Phylogenetic and biochemical characterization of γ-tocopherol like-N-methyltransferase involved in the biosynthesis of biologically active monoterpenoid indole alkaloids

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University of New Brunswick


N-methyltransferases (NMT) are some of the more extensively studied enzymes in the biosynthesis of alkaloids. Along with the discovery of an NMT catalyzing a key step in vinblastine (anticancer drug) biosynthesis, several other homologous NMTs have been characterized in the formation of other monoterpenoid indole alkaloids (MIA). The formation of these MIAs such as ajmaline, Nβ-methylajmaline, ervincine, and perivine, all involve catalysis by evolved NMTs from γ-tocopherol C-methyltransferase (γTLMT) family, which appear to be limited within the Apocynaceae species. To understand the catalytic capacity and diversification of these NMTs, transcriptomes of Catharanthus roseus, Vinca minor, Tabernaemontana elegans, and Amsonia hubrichtii were searched for homologs. Phylogenetic analysis showed distinct grouping of several characterized NMTs with uncharacterized ones. These NMTs were thus cloned and heterologously expressed in E. coli to study their in vitro activities with multiple MIA substrates. This led to the discovery and characterization of multiple enzymes involved in the production of different N-methylated MIA derivatives. Kinetic studies were done to compare catalytic efficiency of a T. elegans perivine NMT (TePeNMT) discovered in this study and its previously characterized C. roseus homolog, CrPeNMT. Two other strictamine NMT from C. roseus were characterized as well.