Microbial β-glucanases: production, properties, and engineering

Enzymolysis for effective grain processing: Computer-aided optimization of a 1,3-1,4-β-glucanase with improved thermostability and catalytic activity

β-Glucanases, widely applied in grain processing, are commonly restricted for efficient industrial application due to the limited thermostability. In this study, a 1,3-1,4-β-glucanase (BisGlu16B_ΔC) was optimized for thermostability through a computer-aided design of energy optimization. Three variants (T40K, Q53L, and S311Y) were selected and generated a combined mutant T40K/Q53L/S311Y (M3). Comparing with the WT, M3 exhibited better thermostability (with t1/2 at 60 °C extend by 126 min), higher specific activity (1.24 folds; 69,700 vs. 56,200 U/mg), higher catalytic effciency (1.18 folds; 14,100 vs. 11,900 mL‧s-1‧mg-1), and improved protease resistance. For mechanism, more hydrogen bonds, salt bridges, and rigid secondary components in M3 led to an enhanced overall rigidity, boosting the thermostability. While enhanced long-range negative interactions affected some key residues in the catalytic channels, improving the catalytic efficiency. For application, M3 showed superiority with higher dry matter digestibility (1.49 folds; 80.3 % vs. 53.9 %) in simulated gastrointestinal system, together with more reduction of filtration time (1.55 folds; 22.2 % vs. 14.3 %) and viscosity (2.37 folds; 10.2 % vs. 4.3 %) during malting, comparing with the WT. Furthermore, the strongest synergistic effects were found between xylanase and M3, among all β-glucanases tested. All results verified M3 as an efficient β-glucanase for grain processing industry.

Statistical and neural network modeling of β-glucanase production by Streptomyces albogriseolus (PQ002238), and immobilization on chitosan-coated magnetic microparticles

β-Glucanases are a series of glycoside hydrolases (GHs) that are of special interest for various medical and biotechnological applications. Numerous β-glucanases were produced by different types of microorganisms. Particularly, bacterial β-glucanases have the privilege of being stable, easily produced, and suitable for large-scale production. This study aimed for finding potent β-glucanase producing bacterial strains and optimizing its production. Soil samples from Egyptian governorates were screened for such strains, and 96 isolates were collected. The β-glucanase activity was qualitatively assessed and quantitatively measured using 3,5-dinitrosalicylic acid (DNS) method. The highest β-glucanase producing strain (0.74 U/ml) was identified as Streptomyces albogriseolus S13-1. The optimum incubation period and temperature, determined one-variable at a time, were estimated as 4 d and 45 ͦ C, respectively. Similarly, yeast β-glucan and beef extract were selected as the best carbon and nitrogen sources, with enzymatic activities of 0.74 and 1.12 U/ml, respectively. Other fermentation conditions were optimized through response surface methodology (RSM); D-optimal design (DOD) with a total of 28 runs. The maximum experimental β-glucanase activity (1.3 U/ml) was obtained with pH 6.5, inoculum volume of 0.5% v/v, agitation speed of 100 rpm, carbon concentration of 1% w/v, and nitrogen concentration of 0.11% w/v. This was 1.76-fold higher compared to unoptimized conditions. Using the same experimental matrix, an artificial neural network (ANN) was built to predict β-glucanase production by the isolated strain. Predicted β-glucanase levels by RSM and ANN were 1.79 and 1.32 U/ml, respectively. Both models slightly over-estimated production levels, but ANN showed higher predictivity and better performance metrics. The enzyme was partially purified through acetone precipitation, characterized, and immobilized on chitosan-coated iron oxide microparticles. The optimal pH and temperature for enzyme activity were 5 and 50 °C, respectively. The immobilized enzyme showed superior characters such as higher stability at temperatures 50, 60, and 70 °C compared to the free enzyme, and satisfactory reusability, losing only 30% of activity after 6 cycles of reuse.

Overview of various protein engineering strategies to improve the catalytic activity, thermostability, and acid/base stability of β-glucanase

β-Glucan is highly valued in the food and medical industries due to its various physiological functions. However, its aqueous solution tends to have high viscosity, which negatively impacts the brewing and feed industries. By hydrolyzing β-glucosidic bonds, β-glucanase could reduce the adverse effects of β-glucan. For this reason, β-glucanase is widely utilized in the brewing and animal feed production. The limited thermal and acid stability of β-glucanase restricts its applications in industrial settings. Therefore, it is of great importance to enhance the stability of existing β-glucanases through protein engineering. This review summarizes current integrated technical methods for the molecular modification of β-glucanases, including error-prone PCR, site-saturation mutagenesis, DNA recombination, sequence alignment, N- and C-terminal modifications, surface charge optimization, intermolecular force optimization, and rigidity of flexible regions. The aim is to provide a theoretical basis and practical guidance for the further modification of β-glucanases.

