Production of Coenzyme Q10 in Recombinant Schizosaccharomyces Pombe through Metabolic Engineering Approaches

Abstract

Coenzyme Q10 is an important cofactor in the electron transport chain, which powers oxidative phosphorylation. Similar to other cofactors such as vitamin B12, deficiency in coenzyme Q10 (CoQ) manifests as clinical symptoms. Hence, coenzyme Q10 can be used as a health supplement. But, difficulty in extracting it from natural sources and the high cost involved explains continuing interest in improving its production titer in various cellular hosts. A metabolic cofactor, and thus naturally of low cellular abundance, various genetic engineering approaches are explored for improving its concentration in heterologous hosts ranging from Escherichia coli to Schizosaccharomyces pombe. While the native pathway for CoQ biosynthesis feeds into that of cholesterol, and is conserved across the three domains of life, slight variation in pathway architecture exists. Specifically, some segments of the pathway are truncated for improving overall metabolic efficiency in hosts. Hence, choice of organisms as production host for CoQ10 is crucial and these typically exhibit high growth rates with ease for genetic manipulation such as heterologous expression of missing pathway genes. Whole cell metabolomics profiled by high performance liquid chromatography tandem mass spectrometry (HPLC- MS/MS) coupled with metabolic flux analysis (MFA) and metabolic flux control (MCA), points to specific metabolic choke points where enhanced expression of enzyme increase the cellular concentration of important precursors and the final coenzyme product. One such choke point is the rate limiting enzyme, HMG-CoA reductase, whose over-expression improves CoQ titer. Systematic exploration of how fermentation parameters affect production yield is another important approach given myriad problems and challenges affecting the industrial use of recombinant CoQ production hosts. But CoQ production by recombinant routes usually results in CoQ of different side chain lengths; thus, efforts are directed towards tunable control of CoQ side chain moiety from the metabolic engineering perspective, which improves product quality and pharmaceutical properties. Another interesting basic science angle involves the conjugation of different cell localization signals for probing subcellular localization of CoQ. Finally, RNA interference (RNAi) mediated modulation of CoQ expression is a useful tool for indirectly assessing cellular energy state and redox balance, which opens up its use in studies examining how energy status affect physiological response to various nutrition and environment stressors. Collectively, much effort has focused on improving CoQ yield through metabolic engineering, and effecting tunable control of side chain length. However, important questions remain on understanding the subcellular localization of CoQ and examining the utility of tuning CoQ expression level for affecting cellular energy level, and its use as a physiology probe.