Functional Modification of the Substrate-Binding Site for Isomaltulose Production Based on Predicted Structure of Sucrose Isomerase from Pantoea dispersa UQ68 J

Sucrose isomerase from Pantoea dispersa UQ68 J (Sim1) converted sucrose into isomaltulose and trehalulose as major products. To improve the product specificity of isomaltulose and trehalulose, we designed the mutants on Y296 and Q299 residues of Sim1, respectively, which were located close to the substrate-binding site. The mutant of Q299E increased the conversion rate of isomaltulose from 90.28 to 94.16%. The 3D homology structure of Sim1 based on the crystal structure of Klebsiella sp. LX3 isomaltulose synthase unraveled the characteristics of catalytic pocket and their substrate-binding mode. The molecular docking simulation results showed that isomaltulose rather than trehalulose was bound to Q299 of Sim1 at the substrate binding site via hydrogen bond interactions. The molecular docking simulation and experimental data demonstrated Q299E, ΔQ299 and Y296D showed significant effect on product specificity.