Coq7 (also known as Clk-1 and CAT5) is a di-iron carboxylate protein occuring in both prokaryotes and eukaryotes that is essential for ubiquinone biosynthesis [, ]. It has been implicated in the aging process as mutations in the Caenorhabditis elegans gene lead to increased lifespan []. Coq7 is a membrane-bound protein that functions as a monooxygenase to hydroxylate demethoxyubiquinone (DMQ or 2-methoxy-5-methyl-6-polyprenyl-1,4-benzoquinone) in the penultimate step of ubiquinone biosynthesis []. Biochemical studies indicate that NADH can serve directly as a reductant for catalytic activation of dioxygen and substrate oxidation by the enzyme, with no requirement for an additional reductase protein component []. This direct reaction with NADH is so far unique amongst members of the di-iron carboxylate protein family.
Ubiquinone biosynthesis protein Coq4 is a component of a multi-subunit COQ enzyme complex (composed of at least Coq3, Coq4, Coq5, Coq6, Coq7 and Coq9), which plays a role in the coenzyme Q (ubiquinone) biosynthetic pathway [, , ]. Coq4 plays an essential role in organising the COQ enzyme complex and is required for steady-state levels of Coq3, Coq6, Coq7 and Coq9 []. This entry represents eukaryotic Coq4.
Coq4 is a component of a multi-subunit COQ enzyme complex, which plays a role in the coenzyme Q (ubiquinone) biosynthetic pathway [, , ]. In budding yeasts, Coq4 plays an essential role in organising the COQ enzyme complex and is required for steady-state levels of Coq3, Coq6, Coq7 and Coq9 [].
This entry represents a family of FAD-dependent hydroxylases (monooxygenases), which are all believed to act in the aerobic ubiquinone biosynthesis pathway []. In Escherichia coli, three enzyme activities have been described: UbiI, UbiH and UbiF []. UbiH and UbiF are similar to one another and form the basis of this subfamily. UbiI (also known as visC) []is highly similar to UbiF, adjacent to UbiH and, when mutated, results in a phenotype similar to that of UbiH (also known as visB) []. Several other species appear to have three homologues in this family, although they assort themselves differently on phylogenetic trees (e.g. Xylella and Mesorhizobium) making it difficult to ascribe a specific activity to each one. Eukaryotes appear to have only a single homologue in this subfamily (COQ6, []) which complements UbiH, but also possess a non-orthologous gene, COQ7 which complements UbiF.
This entry represents FAD-dependent hydroxylases (monooxygenases) which are all believed to act in the aerobic ubiquinone biosynthesis pathway []. A separate set of hydroxylases, as yet undiscovered, are believed to be active under anaerobic conditions []. In Escherichia coli, three enzyme activities have been described: UbiB (which acts first at position 6, see ), UbiH (which acts at position 4, []) and UbiF (which acts at position 5, []). UbiH and UbiF are similar to one another and form the basis of this subfamily. Interestingly, E. coli contains another hydroxylase gene, called visC, that is highly similar to UbiF, adjacent to UbiH and, when mutated, results in a phenotype similar to that of UbiH (which has also been named visB) []. Several other species appear to have three homologs in this family, although they assort themselves differently on phylogenetic trees (e.g. Xylella and Mesorhizobium) making it difficult to ascribe a specific activity to each one. Eukaryotes appear to have only a single homologue in this subfamily (COQ6, []) which complements UbiH, but also possess a non-orthologous gene, COQ7 which complements UbiF.This entry represents the conserved site of the ubiquinone biosynthesis hydroxylase enzyme.
