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PDBsum entry 3ehm
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Sugar binding protein
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PDB id
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3ehm
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References listed in PDB file
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Key reference
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Title
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Structure of a susd homologue, Bt1043, Involved in mucin o-Glycan utilization in a prominent human gut symbiont.
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Authors
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N.Koropatkin,
E.C.Martens,
J.I.Gordon,
T.J.Smith.
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Ref.
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Biochemistry, 2009,
48,
1532-1542.
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PubMed id
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Abstract
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Mammalian distal gut bacteria have an expanded capacity to utilize glycans. In
the absence of dietary sources, some species rely on host-derived mucosal
glycans. The ability of Bacteroides thetaiotaomicron, a prominent human gut
symbiont, to forage host glycans contributes to both its ability to persist
within an individual host and its ability to be transmitted naturally to new
hosts at birth. The molecular basis of host glycan recognition by this species
is still unknown but likely occurs through an expanded suite of outermembrane
glycan-binding proteins that are the primary interface between B.
thetaiotaomicron and its environment. Presented here is the atomic structure of
the B. thetaiotaomicron protein BT1043, an outer membrane lipoprotein involved
in host glycan metabolism. Despite a lack of detectable amino acid sequence
similarity, BT1043 is a structural homologue of the B. thetaiotaomicron
starch-binding protein SusD. Both structures are dominated by tetratrico peptide
repeats that may facilitate association with outer membrane beta-barrel
transporters required for glycan uptake. The structure of BT1043 complexed with
N-acetyllactosamine reveals that recognition is mediated via hydrogen bonding
interactions with the reducing end of beta-N-acetylglucosamine, suggesting a
role in binding glycans liberated from the mucin polypeptide. This is in
contrast to CBM 32 family members that target the terminal nonreducing galactose
residue of mucin glycans. The highly articulated glycan-binding pocket of BT1043
suggests that binding of ligands to BT1043 relies more upon interactions with
the composite sugar residues than upon overall ligand conformation as previously
observed for SusD. The diversity in amino acid sequence level likely reflects
early divergence from a common ancestor, while the unique and conserved
alpha-helical fold the SusD family suggests a similar function in glycan uptake.
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