Prenylation of Flavonoids by Using a Dimethylallyltryptophan Synthase, 7-DMATS, from Aspergillus fumigatus

Prenylation of aromatic amino acids and plant phenolics by an aromatic prenyltransferase from Rasamsonia emersonii

Dimethylallyl tryptophan synthases (DMATSs) are aromatic prenyltransferases that catalyze the transfer of a prenyl moiety from a donor to an aromatic acceptor during the biosynthesis of microbial secondary metabolites. Due to their broad substrate scope, DMATSs are anticipated as biotechnological tools for producing bioactive prenylated aromatic compounds. Our study explored the substrate scope and product profile of a recombinant RePT, a novel DMATS from the thermophilic fungus Rasamsonia emersonii. Among a variety of aromatic substrates, RePT showed the highest substrate conversion for L-tryptophan and L-tyrosine (> 90%), yielding two mono-prenylated products in both cases. Nine phenolics from diverse phenolic subclasses were notably converted (> 10%), of which the stilbenes oxyresveratrol, piceatannol, pinostilbene, and resveratrol were the best acceptors (37-55% conversion). The position of prenylation was determined using NMR spectroscopy or annotated using MS2 fragmentation patterns, demonstrating that RePT mainly catalyzed mono-O-prenylation on the hydroxylated aromatic substrates. On L-tryptophan, a non-hydroxylated substrate, it preferentially catalyzed C7 prenylation with reverse N1 prenylation as a secondary reaction. Moreover, RePT also possessed substrate-dependent organic solvent tolerance in the presence of 20% (v/v) methanol or DMSO, where a significant conversion (> 90%) was maintained. Our study demonstrates the potential of RePT as a biocatalyst for the production of bioactive prenylated aromatic amino acids, stilbenes, and various phenolic compounds. KEY POINTS: • RePT catalyzes prenylation of diverse aromatic substrates. • RePT enables O-prenylation of phenolics, especially stilbenes. • The novel RePT remains active in 20% methanol or DMSO.

Coupling the Isopentenol Utilization Pathway and Prenyltransferase for the Biosynthesis of Licoflavanone in Recombinant Escherichia coli

Prenylflavonoids are promising candidates for food additives and functional foods due to their diverse biological activities and potential health benefits. However, natural prenylflavonoids are generally present in low abundance and are limited to specific plant species. Here, we report the biosynthesis of licoflavanone from naringenin and prenol by recombinant Escherichia coli. By investigating the activities of seven different sources of prenyltransferases overexpressed in E. coli toward various flavonoid substrates, the prenyltransferase AnaPT exhibits substrate preference when naringenin serves as the prenyl acceptor. Furthermore, licoflavanone production was successfully achieved by coupling the isopentenol utilization pathway and AnaPT in recombinant E. coli. In addition, the effects of fermentation temperatures, induction temperatures, naringenin concentrations, and substrate feeding strategies were investigated on the biosynthesis of licoflavanone in recombinant E. coli. Consequently, the recombinant E. coli strain capable of improved dimethylallyl diphosphate (DMAPP) supply and suitable for prenylflavonoid biosynthesis increased licoflavanone titers to 142.1 mg/L in a shake flask and to 537.8 mg/L in a 1.3 L fermentor, which is the highest yield for any prenylflavonoids reported to date. These strategies proposed in this study provide a reference for initiating the production of high-value prenylflavonoids.

Fungal Prenyltransferase AnaPT and Its F265 Mutants Catalyze the Dimethylallylation at the Nonaromatic Carbon of Phloretin

