Production of cinnamates and benzoates glucose esters by bioconversion using Escherichia coli expressing a glucosyltransferase characterized from sweet potato

Sweet potatoes (Ipomoea batatas) produce glucose esters from cinnamates during stress responses. We isolated a glucosyltransferase, IbGT1 (UGT84A20), from sweet potato and characterized its recombinant enzyme heterologously expressed in Escherichia coli. The recombinant IbGT1 enzyme reacted with cinnamates, especially p-coumaric acid, ferulic acid, and sinapic acid, and showed activity against benzoates with an optimum pH of 5.0-5.5. The enzyme also reacted with flavonoids under alkaline conditions (pH 8.0), with the main product being 7-O-glucosides. Bioconversion using E. coli expressing IbGT1 (Ec-IbGT1) as a whole cell biocatalyst converted 200 µM cinnamates such as p-coumaric acid and benzoates such as p-hydroxybenzoic acid into their glucose esters mostly within 3-6 h. The conversion rates for caffeic acid and sinapic acid were much lower than those for the other substrates tested, which took more than 6 h, despite the enzymatic activities of IbGT1 against these compounds being comparable to the others. Scaled-up production combined with repeated administration of sinapic acid, trans-cinnamic acid and p-hydroxybenzoic acid at a concentration of 200 µM yielded their glucose esters with conversion rates of 74-95% in 20-30 h. These results suggest that the Ec-IbGT1 system efficiently produces these glucose esters.