Evolution of Novel O-Methyltransferases from the Vanilla planifolia Caffeic Acid O-Methyltransferase
Huaijun Michael Li, David Rotter, Thomas G. Hartman, Fulya E. Pak, Daphna Havkin-Frenkel, Faith C. Belanger
Department of Plant Biology and Pathology and The Biotechnology Center for Agriculture & the Environment (HML, DR, FEP, DHF, FCB) and Center for Advanced Food Technology (TGH), Cook College, Rutgers University, New Brunswick, NJ 08903
The biosynthesis of many plant secondary compounds involves the methylation of one or more hydroxyl groups, catalyzed by O-methyltransferases. Here we report the characterization of two novel O-methyltransferases, Van OMT-2 and Van OMT-3, from the orchid Vanilla planifolia that catalyze the methylation of a single outer hydroxyl group in substrates possessing a 1,2,3-trihydroxybenzene moiety, such as methyl gallate and myricetin. This is a substrate requirement not previously reported for any O-methyltransferases. Based on sequence analysis these enzymes are most similar to caffeic acid O-methyltransferases (COMTs), but they have negligible activity with typical COMT substrates. Seven of the 12 conserved substrate-binding residues in COMTs are altered in Van OMT-2 and Van OMT-3. Phylogenetic analysis of the sequences suggests that Van OMT-2 and Van OMT-3 evolved from the V. planifolia COMT. These new V. planifolia O-methyltransferases are new instances of COMT-like enzymes with novel substrate preferences.