Thesis presented October 29, 2012
Abstract:
Coenzyme Q (ubiquinone or Q) is a lipophilic organic molecule composed of a substituted benzoquinone and a polyisoprenyl chain containing 6 units in
Saccharomyces cerevisiae (Q6), 8 in
Escherichia coli (Q8) and 10 in humans (Q10). Q has a well known role as an electron carrier in the mitochondrial respiratory chain and also functions as a membrane soluble antioxidant. Primary Q10 deficiency has now been linked to mutations in six genes of Q biosynthesis and results in severe pathologies. The biosynthesis of Q is mitochondrial and requires at least nine proteins in yeast (Coq1-Coq9). 4-hydroxybenzoate (4-HB) and para-aminobenzoic acid (pABA) are the long-known aromatic precursors of the benzoquinone ring of Q. Despite intensive research efforts and the biological importance of Q, some biosynthetic steps are still uncharacterized. Herein we report that Coq6, a predicted flavin-dependent monooxygenase, is involved exclusively in the C5-hydroxylation reaction. We also demonstrate that the overexpression of the protein Coq8, which is proposed to be a kinase, in Δcoq strains restores steady state levels of the unstable Coq proteins. Moreover, we provide evidence that the kinase activity is essential for the stabilizing effect of Coq8 in the Δ<coq strains. The overexpression of Coq8 helped us clarify the role of some proteins (Coq4, Coq9). We also show that using synthetic analogues of 4-HB and pABA allows bypassing deficient biosynthetic steps in some mutants. This result opens new perspectives to address the deficiencies in coenzyme Q which until now are processed by Q supplementation. Finally, the deamination reaction, which is essential for Q6 biosynthesis from pABA remains misunderstood but our results strongly suggest the involvement of Coq6 in this step.
Keywords:
Coenzyme Q, Coq6, Coq8,
Saccharomyces cerevisiae, mitochondria, respiration
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