New α- l -arabinofuranosidase produced by Streptomyces lividans: cloning and DNA sequence of the abfB gene and characterization of the enzyme

A fully secreted alpha-l-arabinofuranosidase was cloned from the homologous expression system of Streptomyces lividans. The gene, located upstream adjacent to the previously described xylanase A gene, was sequenced. It is divergently transcribed from the xlnA gene and the two genes are separated by an intercistronic region of 391nt which contains a palindromic AT-rich sequence. The deduced amino acid sequence of the protein shows that the enzyme contains a distinct catalytic domain which is linked to a specific xylan-binding domain by a linker region. The purified enzyme has a specific arabinofuranose-debranching activity on xylan from Gramineae, acts synergistically with the S. lividans xylanases and binds specifically to xylan. From small arabinoxylo-oligosides, it liberates arabinose and, after prolonged incubation, the purified enzyme exhibits some xylanolytic activity as well.