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PDBsum entry 1sq0
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Blood clotting
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PDB id
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1sq0
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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 the wild-Type von willebrand factor a1-Glycoprotein ibalpha complex reveals conformation differences with a complex bearing von willebrand disease mutations.
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Authors
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J.J.Dumas,
R.Kumar,
T.Mcdonagh,
F.Sullivan,
M.L.Stahl,
W.S.Somers,
L.Mosyak.
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Ref.
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J Biol Chem, 2004,
279,
23327-23334.
[DOI no: ]
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PubMed id
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Abstract
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The adhesion of platelets to the subendothelium of blood vessels at sites of
vascular injury under high shear conditions is mediated by a direct interaction
between the platelet receptor glycoprotein Ibalpha (GpIbalpha) and the A1 domain
of the von Willebrand factor (VWF). Here we report the 2.6-A crystal structure
of a complex comprised of the extracellular domain of GpIbalpha and the
wild-type A1 domain of VWF. A direct comparison of this structure to a
GpIbalpha-A1 complex containing "gain-of-function" mutations, A1-R543Q
and GpIbalpha-M239V, reveals specific structural differences between these
complexes at sites near the two GpIbalpha-A1 binding interfaces. At the smaller
interface, differences in interaction show that the alpha1-beta2 loop of A1
serves as a conformational switch, alternating between an open alpha1-beta2
isomer that allows faster dissociation of GpIbalpha-A1, as observed in the
wild-type complex, and an extended isomer that favors tight association as seen
in the complex containing A1 with a type 2B von Willebrand Disease (VWD)
mutation associated with spontaneous binding to GpIbalpha. At the larger
interface, differences in interaction associated with the GpIbalpha-M239V
platelet-type VWD mutation are minor and localized but feature discrete
gamma-turn conformers at the loop end of the beta-hairpin structure. The
beta-hairpin, stabilized by a strong classic gamma-turn as seen in the mutant
complex, relates to the increased affinity of A1 binding, and the beta-hairpin
with a weak inverse gamma-turn observed in the wild-type complex corresponds to
the lower affinity state of GpIbalpha. These findings provide important details
that add to our understanding of how both type 2B and platelet-type VWD
mutations affect GpIbalpha-A1 binding affinity.
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Figure 2.
FIG. 2. Superposition of GpIb  -A1 and GpIb -M239V/A1-R543Q
complexes. The GpIb is green, and the GpIb
-bound wild-type A1
domain is gold. Regions of GpIb -M239V that differ most
extensively from wild-type A1 are red (  -switch region,
Val227-Ser241; cysteine loop, Asp249-Phe^254) and the remainder
of the molecule is white. The region of A1-R543Q with the most
notable change in conformation compared with the wild-type A1
structure is blue ( 1- 2 loop, Arg543-Arg552),
and the remainder of A1 is white. The structure of mutant
complex is derived from PDB code 1M10 [PDB]
(35).
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Figure 5.
FIG. 5. Superposition of unliganded A1, wild-type GpIb -A1 and
GpIb -M239V-A1-R543Q.
Rearrangement of the 1- 2 loop region of A1 is
highlighted. The 1- 2 loop region of
unliganded A1 (33)(shown in purple) adopts an intermediate
conformation between the closed conformation of 1- 2 in the
mutant complex (blue) and the open conformation of 1- 2 in the
wild-type complex (gold).
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The above figures are
reprinted
by permission from the ASBMB:
J Biol Chem
(2004,
279,
23327-23334)
copyright 2004.
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Secondary reference #1
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Title
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Crystal structure of the gpibalpha-Thrombin complex essential for platelet aggregation.
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Authors
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J.J.Dumas,
R.Kumar,
J.Seehra,
W.S.Somers,
L.Mosyak.
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Ref.
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Science, 2003,
301,
222-226.
[DOI no: ]
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PubMed id
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Figure 1.
Fig. 1. Ribbon representation of two GpIb  -thrombin
complexes related by crystal symmetry. The asymmetric unit
contains one molecule of GpIb and one molecule
of thrombin, which associate as a crystallographically
independent complex. GpIb is colored green,
except for the anionic region (Asp269 to sTyr279), which is in
red, and a region corresponding to peptide Phe^216 to Thr240 is
in gold. The thrombin heavy chain is colored light blue, with
exosite I (Lys21 to Gln24, Tyr71 to Asn74, and Lys106 to Lys107)
and exosite II (Arg98, Arg123, and Arg245 to Lys252) colored
dark blue (numbering for thrombin used here starts at the first
residue of the mature heavy chain of human thrombin, and
addition of 363 converts the numbering to that of prothrombin;
see supporting online text for chymotrypsin numbering). The
thrombin light chain (residues 1 to 29) is in gray.
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Figure 4.
Fig. 4. Schematic diagram of thrombin and GpIb-IX complexes, in
which GpIb and thrombin
molecules are arranged as an adhesive ribbon structure observed
in the crystals (color coding is the same as in Figs. 1, 2, 3).
The region between the last residue observed in GpIb (sTyr279) and the
stalk region is shown as green dotted lines. GpIb is
covalently attached to GpIbß by means of a disulfide bond
near the extracellular surface of the membrane, and GpIb-IX-V is
present as a noncovalent 2:2:1 complex on the platelet surface
(1, 16). GpV is not included in the model, because recent
evidence suggests that the extracellular domain of GpV (removed
from the receptor complex by thrombin cleavage early in the
aggregation process) functions as an inhibitor of platelet
activation and aggregation (14). The model is further simplified
as a 1:1 GpIb-IX complex. The orientation of multiple complexes
with respect to membranes is deduced from the location of the
C-terminal end of the GpIb fragment relative
to the thrombin-binding domains. Simultaneous binding of two
GpIb receptors at two
polar ends of the bridging thrombin molecule stabilizes
antiparallel orientations of adjacent receptors and ensures that
these neighboring receptors extend their C-terminal ends in
opposite directions. The long axis of each GpIb receptor is
oriented roughly normal to the platelet membrane, with the
C-terminal end positioned toward the membrane and extending away
from sites of thrombin attachment. A long O-glycosylated
mucin-like stalk (not drawn to scale) of the GpIb receptor places
its thrombin binding domain  45 nm away from the
platelet membrane surface (39); thus, platelet membranes that
are about 100 nm apart could be linked together by binding
interactions between GpIb and thrombin.
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The above figures are
reproduced from the cited reference
with permission from the AAAs
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