Regiospecific biosynthesis of tamarixetin derivatives in Escherichia coli

A potential anti-oxidant compound tamarixetin, which can reduce the thiol toxicity, and an inhibitor of a complex multicasual disease (gastric ulcer) tamarixetin 3-O-β-d-glucoside were efficiently biosynthesized in Escherichia coli (E. coli). Transfer of O-methyl group by bacterial O-methyltransferase (SpnK) at 4′-hydroxy position of quercetin and quercetin 3-O-β-d-glucose were validated to produce tamarixetin and tamarixetin 3-O-β-d-glucoside. Flavonoid 3-O-glucosyltransferase (UGT78K1) was used to synthesize quercetin 3-O-glucoside which was subsequently O-methylated by SpnK at the 4′-hydroxy position. This is the first report of a bacterial sugar-O-methyltransferase that catalyzed O-methylation at the 4′-hydroxy position of flavonoid compounds. The production of these compounds was enhanced by overexpressing S-adenosylmethionine synthase (MetK) in E. coli. The supplemented 300 mg (∼331 μM) of quercetin to the recombinant cultures resulted in the production of ∼236.5 μM (∼225 mg) of tamarixetin and ∼149.9 μM (∼215.5 mg) of tamarixetin 3-O-β-d-glucoside in lab scale 3-L fermentor. These compounds were characterized spectroscopically.