title: The yeast Coq4 polypeptide organizes a mitochondrial protein complex essential for coenzyme Q biosynthesis.
abstract: Coenzyme Q is a redox active lipid essential for aerobic respiration. The Coq4 polypeptide is required for Q biosynthesis and growth on non-fermentable carbon sources, however its exact function in this pathway is not known. Here we probe the functional roles of Coq4p in a yeast Q biosynthetic polypeptide complex. A yeast coq4-1 mutant harboring an E226K substitution is unable to grow on nonfermentable carbon sources. The coq4-1 yeast mutant retains significant Coq3p O-methyltransferase activity, and mitochondria isolated from coq4-1 and coq4-2 (E(121)K) yeast point mutants contain normal steady state levels of Coq polypeptides, unlike the decreased levels of Coq polypeptides generally found in strains harboring coq gene deletions. Digitonin-solubilized mitochondrial extracts prepared from yeast coq4 point mutants show that Coq3p and Coq4 polypeptides no longer co-migrate as high molecular mass complexes by one- and two-dimensional Blue Native-PAGE. Similarly, gel filtration chromatography confirms that O-methyltransferase activity, Coq3p, Coq4p, and Coq7p migration are disorganized in the coq4-1 mutant mitochondria. The data suggest that Coq4p plays an essential role in organizing a Coq enzyme complex required for Q biosynthesis.
authors.affiliation: Department of Chemistry and Biochemistry and the Molecular Biology Institute, University of California, Los Angeles, CA 90095-1569, USA.
authors.forename: Beth
authors.initials: B
authors.lastname: Marbois
authors.forename: Peter
authors.initials: P
authors.lastname: Gin
authors.forename: Melissa
authors.initials: M
authors.lastname: Gulmezian
authors.forename: Catherine F
authors.initials: CF
authors.lastname: Clarke
mesh_terms: D000595:Amino Acid Sequence; D008780:Methyltransferases / Q000378:metabolism; D024101:Mitochondrial Proteins / Q000235:genetics / Q000502:physiology*; D008969:Molecular Sequence Data; D017354:Point Mutation; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000502:physiology*; D016415:Sequence Alignment; D014451:Ubiquinone / Q000096:biosynthesis*
chemical_list: C433869:COQ4 protein, S cerevisiae; D024101:Mitochondrial Proteins; D029701:Saccharomyces cerevisiae Proteins; D014451:Ubiquinone; D008780:Methyltransferases; C070696:3,4-dihydroxy-5-hexaprenylbenzoate methyltransferase