Recent progress in the enzymatic glycosylation of phenolic compounds

Biochemical and in silico characterization of glycosyltransferases from red sweet cherry (Prunus avium L.) reveals their broad specificity toward phenolic substrates

Polyphenolic compounds are a class of phytonutrients that play important roles in plants and contribute to human health when incorporated into our diet through fruit consumption. A large proportion occur as glycoconjugates but the enzymes responsible for their glycosylation are poorly characterized. Here, we report the biochemical and structural characterization of two glycosyltransferases from sweet cherry named PaUGT1 and PaUGT2. Both are promiscuous glucosyltransferases active on diverse anthocyanidins and flavonols, as well as phenolic acids in the case of PaUGT1. They also exhibit weaker galactosyltransferase activity. The expression of the gene encoding PaUGT1, the most active of the two proteins, follows anthocyanin accumulation during fruit ripening, suggesting that this enzyme is the primary glycosyltransferase involved in flavonoid glycosylation in sweet cherry. It can potentially be used to synthesize diverse glycoconjugates of flavonoids for integration into bioactive formulations, and for generating new fruit cultivars with enhanced health-promoting properties using breeding methods.

Discovery, characterization, and comparative analysis of new UGT72 and UGT84 family glycosyltransferases

Glycosylated derivatives of natural product polyphenols display a spectrum of biological activities, rendering them critical for both nutritional and pharmacological applications. Their enzymatic synthesis by glycosyltransferases is frequently constrained by the limited repertoire of characterized enzyme-catalyzed transformations. Here, we explore the glycosylation capabilities and substrate preferences of newly identified plant uridine diphosphate (UDP)-dependent glycosyltransferases (UGTs) within the UGT72 and UGT84 families, with particular focus on natural polyphenol glycosylation from UDP-glucose. Four UGTs are classified according to their phylogenetic relationships and reaction products, identifying them as biocatalysts for either glucoside (UGT72 enzymes) or glucose ester (UGT84 members) formation from selected phenylpropanoid compounds. Detailed kinetic evaluations expose the unique attributes of these enzymes, including their specific activities and regio-selectivities towards diverse polyphenolic substrates, with product characterizations validating the capacity of UGT84 family members to perform di-O-glycosylation on flavones. Sequence analysis coupled with structural predictions through AlphaFold reveal an unexpected absence of a conserved threonine residue across all four enzymes, a trait previously linked to pentosyltransferases. This comparative analysis broadens the understood substrate specificity range for UGT72 and UGT84 enzymes, enhancing our understanding of their utility in the production of natural phenolic glycosides. The findings from this in-depth characterization provide valuable insights into the functional versatility of UGT-mediated reactions.

Investigating the Potential of Phenolic Compounds and Carbohydrates as Acceptor Substrates for Levansucrase-Catalyzed Transfructosylation Reaction

This study characterizes the acceptor specificity of levansucrases (LSs) from Gluconobacter oxydans (LS1), Vibrio natriegens (LS2), Novosphingobium aromaticivorans (LS3), and Paraburkholderia graminis (LS4) using sucrose as fructosyl donor and selected phenolic compounds and carbohydrates as acceptors. Overall, V. natriegens LS2 proved to be the best biocatalyst for the transfructosylation of phenolic compounds. More than one fructosyl unit could be attached to fructosylated phenolic compounds. The transfructosylation of epicatechin by P. graminis LS4 resulted in the most diversified products, with up to five fructosyl units transferred. In addition to the LS source, the acceptor specificity of LS towards phenolic compounds and their transfructosylation products were found to greatly depend on their chemical structure: the number of phenolic rings, the reactivity of hydroxyl groups and the presence of aliphatic chains or methoxy groups. Similarly, for carbohydrates, the transfructosylation yield was dependent on both the LS source and the acceptor type. The highest yield of fructosylated-trisaccharides was Erlose from the transfructosylation of maltose catalyzed by LS2, with production reaching 200 g/L. LS2 was more selective towards the transfructosylation of phenolic compounds and carbohydrates, while reactions catalyzed by LS1, LS3 and LS4 also produced fructooligosaccharides. This study shows the high potential for the application of LSs in the glycosylation of phenolic compounds and carbohydrates.

