Random mutant generation and its utility in uncovering structural and functional features of cytochromeb inSaccharomyces cerevisiae

Abstract

The generation of random mutations in the mitochondrial cytochrome b gene of Saccharomyces cerevisiae has been used as a most fruitful means of identifying subregions that play a key role in the bc1 complex mechanism, best explained by the protonmotive Q cycle originally proposed by Peter Mitchell. Selection for center i and center o inhibitor resistance mutants, in particular, has yielded much information. The combined approaches of genetics and structural predictions have led to a two-dimensional folding model for cytochrome b that is most compatible with current knowledge of the protonmotive Q cycle. A three-dimensional model is emerging from studies of distant reversions of deficient mutants. Finally, interactions between cytochrome b and the other subunits of the bc1 complex, such as the iron-sulfur protein, can be affected by a single amino acid change.

Role of the Evolutionarily Conserved Cytochrome b Tryptophan 142 in the Ubiquinol Oxidation Catalyzed by the bc1 Complex in the Yeast Saccharomyces cerevisiae

“…[22][23][24][25][26][27][28][29][30]; for review, see Ref. 31) or sitedirected mutagenesis (Refs. 32-36; for review, see Ref.…”

QUINONE BINDING SITES ON CYTOCHOROME b/c COMPLEXES*

“…those compiled for cytochrome b by Widger et aL4 and recently for 200 b-cytochromes by Degli-Esposti et aL5 Numerous reviews have dealt with the functional structure of the complexes. 1,[6][7][8][9][10] Four redox components seem unnecessary for a simple quinol oxidation and cytochrome reduction even considering that a two electron and proton carrying redox center, the quinol, reduces a one electron carrier that does not carry a proton, plastocyanin or cytochrome cl, and that the redox reaction sequence proceeds from the hydrophobic to the hydrophilic space of the chloroplast or mitochondrium. The complex nature of the cytochrome b/cl or cytochrome b6/f complexes is indeed responsible for an additional property of the complex: an additional energy conservation step in *This paper is dedicated to Warren L. Butler on the occasion of his ?To whom correspondence should be addressed.…”

Maesaquinone: A Novel Inhibitor of Plant Mitochondrial Respiratory Enzymes That React with Ubiquinone

“…1) resembles that of Q, MAQ seems likely to interfere with Q binding. Inhibitory compounds with phenol-type structures previously have been used successfully to identify amino acid residues involved in the Q binding of several enzymes involved in photosynthesis (photosystem II [14]) and respiration (cytochrome bc 1 complex [15 ] and SDH [16 ]). Such phenoltype inhibitors have additionally allowed comparative investigations into the actual structure of Q-binding sites of various enzymes (17)(18)(19).…”