Biochemical Characterization of Indole Prenyltransferases

The putative prenyltransferase gene ACLA_031240 belonging to the dimethylallyltryptophan synthase superfamily was identified in the genome sequence of Aspergillus clavatus and overexpressed in Escherichia coli. The soluble His-tagged protein EAW08391 was purified to near homogeneity and used for biochemical investigation with diverse aromatic substrates in the presence of different prenyl diphosphates. It has shown that in the presence of dimethylallyl diphosphate (DMAPP), the recombinant enzyme accepted very well simple indole derivatives with l-tryptophan as the best substrate. Product formation was also observed for tryptophan-containing cyclic dipeptides but with much lower conversion yields. In contrast, no product formation was detected in the reaction mixtures of l-tryptophan with geranyl or farnesyl diphosphate. Structure elucidation of the enzyme products by NMR and MS analyses proved unequivocally the highly regiospecific regular prenylation at C-5 of the indole nucleus of the simple indole derivatives. EAW08391 was therefore termed 5-dimethylallyltryptophan synthase, and it filled the last gap in the toolbox of indole prenyltransferases regarding their prenylation positions. Km values of 5-dimethylallyltryptophan synthase were determined for l-tryptophan and DMAPP at 34 and 76 μm, respectively. Average turnover number (kcat) at 1.1 s−1 was calculated from kinetic data of l-tryptophan and DMAPP. Catalytic efficiencies of 5-dimethylallyltryptophan synthase for l-tryptophan at 25,588 s−1·m−1 and for other 11 simple indole derivatives up to 1538 s−1·m−1 provided evidence for its potential usage as a catalyst for chemoenzymatic synthesis. The putative prenyltransferase gene ACLA_031240 belonging to the dimethylallyltryptophan synthase superfamily was identified in the genome sequence of Aspergillus clavatus and overexpressed in Escherichia coli. The soluble His-tagged protein EAW08391 was purified to near homogeneity and used for biochemical investigation with diverse aromatic substrates in the presence of different prenyl diphosphates. It has shown that in the presence of dimethylallyl diphosphate (DMAPP), the recombinant enzyme accepted very well simple indole derivatives with l-tryptophan as the best substrate. Product formation was also observed for tryptophan-containing cyclic dipeptides but with much lower conversion yields. In contrast, no product formation was detected in the reaction mixtures of l-tryptophan with geranyl or farnesyl diphosphate. Structure elucidation of the enzyme products by NMR and MS analyses proved unequivocally the highly regiospecific regular prenylation at C-5 of the indole nucleus of the simple indole derivatives. EAW08391 was therefore termed 5-dimethylallyltryptophan synthase, and it filled the last gap in the toolbox of indole prenyltransferases regarding their prenylation positions. Km values of 5-dimethylallyltryptophan synthase were determined for l-tryptophan and DMAPP at 34 and 76 μm, respectively. Average turnover number (kcat) at 1.1 s−1 was calculated from kinetic data of l-tryptophan and DMAPP. Catalytic efficiencies of 5-dimethylallyltryptophan synthase for l-tryptophan at 25,588 s−1·m−1 and for other 11 simple indole derivatives up to 1538 s−1·m−1 provided evidence for its potential usage as a catalyst for chemoenzymatic synthesis.