CLONING, EXPRESSION AND CHARACTERIZATION OF XYLANASE GENE XYNB FROM ASPERGILLUS NIGER IN PICHIA PASTORIS

Xylanases have received great attention in the development of environment-benign technologies in the paper and pulp industry. The gene xynB of endo-1,4-xylanase was cloned from Aspetgillus niger nl-1 by using the PCR technique, and then successfully expressed in P pastoris GS115 strain under the control of AOX1 promoter. The full-length gene consists of 745 bp, including all intron of 67 bp which is highly similar to those of family 11 of glycosyl hydrolases reported other microorganisms. The recombinant xylanase had three apparent molecular sizes of about 21, 22.5 and 24 kDa by SDS-PAGE. The produced crude enzyme was detected to reach the highest enzyme activity of 526 IU/ml with highest specific activity of 1813.34 1U/mg(protein) after the recombinant P pastoris GS115 was induced with 0.5% methanol at 28 degrees C ill shake-flask cultivation. The optimum temperature and pH of the recombinant xylanase were at 40-50 degrees C and 4.0-5.5 respectively. It was stable ill a pH range from 2.0 to 8.0. After incubation at pH 5.0, 80 degrees C for 20min, the residual activity of the recombinant xylanase was over 68%. These enzyme properties suggest that this enzyme has great potentiality in the paper and pulp industry.