A New Group of Aromatic Prenyltransferases in Fungi, Catalyzing a 2,7-Dihydroxynaphthalene 3-Dimethylallyl-transferase Reaction

Five fungal genomes from the Ascomycota (sac fungi) were found to contain a gene with sequence similarity to a recently discovered small group of bacterial prenyltransferases that catalyze the C-prenylation of aromatic substrates in secondary metabolism. The genes from Aspergillus terreus NIH2624, Botryotinia fuckeliana B05.10 and Sclerotinia sclerotiorum 1980 were expressed in Escherichia coli, and the resulting His(8)-tagged proteins were purified and investigated biochemically. Their substrate specificity was found to be different from that of any other prenyltransferase investigated previously. Using 2,7-dihydroxynaphthalene (2,7-DHN) and dimethylallyl diphosphate as substrates, they catalyzed a regiospecific Friedel-Crafts alkylation of 2,7-DHN at position 3. Using the enzyme of A. terreus, the Km values for 2,7-DHN and dimethylallyl diphosphate were determined as 324 +/- 25 mu M and 325 +/- 35 mu M, respectively, and k(cat) as 0.026 +/- 0.001 s(-1). A significantly lower level of prenylation activity was found using dihydrophenazine-1-carboxylic acid as aromatic substrate, and only traces of products were detected with aspulvinone E, flaviolin, or 4-hydroxybenzoic acid. No product was formed with L-tryptophan, L-tyrosine, or 4-hydroxyphenylpyruvate. The genes for these fungal prenyltransferases are not located within recognizable secondary metabolic gene clusters. Their physiological function is yet unknown.