A beta 1-6/beta 1-3 galactosidase from Bifidobacterium animalis subsp lactis Bl-04 gives insight into sub-specificities of beta-galactoside catabolism within Bifidobacterium

作者：Viborg Alexander Holm; Fredslund Folmer; Katayama Takane; Nielsen Stinne Kirketerp; Svensson Birte; Kitaoka Motomitsu; Lo Leggio Leila^*; Abou Hachem Maher

来源：Molecular Microbiology, 2014, 94(5): 1024-1040.

DOI：10.1111/mmi.12815

The Bifidobacterium genus harbours several health promoting members of the gut microbiota. Bifidobacteria display metabolic specialization by preferentially utilizing dietary or host-derived -galactosides. This study investigates the biochemistry and structure of a glycoside hydrolase family 42 (GH42) -galactosidase from the probiotic Bifidobacterium animalis subsp. lactisBl-04 (BlGal42A). BlGal42A displays a preference for undecorated 1-6 and 1-3 linked galactosides and populates a phylogenetic cluster with close bifidobacterial homologues implicated in the utilization of N-acetyl substituted 1-3 galactosides from human milk and mucin. A long loop containing an invariant tryptophan in GH42, proposed to bind substrate at subsite +1, is identified here as specificity signature within this clade of bifidobacterial enzymes. Galactose binding at the subsite -1 of the active site induced conformational changes resulting in an extra polar interaction and the ordering of a flexible loop that narrows the active site. The amino acid sequence of this loop provides an additional specificity signature within this GH42 clade. The phylogenetic relatedness of enzymes targeting 1-6 and 1-3 galactosides likely reflects structural differences between these substrates and 1-4 galactosides, containing an axial galactosidic bond. These data advance our molecular understanding of the evolution of sub-specificities that support metabolic specialization in the gut niche.

• 出版日期2014-12