Ionic Liquid Effects on the Activity of β-Glycosidase for the Synthesis of Salidroside in Co-solvent Systems

Strategies for modulating transglycosylation activity, substrate specificity, and product polymerization degree of engineered transglycosylases

Glycosides are widely used in many fields due to their favorable biological activity. The traditional plant extractions and chemical methods for glycosides production are limited by environmentally unfriendly, laborious protecting group strategies and low yields. Alternatively, enzymatic glycosylation has drawn special attention due to its mild reaction conditions, high catalytic efficiency, and specific stereo-/regioselectivity. Glycosyltransferases (GTs) and retaining glycoside hydrolases (rGHs) are two major enzymes for the formation of glycosidic linkages. Therein GTs generally use nucleotide phosphate activated donors. In contrast, GHs can use broader simple and affordable glycosyl donors, showing great potential in industrial applications. However, most rGHs mainly show hydrolysis activity and only a few rGHs, namely non-Leloir transglycosylases (TGs), innately present strong transglycosylation activities. To address this problem, various strategies have recently been developed to successfully tailor rGHs to alleviate their hydrolysis activity and obtain the engineered TGs. This review summarizes the current modification strategies in TGs engineering, with a special focus on transglycosylation activity enhancement, substrate specificity modulation, and product polymerization degree distribution, which provides a reference for exploiting the transglycosylation potentials of rGHs.

Medium engineering of phenylethanoid transfructosylation catalysed by yeast β-fructofuranosidase

Tyrosol and hydroxytyrosol, by-products of olive oil production, are valuable substrates for enzymatic transglycosylation that can provide products with pharmaceutical potential. Phenylethanoid fructosides are produced from sucrose and phenylethanoids by the catalytic action of β-fructofuranosidases. This work dealt with the potential of the most abundant β-fructofuranosidase, baker's yeast invertase, for this bioconversion. The effects of sucrose and phenylethanoid concentrations were investigated with a focus on the selectivity of phenylethanoid transfructosylation and fructoside yields. For this purpose, initial rate and progress curve experiments were carried out for the initial (hydroxy)tyrosol and sucrose concentrations of 0.072-0.3 M and 1-2 M, respectively. Reaction courses exhibited either a maximum or plateau of fructoside yield in the range of about 10-18%. The addition of deep eutectic solvents was applied in the concentration range from 5 to 70% (v/v) to investigate the possibility of shifting the reaction equilibrium towards fructoside synthesis.

Transrutinosylation of tyrosol by flower buds of Sophora japonica

Dried flower buds of Japanese sophora (Sophora japonica) comprising rutinosidase activity were tested in rutinosylation of tyrosol via transglycosylation process from rutin. Optimal conditions for transrutinosylation of tyrosol were 49 mM rutin and 290 mM tyrosol, giving maximum conversion up to 66.4% and 24% yield of isolated and purified rutinoside. The rutinosylation proceeded exclusively on the primary hydroxyl of tyrosol, thus forming rhamnosylated derivative of salidroside. This strict regioselectivity differentiates the sophora biocatalyst from microbial rutinosidases.

Improved synthesis of long-chain alkyl glucosides catalyzed by an engineered β-glucosidase in organic solvents and ionic liquids

OBJECTIVE

To synthesize octyl β-D-glucopyranoside (OG) and decyl β-D-glucopyranoside (DG) in three non-aqueous reaction systems, namely organic solvents, ionic liquids and co-solvent mixtures, via reverse hydrolysis reactions catalyzed by the N189F dalcochinase mutant.

RESULTS

The highest yield of OG (67 mol%) was obtained in the reaction containing 0.5 M glucose, 3 unit ml^-1 enzyme in 20% (v/v) octanol and 70% (v/v) [BMIm][PF₆] at 30 °C. On the other hand, the highest yield of DG (64 mol%) was obtained in the reaction containing 0.5 M glucose, 3 unit ml^-1 enzyme in 20% (v/v) decanol, 20% (v/v) acetone and 50% (v/v) [BMIm][PF₆] at 30 °C. The identities of OG and DG products were confirmed by HRMS and NMR.

CONCLUSION

This is the first report of enzymatic synthesis of OG and DG via reverse hydrolysis reactions in ionic liquids and co-solvent mixtures. The N189F dalcochinase mutant and the non-aqueous reaction systems described here show great potential for future commercial production of long-chain alkyl glucosides.

Comparative study of relationship between structure of phenylethanoid glycopyranosides and their activities using cell-free assays and human cells cultured in vitro

The study focused on protective potential of phytochemicals applicable in prevention and health protection is of great importance. Various structures of these compounds and a wide range of their biological activities have inspired organic chemists to sythesize their effective analogues in order to further increase their efficacy. The aims of our study were (i) to synthesize phenylethanoid glycopyranosides: salidroside (SALI - tyrosol β-d-glucopyranoside), tyrosol β-d-galactopyranoside (TYBGAL), tyrosol α-d-galactopyranoside (TYAGAL), tyrosol α-d-mannopyranoside (TYAMAN), hydroxytyrosol α-d-mannopyranoside (HOTAMA), homosyringyl β-d-glucopyranoside (HSYGLU), hydroxytyrosol β-d-xylopyranoside (HOTXYL) and hydroxysalidroside (HOSALI); (ii) to determine their antioxidant capacities (cell-free approaches); (iii) to evaluate their cytotoxicity (MTT test), protectivity against hydrogen peroxide (H₂O₂; comet assay) and effect on the intracellular glutathione level (iGSH; flow cytometry) in experimental system utilizing human hepatoma HepG2 cells. HOSALI, HOTAMA, HOTXYL and HSYGLU manifested the highest antioxidant capacity in cell-free assays and they were most active in protection of HepG2 cells against H₂O₂. On the other hand, pre-treatment of HepG2 cells with SALI had protective effects even though SALI displayed almost no activity in cell-free assays. Differences in the efficacy of the analogues revealed that structures of their molecules in terms of aglycone combined with sugar moiety affect their activities.

Purification and characterization of a glucose-tolerant β-glucosidase from black plum seed and its structural changes in ionic liquids

The objective of this study was to characterize a plant origin β-glucosidase from black plum seeds and identify its conformational changes in twenty-six imidazolium- and amino acid-based ionic liquids (ILs). The results revealed that the purified 60 kDa enzyme was monomeric in nature, maximally active at 55 °C and pH 5.0, and nearly completely inhibited by Hg²⁺ and Ag⁺. Attractive peculiarities of the relative low kinetic and higher glucose inhibition constants (K_m = 0.58 mM [pNPG]; K_i = 193.5 mM [glucose]) demonstrated its potential applications in food industry. Circular dichroism studies showed that the secondary structural changes of the enzyme depended not only on the anions, but also on the cations of the assayed ILs. Interestingly, no corresponding relations were observed between the changes in enzyme structure induced by ILs and its catalytic activities, suggesting that the influences of ILs on enzymatic processes don't rely simply on enzyme conformational changes.