Enzymatic and selective production of alkyl α-D-glucopyranosides by the α-glucosyl transfer enzyme derived from Xanthomonas campestris WU-9701

Several alkyl glucosides exhibit various bioactivities. 1-Octyl β-D-glucopyranoside produced by organic synthesis is used as a nonionic surfactant. However, no convenient method has been developed for the selective production of alkyl α-glucosides (α-AGs), such as 1-octyl α-D-glucopyranoside (α-OG). Therefore, we developed a simple method for selective production of α-AGs using the glucosyl transfer enzyme XgtA, (E.C. 3.2.1.20), derived from Xanthomonas campestris WU-9701. When 0.80 M alkyl alcohol and 2.5 units XgtA were incubated in 2.0 mL of 30 mM HEPES-NaOH buffer (pH 8.0) containing 1.2 M maltose at 45 °C, a specific α-AG corresponding to each alkyl alcohol (C2–C10) was detected. Under the standard conditions, we examined the selective production of α-OG from 1-octanol and maltose using XgtA. The reaction product was isolated and identified as α-OG via ¹H nuclear magnetic resonance and nuclear overhauser effect spectroscopy analyses. No other glucosylated products, such as maltotriose, were detected in the reaction mixture. Under the standard conditions at 45 °C for 96 h, 243 mM α-OG (71 g/L) was produced in one batch production. Moreover, the addition of glucose isomerase to the reaction mixture decreased the concentration of glucose released via the reaction and increased the amount of α-OG produced; 359 mM α-OG (105 g/L) was maximally produced at 96 h. In conclusion, this study demonstrates the selective production of α-AGs using a simple enzymatic reaction, and XgtA has the potential to selectively produce various α-AGs.