Regiospecific Flavonoid 7-O-Methylation withStreptomyces avermitilisO-Methyltransferase Expressed inEscherichia coli

O-Methylation, commonly found in synthesis of secondary metabolites of plants and micro-organisms, appears to transfer a methyl group to the hydroxyl group of the recipient which increases the hydrophobicity of the recipient. O-Methyltransferase (OMT), SaOMT-2, was isolated and characterized from Streptomyces avermitilis MA-4680. Its amino acid sequence showed 68% similarity with antibiotic C-1027 OMT and 53% similarity with the carminomycin 4-OMT. SaOMT-2 was expressed in E. coli as a His-tag fusion protein and showed that the methyl was transferred onto the 7- hydroxyl group of the isoflavones, daidzein and genistein, and the flavones, kaempferol and quercetin, as well as the flavanone naringenin. NMR and liquid chromatography−mass spectrometry were used to confirm the location of the methyl group on the recipient compound of naringenin, which was biotransformed into sakuranetin by E. coli transformant expressing SaOMT-2 (E. coli Sa-2). Therefore, E. coli Sa-2 would be used for the synthesis of the antifungal flavonoid, sakuranetin, through biotransformation. Keywords: Biotransformation; flavonoids; O-methyltransferase; Streptomyces avermitilis