochondrial. This IBA localization is consistent with all experimental
      evidence and with its role as a mitochondrial complex I assembly factor.
    action: ACCEPT
    supported_by:
    - reference_id: file:human/NDUFAF2/NDUFAF2-uniprot.txt
      supporting_text: "SUBCELLULAR LOCATION: Mitochondrion"
- term:
    id: GO:0032981
    label: mitochondrial respiratory chain complex I assembly
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  qualifier: involved_in
  review:
    summary: >-
      This is the core biological process of NDUFAF2. The phylogenetic (IBA)
      inference agrees with direct experimental evidence that NDUFAF2 is a
      molecular chaperone essential for assembly of mitochondrial complex I.
    action: ACCEPT
    supported_by:
    - reference_id: PMID:16200211
      supporting_text: >-
        These results demonstrate that B17.2L is a bona fide molecular chaperone
        that is essential for the assembly of complex I
- term:
    id: GO:0005739
    label: mitochondrion
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  qualifier: located_in
  review:
    summary: >-
      Electronic mapping from the UniProt Swiss-Prot subcellular-location
      vocabulary; correct and consistent with the experimental mitochondrial
      localization.
    action: ACCEPT
    supported_by:
    - reference_id: file:human/NDUFAF2/NDUFAF2-uniprot.txt
      supporting_text: "SUBCELLULAR LOCATION: Mitochondrion"
- term:
    id: GO:0016020
    label: membrane
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: located_in
  review:
    summary: >-
      Over-general InterPro-based electronic annotation. "Membrane" is
      uninformative for this protein; NDUFAF2 is a soluble/peripheral chaperone
      that associates transiently with membrane-embedded complex I assembly
      intermediates but is not itself an integral membrane protein. The more
      specific mitochondrial inner membrane localization (from Reactome) already
      captures its site of action. Recommend removing this uninformative IEA.
    action: REMOVE
- term:
    id: GO:0045271
    label: respiratory chain complex I
  evidence_type: IEA
  original_reference_id: GO_REF:0000002
  qualifier: part_of
  review:
    summary: >-
      Incorrect. This InterPro-based IEA annotation asserts that NDUFAF2 is
      part_of the respiratory chain complex I (the mature holoenzyme), but NDUFAF2
      is an assembly factor that is explicitly NOT a component of the mature
      complex. The primary experimental study showed the anti-NDUFAF2 antibody
      does not associate with the holoenzyme, and Reactome models the factor
      dissociating before the mature complex forms. The InterPro rule over-applies
      the structural-subunit annotation of its NDUFA12 paralog. Remove.
    action: REMOVE
    supported_by:
    - reference_id: PMID:16200211
      supporting_text: >-
        An anti-B17.2L antibody did not associate with the holoenzyme complex but
        specifically recognized an 830-kDa subassembly
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:32296183
  qualifier: enables
  review:
    summary: >-
      Bare "protein binding" from a high-throughput yeast two-hybrid binary
      interactome screen (HuRI). Uninformative as a molecular function and not
      indicative of a specific biochemical activity. Per curation policy this IPI
      is retained but flagged as over-annotated; the informative binding activity
      of NDUFAF2 is captured by protein-containing complex binding (GO:0044877).
    action: MARK_AS_OVER_ANNOTATED
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:33961781
  qualifier: enables
  review:
    summary: >-
      Bare "protein binding" from a proteome-scale affinity-purification MS
      interactome (BioPlex 3.0). The recorded partner is the complex I subunit
      NDUFA7, consistent with the assembly role, but the generic GO:0005515 term
      is uninformative. Retained but marked over-annotated.
    action: MARK_AS_OVER_ANNOTATED
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:34819669
  qualifier: enables
  review:
    summary: >-
      Bare "protein binding" derived from a multi-scale image/interaction map
      (MuSIC), again reporting an NDUFA7 association. Uninformative MF term;
      retained but marked over-annotated.
