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Authors
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J.Wada,
T.Ando,
M.Kiyohara,
H.Ashida,
M.Kitaoka,
M.Yamaguchi,
H.Kumagai,
T.Katayama,
K.Yamamoto.
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Breast-fed infants often have intestinal microbiota dominated by bifidobacteria
in contrast to formula-fed infants. We found that several bifidobacterial
strains produce a lacto-N-biosidase that liberates lacto-N-biose I
(Galbeta1,3GlcNAc; type 1 chain) from lacto-N-tetraose
(Galbeta1,3GlcNAcbeta1,3Galbeta1,4Glc), which is a major component of human milk
oligosaccharides, and subsequently isolated the gene from Bifidobacterium
bifidum JCM1254. The gene, designated lnbB, was predicted to encode a protein of
1,112 amino acid residues containing a signal peptide and a membrane anchor at
the N and C termini, respectively, and to possess the domain of glycoside
hydrolase family 20, carbohydrate binding module 32, and bacterial
immunoglobulin-like domain 2, in that order, from the N terminus. The
recombinant enzyme showed substrate preference for the unmodified beta-linked
lacto-N-biose I structure. Lacto-N-biosidase activity was found in several
bifidobacterial strains, but not in the other enteric bacteria, such as
clostridia, bacteroides, and lactobacilli, under the tested conditions. These
results, together with our recent finding of a novel metabolic pathway specific
for lacto-N-biose I in bifidobacterial cells, suggest that some of the
bifidobacterial strains are highly adapted for utilizing human milk
oligosaccharides with a type 1 chain.
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