Analyzing and Engineering the Product Selectivity of a 2-Methylenebornane Synthase

Terpenes constitute the largest class of natural products with more than 70 000 compounds. Many different terpenes find applications in the flavor and fragrance industry or can be used as fine chemicals or drugs. In some bacteria, noncanonical terpenes with 11 carbon atoms are synthesized via a GPP-C2-methyltransferase and the subsequent conversion of 2-methyl-GPP by certain terpene synthases into mainly 2-methylisoborneol and 2-methylenebornane. Many other C₁₁-terpenes were reported as side products, but they are synthesized only in minor amounts by the bacterial C₁₁-terpene biosynthesis pathway. To enable biotechnological synthesis of these largely unexplored natural products, we changed the product selectivity of the 2-methylenebornane synthase from Pseudomonas fluorescens by a semirational protein engineering approach. Active site amino acids with impact on the product selectivity were identified and variants with completely altered product spectra could be identified and characterized. The gathered data provide new insights into the structure-function relationship for C₁₁-terpene synthases and demonstrate the production of formerly inaccessible noncanonical terpenes.