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Mol. Biol. Evol. 20(1):145-153. 2003
DOI: 10.1093/molbev/msg016
© 2003 by the Society for Molecular Biology and Evolution. ISSN: 0737-4038

Structure of the bc1 Complex from Seculamonas ecuadoriensis, a Jakobid Flagellate with an Ancestral Mitochondrial Genome

Stefanie Marx*,{ddagger},1, Maja Baumgärtner{dagger}, Sivakumar Kunnan{ddagger}, Hans-Peter Braun*, B. Franz Lang{ddagger} and Gertraud Burger{ddagger}

* Institut für Angewandte Genetik, Universität Hannover, Hannover, Germany
{dagger} Gesellschaft für Biotechnologische Forschung, Braunschweig, Germany
{ddagger} Canadian Institute for Advanced Research, Département de Biochimie, Université de Montréal, Montréal, Québec, Canada

In eubacteria, the respiratory bc1 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 bc1 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.

Key Words: jakobid flagellates • Seculamonas ecuadoriensis • mitochondria • bc1 complex, evolution


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