Enzymatic synthesis of gentiooligosaccharides by transglycosylation with beta-glycosidases from Penicillium multicolor

Biochemical Characterization of a β-1,3-Glucanase from Bacteroidetes sp. Having Transglycosylase Activity Suitable to Synthesize β-Glucooligosaccharides

β-1,3-Glucanases have prospective applications in areas such as functional oligosaccharide preparation, plant protection, and breweries. In this study, a glycoside hydrolase (GH) family 17 β-1,3-glucanase (BbGlc17A) from Bacteroidetes bacterium from a microbial mat metagenome from the Great Salt Lake was identified. BbGlc17A catalyzed the hydrolytic conversion of laminarin into β-glucooligosaccharides with polymerization degrees of 3-8. The optimal catalytic conditions of BbGlc17A were pH 6.5 and 30 °C. In addition to its hydrolytic activity, BbGlc17A also exhibited transglycosidase activities, involving catalysis of the formation of new β-1,6-glycosidic bonds. BbGlc17A exhibits the classic (β/α)8 TIM-barrel structure and possesses an elongated catalytic groove, distinguishing it from other typical β-1,3-glucanases, which promote the forward direction of the transglycoside reaction. This effectively highlights the potential of the enzyme to convert β-1,3-glucan into mixed functional oligosaccharides. These results reveal the catalytic properties and the application potential of the GH family 17 β-1,3-glucanase and provide valuable information about the group of carbohydrate-active enzymes in biochemistry.

Liquid-Phase Adsorption Behavior of β-D-Glucooligosaccharides When Using Activated Carbon for Separation, and the Antioxidant Stress Activity of Purified Fractions

The adsorption characteristics of β-glucooligosaccharides on activated carbon and the purification were systematically investigated. The maximum adsorption capacity of activated carbon reached 0.419 g/g in the optimal conditions. The adsorption behavior was described to be monolayer, spontaneous, and exothermic based on several models' fitting results. Five fractions with different degrees of polymerization (DPs) and structures of β-glucooligosaccharides were obtained by gradient ethanol elution. 10E mainly contained disaccharides with dp2a (G1→6G) and dp2b (G1→3G). 20E possessed trisaccharides with dp3a (G1→6G1→3G) and dp3b (G1→3G1→3G). 30E mainly consisted of dp3a and dp4a (G1→3G1→3(G1→6)G), dp4b (G1→6G1→3G1→3G), and dp4c (G1→3G1→3G1→3G). In addition to tetrasaccharides, 40E and 50E also contained pentasaccharides and hexasaccharides with β-(1→3)-linked or β-(1→6)-linked glucose residues. All fractions could inhibit the accumulation of intracellular reactive oxygen species (ROS) in H2O2-induced Caco-2 cells, and they could improve oxidative stress damage by increasing the activity of superoxide dismutase (SOD) and reduced glutathione (GSH), which were related to their DPs and structures. 50E with high DPs showed better anti-oxidative stress activity.

Conversion of β-1,6-Glucans to Gentiobiose using an endo-β-1,6-Glucanase PsGly30A from Paenibacillus sp. GKG

A plethora of di- and oligosaccharides isolated from the natural sources are used in food and pharmaceutical industry. An enzymatic hydrolysis of fungal cell wall β-glucans is a good alternative to produce the desired oligosaccharides with different functionalities, such as the flavour enhancer gentiobiose. We have previously identified PsGly30A as a potential yeast cell wall degrading β-1,6-glycosidase. The aim of this study is to characterise the PsGly30A enzyme, a member of the GH30 family, and to evaluate its suitability for the production of gentiobiose from β-1,6-glucans. An endo-β-1,6-glucanase PsGly30A encoding gene from Paenibacillus sp. GKG has been cloned and overexpressed in Escherichia coli. The recombinant enzyme has been active towards pustulan and yeast β-glucan, but not on laminarin from the Laminaria digitata, confirming the endo-β-1,6-glucanase mode of action. The PsGly30A shows the highest activity at pH 5.5 and 50 °C. The specific activity of PsGly30A on pustulan (1262±82 U/mg) is among the highest reported for GH30 β-1,6-glycosidases. Moreover, gentiobiose is the major reaction product when pustulan, yeast β-glucan or yeast cell walls have been used as a substrate. Therefore, PsGly30A is a promising catalyst for valorisation of the yeast-related by-products.

