Improving the thermostability of Trichoderma reesei   xylanase 2 by introducing disulfide bonds

Background: Xylanases are considered one of the most important enzymes in many industries. However, their low thermostability hampers their applications in feed pelleting, pulp bleaching, and so on. The main aim of this work was to improve the thermostability of Trichoderma ressei xylanase 2 (Xyn2) by introducing disulfide bonds between the N-terminal and α-helix and the β-sheet core.
Results: In this work, two disulfide bonds were separately introduced in the Xyn2 to connect the N-terminal and α-helix to the β-sheet core of Xyn2. The two disulfide bondswere introduced by site-directed mutagenesis of the corresponding residues. The half-life of the mutants Xyn2^C14–52 (disulfide bond between β-sheets B2 and B3) and Xyn2^C59–149 (disulfide bond between β-sheets A5 and A6) at 60°C was improved by approximately 2.5- and 1.8-fold compared to that of the wild type Xyn2. In addition, the enzyme's resistance to alkali and acid was enhanced.
Conclusion: Our results indicated that the connection of the N-terminal and α-helix to the β-sheet core is due to the stable structure of the entire protein.

Keywords
Disulfide bond introduction; Feed pelleting; Glycoside hydrolase; Industry applications; Pulp bleaching; Site-directed mutagenesis; Stable xylanase; Xylan degradation; Xylanolytic enzymes