Competitive inhibition of family GH5 Aspergillus niger endo-glucanase A (AnglA5) by rice xylanase inhibitor (RIXI): Experimental and in silico insights

In this study, we heterologously expressed the GH5 family endo-β-1,4-glucanase A (AnglA5) from Aspergillus niger in Escherichia coli BL21 (DE3). The recombinant AnglA5 (reAnglA5) demonstrated optimal activity at 50 °C and pH 5.0, with Mn2+ markedly enhancing catalytic efficiency, whereas Cu2+ showed potent inhibitory effects. Competitive inhibition of reAnglA5 by recombinant rice xylanase inhibitor (reERIXI) was observed, with an inhibition constant (Ki) of 245.40 nmol/L. Their interaction resulted in static fluorescence quenching. Molecular dynamics simulations and non-covalent interaction analysis revealed that the α-7 helix of RIXI inserts into the catalytic pocket of AnglA5, overlapping with the substrate-binding cleft. This structural arrangement is mechanistically consistent with competitive inhibition with a binding free energy (ΔG) of -84.5 ± 4.6 kcal/mol for the AnglA5-RIXI system. Residue K235 in the α-7 helix forms stably hydrogen bonds with catalytic residues E132 and E238 of AnglA5. Structural analysis further identified specific hydrogen bonds and van der Waals interactions between RIXI and residues in the peripheral catalytic pocket. This study provides the first evidence of competitive inhibition of GH5 glucanase by a rice xylanase inhibitor, offering insights into the detailed enzyme-inhibitor interactions and contributing to the engineering of XI-resistant glucanase mutants.

Biochemical characterization of the catalytic domain from a novel hyperthermophilic β-glucanase and its application for KOS production

Konjac oligosaccharide (KOS) exhibits various biological activities, and hyperthermophilic β-glucanases offer many advantages for KOS production from konjac glucanmannan (KGM). In this study, a novel β-glucanase, EG003, belonging to the glycosyl hydrolase (GH) subfamily 5_1, was predicted from the genome of the a Thermus strain. The recombinant EG003 and its catalytic domain, EG003A, were successfully expressed and characterized. EG003A displayed maximum activity at 95 °C and pH 8.0, with a specific activity of 1047.6 U/mg and retained approximately 50 % activity after 6 h at 90 °C. The enzyme exhibited both β-1,4-glucanase and β-1,3-1,4-glucanase activity with KGM and sodium carboxymethylcellulose (CMC), lichenan and oat β-glucan as substrates. Degree of polymerization (DP) 3 was the major oligosaccharide from the hydrolysis of KGM, while DP3 and DP4 were predominant products from the hydrolysis of oat β-glucan. Molecular docking analyses revealed that the catalytic mechanism of EG003A is consistent with those of other reported GH5_1 β-glucanases. Additionally, the viscosity of 500 mL solution of 1 % KGM decreased rapidly from 31,193 mPa.s to 4.50 mPa.s in 3 min with 30 U EG003A. This study provides an efficient hyperthermophilic β-glucanase with promising application for KOS production.

Exogenous application of Eucommia ulmoides β-1, 4-glucanase promotes propagation by increasing the expression of wound healing genes

Eucommia ulmoides (E. ulmoides) is a valuable gum-producing plant and traditional Chinese medicine. The utilization value of E. ulmoides varies according to the sex of the plant, and due to its perennial characteristics, the identification of male and female is challenging. To meet production demands, gender selection through grafting has been employed. The fusion of rootstock and scion cells in grafted plants can be enhanced by β-1, 4-glucanase, thus improving the grafting survival rate. However, extracting β-1, 4-glucanase in vivo poses difficulties. In this study, the β-1, 4-glucanase gene of E. ulmoides was cloned, and the total length of the gene was 1917 bp, encoding 638 amino acids. Pichia pastoris engineering bacteria were used to express β-1, 4-glucanase. The optimal fermentation conditions included a pH of 6, a temperature of 28 ℃, a methanol content of 1.5%, and a fermentation period of 96 hours. After purification, the enzyme activity of the target protein was measured to be 286.35 U/mL. Protein concentrations of 5 mg/mL, 10 mg/mL, and 15 mg/mL were tested for E. ulmoides grafting. The results showed that the protein could promote wound healing and improve the survival rate of E. ulmoides grafting. In conclusion, this study successfully developed an enzyme that improves the survival rate of E. ulmoides grafting, and provides valuable insights for the breeding of male and female E. ulmoides grafts.