    action: MARK_AS_OVER_ANNOTATED
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:38949024
  qualifier: enables
  review:
    summary: >-
      Bare "protein binding" IPI recording the experimentally validated
      interaction between NDUFAF2 and the basal-body protein ARMC9. The
      interaction itself is genuine and biologically meaningful (it underlies the
      pleiotropic ciliogenesis role), but the generic GO:0005515 term is
      uninformative. Retained but marked over-annotated; the ciliary role is
      captured separately by the cilium assembly annotation.
    action: MARK_AS_OVER_ANNOTATED
    supported_by:
    - reference_id: PMID:38949024
      supporting_text: >-
        a ciliary protein, armadillo repeat containing 9 (ARMC9), interacts with
        NDUFAF2
- term:
    id: GO:0005739
    label: mitochondrion
  evidence_type: IDA
  original_reference_id: GO_REF:0000052
  qualifier: located_in
  review:
    summary: >-
      Immunofluorescence-based (HPA) direct localization to mitochondrion.
      Correct and concordant with all other evidence.
    action: ACCEPT
    supported_by:
    - reference_id: file:human/NDUFAF2/NDUFAF2-uniprot.txt
      supporting_text: "SUBCELLULAR LOCATION: Mitochondrion"
- term:
    id: GO:0060271
    label: cilium assembly
  evidence_type: IMP
  original_reference_id: PMID:38949024
  qualifier: involved_in
  review:
    summary: >-
      Experimentally supported (IMP) moonlighting role. NDUFAF2 knockout in RPE
      cells and knockdown in zebrafish impair primary cilium formation, and the
      protein participates in early ciliogenesis steps (CP110 removal, ciliary
      vesicle docking, transition-zone establishment) via interaction with ARMC9.
      This is a genuine but non-core, recently discovered pleiotropic function
      distinct from the protein's primary complex I assembly role, and part of the
      effect appears indirect (rescued by NAD+ supplementation). Keep as non-core.
    action: KEEP_AS_NON_CORE
    supported_by:
    - reference_id: PMID:38949024
      supporting_text: >-
        NDUFAF2 is involved in the initial steps of cilia formation, including the
        docking of membrane vesicles, removal of CP110, and establishment of the
        transition zone
- term:
    id: GO:0005739
    label: mitochondrion
  evidence_type: HTP
  original_reference_id: PMID:34800366
  qualifier: located_in
  review:
    summary: >-
      High-throughput mitochondrial-proteome identification placing NDUFAF2 in
      mitochondrion. Concordant with curated localization; accept.
    action: ACCEPT
    supported_by:
    - reference_id: file:human/NDUFAF2/NDUFAF2-uniprot.txt
      supporting_text: "SUBCELLULAR LOCATION: Mitochondrion"
- term:
    id: GO:0044877
    label: protein-containing complex binding
  evidence_type: IDA
  original_reference_id: PMID:16200211
  qualifier: enables
  review:
    summary: >-
      Directly supported molecular function and the most informative MF available
      for this protein. The anti-NDUFAF2 antibody co-immunoprecipitated a subset
      of complex I structural subunits and recognized an ~830 kDa assembly
      subcomplex, demonstrating that NDUFAF2 binds a multi-subunit complex I
      assembly intermediate. This binding underlies its chaperone/assembly-factor
      function. Accept as a core molecular function.
    action: ACCEPT
    supported_by:
    - reference_id: PMID:16200211
      supporting_text: >-
        coimmunoprecipitated a subset of complex I structural subunits from normal
        human heart mitochondria
- term:
    id: GO:0005739
    label: mitochondrion
  evidence_type: IDA
  original_reference_id: PMID:16200211
  qualifier: located_in
  review:
    summary: >-
      Direct experimental mitochondrial localization from the defining functional
      study. Accept.
    action: ACCEPT
    supported_by:
    - reference_id: file:human/NDUFAF2/NDUFAF2-uniprot.txt
      supporting_text: "SUBCELLULAR LOCATION: Mitochondrion"
- term:
    id: GO:0032981
    label: mitochondrial respiratory chain complex I assembly
  evidence_type: IMP
  original_reference_id: PMID:16200211
  qualifier: involved_in
  review:
    summary: >-
      Core biological process, supported by strong experimental evidence (IMP).
