Construction of the Thermostable D-Allulose 3-Epimerase from M30 by Protein Engineering Method.

D-Allulose 3-epimerase catalyzes C-3 epimerization between D-fructose and D-allulose was found in strain M30. The enzyme gene was cloned, and its recombinant enzyme and the mutant variants were expressed in Using the information of the sequence and model structure, we succeed in the improvement of melting temperature for the enzyme without significant loss of the enzyme activity by protein engineering method. The melting temperatures were increased by 2.7, 2.1, 3.7, 5.1, and 8.0 c[C for the mutants Glu75Pro, Arg137Lys, Ala200Lys, Ala270Lys, and Val237Ile, respectively. Each effect of the mutation was independent and additive. By integrating the above mutations, we constructed a thermostable mutant that exhibits a melting temperature 12 c[C higher than wild type, and remains stable at 65 c[C for 2 h. These highly stable properties suggest that the thermostable enzymes represent an ideal enzyme candidate for the industrial production of D-allulose.