A comprehensive review on α-D-Glucans: Structural and functional diversity, derivatization and bioapplications

Isolation and purification of carbohydrate components in functional food: a review

Medicinal plants, increasingly utilized in functional foods, possess potent therapeutic properties and health-promoting functions, with carbohydrates playing a crucial role and exhibiting a range of effects, such as antioxidant, antitumor, immune-enhancing, antibacterial, anticoagulant, and hypoglycemic activities. However, comprehensively, accurately, rapidly, and economically assessing the quality of carbohydrate components is challenging due to their diverse and complex nature. Additionally, the purification and identification of carbohydrates also guarantee related efficacy research. This paper offers a thorough review of research progress carried out by both domestic and international scholars in the last decade on extracting, purifying, separating, identifying, and determining the content of carbohydrate components from functional foods, which are mainly composed of medicinal plants, and also explores the potential for achieving comprehensive quantitative analysis and evaluating structure-activity relationships of carbohydrate components. These findings aim to serve as a valuable reference for the future development and application of natural carbohydrate components in functional food and medicine.

Bottom-Up Synthesized Glucan Materials: Opportunities from Applied Biocatalysis

Linear d-glucans are natural polysaccharides of simple chemical structure. They are comprised of d-glucosyl units linked by a single type of glycosidic bond. Noncovalent interactions within, and between, the d-glucan chains give rise to a broad variety of macromolecular nanostructures that can assemble into crystalline-organized materials of tunable morphology. Structure design and functionalization of d-glucans for diverse material applications largely relies on top-down processing and chemical derivatization of naturally derived starting materials. The top-down approach encounters critical limitations in efficiency, selectivity, and flexibility. Bottom-up approaches of d-glucan synthesis offer different, and often more precise, ways of polymer structure control and provide means of functional diversification widely inaccessible to top-down routes of polysaccharide material processing. Here the natural and engineered enzymes (glycosyltransferases, glycoside hydrolases and phosphorylases, glycosynthases) for d-glucan polymerization are described and the use of applied biocatalysis for the bottom-up assembly of specific d-glucan structures is shown. Advanced material applications of the resulting polymeric products are further shown and their important role in the development of sustainable macromolecular materials in a bio-based circular economy is discussed.

Pleurotus ostreatus as a model mushroom in genetics, cell biology, and material sciences

Pleurotus ostreatus, also known as the oyster mushroom, is a popular edible mushroom cultivated worldwide. This review aims to survey recent progress in the molecular genetics of this fungus and demonstrate its potential as a model mushroom for future research. The development of modern molecular genetic techniques and genome sequencing technologies has resulted in breakthroughs in mushroom science. With efficient transformation protocols and multiple selection markers, a powerful toolbox, including techniques such as gene knockout and genome editing, has been developed, and numerous new findings are accumulating in P. ostreatus. These include molecular mechanisms of wood component degradation, sexual development, protein secretion systems, and cell wall structure. Furthermore, these techniques enable the identification of new horizons in enzymology, biochemistry, cell biology, and material science through protein engineering, fluorescence microscopy, and molecular breeding. KEY POINTS: • Various genetic techniques are available in Pleurotus ostreatus. • P. ostreatus can be used as an alternative model mushroom in genetic analyses. • New frontiers in mushroom science are being developed using the fungus.

Structural Characterization and Functional Studies of Exopolysaccharide by Native Lacticaseibacillus rhamnosus P14 Isolated from the Moroccan Region

