Characterization of a GH5 endoxylanase from Penicillium funiculosum and its synergism with GH16 endo-1,3(4)-glucanase in saccharification of sugarcane bagasse

Rheological investigation of complex lignocellulosic suspensions during hydrolysis using pure and cocktail of enzymes

Enzymatic hydrolysis of lignocellulosic materials at high dry matter content is of crucial interest in bioindustry, and namely for biorefinery. Physical limitations linked to high concentrations must be understood and surpassed. This study used online and in-situ measurements to examine the rheological properties of different cellulosic suspensions and its evolution during enzymatic hydrolysis. Semi-dilute conditions were used to introduce non-Newtonian rheological behaviors while limiting complexity. For all suspensions, the relationship between shear-thinning behavior versus substrate concentration was modeled. During enzymatic digestion using single and cocktails of cellulolytic activities, the evolution in shear-thinning properties was finely quantified. The viscosity-time relationship during hydrolysis was accurately described through first-order kinetics, and a unique, dimensionless representation was obtained. The critical concentrations indicating a shift from diluted to concentrated regime and the viscosity reduction kinetics that were identified should provide a strong foundation for defining an optimal substrate feed rate for fed-batch and continuous processes.

Non-Catalytic Domains of Glycoside Hydrolase Family 5 from Paenibacillus curdlanolyticus are Important for Promoting Multifunctional Enzyme Activities and Degradation of Agricultural Residues

PcGH5 from Paenibacillus curdlanolyticus strain B-6 is a modular protein consisting of a catalytic domain of glycoside hydrolase family 5 (GH5), and three non-catalytic domains (a family 11 carbohydrate-binding module (CBM11), a fibronectin type 3 (Fn3), and a family 3 carbohydrate-binding module (CBM3). In this study, the recombinants full-length PcGH5 and the catalytic domain (PcGH5_CD) were expressed in Escherichia coli and purified. Most GH5 members exhibit endo-cellulase activity. However, the catalytic domain enzyme of strain B-6 exhibited unique properties, showing multifunctional enzyme activities of endo-cellulase, endo-xylanase, endo-mannanase, and endo-1,3-1,4-β-glucanase. The sequence alignment of PcGH5_CD compared to other characterized GH5 enzymes suggests that the two catalytic residues and the six substrate-binding subsites of endo-cellulases were conserved with other different GH5 enzyme properties. Whereas a few conserved amino acid residues and/or short peptides located outside the active site of the GH5 endo-cellulases may be involved in broad substrate specificity of PcGH5_CD enzyme on xylan, mannan and 1,3-1,4-β-glucan. Moreover, the non-catalytic domains (CBM11-Fn3-CBM3) linked to the GH5 catalytic domain are important for promoting the multifunctional enzyme activities of PcGH5 on the β-1,4 glycosidic linkages of crystalline cellulose, highly branched polysaccharides, and β-1,4-1,6 and β-1,3-1,4 glycosidic linkages of polysaccharides, especially for the polysaccharides complex contained in agricultural residues. The full-length PcGH5 is effective in producing oligosaccharides from agricultural residues without pretreatment. Therefore, it is interesting to use it as a source of prebiotics producer for use in various food products.

Crystal structures of Aspergillus oryzae exo-β-(1,3)-glucanase reveal insights into oligosaccharide binding, recognition, and hydrolysis

Exo-β-(1,3)-glucanases are promising enzymes for use in the biofuel industry as they hydrolyse sugars such as laminarin, a major constituent of the algal cell wall. This study reports structural and biochemical characterizations of Aspergillus oryzae exo-β-(1,3)-glucanase (AoBgl) belonging to the GH5 family. Purified AoBgl hydrolyses β-(1,3)-glycosidic linkages of the oligosaccharide laminaritriose and the polysaccharide laminarin effectively. We have determined three high-resolution structures of AoBgl: (a) the apo form at 1.75 Å, (b) the complexed form with bound cellobiose at 1.73 Å and (c) the glucose-bound form at 1.20 Å. The crystal structures, molecular dynamics simulation studies and site-directed mutagenesis reveal the mode of substrate binding and interactions at the active site. The results also indicate that AoBgl effectively hydrolyses trisaccharides and higher oligosaccharides. The findings from our structural and biochemical studies would aid in rational engineering efforts to generate superior AoBgl variants and similar GH5 enzymes for their industrial use.

