AstPT catalyses both reverse N1- and regular C2 prenylation of a methylated bisindolyl benzoquinone

Prenylated bisindolyl benzoquinones exhibit interesting biological activities, such as antidiabetic or anti-HIV activities. A number of these compounds, including asterriquinones, have been isolated from Aspergillus terreus. In this study, we identified two putative genes by genome mining, ATEG_09980 and ATEG_00702, which share high sequence similarity with the known bisindolyl benzoquinone prenyltransferase TdiB from Aspergillus nidulans. The coding sequences were cloned and overexpressed in E. coli. The overproduced recombinant proteins were purified to near homogeneity and used for enzyme assays with asterriquinone D in the presence of dimethylallyl diphosphate. HPLC analysis showed that product formation was only detected in enzyme assays with EAU29429 encoded by ATEG_09980, not in those with EAU39348 encoded by ATEG_00702. Product isolation and structure elucidation by NMR and MS analyses led to identification of N1-reversely and C2-regularly monoprenylated derivatives, as well as N1',N1''reversely, N1'-reversely, C2''-regularly diprenylated derivatives. This proved that EAU29429 functions as an asterriquinone prenyltransferase (AstPT) and indicated the involvement of EAU29429 rather than EAU39348 in the biosynthesis of methylated asterriquinones. Furthermore, incubation of monoprenylated enzyme products with AstPT resulted in the formation of the diprenylated derivatives.