Cloning and characterization of a glycosyltransferase from Catharanthus roseus for glycosylation of cardiotonic steroids and phenolic compounds

Glycosyltransferases: Pioneering roles in agriculture and medicine

Glycosyltransferases (GTs) belong to a diverse family of enzymes that catalyze the transfer of sugar moieties from activated donor sugars to specific acceptors, thus playing a crucial roles in various biological processes. This review explores the pioneering roles of uridine diphosphate-dependent GTs (UGTs), which use uridine diphosphate glucose as donors. UGTs have also been extensively studied in agricultural and medical fields, emphasizing their potential to revolutionize these sectors. In the agricultural sector, the genetic engineering of UGTs has demonstrate potential in developing crops with enhanced stress tolerance, regulated plant development, and increased resistance to pests and diseases. These advancements not only contribute to sustainable farming practices but also address global food security challenges by facilitating the production of more resilient plant varieties. Furthermore, UGTs facilitate the synthesis of complex carbohydrates and glycoconjugates in plants, which are critical for developing drugs and therapeutic strategies targeting various ailments, including cancer and infectious diseases. Thus, this review explored the functions and synthesis methods of flavonoid glycosides, terpenoid glycosides, and polyketosides in detail. Moreover, owing to the functional diversity of UGTs, numerous research methods were reviewed, and novel, more valuable UGTs will be obtained. In summary, this study synthesizes the current research findings and discusses future perspectives to underscore the transgenic technology and synthetic biological impact of UGTs on agriculture and medicine and bridge the gap between fundamental science and practical applications.

Functional characterization and protein engineering of glycosyltransferase for 2"-O-xylosylation of ginsenoside Rg3

The limited abundance of xylosylated ginsenosides and the lack of efficient biocatalysts hinder their pharmacological exploration. This study identified a 2"-O-xylosyltransferase (PnUGT57) from Panax notoginseng that catalyzes the conversion of ginsenoside Rg3 to notoginsenoside ST4. Wild-type PnUGT57 preferred UDP-xylose over UDP-glucose and UDP-rhamnose and displayed limited thermostability (t1/2 = 6.73 h at 30 °C). To enhance UDP-xylose specificity, sequence-guided mutagenesis generated the C140A variant, which achieved remarkable UDP-xylose specificity (100 % conversion) with a 1.34-fold increase in catalytic efficiency while showing weak activity toward UDP-glucose (8.7 %) and UDP-rhamnose (5.2 %) activity. The F367A mutant possesses only xylosyltransferase activity but with reduced catalytic efficiency (0.3-fold of the WT). Molecular docking revealed that the enhanced UDP-xylose specificity in C140A and F367A resulted from the loss of key hydrogen bonding and hydrophobic interactions. To improve thermostability, computational design produced a triple mutant (P101S/L200C/G255D) with an 8.58-fold longer half-life (57.76 h), attributed to optimized surface charge distribution and improved hydration layer formation, as confirmed by molecular dynamics simulation. The combinatorial mutant C140A/P101S/L200C/G255D synergistically improved UDP-xylose specificity, thermostability, and catalytic efficiency, enabling efficient ST4 biosynthesis. This study elucidates the catalytic mechanism of PnUGT57 and presents engineered variants as promising biocatalysts for sustainable ginsenoside production.

Approaches for Cannabinoid Glycosylation Catalyzed by CrUGT74AN3 and BlCGTase

Phytocannabinoids are natural products with highly promising pharmaceutical potential, mainly known from the plant Cannabis sativa. However, their bioavailability is limited due to their high lipophilicity. Modification through glycosylation is known to improve the water solubility and stability of molecules. Enzymatic glycosylation requires specific enzymes with high catalytic activity in combination with efficient production systems. To date, only a few glycosyltransferases with activity toward cannabinoids have been described. In this study, we explore the substrate spectrum of the promiscuous UDP-glycosyltransferase CrUGT74AN3 from Catharanthus roseus and demonstrate activity towards a broad range of cannabinoids and their biosynthetic intermediates. The highest activity was observed using cannabidiol (CBD) as an acceptor molecule. In addition, we show efficient biotransformation of CBD in an engineered Saccharomyces cerevisiae strain. We investigate the influence of the hydrolytic activity of endogenous glucosidases and identify the UDP-glucose supply as a limiting factor in the yeast system. The co-expression of CrUGT74AN3 and a cyclodextrin glycosyltransferase from Bacillus licheniformis in the engineered yeast strain led to the production of CBD-glycosides with up to six glucose moieties from CBD and cyclodextrin in vivo. Finally, we confirm the applicability of the engineered yeast systems to other cannabinoids using cannabigerol and cannabinol.

