Saccharomyces cerevisiae Coq9 polypeptide is a subunit of the mitochondrial coenzyme Q biosynthetic complex

Abstract

Coenzyme Q (Q) is a redox active lipid that is an essential component of the electron transport chain. Here, we show that steady state levels of Coq3, Coq4, Coq6, Coq7 and Coq9 polypeptides in yeast mitochondria are dependent on the expression of each of the other COQ genes. Submitochondrial localization studies indicate Coq9p is a peripheral membrane protein on the matrix side of the mitochondrial inner membrane. To investigate whether Coq9p is a component of a complex of Qbiosynthetic proteins, the native molecular mass of Coq9p was determined by Blue Native-PAGE. Coq9p was found to co-migrate with Coq3p and Coq4p at a molecular mass of approximately 1 MDa. A direct physical interaction was shown by the immunoprecipitation of HA-tagged Coq9 polypeptide with Coq4p, Coq5p, Coq6p and Coq7p. These findings, together with other work identifying Coq3p and Coq4p interactions, identify at least six Coq polypeptides in a multi-subunit Q biosynthetic complex.

Coenzyme Q supplementation or Over-Expression of the Yeast Coq8 Putative Kinase Stabilizes Multi-Subunit Coq Polypeptide Complexes in Yeast Coq Null Mutants

“…Cytochrome c, which peripherally attaches to the inner mitochondrial membrane through electrostatic interactions with fatty acids and acidic phospholipids [65], was released from the sonicated mitoplasts following salt addition, as expected. These results provide further support for the submitochondrial localization data indicating that yeast Coq7 is a peripheral membrane protein on the matrix side as are Coq1, Coq3, Coq4, Coq5, Coq6, Coq8, and Coq9 polypeptides [20,31,36,49,[66][67][68].…”

“…7 and Table 3). The steady-state levels of Coq1, Coq2, and Coq5 polypeptides are not affected by deletions in any of the other COQ genes [20]. While Coq8 overexpression in the coq1 or coq2 null mutants has little effect, Coq8 over-expression in the coq5 null mutant allows production of DDMQ 6 , and enhances steady-state levels of the Coq4, Coq6, Coq9 and Coq7 polypeptides [17].…”

“…The yeast Coq4 and Coq9 polypeptides co-purify with other Coq polypeptides and both migrate at high molecular mass in separation of digitonin extracts of mitochondria [18][19][20][21]. Thus, we used the Coq4 and Coq9 polypeptides as sensitive indicators of the state of the high molecular mass Coq complexes.…”

“…1) [17]. Whereas each of the coq null mutants lacks the designated Coq polypeptide [20], several coq mutants harboring certain amino acid substitution mutations show a less drastic block in Q biosynthesis as compared to coq null mutants. For example, certain coq7 point mutants retain steady-state levels of the Coq7 polypeptide and accumulate demethoxy-Q 6 (DMQ 6 ), a late-stage Q-intermediate missing just one methoxy group [22,23].…”

“…For example, certain coq7 point mutants retain steady-state levels of the Coq7 polypeptide and accumulate demethoxy-Q 6 (DMQ 6 ), a late-stage Q-intermediate missing just one methoxy group [22,23]. Some of the Coq polypeptides physically interact -biotinylated Coq3 co-purifies with Coq4 [18], and Coq9 tagged with the hemagglutinin epitope co-purifies with Coq4, Coq5, Coq6, and Coq7 polypeptides [20]. These studies were performed with digitonin-extracts of purified mitochondria.…”