S. cerevisiae coq5 null mutants require over‐expression of Coq8 kinase for rescue by E. coli COQ5 homolog ubiE

Abstract

Coenzyme Q (Ubiquinone or Q) is an essential lipid electron carrier in the respiratory electron chain. In Saccharomyces cerevisiae, eleven genes (COQ1–9, ARH1, YAH1) are required for coenzyme Q biosynthesis, several of which encode proteins involved in a multi‐subunit complex. One of these genes, COQ5, encodes a C‐methyltransferase responsible for making the late stage intermediate demethoxy Q6 (DMQ6). COQ5 has three conserved methyltransferase motifs, and yeast point mutants within or adjacent to these motifs (coq5–2, coq5–5) lack Coq5 activity but retain steady state levels of the Coq5 polypeptide. We show that ubiE, the E. coli homolog for COQ5, is able to rescue coq5–2 and coq5–5 point mutants, but is unable able to rescue the yeast coq5Δ null mutant. However when putative kinase Coq8 is over‐expressed, ubiE is able to rescue the yeast COQ5 knockout. We demonstrate that co‐expression of COQ8 and ubiE in a coq5Δ null mutant restores Q6 levels and supports growth on non‐fermentable carbon sources. We also show the effects of complementation on the Coq multi‐subunit complex in the coq5 mutants via 2D Blue native‐PAGE. By observing the accumulation of Q intermediates in coq5 mutants, we have been able to elucidate steps within a novel Q biosynthetic pathway.Studies supported by National Science Foundation Grant 0919609.