Yeast coq null mutants harboring multi‐copy COQ8 accumulate novel intermediates in coenzyme Q biosynthesis

Abstract

Coenzyme Q (ubiquinone or Q) is a lipid electron carrier in the electron transport chain. In yeast Saccharomyces cerevisiae nine genes, designated COQ1 through COQ9, have been identified as being required for Q biosynthesis. Deletion of any one of the nine COQ genes leads to decreased steady state levels of other Coq polypeptides, including Coq4, Coq6, Coq7, and Coq9 (Hsieh et al., 2007). In this study, we find overexpression of Coq8p in certain coq null mutants restores steady state level of Coq4p, Coq7p and Coq9p; suggesting Coq8p facilitates the stabilization of the high molecular weight Coq polypeptide complex. Six of the coq null mutants (coq3 – coq9) accumulate early Q‐intermediates such as 3‐hexaprenyl‐4‐amino‐benzoic acid (prenyl‐PABA) and 3‐hexaprenyl‐4‐hydroxy‐benzoic acid (HHB) (Marbois et al., 2010). Here, we utilize liquid chromatography and mass spectrometry (LC‐MS/MS), and show that certain coq null mutants harboring multi‐copy COQ8 now accumulate late stage Q‐intermediates. For example, demethyl‐demethoxy‐Q6 was found in a yeast coq5 null mutant harboring multi‐copy COQ8. We suggest that over‐expression of Coq8 facilitates the assembly of and/or stabilizes the Coq polypeptide complex, allowing the synthesis of Q‐intermediates that can be diagnostic of the blocked step in the corresponding coq null) mutant.