Fermentation of Orange Peels by Lactic Acid Bacteria: Impact on Phenolic Composition and Antioxidant Activity

Orange processing generates peel by-products rich in phenolic compounds, particularly flavanones like hesperidin and narirutin, offering potential health benefits. Utilizing these by-products is of significant interest in supporting Spain's circular bioeconomy. Therefore, the aim of this study was to investigate the fermentation of orange peels by different lactic acid bacteria (LAB) strains and its impact on phenolic composition and antioxidant activity. Three different LAB strains, two Lactiplantibacillus plantarum, and one Levilactobacillus brevis were utilized. The phenolic compounds were measured by HPLC-ESI-TOF-MS, and antioxidant activity was assessed using DPPH and ABTS methods. The growth of the LAB strains varied, showing initial increases followed by gradual declines, with strain-specific patterns observed. Medium acidification occurred during fermentation. A phenolic analysis revealed an 11% increase in phenolic acids in peels fermented by La. plantarum CECT 9567-C4 after 24 h, attributed to glycosylation by LAB enzymes. The flavonoid content exhibited diverse trends, with Le. brevis showing an 8% increase. The antioxidant assays demonstrated strain- and time-dependent variations. Positive correlations were found between antioxidant activity and total phenolic compounds. The results underscore the importance of bacterial selection and fermentation time for tailored phenolic composition and antioxidant activity in orange peel extracts. LAB fermentation, particularly with La. plantarum CECT 9567 and Le. brevis, holds promise for enhancing the recovery of phenolic compounds and augmenting antioxidant activity in orange peels, suggesting potential applications in food and beverage processing.

Unveiling the Immunomodulatory Potential of Phenolic Compounds in Food Allergies

Food allergies are becoming ever more prevalent around the world. This pathology is characterized by the breakdown of oral tolerance to ingested food allergens, resulting in allergic reactions in subsequent exposures. Due to the possible severity of the symptoms associated with this pathology, new approaches to prevent it and reduce associated symptoms are of utmost importance. In this framework, dietary phenolic compounds appear as a tool with a not fully explored potential. Some phenolic compounds have been pointed to with the ability to modulate food allergies and possibly reduce their symptoms. These compounds can modulate food allergies through many different mechanisms, such as altering the bioaccessibility and bioavailability of potentially immunogenic peptides, by modulating the human immune system and by modulating the composition of the human microbiome that resides in the oral cavity and the gastrointestinal tract. This review deepens the state-of-the-art of the modulation of these mechanisms by phenolic compounds. While this review shows clear evidence that dietary supplementation with foods rich in phenolic compounds might constitute a new approach to the management of food allergies, it also highlights the need for further research to delve into the mechanisms of action of these compounds and decipher systematic structure/activity relationships.

Whole-cell bioconversion using non-Leloir transglycosylation reactions: a review

Microbial biocatalysts are evolving technological tools for glycosylation research in food, feed and pharmaceuticals. Advances in bioengineered Leloir and non-Leloir carbohydrate-active enzymes allow for whole-cell biocatalysts to curtail production costs of purified enzymes while enhancing glucan synthesis through continued enzyme expression. Unlike sugar nucleotide-dependent Leloir glycosyltransferases, non-Leloir enzymes require inexpensive sugar donors and can be designed to match the high value, yield and selectivity of the former. This review addresses the current state of bacterial cell-based production of glucans and glycoconjugates via transglycosylation, and describes how alterations made to microbial hosts to surpass purified enzymes as the preferred mode of catalysis are steadily being acquired through genetic engineering, rational design and process optimization. A comprehensive exploration of relevant literature has been summarized to describe whole-cell biocatalysis in non-Leloir glycosylation reactions with various donors and acceptors, and the characterization, application and latest developments in the optimization of their use.

Recent trends in the modification of polyphenolic compounds using hydroxylation and glycosylation

Polyphenols are bioactive molecules that are used in therapeutics. Polyphenol hydroxylation and glycosylation have been shown to increase their bioavailability, solubility, bioactivity, and stability for use in various applications. Ortho-hydroxylation of polyphenols using tyrosinase allows high selectivity and yield without requiring a cofactor, while meta- and para-hydroxylation of polyphenols are mediated by site-specific hydroxylases and cytochrome P450s, although these processes are somewhat rare. O-glycosylation of polyphenols proceeds further after hydroxylation. The O-glycosylation reaction typically requires nucleotide diphosphate (NDP) sugar. However, amylosucrase (AS) has emerged as a promising enzyme for polyphenol glycosylation in large-scale production without requiring NDP-sugar. Overall, this review describes recent findings on the enzymatic mechanisms, enzyme engineering, and applications of enzymatic reactions.

