Molecular characterization of a highly-active thermophilic β-glucosidase from Neosartorya fischeri P1 and its application in the hydrolysis of soybean isoflavone glycosides

Exploring the diversity of β-glucosidase: Classification, catalytic mechanism, molecular characteristics, kinetic models, and applications

High-value chemicals and energy-related products can be produced from biomass. Biorefinery technology offers a sustainable and cost-effective method for this high-value conversion. β-glucosidase is one of the key enzymes in biorefinery processes, catalyzing the production of glucose from aryl-glycosides and cello-oligosaccharides via the hydrolysis of β-glycosidic bonds. Although β-glucosidase plays a critical catalytic role in the utilization of cellulosic biomass, its efficacy is often limited by substrate or product inhibitions, low thermostability, and/or insufficient catalytic activity. To provide a detailed overview of β-glucosidases and their benefits in certain desired applications, we collected and summarized extensive information from literature and public databases, covering β-glucosidases in different glycosidase hydrolase families and biological kingdoms. These β-glucosidases show differences in amino acid sequence, which are translated into varying degrees of the molecular properties critical in enzymatic applications. This review describes studies on the diversity of β-glucosidases related to the classification, catalytic mechanisms, key molecular characteristics, kinetics models, and applications, and highlights several β-glucosidases displaying high stability, activity, and resistance to glucose inhibition suitable for desired biotechnological applications.

Compound probiotics producing cellulase could replace cellulase preparations during solid-state fermentation of millet bran

Low-value agricultural by-products can be converted into high-value biological products by fermentation with probiotic strains or by enzymatic hydrolysis. However, the high costs of enzyme preparations significantly limit their applications in fermentation. In this study, the solid-state fermentation of millet bran was performed using a cellulase preparation and compound probiotics producing cellulase (CPPC), respectively. The results showed that both factors effectively destroyed the fiber structure, reduced the crude fiber content by 23.78% and 28.32%, respectively, and significantly increased the contents of beneficial metabolites and microorganisms. Moreover, CPPC could more effectively reduce the anti-nutrient factors and increase the content of anti-inflammatory metabolites. The correlation analysis revealed that Lactiplantibacillus and Issatchenkia had synergistic growth during fermentation. Overall, these results suggested that CPPC could replace cellulase preparation and improve antioxidant properties while reducing anti-nutrient factors of millet bran, thus providing a theoretical reference for the efficient utilization of agricultural by-products.

A review on applications of β-glucosidase in food, brewery, pharmaceutical and cosmetic industries

β-glucosidases hydrolyse glycosidic bonds to release non-reducing terminal glucosyl residues from glycosides and oligosaccharides via catalytic mechanisms. It is very well known that the β-glucosidase enzyme is used in biorefineries for cellulose degradation, where β-glucosidases is the rate-limiting enzyme for the final glucose production from cellobiose. The β-glucosidase enzyme is used as a catalyst in other industrial sectors, including pharmaceuticals, breweries, dairy, and food processing. With the aid of β-glucosidase enzymes, cyanogenic glycosides and plant glycosides are transformed into sugar moiety and aglycones. These aglycone compounds are employed as aromatic compounds in the food processing and brewing industries. They are also used as medications and dietary supplements based on their pharmacological qualities. Applications of aglycones and the microbiological sources of β-glucosidase in aglycone production have been discussed in this review.

Soil-Borne Neosartorya spp.: A Heat-Resistant Fungal Threat to Horticulture and Food Production-An Important Component of the Root-Associated Microbial Community

Soil-borne Neosartorya spp. are the highly resilient sexual reproductive stage (teleomorph) of Aspergillus spp. Fungi of this genus are relevant components of root-associated microbial community, but they can also excrete mycotoxins and exhibit great resistance to high temperatures. Their ascospores easily transfer between soil and crops; thus, Neosartorya poses a danger to horticulture and food production, especially to the postharvest quality of fruits and vegetables. The spores are known to cause spoilage, mainly in raw fruit produce, juices, and pulps, despite undergoing pasteurization. However, these fungi can also participate in carbon transformation and sequestration, as well as plant protection in drought conditions. Many species have been identified and included in the genus, and yet some of them create taxonomical controversy due to their high similarity. This also contributes to Neosartorya spp. being easily mistaken for its anamorph, resulting in uncertain data within many studies. The review discusses also the factors shaping Neosartorya spp.'s resistance to temperature, preservatives, chemicals, and natural plant extracts, as well as presenting novel solutions to problems created by its resilient nature.

