title: A central functional role for the 49-kDa subunit within the catalytic core of mitochondrial complex I.
abstract: We have analyzed a series of eleven mutations in the 49-kDa protein of mitochondrial complex I (NADH:ubiquinone oxidoreductase) from Yarrowia lipolytica to identify functionally important domains in this central subunit. The mutations were selected based on sequence homology with the large subunit of [NiFe] hydrogenases. None of the mutations affected assembly of complex I, all decreased or abolished ubiquinone reductase activity. Several mutants exhibited decreased sensitivities toward ubiquinone-analogous inhibitors. Unexpectedly, seven mutations affected the properties of iron-sulfur cluster N2, a prosthetic group not located in the 49-kDa subunit. In three of these mutants cluster N2 was not detectable by electron-paramagnetic resonance spectroscopy. The fact that the small subunit of hydrogenase is homologous to the PSST subunit of complex I proposed to host cluster N2 offers a straightforward explanation for the observed, unforeseen effects on this iron-sulfur cluster. We propose that the fold around the hydrogen reactive site of [NiFe] hydrogenase is conserved in the 49-kDa subunit of complex I and has become part of the inhibitor and ubiquinone binding region. We discuss that the fourth ligand of iron-sulfur cluster N2 missing in the PSST subunit may be provided by the 49-kDa subunit.
authors.affiliation: Universitätsklinikum Frankfurt, Institut für Biochemie I, D-60590 Frankfurt am Main, Federal Republic of Germany.
authors.forename: N
authors.initials: N
authors.lastname: Kashani-Poor
authors.forename: K
authors.initials: K
authors.lastname: Zwicker
authors.forename: S
authors.initials: S
authors.lastname: Kerscher
authors.forename: U
authors.initials: U
authors.lastname: Brandt
mesh_terms: D000595:Amino Acid Sequence; D001665:Binding Sites; D017124:Conserved Sequence; D003545:Cysteine / Q000235:genetics; D042967:Electron Transport Complex I; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D006639:Histidine / Q000235:genetics; D006864:Hydrogenase / Q000737:chemistry; D008928:Mitochondria / Q000187:drug effects / Q000201:enzymology*; D008956:Models, Chemical; D008969:Molecular Sequence Data; D009154:Mutation; D009247:NADH, NADPH Oxidoreductases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D021122:Protein Subunits; D004718:Saccharomycetales / Q000201:enzymology*; D017386:Sequence Homology, Amino Acid; D014451:Ubiquinone / Q000378:metabolism
chemical_list: D005656:Fungal Proteins; D021122:Protein Subunits; D014451:Ubiquinone; D006639:Histidine; C043296:nickel-iron hydrogenase; D006864:Hydrogenase; D009247:NADH, NADPH Oxidoreductases; D042967:Electron Transport Complex I; D003545:Cysteine