2015 年 27 巻 156 号 p. E9-E12
The Bifidobacterium genus harbours several health promoting members of the gut microbiota, which display metabolic specialization by preferentially utilizing dietary or host-derived β-galactosides. To approach a deeper understanding of the β-galactoside metabolism in the gut niche, the overall study investigated the bioinformatics, biochemistry and structures of glycoside hydrolase family 42 (GH42) β-galactosidases from Bifidobacterium species associated with the human gut. GH42 β-galactosidases display a large variety of sub-specificities in accordance with the diversity and complexity of β-galactosides available in the gut. The variety of sub-specificities is evident in a phylogenetic distribution where GH42 β-galactosidases segregate according to function. The first function-structure insight in GH42 illustrates that diversity manifested in sub-specificities, correlates through subtle changes in loop regions in the near vicinity of the site of catalysis. The occurrence of, multiple GH42 β-galactosidases with diverse sub-specificities within a single Bifidobacterium strain and the distinct differences among all of them from various species, emphasizes the importance and diversity of β-galactoside metabolism in bifidobacteria.