Abstract
Flavonoids are multi-active ingredients found in most cosmetics and are used as antioxidants and calming agents. They are plant-based naturally occurring pharmacological agents with a great deal of therapeutic potential. Glycosylation of flavonoids is a promising way to produce new therapeutics, fluorescent probes, and cosmetics. Amylosucrase (DgAS) isolated from Deinococcus geothermalis is a versatile enzyme that hydrolyses sucrose as well as catalyses transglucosylation with flavonoids, polyphenols, and others. This study aimed to investigate the reasons behind the differential yields of glycosylated flavonoid and their substrate diversification through in vitro assays. Molecular docking and density function theory (DFT)-based analysis were performed with nine substances (apigenin, daidzein, fisetin, kaempferol, luteolin, morin, myricetin, quercetin, and phloretin) to analyze the efficacy of O-glycosylation by DgAS in the presence of sucrose. We found through in vitro and in silico analyses that there is no glycosylation at the C-5 hydroxyl group of ring A and C-4’ hydroxyl group of ring B in flavonoids when reactions are performed using 0.5 µg/ml DgAS at 40°C for 2 h in 50 mM Tris HCl buffer (pH 7), under conditions where the molar ratio of flavonoids to sucrose was 1:50. However, there is mono-glucosylation at hydroxyl group in flavonoids under the same reaction conditions. On the other hand, natural phenol phloretin yielded a di-glucosylated product. It is concluded that the hydroxyl group of the highest acidity (weaker O-H bond) is more prone to glycosylation, and the planarity and stereochemistry of flavonoids also determine the reaction efficacy.