Structural and Molecular Basis of the Catalytic Mechanism of Geranyl Pyrophosphate C-6 Methyltransferase: Creation of an Unprecedented Farnesyl Pyrophosphate C-6 Methyltransferase.

Prenyl pyrophosphate methyltransferases enhance the structural diversity of terpenoids. However, the molecular basis of their catalytic mechanisms is poorly understood. Here, using multiple strategies, we characterized a geranyl pyrophosphate (GPP) C-6-methyltransferase, BezA. Biochemical analysis revealed that BezA requires Mg 2+ and solely methylates GPP. The crystal structures of BezA and its complex with S -adenosyl homocysteine were solved at 2.10 A and 3.00 A, respectively. Further analyses using site-directed mutagenesis, molecular docking, molecular dynamics simulations, and quantum mechanics/molecular mechanics calculations revealed the molecular basis of the methylation reaction. Importantly, the function of E170 as a catalytic base to complete the methylation reaction was established. We also succeeded in switching the substrate specificity by introducing a W210A substitution, resulting in an unprecedented farnesyl pyrophosphate C-6 methyltransferase.