Regeneration of NADPH Coupled with HMG-CoA Reductase Activity Increases Squalene Synthesis in Saccharomyces cerevisiae

Although overexpression of the tHMG1 gene is a well-known strategy for terpene synthesis in Saccharomyces cerevisiae, the optimal level for tHMG1p has not been established. In the present study, it was observed that two copies of the tHMG1 gene on a dual gene expression cassette improved squalene synthesis in laboratory strain by 16.8 -fold in comparison to single-copy expression. It was also observed that tHMG1p is limited by its cofactor (NADPH), as the overexpression of NADPH regenerating genes', viz., ZWF1 and FOSS (full length and without mitochondrial presequence), has led to its increased enzyme activity. Further, it was demonstrated that overexpression of full-length POSS has improved squalene synthesis in cytosol. Finally, when tHMGI and full-length FOSS were co-overexpressed there was a net 27.5-fold increase in squalene when compared to control strain. These results suggest novel strategies to increase squalene accumulation in S. cerevisiae.