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Publication Abstract from PubMed

The Bifidobacterium genus harbours several health promoting members of the gut microbiota. Bifidobacteria display metabolic specialization by preferentially utilizing dietary or host derived beta-galactosides. This study investigates the biochemistry and structure of a glycoside hydrolase family 42 (GH42) beta-galactosidase from the probiotic Bifidobacterium animalis subsp. lactis Bl-04 (BlGal42A). BlGal42A displays a preference for undecorated beta1-6 and beta1-3 linked galactosides and populates a phylogenetic cluster with close bifidobacterial homologues implicated in the utilization of N-acetyl substituted beta1-3 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 beta1-6 and beta1-3 galactosides likely reflects structural differences between these substrates and beta1-4 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.

A beta1-6/beta1-3 galactosidase from Bifidobacterium animalis subsp. lactis Bl-04 gives insight into sub-specificities of beta-galactoside catabolism within Bifidobacterium.,Viborg AH, Fredslund F, Katayama T, Nielsen SK, Svensson B, Kitaoka M, Leggio LL, Abou Hachem M Mol Microbiol. 2014 Oct 7. doi: 10.1111/mmi.12815. PMID:25287704^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.