A novel efficient β-glucanase from a paddy soil microbial metagenome with versatile activities

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.

Role of metagenomics in prospecting novel endoglucanases, accentuating functional metagenomics approach in second-generation biofuel production: a review

As the fossil fuel reserves are depleting rapidly, there is a need for alternate fuels to meet the day to day mounting energy demands. As fossil fuel started depleting, a quest for alternate forms of fuel was initiated and biofuel is one of its promising outcomes. First-generation biofuels are made from edible sources like vegetable oils, starch, and sugars. Second-generation biofuels (SGB) are derived from lignocellulosic crops and the third-generation involves algae for biofuel production. Technical challenges in the production of SGB are hampering its commercialization. Advanced molecular technologies like metagenomics can help in the discovery of novel lignocellulosic biomass-degrading enzymes for commercialization and industrial production of SGB. This review discusses the metagenomic outcomes to enlighten the importance of unexplored habitats for novel cellulolytic gene mining. It also emphasizes the potential of different metagenomic approaches to explore the uncultivable cellulose-degrading microbiome as well as cellulolytic enzymes associated with them. This review also includes effective pre-treatment technology and consolidated bioprocessing for efficient biofuel production.

Prospects of advanced metagenomics and meta-omics in the investigation of phytomicrobiome to forecast beneficial and pathogenic response

Microorganisms dwell in diverse plant niches as non-axenic biotic components that are beneficial as well pathogenic for the host. They improve nutrients-uptake, stress tolerance, phytohormone synthesis, and strengthening the defense system through phyllosphere, rhizosphere, and endosphere. The negative consequences of the microbial communities are largely in the form of diseases characterized by certain symptoms such as gall, cankers, rots etc. Uncultivable and unspecified nature of different phytomicrobiomes communities is a challenge in the management of plant disease, a leading cause for the loss of the plant products. Metagenomics has opened a new gateway for the exploration of microorganisms that are hitherto unknown, enables investigation of the functional aspect of microbial gene products through metatranscriptomics and metabolomics. Metagenomics offers advantages of characterizing previously unknown microorganisms from extreme environments like hot springs, glaciers, deep seas, animal gut etc. besides bioprospecting gene products such as Taq polymerase, bor encoded indolotryptoline, hydrolases, and polyketides. This review provides a detailed account of the phytomicrobiome networks and highlights the importance and limitations of metagenomics and other meta-omics approaches for the understanding of plant microbial diversity with special focus on the disease control and its management.

Metagenomic Approaches as a Tool to Unravel Promising Biocatalysts from Natural Resources: Soil and Water

Natural resources are considered a promising source of microorganisms responsible for producing biocatalysts with great relevance in several industrial areas. However, a significant fraction of the environmental microorganisms remains unknown or unexploited due to the limitations associated with their cultivation in the laboratory through classical techniques. Metagenomics has emerged as an innovative and strategic approach to explore these unculturable microorganisms through the analysis of DNA extracted from environmental samples. In this review, a detailed discussion is presented on the application of metagenomics to unravel the biotechnological potential of natural resources for the discovery of promising biocatalysts. An extensive bibliographic survey was carried out between 2010 and 2021, covering diverse metagenomic studies using soil and/or water samples from different types and locations. The review comprises, for the first time, an overview of the worldwide metagenomic studies performed in soil and water and provides a complete and global vision of the enzyme diversity associated with each specific environment.

Fungal cellulases: protein engineering and post-translational modifications

Enzymatic degradation of lignocelluloses into fermentable sugars to produce biofuels and other biomaterials is critical for environmentally sustainable development and energy resource supply. However, there are problems in enzymatic cellulose hydrolysis, such as the complex cellulase composition, low degradation efficiency, high production cost, and post-translational modifications (PTMs), all of which are closely related to specific characteristics of cellulases that remain unclear. These problems hinder the practical application of cellulases. Due to the rapid development of computer technology in recent years, computer-aided protein engineering is being widely used, which also brings new opportunities for the development of cellulases. Especially in recent years, a large number of studies have reported on the application of computer-aided protein engineering in the development of cellulases; however, these articles have not been systematically reviewed. This article focused on the aspect of protein engineering and PTMs of fungal cellulases. In this manuscript, the latest literatures and the distribution of potential sites of cellulases for engineering have been systematically summarized, which provide reference for further improvement of cellulase properties. KEY POINTS: •Rational design based on virtual mutagenesis can improve cellulase properties. •Modifying protein side chains and glycans helps obtain superior cellulases. •N-terminal glutamine-pyroglutamate conversion stabilizes fungal cellulases.

