Expression and characterization of a GH39 β-xylosidase II from Caulobacter crescentus.

In the present work, the gene xynB2, encoding a β-xylosidase II of the Glycoside Hydrolase 39 (GH39) family, of Caulobacter crescentus was cloned and successfully overexpressed in Escherichia coli DH10B. The recombinant protein (CcXynB2) was purified using nickel-Sepharose affinity chromatography, with a recovery yield of 75.5 %. CcXynB2 appeared as a single band of 60 kDa on a sodium dodecyl sulfate polyacrylamide gel and was recognized by a specific polyclonal antiserum. The predicted CcXynB2 protein showed a high homology with GH39 β-xylosidases of the genus Xanthomonas. CcXynB2 exhibited an optimal activity at 55 °C and a pH of 6. CcXynB2 displayed stability at pH values of 4.5-7.5 for 24 h and thermotolerance up to 50 °C. The K (M) and V (Max) values were 9.3 ± 0.45 mM and 402 ± 19 μmol min(-1) for ρ-nitrophenyl-β-D-xylopyranoside, respectively. The purified recombinant enzyme efficiently produced reducing sugars from birchwood xylan and sugarcane bagasse fibers pre-treated with a purified xylanase. As few bacterial GH39 family β-xylosidases have been characterized, this work provides a good contribution to this group of enzymes.