A new thermostable [alpha]-l-arabinofuranosidase from a novel thermophilic bacterium

An α-l-arabinofuranosidase gene was identified in a sequenced genome of a novel thermophilic bacterium, which belongs to the recently described phylum of Thermomicrobia. Amino acid sequence comparison of the enzyme (designated AraF) revealed similarity to glycoside hydrolases of family 51. The gene was cloned into Escherichia coli and its recombinant product expressed and purified. The enzyme appeared to be a hexamer. AraF was optimally active at 70 °C (over 10 min) and pH 6 having 92% residual activity after 1 h at 70 °C. AraF had a K^sub m^ value of 0.6 mm and V^sub max^ value of 122 U mg^sup -1^ on p-nitrophenyl-α-l-arabinofuranoside. AraF was almost equally active on branched arabinan and debranched arabinan, properties not previously found in α-l-arabinofuranosidases in GH family 51.[PUBLICATION ABSTRACT]