Molecular cloning and characterization of a thermostable and halotolerant endo-β-1,4-glucanase from Microbulbifer sp. ALW1

The bacterium Microbulbifer sp. ALW1 was previously characterized with the capability to break down the cell wall of brown algae into fine pieces. The biological functions of strain ALW1 were yet to be elucidated. In this study, a gene, namely MaCel5A, was isolated from the ALW1 strain genome, encoding an endo-β-1,4-glucanase. MaCel5A was phylogenetically categorized under the glycoside hydrolase family GH5, with the highest identity to a putative cellulase of Microbulbifer thermotolerans. The recombinant MaCel5A protein purified from heterologous expression in E. coli exhibited maximum activity at 50 °C and pH 6.0, respectively, and functioned selectively toward carboxymethyl cellulose and barley β-glucan. Recombinant MaCel5A demonstrated considerable tolerance to the exposure to high temperature up to 80 °C for 30 min retaining 49% residual activity. In addition, MaCel5A showed moderate stability against pH 5.0-11.0 and strong stability in the presence of nonionic surfactant. MaCel5A exhibited strong halo-stability and halotolerance. The activity of the enzyme increased about tenfold at 0.5 M NaCl, and about fivefold even at 4.0 M NaCl compared to the enzyme activity without the addition of salt. The two conserved glutamic acid residues in MaCel5A featured the typical catalytic acid/base and nucleophile machinery of glycoside hydrolases. These characteristics highlight the industrial application potential of MaCel5A.

A novel bifunctional glucanase exhibiting high production of glucose and cellobiose from rumen bacterium

Herbivores gastrointestinal microbiota is of tremendous interest for mining novel lignocellulosic enzymes for bioprocessing. We previously reported a set of potential carbohydrate-active enzymes from the metatranscriptome of the Hu sheep rumen microbiome. In this study, we isolated and heterologously expressed two novel glucanase genes, Cel5A-h38 and Cel5A-h49, finding that both recombinant enzymes showed the optimum temperatures of 50 °C. Substrate-specificity determination revealed that Cel5A-h38 was exclusively active in the presence of mixed-linked glucans, such as barley β-glucan and Icelandic moss lichenan, whereas Cel5A-h49 (EC 3.2.1.4) exhibited a wider substrate spectrum. Surprisingly, Cel5A-h38 initially released only cellotriose from lichenan and further converted it into an equivalent amount of glucose and cellobiose, suggesting a dual-function as both endo-β-1,3-1,4-glucanase (EC 3.2.1.73) and exo-cellobiohydrolase (EC 3.2.1.91). Additionally, we performed enzymatic hydrolysis of sheepgrass (Leymus chinensis) and rice (Orysa sativa) straw using Cel5A-h38, revealing liberation of 1.91 ± 0.30 mmol/mL and 2.03 ± 0.09 mmol/mL reducing sugars, respectively, including high concentrations of glucose and cellobiose. These results provided new insights into glucanase activity and lay a foundation for bioconversion of lignocellulosic biomass.

Characterization of three bacterial glycoside hydrolase family 9 endoglucanases with different modular architectures isolated from a compost metagenome

BACKGROUND

Environmental bacteria express a wide diversity of glycoside hydrolases (GH). Screening and characterization of GH from metagenomic sources provides an insight into biomass degradation strategies of non-cultivated prokaryotes.

