Altered regioselectivity of a poplar O-methyltransferase, POMT-7.
O-Methylated flavonoids are biosynthesized by regioselective flavonoid O-methyltransferases (OMTs), which may account for the limited number of naturally occurring flavonoids in nature. It was previously shown that poplar POMT-7 regioselectively methylates the 7-hydroxyl group of flavones, whereas rice ROMT-9 regioselectively methylates the 3'-hydroxyl group of the substrate. We co-expressed both OMT genes (POMT-7 and ROMT-9) in E. coli and carried out biotransformation experiments of some flavonoids with the transformed E. coli strain. Contrast to the predicted regioselectivity of both POMT-7 and ROMT-9, unexpected methylation reaction products, i.e. 3',4'-O-methylated flavonoids, in addition to the predicted ones, were obtained with luteolin (5,7,3',4'-tetrahydroxyflavone) and quercetin (3,5,7,3',4'-pentahydroxyflavone) as substrates. Reactions using the 3'-O-methyl derivative of luteolin and quercetin by POMT-7 revealed that the enzyme has altered its regioselectivity from the 7- to the 4'-hydroxyl groups. These results are discussed in terms of molecular modeling of POMT-7 in relation to its methyl donor.
Kim
Bong-Gyu
BG
Department of Bioscience and Biotechnology, Bio/Molecular Informatics Center, Konkuk University, Seoul, Republic of Korea.
Lee
Yoon Jung
YJ
Lee
Sunhee
S
Lim
Yoongho
Y
Cheong
Youhoon
Y
Ahn
Joong-Hoon
JH
D047311:Luteolin / Q000737:chemistry; D008745:Methylation; D008958:Models, Molecular; D032107:Populus / Q000235:genetics / Q000378:metabolism*; D011497:Protein O-Methyltransferase / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D013237:Stereoisomerism
D011497:Protein O-Methyltransferase; D047311:Luteolin