Biphasic Catalysis with Disaccharide Phosphorylases: Chemoenzymatic Synthesis of α-d-Glucosides Using Sucrose Phosphorylase

Production of highly water-soluble genistein α-diglucoside using an engineered O-α-glycoligase with enhanced transglycosylation activity and altered substrate specificity

Genistein is one of isoflavones, showing various biological functions for human health. MalA-D416A, termed O-α-glycoligase, is an acid/base catalytic residue-deficient mutant of a α-glucosidase from Sulfolobus solfataricus, synthesizing genistein 7-O-α-glucoside using α-glucosyl fluoride as the donor substrate. Through mutagenesis toward MalA-D416A, an O-α-glycoligase variant with two mutations (D416R and Q450S) was identified as a biocatalyst with a 58.8-fold enhanced catalytic efficiency for genistein compared to the parent enzyme. The use of a 2:1 ratio of α-glucosyl fluoride and genistein at pH 9 facilitated the synthesis of genistein 7,4'-O-α-diglucoside by MalA-D416R/Q450S. The α-diglucoside exhibited 2,459-fold improved water solubility compared to genistein itself as well as facile deglycosylation by the intestinal α-glucosidase from rat, suggesting the potential of the α-diglucoside for improved bioavailability in human intestine. Through molecular docking analyses the modulation of the active site conformation by these mutations was expected for proper binding of both genistein and the monoglucoside.

Engineered production of bioactive polyphenolic O-glycosides

Polyphenolic compounds (such as quercetin and resveratrol) possess potential medicinal values due to their various bioactivities, but poor water solubility hinders their health benefits to humankind. Glycosylation is a well-known post-modification method to biosynthesize natural product glycosides with improved hydrophilicity. Glycosylation has profound effects on decreasing toxicity, increasing bioavailability and stability, together with changing bioactivity of polyphenolic compounds. Therefore, polyphenolic glycosides can be used as food additives, therapeutics, and nutraceuticals. Engineered biosynthesis provides an environmentally friendly and cost-effective approach to generate polyphenolic glycosides through the use of various glycosyltransferases (GTs) and sugar biosynthetic enzymes. GTs transfer the sugar moieties from nucleotide-activated diphosphate sugar (NDP-sugar) donors to sugar acceptors such as polyphenolic compounds. In this review, we systematically review and summarize the representative polyphenolic O-glycosides with various bioactivities and their engineered biosynthesis in microbes with different biotechnological strategies. We also review the major routes towards NDP-sugar formation in microbes, which is significant for producing unusual or novel glycosides. Finally, we discuss the trends in NDP-sugar based glycosylation research to promote the development of prodrugs that positively impact human health and wellness.

Sucrose Phosphorylase and Related Enzymes in Glycoside Hydrolase Family 13: Discovery, Application and Engineering

Sucrose phosphorylases are carbohydrate-active enzymes with outstanding potential for the biocatalytic conversion of common table sugar into products with attractive properties. They belong to the glycoside hydrolase family GH13, where they are found in subfamily 18. In bacteria, these enzymes catalyse the phosphorolysis of sucrose to yield α-glucose 1-phosphate and fructose. However, sucrose phosphorylases can also be applied as versatile transglucosylases for the synthesis of valuable glycosides and sugars because their broad promiscuity allows them to transfer the glucosyl group of sucrose to a diverse collection of compounds other than phosphate. Numerous process and enzyme engineering studies have expanded the range of possible applications of sucrose phosphorylases ever further. Moreover, it has recently been discovered that family GH13 also contains a few novel phosphorylases that are specialised in the phosphorolysis of sucrose 6F-phosphate, glucosylglycerol or glucosylglycerate. In this review, we provide an overview of the progress that has been made in our understanding and exploitation of sucrose phosphorylases and related enzymes over the past ten years.

