Background: Xylanases are considered one of the most important enzymes in many industry applications. However, its low thermostability hampers its applications such as feed pelleting and pulp bleaching. The main purpose of this work was to improve the thermostability of Trichoderma ressei xylanase 2 (Xyn2) by the separated introducing disulfide between the N-terminal and α-helix to the β-sheet-core.

Results: In this work, two disulfide bonds were introduced separately to the Xyn2 in order to create a closer connection of N-terminal and α-helix to the β-sheet core of the Xyn2. The two disulfide bonds were introduced by site-directed mutagenesis of corresponding residues respectively. The half-life of the mutants Xyn2^C14-52 (contain a disulfide bond between β-sheet B2 and B3) and Xyn2^C59-149 (contain a disulfide bond between β-sheet A5 and A6) at 60ºC were improved by approximately 2.5- and 1.8-fold compare to the wild type Xyn2. In addition, the resistance to alkali and acid were also enhanced.

Conclusion: Our results indicated that the close relationship of the N-terminal and α-helix to the β-sheet core are the result of the stable structure of the entire protein.