Overexpression of the Coq8 Kinase in Saccharomyces cerevisiae coq Null Mutants Allows for Accumulation of Diagnostic Intermediates of the Coenzyme Q6 Biosynthetic Pathway

Most of the Coq proteins involved in coenzyme Q (ubiquinone or Q) biosynthesis are interdependent within a multiprotein complex in the yeast Saccharomyces cerevisiae . Lack of only one Coq polypeptide, as in Δ coq strains, results in the degradation of several Coq proteins. Consequently, Δ coq strains accumulate the same early intermediate of the Q 6 biosynthetic pathway; this intermediate is therefore not informative about the deficient biosynthetic step in a particular Δ coq strain. In this work, we report that the overexpression of the protein Coq8 in Δ coq strains restores steady state levels of the unstable Coq proteins. Coq8 has been proposed to be a kinase, and we provide evidence that the kinase activity is essential for the stabilizing effect of Coq8 in the Δ coq strains. This stabilization results in the accumulation of several novel Q 6 biosynthetic intermediates. These Q intermediates identify chemical steps impaired in cells lacking Coq4 and Coq9 polypeptides, for which no function has been established to date. Several of the new intermediates contain a C4-amine and provide information on the deamination reaction that takes place when para -aminobenzoic acid is used as a ring precursor of Q 6 . Finally, we used synthetic analogues of 4-hydroxybenzoic acid to bypass deficient biosynthetic steps, and we show here that 2,4-dihydroxybenzoic acid is able to restore Q 6 biosynthesis and respiratory growth in a Δ coq7 strain overexpressing Coq8. The overexpression of Coq8 and the use of 4-hydroxybenzoic acid analogues represent innovative tools to elucidate the Q biosynthetic pathway. Background: Several steps of eukaryotic coenzyme Q biosynthesis are still in question. Results: Yeast coq null mutants overexpressing the Coq8 kinase have stable Coq polypeptides and accumulate new Q intermediates that help diagnose the blocked step. Conclusion: New functions for Coq polypeptides are proposed. Significance: Identification of the blocked step allows for the use of alternate ring precursors that rescue Q biosynthesis in some mutants.