Characterization of two thermophilic cellulases from Talaromyces leycettanus JCM12802 and their synergistic action on cellulose hydrolysis

Barley fermentation on nutritional constituents: structural changes and structure-function correlations

Over the past few years, the demand for healthy grains has become increasingly important. Barley is a basic material for food and animal feed, which is considered an excellent source of multiple nutrients. However, due to limitations in processing techniques, the nutritional attributes of barley have not been completely realized. The functional profile of barley nutrients can be effectively improved by fermentation, due in large to the structural alteration of barley nutrients. The current review outlines the structural changes of barley nutrients during fermentation and summarizes the potential mechanisms by which structural alteration occurs. Correlations between the nutrient structures and their nutritional properties are also discussed. In general, fermentation leads to decreased particle size and modified internal structures of macromolecular nutrients. Enzyme action, pH alterations and interactions between nutrient matrices may contribute to these structural alterations. Barley nutrients with modified structure exhibit enhanced health promoting functions and digestive characteristics, which will further contribute to the utilization of barley resources in the food industry.

The functional role of N-link glycosylation in a novel cellobiohydrolase II (LsCel6A) from a white-rot fungus Lentinus sp. WR2

White-rot fungi produce a wide spectrum of lignocellulose-degradation enzymes, which can be used in bioenergy, bioremediation, and other industrial applications. This study identified a cellobiohydrolase II (Cel6A, GH6 cellobiohydrolase, EC 3.2.1.91) with high hydrolytic activity toward crystalline cellulose from a white-rot fungus Lentinus sp. WR2. Both native (nLsCel6A) and recombinant (rLsCel6A) enzymes expressed in Pichia pastoris were purified and characterized. Three N-glycosylation sites at Asn102, Asn145, and Asn392 containing high-mannose glycans, were confirmed by mass spectrometry. To elucidate the functional role of N-linked glycans, three deglycosylated mutants of rLsCel6A, i.e., N102A, N145A, and N392A, were created and characterized for their biochemical and kinetic properties. While no discernible changes in the secondary structure of the three mutants were determined by circular dichroism spectrometry, deterioration of thermostability was revealed in N392A but not in N102A and N145A. Structure modeling and molecular dynamics analyses revealed that the N-linked glycan on Asn392 may restrict the flexibility of the C-terminal loop in LsCel6A, affecting the protein integrity and appropriate dynamics for the enzymatic function. In summary, this study identified a novel LsCel6A enzyme with high catalytic activity against insoluble forms of cellulose and demonstrated the role of N-linked glycosylation in the thermostability of the enzyme.

Hydrolysis Mechanism of Multimodular Endoglucanases with Distinctive Domain Composition in the Saccharification of Cellulosic Substrates

Two multimodular endoglucanases in glycoside hydrolase family 5, ReCel5 and ElCel5, share 73% identity and exhibit similar modular structures: family 1 carbohydrate-binding module (CBM1); catalytic domain; CBMX2; module of unknown function. However, they differed in their biochemical properties and catalytic performance. ReCel5 showed optimal activity at pH 4.0 and 70 °C, maintaining stability at 70 °C (>80% activity). Conversely, ElCel5 is optimal at pH 3.0 and 50 °C (>50% activity at 50 °C). ElCel5 excels in degrading CMC-Na (256 U/mg vs 53 U/mg of ReCel5). Five domain-truncated (TM1-TM5) and four domain-replaced (RM1-RM4) mutants of ReCel5 with the counterparts of ElCel5 were constructed, and their enzymatic properties were compared with those of the wild type. Only RM1, with ElCel5-CBM1, displayed enhanced thermostability and activity. The hydrolysis of pretreated corn stover was reduced in most TM and RM mutants. Molecular dynamics simulations revealed interdomain interactions within the multimodular endoglucanase, potentially affecting its structural stability and complex biological catalytic processes.

Expression and characterization of a novel microbial GH9 glucanase, IDSGLUC9-4, isolated from sheep rumen

OBJECTIVE

This study aimed to identify and characterize a novel endo-β-glucanase, IDSGLUC9-4, from the rumen metatranscriptome of Hu sheep.

METHODS

A novel endo-β-glucanase, IDSGLUC9-4, was heterologously expressed in Escherichia coli and biochemically characterized. The optimal temperature and pH of recombinant IDSGLUC9-4 were determined. Subsequently, substrate specificity of the enzyme was assessed using mixed-linked glucans including barley β-glucan and Icelandic moss lichenan. Thin-layer chromatography (TLC), high-performance liquid chromatography (HPLC), matrix assisted laser desorption ionization time of flight mass spectrometry analyses were conducted to determine the products released from polysaccharides and cello-oligosaccharides substrates.