Plant glycosyltransferases for expanding bioactive glycoside diversity

Glycosylation is a successful strategy to alter the pharmacological properties of small molecules, and it has emerged as a unique approach to expand the chemical space of natural products that can be explored in drug discovery. Traditionally, most glycosylation events have been carried out chemically, often requiring many protection and deprotection steps to achieve a target molecule. Enzymatic glycosylation by glycosyltransferases could provide an alternative strategy for producing new glycosides. In particular, the glycosyltransferase family has greatly expanded in plants, representing a rich enzymatic resource to mine and expand the diversity of glycosides with novel bioactive properties. This article highlights previous and prospective uses for plant glycosyltransferases in generating bioactive glycosides and altering their pharmacological properties.

Synthesis of Alpha-Linked Glucosides from Soybean Isoflavone Aglycones Using Amylosucrase from Deinococcus geothermalis

Soybean isoflavone aglycones (SIAs) have many biological activities but are poorly water-soluble in the human body. Glycosylation provides structural diversity to SIAs and can alter their physicochemical properties, including water solubility. An alpha-linked glucosylation of SIA was achieved using amylosucrase from Deinococcus geothermalis. A total of 13 alpha-linked glucosyl SIAs were obtained, and their colors in solution were confirmed. The structures of the isolated compounds were identified by mass spectrometry and multidimensional nuclear magnetic resonance spectroscopy. The amylosucrase transglycosylation formed new isoflavone glycosides with alpha glycosidic bonds at C-7 and/or C-4' of SIAs, followed by the production of isoflavone glycosides with alpha (1 → 6) glycosidic bonds. The products with a glucosyl moiety attached to the C-4' of SIAs were found to be more water-soluble than their counterparts attached to the C-7 and/or beta-linkages. This study suggests a strategy for the synthesis of bioactive compounds with enhanced water solubility through alpha-linked glucosylation.

Synthesis and Characterization of a Novel Resveratrol Xylobioside Obtained Using a Mutagenic Variant of a GH10 Endoxylanase

Resveratrol is a natural polyphenol with antioxidant activity and numerous health benefits. However, in vivo application of this compound is still a challenge due to its poor aqueous solubility and rapid metabolism, which leads to an extremely low bioavailability in the target tissues. In this work, rXynSOS-E236G glycosynthase, designed from a GH10 endoxylanase of the fungus Talaromyces amestolkiae, was used to glycosylate resveratrol by using xylobiosyl-fluoride as a sugar donor. The major product from this reaction was identified by NMR as 3-O-ꞵ-d-xylobiosyl resveratrol, together with other glycosides produced in a lower amount as 4'-O-ꞵ-d-xylobiosyl resveratrol and 3-O-ꞵ-d-xylotetraosyl resveratrol. The application of response surface methodology made it possible to optimize the reaction, producing 35% of 3-O-ꞵ-d-xylobiosyl resveratrol. Since other minor glycosides are obtained in addition to this compound, the transformation of the phenolic substrate amounted to 70%. Xylobiosylation decreased the antioxidant capacity of resveratrol by 2.21-fold, but, in return, produced a staggering 4,866-fold improvement in solubility, facilitating the delivery of large amounts of the molecule and its transit to the colon. A preliminary study has also shown that the colonic microbiota is capable of releasing resveratrol from 3-O-ꞵ-d-xylobiosyl resveratrol. These results support the potential of mutagenic variants of glycosyl hydrolases to synthesize highly soluble resveratrol glycosides, which could, in turn, improve the bioavailability and bioactive properties of this polyphenol.

Recent Progress on Feasible Strategies for Arbutin Production

Arbutin is a hydroquinone glucoside and a natural product present in various plants. Arbutin potently inhibits melanin formation. This property has been exploited in whitening cosmetics and pharmaceuticals. Arbutin production relies mainly on chemical synthesis. The multi-step and complicated process can compromise product purity. With the increasing awareness of sustainable development, the current research direction prioritizes environment-friendly, biobased arbutin production. In this review, current strategies for arbutin production are critically reviewed, with a focus on plant extraction, chemical synthesis, biotransformation, and microbial fermentation. Furthermore, the bottlenecks and perspectives for future direction on arbutin biosynthesis are discussed.

