Biochemical characterization of a putative wheat caffeic acid O-methyltransferase.
A wheat (Triticum aestivum L., near isogenic line of Hamlet) O-methyltransferase (OMT) was previously reported as a putative caffeic acid OMT (TaCOMT1), involved in lignin biosynthesis, based on its high sequence similarity with a number of graminaceous COMTs. The fact that the putative TaCOMT1 exhibits a significantly high sequence homology to another recently characterized wheat flavone-specific OMT (TaOMT2), and that molecular modeling studies indicated several conserved amino acid residues involved in substrate binding and catalysis of both proteins, prompted an investigation of its appropriate substrate specificity. We report here that TaCOMT1 exhibits highest preference for the flavone tricetin, and lowest activity with the lignin precursors, caffeic acid/5-hydroxyferulic acid as the methyl acceptor molecules, indicating that it is not involved in lignin biosynthesis. We recommend its reannotation to a flavone-specific TaOMT1 that is distinct from TaOMT2.
Zhou
Jian-Min
JM
Plant Biochemistry Laboratory, Concordia University, Montréal, Québec, Canada H4B 1R6.
Seo
Yong Weon
YW
Ibrahim
Ragai K
RK
D000595:Amino Acid Sequence; D047309:Flavones / Q000737:chemistry / Q000378:metabolism; D044948:Flavonols / Q000737:chemistry / Q000378:metabolism; D008780:Methyltransferases / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D015394:Molecular Structure; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism*; D017433:Protein Structure, Secondary; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity; D014908:Triticum / Q000201:enzymology*
D047309:Flavones; D044948:Flavonols; D010940:Plant Proteins; D008780:Methyltransferases; C019608:caffeate O-methyltransferase