title: Isolation and functional expression of human COQ3, a gene encoding a methyltransferase required for ubiquinone biosynthesis.
abstract: The COQ3 gene in Saccharomyces cerevisiae encodes an O-methyltransferase required for two steps in the biosynthetic pathway of ubiquinone (coenzyme Q, or Q). This enzyme methylates an early Q intermediate, 3,4-dihydroxy-5-polyprenylbenzoic acid, as well as the final intermediate in the pathway, converting demethyl-Q to Q. This enzyme is also capable of methylating the distinct prokaryotic early intermediate 2-hydroxy-6-polyprenyl phenol. A full-length cDNA encoding the human homologue of COQ3 was isolated from a human heart cDNA library by sequence homology to rat Coq3. The clone contained a 933-base pair open reading frame that encoded a polypeptide with a great deal of sequence identity to a variety of eukaryotic and prokaryotic Coq3 homologues. In the region between amino acids 89 and 255 in the human sequence, the rat and human homologues are 87% identical, whereas human and yeast are 35% identical. When expressed in multicopy, the human construct rescued the growth of a yeast coq3 null mutant on a nonfermentable carbon source and restored coenzyme Q biosynthesis, although at lower levels than that of wild type yeast. In vitro methyltransferase assays using farnesylated analogues of intermediates in the coenzyme Q biosynthetic pathway as substrates showed that the human enzyme is active with all three substrates tested.
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, USA.
authors.forename: T
authors.initials: T
authors.lastname: Jonassen
authors.forename: C F
authors.initials: CF
authors.lastname: Clarke
mesh_terms: D000375:Aging; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002394:Catechol O-Methyltransferase / Q000737:chemistry; D002851:Chromatography, High Pressure Liquid; D018076:DNA, Complementary / Q000235:genetics; D015723:Gene Library; D006801:Humans; D008780:Methyltransferases / Q000235:genetics* / Q000378:metabolism*; D008956:Models, Chemical; D008969:Molecular Sequence Data; D009154:Mutation; D009206:Myocardium / Q000201:enzymology; D051381:Rats; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D017386:Sequence Homology, Amino Acid; D013997:Time Factors; D014451:Ubiquinone / Q000096:biosynthesis* / Q000378:metabolism
chemical_list: D018076:DNA, Complementary; D014451:Ubiquinone; D008780:Methyltransferases; C070696:3,4-dihydroxy-5-hexaprenylbenzoate methyltransferase; D002394:Catechol O-Methyltransferase