{"uniprot":"E9PQ53","gene":"NDUFC2-KCTD14","name":"NADH dehydrogenase [ubiquinone] 1 subunit C2, isoform 2","organism":"Homo sapiens (Human)","status":"dark","length":114,"sequence":"MIARRNPEPLRFLPDEARSLPPPKLTDPRLLYIGFLGYCSGLIDNLIRRRPIATAGLHRQLLYITAFFFAGYYLVKREDYLYAVRDREMFGYMKLHPEDFPEEDVYCCGAERRG","function_summary":"A small membrane-associated subunit of human mitochondrial Complex I that acts as an assembly and stabilization module rather than a catalytic center. By mediating multivalent protein interactions within the inner-membrane arm of the respiratory chain, it promotes proper biogenesis and maintenance of Complex I, thereby indirectly supporting electron transfer from NADH to ubiquinone within mitochondria.","plain_language":"NDUFC2-KCTD14 has barely been studied. The model's best guess: A small membrane-associated subunit of human mitochondrial Complex I that acts as an assembly and stabilization module rather than a catalytic center. By mediating multivalent protein interactions within the inner-membrane arm of the respiratory chain, it promotes proper biogenesis and maintenance of Complex I, thereby indirectly supporting electron transfer from NADH to ubiquinone within mitochondria.","uniprot_summary":"Accessory subunit of the mitochondrial membrane respiratory chain NADH dehydrogenase (Complex I), that is believed not to be involved in catalysis. Complex I functions in the transfer of electrons from NADH to the respiratory chain. The immediate electron acceptor for the enzyme is believed to be ubiquinone.","go_terms":{"molecular_function":[{"id":"GO:0005515","label":"protein binding"}],"biological_process":[{"id":"GO:0032981","label":"mitochondrial respiratory chain complex I assembly"}],"cellular_component":[{"id":"GO:0005739","label":"mitochondrion"}]},"interpro":[{"id":"IPR009423","name":"NADH dehydrogenase [ubiquinone] 1 subunit C2, NDUC2","type":"family","start":1,"end":104}],"reasoning":"I begin with the InterPro architecture: IPR009423 (NADH dehydrogenase [ubiquinone] 1 subunit C2, NDUC2 family) spans residues 1–104, covering essentially the entire polypeptide. A single full-length family signature that defines a Complex I accessory subunit indicates a compact membrane-associated assembly factor rather than a catalytic core enzyme. NDUC2-family proteins are small, hydrophobic constituents of the membrane arm of mitochondrial Complex I that stabilize and organize the larger respiratory supercomplex. The absence of catalytic motifs and the presence of a full-length accessory-subunit family domain together argue that this protein’s primary role is structural and organizational.\n\nFrom this architecture, the molecular function resolves as protein binding (GO:0005515). Accessory Complex I subunits in the NDUC2 family act through multivalent contacts with other membrane-embedded and matrix-exposed components, guiding assembly and maintaining the integrity of the membrane arm. Such binding-centric roles are typical of small single-pass or multi-pass assembly modules that nucleate local subcomplex formation.\n\nThis binding-driven assembly role causally links to mitochondrial respiratory chain complex I assembly (GO:0032981). By stabilizing intermediate modules and docking additional subunits, the NDUC2-family architecture drives the maturation of Complex I. This assembly function is upstream of electron transfer from NADH to ubiquinone but does not itself catalyze redox chemistry; instead, it ensures the proper installation of the quinone-reactive and proton-pumping modules.\n\nCellular localization follows directly. The NDUC2 family signature and the assembly role place the protein in the mitochondrion (GO:0005739), specifically at the inner membrane where Complex I resides. The biophysical profile of NDUC2-like subunits—small, hydrophobic, and membrane-associated—supports a membrane-embedded position that anchors and organizes the peripheral membrane arm facing the inner membrane and matrix interface.\n\nMechanistically, I hypothesize that this subunit forms a membrane-embedded scaffold that binds neighboring Complex I components to stabilize the quinone-reactive region and to chaperone late-stage assembly. Likely interaction partners include other membrane-embedded accessory subunits and assembly factors that together shape the membrane arm. By creating a stable platform, the protein indirectly supports efficient electron flow from NADH to ubiquinone by ensuring that catalytic centers are correctly assembled and positioned within the inner membrane.","category":"dark","control_evaluation":null,"validation_plan":null,"structure":{"source":"AlphaFold DB","pdb":"/structures/AF-E9PQ53.pdb","alphafold":"https://alphafold.ebi.ac.uk/entry/E9PQ53"},"links":{"uniprot":"https://www.uniprot.org/uniprotkb/E9PQ53/entry","atlas":"/p/E9PQ53"},"provenance":{"model":"BioReason-Pro (ESM3 esm3-sm-open-v1)","source_list":"Pharos Tdark","note":"AI prediction, not experimentally verified"}}