Biochemical Characterization of Two Thermostable Xylanolytic Enzymes Encoded by a Gene Cluster of Caldicellulosiruptor owensensis

The xylanolytic extremely thermophilic bacterium Caldicellulosiruptor owensensis provides a promising platform for xylan utilization. In the present study, two novel xylanolytic enzymes, GH10 endo-beta-1,4-xylanase (Coxyn A) and GH39 beta-1,4-xylosidase (Coxyl A) encoded in one gene cluster of C. owensensis were heterogeneously expressed and biochemically characterized. The optimum temperature of the two xylanlytic enzymes was 75 degrees C, and the respective optimum pH for Coxyn A and Coxyl A was 7.0 and 5.0. The difference of Coxyn A and Coxyl A in solution was existing as monomer and homodimer respectively, it was also observed in predicted secondary structure. Under optimum condition, the catalytic efficiency (k(cat)/K-m) of Coxyn A was 366 mg ml(-1) s(-1) on beechwood xylan, and the catalytic efficiency (k(cat)/K-m) of Coxyl A was 2253 mM(-1) s(-1) on pNP-beta-D-xylopyranoside. Coxyn A degraded xylan to oligosaccharides, which were converted to monomer by Coxyl A. The two intracellular enzymes might be responsible for xylooligosaccharides utilization in C. owensensis, also provide a potential way for xylan degradation in vitro.