Structural analysis of gum arabic side chains from Acacia seyal released by bifidobacterial β-arabino-oligosaccharide 3-O-β-l-arabinopyranosyl-α-l-arabinofuranosidase

Gum arabic is widely used in the food and beverage industries for its emulsifying, stabilizing, and prebiotic effects, which promote Bifidobacterium growth. The two commercially approved varieties of gum arabic, namely, Acacia senegal gum and A. seyal gum, predominantly consist of arabinogalactan protein (AGP), albeit with different side chain modifications. We previously characterized two enzymes belonging to glycoside hydrolase (GH) family 39 in bifidobacteria involved in the release of α-d-Gal-(1→3)-α-l-Ara and β-l-Arap-(1→3)-α-l-Ara from the side chains of A. senegal gum. Although the carbohydrate structure of A. senegal gum is being increasingly explored, limited information is available on A. seyal gum. In this study, we discovered a novel GH39 β-arabino-oligosaccharide 3-O-β-l-arabinopyranosyl-α-l-arabinofuranosidase from Bifidobacterium catenulatum and revealed the accurate structure of β-l-arabino-oligosaccharides released from A. seyal gum as [β-l-Araf-(1→2)-]_n-β-l-Arap-(1→3)-α-l-Araf-(1→) (n = 0-3). Growth assays and intracellular enzyme activity assessments using B. catenulatum revealed that β-l-arabino-oligosaccharides were degraded to l-arabinose by GH127 β-l-arabinofuranosidase and GH36 β-l-arabinopyranosidase. This study provides new insights into the diversity of AGP structures and the utilization mechanisms of A. seyal gum in bifidobacteria.