A Fungal Versatile GH10 Endoxylanase and Its Glycosynthase Variant: Synthesis of Xylooligosaccharides and Glycosides of Bioactive Phenolic Compounds

The study of endoxylanases as catalysts to valorize hemicellulosic residues and to obtain glycosides with improved properties is a topic of great industrial interest. In this work, a GH10 β-1,4-endoxylanase (XynSOS), from the ascomycetous fungus Talaromyces amestolkiae, has been heterologously produced in Pichia pastoris, purified, and characterized. rXynSOS is a highly glycosylated monomeric enzyme of 53 kDa that contains a functional CBM1 domain and shows its optimal activity on azurine cross-linked (AZCL)-beechwood xylan at 70 °C and pH 5. Substrate specificity and kinetic studies confirmed its versatility and high affinity for beechwood xylan and wheat arabinoxylan. Moreover, rXynSOS was capable of transglycosylating phenolic compounds, although with low efficiencies. For expanding its synthetic capacity, a glycosynthase variant of rXynSOS was developed by directed mutagenesis, replacing its nucleophile catalytic residue E236 by a glycine (rXynSOS-E236G). This novel glycosynthase was able to synthesize β-1,4-xylooligosaccharides (XOS) of different lengths (four, six, eight, and ten xylose units), which are known to be emerging prebiotics. rXynSOS-E236G was also much more active than the native enzyme in the glycosylation of a broad range of phenolic compounds with antioxidant properties. The interesting capabilities of rXynSOS and its glycosynthase variant make them promising tools for biotechnological applications.

Reprint of: Advanced glycosidases as ingenious biosynthetic instruments

Until recently, glycosidases, naturally hydrolyzing carbohydrate-active enzymes, have found few synthetic applications in industry, being primarily used for cleaving unwanted carbohydrates. With the establishment of glycosynthase and transglycosidase technology by genetic engineering, the view of glycosidases as industrial biotechnology tools has started to change. Their easy production, affordability, robustness, and substrate versatility, added to the possibility of controlling undesired side hydrolysis by enzyme engineering, have made glycosidases competitive synthetic tools. Current promising applications of engineered glycosidases include the production of well-defined chitooligomers, precious galactooligosaccharides or specialty chemicals such as glycosylated flavonoids. Other synthetic pathways leading to human milk oligosaccharides or remodeled antibodies are on the horizon. This work provides an overview of the synthetic achievements to date for glycosidases, emphasizing the latest trends and outlining possible developments in the field.

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.

Advanced glycosidases as ingenious biosynthetic instruments

Until recently, glycosidases, naturally hydrolyzing carbohydrate-active enzymes, have found few synthetic applications in industry, being primarily used for cleaving unwanted carbohydrates. With the establishment of glycosynthase and transglycosidase technology by genetic engineering, the view of glycosidases as industrial biotechnology tools has started to change. Their easy production, affordability, robustness, and substrate versatility, added to the possibility of controlling undesired side hydrolysis by enzyme engineering, have made glycosidases competitive synthetic tools. Current promising applications of engineered glycosidases include the production of well-defined chitooligomers, precious galactooligosaccharides or specialty chemicals such as glycosylated flavonoids. Other synthetic pathways leading to human milk oligosaccharides or remodeled antibodies are on the horizon. This work provides an overview of the synthetic achievements to date for glycosidases, emphasizing the latest trends and outlining possible developments in the field.

Enzymatic synthesis of phlorizin fructosides

Phlorizin is a low soluble dihydrochalcone with relevant pharmacological properties. In this study, enzymatic fructosylation was approached to enhance the water solubility of phlorizin, and consequently its bioavailability. Three enzymes were assayed for phlorizin fructosylation in aqueous reactions using sucrose as fructosyl donor. Levansucrase (EC 2.4.1.10) from Gluconacetobacter diazotrophicus (Gd_LsdA) was 6.5-fold more efficient than invertase (EC 3.2.1.26) from Rhodotorula mucilaginosa (Rh_Inv), while sucrose:sucrose 1-fructosyltransferase (EC 2.4.1.99) from Schedonorus arundinaceus (Sa_1-SST) failed to modify the non-sugar acceptor. Gd_LsdA synthesized series of phlorizin mono- di- and tri-fructosides with maximal conversion efficiency of 73 %. The three most abundant products were identified by ESI-MS and NMR analysis as β-D-fructofuranosyl-(2→6)-phlorizin (P1a), phlorizin-4'-O-β-D-fructofuranosyl-(2→6)-D-fructofuranoside (P2c) and phlorizin-4-O-monofructofuranoside (P1b), respectively. Purified P1a was 16 times (30.57 g L^-1 at 25 °C) more soluble in water than natural phlorizin (1.93 g L^-1 at 25 °C) and exhibited 44.56 % free radical scavenging activity. Gd_LsdA is an attractive candidate enzyme for the scaled synthesis of phlorizin fructosides in the absence of co-solvent.