Production of Daidzein and Genistein from Seed and Root Extracts of Korean Wild Soybean (Glycine soja) by Thermostable β-Galactosidase from Thermoproteus uzoniensis

Isoflavone glycosides are commonly biotransformed into isoflavone aglycones due to the superior biological activities of the latter. Wild soybeans contain a higher isoflavone content than domesticated soybeans due to their high level of genetic diversity. In this study, we cloned and characterized a thermostable β-galactosidase from the extreme thermophile Thermoproteus uzoniensis for potential application in isoflavone conversion in Korean wild soybeans. The purified recombinant enzyme exhibited a maximum specific activity of 1103 μmol/min/mg at pH 5.0 and 90 °C with a half-life of 46 h and exists as a homodimer of 113 kDa. The enzyme exhibited the highest activity for p-nitrophenyl (pNP)-β-D-galactopyranoside among aryl glycosides and it hydrolyzed isoflavone glycosides in the order genistin > daidzin > ononin > glycitin. The enzyme completely hydrolyzed 2.77 mM daidzin and 3.85 mM genistin in the seed extract of wild soybean after 80 and 70 min with productivities of 1.86 and 3.30 mM/h, respectively, and 9.89 mM daidzin and 1.67 mM genistin in the root extract after 180 and 30 min, with the highest productivities of 3.30 and 3.36 mM/h, respectively, compared to other glycosidases. Our results will contribute to the industrial production of isoflavone aglycone using wild soybean and this is the first report on the enzymatic production of isoflavone aglycones from isoflavone glycosides in wild soybeans.

Characterization of a novel isoflavone glycoside-hydrolyzing β-glucosidase from mangrove soil metagenomic library

For the beneficial pharmacological properties of isoflavonoids and their related glycoconjugates, there is increasingly interest in their enzymatic conversion. In this study, a novel β-glucosidase gene isolated from metagenomic library of mangrove sediment was cloned and overexpressed in Escherichia coli BL21(DE3). The purified recombination β-glucosidase, designated as r-Bgl66, showed high catalytic activity for soy isoflavone glycosides. It converted soy isoflavone flour extract with the productivities of 0.87 mM/h for daidzein, 0.59 mM/h for genistein and 0.42 mM/h for glycitein. The kcat/Km values for daidzin, genistin and glycitin were 208.73, 222.37 and 288.07 mM-1 s-1, respectively. In addition, r-Bgl66 also exhibited the characteristic of glucose-tolerance, and the inhibition constant Ki was 471.4 mM. These properties make it a good candidate in the enzymatic hydrolysis of soy isoflavone glycosides. This study also highlights the utility of metagenomic approach in discovering novel β-glucosidase for soy isoflavone glycosides hydrolysis.

Unconventional β-Glucosidases: A Promising Biocatalyst for Industrial Biotechnology

β-Glucosidases primarily catalyze removal of terminal glucosyl residues from a variety of glucoconjugates and also perform transglycosylation and reverse hydrolysis. These catalytic properties can be readily exploited for degradation of lignocellulosic biomass as well as for pharmaceutical, food and flavor industries. β-Glucosidases have been either isolated in the native form from the producer organism or recombinantly expressed and gaged for their biochemical properties and substrate specificities. Although almond and Aspergillus niger have been instantly recognizable sources of β-glucosidases utilized for various applications, an intricate pool of novel β-glucosidases from different sources can provide their potent replacements. Moreover, one can envisage the better efficacy of these novel candidates in biofuel and biorefinery industries facilitating efficient degradation of biomass. This article reviews properties of the novel β-glucosidases such as glucose tolerance and activation, substrate specificity, and thermostability which can be useful for their applications in lignocellulose degradation, food industry, and pharmaceutical industry in comparison with the β-glucosidases from the conventional sources. Such β-glucosidases have potential for encouraging white biotechnology.