RESULTS

The recombinant IDSGLUC9-4 exhibited temperature and pH optima of 40°C and pH 6.0, respectively. It exclusively hydrolyzed mixed-linked glucans, with significant activity observed for barley β-glucan (109.59±3.61 μmol/mg min) and Icelandic moss lichenan (35.35±1.55 μmol/mg min). TLC and HPLC analyses revealed that IDSGLUC9-4 primarily released cellobiose, cellotriose, and cellotetraose from polysaccharide substrates. Furthermore, after 48 h of reaction, IDSGLUC9-4 removed most of the glucose, indicating transglycosylation activity alongside its endo-glucanase activity.

CONCLUSION

The recombinant IDSGLUC9-4 was a relatively acid-resistant, mesophilic endo-glucanase (EC 3.2.1.4) that hydrolyzed glucan-like substrates, generating predominantly G3 and G4 oligosaccharides, and which appeared to have glycosylation activity. These findings provided insights into the substrate specificity and product profiles of rumen-derived GH9 glucanases and contributed to the expanding knowledge of cellulolytic enzymes and novel herbivore rumen enzymes in general.

Cloning, expression and purification of cellobiohydrolase gene from Caldicellulosiruptor bescii for efficient saccharification of plant biomass

Anthropogenic activities have led to a drastic shift from natural fuels to alternative renewable energy reserves that demand heat-stable cellulases. Cellobiohydrolase is an indispensable member of cellulases that play a critical role in the degradation of cellulosic biomass. This article details the process of cloning the cellobiohydrolase gene from the thermophilic bacterium Caldicellulosiruptor bescii and expressing it in Escherichia coli (BL21) CondonPlus DE3-(RIPL) using the pET-21a(+) expression vector. Multi-alignments and structural modeling studies reveal that recombinant CbCBH contained a conserved cellulose binding domain III. The enzyme's catalytic site included Asp-372 and Glu-620, which are either involved in substrate or metal binding. The purified CbCBH, with a molecular weight of 91.8 kDa, displayed peak activity against pNPC (167.93 U/mg) at 65°C and pH 6.0. Moreover, it demonstrated remarkable stability across a broad temperature range (60-80°C) for 8 h. Additionally, the Plackett-Burman experimental model was employed to assess the saccharification of pretreated sugarcane bagasse with CbCBH, aiming to evaluate the cultivation conditions. The optimized parameters, including a pH of 6.0, a temperature of 55°C, a 24-hour incubation period, a substrate concentration of 1.5% (w/v), and enzyme activity of 120 U, resulted in an observed saccharification efficiency of 28.45%. This discovery indicates that the recombinant CbCBH holds promising potential for biofuel sector.

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.

Enhanced crystalline cellulose degradation by a novel metagenome-derived cellulase enzyme

Metagenomics has revolutionized access to genomic information of microorganisms inhabiting the gut of herbivorous animals, circumventing the need for their isolation and cultivation. Exploring these microorganisms for novel hydrolytic enzymes becomes unattainable without utilizing metagenome sequencing. In this study, we harnessed a suite of bioinformatic analyses to discover a novel cellulase-degrading enzyme from the camel rumen metagenome. Among the protein-coding sequences containing cellulase-encoding domains, we identified and subsequently cloned and purified a promising candidate cellulase enzyme, Celcm05-2, to a state of homogeneity. The enzyme belonged to GH5 subfamily 4 and exhibited robust enzymatic activity under acidic pH conditions. It maintained hydrolytic activity under various environmental conditions, including the presence of metal ions, non-ionic surfactant Triton X-100, organic solvents, and varying temperatures. With an optimal temperature of 40 °C, Celcm05-2 showcased remarkable efficiency when deployed on crystalline cellulose (> 3.6 IU/mL), specifically Avicel, thereby positioning it as an attractive candidate for a myriad of biotechnological applications spanning biofuel production, paper and pulp processing, and textile manufacturing. Efficient biodegradation of waste paper pulp residues and the evidence of biopolishing suggested that Celcm05-2 can be used in the bioprocessing of cellulosic craft fabrics in the textile industry. Our findings suggest that the camel rumen microbiome can be mined for novel cellulase enzymes that can find potential applications across diverse biotechnological processes.

