Substrate-enantiomer selectivity of matairesinol O-methyltransferases

Abstract

Previously we reported a cDNA encoding an O-methyltransferase (OMT) responsible for the O-methylation of matairesinol to afford arctigenin in Carthamus tinctorius. However, the regioselectivity and stereoselectivity of its reaction are not yet well understood. In this paper, we report the characterization and comparison of three matairesinol OMTs (MROMTs) encoded by cDNAs isolated from C. tinctorius (CtMROMT), Anthriscus sylvestris (AsMROMT), and Forsythia koreana (FkMROMT). Although they shared matairesinol as a substrate, each recombinant MROMT showed different catalytic behavior. AsMROMT and CtMROMT methylated matairesinol’s hydroxyl group at the C4′ position giving rise to arctigenin, while FkMROMT methylated the C4 position hydroxyl group giving rise to isoarctigenin. Analysis of the enantiomeric composition of products from racemic matairesinol showed all OMT reactions to be highly selective in terms of the substrate enantiomers and only use the (−)-enantiomer as the substrate.