Whole-cell biocatalytic, enzymatic and green chemistry methods for the production of resveratrol and its derivatives

Resveratrol and the biosynthetically related stilbenes are plant secondary metabolites with diverse pharmacological effects. The versatile functions of these compounds in plant defense mechanisms as phytoalexins on one hand, and in human health as potential pharmaceutical agents on the other, have attracted lots of interest in recent years to understand their biosynthetic pathways and their biological properties. Because of difficulties in obtaining resveratrol and its glucosylated derivatives as well as oligomeric forms in sufficient amounts for evaluation of their activity by plant sourcing or total synthesis, biotechnology may provide a competitive approach for the large-scale and low cost production of biologically active stilbenes. Additionally, one major limitation in the use of resveratrol and related aglycone derivatives as therapeutic agents is associated with their inherent poor aqueous solubility and low bioavailability. This article examines approaches for the synthesis of potential pharmacologically resveratrol derivatives in vivo by exploiting whole microorganisms, enzymatic and biocatalytic approaches allowing their full utilization for medicine, food and cosmetic applications. These methods also have the advantage of enabling the one-step production of stilbene compounds, compared to the time-consuming and environmentally unfriendly procedures used for their total synthesis or their extraction from plants. Increasing the desired products yield and biological activity through glucosylation (β-D-glucosides versus α-D-glucosides) and oligomerization methodologies of resveratrol including green chemistry methods in organic solvent-free media are discussed as well.

Structural Comparison of a Promiscuous and a Highly Specific Sucrose 6F-Phosphate Phosphorylase

In family GH13 of the carbohydrate-active enzyme database, subfamily 18 contains glycoside phosphorylases that act on α-sugars and glucosides. Because their phosphorolysis reactions are effectively reversible, these enzymes are of interest for the biocatalytic synthesis of various glycosidic compounds. Sucrose 6^F-phosphate phosphorylases (SPPs) constitute one of the known substrate specificities. Here, we report the characterization of an SPP from Ilumatobacter coccineus with a far stricter specificity than the previously described promiscuous SPP from Thermoanaerobacterium thermosaccharolyticum. Crystal structures of both SPPs were determined to provide insight into their similarities and differences. The residues responsible for binding the fructose 6-phosphate group in subsite +1 were found to differ considerably between the two enzymes. Furthermore, several variants that introduce a higher degree of substrate promiscuity in the strict SPP from I. coccineus were designed. These results contribute to an expanded structural knowledge of enzymes in subfamily GH13_18 and facilitate their rational engineering.

Inhibitory effect of ethanol extract of Ampelopsis brevipedunculata rhizomes on atopic dermatitis-like skin inflammation

ETHNOPHARMACOLOGICAL RELEVANCE

Extracts from various parts of Ampelopsis brevipedunculata has been used as anti-inflammatory agents in Asian folk medicine.

AIM OF THE STUDY

To demonstrate the medicinal effect of the A. brevipedunculata in skin inflammation, specifically atopic dermatitis (AD).

MATERIALS AND METHODS

The effect of ethanol extract of A. brevipedunculata rhizomes (ABE) on AD was examined using an AD-like skin inflammation model induced by repeated exposure to house dust mite (Dermatophagoides farinae extract, DFE) and 2,4-dinitrochlorobenzene (DNCB). The mechanism study was performed using tumor necrosis factor (TNF)-α and interferon (IFN)-γ-activated human keratinocytes (HaCaT). Serum histamine and immunoglobulin levels were quantified using enzymatic kits, while the gene expression of cytokines and chemokines was analyzed using quantitative real time polymerase chain reaction. The expression of signaling molecules was detected using Western blot.

RESULTS

Oral administration of ABE alleviated DFE/DNCB-induced ear thickening and clinical symptoms, as well as immune cell infiltration (mast cells and eosinophils) into the dermal layer. Serum Immunoglobulin (Ig) E, DFE-specific IgE, IgG2a, and histamine levels were decreased after the administration of ABE. ABE also inhibited CD4⁺IFN-γ⁺ and CD4⁺IL-4⁺ lymphocyte polarization in lymph nodes and expression of TNF-α, IFN-γ, IL-4, IL-13, and IL-31 in the ear tissue. In TNF-α/INF-γ-stimulated keratinocytes, ABE inhibited the gene expression of TNF-α, IL-6, IL-1β, and CCL17. In addition, ABE decreased the nuclear localization of signal transducer and activator of transcription 1 and nuclear factor-κB, and the phosphorylation of extracellular signal-regulated kinase and p38 mitogen-activated protein kinase.