Structural aspects of β-glucosidase of Myceliophthora thermophila (MtBgl3c) by homology modelling and molecular docking

Cellulases are the enzymes with diverse range of industrial applications. Cellulases degrade cellulose into monomeric glucose units by hydrolysing β-1,4-glycosidic bonds. There are three components of cellulases: a) endoglucanase, b) exoglucanase and c) β-glucosidase which act synergistically in cellulose bioconversion. The cellulases are the third largest industrial enzymes with a great potential in bioethanol production. In this investigation, a β-glucosidase of a thermophilic fungus Myceliophthora thermophila (MtBgl3c) was analysed for its structural characterization using in silico approaches. The protein structure of MtBgl3c is unknown, therefore an attempt has been made to model 3D structure using Modeller 9.23 software. The MtBgl3c protein model generated was validated from Verify 3D and ERRAT scores of 89.37% and 71.25%, respectively derived from SAVES. Using RAMPAGE the Ramachandran plot was generated, which predicted the accuracy of the 3D model with 91.5% amino acid residues in the favored region. The ion binding and N-glycosylation sites were also predicted. The generated model was docked with cellobiose to predict the most favorable binding sites of MtBgl3c. The key amino acid residues involved in cellobiose bonding are Val88, Asp106, Asp287, Tyr255, Arg170, Glu514. The catalytic conserved amino residues of MtBgl3c were identified. The dock score of cellobiose with MtBgl3c is much lower (-6.46 kcal/mol) than that of glucose (-5.61 kcal/mol), suggesting its high affinity for cellobiose. The docking data of MtBgl3c with glucose illustrate its tolerance to glucose. The present study provides insight into structural characteristics of the MtBgl3c which can be further validated by experimental data. Highlights3D structure of β-glucosidase (MtBgl3c) of Myceliophthora thermophila is being proposed based on computational analysesThe amino acid residues Asp106, Asp287, Tyr255, Arg170 and Glu514 have been identified to play catalytically important role in substrate bindingDocking and interaction of MtBgl3c with cellobiose and glucose has been confirmedDocking analysis of MtBgl3c with glucose suggested its glucose toleranceThe data would be useful in engineering enzymes for attaining higher catalytic efficiencyCommunicated by Ramaswamy H. Sarma.

A glucotolerant β-glucosidase from the fungus Talaromyces amestolkiae and its conversion into a glycosynthase for glycosylation of phenolic compounds

Background

The interest for finding novel β-glucosidases that can improve the yields to produce second-generation (2G) biofuels is still very high. One of the most desired features for these enzymes is glucose tolerance, which enables their optimal activity under high-glucose concentrations. Besides, there is an additional focus of attention on finding novel enzymatic alternatives for glycoside synthesis, for which a mutated version of glycosidases, named glycosynthases, has gained much interest in recent years.

Results

In this work, a glucotolerant β-glucosidase (BGL-1) from the ascomycete fungus Talaromyces amestolkiae has been heterologously expressed in Pichia pastoris, purified, and characterized. The enzyme showed good efficiency on p-nitrophenyl glucopyranoside (pNPG) (K_m= 3.36 ± 0.7 mM, k_cat= 898.31 s⁻¹), but its activity on cellooligosaccharides, the natural substrates of these enzymes, was much lower, which could limit its exploitation in lignocellulose degradation applications. Interestingly, when examining the substrate specificity of BGL-1, it showed to be more active on sophorose, the β-1,2 disaccharide of glucose, than on cellobiose. Besides, the transglycosylation profile of BGL-1 was examined, and, for expanding its synthetic capacities, it was converted into a glycosynthase. The mutant enzyme, named BGL-1-E521G, was able to use α-d-glucosyl-fluoride as donor in glycosylation reactions, and synthesized glucosylated derivatives of different pNP-sugars in a regioselective manner, as well as of some phenolic compounds of industrial interest, such as epigallocatechin gallate (EGCG).

Conclusions

In this work, we report the characterization of a novel glucotolerant 1,2-β-glucosidase, which also has a considerable activity on 1,4-β-glucosyl bonds, that has been cloned in P. pastoris, produced, purified and characterized. In addition, the enzyme was converted into an efficient glycosynthase, able to transfer glucose molecules to a diversity of acceptors for obtaining compounds of interest. The remarkable capacities of BGL-1 and its glycosynthase mutant, both in hydrolysis and synthesis, suggest that it could be an interesting tool for biotechnological applications.

