title: Respiratory complexes III and IV are not essential for the assembly/stability of complex I in fungi.
abstract: The functional relevance of respiratory supercomplexes in various eukaryotes including mammals, plants, and fungi is hitherto poorly elucidated. However, substantial evidence indicates as a major role the assembly and/or stabilization of mammalian complex I by supercomplex formation with complexes III and IV. Here, we demonstrate by using native electrophoresis that the long-lived Podospora anserina mutant Cyc1-1, respiring exclusively via the alternative oxidase (AOX), lacks an assembled complex III and possesses complex I partially assembled with complex IV into a supercomplex. This resembles the situation in complex-IV-deficient mutants displaying a corresponding phenotype but possessing I-III supercomplexes instead, suggesting that either complex III or complex IV is in a redundant manner necessary for assembly/stabilization of complex I as previously shown in mammals. To corroborate this notion, we constructed the double mutant Cyc1-1,Cox5::ble. Surprisingly, this mutant lacking both complexes III and IV is viable and essentially a phenocopy of mutant Cyc1-1 including the reversal of the phenotype towards wild-type-like characteristics by the several-fold overexpression of the AOX in mutant Cyc1-1,Cox5::ble(Gpd-Aox). Fungal specific features (not found in mammals) that must be responsible for assembly/stabilization of fungal complex I when complexes III and IV are absent, such as the presence of the AOX and complex I dimerization, are addressed and discussed. These intriguing results unequivocally prove that complexes III and IV are dispensable for assembly/stability of complex I in fungi contrary to the situation in mammals, thus highlighting the imperative to unravel the biogenesis of complex I as well as the true supramolecular organization of the respiratory chain and its functional significance in a variety of model eukaryotes. In summary, we present the first obligatorily aerobic eukaryote with an artificial, simultaneous lack of the respiratory complexes III and IV.
authors.affiliation: Centre de Génétique Moléculaire, Centre National de la Recherche Scientifique, 91198 Gif sur Yvette, France.
authors.forename: Marc F P M
authors.initials: MF
authors.lastname: Maas
authors.forename: Frank
authors.initials: F
authors.lastname: Krause
authors.forename: Norbert A
authors.initials: NA
authors.lastname: Dencher
authors.forename: Annie
authors.initials: A
authors.lastname: Sainsard-Chanet
mesh_terms: D003580:Cytochromes / Q000378:metabolism; D042967:Electron Transport Complex I / Q000378:metabolism*; D014450:Electron Transport Complex III / Q000378:metabolism*; D003576:Electron Transport Complex IV / Q000378:metabolism*; D004795:Enzyme Stability; D005656:Fungal Proteins / Q000378:metabolism; D024101:Mitochondrial Proteins; D009154:Mutation / Q000235:genetics; D010088:Oxidoreductases / Q000378:metabolism; D010940:Plant Proteins; D048468:Podospora / Q000166:cytology / Q000201:enzymology*; D013367:Submitochondrial Particles / Q000378:metabolism; D000099188:Alternative Oxidase
chemical_list: D003580:Cytochromes; D042967:Electron Transport Complex I; D014450:Electron Transport Complex III; D003576:Electron Transport Complex IV; D005656:Fungal Proteins; D024101:Mitochondrial Proteins; D010088:Oxidoreductases; D010940:Plant Proteins; D000099188:Alternative Oxidase