Improving the specific activity and pH stability of xylanase XynHBN188A by directed evolution

Abstract

Background

Xylanases have been successfully used in food, paper, and pulp industries and are considered to be a key player in the biodegradation of xylan to valuable end products. However, most of the natural xylanases present poor activity in high-temperature and high-alkali environment. Therefore, it is necessary to modify the enzymes to meet the increasing demands of industries.

Results

Directed evolution was used to improve the specific activity and pH stability of the xylanase (XynHBN188A) that originated from Bacillus pumilus HBP8. The xylanase XynHBN188A was mutated by error-prone PCR. The mutant, XynHBN188A217, was screened from the mutant library by functional screening. The specific activity of XynHBN188A217 was 3986.7 U/mg, which was 2.8-fold higher than that of wild type. The optimum temperature of XynHBN188A and XynHBN188A217 was 50 °C and 55 °C, respectively. The optimum pH of XynHBN188A and XynHBN188A217 was pH 8.0 and pH 7.5, respectively. The half-life at 60 °C of XynHBN188A217 was 20 min. Moreover, the pH stability of XynHBN188A217 was significantly better than that of XynHBN188A. Finally, homology models and molecular docking were used to identify the location of mutation sites and to explore the mechanism of the improved properties.

Conclusion

The xylanase XynHBN188A has been improved in the specific activity and pH stability by directed evolution. Also, the enlarged catalytic channel of mutant is beneficial for the substrates access and products release. It may contribute to the improved activity. The mutant XynHBN188A217 will be a potential candidate to be used for industrial application.

Keywords

Directed evolution / Error-prone PCR / Xylanase / Specific activity / pH stability / Structure analysis

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Funding

Technical innovation special fund of Hubei Province(2018ABA113)

Natural Science Foundation of Hubei Province(ZRMS2019000843)

2016 Wuhan Yellow Crane Talent (Science) Program