A Novel Thermostable GH3 β-Glucosidase from Talaromyce leycettanus with Broad Substrate Specificity and Significant Soybean Isoflavone Glycosides-Hydrolyzing Capability

A novel β-glucosidase gene (Bgl3B) of glycoside hydrolase (GH) family 3 was cloned from the thermophilic fungus Talaromyce leycettanus JM12802 and successfully expressed in Pichia pastoris. The deduced Bgl3B contains 860 amino acid residues with a calculated molecular mass of 91.2 kDa. The purified recombinant Bgl3B exhibited maximum activities at pH 4.5 and 65°C and remained stable at temperatures up to 60°C and pH 3.0-9.0, respectively. The enzyme exhibited broad substrate specificities, showing β-glucosidase, glucanase, cellobiase, xylanase, and isoflavone glycoside hydrolase activities, and its activities were stimulated by short-chain alcohols. The catalytic efficiencies of Bgl3B were 693 and 104/mM/s towards pNPG and cellobiose, respectively. Moreover, Bgl3B was highly effective in converting isoflavone glycosides to aglycones at 37°C within 10 min, with the hydrolysis rates of 95.1%, 76.0%, and 75.3% for daidzin, genistin, and glycitin, respectively. These superior properties make Bgl3B potential for applications in the food, animal feed, and biofuel industries.

An acid-stable β-glucosidase from Aspergillus aculeatus: Gene expression, biochemical characterization and molecular dynamics simulation

β-Glucosidases hydrolyze terminal, non-reducing β-d-glucosyl residues and thereby release β-d-glucose. They have applications in the production of biofuels, beverages and pharmaceuticals. In this study, a β-glucosidase derived from Aspergillus aculeatus (BGLA) was expressed, characterized, and the molecular mechanism of its acid denaturation was comprehensively probed. BGLA exhibited maximal activity at pH 5.0-6.0. Its optimal temperature was 70 °C. Its enzyme activity was enhanced by Mg²⁺, Ca²⁺ and Ba²⁺, while Cu²⁺, Mn²⁺, Zn²⁺, Fe²⁺ and Fe³⁺ had a negative effect. BGLA showed activity on a broad range of substrates including salicin, cellobiose, arbutin, geniposide and polydatin. Finally, the acid-denaturation mechanism of BGLA was probed using molecular dynamics (MD) simulations. The results of simulation at pH 2.0 imply that the contact number, solvent accessible surface area and number of hydrogen bonds in BGLA decreased greatly. Moreover, the distance between the residues Asp280 and Glu509 that are part of the active site increased, which eventually destroyed the enzyme's catalytic activity. These MD results explain the molecular mechanism of acid denaturation of BGLA, which will greatly benefit the rational design of more acid-stable β-glucosidase variants in the future.

Cellulases from Thermophiles Found by Metagenomics

Cellulases are a heterogeneous group of enzymes that synergistically catalyze the hydrolysis of cellulose, the major component of plant biomass. Such reaction has biotechnological applications in a broad spectrum of industries, where they can provide a more sustainable model of production. As a prerequisite for their implementation, these enzymes need to be able to operate in the conditions the industrial process requires. Thus, cellulases retrieved from extremophiles, and more specifically those of thermophiles, are likely to be more appropriate for industrial needs in which high temperatures are involved. Metagenomics, the study of genes and gene products from the whole community genomic DNA present in an environmental sample, is a powerful tool for bioprospecting in search of novel enzymes. In this review, we describe the cellulolytic systems, we summarize their biotechnological applications, and we discuss the strategies adopted in the field of metagenomics for the discovery of new cellulases, focusing on those of thermophilic microorganisms.

The β-glucosidase secreted by Talaromyces amestolkiae under carbon starvation: a versatile catalyst for biofuel production from plant and algal biomass

BACKGROUND

In the last years, the most outstanding trend for obtaining high added-value components and second-generation (2G) biofuels consisted on exploitation of plant biomass. But recently, 3G biofuels, based in algae biomass, have emerged as a great alternative for production of energy.