Advances of microbial xylanases in the application of flour industries: A comprehensive review

Microbial xylanase has a wide range of applications, and many researchers favoring its utilization as an alternative to improve flour products. Wheat flour is the main raw material of flour products, although the content of arabinoxylan is not high in flour products, but it has a great influence on the quality of flour products, microbial xylanase can act on wheat arabinoxylan, so as to play the role of flour product improvement. This review carries out a description of the research progress on the application of xylanases in flour products in terms of xylanase properties, different families of xylanases and improvement mechanisms of xylanases in flour products. According to the properties of various microbial sources of xylanases, the suitable xylanase can be added to flour products, and the effect of xylanase towards wheat arabinoxylan in flour can be used to improve the quality of flour products. The molecular modification based on the properties of xylanase and the crystal structure of different families of xylanase and their substrate specificity toward wheat arabinoxylan are discussed. The article reviews the information about microbial xylanases in order to achieve better results in flour products and to provide a theoretical basis for their industrial application.

Identification and Characterization of Two Novel Extracellular β-Glucanases from Chaetomium globosum against Fusarium sporotrichioides

Chaetomium globosum can inhibit the growth of fusarium by means of their extracellular proteins. Two novel β-glucanases, designated Cgglu17A and Cgglu16B, were separated from the supernatant of C. globosum W7 and verified to have the ability to hydrolyze cell walls of Fusarium sporotrichioides MLS-19. Cgglu17A (397 amino acids) was classified as glycoside hydrolase family 17 while Cgglu16B belongs to the family16 (284 amino acids). Recombinant protein Cgglu17A was successfully expressed in Escherichia coli, and the enzymes were purified by affinity chromatography. Maximum activity of Cgglu17A appeared at the pH 5.5 and temperature 50 °C, but Cgglu16B shows the maximum activity at the pH 5.0 and temperature 50 °C. Most of heavy metal ions had inhibition effect on the two enzymes, but Cgglu17A and Cgglu16B were respectively activated by Ba2+ and Mn2+. Cgglu17A exhibited high substrate specificity, almost only catalyzing the cleavage of β-1,3-glycosidic bond, in various polysaccharose, to liberate glucose. However, Cgglu16B showed high catalytic activities to both β-1,3-glycosidic and β-1,3-1,4-glycosidic bonds. Cgglu17A was an exo-glucanase, but Cgglu16B was an endo-glucanase based on hydrolytic properties assay. Both of two enzymes showed potential antifungal activity, and the synergistic effect was observed in the germination experiment of pathogenic fungus. In conclusion, Cgglu17A (exo-1,3-β-glucanase) and Cgglu16B (endo-1,3(4)-β-glucanase) were confirmed to play a key role in the process of C. globosum controlling fusarium and have potential application value on industry and agriculture for the first time.

A Glycosyl Hydrolase 5 Family Protein Is Essential for Virulence of Necrotrophic Fungi and Can Suppress Plant Immunity

Phytopathogenic fungi normally secrete large amounts of CWDEs to enhance infection of plants. In this study, we identified and characterized a secreted glycosyl hydrolase 5 family member in Sclerotinia sclerotiorum (SsGH5, Sclerotinia sclerotiorum Glycosyl Hydrolase 5). SsGH5 was significantly upregulated during the early stages of infection. Knocking out SsGH5 did not affect the growth and acid production of S. sclerotiorum but resulted in decreased glucan utilization and significantly reduced virulence. In addition, Arabidopsis thaliana expressing SsGH5 became more susceptible to necrotrophic pathogens and basal immune responses were inhibited in these plants. Remarkably, the lost virulence of the ΔSsGH5 mutants was restored after inoculating onto SsGH5 transgenic Arabidopsis. In summary, these results highlight that S. sclerotiorum suppresses the immune responses of Arabidopsis through secreting SsGH5, and thus exerts full virulence for successful infection.