Site-directed Mutagenesis Switching a Dimethylallyl Tryptophan Synthase to a Specific Tyrosine C3-prenylating Enzyme [Enzymology]

December 4th, 2014 by Fan, A., Zocher, G., Stec, E., Stehle, T., Li, S.-M.

The tryptophan prenyltransferases FgaPT2 and 7-DMATS from Aspergillus fumigatus catalyze C4- and C7-prenylation of the indole ring, respectively. 7-DMATS was found to accept L-tyrosine as substrate as well and converted it to an O-prenylated derivative. An acceptance of L-tyrosine by FgaPT2 was also observed in this study. Interestingly, isolation and structure elucidation revealed the identification of a C3-prenylated L-tyrosine as enzyme product. Molecular modeling and site-directed mutagenesis led to creation of a mutant FgaPT2_K174F, which showed much higher specificity towards L-tyrosine than L-tryptophan. Its catalytic efficiency towards L-tyrosine was found to be 4.8-fold in comparison to that of non-mutated FgaPT2, while the activity towards L-tryptophan was less than 0.4 % of that of the wild-type. To the best of our knowledge, this is the first report on an enzymatic C-prenylation of L-tyrosine as free amino acid and altering the substrate preference of a prenyltransferase by mutagenesis.