RESULTS

In this work, a versatile β-glucosidase from the ascomycete fungus Talaromyces amestolkiae has been purified, characterized, and heterologously expressed. The synthesis of this β-glucosidase (BGL-3) was not induced by cellulose, and the presence of a specific carbon source is not required for its production, which is uncommon for β-glucosidases. BGL-3, which was obtained from a basal medium with glucose as carbon source, was profusely secreted under carbon starvation conditions, which was corroborated by qRT-PCR assays. BGL-3 was purified from T. amestolkiae cultures in one step, and biochemically characterized. The enzyme showed high thermal stability, and very high efficiency on pNPG (K_m of 0.14 mM and V_max of 381.1 U/mg), cellobiose (K_m of 0.48 mM and V_max of 447.1 U/mg), and other cello-oligosaccharides. Surprisingly, it also showed remarkable ability to hydrolyze laminarin, a β-1,3-glucan present in algae. The recombinant enzyme, obtained in the yeast Pichia pastoris, exhibited kinetic and physicochemical properties similar to those found for the native protein. Enzyme efficiency was examined in wheat straw saccharification processes, in which BGL-3 worked better supplementing Celluclast 1.5L than the commercial cellulase cocktail N-50010. Besides, BGL-3 hydrolyzed laminarin more efficiently than a commercial laminarinase.

CONCLUSIONS

A very efficient 1,4-β-glucosidase, which also showed activity over 1,3-β-glucose bonds, has been produced, purified, and characterized. This is the first report of such versatility in a 1,4-β-glucosidase. The application of this enzyme for saccharification of wheat straw and laminarin and its comparison with commercial enzymes suggest that it could be an interesting tool for the production of 2G and 3G biofuels.

A novel, highly efficient β-glucosidase with a cellulose-binding domain: characterization and properties of native and recombinant proteins

BACKGROUND

Cellulose, the most abundant biopolymer on earth, is an alternative for fossil fuels as a renewable feedstock for the production of second-generation biofuels and other chemicals. The discovery of novel, highly efficient β-glucosidases remains as one of the major bottlenecks for cellulose degradation. In this context, the ascomycete Talaromyces amestolkiae, isolated from cereal samples, has been studied as a promising source for these enzymes.

RESULTS

BGL-2 is the major β-glucosidase secreted by this fungus in the presence of cellulosic inductors. This enzyme possesses a CBD (Cellulose Binding Domain), an unusual feature among this type of proteins. Besides, when growing on cellulose, the fungus produced two different bgl-2 mRNAs that were cloned and expressed in Pichia pastoris. A complete recombinant protein (BGL-2*) and its truncated form, lacking CBD (BGL-2T*), have been purified, characterized and compared with the native enzyme (BGL-2). The three BGL-2 forms studied are highly stable in a wide pH range, but BGL-2T* showed an improved thermal stability at 50 °C after 72 h. Using p-nitrophenyl-β-d-glucopyranoside as a substrate, the steady-state kinetic characterization of the three proteins showed a similar K_m and k_cat for BGL-2 and BGL-2*, while the truncated protein displayed a threefold higher value for k_cat . All tested BGL-2 enzymes were as well highly efficient using cellobiose and other short oligosaccharides as a substrate. In view of biotechnological applications, the recombinant T. amestolkiae enzymes in saccharification of brewers' spent grain were studied, being comparable to commercial β-glucosidase cocktails.

CONCLUSION

A new β-glucosidase from T. amestolkiae has been studied. The enzyme, containing a functional CBD, has been expressed in P. pastoris. The comparative analyses of the native protein and its recombinant forms, with and without CBD, suggest that they could be suitable tools for valorization of lignocellulosic biomass.