β-Galactosidase: From its source and applications to its recombinant form

Carbohydrate-active enzymes are a group of important enzymes playing a critical role in the degradation and synthesis of carbohydrates. Glycosidases can hydrolyze glycosides into oligosaccharides, polysaccharides, and glycoconjugates via a cost-effective approach. Lactase is an important member of β-glycosidases found in higher plants, animals, and microorganisms. β-Galactosidases can be used to degrade the milk lactose for making lactose-free milk, which is sweeter than regular milk and is suitable for lactose-intolerant people. β-Galactosidase is employed by many food industries to degrade lactose and improve the digestibility, sweetness, solubility, and flavor of dairy products. β-Galactosidase enzymes have various families and are applied in the food-processing industries such as hydrolyzed-milk products, whey, and galactooligosaccharides. Thus, this enzyme is a valuable protein which is now produced by recombinant technology. In this review, origins, structure, recombinant production, and critical modifications of β-galactosidase for improving the production process are discussed. Since β-galactosidase is a valuable enzyme in industry and health care, a study of its various aspects is important in industrial biotechnology and applied biochemistry.

Comprehensive study on transglycosylation of CGTase from various sources

Transglycosylation is the in-vivo or in-vitro process of transferring glycosyl groups from a donor to an acceptor, which is usually performed by enzymatic reactions because of their simplicity, low steric hindrance, high region-specificity, low production cost, and mild processing conditions. One of the enzymes commonly used in the transglycosylation reaction is cyclodextrin glucanotransferase (CGTase). The transglycosylated products, catalyzed by CGTase, are widely used in food additives, supplements, and personal care and cosmetic products. This is due to improvements in the solubility, stability, bioactivity and length of the synthesized products. This paper's focus is on the importance of enzymes used in the transglycosylation reaction, their characteristics and mechanism of action, sources and production yield, and donor and acceptor specificities. Moreover, the influence of intrinsic and extrinsic factors on the enzymatic reaction, catalysis of glycosidic linkages, and advantages of CGTase transglycosylation reactions are discussed in detail.

Regioselective Hydroxylation of Naringin Dihydrochalcone to Produce Neoeriocitrin Dihydrochalcone by CYP102A1 (BM3) Mutants

Naringin dihydrochalcone (DC) is originally derived from the flavonoid naringin, which occurs naturally in citrus fruits, especially in grapefruit. It is used as an artificial sweetener with a strong antioxidant activity with potential applications in food and pharmaceutical fields. At present, enzymatic and chemical methods to make products of naringin DC by hydroxylation reactions have not been developed. Here, an enzymatic strategy for the efficient synthesis of potentially valuable products from naringin DC, a glycoside of phloretin, was developed using Bacillus megaterium CYP102A1 monooxygenase. The major product was identified to be neoeriocitrin DC by NMR and LC-MS analyses. Sixty-seven mutants of CYP102A1 were tested for hydroxylation of naringin DC to produce neoeriocitrin DC. Six mutants with high activity were selected to determine the kinetic parameters and total turnover numbers (TTNs). The kcat value of the most active mutant was 11 min−1 and its TTN was 315. The productivity of neoeriocitrin DC production increased up to 1.1 mM h−1, which corresponds to 0.65 g L−1 h−1. In this study, we achieved a regioselective hydroxylation of naringin DC to produce neoeriocitrin DC.

