Hydroxylation of demethoxy-Q6 constitutes a control point in yeast coenzyme Q6 biosynthesis

Abstract

Coenzyme Q is a lipid molecule required for respiration and antioxidant protection. Q biosynthesis in Saccharomyces cerevisiae requires nine proteins (Coq1p-Coq9p). We demonstrate in this study that Q levels are modulated during growth by its conversion from demethoxy-Q (DMQ), a late intermediate. Similar conversion was produced when cells were subjected to oxidative stress conditions. Changes in Q 6 /DMQ 6 ratio were accompanied by changes in COQ7 gene mRNA levels encoding the protein responsible for the DMQ hydroxylation, the penultimate step in Q biosynthesis pathway. Yeast coq null mutant failed to accumulate any Q late biosynthetic intermediate. However, in coq7 mutants the addition of exogenous Q produces the DMQ synthesis. Similar effect was produced by over-expressing ABC1/COQ8. These results support the existence of a biosynthetic complex that allows the DMQ 6 accumulation and suggest that Coq7p is a control point for the Q biosynthesis regulation in yeast.

Coenzyme Q supplementation or Over-Expression of the Yeast Coq8 Putative Kinase Stabilizes Multi-Subunit Coq Polypeptide Complexes in Yeast Coq Null Mutants

“…Upon the addition of Q 6 , the coq3, coq4, coq6, coq7 and coq9 null mutants accumulate distinct hexaprenyl Q-intermediates and/or show increased steady-state levels of one or more of the indicator Coq polypeptides (Figs 8-11 and Table 3). These findings confirm and extend previous studies showing that addition of exogenous Q 6 restored de novo synthesis of DMQ 6 and increased steady-state levels of the Coq4 polypeptide in a coq7 null mutant [23,34]. These results indicate that Q 6 itself may interact with certain Coq polypeptides and enhance formation of later Q-intermediates.…”

“…It was shown that DMQ 6 co-elutes with Coq3 O-methyltransferase activity and high molecular mass Coq polypeptide complexes during size exclusion chromatography of digitonin extracts of mitochondria [18]. Yeast coq7 null mutants cultured in the presence of exogenous Q 6 were able to synthesize DMQ 6 , and steady-state levels of Coq4 polypeptides were restored, indicating that the presence of Q 6 itself may stabilize the Coq polypeptide complexes [23,34]. Over-expression of Coq8 has no effect on either the coq1 or coq2 null mutants [17], which lack the ability to synthesize polyisoprenylated ring intermediates.…”

Identification of Coq11, a New Coenzyme Q Biosynthetic Protein in the CoQ-Synthome in Saccharomyces cerevisiae

“…Co-precipitation experiments have demonstrated the physical association of several of the Coq proteins; biotinylated Coq3 was shown to co-precipitate Coq4 and HA-tagged Coq9 co-purified Coq4, Coq5, Coq6, and Coq7 (21,25). Although Coq8 has not been shown to be associated in a complex with the other Coq proteins, its putative role as a kinase is important for the stability of several other Coq proteins because overexpression of COQ8 in various coq⌬ mutants stabilizes several of the other Coq proteins, as well as multisubunit Coq polypeptide complexes, and leads to the accumulation of later stage Q biosynthetic intermediates diagnostic of the mutated step (20,28,29).…”

“…Analysis of gel filtration fractions has also shown the association of demethoxy-Q 6 (DMQ 6 ) with the complexes (25). Supplementation of exogenous Q 6 was shown to stabilize the steady-state levels of Coq3 and Coq4 in the coq7⌬ mutant (27), enhance DMQ 6 production in the coq7⌬ mutant (29), and stabilize steady-state levels of Coq9 in the coq3⌬, coq4⌬, coq6⌬, coq7⌬ mutants and steady-state levels of Coq4 in the coq3⌬, coq6⌬, and coq7⌬ mutants (28), suggesting that associated Q 6 plays a role in the stability of the complex.…”

RNA-binding proteins regulate cell respiration and coenzyme Q biosynthesis by post-transcriptional regulation ofCOQ7

“…21 COQ7 enzyme activity is the only step in CoQ biosynthesis in which the non-reactive intermediate demethoxyubiquinone is accumulated by either nutritional limitations or mutant strains, and it is proposed to be a key step in this pathway. 41,42 Recently, it has been described that Clu1/CluA homolog (CLUH) encodes for mRNA binding protein that bound to hundreds of mRNAs encoding mitochondrial-directed proteins, including COQ3 and COQ6 mRNAs although there is not demonstration of its role in their stability and/or translation. 43 COQ7 mRNA was included as a putative target of HuR, 24 and thus we focused on COQ7 mRNA interaction with RBPs as a novel posttranscriptional regulatory mechanism of CoQ biosynthesis.…”