Mutational analysis of the Qi-site proton pathway in yeast cytochrome bc1 complex

Abstract

The respiratory cytochrome bc 1 complex functions as a protonmotive ubiquinol:cytochrome c oxidoreductase. Lysine 228 (K228) located within the quinol reduction (Q i) site of the bc 1 complex, has been reported as a key residue for proton transfer during the redox chemistry cycle to substrate quinone at Q i. In yeast, while single mutations had no effect, the combination of K228L and F225L resulted in a severe respiratory growth defect and inhibition of O 2 consumption in intact cells. The inhibition was overcome by uncoupling the mitochondrial membrane or by suppressor mutations in the region of K228L-F225L. We propose that the K228L mutation introduces energetic (and kinetic) barriers into normal electron-and proton transfer chemistry at Q i , which are relieved by dissipation of the opposing protonmotive force or through the restoration of favourable intraprotein proton transfer networks via suppressor mutation.