Molecular mechanism for endo-type action of glycoside hydrolase family 55 endo-β-1,3-glucanase on β1-3/1-6-glucan

The glycoside hydrolase family 55 (GH55) includes inverting exo-β-1,3-glucosidases and endo-β-1,3-glucanases, acting on laminarin, which is a β1-3/1-6-glucan consisting of a β1-3/1-6-linked main chain and β1-6-linked branches. Despite their different modes of action toward laminarin, endo-β-1,3-glucanases share with exo-β-1,3-glucosidases conserved residues that form the dead-end structure of subsite -1. Here, we investigated the mechanism of endo-type action on laminarin by GH55 endo-β-1,3-glucanase MnLam55A, identified from Microdochium nivale. MnLam55A, like other endo-β-1,3-glucanases, degraded internal β-d-glucosidic linkages of laminarin, producing more reducing sugars than the sum of d-glucose and gentiooligosaccharides detected. β1-3-Glucans lacking β1-6-linkages in the main chain were not hydrolyzed. NMR analysis of the initial degradation of laminarin revealed that MnLam55A preferentially cleaved the nonreducing terminal β1-3-linkage of the laminarioligosaccharide moiety at the reducing end side of the main chain β1-6-linkage. MnLam55A liberates d-glucose from laminaritriose and longer laminarioligosaccharides, but kcat/Km values to laminarioligosaccharides (≤4.21 s-1 mM-1) were much lower than to laminarin (5920 s-1 mM-1). These results indicate that β-glucan binding to the minus subsites of MnLam55A, including exclusive binding of the gentiobiosyl moiety to subsites -1 and -2, is required for high hydrolytic activity. A crystal structure of MnLam55A, determined at 2.4 Å resolution, showed that MnLam55A adopts an overall structure and catalytic site similar to those of exo-β-1,3-glucosidases. However, MnLam55A possesses an extended substrate-binding cleft that is expected to form the minus subsites. Sequence comparison suggested that other endo-type enzymes share the extended cleft. The specific hydrolysis of internal linkages in laminarin is presumably common to GH55 endo-β-1,3-glucanases.

Enzymatic Preparation of Gentiooligosaccharides by a Thermophilic and Thermostable β-Glucosidase at a High Substrate Concentration

Gentiooligosaccharides (GnOS) are a kind of oligosaccharide formed by glucose with β-1-6 glycosidic bonds, which has become a new type of functional oligosaccharide for its unique refreshing bitter taste and valuable probiotic effects. However, the research on the enzymatic preparation of GnOS is not thorough enough. In this study, a GH1 thermophilic β-glucosidase from Thermotoga sp. KOL6 was used as a biocatalyst for the synthesis of GnOS. TsBgl1 exhibited excellent thermophilic and thermostable properties by possessing a melting temperature of 101.5 °C and reacting at 80–90 °C efficiently. Its half-life at 90 °C was approximately 5 h, suggesting its high heat resistance as well. TsBgl1 also showed excellent glucose tolerance with an inhibition constant (K_i) of 1720 mM and was stimulated in the presence of 0–900 mM glucose. TsBgl1 showed the highest hydrolytic activity on laminaribiose (Glc-β-1,3-Glc), but mainly synthetized gentiobiose (Glc-β-1,6-Glc) during transglycosylation. By optimizing the reaction conditions and substrate concentration, the highest yield of GnOS synthesized by TsBgl1 reached 144.3 g·L⁻¹ when 1000 g·L⁻¹ glucose was used as a substrate, which was higher than the highest yield ever reported. The thermophilic and thermostable properties of TsBgl1 were considered to be significant advantages in the industrial production of GnOS, where long periods of high-temperature reactions are required. This study was expected to provide an excellent candidate enzyme for industrial production of GnOS and also provide a reference for studying the transglycosylation of GH1 β-glucosidases.