METHODS

In the present report, we screened a compost metagenome for lignocellulolytic activities and identified six genes encoding enzymes belonging to family GH9 (GH9a-f). Three of these enzymes (GH9b, GH9d and GH9e) were successfully expressed and characterized.

RESULTS

A phylogenetic analysis of the catalytic domain of pro- and eukaryotic GH9 enzymes suggested the existence of two major subgroups. Bacterial GH9s displayed a wide variety of modular architectures and those harboring an N-terminal Ig-like domain, such as GH9b and GH9d, segregated from the remainder. We purified and characterized GH9 endoglucanases from both subgroups and examined their stabilities, substrate specificities and product profiles. GH9e exhibited an original hydrolysis pattern, liberating an elevated proportion of oligosaccharides longer than cellobiose. All of the enzymes exhibited processive behavior and a synergistic action on crystalline cellulose. Synergy was also evidenced between GH9d and a GH48 enzyme identified from the same metagenome.

CONCLUSIONS

The characterized GH9 enzymes displayed different modular architectures and distinct substrate and product profiles. The presence of a cellulose binding domain was shown to be necessary for binding and digestion of insoluble cellulosic substrates, but not for processivity.

GENERAL SIGNIFICANCE

The identification of six GH9 enzymes from a compost metagenome and the functional variety of three characterized members highlight the importance of this enzyme family in bacterial biomass deconstruction.

Novel buffalo rumen metagenome derived acidic cellulase Cel-3.1 cloning, characterization, and its application in saccharifying rice straw and corncob biomass

Lignocellulosic biomass (LCB) is a prominent option for second-generation biofuels production. Cellulase hydrolyses cellulose, a component of LCB by attacking the β-1,4-glycosidic bonds, thus liberating mono, di, and oligosaccharides, which subsequently, can be converted to biofuel. In this study, a novel cellulase (Cel-3.1) of 1593 bp which encodes a 530 amino acid protein was identified from buffalo rumen metagenomic fosmid library, and functional expression was achieved through transformation into Escherichia coli. The molecular weight was estimated as 58 kDa on SDS-PAGE. Cel-3.1 belongs to glycosyl hydrolase family-5 (GH-5) and is predicted to have 14 α-helices and 15 β-strands. The optimal temperature and pH for Cel-3.1 were experimentally determined as 5.0 and 50 °C respectively. The synergistic effect of Ca²⁺ with K⁺ ions improved Cel-3.1 activity significantly (25%) and 1% Polyethylene Glycol (PEG-400), 1% β-mercaptoethanol enhanced the relative activity Cel-3.1 by 31.68%, 12.03% respectively. Further, the enzymatic (Cel-3.1) hydrolysis of pretreated rice straw and corncob released 13.41 ± 0.26 mg/mL and 15.04 ± 0.08 mg/mL reducing sugars respectively. High Performance Liquid Chromatography (HPLC), Scanning Electron Microscope (SEM), and Fourier Transformation Infrared spectroscopy (FTIR) analysis revealed the capability of Cel-3.1 for the breakdown and hydrolysis of both rice straw and corncob to generate various fermentable sugars.

Progress in Ameliorating Beneficial Characteristics of Microbial Cellulases by Genetic Engineering Approaches for Cellulose Saccharification

Lignocellulosic biomass is a renewable and sustainable energy source. Cellulases are the enzymes that cleave β-1, 4-glycosidic linkages in cellulose to liberate sugars that can be fermented to ethanol, butanol, and other products. Low enzyme activity and yield, and thermostability are, however, some of the limitations posing hurdles in saccharification of lignocellulosic residues. Recent advancements in synthetic and systems biology have generated immense interest in metabolic and genetic engineering that has led to the development of sustainable technology for saccharification of lignocellulosics in the last couple of decades. There have been several attempts in applying genetic engineering in the production of a repertoire of cellulases at a low cost with a high biomass saccharification. A diverse range of cellulases are produced by different microbes, some of which are being engineered to evolve robust cellulases. This review summarizes various successful genetic engineering strategies employed for improving cellulase kinetics and cellulolytic efficiency.

