Expression of recombinant Aspergillus niger xylanase A in Pichia pastoris and its action on xylan

The mature peptide of Aspergillus niger xylanase A (AnxA) was successfully expressed in Pichia pastoris at high levels under the control of AOX1 promoter. The recombinant AnxA (reAnxA) was secreted into culture medium. After 96-h 0.25% methanol induction, the activity of reAnxA in the culture supernatant reached the peak, 175 U/mg, which was 1.9 times as high as that of the native AnxA (92 U/mg). Studies on enzymatic properties showed that the optimum temperature and optimum pH of reAnxA were 50 °C and 5.0, respectively. The reAnxA was very stable in a wide pH range of 3.0–8.0. After incubation at the pH 3.0–8.0, 25 °C for 1 h, all the residual activities of reAnxA were over 80%. The Km and kcat values for reAnxA were 4.8 mg/ml and 123.2 s−1, respectively. HPLC analysis showed that xylotriose was the main hydrolysis product of birchwood xylan and bran insoluble xylan by reAnxA.