Preliminary X-ray diffraction analysis of thermostable β-1,4-xylanase from Streptomyces sp. S9.

Xylanase, which catalyzes the random hydrolysis of internal xylosidic linkages, is a critical enzyme participating in xylan decomposition and has been widely applied in industrial utilizations. Xylanase isolated from the extremophilic Streptomyces sp. S9 (XynAS9) possesses broad adaptability to temperature and pH and thus is an attractive candidate in industrial applications. In particular, the major products of XynAS9 are xylose and xylobiose, which enable the subsequent bioconversion to be carried out with higher efficiency. Therefore, the three-dimensional structure of XynAS9 and its catalytic machinery are of great interest. Here, recombinant XynAS9 protein was expressed in Pichia pastoris, purified and crystallized. Crystals belonging to the hexagonal space group P6(5)22, with unit-cell parameters a = b = 80.9, c = 289.3 Å, were obtained by the sitting-drop vapour-diffusion method and diffracted to 2.08 Å resolution. Initial phase determination using molecular replacement indicated that the crystal contains one molecule in an asymmetric unit. Further model building and structural refinement are in progress.