Biochemical characterization of a novel thermostable GH11 xylanase with CBM6 domain from Caldicellulosiruptor kronotskyensis

The extreme thermophilic bacterium Caldicellulosiruptor kronotskyensis can use hemicelluloses and cellulose as carbohydrate source. The gene Calkro_0081 encoded a novel GH11 xylanase (Xyn11A) with a catalytic domain (GH-CD) and a carbohydrate binding module (CBM6). The native Xyn11A and two corresponded truncations Xyn11A-CD (catalytic domain of Xyn11A) and Xyn11A-CBM (carbohydrate binding module of Xyn11A) were respectively cloned, heterologously expressed, and biochemically characterized. The recombinant Xyn11A is active in a wide temperature range from 40 to 95 degrees C with the highest activity at 75 degrees C. Xyn11A was completely stable at 70 degrees C for 6 h and more than 50% activity was retained after incubation for 6 h at 75 degrees C. The optimum pH of Xyn11A was 6.0, and it retained 100% activity after 15 h incubation in pH 5.5-7.5 at 70 degrees C. As for Xyn11A-CD, the optimal pH value and temperature were 6.0 and 65 degrees C, the residual activity retained 30% after 6h at 60 degrees C. The respective specific activities of Xyn11A, Xyn11A-CD, and Xyn11A-CBM were 1752.0, 986.8, and 0 IU/mg on beechwood xylan (BWX) at optimum conditions. The activity of Xyn11A is the highest among the reported thermostable xylanases at 75 C. Using BWX as substrate, the final products were xylose and xylobiose after hydrolysis with Xyn11A or Xyn11A-CD. No hydrolytic activity of CBM6 was found, while which shows crucial functions on thermostability and activity for Xyn11A. The characteristics of thermostability and high activity make Xyn11A a potential enzyme for industry application. (C) 2014 Elsevier B.V. All rights reserved.