Detoxification of aflatoxin B1 by Stenotrophomonas sp. CW117 and characterization the thermophilic degradation process

Mycotoxins are high toxic, widely distributed contaminants in foodstuff. In this study, a aflatoxin B1 (AFB1) degrading strain S. acidoaminiphila CW117 was screened, and its detoxification characteristics were investigated. Substrate AFB1 at 45 μg/L was degraded by CW117 within 24 h; meanwhile, 4.1 mg/L AFB1 was almost degraded within 48 h. After 24 h degradation, the biotoxicity of the detoxified culture was eliminated. Strain CW117 efficient degradation to AFB1 (especially to low AFB1 concentrations) suggested its potential significance to detoxification development on food and feedstuff. The active degradation components present in the cell-free supernatant. The degradation ratio increased constantly with increasing incubation temperature raised (0-90 °C) and was even stable at 90 °C. Degradation was optimal at pH 6-7, and was only partially inhibited by metal-chelators (EDTA and EGTA), proteinase K, and a protein denaturant (sodium dodecyl sulfate, SDS). The recombinant laccase rLC1 (0.5 mg/mL) from CW117 degraded 29.3% of AFB1 within 24 h; however, the cell-free supernatant degraded 76.7% of the toxin in same time, with much lower protein content. The results indicated the CW117 degrades AFB1 via a combination of enzymes and micro-molecule oxides.

Detoxification of ochratoxin A by Lysobacter sp. CW239 and characteristics of a novel degrading gene carboxypeptidase cp4

Ochratoxin A (OTA) is a potent mycotoxin that frequently contaminates agro-products and threatens food safety. A highly efficient OTA degrading strain Lysobacter sp. CW239 was isolated, and the OTA degradation characteristics were investigated. A novel OTA degrading gene carboxypeptidase cp4 was successfully cloned and characterized from CW239. The heterologous recombinant was constructed by gene cp4 and expression vector pET-32a⁽⁺⁾ and overexpressed by E. coli BL21 CodonPlus™ (DE3). The recombinant protein rCP4 was purified, and the OTA-degrading activity was evaluated. Although OTA was efficiently degraded by CW239 (24-h degradation ratio of 86.2%), the 24-h OTA degradation ratio for rCP4 was only 36.8% at fairly high concentration (0.25 mg/mL) protein. The degraded product was obtained by immune affinity column (IAC) and determined by mass spectrometry (MS), and the degraded product was the less toxic ochratoxin α (OTα). Based on the serial investigations of this study, OTA might be simultaneously co-degraded by CP4 and another unknown degrading agent in that degrading strain.

Boundaries in metagenomic screenings using lacZα-based vectors

Metagenomics approaches have been of high relevance for providing enzymes used in diverse industrial applications. In the current study, we have focused on the prospection of protease and glycosyl hydrolase activities from a soil sample by using the lacZα -based plasmid pSEVA232. For this, we used a functional screen based on skimmed milk agar and a pH indicator dye for detection of both enzymes, as previously reported in literature. Although we effectively identified positive clones in the screenings, subsequent experiments revealed that this phenotype was not because of the hydrolytic activity encoded in the metagenomic fragments, but rather due to the insertion of small metagenomic DNA fragments in frame within the coding region of the lacZ gene present in the original vector. Analyses of the thermodynamic stability of mRNA secondary structures indicated that recovering of positive clones was probably due to higher expression levels of the chimeric lacZα-genes in respect to the original from empty vector. We concluded that this method has a higher tendency for recovery false positive clones, when used in combination with a lacZα-based vector. As these vectors are massively used in functional metagenomic screenings, we highlight the importance of reporting boundaries in established metagenomic screenings methodologies.

