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PDBsum entry 1oph
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Hydrolase/hydrolase inhibitor
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PDB id
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1oph
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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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Canonical inhibitor-Like interactions explain reactivity of alpha1-Proteinase inhibitor pittsburgh and antithrombin with proteinases.
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Authors
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A.Dementiev,
M.Simonovic,
K.Volz,
P.G.Gettins.
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Ref.
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J Biol Chem, 2003,
278,
37881-37887.
[DOI no: ]
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PubMed id
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Abstract
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The serpin antithrombin is a slow thrombin inhibitor that requires heparin to
enhance its reaction rate. In contrast, alpha1-proteinase inhibitor (alpha1PI)
Pittsburgh (P1 Met --> Arg natural variant) inhibits thrombin 17 times faster
than pentasaccharide heparin-activated antithrombin. We present here x-ray
structures of free and S195A trypsin-bound alpha1PI Pittsburgh, which show that
the reactive center loop (RCL) possesses a canonical conformation in the free
serpin that does not change upon binding to S195A trypsin and that contacts the
proteinase only between P2 and P2'. By inference from the structure of heparin
cofactor II bound to S195A thrombin, this RCL conformation is also appropriate
for binding to thrombin. Reaction rates of trypsin and thrombin with alpha1PI
Pittsburgh and antithrombin and their P2 variants show that the low
antithrombin-thrombin reaction rate results from the antithrombin RCL sequence
at P2 and implies that, in solution, the antithrombin RCL must be in a similar
canonical conformation to that found here for alpha1PI Pittsburgh, even in the
nonheparin-activated state. This suggests a general, limited, canonical-like
interaction between serpins and proteinases in their Michaelis complexes.
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Figure 4.
FIG. 4. Thrombin and its interactions with inhibitors. a,
superposition, in stereo, of thrombin or S195A thrombin
structures of complexes with PPACK (gold) (Protein Data Bank
code 1HAI [PDB]
), with BPTI (green) (Protein Data Bank code 1BTH [PDB]
), and with heparin cofactor II (red) (Protein Data Bank code
1JMO [PDB]
), showing the identical conformations of all regions except the
surface loops flanking the active site, particularly the 60 loop
and 150 loop. b, stereo representation of the P5-P5' residues of
 [1]PI Pittsburgh (cyan)
from the noncovalent complex with S195A trypsin docked into the
thrombin structure found in the noncovalent complex of S195A
thrombin with heparin cofactor II (HCII in magenta).
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Figure 5.
FIG. 5. Antithrombin RCL conformation and modeled
interaction with thrombin. a, superposition, in stereo, of the
conformations of P5-P5' residues of [1]PI Pittsburgh from
its noncovalent complex with S195A trypsin and of
pentasacharide-activated antithrombin from a structure of the
heterodimer (orange) (Protein Data Bank code 1AZX [PDB]
). These RCLs are aligned such that the P1 residues have the
same horizontal position. The view is rotated 90°
anticlockwise relative to Fig. 1b. b, stereo representation of
the P5-P5' residues of antithrombin from the x-ray structure of
antithrombin heterodimer docked into the thrombin structure
found in the noncovalent complex of S195A thrombin with heparin
cofactor II, showing inappropriate positioning relative to the
catalytic triad and unfavorable interactions with surface loops.
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The above figures are
reprinted
by permission from the ASBMB:
J Biol Chem
(2003,
278,
37881-37887)
copyright 2003.
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