Molecular Cloning and Characterization of a β-L-Arabinobiosidase in Bifidobacterium longum That Belongs to a Novel Glycoside Hydrolase Family

Extensin is a glycoprotein that is rich in hydroxyprolines linked to beta-L-arabinofuranosides. In this study, we cloned a hypBA2 gene that encodes a novel beta-L-arabinobiosidase from Bifidobacterium longum JCM 1217. This enzyme does not have any sequence similarity with other glycoside hydrolase families but has 38-98% identity to hypothetical proteins in Bifidobacterium and Xanthomonas strains. The recombinant enzyme liberated L-arabinofuranose (Araf)-beta 1,2-Araf disaccharide from carrot extensin, potato lectin, and Araf-beta 1,2-Araf-beta 1,2-Araf-beta-Hyp (Ara(3)-Hyp) but not Araf-alpha 1,3-Araf-beta 1,2-Araf-beta 1,2-Araf-beta-Hyp (Ara(4)-Hyp) or Araf-beta 1,2-Araf-beta-Hyp (Ara(2)-Hyp), which indicated that it was specific for unmodified Ara(3)-Hyp substrate. The enzyme also transglycosylated 1-alkanols with retention of the anomeric configuration. This is the first report of an enzyme that hydrolyzes Hyplinked beta-L-arabinofuranosides, which defines a new family of glycoside hydrolases, glycoside hydrolase family 121.