Xylanase II from Trichoderma reesei QM 9414: conformational and catalytic stability to Chaotropes, Trifluoroethanol, and pH changes

Cloning and Heterologous Expression of a Novel Xylanase Gene TAX1 from Trichoderma atroviride and Its Application in the Deconstruction of Corn Stover

Xylanase plays a vital role in the efficient utilization of xylan, which accounts for up to 30% of plant dry matter. However, the production cost of xylanase remains high, and the enzymatic characteristics of xylanases of most microorganisms are not suitable for industrial production. Therefore, it is of great significance to discover and develop new and efficient xylanases. In this study, the xylanase gene TAX1 (672 bp cDNA) was cloned from Trichoderma atroviride 3.3013 and expressed in Pichia pastoris. The TAX1 gene encoded a 223-amino acid protein (TAX1) with a molecular weight of 24.2 kDa which showed high similarity to glycoside hydrolase family 11. Enzyme activity assay verified that the recombinant xylanase TAX1 had optimal activity (215.3 IU/mL) at 50°C and pH 6.0. Stable working conditions were measured as pH 4.0-7.0 and 40-60°C. By adding Zn2+, the relative enzymatic activity of recombinant TAX1 was enhanced by 26%. The recombinant xylanase showed high activity toward birchwood xylan and corn stover. The Km and Kcat for xylan and corn stover were 0.36 mg/mL and 0.204 S-1 and 0.48 mg/mL and 0.149 S-1, respectively. The enzymatic activity of the TAX1 produced by P. pastoris was about 2.4-4 times higher that directly isolated from T. atroviride, so engineered P. pastoris for xylanase production could be an ideal candidate for industrial enzyme production.

Conformational Stability of the NH2-Terminal Propeptide of the Precursor of Pulmonary Surfactant Protein SP-B

Assembly of pulmonary surfactant lipid-protein complexes depends on conformational changes coupled with proteolytic maturation of proSP-B, the precursor of pulmonary surfactant protein B (SP-B), along the surfactant biogenesis pathway in pneumocytes. Conformational destabilization of the N-terminal propeptide of proSP-B (SP-BN) triggers exposure of the mature SP-B domain for insertion into surfactant lipids. We have studied the conformational stability during GdmCl- or urea-promoted unfolding of SP-BN with trp fluorescence and circular dichroism spectroscopies. Binding of the intermediate states to bis-ANS suggests their molten globule-like character. ΔG0H2O was ~ 12.7 kJ·mol-1 either with urea or GdmCl. None of the thermal transitions of SP-BN detected by CD correspond to protein unfolding. Differential scanning calorimetry of SP-BN evidenced two endothermic peaks involved in oligomer dissociation as confirmed with 2 M urea. Ionic strength was relevant since at 150 mM NaCl, the process originating the endotherm at the highest temperature was irreversible (Tm2 = 108.5°C) with an activation energy of 703.8 kJ·mol-1. At 500 mM NaCl the process became reversible (Tm2 = 114.4°C) and data were fitted to the Non-two States model with two subpeaks. No free thiols in the propeptide could be titrated by DTNB with or without 5.7 M GdmCl, indicating disulfide bonds establishment.

Effect of Temperature on Xylanase II from Trichoderma reesei QM 9414: A Calorimetric, Catalytic, and Conformational Study

The secondary structure of xylanase II from Trichoderma reesei is lost in an apparent irreversible cooperative process as temperature is increased with a midpoint transition of 58.8 ± 0.1°C. The shift of the spectral centre of mass above 50°C is also apparently cooperative with midpoint transition of 56.3 ± 0.2°C, but the existence of two isofluorescent points in the fluorescence emission spectra suggests a non-two-state process. Further corroboration comes from differential scanning calorimetry experiments. At protein concentrations ≤0.56 mg·mL⁻¹ the calorimetric transition is reversible and the data were fitted to a non-two-state model and deconvoluted into six transitions, whereas at concentrations greater than 0.56 mg·mL⁻¹ the calorimetric transition is irreversible with an exothermic contribution to the thermogram. The apparent T_m increased linearly with the scan rate according to first order inactivation kinetics. The effect of additives on the calorimetric transition of xylanase is dependent on their nature. The addition of sorbitol transforms reversible transitions into irreversible transitions while stabilizing the protein as the apparent T_m increases linearly with sorbitol concentration. d-Glucono-1,5-lactone, a noncompetitive inhibitor in xylanase kinetics, and soluble xylan change irreversible processes into reversible processes at high protein concentration.

Identification of a novel fungus, Leptosphaerulina chartarum SJTU59 and characterization of its xylanolytic enzymes

Xylanolytic enzymes are widely used in processing industries, e.g., pulp and paper, food, livestock feeds, and textile. Furthermore, certain xylanotic enzymes have demonstrated the capability to improve the resistance and immunity of plants. Screening of high-yield microbial xylanolytic enzyme producers is significant for improving large-scale cost-effective xylanolytic enzyme production. This study provided new evidence of high-level xylanolytic enzyme production by a novel fungus, designated Leptosphaerulina chartarum SJTU59. Under laboratory conditions, L. chartarum SJTU59 produced xylanolytic enzymes of up to 17.566 U/mL (i.e., 878.307 U/g substrate). The enzyme solution was relatively stable over a wide range of pH (pH 3.0 to pH 9.0) and temperature (40°C to 65°C) while showing high resistance to the majority of metal ions tested. Composition analysis of the hydrolytic products of xylan showed sufficient degradation by xylanolytic enzymes from L. chartarum SJTU59, mainly the monosaccharide xylose, and a small amount of xylobiose were enzymatically produced; whereas in the presence of sufficient xylan substrates, mainly xylooligosaccharides, an emerging prebiotic used in food industry, were produced. In addition, the xylanolytic enzyme preparation from L. chartarum SJTU59 could initiate tissue necrosis and oxidative burst in tobacco leaves, which may be related to enhanced plant defense to adversity and disease. L. chartarum SJTU59 possessed a complex xylanolytic enzyme system, from which two novel endo-β-1,4-xylanases of the glycoside hydrolase (GH) family 10, one novel endo-β-1,4-xylanase of the GH family 11, and one novel β-xylosidase of the GH family 43 were obtained via rapid amplification of complementary DNA ends. Given the high yield and stable properties of xylanolytic enzymes produced by L. chartarum SJTU59, future studies will be conducted to characterize the properties of individual xylanolytic enzymes from L. chartarum SJTU59. xylanolytic enzymes-encoding gene(s) of potential use for industrial and agricultural applications will be screened to construct genetically engineered strains.