Structure of the avian mitochondrial cytochrome bc1 complex

There are now four structures of vertebrate mitochondrial bc1 complexes available in the protein databases and structures from yeast and bacterial sources are expected soon. This review summarizes the new information with emphasis on the avian cytochrome bc1 complex (PDB entries 1BCC and 3BCC). The Rieske iron-sulfur protein is mobile and this has been proposed to be important for catalysis. The binding sites for quinone have been located based on structures containing inhibitors and, in the case of the quinone reduction site Qi, the quinone itself.