NDUFA1 (MWFE) — gene review notes

Identity and overview

• UniProt: O15239 (NDUA1_HUMAN); gene symbol NDUFA1; HGNC:7683.
• Aliases: MWFE protein / Complex I-MWFE / CI-MWFE / NADH-ubiquinone oxidoreductase MWFE subunit.
• Small protein, 70 amino acids, single-pass membrane protein.
  [file:human/NDUFA1/NDUFA1-uniprot.txt "SEQUENCE 70 AA"], [file:human/NDUFA1/NDUFA1-uniprot.txt "Single-pass membrane protein"]
• Encoded on the X chromosome (nuclear-encoded, imported into mitochondria).
  PMID:10200266
• Belongs to the "complex I NDUFA1 subunit family".
  [file:human/NDUFA1/NDUFA1-uniprot.txt "Belongs to the complex I NDUFA1 subunit family"]

Molecular function — accessory/structural, NOT catalytic

NDUFA1 is one of the accessory ("supernumerary") subunits of mitochondrial Complex I
(NADH:ubiquinone oxidoreductase). It is a genuine, stable subunit of the mature holoenzyme,
not an assembly factor. It is not one of the 14 conserved core subunits and is
believed not to be involved in catalysis (carries no redox cofactor).

• [file:human/NDUFA1/NDUFA1-uniprot.txt "Accessory subunit of the mitochondrial membrane respiratory"] ... [file:human/NDUFA1/NDUFA1-uniprot.txt "chain NADH dehydrogenase (Complex I), that is believed not to be"] ... [file:human/NDUFA1/NDUFA1-uniprot.txt "involved in catalysis."]
• [PMID:10200266 "This polypeptide is 1 of approximately 28 \"accessory proteins\" identified in complex I"]
• PMID:10200266

Its honest molecular function is therefore structural molecule activity (GO:0005198); it
contributes_to the complex-level NADH dehydrogenase (ubiquinone) activity (GO:0008137)
but does not enable that activity independently. It should NOT be given GO:0008137 as a direct
enables/molecular_function.

Essential for Complex I assembly and activity

Although non-catalytic, MWFE/NDUFA1 is absolutely essential for a functional Complex I:

• A Chinese hamster MWFE mutant (CCL16-B2, deletion producing a truncated protein) has
  Complex I activity reduced to <10%; complementation with hamster NDUFA1 cDNA restored
  rotenone-sensitive Complex I activity to ~100% of parent.
  PMID:10200266,
  PMID:10200266,
  PMID:10200266
• Systematic human knockout study of accessory subunits: 25 of 31 accessory subunits are
  strictly required for assembly of a functional Complex I; loss of a subunit destabilizes
  others in the same structural module.
  PMID:27626371,
  PMID:27626371

Localization

• Mitochondrion inner membrane, matrix side (UniProt subcellular location).
  [file:human/NDUFA1/NDUFA1-uniprot.txt "Mitochondrion inner membrane"]
• Confirmed as a subunit of the inner-membrane Complex I holoenzyme by immunopurification /
  MS (Murray 2003) and by cryo-EM structures.
  PMID:12611891
• High-confidence mitochondrial proteomics (HTP) also places it in mitochondrion
  (Morgenstern 2021, PMID:34800366).

Membership in Complex I / respiratory chain

• Complex I = NADH:ubiquinone oxidoreductase, first enzyme of the respiratory chain,
  ~45 subunits in humans.
  PMID:27626371
• Function of the complex: transfer of electrons from NADH to ubiquinone, coupled to proton
  translocation across the inner membrane.
  PMID:9878551
• NDUFA1 is assigned within human CI in the cryo-EM megacomplex structure (Guo 2017,
  PMID:28844695), which "reveals the precise assignment of individual subunits of human CI".
  PMID:28844695
• Complex I participates in respiratory supercomplexes (respirasomes) with CIII and CIV
  (PMID:28844695, PMID:30030361), which underlie the aerobic respiration / proton-motive-force
  and ATP-synthesis roles attributed at the complex level (ComplexPortal NAS annotations,
  PMID:30030361).

Core biological process

• GO:0006120 mitochondrial electron transport, NADH to ubiquinone (core).
• GO:0032981 mitochondrial respiratory chain complex I assembly (NDUFA1 is required for
  assembly; PMID:27626371, PMID:10200266) — reasonable additional core BP.
• Aerobic respiration (GO:0009060) and proton-motive-force ATP synthesis (GO:0042776) are
  complex/pathway-level processes annotated by ComplexPortal (NAS); reasonable to keep as
  non-core context.

Disease

• X-linked; mutations cause Mitochondrial complex I deficiency, nuclear type 12 (MC1DN12,
  MIM:301020), a mitochondrial encephalomyopathy. Pathogenic missense variants G8R and R37S.
  [file:human/NDUFA1/NDUFA1-uniprot.txt "Mitochondrial complex I deficiency, nuclear type 12 (MC1DN12)"],
  [file:human/NDUFA1/NDUFA1-uniprot.txt "VARIANTS MC1DN12 ARG-8 AND SER-37."]

Annotation review reasoning summary

• respiratory chain complex I (GO:0045271, part_of) — multiple independent IDA/IPI plus IBA
  → ACCEPT as core CC. It is a bona fide holoenzyme subunit.
• structural molecule activity (GO:0005198) — best MF; not present in GOA but is the honest
  MF; put in core_functions.
• NADH dehydrogenase (ubiquinone) activity (GO:0008137), enables (NAS PMID:9878551; TAS
  PMID:10200266) — this is the complex-level catalytic activity. NDUFA1 does NOT enable it
  independently (non-catalytic accessory subunit). Direct enables is an over-annotation →
  MARK_AS_OVER_ANNOTATED; captured instead as contributes_to_molecular_function in core_functions.
• mitochondrial inner membrane (GO:0005743) / mitochondrion (GO:0005739) / mitochondrial
  membrane (GO:0031966) — correct localization, accept (inner membrane most specific/core).
• mitochondrion IDA PMID:16729965 — that paper is about OCTN1 localization; the NDUFA1 IDA
  is a plausible curator/MGI co-annotation of an endogenous mitochondrial marker. Location is
  correct but generic and the cited paper is not about NDUFA1 function → KEEP_AS_NON_CORE.
• aerobic respiration (GO:0009060) / proton-motive-force ATP synthesis (GO:0042776) —
  complex/pathway-level BPs (ComplexPortal NAS) → KEEP_AS_NON_CORE.
• proton transmembrane transport (GO:1902600, IEA GO_REF:0000108) — inter-ontology inference
  from GO:0008137. Since NDUFA1 does not itself have GO:0008137 activity and is non-catalytic
  (does not itself translocate protons), this inferred transport annotation is an
  over-propagation → MARK_AS_OVER_ANNOTATED (electronic, but keep per policy for a term whose
  essence — the complex pumps protons — is not entirely wrong).
• Reactome TAS inner-membrane localization annotations → ACCEPT (correct CC, TAS).