Engineering of (−)‐Limonene‐3‐Hydroxylase to Enhance Its Regioselectivity for Biosynthesis of (−)‐Menthol

Abstract There is high market demand for (−)‐menthol because of its unique aroma and cooling properties. The first bottleneck encountered in the biosynthesis of (−)‐menthol in Escherichia coli is the low hydroxylation efficiency of (−)‐limonene‐3‐hydroxylase. Few known enzymes can hydroxylate the third carbon atom of (−)‐limonene. In this work, initially, we searched for new enzymes and screened a library of cytochrome P450BM3 variants aiming to improve catalysis of this reaction, but did not identify any variants with improved activity or regioselectivity. Then, through protein engineering of a cytochrome P450 monooxygenase variant from Pseudomonas putida ( Pp cam Y96F/V247L ), we obtained variant Pp cam F87W/Y96F/L244I/V247L/V396A with regioselectivity of 93% (starting from 70%) toward (−)‐limonene without losing activity. Because of the improvement in regioselectivity, its turnover number was 1.5 times that of the starting enzyme. We analyzed the reasons for the improvement through molecular dynamics simulations. The new variant also exhibited 95% regioselectivity toward (+)‐limonene. This enzyme variant can be applied in biosynthesis of (−)‐menthol.