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PDBsum entry 2pf5
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Cell adhesion
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PDB id
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2pf5
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Contents |
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88 a.a.
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94 a.a.
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96 a.a.
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85 a.a.
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References listed in PDB file
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Key reference
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Title
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Plasticity of the tsg-6 ha-Binding loop and mobility in the tsg-6-Ha complex revealed by nmr and x-Ray crystallography.
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Authors
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V.A.Higman,
C.D.Blundell,
D.J.Mahoney,
C.Redfield,
M.E.Noble,
A.J.Day.
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Ref.
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J Mol Biol, 2007,
371,
669-684.
[DOI no: ]
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PubMed id
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Abstract
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Tumour necrosis factor-stimulated gene-6 (TSG-6) is a glycosaminoglycan-binding
protein expressed during inflammatory and inflammation-like processes.
Previously NMR structures were calculated for the Link module of TSG-6
(Link_TSG6) in its free state and when bound to an octasaccharide of hyaluronan
(HA(8)). Heparin was found to compete for HA binding even though it interacts at
a site that is distinct from the HA-binding surface. Here we present
crystallography data on the free protein, and (15)N NMR relaxation data for the
uncomplexed and HA(8)-bound forms of Link_TSG6. Although the Link module is
comparatively rigid overall, the free protein shows a high degree of mobility in
the beta4/beta5 loop and at the Cys47-Cys68 disulfide bond, both of which are
regions involved in HA binding. When bound to HA(8), this dynamic behaviour is
dampened, but not eliminated, suggesting a degree of dynamic matching between
the protein and sugar that may decrease the entropic penalty of complex
formation. A further highly dynamic residue is Lys54, which is distant from the
HA-binding site, but was previously shown to be involved in heparin binding.
When HA is bound, Lys54 becomes less mobile, providing evidence for an
allosteric effect linking the HA and heparin-binding sites. A mechanism is
suggested involving the beta2-strand and alpha2-helix. The crystal structure of
free Link_TSG6 contains five molecules in the asymmetric unit that are highly
similar to the NMR structure and support the dynamic behaviour seen near the
HA-binding site: they show little or no electron density for the beta4/beta5
loop and display multiple conformations for the Cys47-Cys68 disulfide bond. The
crystal structures were used in docking calculations with heparin. An extended
interface between a Link_TSG6 dimer and heparin 11-mer was identified that is in
excellent agreement with previous mutagenesis and calorimetric data, providing
the basis for further investigation of this interaction.
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Figure 1.
Figure 1. ^15N{^1H} NOE as I[sat]/I[nonsat] for free (black)
and HA[8]-bound (red) Link_TSG6. Data were collected at 500 MHz.
The secondary structure organisation of Link_TSG6 is indicated
along the top of the graph. Also indicated is the B-factor as a
function of residue for chains A (yellow), B (light green), C
(cyan), D (light blue) and E (bright blue) of the crystal
structure of Link_TSG6.
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Figure 4.
Figure 4. (a) Superposition of chains A–E (yellow, light
green, cyan, light blue, bright blue, respectively) of the
crystal structure of Link_TSG6 showing the β4/β5 loop region.
(b) Superposition of chains A–E of the crystal structure of
Link_TSG6 as in (a) with the lowest energy NMR structures of
free (magenta) and HA[8]-bound (purple) Link_TSG6. (c) and (d)
are as (a) and (b), respectively, but showing the β4/β5 loop
region only.
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The above figures are
reprinted
by permission from Elsevier:
J Mol Biol
(2007,
371,
669-684)
copyright 2007.
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