Sy. Lee et al., The functional role of conserved acidic residues of the Qcr7 protein of the cytochrome bc(1) complex in Saccharomyces cerevisiae, ARCH BIOCH, 393(2), 2001, pp. 207-214
The 14-kDa Qcr7 protein represents one of the 10 subunits that are componen
ts of a functional cytochrome bc(1) complex in Sacharomyces cerevisiae. Pre
vious studies have shown that the N-terminus of the Qcr7 protein may be inv
olved in the assembly of the cytochrome bc(1), complex and its C-terminus b
y interacting with cytochrome b and QCR8 proteins. It has also been suggest
ed that Qcr7 protein may be involved in proton pumping. The coding sequence
for two highly conserved aspartate residues, D46 and D47, in the QCR7 gene
was altered by site-directed mutagenesis and the mutated genes expressed i
n cells lacking a functional QCR7 gene. Mutants D46E, D46G, D46N, and D47E
were comparable to wild type in growth phenotype on nonfermentable carbon s
ources. Mutants D47G and D47N were respiratory deficient and analysis of co
mplex components by immunoblotting and spectral analysis of cytochrome b su
ggests defective assembly. Despite being respiratory competent and having n
ormal electron transport rates in broken mitochondria, the mutant D46G had
markedly reduced ATP synthesis from electron transport reactions catalyzed
by complexes II plus III of the respiratory chain. This suggests that the g
eometry of proton uptake by the bc(1), complex is disturbed by the mutation
in D46. (C) 2001 Academic Press.