Dietary Fiber in Plant Cell Walls—The Healthy Carbohydrates

Dietary fiber (DF) is one of the major classes of nutrients for humans. It is widely distributed in the edible parts of natural plants, with the cell wall being the main DF-containing structure. The DF content varies significantly in different plant species and organs, and the processing procedure can have a dramatic effect on the DF composition of plant-based foods. Given the considerable nutritional value of DF, a deeper understanding of DF in food plants, including its composition and biosynthesis, is fundamental to the establishment of a daily intake reference of DF and is also critical to molecular breeding programs for modifying DF content. In the past decades, plant cell wall biology has seen dramatic progress, and such knowledge is of great potential to be translated into DF-related food science research and may provide future research directions for improving the health benefits of food crops. In this review, to spark interdisciplinary discussions between food science researchers and plant cell wall biologists, we focus on a specific category of DF—cell wall carbohydrates. We first summarize the content and composition of carbohydrate DF in various plant-based foods, and then discuss the structure and biosynthesis mechanism of each carbohydrate DF category, in particular the respective biosynthetic enzymes. Health impacts of DF are highlighted, and finally, future directions of DF research are also briefly outlined.

A Novel Neutral and Mesophilic β-Glucosidase from Coral Microorganisms for Efficient Preparation of Gentiooligosaccharides

β-glucosidases can produce gentiooligosaccharides that are lucrative and promising for the prebiotic and alternative food industries. However, the commercial production of gentiooligosaccharides using β-glucosidase is challenging, as this process is limited by the need for high thermal energy and increasing demand for the enzyme. Here, a putative β-glucosidase gene, selected from the coral microbial metagenome, was expressed in Escherichia coli. Reverse hydrolysis of glucose by Blg163 at pH 7.0 and 40 °C achieved a gentiooligosaccharide yield of 43.02 ± 3.20 g·L⁻¹ at a conversion rate of 5.38 ± 0.40%. Transglycosylation of mixed substrates, glucose and cellobiose, by Blg163 consumed 21.6 U/0.5 g glucose/g cellobiose, achieving a gentiooligosaccharide yield of 70.34 ± 2.20 g·L⁻¹ at a conversion rate of 15.63%, which is close to the highest yield reported in previous findings. Blg163-mediated synthesis of gentiooligosaccharides is the mildest reaction and the lowest β-glucosidase consumption reported to date.

Improvements in xylose stability and thermalstability of GH39 β-xylosidase from Dictyoglomus thermophilum by site-directed mutagenesis and insights into its xylose tolerance mechanism

β-Xylosidases are often inhibited by its reaction product xylose or inactivated by high temperature environment, which limited its application in hemicellulosic biomass conversion to fuel and food processing. Remarkably, some β-xylosidases from GH39 family are tolerant to xylose. Therefore, it is of great significance to elucidate the effect mechanism of xylose on GH39 β-xylosidases to improve their application. In this paper, based on the homologous model and prediction of protein active pocket constructed by I-TASSA and PyMOL, two putative xylose tolerance relevant sites (283 and 284) were mutated at the bottom of the protein active pocket, where xylose sensitivity and thermostability of Dictyoglomus thermophilum β-xylosidase Xln-DT were improved by site-directed mutagenesis. The Xln-DT mutant Xln-DT-284ASP and Xln-DT-284ALA showed high xylose tolerance, with the K_i values of 4602 mM and 3708 mM, respectively, which increased by 9-35% compared with the wildtype Xln-DT. The thermostability of mutant Xln-DT-284ASP was significantly improved at 75 and 85 °C, while the activity of the wild enzyme Xln-DT decreased to 40-20%, the activity of the mutant enzyme still remained 100%. The mutant Xln-DT-284ALA showed excellent stability at pH 4.0-7.0, but Xln-DT-284ASP showed slightly decreased activity. Furthermore, in order to explore the key sites and mechanism of xylose's effect on β-xylosidase activity, the interaction between xylose and enzyme was simulated by molecular docking. Besides binding to the active sites at the bottom of the substrate channel, xylose can also bind to sites in the middle or entrance of the channel with different affinities, which may determine the xylose inhibition of β-xylosidase. In conclusion, the improved xylose tolerance of mutant enzyme could be more advantageous in the degradation of hemicellulose and the biotransformation of other natural active substances containing xylose. This study supplies new insights into general mechanism of xylose effect on the activity of GH 39 β-xylosidases as well as related enzymes that modulate their activity via feedback control mechanism.

