Detailed Mode of Action of Arabinan-Debranching α--Arabinofuranosidase GH51 from .

The gene encoding an α--arabinofuranosidase (BvAF) GH51 from FZB42 was cloned and expressed in . The corresponding open reading frame consists of 1,491 nucleotides which encode 496 amino acids with the molecular mass of 56.9 kDa. BvAF showed the highest activity against sugar beet (branched) arabinan in 50 mM sodium acetate buffer (pH 6.0) at 45°C. However, it could hardly hydrolyze debranched arabinan and arabinoxylans. The time-course hydrolyses of branched arabinan and arabinooligosaccharides (AOS) revealed that BvAF is a unique -hydrolase producing exclusively L-arabinose. BvAF could cleave α-(1,2)- and/or α-(1,3)--arabinofuranosidic linkages of the branched substrates to produce the debranched forms of arabinan and AOS. Although the excessive amount of BvAF could liberate -arabinose from linear AOS, it was extremely lower than that on branched AOS. In conclusion, BvAF is the arabinan-specific exo-acting α--arabinofuranosidase possessing high debranching activity towards α-(1,2)- and/or α-(1,3)-linked branches of arabinan, which can facilitate the successive degradation of arabinan by -α-(1,5)--arabinanase.