Abstract
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.
Highlights
Plant flavonoid prenyltransferases (FPTs) transfer prenyl moiety to flavonoid cores and have previously been identified only in Leguminosae
In this report we describe the characterization of two new FPTs, Morus alba isoliquiritigenin 3-dimethylallyltransferase (MaIDT) and Cudrania tricuspidata isoliquiritigenin 3-dimethylallyltransferase (CtIDT), from the cell suspension cultures of M. alba and C. tricuspidata, respectively
We initially hypothesized that the FPTs of M. alba would cluster together with the leguminous FPTs and used degenerated primer pairs based on these FPTs to clone the candidate gene(s)
Summary
Plant flavonoid prenyltransferases (FPTs) transfer prenyl moiety to flavonoid cores and have previously been identified only in Leguminosae. Conclusion: MaIDT and CtIDT evolved independently from leguminous FPTs. Significance: These findings are valuable for identifying additional evolutionarily different non-Leguminosae FPTs. Prenylated flavonoids are attractive specialized metabolites with a wide range of biological activities and are distributed in several plant families. Further progress was achieved in the molecular biological and biochemical investigations of plant FPTs, and additional relevant genes have been cloned and functionally characterized (Table 1) Due to their substrate promiscuity in vitro, some soluble types of aromatic PTs from microbes have been demonstrated to be capable of catalyzing the prenylation of flavonoids; e.g. 7-DMATS, a member of DMATS superfamily from Aspergillus fumigatus [18, 19], and some PTs of the CloQ/ NphB group from the actinomycetes Streptomyces [20, 21]. Further chemical investigations confirmed that the prenylated flavonoids formed the main chemical compositions of both of the two plant cell suspension cultures and that Diels-Alder-type adducts were present in large amounts in the cell suspension
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