Inhibitor Complexed Structures of the Cytochrome bc1 from the Photosynthetic Bacterium Rhodobacter Sphaeroides

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The cytochrome bc1 complex (bc1) is a major contributor to the proton motive force across the membrane by coupling electron transfer to proton translocation. The crystal structures of wild type and mutant bc1 complexes from the photosynthetic purple bacterium Rhodobacter sphaeroides (Rsbc1), stabilized with the quinol oxidation (QP) site inhibitor stigmatellin alone or in combination of with the quinone reduction (QN) site inhibitor antimycin, were determined. The high quality electron density permitted assignments of a new metal‐binding site to the cytochrome c1 subunit and a number of lipid and detergent molecules. Structural differences between Rsbc1 and its mitochondrial counterparts are mostly extra membranous and provide a basis for understanding the function of the predominantly longer sequences in the bacterial subunits. Functional implications for the bc1 complex are derived from analyses of 10 independent molecules in various crystal forms and from comparisons with mitochondrial complexes.