Yeast and rat Coq3 and Escherichia coli UbiG polypeptides catalyze both O-methyltransferase steps in coenzyme Q biosynthesis.
Ubiquinone (coenzyme Q or Q) is a lipid that functions in the electron transport chain in the inner mitochondrial membrane of eukaryotes and the plasma membrane of prokaryotes. Q-deficient mutants of Saccharomyces cerevisiae harbor defects in one of eight COQ genes (coq1-coq8) and are unable to grow on nonfermentable carbon sources. The biosynthesis of Q involves two separate O-methylation steps. In yeast, the first O-methylation utilizes 3, 4-dihydroxy-5-hexaprenylbenzoic acid as a substrate and is thought to be catalyzed by Coq3p, a 32.7-kDa protein that is 40% identical to the Escherichia coli O-methyltransferase, UbiG. In this study, farnesylated analogs corresponding to the second O-methylation step, demethyl-Q(3) and Q(3), have been chemically synthesized and used to study Q biosynthesis in yeast mitochondria in vitro. Both yeast and rat Coq3p recognize the demethyl-Q(3) precursor as a substrate. In addition, E. coli UbiGp was purified and found to catalyze both O-methylation steps. Futhermore, antibodies to yeast Coq3p were used to determine that the Coq3 polypeptide is peripherally associated with the matrix-side of the inner membrane of yeast mitochondria. The results indicate that one O-methyltransferase catalyzes both steps in Q biosynthesis in eukaryotes and prokaryotes and that Q biosynthesis is carried out within the matrix compartment of yeast mitochondria.
Poon
W W
WW
Department of Chemistry and Biochemistry and the Molecular Biology Institute, University of California, Los Angeles, California 90095, USA.
Barkovich
R J
RJ
Hsu
A Y
AY
Frankel
A
A
Lee
P T
PT
Shepherd
J N
JN
Myles
D C
DC
Clarke
C F
CF
D000818:Animals; D002851:Chromatography, High Pressure Liquid; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins; D007202:Indicators and Reagents; D008780:Methyltransferases / Q000378:metabolism*; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology*; D014451:Ubiquinone / Q000096:biosynthesis* / Q000138:chemical synthesis*
D029968:Escherichia coli Proteins; D007202:Indicators and Reagents; D011993:Recombinant Fusion Proteins; D014451:Ubiquinone; D008780:Methyltransferases; C019616:UbiG protein, E coli; C070696:3,4-dihydroxy-5-hexaprenylbenzoate methyltransferase