Phloretin is widely found in fruit and shows various biological activities. Here, we demonstrate the dimethylallylation, geranylation, and farnesylation, particularly the first dimethylallylation at the nonaromatic carbon of phloretin (1) by the fungal prenyltransferase AnaPT and its mutants. F265 was identified as a key amino acid residue related to dimethylallylation at the nonaromatic carbon of phloretin. Mutants AnaPT_F265D, AnaPT_F265G, AnaPT_F265P, AnaPT_F265C, and AnaPT_F265Y were discovered to generally increase prenylation activity toward 1. AnaPT_F265G catalyzes the O-geranylation selectively at the C-2' hydroxyl group, which involves an intramolecular hydrogen bond with the carbonyl group of 1. Seven products, 1D5, 1D7-1D9, 1G2, 1G4, and 1F2, have not been reported prior to this study. Twelve compounds, 1D3-1D9, 1G1-1G3, and 1F1-1F2, exhibited potential inhibitory effects on α-glucosidase with IC50 values ranging from 11.45 ± 0.87 to 193.80 ± 6.52 μg/mL. Among them, 1G1 with an IC50 value of 11.45 ± 0.87 μg/mL was the most potential α-glucosidase inhibitor, which is about 30 times stronger than the positive control acarbose with an IC50 value of 346.63 ± 15.65 μg/mL.

Phytochemistry and pharmacology of natural prenylated flavonoids

Prenylated flavonoids are a special kind of flavonoid derivative possessing one or more prenyl groups in the parent nucleus of the flavonoid. The presence of the prenyl side chain enriched the structural diversity of flavonoids and increased their bioactivity and bioavailability. Prenylated flavonoids show a wide range of biological activities, such as anti-cancer, anti-inflammatory, neuroprotective, anti-diabetic, anti-obesity, cardioprotective effects, and anti-osteoclastogenic activities. In recent years, many compounds with significant activity have been discovered with the continuous excavation of the medicinal value of prenylated flavonoids, and have attracted the extensive attention of pharmacologists. This review summarizes recent progress on research into natural active prenylated flavonoids to promote new discoveries of their medicinal value.

Bioactive prenylated phenolic compounds from the aerial parts of Glycyrrhiza uralensis

In this work, a bioassay-guided fractionation strategy was used to isolate 26 phenolic compounds from the ethyl acetate partition of an ethanol extract of the aerial parts of Glycyrrhiza uralensis Fisch. ex DC. Among them, 8 prenylated phenolic compounds (glycyuralins Q-X) were described for the first time. The two enantiomers of glycyuralin Q were purified and their absolute configurations were established by ECD spectral calculations. (1″R, 2″S)-glycyuralin Q and (1″S, 2″R)-glycyuralin Q showed significant inhibitory activities against SARS-CoV-2 virus proteases 3CL^pro with IC₅₀ values of 1.5 ± 1.0 and 4.0 ± 0.3 μM, and PL^pro with IC₅₀ values of 2.4 ± 0.2 and 1.9 ± 0.1 μM, respectively. Four compounds showed potent cytotoxic activities against A549, Huh-7, and HepG2 human cancer cells with IC₅₀ values ranging from 0.5 to 2.5 μM.

Enzymatic formation of a prenyl β-carboline by a fungal indole prenyltransferase

CdpNPT from Aspergillus fumigatus is a fungal indole prenyltransferase (IPT) with remarkable substrate promiscuity to generate prenylated compounds. Our first investigation of the catalytic potential of CdpNPT against a β-carboline, harmol (1), revealed that the enzyme also accepts 1 as the prenyl acceptor with dimethylallyl diphosphate (DMAPP) as the prenyl donor and selectively prenylates the C-6 position of 1 by the "regular-type" dimethylallylation to produce 6-(3-dimethylallyl)harmol (2). Furthermore, our X-ray crystal structure analysis of the C-His₆-tagged CdpNPT (38-440) truncated mutant complexed with 1 and docking studies of DMAPP to the crystal structure of the CdpNPT (38-440) mutant suggested that CdpNPT could employ the two-step prenylation system to produce 2.

Increasing Structural Diversity of Prenylated Chalcones by Two Fungal Prenyltransferases

Prenylated chalcones are found mainly in plants and exhibit diverse biological and pharmacological activities. Some of these compounds are components of food and dietary supplements with significant health benefits. In plants, they are derived from chalcones by prenylation with membrane-bound prenyltransferases. In this study, we demonstrate prenylations of 10 chalcones by two fungal prenyltransferases (AtaPT/AnaPT) in the presence of dimethylallyl diphosphate. Eleven mono- (1a-10a and 9b) and four diprenylated products (8b, 9c, 10b, and 10c) were obtained. Among them, 12 have new structures (1a, 2a, 4a-6a, 8a, 8b, 9b, 9c, 10a, 10b, and 10c). Most of the obtained prenylated chalcones are products of AnaPT and carry prenyl moieties at ring B. Our study provides an excellent example for increasing structural diversity of plant metabolites with microbial enzymes.