A glucotolerant β-glucosidase from the fungus Talaromyces amestolkiae and its conversion into a glycosynthase for glycosylation of phenolic compounds

Background

The interest for finding novel β-glucosidases that can improve the yields to produce second-generation (2G) biofuels is still very high. One of the most desired features for these enzymes is glucose tolerance, which enables their optimal activity under high-glucose concentrations. Besides, there is an additional focus of attention on finding novel enzymatic alternatives for glycoside synthesis, for which a mutated version of glycosidases, named glycosynthases, has gained much interest in recent years.

Results

In this work, a glucotolerant β-glucosidase (BGL-1) from the ascomycete fungus Talaromyces amestolkiae has been heterologously expressed in Pichia pastoris, purified, and characterized. The enzyme showed good efficiency on p-nitrophenyl glucopyranoside (pNPG) (K_m= 3.36 ± 0.7 mM, k_cat= 898.31 s⁻¹), but its activity on cellooligosaccharides, the natural substrates of these enzymes, was much lower, which could limit its exploitation in lignocellulose degradation applications. Interestingly, when examining the substrate specificity of BGL-1, it showed to be more active on sophorose, the β-1,2 disaccharide of glucose, than on cellobiose. Besides, the transglycosylation profile of BGL-1 was examined, and, for expanding its synthetic capacities, it was converted into a glycosynthase. The mutant enzyme, named BGL-1-E521G, was able to use α-d-glucosyl-fluoride as donor in glycosylation reactions, and synthesized glucosylated derivatives of different pNP-sugars in a regioselective manner, as well as of some phenolic compounds of industrial interest, such as epigallocatechin gallate (EGCG).

Conclusions

In this work, we report the characterization of a novel glucotolerant 1,2-β-glucosidase, which also has a considerable activity on 1,4-β-glucosyl bonds, that has been cloned in P. pastoris, produced, purified and characterized. In addition, the enzyme was converted into an efficient glycosynthase, able to transfer glucose molecules to a diversity of acceptors for obtaining compounds of interest. The remarkable capacities of BGL-1 and its glycosynthase mutant, both in hydrolysis and synthesis, suggest that it could be an interesting tool for biotechnological applications.

Transglycosylation products generated by Talaromyces amestolkiae GH3 β-glucosidases: effect of hydroxytyrosol, vanillin and its glucosides on breast cancer cells

Background

Transglycosylation represents one of the most promising approaches for obtaining novel glycosides, and plant phenols and polyphenols are emerging as one of the best targets for creating new molecules with enhanced capacities. These compounds can be found in diet and exhibit a wide range of bioactivities, such as antioxidant, antihypertensive, antitumor, neuroprotective and anti-inflammatory, and the eco-friendly synthesis of glycosides from these molecules can be a suitable alternative for increasing their health benefits.

Results

Transglycosylation experiments were carried out using different GH3 β-glucosidases from the fungus Talaromyces amestolkiae. After a first screening with a wide variety of potential transglycosylation acceptors, mono-glucosylated derivatives of hydroxytyrosol, vanillin alcohol, 4-hydroxybenzyl alcohol, and hydroquinone were detected. The reaction products were analyzed by thin-layer chromatography, high-pressure liquid chromatography, and mass spectrometry. Hydroxytyrosol and vanillyl alcohol were selected as the best options for transglycosylation optimization, with a final conversion yield of 13.8 and 19% of hydroxytyrosol and vanillin glucosides, respectively. NMR analysis confirmed the structures of these compounds. The evaluation of the biological effect of these glucosides using models of breast cancer cells, showed an enhancement in the anti-proliferative capacity of the vanillin derivative, and an improved safety profile of both glucosides.

Conclusions

GH3 β-glucosidases from T. amestolkiae expressed in P. pastoris were able to transglycosylate a wide variety of acceptors. Between them, phenolic molecules like hydroxytyrosol, vanillin alcohol, 4-hydroxybenzyl alcohol, and hydroquinone were the most suitable for its interesting biological properties. The glycosides of hydroxytyrosol and vanillin were tested, and they improved the biological activities of the original aglycons on breast cancer cells.

Electronic supplementary material

The online version of this article (10.1186/s12934-019-1147-4) contains supplementary material, which is available to authorized users.

