“Head‐to‐Middle” and “Head‐to‐Tail” cis ‐Prenyl Transferases: Structure of Isosesquilavandulyl Diphosphate Synthase

Structural and Molecular Basis of the Catalytic Mechanism of Geranyl Pyrophosphate C6-Methyltransferase: Creation of an Unprecedented Farnesyl Pyrophosphate C6-Methyltransferase

Prenyl pyrophosphate methyltransferases enhance the structural diversity of terpenoids. However, the molecular basis of their catalytic mechanisms is poorly understood. In this study, using multiple strategies, we characterized a geranyl pyrophosphate (GPP) C6-methyltransferase, BezA. Biochemical analysis revealed that BezA requires Mg²⁺ and solely methylates GPP. The crystal structures of BezA and its complex with S-adenosyl homocysteine were solved at 2.10 and 2.56 Å, 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 C6-methyltransferase.

Structure, catalysis, and inhibition mechanism of prenyltransferase

Isoprenoids, also known as terpenes or terpenoids, represent a large family of natural products composed of five‐carbon isopentenyl diphosphate or its isomer dimethylallyl diphosphate as the building blocks. Isoprenoids are structurally and functionally diverse and include dolichols, steroid hormones, carotenoids, retinoids, aromatic metabolites, the isoprenoid side‐chain of ubiquinone, and isoprenoid attached signaling proteins. Productions of isoprenoids are catalyzed by a group of enzymes known as prenyltransferases, such as farnesyltransferases, geranylgeranyltransferases, terpenoid cyclase, squalene synthase, aromatic prenyltransferase, and cis‐ and trans‐prenyltransferases. Because these enzymes are key in cellular processes and metabolic pathways, they are expected to be potential targets in new drug discovery. In this review, six distinct subsets of characterized prenyltransferases are structurally and mechanistically classified, including (1) head‐to‐tail prenyl synthase, (2) head‐to‐head prenyl synthase, (3) head‐to‐middle prenyl synthase, (4) terpenoid cyclase, (5) aromatic prenyltransferase, and (6) protein prenylation. Inhibitors of those enzymes for potential therapies against several diseases are discussed. Lastly, recent results on the structures of integral membrane enzyme, undecaprenyl pyrophosphate phosphatase, are also discussed.

Chimeric Terpene Synthases Possessing both Terpene Cyclization and Prenyltransfer Activities

Prenyltransferase (PT) and terpene synthase (TPS) are key enzymes in the formation of the basic carbon skeletons of terpenoids. The PTs determine the prenyl carbon chain length, whereas TPSs generate the structural complexity of the molecular scaffolds, forming various ring structures. Normally, PTs and TPSs are separate, independent enzymes. However, in 2007, a chimeric enzyme, in which the PT was fused with the TPS, was found in a fungus. Recent studies have revealed that such chimeric TPSs are widely distributed in fungi and function in the biosyntheses of various terpene natural products, including sesterterpenes, which are a relatively rare group of terpenoids. This review summarizes the accumulated knowledge of these recently discovered, unique, chimeric TPSs.