Molecular Docking Analysis and Biochemical Evaluation of Levansucrase from <i>Sphingobium chungbukense</i> DJ77

Bacterial exopolymer Levan (β-(2,6) polyfructan) synthesized by levansucrase has attracted interest for various applications due to its low intrinsic viscosity compared with other polysaccharides. We report a novel levansucrase (Lsc) isolated from <i>Sphingobium chunbukense</i> DJ77 and verify its biochemical characteristics by comparative analysis of molecular docking analysis (MOE) and catalytic residue analysis. The complete sequence of the Lsc encoding gene (<i>lsc</i>) was cloned under the direction of the T7 promoter and purified in an <i>Escherichia coli</i> BL21 (DE3) protein expression system. The enzyme activity analysis and ligand docking MOE study of <i>S. chungbukense</i> DJ77 Lsc revealed that Arg 77, Ser112, Arg 195, Asp196, Glu257, and Gln275 were involved in the sucrose binding and splitting as well as transfructosylation activity. A catalytic comparison of Lsc of <i>S. chungbukense</i> DJ77 with the results of site-directed mutational analysis indicated that Gln275 may coordinate a favorable substrate binding environment, offering broad pH resistance in the range of 5–10. The results suggest that the recombinant <i>E. coli</i> carrying <i>S. chungbukense</i> DJ77 Lsc might produce levan under the regular growth conditions with less need for pH manipulation