Lignocellulose degrading extremozymes produced by Pichia pastoris: current status and future prospects

In this review article, extremophilic lignocellulosic enzymes with special interest on xylanases, β-mannanases, laccases and finally cellulases, namely, endoglucanases, exoglucanases and β-glucosidases produced by Pichia pastoris are reviewed for the first time. Recombinant lignocellulosic extremozymes are discussed from the perspectives of their potential application areas; characteristics of recombinant and native enzymes; the effects of P. pastoris expression system on recombinant extremozymes; and their expression levels and applied strategies to increase the enzyme expression yield. Further, effects of enzyme domains on activity and stability, protein engineering via molecular dynamics simulation and computational prediction, and site-directed mutagenesis and amino acid modifications done are also focused. Superior enzyme characteristics and improved stability due to the proper post-translational modifications and better protein folding performed by P. pastoris make this host favourable for extremozyme production. Especially, glycosylation contributes to the structure, function and stability of enzymes, as generally glycosylated enzymes produced by P. pastoris exhibit better thermostability than non-glycosylated enzymes. However, there has been limited study on enzyme engineering to improve catalytic efficiency and stability of lignocellulosic enzymes. Thus, in the future, studies should focus on protein engineering to improve stability and catalytic efficiency via computational modelling, mutations, domain replacements and fusion enzyme technology. Also metagenomic data need to be used more extensively to produce novel enzymes with extreme characteristics and stability.

Revisiting overexpression of a heterologous β-glucosidase in Trichoderma reesei: fusion expression of the Neosartorya fischeri Bgl3A to cbh1 enhances the overall as well as individual cellulase activities

Background

The filamentous fungus Trichoderma reesei has the capacity to secret large amounts of cellulase and is widely used in a variety of industries. However, the T. reesei cellulase is weak in β-glucosidase activity, which results in accumulation of cellobiose inhibiting the endo- and exo-cellulases. By expressing an exogenous β-glucosidase gene, the recombinant T. reesei cellulase is expected to degrade cellulose into glucose more efficiently.

Results

The thermophilic β-glucosidase NfBgl3A from Neosartorya fischeri is chosen for overexpression in T. reesei due to its robust activity. In vitro, the Pichia pastoris-expressed NfBgl3A aided the T. reesei cellulase in releasing much more glucose with significantly lower amounts of cellobiose from crystalline cellulose. The NfBgl3A gene was hence fused to the cbh1 structural gene and assembled between the strong cbh1 promoter and cbh1 terminator to obtain pRS-NfBgl3A by using the DNA assembler method. pRS-NfBgl3A was transformed into the T. reesei uridine auxotroph strain TU-6. Six positive transformants showed β-glucosidase activities of 2.3–69.7 U/mL (up to 175-fold higher than that of wild-type). The largely different β-glucosidase activities in the transformants may be ascribed to the gene copy numbers of NfBgl3A or its integration loci. The T. reesei-expressed NfBgl3A showed highly similar biochemical properties to that expressed in P. pastoris. As expected, overexpression of NfBgl3A enhanced the overall cellulase activity of T. reesei. The CBHI activity in all transformants increased, possibly due to the extra copies of cbh1 gene introduced, while the endoglucanase activity in three transformants also largely increased, which was not observed in any other studies overexpressing a β-glucosidase. NfBgl3A had significant transglycosylation activity, generating sophorose, a potent cellulase inducer, and other oligosaccharides from glucose and cellobiose.

Conclusions

We report herein the successful overexpression of a thermophilic N. fischeri β-glucosidase in T. reesei. In the same time, the fusion of NfBgl3A to the cbh1 gene introduced extra copies of the cellobiohydrolase 1 gene. As a result, we observed improved β-glucosidase and cellobiohydrolase activity as well as the overall cellulase activity. In addition, the endoglucanase activity also increased in some of the transformants. Our results may shed light on design of more robust T. reesei cellulases.

Engineering a highly active thermophilic β-glucosidase to enhance its pH stability and saccharification performance

BACKGROUND

β-Glucosidase is an important member of the biomass-degrading enzyme system, and plays vital roles in enzymatic saccharification for biofuels production. Candidates with high activity and great stability over high temperature and varied pHs are always preferred in industrial practice. To achieve cost-effective biomass conversion, exploring natural enzymes, developing high level expression systems and engineering superior mutants are effective approaches commonly used.

