Structural basis of multifunctional bovine mitochondrial cytochrome bc(1) complex

The mitochondrial cytochrome bc(1) complex is a multifunctional membrane pr otein complex. It catalyzes electron transfer, proton translocation, peptid e processing, and superoxide generation. Crystal structure data at 2.9 Angs trom resolution not only establishes the location of the redox centers and inhibitor binding sites, but also suggests a movement of the head domain of the iron-sulfur protein (ISP) during bc(1) catalysis and inhibition of pep tide-processing activity during complex maturation. The functional importan ce of the movement of extramembrane (head) domain of ISP in the bc(1) compl ex is confirmed by analysis of the Rhodobacter sphaeroides bc(1) complex mu tants with increased rigidity in the ISP neck-and by the determination of r ate constants for acid/base-induced intramolecular electron transfer betwee n [2Fe-2S] and heme c(1) in native and inhibitor-loaded beef complexes. The peptide-processing activity is activated in bovine heart mitochondrial bc( 1) complex by nonionic detergent at concentrations that inactivate electron transfer activity. This peptide-processing activity is shown to be associa ted with subunits and II by cloning, overexpression and in vitro reconstitu tion. The superoxide-generation site of the cytochrome bc(1) complex is loc ated at reduced b(L) and Q(.-). The reaction is membrane potential-, and cy tochrome c-dependent.