Oligosaccharides from Traditional Chinese Herbal Medicines: A Review of Chemical Diversity and Biological Activities

Most of traditional Chinese herbal medicine (TCHM) substances come from medicinal plants, among which oligosaccharides have gradually attracted widespread attention at home and abroad due to their important biological activities and great medicinal potential. Numerous in vitro and in vivo experiments exhibited that oligosaccharides possess various activities, such as antitumor, anti-oxidation, modulate the gut microflora, anti-inflammatory, anti-infection, and immune-regulatory activities. Generally, biological activities are closely related to chemical structures, including molecular weight, monosaccharide composition, glycosidic bond connection, etc. The structural analysis of oligosaccharides is an important basis for studying their structure-activity relationship, but the structural diversity and complexity of carbohydrate compounds limit the study of oligosaccharides activities. Understanding the structures and biological functions of oligosaccharides is important for the development of new bioactive substances with natural oligosaccharides. This review provides a systematic introduction of the current knowledge of the chemical structures and biological activities of oligosaccharides. Most importantly, the reported chemical characteristics and biological activities of the famous TCHM oligosaccharides were briefly summarized, including Morinda officinalis, Rehmannia glutinosa, Arctium lappa, Polygala tenuifolia, Panax ginseng, Lycium barbarum and Astragalus membranaceus. TCHM oligosaccharides play an important role in nutrition, health care, disease diagnosis and prevention as well as have broad application prospects in the field of medicine.

Gtgen3A, a novel plant GH3 β-glucosidase, modulates gentio-oligosaccharide metabolism in Gentiana

Gentiobiose, a β-1,6-linked glycosyl-disaccharide, accumulates abundantly in Gentianaceae and is involved in aspects of plant development, such as fruits ripening and release of bud dormancy. However, the mechanisms regulating the amount of gentio-oligosaccharide accumulation in plants remain obscure. The present study aimed to identify an enzyme that modulates gentio-oligosaccharide amount in gentian (Gentiana triflora). A protein responsible for gentiobiose hydrolysis, GtGen3A, was identified by partial purification and its peptide sequence analysis. The enzyme had a molecular mass of ∼67 kDa without a secretory signal peptide sequence. Sequence analysis revealed that GtGen3A could be a β-glucosidase member belonging to glycoside hydrolase family 3 (GH3). GtGen3A showed a homology to GH3 β-glucan exohydrolases, ExoI of Hordeum vulgare, and ExgI from Zea mays, which preferentially hydrolyzed β-1,3- and β-1,4-linked oligosaccharides. The purified recombinant GtGen3A (rGtGen3A) produced in Escherichia coli showed optimal reaction at pH 6.5 and 20°C. The rGtGen3A liberated glucose from β-1,2-, β-1,3-, β-1,4-, and β-1,6-linked oligosaccharides, and showed the highest activity toward gentiotriose among the substrates tested. Kinetic analysis also revealed that rGtGen3A preferentially hydrolyzed gentiotriose. Virus-induced gene silencing of Gtgen3A in gentian plantlets resulted in predominant accumulation of gentiotriose rather than gentiobiose. Furthermore, the expression level of Gtgen3A was almost similar to the amount of gentiobiose in field-grown gentians. These findings suggest that the main function of GtGen3A is the hydrolysis of gentiotriose to gentiobiose, and that GtGen3A plays a role in modulating gentiobiose amounts in gentian.

Preparation of gentiooligosaccharides using Trichoderma viride β-glucosidase

The recombinant plasmid pPIC9K-bgl1 containing β-glucosidase bgl1 from Trichoderma viride was constructed by overlapping PCR and integrated into Pichia pastoris KM71. In order to assist the formation of disulfide bonds and thus improve protein folding efficiency, protein disulfide isomerase pdi was co-expressed in the P. pastoris KM71/pPIC9K-bgl1/pPICZ-A-pdi strain, and fermentation in flasks resulted in enzyme activity of 143 U/ml. The enzyme activity of β-glucosidase reached 1402 U/ml following optimisation of fermentation conditions in a 3.6 l bioreactor. With 80% glucose as substrate, gentiooligosaccharides were synthesised by β-glucosidase-based reverse hydrolysis. A yield of 130 g/l was achieved with a conversion rate of 16.25%. With 20% glucose and 40% cellobiose as substrates, gentiooligosaccharides were synthesised by transglycosylation with a yield of 116 g/l and a conversion rate of 19.4%.

