Mutational analyses for product specificity of YjiC towards α-mangostin mono-glucoside

A novel glycosyltransferase from Bacillus subtilis achieves zearalenone detoxification by diglycosylation modification

Zearalenone (ZEN), a nonsteroidal estrogenic mycotoxin produced by Fusarium spp., contaminates cereals and threatens human and animal health by inducing hepatotoxicity, immunotoxicity, and genotoxicity. In this study, a new Bacillus subtilis strain, YQ-1, with a strong ability to detoxify ZEN, was isolated from soil samples and characterized. YQ-1 was confirmed to degrade more than 46.26% of 20 μg mL-1 ZEN in Luria-Bertani broth and 98.36% in fermentation broth within 16 h at 37 °C; one of the two resulting products was ZEN-diglucoside. Under optimal reaction conditions (50 °C and pH 5.0-9.0), the reaction mixture generated by YQ-1 catalyzing ZEN significantly reduced the promoting effect of ZEN on MCF-7 cell proliferation, effectively eliminating the estrogenic toxicity of ZEN. In addition, a new glycosyltransferase gene (yqgt) from B. subtilis YQ-1 was cloned with 98% similarity to Bs-YjiC from B. subtilis 168 and over-expressed in E. coli BL21 (DE3). ZEN glycosylation activity converted 25.63% of ZEN (20 μg mL-1) to ZEN-diG after 48 h of reaction at 37 °C. The characterization of ZEN degradation by B. subtilis YQ-1 and the expression of YQGT provide a theoretical basis for analyzing the mechanism by which Bacillus spp. degrades ZEN.

Evaluation of double expression system for co-expression and co-immobilization of flavonoid glucosylation cascade

Glucosylation cascade consisting of Leloir glycosyltransferase and sucrose synthase with in situ regeneration system of expensive and low available nucleotide sugars is a game-changing strategy for enzyme-based production of glycoconjugates of relevant natural products. We designed a stepwise approach including co-expression and one-step purification and co-immobilization on glass-based EziG resins of sucrose synthase from Glycine max (GmSuSy) with promiscuous glucosyltransferase YjiC from Bacillus licheniformis to produce efficient, robust, and versatile biocatalyst suited for preparative scale flavonoid glucosylation. The undertaken investigations identified optimal reaction conditions (30 °C, pH 7.5, and 10 mM Mg2+) and the best-suited carrier (EziG Opal). The prepared catalyst exhibited excellent reusability, retaining up to 96% of initial activity after 12 cycles of reactions. The semi-preparative glucosylation of poorly soluble isoflavone Biochanin A resulted in the production of 73 mg Sissotrin (Biochanin A 7-O-glucoside). Additionally, the evaluation of the designed double-controlled, monocistronic expression system with two independently induced promoters (rhaBAD and trc) brought beneficial information for dual-expression plasmid design. KEY POINTS: • Simultaneous and titratable expression from two independent promoters is possible, although full control over the expression is limited. • Designed catalyst managed to glucosylate poorly soluble isoflavone. • The STY of Sissotrin using the designed catalyst reached 0.26 g/L∙h∙g of the resin.

Insight into glucocorticoids glucosylation by glucosyltransferase: A combined experimental and in-silico approach

Glucosyltransferases catalyze the glucosidic bond formation by transferring a glucose molecule from an activated sugar donor to an acceptor substrate. Glucocorticoids (GCs) are adrenal-derived steroid hormones most widely used for anti-inflammatory treatments. In this study, we biotransformed two selected GCs, cortisone and prednisone, into their O-glucoside derivatives using a versatile UDP-glycosyltransferase UGT-1. Complete structural assignment of glucosylated products revealed that the bioconversion by regio-selective glucosylation of cortisone and prednisone produced cortisone 21-glucoside and prednisone 21-glucoside, respectively. We also combined molecular dynamics (MD) simulation to study the binding feature and mechanism of glucosylation. MD simulation studies showed the formation of a stable complex between protein, glucose donor, and substrate, stabilized by hydrogen bonds. Overall, we were able to provide explanations for the experimentally observed selectivity for glucosylation by integrating experimental and computational techniques.

Structural and biochemical studies of the glycosyltransferase Bs-YjiC from Bacillus subtilis

Glycosylation possess prominent biological and pharmacological significance in natural product and drug candidate synthesis. The glycosyltransferase YjiC, discovered from Bacillus subtilis (Bs-YjiC), shows potential applications in drug development due to its wide substrate spectrums. In order to elucidate its catalytic mechanism, we solved the crystal structure of Bs-YjiC, demonstrating that Bs-YjiC adopts a typical GT-B fold consisting of a flexible N-domain and a relatively rigid C-domain. Structural analysis coupled with site-directed mutagenesis studies revealed that site Ser277 was critical for Nucleoside Diphosphate (NDP) recognition, while Glu317, Gln318, Ser128 and Ser129 were crucial for glycosyl moiety recognition. Our results illustrate the structural basis for acceptor promiscuity in Bs-YjiC and provide a starting point for further protein engineering of Bs-YjiC in industrial and pharmaceutical applications.

An Ambidextrous Polyphenol Glycosyltransferase PaGT2 from Phytolacca americana

The glycosylation of small hydrophobic compounds is catalyzed by uridine diphosphate glycosyltransferases (UGTs). Because glycosylation is an invaluable tool for improving the stability and water solubility of hydrophobic compounds, UGTs have attracted attention for their application in the food, cosmetics, and pharmaceutical industries. However, the ability of UGTs to accept and glycosylate a wide range of substrates is not clearly understood due to the existence of a large number of UGTs. PaGT2, a UGT from Phytolacca americana, can regioselectively glycosylate piceatannol but has low activity toward other stilbenoids. To elucidate the substrate specificity and catalytic mechanism, we determined the crystal structures of PaGT2 with and without substrates and performed molecular docking studies. The structures have revealed key residues involved in substrate recognition and suggest the presence of a nonconserved catalytic residue (His81) in addition to the highly conserved catalytic histidine in UGTs (His18). The role of the identified residues in substrate recognition and catalysis is elucidated with the mutational assay. Additionally, the structure-guided mutation of Cys142 to other residues, Ala, Phe, and Gln, allows PaGT2 to glycosylate resveratrol with high regioselectivity, which is negligibly glycosylated by the wild-type enzyme. These results provide a basis for tailoring an efficient glycosyltransferase.

OleD Loki as a Catalyst for Hydroxamate Glycosylation

Herein we describe the ability of the permissive glycosyltransferase (GT) OleD Loki to convert a diverse set of >15 histone deacetylase (HDAC) inhibitors (HDACis) into their corresponding hydroxamate glycosyl esters. Representative glycosyl esters were subsequently evaluated in assays for cancer cell line cytotoxicity, chemical and enzymatic stability, and axolotl embryo tail regeneration. Computational substrate docking models were predictive of enzyme-catalyzed turnover and suggest certain HDACis may form unproductive, potentially inhibitory, complexes with GTs.