Yeast Coq9 controls deamination of coenzyme Q intermediates that derive from para-aminobenzoic acid

Coq9 is a polypeptide subunit in a mitochondrial multi-subunit complex, termed the CoQ-synthome, required for biosynthesis of coenzyme Q (ubiquinone or Q). Deletion of COQ9 results in dissociation of the CoQ-synthome, but over-expression of Coq8 putative kinase stabilizes the CoQ-synthome in the coq9 null mutant and leads to the accumulation of two nitrogen containing Q-intermediates, imino-demethoxy-Q(6) (IDMQ(6)) and 3-hexaprenyl-4-aminophenol (4-AP) when para-aminobenzoic acid (pABA) is provided as a ring precursor. To investigate whether Coq9 is responsible for deamination steps in Q biosynthesis, we utilized the yeast coq5-5 point mutant. The yeast coq5-5 point mutant is defective in the C-methyltransferase step of Q biosynthesis, but retains normal steady-state levels of the Coq5 polypeptide. Here we show that when high amounts of (13)C(6)-pABA are provided, the coq5-5 mutant accumulates both (13)C(6)-imino-demethyl-demethoxy-Q(6) ((13)C(6)-IDDMQ(6)) and demethyl-demethoxy-Q(6) ((13)C(6)-DDMQ(6)). Deletion of COQ9 in the yeast coq5-5 mutant along with Coq8 over-expression and (13)C(6)-pABA labeling leads to the absence of (13)C(6)-DDMQ(6), and the nitrogen-containing intermediates (13)C(6)-4-AP and (13)C(6)-IDDMQ(6) persist. We describe a coq9 temperature sensitive mutant and show that at the non-permissive temperature, steady state polypeptide levels of Coq9-ts19 increased, while Coq4, Coq5, Coq6, and Coq7 decreased. The coq9-ts19 mutant had decreased Q(6) content and increased levels of nitrogen-containing intermediates. These findings identify Coq9 as a multi-functional protein that is required for the function of Coq6 and Coq7 hydroxylases, for removal of the nitrogen substituent from pABA-derived Q-intermediates, and is an essential component of the CoQ synthome