Functions of Novel Glycosidases Isolated from Bifidobacteria

Abstract

The genes for 1,2-α-L-fucosidase and endo-α-N-acetylgalactosaminidase have been cloned from Bifidobacterium bifidum JCM1254 andBifidobacterium longum JCM1217, respectively. The catalytic domain of 1,2-α-L-fucosidase (AfcA) specifically hydrolyzed the terminal α(1→2)-fucosidic linkages of human milk oligosaccharides and sugar chains of glycoproteins. It exhibited high sequence similarity to several hypothetical proteins in a database, and thus, novel glycoside hydrolase (GH) family 95 has been created. Catalytically important residues of the domain, which were revealed by X-ray crystallographic analysis, were well conserved within the family except for one residue located at the +1 subsite. Endo-α-N-acetylgalactosaminidase (EngBF) that was expressed as C-terminally histidine-tagged protein wasfound to liberate Galβ1,3GalNAc disaccharide from Core 1-type O-glycans. Its homologues were found in the genomes of severalbacteria, and thus a novel GH family (GH101) has been established. Considering that both AfcA and EngBF were able to degrade naturalsubstrates present in intestine, it was envisaged that the enzymes play important roles for the organisms in making their habitats in thecolon. The recent finding of the GNB/LNB pathway in bifidobacterial cells by Kitaoka’s group further supports this notion.