Highly Efficient Biosynthesis of Glycyrrhetinic Acid Glucosides by Coupling of Microbial Glycosyltransferase to Plant Sucrose Synthase

Directional co-immobilization of artificial multimeric-enzyme complexes as a robust biocatalyst for biosynthesis curcumin glucosides and regeneration of UDP-glucose

Site-directed protein immobilization allows the homogeneous orientation of proteins while maintaining high activity, which is advantageous for various applications. In this study, the use of SpyCatcher/SpyTag technology and magnetic nickel ferrite (NiFe2O4 NPs) nanoparticles were used to prepare a site-directed immobilization of BsUGT2m from Bacillus subtilis and AtSUSm from Arabidopsis thaliana for enhancing curcumin glucoside production with UDP-glucose regeneration from sucrose and UDP. The immobilization of self-assembled multienzyme complex (MESAs) enzymes were characterized for immobilization parameters and stability, including thermal, pH, storage stability, and reusability. The immobilized MESAs exhibited a 2.5-fold reduction in UDP consumption, enhancing catalytic efficiency. Moreover, the immobilized MESAs demonstrated high storage and temperature stability over 21 days at 4 °C and 25 °C, outperforming their free counterparts. Reusability assays showed that the immobilized MESAs retained 78.7 % activity after 10 cycles. Utilizing fed-batch technology, the cumulative titer of curcumin 4'-O-β-D-glucoside reached 6.51 mM (3.57 g/L) and 9.45 mM (5.18 g/L) for free AtSUSm/BsUGT2m and immobilized MESAs, respectively, over 12 h. This study demonstrates the efficiency of magnetic nickel ferrite nanoparticles in co-immobilizing enzymes, enhancing biocatalysts' catalytic efficiency, reusability, and stability.

A growth selection system for sucrose synthases (SuSy): design and test

High throughput screening (HTS) methods of enzyme variants are essential for the development of robust biocatalysts suited for low impact, industrial scale, biobased synthesis of a myriad of compounds. However, for the majority of enzyme classes, current screening methods have limited throughput, or need expensive substrates in combination with sophisticated setups. Here, we present a straightforward, high throughput selection system that couples sucrose synthase activity to growth. Enabling high throughput screening of this enzyme class holds the potential to facilitate the creation of robust variants, which in turn can significantly impact the future of cost effective industrial glycosylation.

Recent advances in triterpenoid pathway elucidation and engineering

Triterpenoids are among the most assorted class of specialized metabolites found in all the taxa of living organisms. Triterpenoids are the leading active ingredients sourced from plant species and are utilized in pharmaceutical and cosmetic industries. The triterpenoid precursor 2,3-oxidosqualene, which is biosynthesized via the mevalonate (MVA) pathway is structurally diversified by the oxidosqualene cyclases (OSCs) and other scaffold-decorating enzymes such as cytochrome P450 monooxygenases (P450s), UDP-glycosyltransferases (UGTs) and acyltransferases (ATs). A majority of the bioactive triterpenoids are harvested from the native hosts using the traditional methods of extraction and occasionally semi-synthesized. These methods of supply are time-consuming and do not often align with sustainability goals. Recent advancements in metabolic engineering and synthetic biology have shown prospects for the green routes of triterpenoid pathway reconstruction in heterologous hosts such as Escherichia coli, Saccharomyces cerevisiae and Nicotiana benthamiana, which appear to be quite promising and might lead to the development of alternative source of triterpenoids. The present review describes the biotechnological strategies used to elucidate complex biosynthetic pathways and to understand their regulation and also discusses how the advances in triterpenoid pathway engineering might aid in the scale-up of triterpenoid production in engineered hosts.