Exopolysaccharides (EPS) are natural polymers synthesized by several microorganisms, including lactic acid bacteria (LAB). They are characterized by a great structural diversity, which gives them interesting biological and pharmacological properties. This work investigates the physicochemical and biological characterization of a new exopolysaccharide (EPS) produced by a wild Lacticaseibacillus rhamnosus P14. The functional groups, chemical bonds, and thermal and morphological properties of the purified EPS-P14 were determined using Fourier Transform Infrared, Nuclear Magnetic Resonance, and X-ray diffraction spectroscopies, as well as Thermo-gravimetric analysis, Differential Scanning Calorimetry and Scanning Electron Microscopy. The functional properties, namely antioxidant and emulsifying activities, were also assessed. The physicochemical analysis revealed that EPS-P14 is a porous and thermally stable polysaccharide with a degradation temperature of 307 °C. NMR and FT-IR studies identified it as a homogeneous α-D-glucan with mainly α-(1 → 6) glycosidic linkage and some α-(1 → 3) branching. EPS-P14 was highly water-soluble and exhibited strong emulsifying and stabilizing properties in a concentration-dependent manner. Furthermore, EPS-P14 demonstrated significant DPPH scavenging and ferric-reducing capacities. These findings suggest that EPS-P14 is a bioactive polysaccharide with potential effects, which could be a promising natural candidate for prospective application.

The European Polysaccharide Network of Excellence (EPNOE) research roadmap 2040: Advanced strategies for exploiting the vast potential of polysaccharides as renewable bioresources

Polysaccharides are among the most abundant bioresources on earth and consequently need to play a pivotal role when addressing existential scientific challenges like climate change and the shift from fossil-based to sustainable biobased materials. The Research Roadmap 2040 of the European Polysaccharide Network of Excellence (EPNOE) provides an expert's view on how future research and development strategies need to evolve to fully exploit the vast potential of polysaccharides as renewable bioresources. It is addressed to academic researchers, companies, as well as policymakers and covers five strategic areas that are of great importance in the context of polysaccharide related research: (I) Materials & Engineering, (II) Food & Nutrition, (III) Biomedical Applications, (IV) Chemistry, Biology & Physics, and (V) Skills & Education. Each section summarizes the state of research, identifies challenges that are currently faced, project achievements and developments that are expected in the upcoming 20 years, and finally provides outlines on how future research activities need to evolve.

α-Glucan derivatives as selective blockers of aldolase A: Computer-aided structure optimization and the effects on HCC

Aldolase A (ALDOA) promotes hepatocellular carcinoma (HCC) growth and is a potential therapeutic target. A previous study found an α-D-glucan (α-D-(1,6)-Glcp-α-D-(1,4)-Glcp, 10.0:1.0), named HDPS-4II, that could specifically inhibit ALDOA but its activity was not high enough. In this study, the derivatives of α-D-glucan binding to ALDOA were optimized using molecular docking, and its sulfated modification demonstrated the highest affinity with ALDOA among sulfated, carboxylated, and aminated derivatives. Sulfated HDPS-4II and dextrans with different molecular weights (1000 Da, 3000 Da, and 4000 Da) were prepared. Using MST assay, 3-O-sulfated HDPS-4II (SHDPS-4II) and 1000 Da dextran (SDextran1) showed higher affinities to ALDOA with Kd of 1.83 μM and 85.04 μM, respectively. Furthermore, SHDPS-4II and SDextran1 markedly inhibited the proliferation of HCC cells both in vitro and in vivo by blocking ALDOA. These results demonstrate that sulfated modification of α-D-glucans could enhance their affinities with ALDOA and anti-HCC effects.

Recent Progress in 1,2-cis glycosylation for Glucan Synthesis

Controlling the stereoselectivity of 1,2-cis glycosylation is one of the most challenging tasks in the chemical synthesis of glycans. There are various 1,2-cis glycosides in nature, such as α-glucoside and β-mannoside in glycoproteins, glycolipids, proteoglycans, microbial polysaccharides, and bioactive natural products. In the structure of polysaccharides such as α-glucan, 1,2-cis α-glucosides were found to be the major linkage between the glucopyranosides. Various regioisomeric linkages, 1→3, 1→4, and 1→6 for the backbone structure, and 1→2/3/4/6 for branching in the polysaccharide as well as in the oligosaccharides were identified. To achieve highly stereoselective 1,2-cis glycosylation, including α-glucosylation, a number of strategies using inter- and intra-molecular methodologies have been explored. Recently, Zn salt-mediated cis glycosylation has been developed and applied to the synthesis of various 1,2-cis linkages, such as α-glucoside and β-mannoside, via the 1,2-cis glycosylation pathway and β-galactoside 1,4/6-cis induction. Furthermore, the synthesis of various structures of α-glucans has been achieved using the recent progressive stereoselective 1,2-cis glycosylation reactions. In this review, recent advances in stereoselective 1,2-cis glycosylation, particularly focused on α-glucosylation, and their applications in the construction of linear and branched α-glucans are summarized.