Microbial β-glucanases: production, properties, and engineering

Lignocellulosic biomass, which mainly consists of cellulose and hemicellulose, is the most abundant renewable biopolymer on earth. β-Glucanases are glycoside hydrolases (GHs) that hydrolyze β-glucan, one of the dominant components of the plant cell wall, into cello-oligosaccharides and glucose. Among them, endo-β-1,4-glucanase (EC 3.2.1.4), exo-glucanase/cellobiohydrolase (EC 3.2.1.91), and β-glucosidase (EC 3.2.1.21) play critical roles in the digestion of glucan-like substrates. β-Glucanases have attracted considerable interest within the scientific community due to their applications in the feed, food, and textile industries. In the past decade, there has been considerable progress in the discovery, production, and characterization of novel β-glucanases. Advances in the development of next-generation sequencing techniques, including metagenomics and metatranscriptomics, have unveiled novel β-glucanases isolated from the gastrointestinal microbiota. The study of β-glucanases is beneficial for research and development of commercial products. In this study, we review the classification, properties, and engineering of β-glucanases.

Enhancement of catalytic activity and alkaline stability of cellobiohydrolase by structure-based protein engineering

Alkaline cellobiohydrolases have the potential for application in various industries, including pulp processing and laundry where operation under high pH conditions is preferred. In this study, variants of CtCel6A cellobiohydrolase from Chaetomium thermophilum were generated by structural-based protein engineering with the rationale of increasing catalytic activity and alkaline stability. The variants included removal of the carbohydrate-binding module (CBM) and substitution of residues 173 and 200. The CBM-deleted enzyme with Y200F mutation predicted to mediate conformational change at the N-terminal loop demonstrated increased alkaline stability at 60 °C, pH 8.0 for 24 h up to 2.25-fold compared with the wild-type enzyme. Another CBM-deleted enzyme with L173E mutation predicted to induce a new hydrogen bond in the substrate-binding cleft showed enhanced hydrolysis yield of pretreated sugarcane trash up to 4.65-fold greater than that of the wild-type enzyme at the pH 8.0. The variant enzymes could thus be developed for applications on cellulose hydrolysis and plant fiber modification operated under alkaline conditions.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03339-4.

Recombinant cellobiohydrolase of Myceliophthora thermophila: characterization and applicability in cellulose saccharification

A codon optimized cellobiohydrolase (CBH) encoding synthetic gene of 1188 bp from a thermophilic mold Myceliophthora thermophila (MtCel6A) was cloned and heterologously expressed in Escherichia coli for the first time. In silico analysis suggested that MtCel6A is a GH6 CBH and belongs to CBHII family, which is structurally similar to Cel6A of Humicola insolens. The recombinant MtCel6A is expressed as active inclusion bodies, and the molecular mass of the purified enzyme is ~ 45 kDa. The rMtCel6A is active in a wide range of pH (4-12) and temperatures (40-100 °C) with optima at pH 10.0 and 60 °C. It exhibits T1/2 of 6.0 and 1.0 h at 60 and 90 °C, respectively. The rMtCel6A is an extremozyme with organic solvent, salt and alkali tolerance. The Km, Vmax, kcat and kcat/Km values of the enzyme are 3.2 mg mL-1, 222.2 μmol mg-1 min-1, 2492 s-1 and 778.7 s-1 mg-1 mL-1, respectively. The product analysis of rMtCel6A confirmed that it is an exoenzyme that acts from the non-reducing end of cellulose. The addition of rMtCel6A to the commercial cellulase mix (Cellic CTec2) led to 1.9-fold increase in saccharification of the pre-treated sugarcane bagasse. The rMtCel6A is a potential CBH that finds utility in industrial processes such as in bioethanol, paper pulp and textile industries.

Improvement of thermostability and catalytic efficiency of glucoamylase from Talaromyces leycettanus JCM12802 via site-directed mutagenesis to enhance industrial saccharification applications

BACKGROUND

Glucoamylase is an important industrial enzyme in the saccharification of starch into glucose. However, its poor thermostability and low catalytic efficiency limit its industrial saccharification applications. Therefore, improving these properties of glucoamylase is of great significance for saccharification in the starch industry.

RESULTS

In this study, a novel glucoamylase-encoding gene TlGa15B from the thermophilic fungus Talaromyces leycettanus JCM12802 was cloned and expressed in Pichia pastoris. The optimal temperature and pH of recombinant TlGa15B were 65 ℃ and 4.5, respectively. TlGa15B exhibited excellent thermostability at 60 ℃. To further improve thermostability without losing catalytic efficiency, TlGa15B-GA1 and TlGa15B-GA2 were designed by introducing disulfide bonds and optimizing residual charge-charge interactions in a region distant from the catalytic center. Compared with TlGa15B, mutants showed improved optimal temperature, melting temperature, specific activity, and catalytic efficiency. The mechanism underlying these improvements was elucidated through molecular dynamics simulation and dynamics cross-correlation matrices analysis. Besides, the performance of TlGa15B-GA2 was the same as that of the commercial glucoamylase during saccharification.

