Abstract
β-L-Arabinofuranosides are hydroxyproline (Hyp)-linked sugar chains of extensin observed in plant cell wall fractions. Despite the broad distribution of β-L-arabinofuranosyl residues in plants, degradative enzymes have not yet been identified. In 2011, we cloned and characterized the first degradative enzymes for Hyp-linked β-L-arabinofuranosides from Bifidobacterium longum. These enzymes were composed of a glycoside hydrolase (GH) family 43 α-L-arabinofuranosidase (HypAA) releasing L-arabinose from Arafα1-3Arafβ1-2Arafβ1-2Arafβ-Hyp, a GH121 β-L-arabinobiosidase (HypBA2) releasing Arafβ1-2Araf (β-Ara2) from Arafβ1-2Arafβ1-2Arafβ-Hyp, and a GH127 β-L-arabinofuranosidase (HypBA1) degrading β-Ara2 to L-arabinose. These enzymes are encoded in a conserved gene cluster on several B. longum genomes, but not in genome sequences of other intestinal bacteria. Hyp-linked β-L-arabinofuranosides were utilized as carbohydrate sources by B. longum. This review presents the functional features of enzymes for Hyp-linked β-L-arabinofuranosides and the predicted metabolic pathway in B. longum.
