Diversity of sugar acceptor of glycosyltransferase 1 from Bacillus cereus and its application for glucoside synthesis

Insight on Mercapto-Coumarins: Synthesis and Reactivity

Mercapto (or sulfanyl)-coumarins are heterocycles of great interest in the development of valuable active structures in material and biological domains. They represent a highly exploitable class of compounds that open many possibilities for further chemical transformations. The present review aims to draw focus toward the synthetic applicability of various forms of mercapto-coumarins and their representations in pharmaceuticals and industries. This work covers the literature issued from 1970 to 2021.

Controllable Iterative β-Glucosylation from UDP-Glucose by Bacillus cereus Glycosyltransferase GT1: Application for the Synthesis of Disaccharide-Modified Xenobiotics

Glycosylation in natural product metabolism and xenobiotic detoxification often leads to disaccharide-modified metabolites. The chemical synthesis of such glycosides typically separates the glycosylation steps in space and time. The option to perform the two-step glycosylation in one pot, and catalyzed by a single permissive enzyme, is interesting for a facile access to disaccharide-modified products. Here, we reveal the glycosyltransferase GT1 from Bacillus cereus (BcGT1; gene identifier: KT821092) for iterative O-β-glucosylation from uridine 5'-diphosphate (UDP)-glucose to form a β-linked disaccharide of different metabolites, including a C15 hydroxylated detoxification intermediate of the agricultural herbicide cinmethylin (15HCM). We identify thermodynamic and kinetic requirements for the selective formation of the disaccharide compared to the monosaccharide-modified 15HCM. As shown by NMR and high-resolution MS, β-cellobiosyl and β-gentiobiosyl groups are attached to the aglycone's O15 in a 2:1 ratio. Glucosylation reactions on methylumbelliferone and 4-nitrophenol involve reversible glycosyl transfer from and to UDP as well as UDP-glucose hydrolysis, both catalyzed by BcGT1. Collectively, this study delineates the iterative β-d-glucosylation of aglycones by BcGT1 and demonstrates applicability for the programmable one-pot synthesis of disaccharide-modified 15HCM.

Selective β-Mono-Glycosylation of a C15-Hydroxylated Metabolite of the Agricultural Herbicide Cinmethylin Using Leloir Glycosyltransferases

Cinmethylin is a well-known benzyl-ether derivative of the natural terpene 1,4-cineole that is used industrially as a pre-emergence herbicide in grass weed control for crop protection. Cinmethylin detoxification in plants has not been reported, but in animals, it prominently involves hydroxylation at the benzylic C15 methyl group. Here, we show enzymatic β-glycosylation of synthetic 15-hydroxy-cinmethylin to prepare a putative phase II detoxification metabolite of the cinmethylin in plants. We examined eight Leloir glycosyltransferases for reactivity with 15-hydroxy cinmethylin and revealed the selective formation of 15-hydroxy cinmethylin β-d-glucoside from uridine 5'-diphosphate (UDP)-glucose by the UGT71E5 from safflower (Carthamus tinctorius). The UGT71E5 showed a specific activity of 431 mU/mg, about 300-fold higher than that of apple (Malus domestica) UGT71A15 that also performed the desired 15-hydroxy cinmethylin mono-glycosylation. Bacterial glycosyltransferases (OleD from Streptomyces antibioticus, 2.9 mU/mg; GT1 from Bacillus cereus, 60 mU/mg) produced mixtures of 15-hydroxy cinmethylin mono- and disaccharide glycosides. Using UDP-glucose recycling with sucrose synthase, 15-hydroxy cinmethylin conversion with UGT71E5 efficiently provided the β-mono-glucoside (≥95% yield; ∼9 mM) suitable for biological studies.

