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PDBsum entry 2ric
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Sugar binding protein
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PDB id
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2ric
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References listed in PDB file
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Key reference
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Title
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Recognition of heptoses and the inner core of bacterial lipopolysaccharides by surfactant protein d.
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Authors
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H.Wang,
J.Head,
P.Kosma,
H.Brade,
S.Müller-Loennies,
S.Sheikh,
B.Mcdonald,
K.Smith,
T.Cafarella,
B.Seaton,
E.Crouch.
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Ref.
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Biochemistry, 2008,
47,
710-720.
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PubMed id
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Abstract
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Lipopolysaccharides (LPS) of Gram-negative bacteria are important mediators of
bacterial virulence that can elicit potent endotoxic effects. Surfactant protein
D (SP-D) shows specific interactions with LPS, both in vitro and in vivo. These
interactions involve binding of the carbohydrate recognition domain (CRD) to LPS
oligosaccharides (OS); however, little is known about the mechanisms of LPS
recognition. Recombinant neck+CRDs (NCRDs) provide an opportunity to directly
correlate binding interactions with a crystallographic analysis of the binding
mechanism. In these studies, we examined the interactions of wild-type and
mutant trimeric NCRDs with rough LPS (R-LPS). Although rat NCRDs bound more
efficiently than human NCRDs to Escherichia coli J-5 LPS, both proteins
exhibited efficient binding to solid-phase Rd2-LPS and to Rd2-LPS aggregates
presented in the solution phase. Involvement of residues flanking calcium at the
sugar binding site was demonstrated by reciprocal exchange of lysine and
arginine at position 343 of rat and human CRDs. The lectin activity of hNCRDs
was inhibited by specific heptoses, including l-glycero-alpha-d-manno-heptose
(l,d-heptose), but not by 3-deoxy-alpha-d-manno-oct-2-ulosonic acid (Kdo).
Crystallographic analysis of the hNCRD demonstrated a novel binding orientation
for l,d-heptose, involving the hydroxyl groups of the side chain. Similar
binding was observed for a synthetic alpha1-->3-linked heptose disaccharide
corresponding to heptoses I and II of the inner core region in many LPS.
7-O-Carbamoyl-l,d-heptose and d-glycero-alpha-d-manno-heptose were bound via
ring hydroxyl groups. Interactions with the side chain of inner core heptoses
provide a potential mechanism for the recognition of diverse types of LPS by
SP-D.
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