Crystal structure of ?-L-arabinobiosidase belonging to glycoside hydrolase family 121.

ABSTRACT: Enzymes acting on ?-L-arabinofuranosides have been extensively studied; however, the structures and functions of ?-L-arabinofuranosidases are not fully understood. Three enzymes and an ABC transporter in a gene cluster of Bifidobacterium longum JCM 1217 constitute a degradation and import system of ?-L-arabinooligosaccharides on plant hydroxyproline-rich glycoproteins. An extracellular ?-L-arabinobiosidase (HypBA2) belonging to the glycoside hydrolase (GH) family 121 plays a key role in the degradation pathway by releasing ?-1,2-linked arabinofuranose disaccharide (?-Ara2) for the specific sugar importer. Here, we present the crystal structure of the catalytic region of HypBA2 as the first three-dimensional structure of GH121 at 1.85 Å resolution. The HypBA2 structure consists of a central catalytic (?/?)6 barrel domain and two flanking (N- and C-terminal) ?-sandwich domains. A pocket in the catalytic domain appears to be suitable for accommodating the ?-Ara2 disaccharide. Three acidic residues Glu383, Asp515, and Glu713, located in this pocket, are completely conserved among all members of GH121; site-directed mutagenesis analysis showed that they are essential for catalytic activity. The active site of HypBA2 was compared with those of structural homologs in other GH families: GH63 ?-glycosidase, GH94 chitobiose phosphorylase, GH142 ?-L-arabinofuranosidase, GH78 ?-L-rhamnosidase, and GH37 ?,?-trehalase. Based on these analyses, we concluded that the three conserved residues are essential for catalysis and substrate binding. ?-L-Arabinobiosidase genes in GH121 are mainly found in the genomes of bifidobacteria and Xanthomonas species, suggesting that the cleavage and specific import system for the ?-Ara2 disaccharide on plant hydroxyproline-rich glycoproteins are shared in animal gut symbionts and plant pathogens.

SUBMITTER: Saito K 

PROVIDER: S-EPMC7263609 | biostudies-literature | 2020

REPOSITORIES: biostudies-literature