Smart fermentation engineering for butanol production: designed biomass and consolidated bioprocessing systems

There is a renewed interest in acetone-butanol-ethanol (ABE) fermentation from renewable substrates for the sustainable and environment-friendly production of biofuel and platform chemicals. However, the ABE fermentation is associated with several challenges due to the presence of heterogeneous components in the renewable substrates and the intrinsic characteristics of ABE fermentation process. Hence, there is a need to select optimal substrates and modify their characteristics suitable for the ABE fermentation process or microbial strain. This "designed biomass" can be used to establish the consolidated bioprocessing systems. As there are very few reports on designed biomass, the main objectives of this review are to summarize the main challenges associated with ABE fermentation from renewable substrates and to introduce feasible strategies for designing the substrates through pretreatment and hydrolysis technologies as well as through the establishment of consolidated bioprocessing systems. This review offers new insights on improving the efficiency of ABE fermentation from designed renewable substrates.

Biochemical Characterization of a Novel Monospecific Endo-β-1,4-Glucanase Belonging to GH Family 5 From a Rhizosphere Metagenomic Library

Cellulases have a broad range of different industrial applications, ranging from food and beverages to pulp and paper and the biofuels area. Here a metagenomics based strategy was used to identify the cellulolytic enzyme CelRH5 from the rhizosphere. CelRH5 is a novel monospecific endo-β-1,4-glucanase belonging to the glycosyl hydrolase family 5 (GH5). Structural based modeling analysis indicated that CelRH5 is related to endo-β-1,4-glucanases derived from thermophilic microorganisms such as Thermotoga maritima, Fervidobacterium nodosum, and Ruminiclostridium thermocellum sharing 30-40% amino acid sequence identity. The molecular weight of the enzyme was determined as 40.5 kDa. Biochemical analyses revealed that the enzyme displayed good activity with soluble forms of cellulose as a substrate such as ostazin brilliant red hydroxyethyl cellulose (OBR-HEC), carboxymethylcellulose (CMC), hydroxyethyl cellulose (HEC), and insoluble azurine cross-linked hydroxyethylcellulose (AZCL-HEC). The enzyme shows highest enzymatic activity at pH 6.5 with high pH tolerance, remaining stable in the pH range 4.5–8.5. Highest activity was observed at 40°C, but CelRH5 is psychrotolerant being active and stable at temperatures below 30°C. The presence of the final products of cellulose hydrolysis (glucose and cellobiose) or metal ions such as Na⁺, K⁺, Li⁺, and Mg²⁺, as well as ethylenediaminetetraacetic acid (EDTA), urea, dithiothreitol (DTT), dimethyl sulfoxide (DMSO), 2-mercaptoethanol (2-ME) or glycerol, did not have a marked effect on CelRH5 activity. However, the enzyme is quite sensitive to the presence of 10 mM ions Zn²⁺, Ni²⁺, Co²⁺, Fe³⁺ and reagents such as 1 M guanidine HCl, 0.1% sodium dodecyl sulfate (SDS) and 20% ethanol. Given that it is psychrotolerant and retains activity in the presence of final cellulose degradation products, metal ions and various reagents, which are common in many technological processes; CelRH5 may be potential suitability for a variety of different biotechnological applications.

Novel Ethanol- and 5-Hydroxymethyl Furfural-Stimulated β-Glucosidase Retrieved From a Brazilian Secondary Atlantic Forest Soil Metagenome

