Over-expression of ICE2 stabilizes cytochrome P450 reductase in Saccharomyces cerevisiae and Pichia pastoris

Membrane-anchored cytochrome P450 enzymes (CYPs) are a versatile and interesting class of enzymes for industrial applications, as they are capable of regio- and stereoselectively hydroxylating hydrophobic molecules. However, CYP activity requires sufficient levels of suitable cytochrome P450 reductases (CPRs) for regeneration of catalytic capacity, which is a bottleneck in many industrial applications. Searching for positive effectors of membrane-anchored CYP/CPR function, we transformed and screened selected strains from a Saccharomyces cerevisiae knockout collection for Hyoscyamus muticus premnaspirodiene oxygenase (HPO; CYP) and Arabidopsis thaliana CPR (AtCPR) expression levels, as well as for activity towards (+)-valencene. We found that in cells lacking the type III membrane protein Ice2p, AtCPR was destabilized. Remarkably, over-expression of ICE2 improved (+)-valencene hydroxylation to trans-nootkatol by 40-50%, both in resting cells and in vivo. Time-resolved immunoblot analysis and cytochrome c reductase activity assays revealed that Ice2 up-regulation stabilized AtCPR levels and activity over extended periods of bioconversion. To underscore that we had identified a novel positive effector of recombinant CYP/CPR function, we confirmed the beneficial effect of ICE2 over-expression for two further CYP/CPR combinations and the alternative host Pichia pastoris. Thus, we propose Ice2 up-regulation as a general tool for improving the applications of recombinant CYPs in yeasts.