Study of a Respiratory Supercomplex from the Low GC Firmicute Geobacillus Stearothermophilus

The respiratory chain produces energy by translocating electrons and protons across the membrane, building up an electrochemical potential. This chain is composed by several complexes, among them the Rieske/cytochrome b complexes (complex III) and cytochrome c oxidase complexes. It has been shown by electron microscopy than the respiratory chain complexes can associate to form supercomplexes, such as I1III2IV1 in the bovine heart mitochondria1 or III2IV2 in the yeast mitochondria2.Here, we set out to study protein/protein and protein/lipid interfaces on the cytochrome b6c:cytochrome c oxidase caa3 supercomplex from Geobacillus stearothermophilus, a thermophilic bacterium. This complex cytochrome b6c is more closely related to cytochrome b6f from photosynthetic reaction chains than to cytochrome bc1 from the mitochondrial respiratory chain, and possess an additional cofactor (heme ci) in the quinone reducing site, with an unknown function3. This supercomplex has been enriched by anion exchange chromatography and density gradient centrifugation. Here we present a first characterization by UV/VIS and EPR spectroscopy.∗Correspondance : lucie.bergdoll@ibpc.fr1. Althoff and al. 2011. Arrangement of electron transport chain components in bovine mitochondrial supercomplex I1III2IV1. EMBO journal 30, 46524664.2. Mileykovskaya and al. 2012.Arrangement of the Respiratory Chain Complexes in Saccharomyces cerevisiae Supercomplex III2IV2 Revealed by Single Particle Cryo-Electron Microscopy, JBC. VOL. 287, NO. 27.3. Stroebel D, Choquet Y, Popot JL & Picot D. 2003. An atypical heam in the cytochrome b6f complex, Nature. 426:413-18