Thioglycoligase derived from fungal GH3 β-xylosidase is a multi-glycoligase with broad acceptor tolerance

The synthesis of customized glycoconjugates constitutes a major goal for biocatalysis. To this end, engineered glycosidases have received great attention and, among them, thioglycoligases have proved useful to connect carbohydrates to non-sugar acceptors. However, hitherto the scope of these biocatalysts was considered limited to strong nucleophilic acceptors. Based on the particularities of the GH3 glycosidase family active site, we hypothesized that converting a suitable member into a thioglycoligase could boost the acceptor range. Herein we show the engineering of an acidophilic fungal β-xylosidase into a thioglycoligase with broad acceptor promiscuity. The mutant enzyme displays the ability to form O-, N-, S- and Se- glycosides together with sugar esters and phosphoesters with conversion yields from moderate to high. Analyses also indicate that the pKa of the target compound was the main factor to determine its suitability as glycosylation acceptor. These results expand on the glycoconjugate portfolio attainable through biocatalysis.

Recent Advances in the Metabolic Engineering of Yeasts for Ginsenoside Biosynthesis

Ginsenosides are a group of glycosylated triterpenes isolated from Panax species. Ginsenosides are promising candidates for the prevention and treatment of cancer as well as food additives. However, owing to a lack of efficient approaches for ginsenoside production from plants and chemical synthesis, ginsenosides may not yet have reached their full potential as medicinal resources. In recent years, an alternative approach for ginsenoside production has been developed using the model yeast Saccharomyces cerevisiae and non-conventional yeasts such as Yarrowia lipolytica and Pichia pastoris. In this review, various metabolic engineering strategies, including heterologous gene expression, balancing, and increasing metabolic flux, and enzyme engineering, have been described as recent advanced engineering techniques for improving ginsenoside production. Furthermore, the usefulness of a systems approach and fermentation strategy has been presented. Finally, the present challenges and future research direction for industrial cell factories have been discussed.

Identification of a UDP-Glucosyltransferase favouring substrate- and regio-specific biosynthesis of flavonoid glucosides in Cyclocarya paliurus

Cyclocarya paliurus (Batalin) Iljinsk is a medicinal plant belonging to the Juglandaceae family, and its leaves are used for a traditional sweet herbal tea with bioactivity against obesity and hyperglycaemia in China. It contains various bioactive specialised metabolites, such as flavonoids, triterpenes and their glucosides, while no glycosyltransferases (GTs) have been reported in C. paliurus to date. Herein, we identified and cloned the first glucosyltransferase C. paliurus GT1. The expression profiles of C. paliurus GT1 showed very high expression in young leaves, callus and branches, but relatively low expression in old leaves and bark and no expression in root. The recombinant C. paliurus GT1 protein was heterologously expressed in Escherichia coli and exhibited catalytic activity towards multiple flavonoids favouring substrate- and regio-specific biosynthesis. Further enzyme assays indicated a preference for certain hydroxyl group glucosylation by C. paliurus GT1. C. paliurus GT1 actively catalysed the glucosylation of flavones and flavonols, but it was less active towards isoflavones, flavanones or triterpenes. C. paliurus GT1 was also able to catalyse the attachment of sugars to the thiol (S-) or amine (N-) sites on aromatic compounds but not on aliphatic compounds. Molecular docking and site-directed mutagenesis analyses indicated that A43F, V84P, and M201Y dramatically altered the regio-selectivity and activity, and the W283M mutation and deletion of the V309-D320 region enhanced the activity and the formation of disaccharides. Herein, we present the identification and characterization of the first multi-functional glucosyltransferase in C. paliurus and provide a basis for understanding the biosynthesis of flavonoid glucosides. C. paliurus GT1 could be utilized as a synthetic biology tool for the synthesis of O-, N-, or S-glucosylated natural/unnatural products.