Thermothelomyces thermophilus cultivated with residues from the fruit pulp industry: enzyme immobilization on ionic supports of a crude cocktail with enhanced production of lichenase

β-Glucans comprise a group of β-D-glucose polysaccharides (glucans) that occur naturally in the cell walls of bacteria, fungi, and cereals. Its degradation is catalyzed by β-glucanases, enzymes that catalyze the breakdown of β-glucan into cello-oligosaccharides and glucose. These enzymes are classified as endo-glucanases, exo-glucanases, and glucosidases according to their mechanism of action, being the lichenases (β-1,3;1,4-glucanases, EC 3.2.1.73) one of them. Hence, we aimed to enhance lichenase production by Thermothelomyces thermophilus through the application of response surface methodology, using tamarind (Tamarindus indica) and jatoba (Hymenaea courbaril) seeds as carbon sources. The crude extract was immobilized, with a focus on improving lichenase activity, using various ionic supports, including MANAE (monoamine-N-aminoethyl), DEAE (diethylaminoethyl)-cellulose, CM (carboxymethyl)-cellulose, and PEI (polyethyleneimine)-agarose. Regarding lichenase, the optimal conditions yielding the highest activity were determined as 1.5% tamarind seeds, cultivation at 50 °C under static conditions for 72 h. Moreover, transitioning from Erlenmeyer flasks to a bioreactor proved pivotal, resulting in a 2.21-fold increase in activity. Biochemical characterization revealed an optimum temperature of 50 °C and pH of 6.5. However, sustained stability at varying pH and temperature levels was challenging, underscoring the necessity of immobilizing lichenase on ionic supports. Notably, CM-cellulose emerged as the most effective immobilization medium, exhibiting an activity of 1.01 U/g of the derivative (enzyme plus support), marking a substantial enhancement. This study marks the first lichenase immobilization on these chemical supports in existing literature.

Novel, cold-adapted D-laminaribiose- and D-glucose-releasing GH16 endo-β-1,3-glucanase from Hymenobacter siberiensis PAMC 29290, a psychrotolerant bacterium from Arctic marine sediment

Endo-β-1,3-glucanase is a glycoside hydrolase (GH) that plays an essential role in the mineralization of β-glucan polysaccharides. In this study, the novel gene encoding an extracellular, non-modular GH16 endo-β-1,3-glucanase (GluH) from Hymenobacter siberiensis PAMC 29290 isolated from Arctic marine sediment was discovered through an in silico analysis of its whole genome sequence and subsequently overexpressed in Escherichia coli BL21. The 870-bp GluH gene encoded a protein featuring a single catalytic GH16 domain that shared over 61% sequence identity with uncharacterized endo-β-1,3-glucanases from diverse Hymenobacter species, as recorded in the National Center for Biotechnology Information database. The purified recombinant endo-β-1,3-glucanase (rGluH: 31.0 kDa) demonstrated peak activity on laminarin at pH 5.5 and 40°C, maintaining over 40% of its maximum endo-β-1,3-glucanase activity even at 25°C. rGluH preferentially hydrolyzed D-laminarioligosaccharides and β-1,3-linked polysaccharides, but did not degrade D-laminaribiose or structurally unrelated substrates, confirming its specificity as a true endo-β-1,3-glucanase without ancillary GH activities. The biodegradability of various substrate polymers by the enzyme was evaluated in the following sequence: laminarin > barley β-glucan > carboxymethyl-curdlan > curdlan > pachyman. Notably, the specific activity (253.1 U mg-1) and catalytic efficiency (k cat /K m : 105.72 mg-1 s-1 mL) of rGluH for laminarin closely matched its specific activity (250.2 U mg-1) and k cat /K m value (104.88 mg-1 s-1 mL) toward barley β-glucan. However, the k cat /K m value (9.86 mg-1 s-1 mL) of rGluH for insoluble curdlan was only about 9.3% of the value for laminarin, which correlates well with the observation that rGluH displayed weak binding affinity (< 40%) to the insoluble polymer. The biocatalytic hydrolysis of D-laminarioligosaccharides with a degree of polymerization between 3 and 6 and laminarin generally resulted in the formation of D-laminaribiose as the predominant product and D-glucose as the secondary product, with a ratio of approximately 4:1. These findings suggest that highly active rGluH is an acidic, cold-adapted D-laminaribiose- and D-glucose-releasing GH16 endo-β-1,3-glucanase, which can be exploited as a valuable biocatalyst for facilitating low temperature preservation of foods.

Saccharide mapping as an extraordinary method on characterization and identification of plant and fungi polysaccharides: A review

Saccharide mapping was a promising scheme to unveil the mystery of polysaccharide structure by analysis of the fragments generated from polysaccharide decomposition process. However, saccharide mapping was not widely applied in the polysaccharide analysis for lacking of systematic introduction. In this review, a detailed description of the establishment process of saccharide mapping, the pros and cons of downstream technologies, an overview of the application of saccharide mapping, and practical strategies were summarized. With the updating of the available downstream technologies, saccharide mapping had been expanding its scope of application to various kinds of polysaccharides. The process of saccharide mapping analysis included polysaccharides degradation and hydrolysates analysis, and the degradation process was no longer limited to acid hydrolysis. Some downstream technologies were convenient for rapid qualitative analysis, while others could achieve quantitative analysis. For the more detailed structure information could be provided by saccharide mapping, it was possible to improve the quality control of polysaccharides during preparation and application. This review filled the blank of basic information about saccharide mapping and was helpful for the establishment of a professional workflow for the saccharide mapping application to promote the deep study of polysaccharide structure.

