Production of cinnamates and benzoates glucose esters by bioconversion using <i>Escherichia coli</i> expressing a glucosyltransferase from sweet potato

Sweet potatoes (<i>Ipomoea batatas</i>) produce glucose esters from cinnamates during stress responses. We isolated a glucosyltransferase, <i>IbGT1</i> (UGT84A20), from sweet potato and characterized its recombinant enzyme heterologously expressed in <i>Escherichia coli</i>. The recombinant IbGT1 enzyme reacted with cinnamates, especially <i>p</i>-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-<i>O</i>-glucosides. Bioconversion using <i>E. coli</i> expressing IbGT1 (Ec-IbGT1) as a whole cell biocatalyst converted 200 µM cinnamates such as <i>p</i>-coumaric acid and benzoates such as <i>p</i>-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, <i>trans</i>-cinnamic acid and <i>p</i>-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.