The alkaline xylanase Xyn11A-LC from the alkalophilic Bacillus sp. SN5 was expressed in E. coli, purified and crystallized. The crystal structure was determined at a resolution of 1.49 . Xyn11A-LC has the beta-jelly roll structure typical of family 11 xylanases. To improve its thermostability and thermophilicity, a mutant SB3 was constructed by introducing three arginines on the different sides of the protein surface. SB3 increased the optimum temperature by 5 A degrees C. The wild type and SB3 had the half-lives of 22 and 68 min at 65 A degrees C at pH 8.0 (Tris/HCl buffer), respectively. CD spectroscopy revealed that the melting temperature (T (m)) of the wild type and SB3 were 55.3 and 66.9 A degrees C, respectively. These results showed that the introduction of arginines enhance the thermophilicity and thermostability of Xyn11A-LC.