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PDBsum entry 1r14
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Sugar binding protein
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PDB id
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1r14
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Contents |
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* Residue conservation analysis
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References listed in PDB file
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Key reference
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Title
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Crystal structure of trimeric carbohydrate recognition and neck domains of surfactant protein a.
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Authors
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J.F.Head,
T.R.Mealy,
F.X.Mccormack,
B.A.Seaton.
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Ref.
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J Biol Chem, 2003,
278,
43254-43260.
[DOI no: ]
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PubMed id
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Abstract
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Surfactant protein A (SP-A), one of four proteins associated with pulmonary
surfactant, binds with high affinity to alveolar phospholipid membranes,
positioning the protein at the first line of defense against inhaled pathogens.
SP-A exhibits both calcium-dependent carbohydrate binding, a characteristic of
the collectin family, and specific interactions with lipid membrane components.
The crystal structure of the trimeric carbohydrate recognition domain and neck
domain of SP-A was solved to 2.1-A resolution with multiwavelength anomalous
dispersion phasing from samarium. Two metal binding sites were identified, one
in the highly conserved lectin site and the other 8.5 A away. The interdomain
carbohydrate recognition domain-neck angle is significantly less in SP-A than in
the homologous collectins, surfactant protein D, and mannose-binding protein.
This conformational difference may endow the SP-A trimer with a more extensive
hydrophobic surface capable of binding lipophilic membrane components. The
appearance of this surface suggests a putative binding region for
membrane-derived SP-A ligands such as phosphatidylcholine and lipid A, the
endotoxic lipid component of bacterial lipopolysaccharide that mediates the
potentially lethal effects of Gram-negative bacterial infection.
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Figure 4.
FIG. 4. Samarium binding sites in SP-A. A, stereoview of
the two sites in SP-A, where the bound lanthanide ions are shown
as spheres and labeled 1 and 2 for primary and auxiliary,
respectively. Coordination bonds appear as green dotted lines.
B, comparison of primary (P) and auxiliary (A) sites by backbone
superposition of CRD regions in SP-A (blue), SP-D (magenta), and
MBP (yellow). SP-D and MBP coordinates are from PDB accession
codes 1BO8 [PDB]
and 1KWT [PDB]
, respectively.
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Figure 5.
FIG. 5. Electrostatic surface representations of SP-A
(right) and SP-D (left). Top, calcium is present (one ion in
primary site for SP-A, one ion in primary site and two ions in
auxiliary sites for SP-D). Bottom, calcium is omitted from
model. Positive and negative charges are represented by blue and
red, respectively.
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The above figures are
reprinted
by permission from the ASBMB:
J Biol Chem
(2003,
278,
43254-43260)
copyright 2003.
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