Engineering of cyclodextrin glycosyltransferase from Paenibacillus macerans for enhanced product specificity of long-chain glycosylated sophoricosides

Anchor Peptide-Based Immobilization Strategy Promote the Applications of Pickering Emulsion System in Natural Products Glycosylation

Pickering emulsion systems serve as an advanced platform for efficient fine chemical production in biphasic enzymatic catalysis, though their applications are currently limited to a few commercial enzyme classes. Herein, we designed an anchor peptide-based immobilization strategy for Pickering emulsions to achieve efficient glycosylation of natural products by glycosyltransferases (GTs). Firstly, through enzyme mining, natural GTs were utilized to synthesize pharmaceutically important acacetin glucoside and galactoside. However, the best-performing enzymes, BacGT and BarGT-3, still showed low conversions for acacetin glucoside (<40%) and galactoside (<10%). Then, Spy chemistry was employed to cyclize these two GTs (Spy_BacGT and Spy_BarGT-3) for improved robustness, and a Pickering emulsion was formed with the free two Spy_GTs, using 20% 2-hexanone and 1% mesoporous silica nanoparticles (carriers of mesoporous, CM), achieving 70% and 66% conversions of acacetin glucoside and galactoside, respectively. Further immobilization of the cyclized GTs onto CM via the anchor peptide liquid chromatography peak I (LCI) (Spy_BacGT/BarGT-3_LCI@CM) further enabled the system to reach more than 90% conversions of acacetin glycosides, retaining 90% conversions after 6-8 cycles. Moreover, this strategy was applied to GTs exhibiting substrate selectivity, achieving efficient nonselective catalysis. This study provides a simple and efficient immobilization strategy to broaden the applications of the Pickering emulsion system in enzymatic glycosylation.

Glycosylation of flavonoids by sucrose- and starch-utilizing glycoside hydrolases: A practical approach to enhance glycodiversification

Flavonoids are ubiquitous and diverse in plants and inseparable from the human diet. However, in terms of human health, their further research and application in functional food and pharmaceutical industries are hindered by their low water solubility. Therefore, flavonoid glycosylation has recently attracted research attention because it can modulate the physicochemical and biochemical properties of flavonoids. This review represents a comprehensive overview of the O-glycosylation of flavonoids catalyzed by sucrose- and starch-utilizing glycoside hydrolases (GHs). The characteristics of this feasible biosynthesis approach are systematically summarized, including catalytic mechanism, specificity, reaction conditions, and yields of the enzymatic reaction, as well as the physicochemical properties and bioactivities of the product flavonoid glycosides. The cheap glycosyl donor substrates and high yields undoubtedly make it a practical flavonoid modification approach to enhance glycodiversification.

Engineering of Cyclodextrin Glycosyltransferase through a Size/Polarity Guided Triple-Code Strategy with Enhanced α-Glycosyl Hesperidin Synthesis Ability

Hesperidin, a flavonoid enriched in citrus peel, can be enzymatically glycosylated using CGTase with significantly improved water solubility. However, the reaction catalyzed by wild-type CGTase is rather inefficient, reflected in the poor production rate and yield. By focusing on the aglycon attacking step, seven residues were selected for mutagenesis in order to improve the transglycosylation efficiency. Due to the lack of high-throughput screening technology regarding to the studied reaction, we developed a size/polarity guided triple-code strategy in order to reduce the library size. The selected residues were replaced by three rationally chosen amino acids with either changed size or polarity, leading to an extremely condensed library with only 32 mutants to be screened. Twenty-five percent of the constructed mutants were proved to be positive, suggesting the high quality of the constructed library. Specific transglycosylation activity of the best mutant Y217F was assayed to be 935.7 U/g, and its k_cat/K_mA is 6.43 times greater than that of the wild type. Homology modeling and docking computation suggest the source of notably enhanced catalytic efficiency is resulted from the combination of ligand transfer and binding effect. IMPORTANCE Size/polarity guided triple-code strategy, a novel semirational mutagenesis strategy, was developed in this study and employed to engineer the aglycon attacking site of CGTase. Screening pressure was set as improved hesperidin glucoside synthesis ability, and eight positive mutants were obtained by screening only 32 mutants. The high quality of the designed library confirms the effectiveness of the developed strategy is potentially valuable to future mutagenesis studies. Mechanisms of positive effect were explained. The best mutant exhibits 6.43 times enhanced k_cat/K_mA value and confirmed to be a superior whole-cell catalyst with potential application value in synthesizing hesperidin glucosides.