Regiospecific methylation of naringenin to ponciretin by soybean O-methyltransferase expressed in Escherichia coli |
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Authors: | Kim Dae Hwan Kim Bong-Gyu Lee Youngshim Ryu Ji Young Lim Yoongho Hur Hor-Gil Ahn Joong-Hoon |
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Affiliation: | Department of Molecular Biotechnology, Bio/Molecular Informatics Center, Konkuk University, 1 Hwayang-dong, Kwangjin-gu, Seoul 143-701, Korea. |
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Abstract: | Flavonoids found in plants most likely undergo a variety of modification reactions such as hydroxylation, glycosylation, and/or methylation. Among these, O-methylation has an effect on the solubility and thus on the antimicrobial activity of the flavonoids. We analyzed the conversion of naringenin with a methyltransferase, SOMT-2, from Glycine max. SOMT-2 was expressed in Escherichia coli as a glutathion S-transferase fusion protein. E. coli harboring SOMT-2 was grown with daidzein, geninstein, apigenin, naringenin, and quercetin, respectively, and reaction products were analyzed with thin layer chromatography and HPLC. SOMT-2 could convert apigenin, daidzein, genistein, and quercetin into the corresponding 4'-O-methylated compounds such as acacetin, formononetin, biochanine A, and 4'-methylated quercetin whereas naringenin turned out to be the best substrate tested. SOMT-2 stoichiometically converted naringenin (4',5,7-trihyroxyflavanone) into a ponciretin (4'-methoxy-5,7-dihydroxyflavanone), whose structure was determined by NMR and LC/mass spectral analyses. Considering the reactions, SOMT-2 may have a regiospecific methylation activity, resulting in transforming 4'-hydroxyl group of flavonoids B-ring to 4'-methyl group. |
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