Characterization of a thermostable endo-1,3(4)-β-glucanase from Caldicellulosiruptor sp. strain F32 and its application for yeast lysis

Truncation of a novel C-terminal domain of a β-glucanase improves its thermal stability and specific activity

Enzymes that degrade β-glucan play important roles in various industries, including those related to brewing, animal feed, and health care. Csph16A, an endo-β-1,3(4)-glucanase encoded by a gene from the halotolerant, xerotolerant, and radiotrophic black fungus Cladosporium sphaerospermum, was cloned and expressed in Pichia pastoris. Two isoforms (Csph16A.1 and Csph16A.2) are produced, arising from differential glycosylation. The proteins were predicted to contain a catalytic Lam16A domain, along with a C-terminal domain (CTD) of unknown function which exhibits minimal secondary structure. Employing PCR-mediated gene truncation, the CTD of Csph16A was excised to assess its functional impact on the enzyme and determine potential alterations in biotechnologically relevant characteristics. The truncated mutant, Csph16A-ΔC, exhibited significantly enhanced thermal stability at 50°C, with D-values 14.8 and 23.5 times greater than those of Csph16A.1 and Csph16A.2, respectively. Moreover, Csph16A-ΔC demonstrated a 20%-25% increase in halotolerance at 1.25 and 1.5 M NaCl, respectively, compared to the full-length enzymes. Notably, specific activity against cereal β-glucan, lichenan, and curdlan was increased by up to 238%. This study represents the first characterization of a glucanase from the stress-tolerant fungus C. sphaerospermum and the first report of a halotolerant and engineered endo-β-1,3(4)-glucanase. Additionally, it sheds light on a group of endo-β-1,3(4)-glucanases from Antarctic rock-inhabiting black fungi harboring a Lam16A catalytic domain and a novel CTD of unknown function.

Biochemical characterization of Fsa16295Glu from "Fervidibacter sacchari," the first hyperthermophilic GH50 with β-1,3-endoglucanase activity and founding member of the subfamily GH50_3

The aerobic hyperthermophile "Fervidibacter sacchari" catabolizes diverse polysaccharides and is the only cultivated member of the class "Fervidibacteria" within the phylum Armatimonadota. It encodes 117 putative glycoside hydrolases (GHs), including two from GH family 50 (GH50). In this study, we expressed, purified, and functionally characterized one of these GH50 enzymes, Fsa16295Glu. We show that Fsa16295Glu is a β-1,3-endoglucanase with optimal activity on carboxymethyl curdlan (CM-curdlan) and only weak agarase activity, despite most GH50 enzymes being described as β-agarases. The purified enzyme has a wide temperature range of 4-95°C (optimal 80°C), making it the first characterized hyperthermophilic representative of GH50. The enzyme is also active at a broad pH range of at least 5.5-11 (optimal 6.5-10). Fsa16295Glu possesses a relatively high kcat/KM of 1.82 × 107 s-1 M-1 with CM-curdlan and degrades CM-curdlan nearly completely to sugar monomers, indicating preferential hydrolysis of glucans containing β-1,3 linkages. Finally, a phylogenetic analysis of Fsa16295Glu and all other GH50 enzymes revealed that Fsa16295Glu is distant from other characterized enzymes but phylogenetically related to enzymes from thermophilic archaea that were likely acquired horizontally from "Fervidibacteria." Given its functional and phylogenetic novelty, we propose that Fsa16295Glu represents a new enzyme subfamily, GH50_3.

Distinct roles of carbohydrate-binding modules in multidomain β-1,3-1,4-glucanase on polysaccharide degradation

