An Enzyme Catalyzing O‐Prenylation of the Glucose Moiety of Fusicoccin A, a Diterpene Glucoside Produced by the Fungus Phomopsis amygdali

Isoprenoids form the largest family of compounds found in nature. Isoprenoids are often attached to other moieties such as aromatic compounds, indoles/tryptophan, and flavonoids. These reactions are catalyzed by three phylogenetically distinct prenyltransferases: soluble aromatic prenyltransferases identified mainly in actinobacteria, soluble indole prenyltransferases mostly in fungi, and membrane‐bound prenyltransferases in various organisms. Fusicoccin A (FC A) is a diterpene glycoside produced by the plant‐pathogenic fungus Phomopsis amygdali and has a unique O‐prenylated glucose moiety. In this study, we identified for the first time, from a genome database of P. amygdali , a gene ( papt ) encoding a prenyltransferase that reversibly transfers dimethylallyl diphosphate (DMAPP) to the 6′‐hydroxy group of the glucose moiety of FC A to yield an O‐prenylated sugar. An in vitro assay with a recombinant enzyme was also developed. Detailed analyses with recombinant PAPT showed that the enzyme is likely to be a monomer and requires no divalent cations. The optimum pH and temperature were 8.0 and 50 °C, respectively. K m values were calculated as 0.49±0.037 μ M for FC P (a plausible intermediate of FC A biosynthesis) and 8.3±0.63 μ M for DMAPP, with a k cat of 55.3±3.3×10 −3 s. The enzyme did not act on representative substrates of the above‐mentioned three types of prenyltransferase, but showed a weak transfer activity of geranyl diphosphate to FC P.