Characterization and constitutive expression of an acidic mesophilic endo-1,4-β-d-xylanohydrolase with high thermotolerance and catalytic efficiency in Pichia pastoris

A putative endo-1,4-beta-d-xylanohydrolase gene xyl11 from Aspergillus niger, encoding a 188-residue xylanase of glycosyl hydrolase family 11, was constitutively expressed in Pichia pastoris. The recombinant Xyl11 exhibited optimal activity at pH 5.0 and 50 A degrees C, and displayed more than 68 % of the maximum activity over the temperature range 35-65 A degrees C and 33 % over the pH range 2.2-7.0. It maintained more than 40 % of the original activity after incubation at 90 A degrees C (pH 5.0) for 10 min and more than 75 % of the original activity after incubation at pH 2.2-11.0 (room temperature) for 2 h. The specific activity, K (m) and V (max) of purified Xyl11 were 22,253 U mg(-1), 6.57 mg ml(-1) and 51,546.4 mu mol min(-1) mg(-1). It could degrade xylan to a series of xylooligosaccharides and no xylose was detected. The recombinant enzyme with high stability and catalytic efficiency could work over wide ranges of pH and temperature and thus has the potential for various industrial applications.