Cloning, purification, and characterization of a thermostable alpha-L-arabinofuranosidase from Anoxybacillus kestanbolensis AC26Sari

The gene, AbfAC26Sari, encoding an alpha-L-arabinofuranosidase from Anoxybacillus kestanbolensis AC26Sari, was isolated, cloned, sequenced, and characterizated. On the basis of amino acid sequence similarities, this 57-kDa enzyme could be assigned to family 51 of the glycosyl hydrolase classification system. Characterization of the purified recombinant alpha-L-arabinofuranosidase produced in Escherichia coli BL21 revealed that it is active at a broad pH range (pH 4.5 to 9.0) and at a broad temperature range (45-85 degrees C) and it has an optimum pH of 5.5 and an optimum temperature of 65 degrees C. Kinetic experiment at 65 degrees C with p-nitrophenyl alpha-L-arabinofuranoside as a substrate gave a V-max and K-m values of 1,019 U/mg and 0.139 mM, respectively. The enzyme had no apparent requirement of metal ions for activity, and its activity was strongly inhibited by 1 mM Cu2+ and Hg2+. The recombinant arabinofuranosidase released L-arabinose from arabinan, arabinoxylan, oat spelt xylan, arabinobiose, arabinotriose, arabinotetraose, and arabinopentaose. Endoarabinanase activity was not detected. These findings suggest that AbfAC26Sari is an exo-acting enzyme.