Genomics of sterols biosynthesis in plants: Current status and future prospects

Sterols produced by bacteria and all eukaryotic organisms are essential for membrane functionality and stability. They play a vital role in growth, development and in abiotic stress tolerance. They are involved in diverse responses to biotic and abiotic stresses that lead to providing resistance against multiple diseases. Additionally, sterols serve as defensive compounds against herbivorous insects and animals. Phytosterols derived from plants, improve human nutrition and health and cure different ailments. The biosynthetic pathways for sterols and triterpenes exhibit similarities until the synthesis of 2,3-oxidosqualene. The complexity of sterol pathways increases during the advanced stages of polycyclic structure synthesis, and remain poorly comprehended in plants. This review explores the various omics techniques used to unveil the functions of genes associated with the phytosterol pathways. The study investigates the biosynthetic gene clusters to clarify the structural arrangements of genes linked to metabolic pathways. Both the upstream and downstream genes associated with these pathways, as well as their evolutionary connections and interrelations within the pathways were brought to the forefront. Moreover, developing strategies to unravel the biosynthesis completely and their multi-layered regulation are crucial to comprehend the global roles that sterols play in plant growth, development, stress tolerance and in imparting defence against pathogens.

Recent developments in the enzymatic modifications of steroid scaffolds

Steroids are an important family of bioactive compounds. Steroid drugs are renowned for their multifaceted pharmacological activities and are the second-largest category in the global pharmaceutical market. Recent developments in biocatalysis and biosynthesis have led to the increased use of enzymes to enhance the selectivity, efficiency, and sustainability for diverse modifications of steroids. This review discusses the advancements achieved over the past five years in the enzymatic modifications of steroid scaffolds, focusing on enzymatic hydroxylation, reduction, dehydrogenation, cascade reactions, and other modifications for future research on the synthesis of novel steroid compounds and related drugs, and new therapeutic possibilities.

A highly versatile fungal glucosyltransferase for specific production of quercetin-7-O-β-D-glucoside and quercetin-3-O-β-D-glucoside in different hosts

Glycosylation is an effective way to improve the water solubility of natural products. In this work, a novel glycosyltransferase gene (BbGT) was discovered from Beauveria bassiana ATCC 7159 and heterologously expressed in Escherichia coli. The purified enzyme was functionally characterized through in vitro enzymatic reactions as a UDP-glucosyltransferase, converting quercetin to five monoglucosylated and one diglucosylated products. The optimal pH and temperature for BbGT are 35 ℃ and 8.0, respectively. The activity of BbGT was stimulated by Ca²⁺, Mg²⁺, and Mn²⁺, but inhibited by Zn²⁺. BbGT enzyme is flexible and can glycosylate a variety of substrates such as curcumin, resveratrol, and zearalenone. The enzyme was also expressed in other microbial hosts including Saccharomyces cerevisiae, Pseudomonas putida, and Pichia pastoris. Interestingly, the major glycosylation product of quercetin in E. coli, P. putida, and P. pastoris was quercetin-7-O-β-D-glucoside, while the enzyme dominantly produced quercetin-3-O-β-D-glucoside in S. cerevisiae. The BbGT-harboring E. coli and S. cerevisiae strains were used as whole-cell biocatalysts to specifically produce the two valuable quercetin glucosides, respectively. The titer of quercetin-7-O-β-D-glucosides was 0.34 ± 0.02 mM from 0.83 mM quercetin in 24 h by BbGT-harboring E. coli. The yield of quercetin-3-O-β-D-glucoside was 0.22 ± 0.02 mM from 0.41 mM quercetin in 12 h by BbGT-harboring S. cerevisiae. This work thus provides an efficient way to produce two valuable quercetin glucosides through the expression of a versatile glucosyltransferase in different hosts. KEY POINTS: • A highly versatile glucosyltransferase was identified from B. bassiana ATCC 7159. • BbGT converts quercetin to five mono- and one di-glucosylated derivatives in vitro. • Different quercetin glucosides were produced by BbGT in E. coli and S. cerevisiae.

A new synthetic biology approach for the production of curcumin and its glucoside in Atropa belladonna hairy roots

Curcumin has ignited global interest as an elite drugable molecule, owing to its time-honoured pharmacological activities against diverse human ailments. Limited natural accessibility and poor oral bioavailability caused major hurdles in the curcumin-based drug development process. We report the first successful testimony of curcumin and its glucoside synthesis in Atropa belladonna hairy roots (HR) through metabolic engineering. Re-routing the inherent biosynthetic precursors of the phenylpropanoid pathway of A. belladonna by heterologous expression of key curcumin biosynthetic pathway genes (i.e., Diketide-CoA synthase-DCS and Curcumin synthase-CURS3) and glucosyltransferase gene (CaUGT2) resulted in the production of curcumin and its glucoside in HR clones. Under shake-flask cultivation, the PGD2-HR1clone bearing DCS/ CURS3 genes showed the maximum curcumin yield (180.62 ± 4.7 μg/g DW), while the highest content of curcumin monoglucoside (32.63 ± 2.27 μg/g DW) along with curcumin (67.89 ± 2.56 μg/g DW) were noted in the PGD3-HR3 clone co-expressing DCS/CURS3 and CaUGT2 genes. Bioreactor up-scaling showed yield improvements in the PGD2-HR1 (2.3 fold curcumin) and the PGD3-HR3 clone (0.9 and 1.65 folds of curcumin-monoglucoside and curcumin respectively). These findings proved the advantageous use of HR cultures as the production source for curcumin and its glucoside, which remained unexplored so far.