Ca2+ assisted glycosylation of phenolic compounds by phenolic-UDP-glycosyltransferase from Bacillus subtilis PI18.

A phenolic-UDP-glycosyltransferase Bs-PUGT from Bacillus subtilis PI18 was cloned and expressed in Escherichia coli BL21 (DE3). The purified Bs-PUGT could catalyze the glycosylation of tyrosol, 4-hydroxybenzyl alcohol, 2-hydroxybenzyl alcohol, caffeic acid, cinnamic alcohol, ferulic acid, and so on. This enzyme showed a high activity and stability over a broad pH range and was sensitive to temperature. Studies on the kinetic parameters indicated that the affinity of Bs-PUGT to UDP-G (Km) and its catalytic efficiency (Kcat) increased by 1.5-fold and 1.7-fold, respectively, with the addition of 10 mM Ca2+. The most effective glycosylation of caffeic acid catalyzed by whole-cell E. coli/Bs-PUGT was achieved with a molar yield of 78.3% in a system with pH 8.0, 30 °C, 25 g/L sucrose, 10 mM Ca2+, and 0.5 g/L substrate concentration. The addition of Ca2+ increased the molar yield of caffeic acid glucosides and shortened the reaction. This work proposes a strategy for the efficient glycosylation of phenolic compounds by microbe-derived glycosyltransferase assisted by metal ions.