RESULTS

A newly identified β-glucosidase of GH3, Bgl3A, from Talaromyces leycettanus JCM12802, was overexpressed in yeast strain Pichia pastoris GS115, yielding a crude enzyme activity of 6000 U/ml in a 3 L fermentation tank. The purified enzyme exhibited outstanding enzymatic properties, including favorable temperature and pH optima (75 °C and pH 4.5), good thermostability (maintaining stable at 60 °C), and high catalytic performance (with a specific activity and catalytic efficiency of 905 U/mg and 9096/s/mM on pNPG, respectively). However, the narrow stability of Bgl3A at pH 4.0-5.0 would limit its industrial applications. Further site-directed mutagenesis indicated the role of excessive O-glycosylation in pH liability. By removing the potential O-glycosylation sites, two mutants showed improved pH stability over a broader pH range (3.0-10.0). Besides, with better stability under pH 5.0 and 50 °C compared with wild type Bgl3A, saccharification efficiency of mutant M1 was improved substantially cooperating with cellulase Celluclast 1.5L. And mutant M1 reached approximately equivalent saccharification performance to commercial β-glucosidase Novozyme 188 with identical β-glucosidase activity, suggesting its great prospect in biofuels production.

CONCLUSIONS

In this study, we overexpressed a novel β-glucosidase Bgl3A with high specific activity and high catalytic efficiency in P. pastoris. We further proved the negative effect of excessive O-glycosylation on the pH stability of Bgl3A, and enhanced the pH stability by reducing the O-glycosylation. And the enhanced mutants showed much better application prospect with substantially improved saccharification efficiency on cellulosic materials.

A Novel GH7 Endo-β-1,4-Glucanase from Neosartorya fischeri P1 with Good Thermostability, Broad Substrate Specificity and Potential Application in the Brewing Industry

An endo-β-1,4-glucanase gene, cel7A, was cloned from the thermophilic cellulase-producing fungus Neosartorya fischeri P1 and expressed in Pichia pastoris. The 1,410-bp full-length gene encodes a polypeptide of 469 amino acids consisting of a putative signal peptide at residues 1–20, a catalytic domain of glycoside hydrolase family 7 (GH7), a short Thr/Ser-rich linker and a family 1 carbohydrate-binding module (CBM 1). The purified recombinant Cel7A had pH and temperature optima of pH 5.0 and 60°C, respectively, and showed broad pH adaptability (pH 3.0–6.0) and excellent stability at pH3.0–8.0 and 60°C. Belonging to the group of nonspecific endoglucanases, Cel7A exhibited the highest activity on barley β-glucan (2020 ± 9 U mg^–1), moderate on lichenan and CMC-Na, and weak on laminarin, locust bean galactomannan, Avicel, and filter paper. Under simulated mashing conditions, addition of Cel7A (99 μg) reduced the mash viscosity by 9.1% and filtration time by 24.6%. These favorable enzymatic properties make Cel7A as a good candidate for applications in the brewing industry.

Molecular cloning and expression of thermostable glucose-tolerant β-glucosidase of Penicillium funiculosum NCL1 in Pichia pastoris and its characterization

A partial peptide sequence of β-glucosidase isoform (Bgl4) of Penicillium funiculosum NCL1 was identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The cDNA (bgl4) encoding Bgl4 protein was cloned from P. funiculosum NCL1 RNA by consensus RT-PCR. The bgl4 gene encoded 857 amino acids that contained catalytic domains specific for glycoside hydrolase family 3. The cDNA was over-expressed in Pichia pastoris KM71H and the recombinant protein (rBgl4) was purified with the specific activity of 1,354.3 U/mg. The rBgl4 was a glycoprotein with the molecular weight of ~130 kDa and showed optimal activity at pH 5.0 and 60 °C. The enzyme was thermo-tolerant up to 60 °C for 60 min. The rBgl4 was highly active on aryl substrates with β-glucosidic, β-xylosidic linkages and moderately active on cellobiose and salicin. It showed remarkably high substrate conversion rate of 3,332 and 2,083 μmol/min/mg with the substrates p-nitrophenyl β-glucoside and cellobiose respectively. In addition, the rBgl4 showed tolerance to glucose concentration up to 400 mM. It exhibited twofold increase in glucose yield when supplemented with crude cellulase of Trichoderma reesei Rut-C30 in cellulose hydrolysis. These results suggested that rBgl4 is a thermo- and glucose-tolerant β-glucosidase and is a potential supplement for commercial cellulase in cellulose hydrolysis and thereby assures profitability in bioethanol production.