Lam16A is a novel GH16 β-1,3-1,4-lichenase isolated from the genus Caldicellulosiruptor which can utilize untreated carbohydrate components of plant cell walls. Its catalytic module has been characterized that the six carbohydrate-binding modules (CBMs) were queued in the C-terminus, but their roles were still unclear. Here, full-length and CBM-truncated mutants of Lam16A were purified and characterized through heterologous expression in Escherichia coli. The profiles of these proteins, including the enzyme activity, degrading efficiency, substrate-binding affinity, and thermostability, were explored. Full-length Lam16A with six CBMs showed excellent thermostability and the highest activity against barley β-glucan and laminarin with optimum pH of 6.5. The CBMs stimulated degrading ability of the catalytic module, especially against β-1,3(4)-glucan-based polysaccharides. The released products from β-1,3-1,4-glucan by Lam16A or its truncated mutants revealed an endo-type glycoside hydrolase. Lam16As exhibited strong binding affinities to the insoluble polysaccharides, especially Lam16A-1CBM. The degradation of yeast cell walls by Lam16A enzyme solution relative to the control reduced the absorbance values at OD₈₀₀ by ~ 85% ± 1.2, enabling the release of up to ~ 0.057 ± 0.0039 µg/mL of the cytoplasmic protein into the supernatant, lowering the viability of the cells by ~ 70.3% ± 6.9, thus causing significant damage in the cell wall structure. Taken together, CBMs could influence the substrate specificity, thermal stability, and binding affinity of β-1,3-1,4-glucanase. These results demonstrate the great potential of these enzymes to promote the bioavailability of β-1,3-glucan oligosaccharides for health benefits. KEY POINTS: • Carbohydrate-binding modules strongly influenced the enzyme activity and binding affinity, and further impacted glycoside hydrolase activity. • Lam16A enzymes have sufficient ability to hydrolyze β-1,3-1,4-glucan-based polysaccharides. • Lam16As provide a powerful tool to promote the bioavailability of β-1,3-glucan oligosaccharides.

Coordinated β-glucosidase activity with the cellulosome is effective for enhanced lignocellulose saccharification

Consolidated bio-saccharification (CBS) technology employs cellulosome-producing bacterial cells, rather than fungal cellulases, as biocatalysts for cost-effective production of lignocellulosic sugars. Extracellular β-glucosidase (BGL) expression in the whole-cell arsenal is indispensable, due to severe cellobiose inhibition of the cellulosome. However, high-level BGL expression in Clostridium thermocellum is challenging, and the optimal BGL production level for efficient cellulose saccharification is currently unknown. Herein, we obtained new CBS biocatalysts by transforming BGL-expressing plasmids into C. thermocellum, which produced abundant BGL proteins and hydrolyzed cellulose effectively. The optimal ratio of extracellular BGL-to-cellulosome activity was determined to be in a range of 5.5 to 21.6. Despite the critical impact of BGL, both excessive BGL expression and its assembly on the cellulosome via type I cohesin-dockerin interaction led to reduced cellulosomal activity, which further confirmed the importance of coordinated BGL expression with the cellulosome. This study will further promote industrial CBS application in lignocellulose conversion.

An Aspergillus nidulans endo-β-1,3-glucanase exhibited specific catalytic features and was used to prepare 3-O-β-cellobiosyl-d-glucose and 3-O-β-gentiobiosyl-d-glucose with high antioxidant activity from barley β-glucan and laminarin, respectively

An endo-β-1,3(4)-glucanase AnENG16A from Aspergillus nidulans shows distinctive catalytic features for hydrolysis of β-glucans. AnENG16A hydrolyzed Eisenia bicyclis laminarin to mainly generate 3-O-β-gentiobiosyl-d-glucose and hydrolyzed barley β-glucan to mainly produce 3-O-β-cellobiosyl-d-glucose. Using molecular exclusion chromatography, we isolated and purified 3-O-β-cellobiosyl-d-glucose and 3-O-β-gentiobiosyl-d-glucose, respectively, from AnENG16A-hydrolysate of barley β-glucan and E. bicyclis laminarin. Further study reveals that 3-O-β-cellobiosyl-d-glucose had 8.99-fold higher antioxidant activity than barley β-glucan and 3-O-β-gentiobiosyl-d-glucose exhibited 43.0% higher antioxidant activity than E. bicyclis laminarin. Notably, 3-O-β-cellobiosyl-d-glucose and 3-O-β-gentiobiosyl-d-glucose exhibited 148.9% and 116.0% higher antioxidant activity than laminaritriose, respectively, indicating that β-1,4-linkage or -1,6-linkage at non-reducing end of β-glucotrioses had enhancing effect on antioxidant activity compared to β-1,3-linkage. Furthermore, 3-O-β-cellobiosyl-d-glucose showed 237.9% higher antioxidant activity than cellotriose, and laminarin showed 5.06-fold higher antioxidant activity than barley β-glucan, indicating that β-1,4-linkage at reducing end of β-glucans or oligosaccharides resulted in decrease of antioxidant activity compared to β-1,3-linkage.