Biochemical Characterization of a Novel Prenyltransferase from Streptomyces sp. NT11 and Development of a Recombinant Strain for the Production of 6-Prenylnaringenin

Prenyl groups increase the lipophilicity of flavonoids, endowing them with a special activity, selectivity, and pharmacological properties by prenylation. Herein, a novel prenyltransferase (ShFPT) gene from Streptomyces sp. NT11 was expressed in Escherichia coli, and its biochemical characteristics were determined. ShFPT exhibited high selectivity to prenylate naringenin at C-6 to generate 6-prenylnaringenin. The optimal activity was observed at pH 6.0 and 55 °C. The K_cat and K_m for naringenin were 0.0095 s^-1 and 0.20 mM, respectively. Several promiscuous kinase and isopentenyl phosphate kinase genes were screened to develop the most efficient dimethylallyl diphosphate (DMAPP) synthesis pathway for 6-prenylnaringenin synthesis in E. coli. The 6-prenylnaringenin production was improved by changing the induction strategies and optimizing the bioconversion conditions. Finally, 6-prenylnaringenin production reached the highest yield of 69.9 mg/L with average productivity of 4.0 mg/L/h after 16 h incubation, which is the highest yield for any prenylated flavonoid reported to date in E. coli. Therefore, this study provides an efficient method for 6-prenylnaringenin production and reveals the DMAPP synthesis pathway.

Hemisynthesis and Biological Evaluation of Cinnamylated, Benzylated, and Prenylated Dihydrochalcones from a Common Bio-Sourced Precursor

Several families of naturally occurring C-alkylated dihydrochalcones display a broad range of biological activities, including antimicrobial and cytotoxic properties, depending on their alkylation sidechain. The catalytic Friedel-Crafts alkylation of the readily available aglycon moiety of neohesperidin dihydrochalcone was performed using cinnamyl, benzyl, and isoprenyl alcohols. This procedure provided a straightforward access to a series of derivatives that were structurally related to natural balsacones, uvaretin, and erioschalcones, respectively. The antibacterial and cytotoxic potential of these novel analogs was evaluated in vitro and highlighted some relations between the structure and the pharmacological properties of alkylated dihydrochalcones.

Regiospecific 7-O-prenylation of anthocyanins by a fungal prenyltransferase

Anthocyanins are a type of well-known natural flavonoids for their various beneficial health effects. However, prenylated anthocyanins are not discovered in nature although prenylation is believed to generally enhance the biological accessibility of flavonoids. In this article, we demonstrate the first example for prenylation of anthocyanins. A chemo-enzymatic approach was achieved for the synthesis of a series of 7-O-prenylated anthocyanins, using the fungal prenyltransferase CdpC3PT from Neosartorya fischeri.

Plant Aromatic Prenyltransferases: Tools for Microbial Cell Factories

In plants, prenylation of aromatic compounds, such as (iso)flavonoids and stilbenoids, by membrane-bound prenyltransferases (PTs), is an essential step in the biosynthesis of many bioactive compounds. Prenylated aromatic compounds have various health-beneficial properties that are interesting for industrial applications, but their exploitation is limited due to their low abundance in nature. Harnessing plant aromatic PTs for prenylation in microbial cell factories may be a sustainable and economically viable alternative. Limitations in prenylated aromatic compound production have been identified, including availability of prenyl donor substrate. In this review, we summarize the current knowledge about plant aromatic PTs and discuss promising strategies towards the optimized production of prenylated aromatic compounds by microbial cell factories.

