Production of bioactive flavonol rhamnosides by expression of plant genes in Escherichia coli.

Biotransformation of flavonoids using Escherichia coli harboring specific glycosyltransferases is an excellent method for the regioselective synthesis of flavonoid glycosides. Flavonol rhamnosides have been shown to contain better antiviral and antibacterial activities compared to flavonol aglycones. To synthesize flavonoid rhamnoside, a strain of E. coli expressing UDP-rhamnose flavonol glycosyltransferase (AtUGT78D1) from Arabidopsis thaliana was used to produce quercetin 3-O-rhamnoside. The biotransformation of quercetin using this E. coli transformant resulted in the production of quercetin 3-O-rhamnoside as a major product. A strain of E. coli rfbD (encoding dTDP-4-dehydrorhamnose reductase) expressing AtUGT78D1, which is involved in the final step of thymidine diphosphate rhamnose (TDP-rhamnose) biosynthesis, did not produce quercetin 3-O-rhamnoside, meaning that AtUGT78D1 used endogenous TDP-rhamnose as a sugar donor to produce quercetin 3-O-rhamnoside. The production of quercetin 3-O-rhamnoside could be increased by up to 160% by co-expressing AtUGT78D1 and rhamnose synthase gene 2 (RHM2), which catalyzes the conversion of UDP-glucose into UDP-rhamnose. Using an E. coli strain harboring AtUGT78D1 and RHM2, 150 mg/L quercetin 3-O-rhamnoside and 200 mg/L kaempferol 3-O-rhamnoside were produced in 48 h.