Developing a xylanase XYNZG from Plectosphaerella cucumerina for baking by heterologously expressed in Kluyveromyces lactis

Combined strategies for improving the heterologous expression of a novel xylanase from Fusarium oxysporum Fo47 in Pichia pastoris

Xylanase, an enzyme capable of hydrolyzing non-starch polysaccharides found in grain structures like wheat, has been found to improve the organizational structure of dough and thus increase its volume. In our past work, one promising xylanase FXYL derived from Fusarium oxysporum Fo47 and first expressed 779.64 U/mL activity in P. pastoris. It has shown significant potential in improving the quality of whole wheat bread, making it become a candidate for development as a new flour improver. After optimization of expression elements and gene dose, the xylanase activity of FXYL strain carrying three-copies reached 4240.92 U/mL in P. pastoris. In addition, 12 factors associated with the three stages of protein expression pathway were co-expressed individually in order in three-copies strain, and the translation factor Pab1 co-expression increased FXYL activity to 8893.53 U/mL. Nevertheless, combining the most effective or synergistic factors from three stages did not exhibit better results than co-expressing them alone. To further evaluate the industrial potential, the xylanase activity and protein concentration reached 81184.51 U/mL and 11.8 g/L in a 5 L fed-batch fermenter. These engineering strategies improved the expression of xylanase FXYL by more than 104-fold, providing valuable insights for the cost-effective industrial application of FXYL in the baking field.

Characterization and application of a novel xylanase from Halolactibacillus miurensis in wholewheat bread making

The presence of arabinoxylan in wholewheat flour affects its quality significantly. Here, an efficient arabinoxylan hydrolytic enzyme, Hmxyn, from Halolactibacillus miurensis was identified and heterologously expressed in pichia pastoris. Moreover, its relevant properties, including potential application in the wholewheat bread were evaluated. Recombinant Hmxyn exhibited maximal activity at 45°C and pH 6.5, and was stable at mid-range temperature (<55°C) and pH (5.5–8.0) conditions. Hmxyn had a clear hydrolysis effect on wheat arabinoxylan in dough and caused the degradation of the water-unextractable arabinoxylan, which increased the content of wheat soluble arabinoxylan of dough. The fermentation characteristics results and microstructure analysis revealed that Hmxyn improved the organizational structure and air holding capacity of fermented dough, thus promoting the dough expansion. Baking experiments further showed that Hmxyn significantly increased specific volume- and texture-linked properties of wholewheat breads. This study indicates the application potential of Hmxyn in the preparation of wholewheat bread.

Cloning, expression, and characterization of a recombinant xylanase from Bacillus sonorensis T6

Xylanase is one of industrial enzymes with diverse applications including the paper-bleaching industry and feed additives. Here, a strain having xylanolytic activity and identified as Bacillus sonorensis T6 was isolated from soil. A secretory enzyme was identified by mass-spectrometry as a xylanase of glycosyl hydrolase family 11, with a molecular weight of 23.3 kDa. The xylanase gene of Bacillus sonorensis T6 was cloned and expressed in Escherichia coli (yielding an enzyme designated as rXynT6-E) and in Pichia pastoris (yielding rXynT6-P). The recombinant xylanases were found to have optimal activity at 47–55°C and pH 6.0–7.0. The recombinant xylanase expressed in P. pastoris has 40% higher thermal stability than that expressed in E. coli. The recombinant xylanases retained 100% of activity after 10 h incubation in the pH range 3–11 and 68% of activity after 1 h at pH 2.0. The xylanase activities of rXynT6-E and rXynT6-P under optimal conditions were 1030.2 and 873.8 U/mg, respectively. The good stability in a wide range of pH and moderate temperatures may make the xylanase from Bacillus sonorensis T6 useful for various biotechnological applications, e.g., as an enzyme additive in the feed industry.

Tunnel engineering to accelerate product release for better biomass-degrading abilities in lignocellulolytic enzymes

BACKGROUND

For enzymes with buried active sites, transporting substrates/products ligands between active sites and bulk solvent via access tunnels is a key step in the catalytic cycle of these enzymes. Thus, tunnel engineering is becoming a powerful strategy to refine the catalytic properties of these enzymes. The tunnel-like structures have been described in enzymes catalyzing bulky substrates like glycosyl hydrolases, while it is still uncertain whether these structures involved in ligands exchange. Till so far, no studies have been reported on the application of tunnel engineering strategy for optimizing properties of enzymes catalyzing biopolymers.

