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.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005739 mitochondrion | IBA GO_REF:0000033 | ACCEPT | 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. Supporting Evidence: file:human/NDUFAF2/NDUFAF2-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion |
| GO:0032981 mitochondrial respiratory chain complex I assembly | IBA GO_REF:0000033 | ACCEPT | 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. Supporting Evidence: PMID:16200211 These results demonstrate that B17.2L is a bona fide molecular chaperone that is essential for the assembly of complex I |
| GO:0005739 mitochondrion | IEA GO_REF:0000044 | ACCEPT | Summary: Electronic mapping from the UniProt Swiss-Prot subcellular-location vocabulary; correct and consistent with the experimental mitochondrial localization. Supporting Evidence: file:human/NDUFAF2/NDUFAF2-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion |
| GO:0016020 membrane | IEA GO_REF:0000002 | REMOVE | 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. |
| GO:0045271 respiratory chain complex I | IEA GO_REF:0000002 | REMOVE | 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. Supporting Evidence: PMID:16200211 An anti-B17.2L antibody did not associate with the holoenzyme complex but specifically recognized an 830-kDa subassembly |
| GO:0005515 protein binding | IPI PMID:32296183 A reference map of the human binary protein interactome. | MARK AS OVER ANNOTATED | 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). |
| GO:0005515 protein binding | IPI PMID:33961781 Dual proteome-scale networks reveal cell-specific remodeling... | MARK AS OVER ANNOTATED | 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. |
| GO:0005515 protein binding | IPI PMID:34819669 A multi-scale map of cell structure fusing protein images an... | MARK AS OVER ANNOTATED | 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. |
| GO:0005515 protein binding | IPI PMID:38949024 Primary cilia formation requires the Leigh syndrome-associat... | MARK AS OVER ANNOTATED | 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. Supporting Evidence: PMID:38949024 a ciliary protein, armadillo repeat containing 9 (ARMC9), interacts with NDUFAF2 |
| GO:0005739 mitochondrion | IDA GO_REF:0000052 | ACCEPT | Summary: Immunofluorescence-based (HPA) direct localization to mitochondrion. Correct and concordant with all other evidence. Supporting Evidence: file:human/NDUFAF2/NDUFAF2-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion |
| GO:0060271 cilium assembly | IMP PMID:38949024 Primary cilia formation requires the Leigh syndrome-associat... | KEEP AS NON CORE | 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. Supporting Evidence: PMID:38949024 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 |
| GO:0005739 mitochondrion | HTP PMID:34800366 Quantitative high-confidence human mitochondrial proteome an... | ACCEPT | Summary: High-throughput mitochondrial-proteome identification placing NDUFAF2 in mitochondrion. Concordant with curated localization; accept. Supporting Evidence: file:human/NDUFAF2/NDUFAF2-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion |
| GO:0044877 protein-containing complex binding | IDA PMID:16200211 A molecular chaperone for mitochondrial complex I assembly i... | ACCEPT | 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. Supporting Evidence: PMID:16200211 coimmunoprecipitated a subset of complex I structural subunits from normal human heart mitochondria |
| GO:0005739 mitochondrion | IDA PMID:16200211 A molecular chaperone for mitochondrial complex I assembly i... | ACCEPT | Summary: Direct experimental mitochondrial localization from the defining functional study. Accept. Supporting Evidence: file:human/NDUFAF2/NDUFAF2-uniprot.txt SUBCELLULAR LOCATION: Mitochondrion |
| GO:0032981 mitochondrial respiratory chain complex I assembly | IMP PMID:16200211 A molecular chaperone for mitochondrial complex I assembly i... | ACCEPT | 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. Supporting Evidence: PMID:16200211 These results demonstrate that B17.2L is a bona fide molecular chaperone that is essential for the assembly of complex I |
| GO:0005743 mitochondrial inner membrane | TAS Reactome:R-HSA-6799179 | ACCEPT | 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. |
| GO:0005743 mitochondrial inner membrane | TAS Reactome:R-HSA-6799196 | ACCEPT | 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. |
| GO:0005743 mitochondrial inner membrane | TAS Reactome:R-HSA-6800870 | ACCEPT | 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. |
| GO:0005739 mitochondrion | IDA PMID:22587331 Effects of the novel mitochondrial protein mimitin in insuli... | ACCEPT | 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. Supporting Evidence: PMID:22587331 Mimitin, a novel mitochondrial protein, has been shown to act as a molecular chaperone for the mitochondrial complex I and to regulate ATP synthesis. |
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