Enzyme-Catalyzed Glycosylation of Curcumin and Its Analogues by Glycosyltransferases from Bacillus subtilis ATCC 6633

Curcumin is a naturally occurring polyphenolic compound that is commonly used in both medicine and food additives, but its low aqueous solubility and poor bioavailability hinder further clinical applications. For assessing the effect of the glycosylation of curcumin on its aqueous solubility, two glycosyltransferase genes (BsGT1andBsGT2) were cloned from the genome of the strainBacillus subtilisATCC 6633 and over-expressed inEscherichia coli.Then, the two glycosyltransferases were purified, and their glycosylation capacity toward curcumin and its two analogues was verified. The results showed that bothBsGT1andBsGT2could convert curcumin and its two analogues into their glucosidic derivatives. Then, the structures of the derivatives were characterized as curcumin 4′-O-β-D-glucoside and two new curcumin analogue monoglucosides namely, curcumoid-O-α-D-glucoside (2a) and 3-pentadienone-O-α-D-glucoside (3a) by nuclear magnetic resonance (NMR) spectroscopy. Subsequently, the dissolvability of curcumin 4′-O-β-D-glucoside was measured to be 18.78 mg/L, while its aglycone could not be determined. Furthermore, the optimal catalyzing conditions and kinetic parameters ofBsGT1andBsGT2toward curcumin were determined, which showed that the Kcat value ofBsGT1was about 2.6-fold higher than that ofBsGT2, indicating that curcumin is more favored forBsGT2. Our findings effectively apply the enzymatic approach to obtain glucoside derivatives with enhanced solubility.Keywords:curcumin 4′-O-β-D-glucoside;glycosyltransferases;Bacillus subtilisATCC 6633