Utilization of glycosyltransferases as a seamless tool for synthesis and modification of the oligosaccharides-A review

Glycosyltransferases (GTs) catalyze the transfer of active monosaccharide donors to carbohydrates to create a wide range of oligosaccharide structures. GTs display strong regioselectivity and stereoselectivity in producing glycosidic bonds, making them extremely valuable in the in vitro synthesis of oligosaccharides. The synthesis of oligosaccharides by GTs often gives high yields; however, the enzyme activity may experience product inhibition. Additionally, the higher cost of nucleotide sugars limits the usage of GTs for oligosaccharide synthesis. In this review, we comprehensively discussed the structure and mechanism of GTs based on recent literature and the CAZY website data. To provide innovative ideas for the functional studies of GTs, we summarized several remarkable characteristics of GTs, including folding, substrate specificity, regioselectivity, donor sugar nucleotides, catalytic reversibility, and differences between GTs and GHs. In particular, we highlighted the recent advancements in multi-enzyme cascade reactions and co-immobilization of GTs, focusing on overcoming problems with product inhibition and cost issues. Finally, we presented various types of GT that have been successfully used for oligosaccharide synthesis. We concluded that there is still an opportunity for improvement in enzymatically produced oligosaccharide yield, and future research should focus on improving the yield and reducing the production cost.

Solvent Engineering for Nonpolar Substrate Glycosylation Catalyzed by the UDP-Glucose-Dependent Glycosyltransferase UGT71E5: Intensification of the Synthesis of 15-Hydroxy Cinmethylin β-d-Glucoside

Sugar nucleotide-dependent glycosyltransferases are powerful catalysts of the glycosylation of natural products and xenobiotics. The low solubility of the aglycone substrate often limits the synthetic efficiency of the transformation catalyzed. Here, we explored different approaches of solvent engineering for reaction intensification of β-glycosylation of 15HCM (a C15-hydroxylated, plant detoxification metabolite of the herbicide cinmethylin) catalyzed by safflower UGT71E5 using UDP-glucose as the donor substrate. Use of a cosolvent (DMSO, ethanol, and acetonitrile; ≤50 vol %) or a water-immiscible solvent (n-dodecane, n-heptane, n-hexane, and 1-hexene) was ineffective due to enzyme activity and stability, both impaired ≥10-fold compared to a pure aqueous solvent. Complexation in 2-hydroxypropyl-β-cyclodextrin enabled dissolution of 50 mM 15HCM while retaining the UGT71E5 activity (∼0.32 U/mg) and stability. Using UDP-glucose recycling, 15HCM was converted completely, and 15HCM β-d-glucoside was isolated in 90% yield (∼150 mg). Collectively, this study highlights the requirement for a mild, enzyme-compatible strategy for aglycone solubility enhancement in glycosyltransferase catalysis applied to glycoside synthesis.

GA signaling protein LsRGL1 interacts with the abscisic acid signaling-related gene LsWRKY70 to affect the bolting of leaf lettuce

A variety of endogenous hormone signals, developmental cues, and environmental stressors can trigger and promote leaf lettuce bolting. One such factor is gibberellin (GA), which has been linked to bolting. However, the signaling pathways and the mechanisms that regulate the process have not been discussed in full detail. To clarify the potential role of GAs in leaf lettuce, significant enrichment of GA pathway genes was found by RNA-seq, among which the LsRGL1 gene was considered significant. Upon overexpression of LsRGL1, a noticeable inhibition of leaf lettuce bolting was observed, whereas its knockdown by RNA interference led to an increase in bolting. In situ hybridization analysis indicated a significant accumulation of LsRGL1 in the stem tip cells of overexpressing plants. Leaf lettuce plants stably expressing LsRGL1 were examined concerning differentially expressed genes through RNA-seq analysis, and the data indicated enhanced enrichment of these genes in the 'plant hormone signal transduction' and 'phenylpropanoid biosynthesis' pathways. Additionally, significant changes in LsWRKY70 gene expression were identified in COG (Clusters of Orthologous Groups) functional classification. The results of yeast one-hybrid, β-glucuronidase (GUS), and biolayer interferometry (BLI) experiments showed that LsRGL1 proteins directly bind to the LsWRKY70 promoter. Silencing LsWRKY70 by virus-induced gene silencing (VIGS) can delay bolting, regulate the expression of endogenous hormones, abscisic acid (ABA)-linked genes, and flowering genes, and improve the nutritional quality of leaf lettuce. These results strongly associate the positive regulation of bolting with LsWRKY70 by identifying its vital functions in the GA-mediated signaling pathway. The data obtained in this research are invaluable for further experiments concerning the development and growth of leaf lettuce.