RESULTS

In this study, xylanase S7-xyl (PDB: 2UWF) with a deep active cleft was chosen as a study model to evaluate the functionalities of tunnel-like structures on the properties of biopolymer-degrading enzymes. Three tunnel-like structures in S7-xyl were identified and simultaneously reshaped through multi-sites saturated mutagenesis; the most advantageous mutant 254RL1 (V207N/Q238S/W241R) exhibited 340% increase in specific activity compared to S7-xyl. Deconvolution analysis revealed that all three mutations contributed synergistically to the improved activity of 254RL1. Enzymatic characterization showed that larger end products were released in 254RL1, while substrate binding and structural stability were not changed. Dissection of the structural alterations revealed that both the tun_1 and tun_2 in 254RL1 have larger bottleneck radius and shorter length than those of S7-xyl, suggesting that these tunnel-like structures may function as products transportation pathways. Attributed to the improved catalytic efficiency, 254RL1 represents a superior accessory enzyme to enhance the hydrolysis efficiency of cellulase towards different pretreated lignocellulose materials. In addition, tunnel engineering strategy was also successfully applied to improve the catalytic activities of three other xylanases including xylanase NG27-xyl from Bacillus sp. strain NG-27, TSAA1-xyl from Geobacillus sp. TSAA1 and N165-xyl from Bacillus sp. N16-5, with 80%, 20% and 170% increase in specific activity, respectively.

CONCLUSIONS

This study represents a pilot study of engineering and functional verification of tunnel-like structures in enzymes catalyzing biopolymer. The specific activities of four xylanases with buried active sites were successfully improved by tunnel engineering. It is highly likely that tunnel reshaping can be used to engineer better biomass-degrading abilities in other lignocellulolytic enzymes with buried active sites.

High copy and stable expression of the xylanase XynHB in Saccharomyces cerevisiae by rDNA-mediated integration

Xylanase is a widely-used additive in baking industry for enhancing dough and bread quality. Several xylanases used in baking industry were expressed in different systems, but their expression in antibiotic free vector system is highly essential and safe. In the present study, an alternative rDNA-mediated technology was developed to increase the copy number of target gene by integrating it into Saccharomyces cerevisiae genome. A xylanase-encoding gene xynHB from Bacillus sp. was cloned into pHBM367H and integrated into S. cerevisiae genome through rDNA-mediated recombination. Exogenous XynHB expressed by recombinant S. cerevisiae strain A13 exhibited higher degradation activity towards xylan than other transformants. The real-time PCR analysis on A13 genome revealed the presence of 13.64 copies of xynHB gene. Though no antibiotics have been used, the genetic stability and the xylanase activity of xynHB remained stable up to 1,011 generations of cultivation. S. cerevisiae strain A13 expressing xylanase reduced the required kneading time and increased the height and diameter of the dough size, which would be safe and effective in baking industry as no antibiotics-resistance risk. The new effective rDNA-mediated technology without using antibiotics here provides a way to clone other food related industrial enzymes for applications.

Functional diversity and properties of multiple xylanases from Penicillium oxalicum GZ-2

A multiple xylanase system with high levels of xylanase activity produced from Penicillium oxalicum GZ-2 using agricultural waste as a substrate has been previously reported. However, the eco-physiological properties and origin of the multiplicity of xylanases remain unclear. In the present study, eight active bands were detected using zymography, and all bands were identified as putative xylanases using MALDI-TOF-MS/MS. These putative xylanases are encoded by six different xylanase genes. To evaluate the functions and eco-physiological properties of xylanase genes, xyn10A, xyn11A, xyn10B and xyn11B were expressed in Pichia pastoris. The recombinant enzymes xyn10A and xyn10B belong to the glycoside hydrolase (GH) family 10 xylanases, while xyn11A and xyn11B belong to GH11 xylanases. Biochemical analysis of the recombinant proteins revealed that all enzymes exhibited xylanase activity against xylans but with different substrate specificities, properties and kinetic parameters. These results demonstrated that the production of multiple xylanases in P. oxalicum GZ-2 was attributed to the genetic redundancy of xylanases and the post-translational modifications, providing insight into a more diverse xylanase system for the efficient degradation of complex hemicelluloses.