title: Structure of the bc1 complex from Seculamonas ecuadoriensis, a jakobid flagellate with an ancestral mitochondrial genome.
abstract: In eubacteria, the respiratory bc(1) complex (complex III) consists of three or four different subunits, whereas that of mitochondria, which have descended from an alpha-proteobacterial endosymbiont, contains about seven additional subunits. To understand better how mitochondrial protein complexes evolved from their simpler bacterial predecessors, we purified complex III of Seculamonas ecuadoriensis, a member of the jakobid protists, which possess the most bacteria-like mitochondrial genomes known. The S. ecuadoriensis complex III has an apparent molecular mass of 460 kDa and exhibits antimycin-sensitive quinol:cytochrome c oxidoreductase activity. It is composed of at least eight subunits between 6 and 46 kDa in size, including two large "core" subunits and the three "respiratory" subunits. The molecular mass of the S. ecuadoriensis bc(1) complex is slightly lower than that reported for other eukaryotes, but about 2x as large as complex III in bacteria. This indicates that the departure from the small bacteria-like complex III took place at an early stage in mitochondrial evolution, prior to the divergence of jakobids. We posit that the recruitment of additional subunits in mitochondrial respiratory complexes is a consequence of the migration of originally alpha-proteobacterial genes to the nucleus.
authors.affiliation: Institut für Angewandte Genetik, Universität Hannover, Hannover, Germany.
authors.forename: Stefanie
authors.initials: S
authors.lastname: Marx
authors.forename: Maja
authors.initials: M
authors.lastname: Baumgärtner
authors.forename: Sivakumar
authors.initials: S
authors.lastname: Kannan
authors.forename: Hans-Peter
authors.initials: HP
authors.lastname: Braun
authors.forename: B Franz
authors.initials: BF
authors.lastname: Lang
authors.forename: Gertraud
authors.initials: G
authors.lastname: Burger
authors.forename: Sivakumar
authors.initials: S
authors.lastname: Kunnan
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002478:Cells, Cultured; D014450:Electron Transport Complex III / Q000737:chemistry* / Q000235:genetics*; D056890:Eukaryota / Q000737:chemistry* / Q000235:genetics; D019143:Evolution, Molecular; D006801:Humans; D008928:Mitochondria / Q000235:genetics* / Q000502:physiology; D008969:Molecular Sequence Data; D020836:Protein Structure, Quaternary; D021122:Protein Subunits / Q000737:chemistry / Q000235:genetics; D016415:Sequence Alignment
chemical_list: D021122:Protein Subunits; D014450:Electron Transport Complex III