Abstract
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 (BsGT1 and BsGT2) were cloned from the genome of the strain Bacillus subtilis ATCC 6633 and over-expressed in Escherichia coli. Then, the two glycosyltransferases were purified, and their glycosylation capacity toward curcumin and its two analogues was verified. The results showed that both BsGT1 and BsGT2 could 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 of BsGT1 and BsGT2 toward curcumin were determined, which showed that the Kcat value of BsGT1 was about 2.6-fold higher than that of BsGT2, indicating that curcumin is more favored for BsGT2. Our findings effectively apply the enzymatic approach to obtain glucoside derivatives with enhanced solubility.
Highlights
IntroductionCurcumin (diferuloylmethane) is extracted from the rhizome of traditional Chinese medicine
Curcumin is extracted from the rhizome of traditional Chinese medicineZedoary turmeric and Curcuma longa, and is a natural polyphenolic compound that is used as a food coloring in pastries, mustards, curries, and dairy food, as well as rice, meat, and fish dishes in the USA and England [1,2]
In this study, compared with YjiC from Bacillus licheniformis DSM 13, CaUGT2 from Catharanthus roseus, and UGT76G1 from Stevia rebaudiana catalyzing curcumin to diglucoside and monoglucoside [33,34,35], BsGT1 and BsGT2 could catalyze curcumin and its two analogues to only their monoglucosides, which indicate that the two GTs are highly selective to the single phenolic hydroxyl group of such compounds
Summary
Curcumin (diferuloylmethane) is extracted from the rhizome of traditional Chinese medicine. Zedoary turmeric and Curcuma longa, and is a natural polyphenolic compound that is used as a food coloring in pastries, mustards, curries, and dairy food, as well as rice, meat, and fish dishes in the USA and England [1,2] Besides these usages, curcumin exerts promising pharmacological properties, such as anti-oxidant, anticancer, anti-inflammatory and antifibrinolytic effects [3,4,5]. While many curcumin analogues have been synthesized in an attempt to unearth new substitutes, none have possessed good drug candidate properties [12] This is an imperative issue that has attracted scientists’ interest in significantly improving its aqueous solubility. The glycosylation of natural products (NPs) has the potential to enhance the aqueous solubility of hydrophobic compounds notably, and catalysis by GTs (glycosyltransferases) plays a prominent role in drug discovery and development [13,14,15]. The aqueous solubility of the curcumin and its glucoside derivative were measured
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