Structural basis for the anticoagulant activity of the thrombin-thrombomodulin complex.
The serine proteinase alpha-thrombin causes blood clotting through proteolytic cleavage of fibrinogen and protease-activated receptors and amplifies its own generation by activating the essential clotting factors V and VIII. Thrombomodulin, a transmembrane thrombin receptor with six contiguous epidermal growth factor-like domains (TME1-6), profoundly alters the substrate specificity of thrombin from pro- to anticoagulant by activating protein C. Activated protein C then deactivates the coagulation cascade by degrading activated factors V and VIII. The thrombin-thrombomodulin complex inhibits fibrinolysis by activating the procarboxypeptidase thrombin-activatable fibrinolysis inhibitor. Here we present the 2.3 A crystal structure of human alpha-thrombin bound to the smallest thrombomodulin fragment required for full protein-C co-factor activity, TME456. The Y-shaped thrombomodulin fragment binds to thrombin's anion-binding exosite-I, preventing binding of procoagulant substrates. Thrombomodulin binding does not seem to induce marked allosteric structural rearrangements at the thrombin active site. Rather, docking of a protein C model to thrombin-TME456 indicates that TME45 may bind substrates in such a manner that their zymogen-activation cleavage sites are presented optimally to the unaltered thrombin active site.
Fuentes-Prior
P
P
Max-Planck-Institut für Biochemie, Martinsried, Germany. fuentes@biochem.mpg.de
Iwanaga
Y
Y
Huber
R
R
Pagila
R
R
Rumennik
G
G
Seto
M
M
Morser
J
J
Light
D R
DR
Bode
W
W
D000595:Amino Acid Sequence; D000925:Anticoagulants / Q000737:chemistry*; D025901:Carboxypeptidase B2; D002268:Carboxypeptidases / Q000737:chemistry; D018360:Crystallography, X-Ray; D006801:Humans; D046911:Macromolecular Substances; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry; D011485:Protein Binding; D011486:Protein C / Q000737:chemistry; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D055672:Static Electricity; D013329:Structure-Activity Relationship; D013917:Thrombin / Q000737:chemistry* / Q000502:physiology; D018180:Thrombomodulin / Q000737:chemistry* / Q000502:physiology
D000925:