Macromolecular α-glucans with α-1,3/α-1,4 branching structures produced using dual glycosyltransferases: Elucidation of physicochemical and slowly digestible properties

Amylosucrase from Neisseria polysaccharea (NpAS) produces the linear amylose-like α-glucans by the elongation property from sucrose, and 4,3-α-glucanotransferase from Lactobacillus fermentum NCC 2970 (4,3-αGT) newly synthesizes the α-1,3 linkages after cleaving the α-1,4 linkages by the glycosyltransferring property. This study focused on the synthesis of high molecular α-1,3/α-1,4-linked glucans by combining NpAS and 4,3-αGT and analyzed their structural and digestive properties. The enzymatically synthesized α-glucans have a molecular weight of >1.6 × 10⁷ g mol^-1, and the α-4,3 branching ratios on the structures increased as the amount of 4,3-αGT increased. The synthesized α-glucans were hydrolyzed to linear maltooligosaccharides and α-4,3 branched α-limit dextrins (α-LDx) by human pancreatic α-amylase, and the amounts of produced α-LDx were increased depending on the ratio of synthesized α-1,3 linkages. In addition, approximately 80 % of the synthesized products were partially hydrolyzed by mammalian α-glucosidases, and the glucose generation rates decelerated as the amounts of α-1,3 linkages increased. In conclusion, new types of α-glucans with α-1,4 and α-1,3 linkages were successfully synthesized by a dual enzyme reaction. These can be utilized as slowly digestible and prebiotic ingredients in the gastrointestinal tract due to their novel linkage patterns and high molecular weights.

Structural characterization and antinociceptive activity of polysaccharides from Anoectochilus elatus

Anoectochilus elatus is a new record species from Yunnan province in China discovered by our group in 2018, used in folk as the most popular Anoectochilus species A. roxburghii for medicinal and culinary purposes. The crude polysaccharide of Anoectochilus elatus (AEP) exhibited significant antinociceptive effects against both chemical and thermal nociception in vivo. Bio-guided isolation identified GJXL-1 as the leading analgesic polysaccharide in AEP. Detailed structural analyses rationalized GJXL-1 (molecular weight: 10.3 kDa) as an α-D-1,4-linked glucan unexpectedly branched at O-3, and O-6 position. GJXL-1 dose-dependently suppressed acetic acid-induced writhing in mice and decreased the serum levels of NO, IL-6 and TNF-α, which also repressed the licking times in both the first and second phases in formalin test. Furthermore, only L-nitroarginine partly reversed the analgesic activity of GJXL-1, indicating that GJXL-1's efficacy was partially mediated by NO regulation, possibly through inhibiting IRAK4/TAK1/NF-κB signaling pathway, and modulating gut microbiota and short-chain fatty acids production. In addition, the motor impairment and hypnotic effects of GJXL-1 were excluded. Our study suggests that GJXL-1 can be regarded as a promising and safe drug candidate for diverse pain disorders, and also a promising prebiotic candidate to maintain intestinal homeostasis and promote human gut health.