Production of the versatile cellulase for cellulose bioconversion and cellulase inducer synthesis by genetic improvement of Trichoderma reesei

BACKGROUND

The enzymes for efficient hydrolysis of lignocellulosic biomass are a major factor in the development of an economically feasible cellulose bioconversion process. Up to now, low hydrolysis efficiency and high production cost of cellulases remain the significant hurdles in this process. The aim of the present study was to develop a versatile cellulase system with the enhanced hydrolytic efficiency and the ability to synthesize powerful inducers by genetically engineering Trichoderma reesei.

RESULTS

In our study, we employed a systematic genetic strategy to construct the carbon catabolite-derepressed strain T. reesei SCB18 to produce the cellulase complex that exhibited a strong cellulolytic capacity for biomass saccharification and an extraordinary high β-glucosidase (BGL) activity for cellulase-inducing disaccharides synthesis. We first identified the hypercellulolytic and uracil auxotrophic strain T. reesei SP4 as carbon catabolite repressed, and then deleted the carbon catabolite repressor gene cre1 in the genome. We found that the deletion of cre1 with the selectable marker pyrG led to a 72.6% increase in total cellulase activity, but a slight reduction in saccharification efficiency. To facilitate the following genetic modification, the marker pyrG was successfully removed by homologous recombination based on resistance to 5-FOA. Furthermore, the Aspergillus niger BGLA-encoding gene bglA was overexpressed, and the generated strain T. reesei SCB18 exhibited a 29.8% increase in total cellulase activity and a 51.3-fold enhancement in BGL activity (up to 103.9 IU/mL). We observed that the cellulase system of SCB18 showed significantly higher saccharification efficiency toward differently pretreated corncob residues than the control strains SDC11 and SP4. Moreover, the crude enzyme preparation from SCB18 with high BGL activity possessed strong transglycosylation ability to synthesize β-disaccharides from glucose. The transglycosylation product was finally utilized as the inducer for cellulase production, which provided a 63.0% increase in total cellulase activity compared to the frequently used soluble inducer, lactose.

CONCLUSIONS

In summary, we constructed a versatile cellulase system in T. reesei for efficient biomass saccharification and powerful cellulase inducer synthesis by combinational genetic manipulation of three distinct types of genes to achieve the customized cellulase production, thus providing a viable strategy for further strain improvement to reduce the cost of biomass-based biofuel production.

Synthesis of 3-aminopropyl β-(1 → 6)-d-glucotetraoside and its biotinylated derivative

3-Aminopropyl β-(1 → 6)-d-glucotetraoside has been synthesized from 3-benzyloxycarbonylaminopropanol and 6-O-acetyl-2,3,4-tri-O-benzoyl-d-glucopyranosyl trichloroacetimidate by successive attachment of one monosaccharide unit in total yield of 22%. Free aminopropyl glycoside was converted into a biotin derivative that can be used for controlled immobilization of the oligosaccharide on streptavidin-coated ELISA plates and for tracing carbohydrate binding molecules.

Prebiotic Oligosaccharides: Special Focus on Fructooligosaccharides, Its Biosynthesis and Bioactivity

The bacterial groups in the gut ecosystem play key role in the maintenance of host's metabolic and structural functionality. The gut microbiota enhances digestion processing, helps in digestion of complex substances, synthesizes beneficial bioactive compounds, enhances bioavailability of minerals, impedes growth of pathogenic microbes, and prevents various diseases. It is, therefore, desirable to have an adequate intake of prebiotic biomolecules, which promote favorable modulation of intestinal microflora. Prebiotics are non-digestible and chemically stable structures that significantly enhance growth and functionality of gut microflora. The non-digestible carbohydrate, mainly oligosaccharides, covers a major part of total available prebiotics as dietary additives. The review describes the types of prebiotic low molecular weight carbohydrates, i.e., oligosaccharides, their structure, biosynthesis, functionality, and applications, with a special focus given to fructooligosaccharides (FOSs). The review provides an update on enzymes executing hydrolytic and fructosyltransferase activities producing prebiotic FOS biomolecules, and future perspectives.