Screening and characterisation of β-glucosidase production strains from Rosa roxburghii Tratt

The β-glucosidase properties from one yeast isolate identified as Wickerhamomyces anomalus C4 were characterised. The β-glucosidase activity of W. anomalus C4 was 41.83 ± 0.25 mU/mL, and the optimum temperature and pH were 40 °C and 5.0, respectively. The glucose, 10% v/v of ethanol and 10 mmol/L of Cu2+ inhibited the β-glycosidases activities. The isolate W. anomalus C4 had a stronger alcohol metabolism capacity than commercial Saccharomyces cerevisiae X16. Besides, fermentation with W. anomalus C4 alone and co-fermentations with S. cerevisiae X16 and W. anomalus C4 reduced the volatile acids content and the sourness value compared to S. cerevisiae X16 control. Moreover, inoculation with W. anomalus C4 could enhance volatile aroma richness and complexity of Rosa roxburghii wines, regardless of type or amount thereof. Therefore, the R. roxburghii native yeast isolate W. anomalus C4 may have some application potentials for R. roxburghii wine-making.

A Novel Digestive GH16 β-1,3(4)-Glucanase from the Fungus-Growing Termite Macrotermes barneyi

β-1,3-glucanases are the main digestive enzymes of plant and fungal cell wall. Transcriptomic analysis of the fungus-growing termite Macrotermes barneyi revealed a high expression of a predicted β-1,3(4)-glucanase (Mbbgl) transcript in termite gut. Here, we described the cDNA cloning, heterologous expression, and enzyme characterization of Mbbgl. Sequence analysis and RT-PCR results showed that Mbbgl is a termite-origin GH16 β-1,3(4)-glucanase. The recombinant enzyme showed the highest activity towards laminarin and was active optimally at 50 °C, pH 5.5. The enzyme displayed endo/exo β-1,3(4)-glucanase activities. Moreover, Mbbgl had weak transglycosylation activity. The results indicate that Mbbgl is an endogenous digestive β-1,3(4)-glucanase, which contributes to the decomposition of plant biomass and fungal hyphae. Additionally, the multiple activities, pH, and ion stabilities make Mbbgl a potential candidate for application in the food industry.

Comparative Analysis and Biochemical Characterization of Two Endo-β-1,3-Glucanases from the Thermophilic Bacterium Fervidobacterium sp

Laminarinases exhibit potential in a wide range of industrial applications including the production of biofuels and pharmaceuticals. In this study, we present the genetic and biochemical characteristics of FLamA and FLamB, two laminarinases derived from a metagenomic sample from a hot spring in the Azores. Sequence comparison revealed that both genes had high similarities to genes from Fervidobacterium nodosum Rt17-B1. The two proteins showed sequence similarities of 62% to each other and belong to the glycoside hydrolase (GH) family 16. For biochemical characterization, both laminarinases were heterologously produced in Escherichia coli and purified to homogeneity. FLamA and FLamB exhibited similar properties and both showed highest activity towards laminarin at 90 °C and pH 6.5. The two enzymes were thermostable but differed in their half-life at 80 °C with 5 h and 1 h for FLamA and FLamB, respectively. In contrast to other laminarinases, both enzymes prefer β-1,3-glucans and mixed-linked glucans as substrates. However, FLamA and FLamB differ in their catalytic efficiency towards laminarin. Structure predictions were made and showed minor differences particularly in a kink adjacent to the active site cleft. The high specific activities and resistance to elevated temperatures and various additives make both enzymes suitable candidates for application in biomass conversion.

Catalytic Mechanism of a Novel Glycoside Hydrolase Family 16 "Elongating" β-Transglycosylase

Carbohydrates are complex macromolecules in biological metabolism. Enzymatic synthesis of carbohydrates is recognized as a powerful tool to overcome the problems associated with large scale synthesis of carbohydrates. Novel enzymes with significant transglycosylation ability are still in great demand in glycobiology studies. Here we report a novel glycoside hydrolase family 16 "elongating" β-transglycosylase from Paecilomyces thermophila (PtBgt16A), which efficiently catalyzes the synthesis of higher polymeric oligosaccharides using β-1,3/1,4-oligosaccharides as donor/acceptor substrates. Further structural information reveals that PtBgt16A has a binding pocket around the -1 subsite. The catalytic mechanism of PtBgt16A is partly similar to an exo-glycoside hydrolase, which cleaves the substrate from the non-reducing end one by one. However, PtBgt16A releases the reducing end product and uses the remainder glucosyl as a transglycosylation donor. This catalytic mechanism has similarity with the catalytic mode of amylosucrase, which catalyzes the transglycosylation products gradually extend by one glucose unit. PtBgt16A thus has the potential to be a tool enzyme for the enzymatic synthesis of new β-oligosaccharides and glycoconjugates.