Improving the Transglycosylation Activity of α-Glucosidase from Xanthomonas campestris Through Semi-rational Design for the Synthesis of Ethyl Vanillin-α-Glucoside

The α-glucosidase (EC 3.2.1.20) XgtA produced by Xanthomonas campestris shows high α-glucosyl transfer activity toward alcoholic and phenolic hydroxyl groups. Ethyl vanillin-α-glucoside, a precursor-aroma compound with improved water solubility and thermal stability, can be synthesized through the transglycosylation of ethyl vanillin by XgtA. However, its low ethyl vanillin-α-glucoside yield and ability to hydrolyze ethyl vanillin-α-glucoside limits for industrial applications. Rational design and site-directed mutagenesis were employed to generate three variants of X. campestris α-glucosidase, L145I, S272T, and L145I/S272T, with improved transglycosylation activity toward EV. The highest yield is up to 52.41% by L145I/S272T, which also displayed remarkably lower hydrolysis activity toward the glycoside product EVG compared to XgtA. These results also showed that the mutation in sugar-binding subsite + 1 is more effective than subsite -1 for enhancing the ratio of transglycosylation/hydrolysis for the α-glucosidase XgtA.