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PDBsum entry 1jmj
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Blood clotting
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PDB id
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1jmj
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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 structures of native and thrombin-Complexed heparin cofactor ii reveal a multistep allosteric mechanism.
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Authors
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T.P.Baglin,
R.W.Carrell,
F.C.Church,
C.T.Esmon,
J.A.Huntington.
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Ref.
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Proc Natl Acad Sci U S A, 2002,
99,
11079-11084.
[DOI no: ]
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PubMed id
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Abstract
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The serine proteases sequentially activated to form a fibrin clot are inhibited
primarily by members of the serpin family, which use a unique beta-sheet
expansion mechanism to trap and destroy their targets. Since the discovery that
serpins were a family of serine protease inhibitors there has been controversy
as to the role of conformational change in their mechanism. It now is clear that
protease inhibition depends entirely on rapid serpin beta-sheet expansion after
proteolytic attack. The regulatory advantage afforded by the conformational
mobility of serpins is demonstrated here by the structures of native and S195A
thrombin-complexed heparin cofactor II (HCII). HCII inhibits thrombin, the final
protease of the coagulation cascade, in a glycosaminoglycan-dependent manner
that involves the release of a sequestered hirudin-like N-terminal tail for
interaction with thrombin. The native structure of HCII resembles that of native
antithrombin and suggests an alternative mechanism of allosteric activation,
whereas the structure of the S195A thrombin-HCII complex defines the molecular
basis of allostery. Together, these structures reveal a multistep allosteric
mechanism that relies on sequential contraction and expansion of the central
beta-sheet of HCII.
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Figure 2.
Fig 2. Crystallographic structure of the HCII-thrombin
Michaelis complex. (a) A stereo representation of the Michaelis
complex between S195A thrombin (cyan) and HCII (colored as
described for Fig. 1), with the  -loop in front and the
60-insertion loop behind the reactive center loop. (b) Stereo
representation of the electron density covering the portion of
the acidic tail (yellow) that interacts with thrombin (magenta),
contoured at 1  . (c) The subsite
interactions between the reactive center residues of HCII (rods)
and the active site cleft of thrombin (surface representation)
are extensive and complementary in both electrostatic (Left,
negative potential is red, and positive is blue) and hydrophobic
(Right, green for hydrophobic side chains) properties. (d) The
interaction between exosite I of thrombin (surface
representation as described for c) and the hirudin-like
N-terminal tail of HCII (rods, the side chains of residues not
interacting with thrombin were removed for clarity) is primarily
hydrophobic. The only ionic interactions are between Asp-70 and
Asp-72 of HCII and L110H of thrombin. Sulfated tyrosines, 60 and
73, make no contacts with thrombin and are not shown.
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Figure 3.
Fig 3. The sequential mechanism of GAG-mediated thrombin
inhibition by HCII (as described in Results and Discussion). For
a video of this mechanism, see Movie 2.
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