Substitution of Two Active-Site Residues Alters C9-Hydroxylation in a Class II Diterpene Synthase.

Diterpenes form a vast and diverse class of natural products of both ecological and economic importance. Class II diterpene synthase (diTPS) enzymes control the committed biosynthetic reactions underlying diterpene chemical diversity. Homology modelling with site-directed mutagenesis identified two active-site residues in the horehound (Marrubium vulgare) class II diTPS peregrinol diphosphate synthase (MvCPS1); residue substitutions abolished the unique MvCPS1-catalysed water-capture reaction at C9 and redirected enzyme activity toward formation of an alternative product, halima-5(10),13-dienyl diphosphate. These findings contributed new insight into the steric interactions that govern diTPS-catalysed regiospecific oxygenation reactions and highlight the feasibility of diTPS engineering to provide a broader spectrum of bioactive diterpene natural products.