Hydrolytic properties of a thermostable α‐ l ‐arabinofuranosidase from Caldicellulosiruptor saccharolyticus

Aims:  To characterize of a thermostable recombinant α‐ l ‐arabinofuranosidase from Caldicellulosiruptor saccharolyticus for the hydrolysis of arabino‐oligosaccharides to l ‐arabinose. Methods and Results:  A recombinant α‐ l ‐arabinofuranosidase from C. saccharolyticus was purified by heat treatment and Hi‐Trap anion exchange chromatography with a specific activity of 28·2 U mg −1 . The native enzyme was a 58‐kDa octamer with a molecular mass of 460 kDa, as measured by gel filtration. The catalytic residues and consensus sequences of the glycoside hydrolase 51 family of α‐ l ‐arabinofuranosidases were completely conserved in α‐ l ‐arabinofuranosidase from C. saccharolyticus . The maximum enzyme activity was observed at pH 5·5 and 80°C with a half‐life of 49 h at 75°C. Among aryl‐glycoside substrates, the enzyme displayed activity only for p ‐nitrophenyl‐α‐ l ‐arabinofuranoside [maximum k cat / K m of 220 m(mol l −1 ) −1  s −1 ] and p ‐nitrophenyl‐α‐ l ‐arabinopyranoside. This substrate specificity differs from those of other α‐ l ‐arabinofuranosidases. In a 1 mmol l −1 solution of each sugar, arabino‐oligosaccharides with 2–5 monomer units were completely hydrolysed to l ‐arabinose within 13 h in the presence of 30 U ml −1 of enzyme at 75°C. Conclusions:  The novel substrate specificity and hydrolytic properties for arabino‐oligosaccharides of α‐ l ‐arabinofuranosidase from C. saccharolyticus demonstrate the potential in the commercial production of l ‐arabinose in concert with endoarabinanase and/or xylanase. Significance and Impact of the Study:  The findings of this work contribute to the knowledge of hydrolytic properties for arabino‐oligosaccharides performed by thermostable α‐ l ‐arabinofuranosidase.