Regiospecific synthesis of prenylated flavonoids by a prenyltransferase cloned from Fusarium oxysporum

Due to their impressive pharmaceutical activities and safety, prenylated flavonoids have a high potent to be applied as medicines and nutraceuticals. Biocatalysis is an effective technique to synthesize prenylated flavonoids. The major concern of this technique is that the microbe-derived prenyltransferases usually have poor regiospecificity and generate multiple prenylated products. In this work, a highly regiospecific prenyltransferase (FoPT1) was found from Fusarium oxysporum. It could recognize apigenin, naringenin, genistein, dihydrogenistein, kampferol, luteolin and hesperetin as substrates, and only 6-C-prenylated flavonoids were detected as the products. The catalytic efficiency of FoPT1 on flavonoids was in a decreasing order with hesperetin >naringenin >apigenin >genistein >luteolin >dihydrogenistein >kaempferol. Chalcones, flavanols and stilbenes were not active when acting as the substrates. 5,7-Dihydroxy and 4-carbonyl groups of flavonid were required for the catalysis. 2,3-Alkenyl was beneficial to the catalysis whereas 3-hydroxy impaired the prenylation reaction. Docking studies simulated the prenyl transfer reaction of FoPT1. E186 was involved in the formation of prenyl carbonium ion. E98, F89, F182, Y197 and E246 positioned apigenin for catalysis.

Complementary Flavonoid Prenylations by Fungal Indole Prenyltransferases

Flavonoids are found mainly in plants and exhibit diverse biological and pharmacological activities, which can often be enhanced by prenylations. In plants, such reactions are catalyzed by membrane-bound prenyltransferases. In this study, the prenylation of nine flavonoids from different classes by a soluble fungal prenyltransferase (AnaPT) involved in the biosynthesis of the prenylated indole alkaloid acetylaszonalenin is demonstrated. The behavior of AnaPT toward flavonoids regarding substrate acceptance and prenylation positions clearly differs from that of the indole prenyltransferase 7-DMATS. The two enzymes are therefore complementary in flavonoid prenylations.

Impacts and perspectives of prenyltransferases of the DMATS superfamily for use in biotechnology

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.

Biotransformations and biological activities of hop flavonoids

Female hop cones are used extensively in the brewing industry, but there is now increasing interest in possible uses of hops for non-brewing purposes, especially in the pharmaceutical industry. Among pharmaceutically important compounds from hops are flavonoids, having proven anticarcinogenic, antioxidant, antimicrobial, anti-inflammatory and estrogenic effects. In this review we aim to present current knowledge on the biotransformation of flavonoids from hop cones with respect to products, catalysis and conversion. A list of microbial enzymatic reactions associated with gastrointestinal microbiota is presented. A comparative analysis of the biological activities of hop flavonoids and their biotransformation products is described, indicating where further research has potential for applications in the pharmaceutical industry.

Site-directed mutagenesis switching a dimethylallyl tryptophan synthase to a specific tyrosine C3-prenylating enzyme

The tryptophan prenyltransferases FgaPT2 and 7-DMATS (7-dimethylallyl tryptophan synthase) from Aspergillus fumigatus catalyze C(4)- and C(7)-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 C(3)-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 toward l-tyrosine than l-tryptophan. Its catalytic efficiency toward l-tyrosine was found to be 4.9-fold in comparison with that of non-mutated FgaPT2, whereas the activity toward 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.

Molecular characterization and phylogenetic analysis of two novel regio-specific flavonoid prenyltransferases from Morus alba and Cudrania tricuspidata