      A null mutation in NDUFAF2 causes a complex I assembly defect that is fully
      rescued by re-expression of wild-type NDUFAF2, and the protein associates
      with a late (~830 kDa) assembly intermediate. This is the central,
      well-established function of the gene. Accept as core.
    action: ACCEPT
    supported_by:
    - reference_id: PMID:16200211
      supporting_text: >-
        These results demonstrate that B17.2L is a bona fide molecular chaperone
        that is essential for the assembly of complex I
- term:
    id: GO:0005743
    label: mitochondrial inner membrane
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-6799179
  qualifier: located_in
  review:
    summary: >-
      Traceable author statement (Reactome) placing NDUFAF2 at the mitochondrial
      inner membrane, the site of complex I assembly, where it associates with
      the membrane-embedded assembly intermediate. This is a more specific and
      biologically appropriate location than the generic InterPro "membrane"
      term. Accept.
    action: ACCEPT
- term:
    id: GO:0005743
    label: mitochondrial inner membrane
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-6799196
  qualifier: located_in
  review:
    summary: >-
      Reactome TAS for mitochondrial inner membrane localization, from the
      complex I biogenesis pathway step in which the assembly factors (including
      NDUFAF2) dissociate from the 980 kDa complex. Consistent with its transient
      inner-membrane-associated assembly role. Accept.
    action: ACCEPT
- term:
    id: GO:0005743
    label: mitochondrial inner membrane
  evidence_type: TAS
  original_reference_id: Reactome:R-HSA-6800870
  qualifier: located_in
  review:
    summary: >-
      Reactome TAS for mitochondrial inner membrane localization (FP subcomplex
      assembly step). Redundant with the other two Reactome inner-membrane
      annotations but consistent with the assembly site. Accept.
    action: ACCEPT
- term:
    id: GO:0005739
    label: mitochondrion
  evidence_type: IDA
  original_reference_id: PMID:22587331
  qualifier: located_in
  review:
    summary: >-
      Direct mitochondrial localization annotation (MGI) from the mimitin study
      in insulin-secreting cells. The paper describes mimitin (NDUFAF2) as a
      mitochondrial protein acting as a complex I chaperone. Concordant with all
      other localization evidence. Accept.
    action: ACCEPT
    supported_by:
    - reference_id: PMID:22587331
      supporting_text: >-
        Mimitin, a novel mitochondrial protein, has been shown to act as a
        molecular chaperone for the mitochondrial complex I and to regulate ATP
        synthesis.
core_functions:
- description: >-
    Molecular chaperone / assembly factor for mitochondrial respiratory chain
    complex I. NDUFAF2 binds a large late-stage complex I assembly intermediate
    (containing subunits of both the matrix and membrane arms) at the
    mitochondrial inner membrane, stabilizing it and promoting efficient assembly
    of the holoenzyme, from which NDUFAF2 is then released. It is not a stable
    structural subunit and has no catalytic activity of its own.
  molecular_function:
    id: GO:0044877
    label: protein-containing complex binding
  directly_involved_in:
  - id: GO:0032981
    label: mitochondrial respiratory chain complex I assembly
  locations:
  - id: GO:0005739
    label: mitochondrion
  - id: GO:0005743
    label: mitochondrial inner membrane
  supported_by:
  - reference_id: PMID:16200211
    supporting_text: >-
      These results demonstrate that B17.2L is a bona fide molecular chaperone
      that is essential for the assembly of complex I
  - reference_id: PMID:16200211
    supporting_text: >-
      coimmunoprecipitated a subset of complex I structural subunits from normal
      human heart mitochondria
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: PMID:16200211
  title: A molecular chaperone for mitochondrial complex I assembly is mutated in
    a progressive encephalopathy.
  findings:
  - statement: >-
      NDUFAF2 (B17.2L) is a paralog of the B17.2/NDUFA12 structural subunit and is
      a bona fide molecular chaperone essential for complex I assembly; a null
      mutation causes complex I deficiency rescued by re-expression.
    reference_section_type: RESULTS
  - statement: >-
      NDUFAF2 does not associate with the mature holoenzyme but binds an ~830 kDa
      late assembly intermediate and co-immunoprecipitates a subset of complex I
      structural subunits from human heart mitochondria.
    reference_section_type: RESULTS
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      PMC full text available and read; defining functional study establishing the
      chaperone / assembly-factor role and its transient association with a late
      complex I subassembly. Supporting_text quotes verified verbatim.