Production and characterization of exopolysaccharides from salinity-induced Auxenochlorella protothecoides and the analysis of anti-inflammatory activity

The set scenario of this work was to investigate the production, physicochemical characteristics, and anti-inflammatory activities of exopolysaccharides from salinity-induced Auxenochlorella protothecoides. The results demonstrated that 10 ‰ salinity manipulation endowed preferable exopolysaccharide production by A. protothecoides. Under this salinity stress, ACPEPS1A and ACPEPS2A were purified from exopolysaccharide production by anion chromatography and molecular exclusion chromatography. ACPEPS1A exhibited a molecular weight (Mw) of 132 kDa and mainly consisted of galactose. ACPEPS2A was a heteropolysaccharide with an Mw of 170 kDa and the main monosaccharides of galactose and rhamnose with separate molar percents of 42.41 % and 35.29 %, respectively. FTIR, ¹H and ¹³C NMR supported that monosaccharide components of ACPEPS1A and ACPEPS2A possessed both α- and β-configuration pyranose rings. Further evidence indicated that ACPEPS1A and ACPEPS2A could effectively inhibit the inflammatory response in lipopolysaccharide (LPS) induced RAW264.7 cells by quenching inflammatory factor levels such as ROS, iNOS, TNF-α, and IL-6. The potential anti-inflammatory possibilities were that the monosaccharides of ACPEPS1A and ACPEPS2A possessed higher affinity with receptors on the macrophage surface than LPS and hampered LPS-induced inflammation. The findings of this work would favor innovative applications of exopolysaccharides from microalgae in complementary medicines or functional foods.

Development of thermostable dextranase from Streptococcus mutans (SmdexTM) through in silico design employing B-factor and Cartesian-ΔΔG

The thermal stability of enzymes dramatically limits their application in the industrial field. Based on the crystal structure, we conducted a semi-rational design according to the B-factor and free energy values to improve the stability of dextranase from Streptococcus mutans (SmdexTM). The B-factor values of Asn102, Asn503, Asp501 and Asp500 were the highest predicted by B-FITTER. Then Rosetta was used to simulate the saturation mutations of Asn102, Asn503, Asp501 and Asp500. The mutated amino acid was designed according to the change of acG. The results showed that the thermal stability of N102P, N102C, D500G, and D500T was improved, and the half-lives of N102P/D500G and N102P/D500T at 45 °C were increased to 3.14 times and 2.44 times, respectively. Analyzing the interaction of amino acids by using Discovery Studio 4.5, it was observed that the thermal stability of dextranase was improved due to the increase in hydrophobicity and the number of hydrogen bonds of the mutant enzyme. The catalytic efficiency of N102P/D500T was increased. Compared with the hydrolyzed products of SmdexTM, the mutant enzymes do not change the specificity of hydrolysates.

Bioactivity of Biomass and Crude Exopolysaccharides Obtained by Controlled Submerged Cultivation of Medicinal Mushroom Trametes versicolor

The aim of this study is to characterize the bioactivity of mycelial biomass and crude exopolysaccharides (EPS) produced by Trametes versicolor NBIMCC 8939 and to reveal its nutraceutical potential. The EPS (1.58 g/L) were isolated from a culture broth. The macrofungal biomass was rich in protein, insoluble dietary fibers and glucans. The amino acid composition of the biomass was analyzed and 18 amino acids were detected. Three mycelial biomass extracts were prepared and the highest total polyphenol content (16.11 ± 0.14 mg GAE/g DW) and the total flavonoid content (5.15 ± 0.03 mg QE/g DW) were found in the water extract. The results indicated that the obtained EPS were heteropolysaccharides with glucose as the main building monosaccharide and minor amounts of mannose, xylose, galactose, fucose and glucuronic acid. Fourier Transform Infrared Spectroscopy (FTIR) confirmed the complex structure of the crude EPS. Five probiotic lactic acid bacteria strains were used for the determination of the prebiotic effect of the crude EPS. The anti-inflammatory potential was tested in vitro using cell line HT-29. The significant decrease of IL-1 and IL-8 and increase of TGF-beta expression revealed anti-inflammatory potential of the crude exopolysaccharides from T. versicolor.