Prenylated flavonoids are attractive specialized metabolites with a wide range of biological activities and are distributed in several plant families. The prenylation catalyzed by prenyltransferases represents a Friedel-Crafts alkylation of the flavonoid skeleton in the biosynthesis of natural prenylated flavonoids and contributes to the structural diversity and biological activities of these compounds. To date, all identified plant flavonoid prenyltransferases (FPTs) have been identified in Leguminosae. In the present study two new FPTs, Morus alba isoliquiritigenin 3'-dimethylallyltransferase (MaIDT) and Cudrania tricuspidata isoliquiritigenin 3'-dimethylallyltransferase (CtIDT), were identified from moraceous plants M. alba and C. tricuspidata, respectively. MaIDT and CtIDT shared low levels of homology with the leguminous FPTs. MaIDT and CtIDT are predicted to be membrane-bound proteins with predicted transit peptides, seven transmembrane regions, and conserved functional domains that are similar to other homogentisate prenyltransferases. Recombinant MaIDT and CtIDT were able to regioselectively introduce dimethylallyl diphosphate into the A ring of three flavonoids with different skeleton types (chalcones, isoflavones, and flavones). Phylogenetic analysis revealed that MaIDT and CtIDT are distantly related to their homologs in Leguminosae, which suggests that FPTs in Moraceae and Leguminosae might have evolved independently. MaIDT and CtIDT represent the first two non-Leguminosae FPTs to be identified in plants and could thus lead to the identification of additional evolutionarily varied FPTs in other non-Leguminosae plants and could elucidate the biosyntheses of prenylated flavonoids in various plants. Furthermore, MaIDT and CtIDT might be used for regiospecific prenylation of flavonoids to produce bioactive compounds for potential therapeutic applications due to their high efficiency and catalytic promiscuity.

A promiscuous prenyltransferase from Aspergillus oryzae catalyses C-prenylations of hydroxynaphthalenes in the presence of different prenyl donors

Prenyltransferases of the dimethylallyltryptophan synthase (DMATS) superfamily are involved in the biosynthesis of secondary metabolites and show broad substrate specificity towards their aromatic substrates with a high regioselectivity for the prenylation reactions. Most members of this superfamily accepted as prenyl donor exclusively dimethylallyl diphosphate (DMAPP). One enzyme, AnaPT from Neosartorya fischeri, was reported recently to use both DMAPP and geranyl diphosphate (GPP) as prenyl donors. In this study, we demonstrate the acceptance of DMAPP, GPP and farnesyl diphosphate (FPP) by a new member of this superfamily, BAE61387 from Aspergillus oryzae DSM1147, for C-prenylations of hydroxynaphthalenes.

Substrate and catalytic promiscuity of secondary metabolite enzymes: O-prenylation of hydroxyxanthones with different prenyl donors by a bisindolyl benzoquinone C- and N-prenyltransferase

Supplied with unnatural substrates like hydroxyxanthones, the C- and N-prenyltransferase AstPT performs O-prenylation using DMAPP, GPP and also FPP as prenyl donor.

Structure-based engineering increased the catalytic turnover rate of a novel phenazine prenyltransferase

Prenyltransferases (PTs) catalyze the regioselective transfer of prenyl moieties onto aromatic substrates in biosynthetic pathways of microbial secondary metabolites. Therefore, these enzymes contribute to the chemical diversity of natural products. Prenylation is frequently essential for the pharmacological properties of these metabolites, including their antibiotic and antitumor activities. Recently, the first phenazine PTs, termed EpzP and PpzP, were isolated and biochemically characterized. The two enzymes play a central role in the biosynthesis of endophenazines by catalyzing the regiospecific prenylation of 5,10-dihydrophenazine-1-carboxylic acid (dhPCA) in the secondary metabolism of two different Streptomyces strains. Here we report crystal structures of EpzP in its unliganded state as well as bound to S-thiolodiphosphate (SPP), thus defining the first three-dimensional structures for any phenazine PT. A model of a ternary complex resulted from in silico modeling of dhPCA and site-directed mutagenesis. The structural analysis provides detailed insight into the likely mechanism of phenazine prenylation. The catalytic mechanism suggested by the structure identifies amino acids that are required for catalysis. Inspection of the structures and the model of the ternary complex furthermore allowed us to rationally engineer EpzP variants with up to 14-fold higher catalytic reaction rate compared to the wild-type enzyme. This study therefore provides a solid foundation for additional enzyme modifications that should result in efficient, tailor-made biocatalysts for phenazines production.