Effect of α-Glucosylation on the Stability, Antioxidant Properties, Toxicity, and Neuroprotective Activity of (-)-Epigallocatechin Gallate

(–)-Epigallocatechin gallate (EGCG), the predominant catechin (≥50%) in green tea (Camellia sinensis), displays several bioactive properties but its stability and bioavailability are low. In this work, the properties of two α-glucosyl derivatives of EGCG (3′- and 7-O-α-D-glucopyranoside), obtained by enzymatic synthesis, were assessed. The α-glucosylation enhanced the pH and thermal stability of EGCG. The analysis of scavenging activity toward ABTS^·+ radicals showed that the α-glucosylation at C-7 of A-ring caused a higher loss of antioxidant activity compared with the sugar conjugation at C-3′ of B-ring. The 3′-glucoside also showed higher potential to alleviate intracellular reactive oxygen species (ROS) levels and to boost REDOX activity. The toxicity of EGCG and its monoglucosides was tested in human SH-S5Y5 neurons, RAW 264.7 macrophages, MRC5 fibroblasts, and HT-29 colon cancer cells. Interestingly, the 3′-O-α-D-glucoside increased the viability of neural cells in vitro (2.75-fold at 100 μM) in the presence of H₂O₂, whilst EGCG gave rise only to a 1.7-fold enhancement. In conclusion, the α-glucoside of EGCG at C-3′ has a great potential for nutraceutical, cosmetic and biomedical applications.

Functional annotation of putative QTL associated with black tea quality and drought tolerance traits

The understanding of black tea quality and percent relative water content (%RWC) traits in tea (Camellia sinensis) by a quantitative trait loci (QTL) approach can be useful in elucidation and identification of candidate genes underlying the QTL which has remained to be difficult. The objective of the study was to identify putative QTL controlling black tea quality and percent relative water traits in two tea populations and their F1 progeny. A total of 1,421 DArTseq markers derived from the linkage map identified 53 DArTseq markers to be linked to black tea quality and %RWC. All 53 DArTseq markers with unique best hits were identified in the tea genome. A total of 5,592 unigenes were assigned gene ontology (GO) terms, 56% comprised biological processes, cellular component (29%) and molecular functions (15%), respectively. A total of 84 unigenes in 15 LGs were assigned to 25 different Kyoto Encyclopedia of Genes and Genomes (KEGG) database pathways based on categories of secondary metabolite biosynthesis. The three major enzymes identified were transferases (38.9%), hydrolases (29%) and oxidoreductases (18.3%). The putative candidate proteins identified were involved in flavonoid biosynthesis, alkaloid biosynthesis, ATPase family proteins related to abiotic/biotic stress response. The functional annotation of putative QTL identified in this current study will shed more light on the proteins associated with caffeine and catechins biosynthesis and % RWC. This study may help breeders in selection of parents with desirable DArTseq markers for development of new tea cultivars with desirable traits.

"Sweet Flavonoids": Glycosidase-Catalyzed Modifications

Natural flavonoids, especially in their glycosylated forms, are the most abundant phenolic compounds found in plants, fruit, and vegetables. They exhibit a large variety of beneficial physiological effects, which makes them generally interesting in a broad spectrum of scientific areas. In this review, we focus on recent advances in the modifications of the glycosidic parts of various flavonoids employing glycosidases, covering both selective trimming of the sugar moieties and glycosylation of flavonoid aglycones by natural and mutant glycosidases. Glycosylation of flavonoids strongly enhances their water solubility and thus increases their bioavailability. Antioxidant and most biological activities are usually less pronounced in glycosides, but some specific bioactivities are enhanced. The presence of l-rhamnose (6-deoxy-α-l-mannopyranose) in rhamnosides, rutinosides (rutin, hesperidin) and neohesperidosides (naringin) plays an important role in properties of flavonoid glycosides, which can be considered as "pro-drugs". The natural hydrolytic activity of glycosidases is widely employed in biotechnological deglycosylation processes producing respective aglycones or partially deglycosylated flavonoids. Moreover, deglycosylation is quite commonly used in the food industry aiming at the improvement of sensoric properties of beverages such as debittering of citrus juices or enhancement of wine aromas. Therefore, natural and mutant glycosidases are excellent tools for modifications of flavonoid glycosides.

