Microbial β-glucanases: production, properties, and engineering

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.