CONCLUSIONS

We provide an effective strategy to simultaneously improve both thermostability and catalytic efficiency of glucoamylase. The excellent thermostability and high catalytic efficiency of TlGa15B-GA2 make it a good candidate for industrial saccharification applications.

A Thermophilic GH5 Endoglucanase from Aspergillus fumigatus and Its Synergistic Hydrolysis of Mannan-Containing Polysaccharides

In this study, we isolated and identified a thermophilic strain of Aspergillus fumigatus from the “Daqu” samples. Transcriptomic analysis of A. fumigatus identified 239 carbohydrate-active enzymes (CAZy)-encoding genes, including 167 glycoside hydrolase (GH)-encoding genes, 58 glycosyltransferase (GT)-encoding genes, 2 polysaccharide lyase (PLs)-encoding genes and 12 carbohydrate esterase (CEs)-encoding genes, which indicates that the strain has a strong potential for application for enzyme production. Furthermore, we also identified a novel endoglucanase gene (AfCel5A), which was expressed in Pichia pastoris and characterized. The novel endoglucanase AfCel5A exhibited the highest hydrolytic activity against CMC-Na and the optimal activity at 80 °C and pH 4.0 and also showed good stability at pH 3.0–11.0 and below 70 °C. The Km and Vmax values of AfCel5 were 0.16 ± 0.05 mg·mL−1 and 7.23 ± 0.33 mol mg−1·min−1, respectively, using CMC-Na as a substrate. Further, the endoglucanase exhibited a high tolerance toward NaCl as well as glucose. In addition, the finding that the endoglucanase AfCel5A in combination with β-mannanse (ManBK) clearly increased the release of total reducing sugars of glucomannan by up to 74% is significant.

Hemicellulases from Penicillium and Talaromyces for lignocellulosic biomass valorization: A review

The term hemicellulose groups different polysaccharides with heterogeneous structures, mannans, xyloglucans, mixed-linkage β-glucans and xylans, which differ in their backbone and branches, and in the type and distribution of glycosidic linkages. The enzymatic degradation of these complex polymers requires the concerted action of multiple hemicellulases and auxiliary enzymes. Most commercial enzymes are produced by Trichoderma and Aspergillus species, but recent studies have disclosed Penicillium and Talaromyces as promising sources of hemicellulases. In this review, we summarize the current knowledge on the hemicellulolytic system of these genera, and the role of hemicellulases in the disruption and synthesis of glycosidic bonds. In both cases, the enzymes from Penicillium and Talaromyces represent an interesting alternative for valorization of lignocellulosic biomass in the current framework of circular economy.

A Novel Dimeric Exoglucanase (GH5_38): Biochemical and Structural Characterisation towards its Application in Alkyl Cellobioside Synthesis

An exoglucanase (Exg-D) from the glycoside hydrolase family 5 subfamily 38 (GH5_38) was heterologously expressed and structurally and biochemically characterised at a molecular level for its application in alkyl glycoside synthesis. The purified Exg-D existed in both dimeric and monomeric forms in solution, which showed highest activity on mixed-linked β-glucan (88.0 and 86.7 U/mg protein, respectively) and lichenin (24.5 and 23.7 U/mg protein, respectively). They displayed a broad optimum pH range from 5.5 to 7 and a temperature optimum from 40 to 60 °C. Kinetic studies demonstrated that Exg-D had a higher affinity towards β-glucan, with a Km of 7.9 mg/mL and a kcat of 117.2 s-1, compared to lichenin which had a Km of 21.5 mg/mL and a kcat of 70.0 s-1. The circular dichroism profile of Exg-D showed that its secondary structure consisted of 11% α-helices, 36% β-strands and 53% coils. Exg-D performed transglycosylation using p-nitrophenyl cellobioside as a glycosyl donor and several primary alcohols as acceptors to produce methyl-, ethyl- and propyl-cellobiosides. These products were identified and quantified via thin-layer chromatography (TLC) and liquid chromatography-mass spectrometry (LC-MS). We concluded that Exg-D is a novel and promising oligomeric glycoside hydrolase for the one-step synthesis of alkyl glycosides with more than one monosaccharide unit.