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

Background: Yeast synthesizes coenzyme Q via a macromolecular protein complex. Results: The Q biosynthetic complex includes Coq8 and the uncharacterized protein YLR290C; the ylr290cΔ mutant exhibits impaired Q synthesis. Conclusion: YLR290C (Coq11) is a novel protein required for efficient yeast Q biosynthesis. Significance: Discovery and characterization of yeast Coq biosynthetic proteins leads to an improved understanding of coenzyme Q biosynthesis and regulation. Coenzyme Q (Q or ubiquinone) is a redox active lipid composed of a fully substituted benzoquinone ring and a polyisoprenoid tail and is required for mitochondrial electron transport. In the yeast Saccharomyces cerevisiae, Q is synthesized by the products of 11 known genes, COQ1–COQ9, YAH1, and ARH1. The function of some of the Coq proteins remains unknown, and several steps in the Q biosynthetic pathway are not fully characterized. Several of the Coq proteins are associated in a macromolecular complex on the matrix face of the inner mitochondrial membrane, and this complex is required for efficient Q synthesis. Here, we further characterize this complex via immunoblotting and proteomic analysis of tandem affinity-purified tagged Coq proteins. We show that Coq8, a putative kinase required for the stability of the Q biosynthetic complex, is associated with a Coq6-containing complex. Additionally Q6 and late stage Q biosynthetic intermediates were also found to co-purify with the complex. A mitochondrial protein of unknown function, encoded by the YLR290C open reading frame, is also identified as a constituent of the complex and is shown to be required for efficient de novo Q biosynthesis. Given its effect on Q synthesis and its association with the biosynthetic complex, we propose that the open reading frame YLR290C be designated COQ11.