Attachment of isoprene units to various acceptors by prenylation plays an important role in primary and secondary metabolism of living organisms. Protein prenylation belongs to posttranslational modification and is involved in cellular regulation process. Prenylated secondary metabolites usually demonstrate promising biological and pharmacological activities. Prenyl transfer reactions catalyzed by prenyltransferases represent the key steps in the biosynthesis and contribute significantly to the structural and biological diversity of these compounds. In the last decade, remarkable progress has been achieved in the biochemical, molecular, and structural biological investigations of prenyltransferases, especially on those of the members of the dimethylallyltryptophan synthase (DMATS) superfamily. Until now, more than 40 of such soluble enzymes are identified and characterized biochemically. They catalyze usually regioselective and stereoselective prenylations of a series of aromatic substances including tryptophan, tryptophan-containing peptides, and other indole derivatives as well as tyrosine or even nitrogen-free substrates. Crystal structures of a number of prenyltransferases have been solved in the past 10 years and provide a solid basis for understanding the mechanism of prenyl transfer reactions.

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.

Prenylated compounds are ubiquitously found in nature and demonstrate interesting biological and pharmacological activities. Prenyltransferases catalyze the attachment of prenyl moieties from different prenyl donors to various acceptors and contribute significantly to the structural and biological diversity of natural products. In the last decade, significant progress has been achieved for the prenyltransferases of the dimethylallyltryptophan synthase (DMATS) superfamily. More than 40 members of these soluble enzymes are identified in microorganisms and characterized biochemically. These enzymes were also successfully used for production of a large number of prenylated derivatives. N1-, C4-, C5-, C6-, and C7-prenylated tryptophan and N1-, C2-, C3-, C4-, and C7-prenylated tryptophan-containing peptides were obtained by using DMATS enzymes as biocatalysts. Tyrosine and xanthone prenyltransferases were used for production of prenylated derivatives of their analogs. More interestingly, the members of the DMATS superfamily demonstrated intriguing substrate and catalytic promiscuity and also used structurally quite different compounds as prenyl acceptors. Prenylated hydroxynaphthalenes, flavonoids, indolocarbazoles, and acylphloroglucinols, which are typical bacterial or plant metabolites, were produced by using several fungal DMATS enzymes. Furthermore, the potential usage of these enzymes was further expanded by using natural or unnatural DMAPP analogs as well as by coexpression with other genes like NRPS and by development of whole cell biocatalyst.

The behavior of four dimethylallyltryptophan synthases (DMATSs) (5‐DMATS and 5‐DMATSSc as tryptophan C5‐prenyltransferases, and 6‐DMATSSa and 6‐DMATSSv as C6‐prenyltransferases) and one L‐tyrosine prenyltransferase with a tryptophan C7‐prenyltransferase activity was investigated in the presence of two unnatural alkyl donors (methylallyl and 2‐pentenyl diphosphate) and one benzyl donor (benzyl diphosphate). Detailed biochemical investigations revealed the acceptance of these dimethylallyl diphosphate (DMAPP) analogues by all tested enzymes with different relative activities. Enzyme products with the allyl or benzyl moiety attached to different positions were identified in the reaction mixtures, whereby C‐6 alkylated or benzylated L‐tryptophan was found as one of the main products. This observation demonstrates a preference of the five prenyltransferases toward C‐6 of the indole ring in the presence of unnatural DMAPP derivatives. Molecular dynamics simulation experiments with a homologous model of 5‐DMATS explained well its reactions with methylallyl and 2‐pentenyl diphosphate. Furthermore this study expands significantly the potential usage of tryptophan prenylating enzymes as biocatalysts for Friedel–Crafts alkylation.magnified image

Prenylated secondary metabolites including indole derivatives usually demonstrate improved biological and pharmacological activities, which make them promising candidates for drug discovery and development. The transfer reactions of a prenyl moiety from a prenyl donor, e.g. dimethylallyl diphosphate (DMAPP), to an acceptor is catalysed by prenyltransferases. One special group of such enzymes uses DMAPP and tryptophan as substrates with dimethylallyltryptophans as reaction products and functions therefore as dimethylallyltryptophan synthases (DMATSs). Sequence homology search with known tryptophan prenyltransferases from Streptomyces led to identification of a putative prenyltransferase gene MolI14.36 in Micromonospora olivasterospora. Expression and biochemical investigations revealed that MolI14.36 acts as a tryptophan C6-prenyltransferase (6-DMATS). Study on substrate specificity of 6-DMATS displayed a significantly high activity towards d-tryptophan, which prompted us to carry out comparative studies on enantioselectivity, regioselectivity and multiple prenylation ability of additional DMATSs including FgaPT2, 5-DMATS, 5-DMATS, 6-DMATS, 6-DMATS and 7-DMATS towards l- and d-isomers of tryptophan and their analogues. The relative activities of the tested enzymes towards d-tryptophan differ clearly from each other. Incubation of l-, d-isomers or the racemates of 5-, 6- and 7-methyltryptophan revealed distinctly different preferences of the DMATS enzymes. Interestingly, 6-DMATS and 5-DMATS accepted 5-methyl-d-tryptophan much better than the l-enantiomer. Furthermore, the conversion yields of the d-isomers were strongly inhibited in the reactions with racemates. More interestingly, the regioselectivities of FgaPT2, 5-DMATS and 7-DMATS towards d-tryptophan and its C5-methylated derivative differed clearly from those of the l-forms. In addition, both mono- and diprenylated products were clearly detected for 5-DMATS with l- and d-enantiomers of tryptophan and their methylated derivatives.