Oligosaccharides: a boon from nature's desk

This article reviews the varied sources of oligosaccharides available in nature as silent health promoting, integral ingredients of plants as well as animal products like honey and milk. The article focuses on exotic and unfamiliar oligosaccharides like Galactooligosaccharides, Lactulose derived Galactooligosaccharides, Xylooligosaccharides, Arabinooligosaccharides and algae derived Marine oligosaccharides along with the most acknowledged prebiotic fructooligosaccharides. The oligosaccharides are named as on the grounds of the monomeric units forming oligomers with functional properties. The chemical structures, natural sources, microbial enzyme mediated synthesis and physiological effects are discussed. An elaborate account of the different types of oligosaccharides with special reference to fructooligosaccharides are presented. Finally, the profound health benefits of oligosaccharides are rigourously discussed limelighting its positive physiological sequel.

Gentio-oligosaccharides from Leuconostoc mesenteroides NRRL B-1426 dextransucrase as prebiotics and as a supplement for functional foods with anti-cancer properties

Gentio-oligosaccharides (GnOS) were synthesized by the acceptor reaction of dextransucrase from Leuconostoc mesenteroides NRRL B-1426 with gentiobiose and sucrose. GnOS were purified by gel permeation chromatography using a Bio-Gel P-2 column and identified by mass spectrometry. The purified GnOS (degree of polymerization ≥3) were investigated for their in vitro prebiotic and cytotoxic activity. GnOS exhibited a significantly lower degree of digestibility of 18.1% by simulated human gastric juice (pH 1.0) and 7.1% by human α-amylase (pH 7.0) after 6 h, whereas inulin, a standard prebiotic, showed 39.7% and 12.8% of digestibility, respectively. The prebiotic score showed that GnOS significantly supported the growth of probiotics such as Bifidobacterium infantis and Lactobacillus acidophilus and was comparable to that of inulin. The selective inhibitory effect of GnOS on human colon carcinoma (HT-29) cells revealed its potential as an anti-cancer agent that can serve as a functional food additive for the benefit of human health.

Liquid phase adsorption behavior of inulin-type fructan onto activated charcoal

This study describes liquid phase adsorption characteristics of inulin-type fructan onto activated charcoal. Batch mode experiments were conducted to study the effects of pH, contact time, temperature and initial concentration of inulin. Nearly neutral solution (pH 6-8) was favorable to the adsorption and the equilibrium was attained after 40 min with the maximum adsorption Qmax 0.182 g/g (adsorbate/adsorbent) at 298 K. The experimental data analysis indicated that the adsorption process fitted well with the pseudo-second-order kinetic model (R(2) = 1) and Langmuir isotherms model (R(2) > 0.99). Thermodynamic parameters revealed that the adsorption process was spontaneous and exothermic with a physical nature. Inulin desorption could reach 95.9% using 50% ethanol solution and activated charcoal could be reused without significant losses in adsorption capacity. These results are of practical significance for the application of activated charcoal in the production and purification of inulin-type fructan.

Bioproduction of chitooligosaccharides: present and perspectives

Chitin and chitosan oligosaccharides (COS) have been traditionally obtained by chemical digestion with strong acids. In light of the difficulties associated with these traditional production processes, environmentally compatible and reproducible production alternatives are desirable. Unlike chemical digestion, biodegradation of chitin and chitosan by enzymes or microorganisms does not require the use of toxic chemicals or excessive amounts of wastewater. Enzyme preparations with chitinase, chitosanase, and lysozymeare primarily used to hydrolyze chitin and chitosan. Commercial preparations of cellulase, protease, lipase, and pepsin provide another opportunity for oligosaccharide production. In addition to their hydrolytic activities, the transglycosylation activity of chitinolytic enzymes might be exploited for the synthesis of desired chitin oligomers and their derivatives. Chitin deacetylase is also potentially useful for the preparation of oligosaccharides. Recently, direct production of oligosaccharides from chitin and crab shells by a combination of mechanochemical grinding and enzymatic hydrolysis has been reported. Together with these, other emerging technologies such as direct degradation of chitin from crustacean shells and microbial cell walls, enzymatic synthesis of COS from small building blocks, and protein engineering technology for chitin-related enzymes have been discussed as the most significant challenge for industrial application.

