SUMMARY PARAGRAPH for QCR10
The cytochrome bc1 complex (also known as ubiquinol:cytochrome c oxidoreductase, ubiquinol:ferricytochrome c oxidoreductase, and respiratory complex III) is a highly conserved enzyme of the mitochondrial respiratory chain (reviewed in 3). In S. cerevisiae it consists of three catalytic subunits, Cobp, Rip1p, and Cyt1p, plus seven additional subunits: Cor1p, Qcr2p, Qcr6p, Qcr7p, Qcr8p, Qcr9p, and Qcr10p (3, 1). The crystal structure of the complex shows that two functional units, each containing these ten subunits, associate with each other in the mitochondrial inner membrane (4). Assembly of a functional complex requires two proteins, Cbp3p and Cbp4p, that are not components of the complex but may associate with it during assembly (5). It also requires Bcs1p, an AAA-family ATPase that interacts with a precursor of the complex to mediate incorporation of the Rip1p and Qcr10p subunits (6). The mechanism of energy transfer by the complex, known as the protonmotive Q cycle, has been studied in detail (reviewed in 3). The net result of the Q cycle is the stepwise transfer of an electron through the complex from ubiquinol to cytochrome c (Cyc1p), coupled with the translocation of a proton across the mitochondrial inner membrane (3). The function of the cytochrome bc1 complex is essential to the energy-generating process of oxidative phosphorylation, which is carried out by the enzyme complexes of the mitochondrial respiratory chain.
Qcr10p is a small subunit of the cytochrome bc1 complex (8.5 kDa) that is the last subunit to be assembled into the complex; its assembly requires the prior incorporation of the catalytic subunit Rip1p (6). Qcr10p is not required for respiratory growth, since the qcr10 null mutant is able to respire, but the qcr6 qcr10 double null mutant lacking two subunits of the cytochrome bc1 complex displays a synthetic respiratory growth defect (1). The qcr10 null mutation causes a reduction in detectable cytochrome bc1 activity, even though the effect is not strong enough to be observed as a respiratory growth phenotype (1). In addition, the stability of the complex in the qcr10 null mutant is apparently lower than in wild type, since most of the catalytic Rip1p subunit is lost from the complex during purification under conditions where the wild-type enzyme remains intact (1). QCR10 is conserved in other eukaryotes (7), and is the ortholog of human UCQR (OMIM).
Last updated: 2007-07-26