Wang_2020_Int.J.Biol.Macromol_60_1189

To improve the thermostability of r27RCL from Rhizopus chinensis and broaden its industrial applications, we used rational design (FoldX) according to DeltaDeltaG calculation to predict mutations. Four thermostable variants S142A, D217V, Q239F, and S250Y were screened out and then combined together to generate a quadruple-mutation (S142A/D217V/Q239F/S250Y) variant, called m31. m31 exhibited enhanced thermostability with a 41.7-fold longer half-life at 60 degrees C, a 5 degrees C higher of topt, and 15.8 degrees C higher of T30 50 compared to that of r27RCL expressed in P. pastoris. Molecular dynamics simulations were conducted to analyze the mechanism of the thermostable mutant. The results indicated that the rigidity of m31 was improved due to the decreased solvent accessible surface area, a newly formed salt bridge of Glu292:His171, and the increased DeltaDeltaG of m31. According to the root-mean-square-fluctuation analysis, three positive mutations S142A, D217V, and Q239F located in the thermal weak regions and greatly decreased the distribution of thermal-fluctuated regions of m31, compared to that of r27RCL. These results suggested that to simultaneously implement MD simulations and DeltaDeltaG-based rational approaches will be more accurate and efficient for the improvement of enzyme thermostability.