Beta-glucosidases are key enzymes involved in lignocellulosic biomass degradation for bioethanol production, which complete the final step during cellulose hydrolysis by converting cellobiose into glucose. Currently, industry requires enzymes with improved catalytic performance or tolerance to process-specific parameters. In this sense, metagenomics has become a powerful tool for accessing and exploring the biochemical biodiversity present in different natural environments. Here, we report the identification of a novel β-glucosidase from metagenomic DNA isolated from soil samples enriched with decaying plant matter from a Secondary Atlantic Forest region. For this, we employed a functional screening approach using an optimized and synthetic broad host-range vector for library production. The novel β-glucosidase – named Lfa2 – displays three GH3-family conserved domains and conserved catalytic amino acids D283 and E487. The purified enzyme was most active in pH 5.5 and at 50°C, and showed hydrolytic activity toward several pNP synthetic substrates containing β-glucose, β-galactose, β-xylose, β-fucose, and α-arabinopyranose, as well as toward cellobiose. Lfa2 showed considerable glucose tolerance, exhibiting an IC₅₀ of 300 mM glucose and 30% of remaining activity in 600 mM glucose. In addition, Lfa2 retained full or slightly enhanced activity in the presence of several metal ions. Further, β-glucosidase activity was increased by 1.7-fold in the presence of 10% (v/v) ethanol, a concentration that can be reached in conventional fermentation processes. Similarly, Lfa2 showed 1.7-fold enhanced activity at high concentrations of 5-hydroxymethyl furfural, one of the most important cellulase inhibitors in pretreated sugarcane bagasse hydrolysates. Moreover, the synergistic effect of Lfa2 on Bacillus subtilis GH5-CBM3 endoglucanase activity was demonstrated by the increased production of glucose (1.6-fold). Together, these results indicate that β-glucosidase Lfa2 is a promissory enzyme candidate for utilization in diverse industrial applications, such as cellulosic biomass degradation or flavor enhancement in winemaking and grape processing.

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.

Metagenomics and CAZyme Discovery

Microorganisms play a primary role in regulating biogeochemical cycles and are a valuable source of enzymes that have biotechnological applications, such as carbohydrate-active enzymes (CAZymes). However, the inability to culture the majority of microorganisms that exist in natural ecosystems using common culture-dependent techniques restricts access to potentially novel cellulolytic bacteria and beneficial enzymes. The development of molecular-based culture-independent methods such as metagenomics enables researchers to study microbial communities directly from environmental samples, and presents a platform from which enzymes of interest can be sourced. We outline key methodological stages that are required as well as describe specific protocols that are currently used for metagenomic projects dedicated to CAZyme discovery.

Biochemical and structural characterization of a novel halotolerant cellulase from soil metagenome

Cellulase catalyzes the hydrolysis of β-1,4-linkages of cellulose to produce industrially relevant monomeric subunits. Cellulases find their applications in pulp and paper, laundry, food and feed, textile, brewing industry and in biofuel production. These industries always have great demand for cellulases that can work efficiently even in harsh conditions such as high salt, heat, and acidic environments. While, cellulases with high thermal and acidic stability are already in use, existence of a high halotolerant cellulase is still elusive. Here, we report a novel cellulase Cel5R, obtained from soil metagenome that shows high halotolerance and thermal stability. The biochemical and functional characterization of Cel5R revealed its endoglucanase activity and high halostability. In addition, the crystal structure of Cel5R determined at 2.2 Å resolution reveals a large number of acidic residues on the surface of the protein that contribute to the halophilic nature of this enzyme. Moreover, we demonstrate that the four free and non-conserved cysteine residues (C65, C90, C231 and C273) contributes to the thermal stability of Cel5R by alanine scanning experiments. Thus, the newly identified endoglucanase Cel5R is a promising candidate for various industrial applications.

Transglycosylation, a new role for multifunctional cellulase in overcoming product inhibition during the cellulose hydrolysis

Cellulase mainly consisting of exo-glucanase, endo-glucanase and β-glucosidase, was considered as the most important biocatalyst for bioconversion of ethanol and other biofuels, feedstuffs and pharmaceuticals. Hydrolysis product inhibition, especially of glucose inhibition, is one of the critical difficulty awaiting to be overcome during cellulose bioconversion. Recently, several studies showed that some multifunctional cellulases (e.g., Umcel9y-1, Td2F2 and CoGH1A) could eliminate or relieve the product inhibition through transglycosylation actions during the cellulose hydrolysis. Transglycosylation confers multifunctional cellulases insensitive character to the end products (glucose and/or cellobiose), and provides a potential access in overcoming the inhibition of biofuels conversion. Moreover, transglycosylation harboring cellulases are also attracted as substitute of glycosyltransferase in synthesis of functional foods, nutraceuticals, or pharmaceuticals. Here, several interested transglycosylation harboring cellulases were summarized and assessed for the potential values in bioengineering application.