Characterization of a novel cold-adapted GH1 β-glucosidase from Psychrobacillus glaciei and its application in the hydrolysis of soybean isoflavone glycosides

The novel β-glucosidase gene (pgbgl1) of glycoside hydrolase (GH) family 1 from the psychrotrophic bacterium Psychrobacillus glaciei sp. PB01 was successfully expressed in Escherichia coli BL21 (DE3). The deduced PgBgl1 contained 447 amino acid residues with a calculated molecular mass of 51.4 kDa. PgBgl1 showed its maximum activity at pH 7.0 and 40 °C, and still retained over 10% activity at 0 °C, suggesting that the recombinant PgBgl1 is a cold-adapted enzyme. The substrate specificity, Km, Vmax, and Kcat/Km for the p-Nitrophenyl-β-D-glucopyranoside (pNPG) as the substrate were 1063.89 U/mg, 0.36 mM, 1208.31 U/mg and 3871.92/s, respectively. Furthermore, PgBgl1 demonstrated remarkable stimulation of monosaccharides such as glucose, xylose, and galactose, as well as NaCl. PgBgl1 also demonstrated a high capacity to convert the primary soybean isoflavone glycosides (daidzin, genistin, and glycitin) into their respective aglycones. Overall, PgBgl1 exhibited high catalytic activity towards aryl glycosides, suggesting promising application prospects in the food, animal feed, and pharmaceutical industries.

A rumen-derived bifunctional glucanase/mannanase uncanonically releases oligosaccharides with a high degree of polymerization preferentially from branched substrates

Glycoside hydrolases (GHs) are known to depolymerize polysaccharides into oligo-/mono-saccharides, they are extensively used as additives for both animals feed and our food. Here we reported the characterization of IDSGH5-14(CD), a weakly-acidic mesophilic bifunctional mannanase/glucanase of GH5, originally isolated from sheep rumen microbes. Biochemical characterization studies revealed that IDSGH5-14(CD) exhibited preferential hydrolysis of mannan-like and glucan-like substrates. Interestingly, the enzyme exhibited significantly robust catalytic activity towards branched-substrates compared to linear polysaccharides (P < 0.05). Substrate hydrolysis pattern indicated that IDSGH5-14(CD) predominantly liberated oligosaccharides with a degree of polymerization (DP) of 3-7 as the end products, dramatically distinct from canonical endo-acting enzymes. Comparative modeling revealed that IDSGH5-14(CD) was mainly comprised of a (β/α)8-barrel-like structure with a spacious catalytic cleft on surface, facilitating the enzyme to target high-DP or branched oligosaccharides. Molecular dynamics (MD) simulations further suggested that the branched-ligand, 64-α-D-galactosyl-mannohexose, was steadily accommodated within the catalytic pocket via a two-sided clamp formed by the aromatic residues. This study first reports a bifunctional GH5 enzyme that predominantly generates high-DP oligosaccharides, preferentially from branched-substrates. This provides novel insights into the catalytic mechanism and molecular underpinnings of polysaccharide depolymerization, with potential implications for feed additive development and high-DP oligosaccharides preparation.

Structure, in vitro digestive characteristics and effect on gut microbiota of sea cucumber polysaccharide fermented by Bacillus subtilis Natto

This study aimed to understand the structural, digestion and fecal fermentation behaviors of sea cucumber polysaccharide fermented by Bacillus subtilis Natto. Results showed that both sea cucumber polysaccharide (SP) and fermented sea cucumber polysaccharide (FSP) were sulfated polysaccharides mainly containing fucose. The physicochemical property, molecular weight, thermal property, and functional groups were no significant difference between SP and FSP, but the microscopic morphology and monosaccharide composition of FSP changed. Both SP and FSP showed similar digestion and fecal fermentation characteristics, that is, they could not be digested by saliva and gastric juice, but could be partially degraded by small intestine. Due to the decomposition of glycosidic bonds after intestinal digestion and fecal fermentation, the relative molecular mass of SP and FSP decreased. In terms of impacts on gut microbiota, Lachnospira, Bacteroides finegoldii, and Bifidobacteriaceae were significantly increased in SP, while Acinetobacter was significantly increased in FSP. This study provides a good understanding of the changes in the structure and digestive characteristics of sea cucumber polysaccharides caused by fermentation. That information will be beneficial for the development and application of new fermented sea cucumber products.