Mutational analysis of assembly and function of the iron-sulfur protein of the cytochrome bc1 complex in Saccharomyces cerevisiae.

The iron-sulfur protein of the cytochrome bc1 complex oxidizes ubiquinol at center P in the protonmotive Q cycle mechanism, transferring one electron to cytochrome c1 and generating a low-potential ubisemiquinone anion which reduces the low-potential cytochrome b-566 heme group. In order to catalyze this divergent transfer of two reducing equivalents from ubiquinol, the iron-sulfur protein must be structurally integrated into the cytochrome bc1 complex in a manner which facilitates electron transfer from the iron-sulfur cluster to cytochrome c1 and generates a strongly reducing ubisemiquinone anion radical which is proximal to the b-566 heme group. This radical must also be sequestered from spurious reactivities with oxygen and other high-potential oxidants. Experimental approaches are described which are aimed at understanding how the iron-sulfur protein is inserted into center P, and how the iron-sulfur cluster is inserted into the apoprotein.