Regiospecificities and prenylation mode specificities of the fungal indole diterpene prenyltransferases AtmD and PaxD.

We recently reported the function of paxD, which is involved in the paxilline (compound 1) biosynthetic gene cluster in Penicillium paxilli. Recombinant PaxD catalyzed a stepwise regular-type diprenylation at the 21 and 22 positions of compound 1 with dimethylallyl diphosphate (DMAPP) as the prenyl donor. In this study, atmD, which is located in the aflatrem (compound 2) biosynthetic gene cluster in Aspergillus flavus and encodes an enzyme with 32% amino acid identity to PaxD, was characterized using recombinant enzyme. When compound 1 and DMAPP were used as substrates, two major products and a trace of minor product were formed. The structures of the two major products were determined to be reversely monoprenylated compound 1 at either the 20 or 21 position. Because compound 2 and β-aflatrem (compound 3), both of which are compound 1-related compounds produced by A. flavus, have the same prenyl moiety at the 20 and 21 position, respectively, AtmD should catalyze the prenylation in compound 2 and 3 biosynthesis. More importantly and surprisingly, AtmD accepted paspaline (compound 4), which is an intermediate of compound 1 biosynthesis that has a structure similar to that of compound 1, and catalyzed a regular monoprenylation of compound 4 at either the 21 or 22 position, though the reverse prenylation was observed with compound 1. This suggests that fungal indole diterpene prenyltransferases have the potential to alter their position and regular/reverse specificities for prenylation and could be applicable for the synthesis of industrially useful compounds.