Degradative enzymes for type II arabinogalactan side chains in Bifidobacterium longum subsp. longum
Type II arabinogalactan (AG) is a soluble prebiotic fiber stimulating the proliferation of bifidobacteria in the human gut. Larch AG, which is comprised of type II AG, is known to be utilized as an energy source for Bifidobacterium longum subsp. longum (B. longum). We have previously characterized GH43_24 exo-β-1,3-galactanase (Bl1,3Gal) for the degradation of type II AG main chains in B. longum JCM1217. In this study, we characterized GH30_5 exo-β-1,6-galactobiohydrolase (Bl1,6Gal) and GH43_22 α-l-arabinofuranosidase (BlArafA), which are degradative enzymes for type II AG side chains in cooperation with exo-β-1,3-galactanase. The recombinant exo-β-1,6-galactobiohydrolase specifically released β-1,6-galactobiose (β-1,6-Gal2) from the nonreducing terminal of β-1,6-galactooligosaccharides, and the recombinant α-l-arabinofuranosidase released arabinofuranose (Araf) from α-1,3-Araf-substituted β-1,6-galactooligosaccharides. β-1,6-Gal2 was additively released from larch AG by the combined use of type II AG degradative enzymes, including Bl1,3Gal, Bl1,6Gal, and BlArafA. The gene cluster encoding the type II AG degradative enzymes is conserved in all B. longum strains, but not in other bifidobacterial species. The degradative enzymes for type II AG side chains are thought to be important for the acquisition of type II AG in B. longum.
KeywordsBifidobacterium longum Type II arabinogalactan Prebiotic Exo-β-1,6-galactobiohydrolase α-l-Arabinofuranosidase
This work was supported in part by JSPS KAKENHI Grant-in-Aid for Scientific Research (C), Grant Number 24580144.
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Conflict of interest
The authors declare that they have no conflict of interest.
This article does not contain any studies with animals performed by any of the authors.
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