Biochemical characterization of a novel thermostable β-1,4-xylosidase from Caldicellulosiruptor owensensis OL

[Objective] A thermostable β-xylosidase from the thermophile Caldicellulosiruptor owensensis OL (CoXyl B) was characterized. [Methods] Recombinant CoXyl B was heterogeneously expressed in Escherichia coli and then purified using Ni-NTA, anion exchange and Superdex 200 chromatography. Further, the hydrolysis activity of CoXyl B was studied using p-nitrophenyl-D-xyloside (pNPX) and xylooligosaccharide as substrates. [Results] The optimum temperature and pH of CoXyl B was 90 °C and pH 6.0, respectively. CoXyl B maintained stable at temperature between 40 °C and 70 °C. After incubation at 70 °C for 1 h, CoXyl B retained more than 80% of its initial activity at both pH 5.0 and 6.0. Significantly, Ag⁺, SDS and PMSF exhibited negative effect on the activity of CoXyl B, whereas Mg²⁺, Li⁺ and EDTA significantly enhanced the activity of CoXyl B. The kinetic parameters of CoXyl B towards pNPX were k_cat of 5.0×10^–3 s^–1 and K_m of 1.9 mmol/L. Moreover, CoXyl B exhibited efficient hydrolysis activity towards xylobiose, xylotriose and xylotetraose. [Conclusion] Our work suggested the application potential of a new thermostable β-xylosidase (CoXyl B) in the area of xylan degradation at high temperature.