One-pot biosynthesis of gastrodin using UDP-glycosyltransferase itUGT2 with an in situ UDP-glucose recycling system

Gastrodin, the major effective ingredient in Tianma (Gastrodia elata), is a p-hydroxybenzoic acid derivative with various activities. Gastrodin has been widely investigated for food and medical applications. The last biosynthetic step for gastrodin is UDP-glycosyltransferase (UGT)-mediated glycosylation with UDP-glucose (UDPG) as glycosyl donor. In this study, we performed a one-pot reaction both in vitro and in vivo to synthesize gastrodin from p-hydroxybenzyl alcohol (pHBA) by coupling UDP-glucosyltransferase from Indigofera tinctoria (itUGT2) to sucrose synthase from Glycine max (GmSuSy) for regeneration of UDPG. The in vitro results showed that itUGT2 transferred a glucosyl group to pHBA to generate gastrodin. After 37 UDPG regeneration cycles with 2.5% (molar ratio) UDP, the pHBA conversion reached 93% at 8 h. Furthermore, a recombinant strain with itUGT2 and GmSuSy genes was constructed. Through optimizing the incubation conditions, a 95% pHBA conversion rate (220 mg/L gastrodin titer) was achieved in vivo without addition of UDPG, which was 2.6-fold higher than that without GmSuSy. This in situ system for gastrodin biosynthesis provides a highly efficient strategy for both in vitro gastrodin synthesis and in vivo biosynthesis of gastrodin in E. coli with UDPG regeneration.

Multienzyme Synthesis of Glycyrrhetic Acid 3-O-mono-β-d-glucuronide by Coupling UGT73F15 to UDP-Glucuronic Acid Regeneration Module

Glycyrrhetic acid 3-O-mono-β-d-glucuronide (GAMG), a rare and innovative compound in licorice, exhibits high-potency sweetness and improved physiological activities. However, low amounts of GAMG from plants cannot meet the demands of growing markets. In this study, an efficient one-pot multienzyme cascade reaction for GAMG biosynthesis was constructed using a coupled catalysis of glycosyltransferase and uridine 5′-diphosphate (UDP) glucuronic acid (GlcA) regeneration system. The Glycyrrhiza uralensis glycosyltransferase UGT73F15 was expressed in Escherichia coli BL21 (DE3). The optimal reaction conditions of UGT73F15 were found to be pH 7.5 and 35 °C. The catalytic efficiency (kcat/Km) for glycyrrhetic acid (GA) was 2.14 min−1 mM−1 when using UDP-GlcA as sugar donor. To regenerate costly UDP-GlcA, the one-pot multienzyme cascade reaction including UGT73F15, sucrose synthase, UDP-glucose dehydrogenase, and lactate dehydrogenase was adopted to synthesize GAMG from GA on the basis of the UDP-GlcA regeneration system. By optimizing the cascade reaction conditions, the GAMG production successfully achieved 226.38 mg/L. Our study developed an economical and efficient one-pot multienzyme cascade method for facile synthesis of GAMG and other bioactive glucuronosides.

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.

Novel Biotransformation of Maslinic Acid to MA-2-O-β-D-Glucoside by UDP-Glycosyltransferases from Bacillus subtilis

Maslinic acid (MA) is a pentacyclic triterpenoid which originates from olive and other plants. Though MA possesses multiple biological activities, it has limitations due to its poor water solubility. YojK, YjiC, and UGT109A3 UDP-glycosyltransferases (UGTs) from Bacillus subtilis (B. subtilis) were utilized to catalyze the conjugation of MA with UDP-Glucose to generate a new MA glycosylation product, MA-2-O-β-D-glucoside (MA-2-O-β-D-Glu). The experimental results indicated that the resultant water solubility of MA-2-O-β-D-Glu is 1.69 times higher than that of MA. In addition, the recombinant YojK showed maximum activity at 40 °C with a pH range of 8.0−10.0, while the recombinant YjiC showed maximum activity at 45 °C with a pH of 8.0, and the recombinant UGT109A3 showed maximum activity at 40 °C with a pH of 8.0. Mg2+ is an important factor for efficient catalysis by three recombinant glycosyltransferases. The chemical conversion rate of the recombinant YojK, YjiC, and UGT109A3 is nearly 100% at their optimum pH, temperature, and metal ions. Furthermore, eight essential residues of three UGTs for MA glycosylation modification were further determined by molecular docking and site-directed mutagenesis. Thus, efficient glycosylation modification improves the water solubility of MA and provides a new potential method for the glycosylation modification of other pentacyclic triterpenoids.