Bioproduction of chitooligosaccharides: present and perspectives

Chitin and chitosan oligosaccharides (COS) have been traditionally obtained by chemical digestion with strong acids. In light of the difficulties associated with these traditional production processes, environmentally compatible and reproducible production alternatives are desirable. Unlike chemical digestion, biodegradation of chitin and chitosan by enzymes or microorganisms does not require the use of toxic chemicals or excessive amounts of wastewater. Enzyme preparations with chitinase, chitosanase, and lysozymeare primarily used to hydrolyze chitin and chitosan. Commercial preparations of cellulase, protease, lipase, and pepsin provide another opportunity for oligosaccharide production. In addition to their hydrolytic activities, the transglycosylation activity of chitinolytic enzymes might be exploited for the synthesis of desired chitin oligomers and their derivatives. Chitin deacetylase is also potentially useful for the preparation of oligosaccharides. Recently, direct production of oligosaccharides from chitin and crab shells by a combination of mechanochemical grinding and enzymatic hydrolysis has been reported. Together with these, other emerging technologies such as direct degradation of chitin from crustacean shells and microbial cell walls, enzymatic synthesis of COS from small building blocks, and protein engineering technology for chitin-related enzymes have been discussed as the most significant challenge for industrial application.

Synthesis of novel bioactive lactose-derived oligosaccharides by microbial glycoside hydrolases

Prebiotic oligosaccharides are increasingly demanded within the Food Science domain because of the interesting healthy properties that these compounds may induce to the organism, thanks to their beneficial intestinal microbiota growth promotion ability. In this regard, the development of new efficient, convenient and affordable methods to obtain this class of compounds might expand even further their use as functional ingredients. This review presents an overview on the most recent interesting approaches to synthesize lactose-derived oligosaccharides with potential prebiotic activity paying special focus on the microbial glycoside hydrolases that can be effectively employed to obtain these prebiotic compounds. The most notable advantages of using lactose-derived carbohydrates such as lactosucrose, galactooligosaccharides from lactulose, lactulosucrose and 2-α-glucosyl-lactose are also described and commented.

Characterization of novel β-glucosidases with transglycosylation properties from Trichosporon asahii

Two novel β-glucosidases from Trichosporon asahii, named BG1 and BG2, were purified to electrophoretic homogeneity using ammonium sulfate precipitation, hydrophobic interaction, ion exchange, and gelfiltration chromatography. The molecular weight of BG1 and BG2 were estimated as 160 kDa and 30 kDa, respectively. The K(m), V(max), K(cat), and K(cat)/K(m) values of the two β-glucosidases for p-nitrophenyl-β-D-glucopyranoside were determined. Both enzymes showed relatively high affinity to p-nitrophenyl-β-D-glucopyranoside in 4-nitrophenol glycosides and gentiobiose in saccharide substrates. The enzymes exhibited optimum activity at pH 6.0 and pH 5.5, respectively. Their respective optimum temperatures were 70 and 50 °C. Metal ions and inhibitors had different effects on the enzymes activities. Circular dichroism (CD) spectroscopy demonstrated that the purified BG1 exhibited a β-sheet-rich structure and that BG2 displayed a high random coil conformation. HPLC analysis of transglycosylation and reverse hydrolysis assays revealed that only BG1 possessed transglycosylation activity and synthesized cello-oligosaccharides by the addition of glucose. This suggested that BG1 could be used to produce complex bioactive glycosides and could be considered as a potential enzyme for industrial application.