Chemical Synthesis and Evaluation of Exopolysaccharide Fragments Produced by Leuconostoc mesenteroides Strain NTM048

Exopolysaccharides (EPSs) occur widely in natural products made by bacteria, fungi and algae. Some EPSs have intriguing biological properties such as anticancer and immunomodulatory activities. Our group has recently found that EPSs generated from Leuconostoc mesenteroides ssp. mesenteroides strain NTM048 (NTM048 EPS) enhanced a production of mucosal immunoglobulin A (IgA) of mouse. Herein, we described the synthesis and evaluation of the tetrasaccharide fragments of NTM048 EPS to obtain information about the molecular mechanism responsible for the IgA-inducing activity.

Rationalizing the Stereoelectronic Influence of Interglycosidic Bond Conformations on the Reactivity of 1,4-O-Linked Disaccharide Donors

Disaccharide donors are key precursors in convergent glycan synthesis strategies. Unexpectedly, we observed that disaccharide thioglycosyl donors containing 1,4-O-linked α-glycosidic bonds are much more reactive than their β-analogues with the same protecting group pattern. Herein, we rationalized that such a difference in their reactivity is attributed to the conformation of the 1,4-O-interglycosidic bond which is controlled by anomeric and exo-anomeric effects. Moreover, the conformational preferences of these donors are dictated by the dihedral angles ϕ and ψ of their interglycosidic linkages and the torsional angle ω of their side chain along the C5-C6 bond. This fundamental research clarifies how the long-range stereoelectronic effects from the nonreducing end sugar can influence the reactivity of the leaving group at the reducing end and the behavior of disaccharide donors thereof.

Fungal α-1,3-Glucan as a New Pathogen-Associated Molecular Pattern in the Insect Model Host Galleria mellonella

Recognition of pathogen-associated molecular patterns (PAMPs) by appropriate pattern recognition receptors (PRRs) is a key step in activating the host immune response. The role of a fungal PAMP is attributed to β-1,3-glucan. The role of α-1,3-glucan, another fungal cell wall polysaccharide, in modulating the host immune response is not clear. This work investigates the potential of α-1,3-glucan as a fungal PAMP by analyzing the humoral immune response of the greater wax moth Galleria mellonella to Aspergillus niger α-1,3-glucan. We demonstrated that 57-kDa and 61-kDa hemolymph proteins, identified as β-1,3-glucan recognition proteins, bound to A. niger α-1,3-glucan. Other hemolymph proteins, i.e., apolipophorin I, apolipophorin II, prophenoloxidase, phenoloxidase activating factor, arylphorin, and serine protease, were also identified among α-1,3-glucan-interacting proteins. In response to α-1,3-glucan, a 4.5-fold and 3-fold increase in the gene expression of antifungal peptides galiomicin and gallerimycin was demonstrated, respectively. The significant increase in the level of five defense peptides, including galiomicin, corresponded well with the highest antifungal activity in hemolymph. Our results indicate that A. niger α-1,3-glucan is recognized by the insect immune system, and immune response is triggered by this cell wall component. Thus, the role of a fungal PAMP for α-1,3-glucan can be postulated.

Bacterial α-Glucan and Branching Sucrases from GH70 Family: Discovery, Structure-Function Relationship Studies and Engineering

Glucansucrases and branching sucrases are classified in the family 70 of glycoside hydrolases. They are produced by lactic acid bacteria occupying very diverse ecological niches (soil, buccal cavity, sourdough, intestine, dairy products, etc.). Usually secreted by their producer organisms, they are involved in the synthesis of α-glucans from sucrose substrate. They contribute to cell protection while promoting adhesion and colonization of different biotopes. Dextran, an α-1,6 linked linear α-glucan, was the first microbial polysaccharide commercialized for medical applications. Advances in the discovery and characterization of these enzymes have remarkably enriched the available diversity with new catalysts. Research into their molecular mechanisms has highlighted important features governing their peculiarities thus opening up many opportunities for engineering these catalysts to provide new routes for the transformation of sucrose into value-added molecules. This article reviews these different aspects with the ambition to show how they constitute the basis for promising future developments.