Ubiquinone biosynthesis inSaccharomyces cerevisiae: the molecular organization ofO-methylase Coq3p depends on Abc1p/Coq8p

Abstract

Coenzyme Q is a redox-active lipid that functions as an electron carrier in the mitochondrial respiratory chain. Q-biosynthesis in Saccharomyces cerevisiae requires at least nine proteins (Coq1p-Coq9p). The molecular function of Coq8p is still unknown; however, lack of Q and the concomitant accumulation of the intermediate 3-hexaprenyl-4-hydroxybenzoic acid in the absence of Coq8p suggest an essential role in Q-biosynthesis. Localization studies identify Coq8p as a soluble mitochondrial protein, with characteristics of a protein of the matrix or associated with the inner mitochondrial membrane. Coq8p forms homomeric structure(s) as revealed by two-hybrid analysis and tandem affinity purification. Two-dimensional (2D)-Blue Native/sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis suggests that Coq8p - together with Coq2p and Coq10p - is predominantly associated with a complex of about 500 kDa, whereas Coq3p, Coq5p and Coq9p are mainly organized in a 1.3 MDa Q-biosynthesis complex that is not associated with the complex III and IV supracomplexes of the respiratory chain. Loss of Coq8p is accompanied by destabilization of Coq3p, but not of Coq9p from the 1.3 MDa Q-biosynthesis complex. This effect cannot be reversed by Q(6) supplementation. The detection of Coq3p isoforms by 2D-isoelectric focusing is in line with the proposed function of Coq8p as a kinase, with Coq3p as a target.

Overexpression of the Coq8 Kinase in Saccharomyces cerevisiae coq Null Mutants Allows for Accumulation of Diagnostic Intermediates of the Coenzyme Q6 Biosynthetic Pathway

“…3A). Although previous studies indicated that the Coq3 polypeptide was labile in ⌬coq strains (6), subsequent experiments performed in the presence of both protease and phosphatase inhibitors preserved steady state levels of Coq3 (12,15). In agreement, Coq3 levels were unaffected in ⌬coq5 or ⌬coq6 cells (Fig.…”

“…Coq8 has been proposed to possess a kinase activity (11) and has been shown to be necessary for the existence of phosphorylated forms of Coq3, Coq5, and Coq7 in vivo (12,15). A G130D mutation in Coq8 abolishes the phosphorylated form of Coq3 suggesting that this mutation impairs the kinase activity (12).…”

“…Mutations in ADCK3, the human orthologue of COQ8, were shown to cause Q 10 deficiency and cerebellar ataxia (13,14). In yeast, Coq8 is essential for phosphorylation of Coq3 and for its association with the Q biosynthetic complex (12,15). In addition, several phosphorylated forms of Coq5 and Coq7 disappear in a yeast strain expressing the G130D mutant form of Coq8 (12), which mimics the pathogenic G272D mutation found in ADCK3 (14).…”

Focal segmental glomerulosclerosis is associated with aPDSS2haplotype and, independently, with a decreased content of coenzyme Q10

“…Ding and colleagues (10) developed a statistical method for measuring the overlap between skin cells and lymphoblastoid cells in levels of gene expression and found that ϳ70% of the quantitative trait loci detected in lymphoblastoid cells were also observed in skin. Our findings are consistent with the idea that Q 10 content in cells reflects not only expression of Ն11 genes required for de novo synthesis, but also the assembly of a mitochondrial multisubunit protein-lipid complex known to be modulated by phosphorylation (54,56,64). Such multisubunit complexes may be particularly sensitive to polymorphisms.…”

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

“…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.…”