Improvement of thermostability of β-1,3-1,4-glucanase from Bacillus amyloliquefaciens BS5582 through in vitro evolution

Abstract:

In vitro evolution methods are often used to modify protein with improved characteristics. We developed a directed evolution protocol to enhance the thermostability of the β-1,3-1,4-glucanase. The thermostability of the enzyme was significantly improved after two rounds of directed evolution. Three variants with higher thermostability were obtained. The mutant enzymes were further analyzed by their melting temperature, halftime and kinetic parameters. Comparing to intact enzyme, the T50 of mutant enzymes 2-JF-01, 2-JF-02 and 2-JF-03 were increased by 2.2°C, 5.5°C and 3.5°C, respectively, the halftime (t1/2, 60°C) of mutant enzymes 2-JF-01, 2-JF-02 and 2-JF-03 were shortened by 4,13 and 17 min, respectively, the Vmax of mutant enzymes were decreased by 8.3%, 2.6% and 10.6%, respectively, while Km of mutant enzymes were nearly unchanged. Sequence analysis revealed seven single amino acid mutant happened among three mutant enzymes, such as 2-JF-01 (N36S, G213R), 2-JF-02 (C86R, S115I, N150G) and 2-JF-03 (E156V, K105R). Homology-modeling showed that five of seven substituted amino acids were located on the surface of or in hole of protein. 42.8% of substituted amino acids were arginine, which indicated that arginine may play a role in the improvement of the thermostability of the β-1,3-1,4-glucanase.This study provide some intresting results of the structural basis of the thermostability of β-1,3-1,4-glucanase,and provide some new point of view in modifying enzyme for future industrial use.

Key words:β-1,3-1,4-glucanase, vitro evolution, error-prone PCR, thermostability