CONCLUSION

Collectively, our data demonstrate the pharmacological role and signaling mechanism of ABE in the regulation of skin allergic inflammation, which supports our suggestion that ABE could be developed as a potential therapeutic agent for the treatment of AD.

Inhibitory Effects of Compounds and Extracts from Ampelopsis brevipedunculata on IL-6-Induced STAT3 Activation

Ampelopsis brevipedunculata (Maxim.) Trautv. (AB), a traditional East Asian medicine, exhibits protective effects against several inflammatory diseases. Our search for an inhibitor of IL-6-induced JAK2/STAT3 activation revealed that AB ethanolic extract (ABE) had a significant inhibitory effect on IL-6-induced STAT3 expression in Hep3B cells. The isolation and purification of an EtOAc-soluble fraction of ABE (ABEA) using reversed-phase high-performance liquid chromatography (RP-HPLC) afforded 17 compounds. The structures of these compounds (1-17) were elucidated based on ¹H and ¹³C nuclear magnetic resonance (NMR) spectroscopy as well as electrospray-ionization mass spectrometry (ESI-MS) data. ABE and ABEA were screened by a luciferase assay using Hep3B cells transfected with the STAT3 reporter gene. ABEA exhibited potent inhibitory effects on IL-6-induced STAT3 expression; moreover, these effects arose from the inhibition of the phosphorylation of the STAT3, JAK2, and ERK proteins in U266 cells. In addition, the compounds isolated from ABEA were measured for their inhibitory effects on IL-6-stimulated STAT3 expression. Of the compounds isolated, betulin showed the greatest inhibitory effects on IL-6-induced STAT3 activation in the luciferase assay (IC₅₀ value: 3.12 μM). Because of its potential for inhibiting STAT3 activation, A. brevipedunculata could be considered a source of compounds of pharmaceutical interest.

Discovery of a Kojibiose Phosphorylase in Escherichia coli K-12

The substrate profiles for three uncharacterized enzymes (YcjM, YcjT, and YcjU) that are expressed from a cluster of 12 genes ( ycjM-W and ompG) of unknown function in Escherichia coli K-12 were determined. Through a comprehensive bioinformatic and steady-state kinetic analysis, the catalytic function of YcjT was determined to be kojibiose phosphorylase. In the presence of saturating phosphate and kojibiose (α-(1,2)-d-glucose-d-glucose), this enzyme catalyzes the formation of d-glucose and β-d-glucose-1-phosphate ( k_cat = 1.1 s^-1, K_m = 1.05 mM, and k_cat/ K_m = 1.12 × 10³ M^-1 s^-1). Additionally, it was also shown that in the presence of β-d-glucose-1-phosphate, YcjT can catalyze the formation of other disaccharides using 1,5-anhydro-d-glucitol, l-sorbose, d-sorbitol, or l-iditol as a substitute for d-glucose. Kojibiose is a component of cell wall lipoteichoic acids in Gram-positive bacteria and is of interest as a potential low-calorie sweetener and prebiotic. YcjU was determined to be a β-phosphoglucomutase that catalyzes the isomerization of β-d-glucose-1-phosphate ( k_cat = 21 s^-1, K_m = 18 μM, and k_cat/ K_m = 1.1 × 10⁶ M^-1 s^-1) to d-glucose-6-phosphate. YcjU was also shown to exhibit catalytic activity with β-d-allose-1-phosphate, β-d-mannose-1-phosphate, and β-d-galactose-1-phosphate. YcjM catalyzes the phosphorolysis of α-(1,2)-d-glucose-d-glycerate with a k_cat = 2.1 s^-1, K_m = 69 μM, and k_cat/ K_m = 3.1 × 10⁴ M^-1 s^-1.

