Substrate specificity of three recombinant α-l-arabinofuranosidases from Bifidobacterium adolescentis and their divergent action on arabinoxylan and arabinoxylan oligosaccharides

Bifidobacterium adolescentis possesses several arabinofuranosidases able to hydrolyze arabinoxylans (AX) and AX oligosaccharides (AXOS), the latter being bifidogenic carbohydrates with potential prebiotic properties. We characterized two new recombinant arabinofuranosidases, AbfA and AbfB, and AXH-d3, a previously studied arabinofuranosidase from B. adolescentis. AbfA belongs to glycoside hydrolase family (GH) 43 and removed arabinose from the C(O)2 and C(O)3 position of monosubstituted xylose residues. Furthermore, hydrolytic activity of AbfA was much larger towards substrates with a low amount of arabinose substitutions. AbfB from GH 51 only cleaved arabinoses on position C(O)3 of disubstituted xyloses, similar to GH 43 AXH-d3, making it to our knowledge, the first reported enzyme with this specificity in GH 51. AbfA acted synergistically with AbfB and AXH-d3. In combination with AXH-d3, it released 60% of arabinose from wheat AX. Together with recent studies on other AXOS degrading enzymes from B. adolescentis, these findings allowed us to postulate a mechanism for the uptake and hydrolysis of bifidogenic AXOS by this organism.

Research highlights
► AbfA is an arabinofuranosidase which cleaves arabinoses linked to C(O)2 and C(O)3 of monosubstituted xyloses.
► AbfB is an arabinofuranosidase which cleaves arabinoses linked to C(O)3 of disubstituted xyloses.
► AbfA is strongly influenced by the degree of substitution of the substrate.
► AbfA acts synergistically with AbfB and AXH-d3.
► A combination of AbfA and AXH-d3 releases the majority (60%) of arabinoses in wheat arabinoxylan.