Enzymatic Synthesis of a Novel Pterostilbene α-Glucoside by the Combination of Cyclodextrin Glucanotransferase and Amyloglucosidase

The synthesis of a novel α-glucosylated derivative of pterostilbene was performed by a transglycosylation reaction using starch as glucosyl donor, catalyzed by cyclodextrin glucanotransferase (CGTase) from Thermoanaerobacter sp. The reaction was carried out in a buffer containing 20% (v/v) DMSO to enhance the solubility of pterostilbene. Due to the formation of several polyglucosylated products with CGTase, the yield of monoglucoside was increased by the treatment with a recombinant amyloglucosidase (STA1) from Saccharomyces cerevisiae (var. diastaticus). This enzyme was not able to hydrolyze the linkage between the glucose and pterostilbene. The monoglucoside was isolated and characterized by combining ESI-MS and 2D-NMR methods. Pterostilbene α-d-glucopyranoside is a novel compound. The α-glucosylation of pterostilbene enhanced its solubility in water to approximately 0.1 g/L. The α-glucosylation caused a slight loss of antioxidant activity towards ABTS˙⁺ radicals. Pterostilbene α-d-glucopyranoside was less toxic than pterostilbene for human SH-S5Y5 neurons, MRC5 fibroblasts and HT-29 colon cancer cells, and similar for RAW 264.7 macrophages.

Selected Plant Metabolites Involved in Oxidation-Reduction Processes during Bud Dormancy and Ontogenetic Development in Sweet Cherry Buds (Prunus avium L.)

Many biochemical processes are involved in regulating the consecutive transition of different phases of dormancy in sweet cherry buds. An evaluation based on a metabolic approach has, as yet, only been partly addressed. The aim of this work, therefore, was to determine which plant metabolites could serve as biomarkers for the different transitions in sweet cherry buds. The focus here was on those metabolites involved in oxidation-reduction processes during bud dormancy, as determined by targeted and untargeted mass spectrometry-based methods. The metabolites addressed included phenolic compounds, ascorbate/dehydroascorbate, reducing sugars, carotenoids and chlorophylls. The results demonstrate that the content of phenolic compounds decrease until the end of endodormancy. After a long period of constancy until the end of ecodormancy, a final phase of further decrease followed up to the phenophase open cluster. The main phenolic compounds were caffeoylquinic acids, coumaroylquinic acids and catechins, as well as quercetin and kaempferol derivatives. The data also support the protective role of ascorbate and glutathione in the para- and endodormancy phases. Consistent trends in the content of reducing sugars can be elucidated for the different phenophases of dormancy, too. The untargeted approach with principle component analysis (PCA) clearly differentiates the different timings of dormancy giving further valuable information.

Non-targeted glycosidic profiling of international wines using neutral loss-high resolution mass spectrometry

Many metabolites naturally occur as glycosides, since sugar moieties can be crucial for their biological activity and increase their water solubility. In the plant kingdom they may occur as glycosides or sugar esters, depending on precursor chemical structure, and in wine they have traditionally attracted attention due to their organoleptic properties, such as astringency and bitterness, and because they affect the colour and aroma of wines. A new approach directed at detailed description of glycosides in a large selection of monovarietal wines (8 samples each of Pinot Blanc, Muller Thurgau, Riesling, Traminer, Merlot, Pinot Noir and Cabernet Sauvignon) was developed by combining high performance liquid chromatography with high resolution tandem mass spectrometry. Analytical separation was performed on an Accucore™ Polar Premium LC column, while mass analysis was performed in negative ion mode with an non-targeted screening approach, using a Full MS/AIF/NL dd-MS² experiment at a resolving power of 140,000 FWHM. Over 280 glycoside-like compounds were detected, of which 133 (including low-molecular weight phenols, flavonoids and monoterpenols) were tentatively identified in the form of pentose (6), deoxyhexose (17), hexose (73), hexose-pentose (16), hexose-deoxyhexose (7), dihexose (5) and hexose ester (9) derivatives. It was not possible to univocally define the corresponding chemical structure for the remaining 149 glycosides. Non-parametric statistical analysis showed it was possible to well characterise the glycosylated profile of all red and Traminer wines, while the identified glycosides were almost entirely lacking in Pinot Blanc, Riesling and Muller Thurgau wines. Also Tukey's Honestly Significant Difference test (p < 0.05) and Principal Component Analysis confirmed that it was possible to almost entirely distinguish the selected red wines from each other according to their glycosylated profile.

Growth of epithelial cells on films of enzymatically synthesized poly(gallic acid) crosslinked to carboxymethylcellulose

Enzyme-mediated poly(gallic acid) crosslinked to carboxymethylcellulose toward a novel material for skin tissue engineering.