Efficient Synthesis of Crocins from Crocetin by a Microbial Glycosyltransferase from Bacillus subtilis 168

Crocins are the most important active ingredient found in Crocus sativus, a well-known "plant gold". The glycosyltransferase-catalyzed glycosylation of crocetin is the last step of biosynthesizing crocins and contributes to their structural diversity. Crocin biosynthesis is now hampered by the lack of efficient glycosyltransferases with activity toward crocetin. In this study, two microbial glycosyltransferases (Bs-GT and Bc-GTA) were successfully mined based on the comprehensive analysis of the PSPG motif and the N-terminal motif of the target plant-derived UGT75L6 and Cs-GT2. Bs-GT from Bacillus subtilis 168, an enzyme with a higher activity of glycosylation toward crocetin than that of Bc-GTA, was characterized. The efficient synthesis of crocins from crocetin catalyzed by microbial GT (Bs-GT) was first reported with a high molecular conversion rate of 81.9%, resulting in the production of 476.8 mg/L of crocins. The glycosylation of crocetin on its carboxyl groups by Bs-GT specifically produced crocin-5 and crocin-3, the important rare crocins.

One-Pot Synthesis of Ginsenoside Rh2 and Bioactive Unnatural Ginsenoside by Coupling Promiscuous Glycosyltransferase from Bacillus subtilis 168 to Sucrose Synthase

Ginsenosides, the major effective ingredients of Panax ginseng, exhibit various biological properties. UDP-glycosyltransferase (UGT)-mediated glycosylation is the last biosynthetic step of ginsenosides and contributes to their immense structural and functional diversity. In this study, UGT Bs-YjiC from Bacillus subtilis 168 was demonstrated to transfer a glucosyl moiety to the free C3-OH and C12-OH of protopanaxadiol (PPD) and PPD-type ginsenosides to synthesize natural and unnatural ginsenosides. In vitro assays showed that unnatural ginsenoside F12 (3- O-β-d-glucopyranosyl-12- O-β-d-glucopyranosyl-20( S)-protopanaxadiol) exhibited remarkable activity against diverse human cancer cell lines. A one-pot reaction by coupling Bs-YjiC to sucrose synthase (SuSy) was performed to regenerate UDP-glucose from sucrose and UDP. With PPD as the aglycon, an unprecedented high yield of ginsenosides F12 (3.98 g L^-1) and Rh2 (0.20 g L^-1) was obtained by optimizing the conversion conditions. This study provides an efficient approach for the biosynthesis of ginsenosides using a UGT-SuSy cascade reaction.

Use of a Promiscuous Glycosyltransferase from Bacillus subtilis 168 for the Enzymatic Synthesis of Novel Protopanaxatriol-Type Ginsenosides

Ginsenosides are the principal bioactive ingredients of Panax ginseng and possess diverse notable pharmacological activities. UDP-glycosyltransferase (UGT)-mediated glycosylation of the C6-OH and C20-OH of protopanaxatriol (PPT) is the prominent biological modification that contributes to the immense structural and functional diversity of PPT-type ginsenosides. In this study, the glycosylation of PPT and PPT-type ginsenosides was achieved using a promiscuous glycosyltransferase (Bs-YjiC) from Bacillus subtilis 168. PPT was selected as the probe for the in vitro glycodiversification of PPT-type ginsenosides using diverse UDP-sugars as sugar donors. Structural analysis of the newly biosynthesized products demonstrated that Bs-YjiC can transfer a glucosyl moiety to the free C3-OH, C6-OH, and C12-OH of PPT. Five PPT-type ginsenosides were biosynthesized, including ginsenoside Rh1 and four unnatural ginsenosides. The present study suggests flexible microbial UGTs play an important role in the enzymatic synthesis of novel ginsenosides.

Enzymatic synthesis of glycosides: from natural O- and N-glycosides to rare C- and S-glycosides

Carbohydrate related enzymes, like glycosyltransferases and glycoside hydrolases, are nowadays more easily accessible and are thought to represent powerful and greener alternatives to conventional chemical glycosylation procedures. The knowledge of their corresponding mechanisms has already allowed the development of efficient biocatalysed syntheses of complex O-glycosides. These enzymes can also now be applied to the formation of rare or unnatural glycosidic linkages.