Identification of the verruculogen prenyltransferase FtmPT3 by a combination of chemical, bioinformatic and biochemical approaches

Previous studies showed that verruculogen is the end product of a biosynthetic gene cluster for fumitremorgin-type alkaloids in Aspergillus fumigatus and Neosartorya fischeri. In this study, we isolated fumitremorgin A from N. fischeri. This led to the identification of the responsible gene, ftmPT3, for O-prenylation of an aliphatic hydroxy group in verruculogen. This gene was found at a different location in the genome of N. fischeri than the identified cluster. The coding sequence of ftmPT3 was amplified by fusion PCR and overexpressed in Escherichia coli. The enzyme product of the soluble His(8)-FtmPT3 with verruculogen and dimethylallyl diphosphate (DMAPP) was identified unequivocally as fumitremorgin A by NMR and MS analyses. K(M) values of FtmPT3 were determined for verruculogen and DMAPP at 5.7 and 61.5 μM, respectively. Average turnover number (k(cat)) was calculated from kinetic parameters of verruculogen and DMAPP to be 0.069 s(-1). FtmPT3 also accepted biosynthetic precursors of fumitremorgin A, for example, fumitremorgin B and 12,13-dihydroxyfumitremorgin C, as substrates and catalyses their prenylation.

Expansion of enzymatic Friedel-Crafts alkylation on indoles: acceptance of unnatural β-unsaturated allyl diphospates by dimethylallyl-tryptophan synthases

Prenyltransferases of the dimethylallyl-tryptophan synthase (DMATS) superfamily catalyze Friedel-Crafts alkylation with high flexibility for aromatic substrates, but the high specificity for dimethylallyl diphosphate (DMAPP) prohibits their application as biocatalysts. We demonstrate here that at least one methyl group in DMAPP can be deleted or shifted to the δ-position. For acceptance by some DMATS enzymes, however, a double bond must be situated at the β-position. Furthermore, the alkylation position of an analogue can differ from that of DMAPP.

Prenylation of a nonaromatic carbon of indolylbutenone by a fungal indole prenyltransferase

FtmPT1 from Aspergillus fumigatus is a fungal indole prenyltransferase (PT) that normally catalyzes the regiospecific prenylation of brevianamide F (cyclo-L-Trp-L-Pro) at the C-2 position of the indole ring with dimethylallyl diphosphate (DMAPP). Interestingly, FtmPT1 exhibited remarkable substrate tolerance and accepted (E)-4-(1H-indol-3-yl)but-3-en-2-one (1) as a substrate to produce an unnatural novel α-prenylindolylbutenone (1a). This is the first demonstration of the prenylation of a nonaromatic carbon of the acceptor substrate by a fungal indole PT.

Mutagenesis and biochemical studies on AuaA confirmed the importance of the two conserved aspartate-rich motifs and suggested difference in the amino acids for substrate binding in membrane-bound prenyltransferases

AuaA is a membrane-bound farnesyltransferase from the myxobacterium Stigmatella aurantiaca involved in the biosynthesis of aurachins. Like other known membrane-bound aromatic prenyltransferases, AuaA contains two conserved aspartate-rich motifs. Several amino acids in the first motif NXxxDxxxD were proposed to be responsible for prenyl diphosphate binding via metal ions like Mg(2+). Site-directed mutagenesis experiments demonstrated in this study that asparagine, but not the arginine residue in NRxxDxxxD, is important for the enzyme activity of AuaA, differing from the importance of NQ or ND residues in the NQxxDxxxD or NDxxDxxxD motifs observed in some membrane-bound prenyltransferases. The second motif of known membrane-bound prenyltransferases was proposed to be involved in the binding of their aromatic substrates. KDIxDxEGD, also found in AuaA, had been previously speculated to be characteristic for binding of flavonoids or homogenisate. Site-directed mutagenesis experiments with AuaA showed that KDIxDxEGD was critical for the enzyme activity. However, this motif is very likely not specific for flavonoid or homogenisate prenyltransferases, because none of the tested flavonoids was accepted by AuaA or its mutant R53A in the presence of farnesyl, geranyl or dimethylallyl diphosphate.

Biochemical characterization of indole prenyltransferases: filling the last gap of prenylation positions by a 5-dimethylallyltryptophan synthase from Aspergillus clavatus

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. K(m) values of 5-dimethylallyltryptophan synthase were determined for L-tryptophan and DMAPP at 34 and 76 μM, respectively. Average turnover number (k(cat)) 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.