Walking a Fine Line with Sucrose Phosphorylase: Efficient Single-Step Biocatalytic Production of l-Ascorbic Acid 2-Glucoside from Sucrose

The 2-O-α-d-glucoside of l-ascorbic acid (AA-2G) is a highly stabilized form of vitamin C, with important industrial applications in cosmetics, food, and pharmaceuticals. AA-2G is currently produced through biocatalytic glucosylation of l-ascorbic acid from starch-derived oligosaccharides. Sucrose would be an ideal substrate for AA-2G synthesis, but it lacks a suitable transglycosidase. We show here that in a narrow pH window (pH 4.8-6.0, with sharp optimum at pH 5.2), sucrose phosphorylases catalyzed the 2-O-α-glucosylation of l-ascorbic acid from sucrose with high efficiency and perfect site-selectivity. Optimized synthesis with the enzyme from Bifidobacterium longum at 40 °C gave a concentrated product (155 g L^-1 ; 460 mm), from which pure AA-2G was readily recovered in ∼50 % overall yield, thus providing the basis for advanced production. The peculiar pH dependence is suggested to arise from a "reverse-protonation" mechanism in which the catalytic base Glu232 on the glucosyl-enzyme intermediate must be protonated for attack on the anomeric carbon from the 2-hydroxyl of the ionized l-ascorbate substrate.

Enzymatic Glycosylation of Phenolic Antioxidants: Phosphorylase-Mediated Synthesis and Characterization

Although numerous biologically active molecules exist as glycosides in nature, information on the activity, stability, and solubility of glycosylated antioxidants is rather limited to date. In this work, a wide variety of antioxidants were glycosylated using different phosphorylase enzymes. The resulting antioxidant library, containing α/β-glucosides, different regioisomers, cellobiosides, and cellotriosides, was then characterized. Glycosylation was found to significantly increase the solubility and stability of all evaluated compounds. Despite decreased radical-scavenging abilities, most glycosides were identified to be potent antioxidants, outperforming the commonly used 2,6-bis(1,1-dimethylethyl)-4-methylphenol (BHT). Moreover, the point of attachment, the anomeric configuration, and the glycosidic chain length were found to influence the properties of these phenolic glycosides.

Development of an in vivo glucosylation platform by coupling production to growth: Production of phenolic glucosides by a glycosyltransferase of Vitis vinifera

Glycosylation of small molecules can significantly alter their properties such as solubility, stability, and/or bioactivity, making glycosides attractive and highly demanded compounds. Consequently, many biotechnological glycosylation approaches have been developed, with enzymatic synthesis and whole-cell biocatalysis as the most prominent techniques. However, most processes still suffer from low yields, production rates and inefficient UDP-sugar formation. To this end, a novel metabolic engineering strategy is presented for the in vivo glucosylation of small molecules in Escherichia coli W. This strategy focuses on the introduction of an alternative sucrose metabolism using sucrose phosphorylase for the direct and efficient generation of glucose 1-phosphate as precursor for UDP-glucose formation and fructose, which serves as a carbon source for growth. By targeted gene deletions, a split metabolism is created whereby glucose 1-phosphate is rerouted from the glycolysis to product formation (i.e., glucosylation). Further, the production pathway was enhanced by increasing and preserving the intracellular UDP-glucose pool. Expression of a versatile glucosyltransferase from Vitis vinifera (VvGT2) enabled the strain to efficiently produce 14 glucose esters of various hydroxycinnamates and hydroxybenzoates with conversion yields up to 100%. To our knowledge, this fast growing (and simultaneously producing) E. coli mutant is the first versatile host described for the glucosylation of phenolic acids in a fermentative way using only sucrose as a cheap and sustainable carbon source.

Biotechnological advances in UDP-sugar based glycosylation of small molecules

Glycosylation of small molecules like specialized (secondary) metabolites has a profound impact on their solubility, stability or bioactivity, making glycosides attractive compounds as food additives, therapeutics or nutraceuticals. The subsequently growing market demand has fuelled the development of various biotechnological processes, which can be divided in the in vitro (using enzymes) or in vivo (using whole cells) production of glycosides. In this context, uridine glycosyltransferases (UGTs) have emerged as promising catalysts for the regio- and stereoselective glycosylation of various small molecules, hereby using uridine diphosphate (UDP) sugars as activated glycosyldonors. This review gives an extensive overview of the recently developed in vivo production processes using UGTs and discusses the major routes towards UDP-sugar formation. Furthermore, the use of interconverting enzymes and glycorandomization is highlighted for the production of unusual or new-to-nature glycosides. Finally, the technological challenges and future trends in UDP-sugar based glycosylation are critically evaluated and summarized.