Enzymatic synthesis of an α-chitin-like substance via lysozyme-mediated transglycosylation

The enzymatic synthesis of an α-chitin-like substance via a non-biosynthetic pathway has been achieved by transglycosylation in an aqueous system of the corresponding substrate, tri-N-acetylchitotriose [(GlcNAc)(3)] for lysozyme. A significant amount of water-insoluble product precipitated out from the reaction system. MALDI-TOFMS analysis showed that the resulting precipitate had a degree of polymerization (DP) of up to 15 from (GlcNAc)(3). Solid-state (13)C NMR analysis revealed that the resulting water-insoluble product is a chitin-like substance consisting of N-acetylglucosamine (GlcNAc) residues joined exclusively in a β-(1→4)-linked chain with stringent regio-/stereoselection. X-ray diffraction (XRD) measurement as well as (13)C NMR analysis showed that the crystal structure of synthetic product corresponds to α-chitin with a high degree of crystallinity. We propose that the multiple oligomers form an α-chitin-like substance as a result of self-assembly via oligomer-oligomer interaction when they precipitate.

A comparative study of activity and apparent inhibition of fungal β-glucosidases

β-Glucosidases (BGs) from Aspergillus fumigates, Aspergillus niger, Aspergillus oryzae, Chaetomium globosum, Emericella nidulans, Magnaporthe grisea, Neurospora crassa, and Penicillium brasilianum were purified to homogeneity, and analyzed by isothermal titration calorimetry with respect to their hydrolytic activity and its sensitivity to glucose (product) using cellobiose as substrate. Global non-linear regression of several reactions, with or without added glucose, to a product inhibition equation enabled the concurrent derivation of the kinetic parameters k(cat), K(m), and the apparent product inhibition constant (app)K(i) for each of the enzymes. A more simple fit is not advisable to use as the determined (app)K(i) are in the same range as their K(m) for some of the tested BGs and produced glucose would in these cases interfere. The highest value for k(cat) was determined for A. fumigatus (768 s(-1)) and the lowest was a factor 9 less. K(m) varied by a factor of 3 with the lowest value determined for C. globosum (0.95 mM). The measured (app)K(i) varied a factor of 15; the hydrolytic activity of N. crassa being the most resistant to glucose with an apparent product inhibition constant of 10.1 mM. Determination of (app)K(i) using cellobiose as substrate is important as it reflects to what extent the different BGs are hydrolytically active under industrial conditions where natural substrates are hydrolyzed and the final glucose concentrations are high.

Enzymatic synthesis of alpha-glucosyl-timosaponin BII catalyzed by the extremely thermophilic enzyme: Toruzyme 3.0L

Timosaponin BII (BII), a steroidal saponin showing potential anti-dementia activity, was converted into its glucosylation derivatives by Toruzyme 3.0L. Nine products with different degrees of glucosylation were purified and their structures were elucidated on the basis of (13)C NMR, HR-ESI-MS, and FAB-MS spectra data. The active enzyme in Toruzyme 3.0L was purified to electrophoretic homogeneity by tracking BII-glycosylase activity and was identified as Cyclodextrin-glycosyltransferase (CGTase, EC 2.4.1.19) by ESI-Q-TOF MS/MS. In this work, we found that the active enzyme catalyzed the synthesis of alpha-(1-->4)-linked glucosyl-BII when dextrin instead of an expensive activated sugar was used as the donor and showed a high thermal tolerance with the most favorable enzymatic activity at 100 degrees C. In addition, we also found that the alpha-amylases and CGTase, that is, GH13 family enzymes, all exhibited similar activities, which were able to catalyze glucosylation in steroidal saponins. But other kinds of amylases, such as gamma-amylase (GH15 family), had no such activity under the same reaction conditions.

Recent progress in chemical and chemoenzymatic synthesis of carbohydrates

The important roles that carbohydrates play in biological processes and their potential application in diagnosis, therapeutics, and vaccine development have made them attractive synthetic targets. Despite ongoing challenges, tremendous progresses have been made in recent years for the synthesis of carbohydrates. The chemical glycosylation methods have become more sophisticated and the synthesis of oligosaccharides has become more predictable. Simplified one-pot glycosylation strategy and automated synthesis are increasingly used to obtain biologically important glycans. On the other hand, chemoenzymatic synthesis continues to be a powerful alternative for obtaining complex carbohydrates. This review highlights recent progress in chemical and chemoenzymatic synthesis of carbohydrates with a particular focus on the methods developed for the synthesis of oligosaccharides, polysaccharides, glycolipids, and glycosylated natural products.