- id: PMID:22587331
  title: Effects of the novel mitochondrial protein mimitin in insulin-secreting cells.
  findings:
  - statement: >-
      Mimitin (NDUFAF2) is a mitochondrial protein that acts as a molecular
      chaperone for complex I and regulates ATP synthesis; it modulates
      insulin-secreting beta-cell function.
    reference_section_type: ABSTRACT
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: >-
      Abstract-only cache (full_text_available false). Supports mitochondrial
      localization and the complex I chaperone role under an alias (mimitin);
      beta-cell effects are downstream/physiological context.
- id: PMID:32296183
  title: A reference map of the human binary protein interactome.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: >-
      HuRI yeast two-hybrid binary interactome; source of several bare
      GO:0005515 protein-binding IPI annotations. High-throughput screen with no
      NDUFAF2-specific functional insight.
- 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 affinity-purification MS interactome; source of a bare
      protein-binding IPI (partner NDUFA7). No specific functional claim about
      NDUFAF2.
- id: PMID:34800366
  title: Quantitative high-confidence human mitochondrial proteome and its dynamics
    in cellular context.
  findings:
  - statement: NDUFAF2 is detected as a high-confidence component of the human mitochondrial proteome.
    reference_section_type: RESULTS
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: >-
      High-throughput mitochondrial-proteome study; supports mitochondrial
      localization only.
- id: PMID:34819669
  title: A multi-scale map of cell structure fusing protein images and interactions.
  findings: []
  reference_review:
    relevance: LOW
    correctness: VERIFIED
    review_notes: >-
      MuSIC multi-scale cell map; source of a bare protein-binding IPI (partner
      NDUFA7). No NDUFAF2-specific functional insight.
- id: PMID:38949024
  title: Primary cilia formation requires the Leigh syndrome-associated mitochondrial
    protein NDUFAF2.
  findings:
  - statement: >-
      NDUFAF2 interacts with the basal-body protein ARMC9 and is required for the
      initial steps of primary cilium formation (CP110 removal, ciliary vesicle
      docking, transition-zone establishment).
    reference_section_type: RESULTS
  reference_review:
    relevance: HIGH
    correctness: VERIFIED
    review_notes: >-
      PMC full text read; establishes the pleiotropic ciliogenesis role and the
      ARMC9 interaction. Supports the cilium assembly (IMP) and ARMC9 IPI
      annotations. Role is non-core relative to complex I assembly.
- id: Reactome:R-HSA-6799179
  title: Peripheral arm subunits bind the 815kDa complex to form a 980kDa complex
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: >-
      Reactome complex I biogenesis step; supports mitochondrial inner membrane
      localization during assembly.
- id: Reactome:R-HSA-6799196
  title: The MCIA complex, NDUFAF2-7 all dissociate from the 980kDa complex, resulting
    in Complex I
  findings:
  - statement: >-
      In the final biogenesis step the assembly factors including NDUFAF2
      dissociate from the 980 kDa complex to leave mature Complex I, confirming
      NDUFAF2 is not a component of the mature holoenzyme.
    reference_section_type: OTHER
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: >-
      Reactome step; explicitly models NDUFAF2 as an assembly factor that
      dissociates before the mature complex, supporting removal of the
      "part_of complex I" IEA.
- id: Reactome:R-HSA-6800870
  title: NDUF subunits bind to form the FP subcomplex
  findings: []
  reference_review:
    relevance: MEDIUM
    correctness: VERIFIED
    review_notes: >-
      Reactome FP subcomplex assembly step; supports mitochondrial inner membrane
      localization during assembly.