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Abstract In order to obtain the more thermostable β-glucanase, directed evolution was used to evolve the β-glucanase gene, and the enzyme properties were analyzed. The two mutants, i.e., EGs1 and EGs2, were obtained. The results of the enzyme properties analysis indicated that the melting temperatures of EGs1 and EGs2 were increased by 3℃ and 5℃, and approached 65.5 ℃ and 67.5℃; The optimum temperatures of the two mutants were increased by 5℃, and approached 60℃;The abilities to produce reducing sugar from lichenin were either much higher (28%) for the former or much lower (21.6%) for the latter ;The affinities of the two mutants for the lichenin were basically unchanged in comparison with their parental enzymes. The optimum pH were 6.5 for the EGs1 and wild-type, and 7.0 for EGs2; The pH stability for all enzymes was good, the activity of parental enzyme and the two mutant enzymes have no loss at pH 6.0-8.0 and pH 6.5-8.0 for 48 hours, respectively; The plasmids stability of the two mutants were good and their expression ability of β-glucanase kept stable after 50 generations. The results demonstrate that directed evolution is an effective approach to improve the properties of a mesophilic enzyme.
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Received: 01 August 2006
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