P106: Aromatic prenyltransferases of Ascomycota catalysing a 2,7-dihydroxynaphthalene 3-dimethylallyl-transferase reaction

Aromatic prenyltransferases transfer prenyl moieties onto aromatic acceptor molecules, catalyzing an electrophilic substitution of the aromatic ring under formation of carbon–carbon bonds. Several Ascomycota (sac fungi) including A. terreus were now found to contain a gene with sequence similarity to a recently discovered small group of bacterial prenyltransferases which catalyse 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 E. coli and the resulting His₈-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 (DMAPP) as substrates, they catalysed a regiospecific Friedel-Crafts alkylation of 2,7-DHN at position 3. Using the enzyme of A. terreus, the K_m values for 2,7-DHN and DMAPP were determined as 324 ± 25 µM and 325 ± 35 µM, respectively, and k_cat as 0.026 ± 0.001 s^-1. No product was formed with L-tryptophan, L-tyrosine or 4-hydroxyphenylpyruvate. The genes for these fungal prenyltransferases are not located within recognisable secondary metabolic gene clusters, and their physiological function is yet unknown. These prenyltransferases are soluble biocatalysts which can easily be obtained as homogeneous proteins in significant amounts. Bioinformatic predictions suggest that their threedimensional structure is characterized by the so called PT fold. The enzymes of this family represent attractive tools for the chemoenzymatic synthesis of bioactive molecules.