Biochemical investigations of two 6-DMATS enzymes from Streptomyces reveal new features of L-tryptophan prenyltransferases.

Two putative prenyltransferase genes, SAML0654 and Strvi8510, were identified in Streptomyces ambofaciens and Streptomyces violaceusniger, respectively. Their deduced products share 63% sequence identity. Biochemical investigations with recombinant proteins demonstrated that L-tryptophan and derivatives, including D-tryptophan, 4-, 5-, 6- and 7-methyl-dl-tryptophan, were well accepted by both enzymes in the presence of DMAPP. Structural elucidation of the isolated products revealed regiospecific prenylation at C-6 of the indole ring and proved unequivocally the identification of two very similar 6-dimethylallyltryptophan synthases (6-DMATS). Detailed biochemical investigations with SAML0654 proved L-tryptophan to be the best substrate (K(m) 18 μm, turnover 0.3 s(-1)). Incubation with different prenyl donors showed that they also accepted GPP and catalyzed the same specific prenylation. Utilizing GPP as a prenyl donor has not been reported for tryptophan prenyltransferases previously. Both enzymes also catalyzed prenylation of some hydroxynaphthalenes; this has not previously been described for bacterial indole prenyltransferases. Interestingly, SAML0654 transferred prenyl moieties onto the unsubstituted ring of hydroxynaphthalenes.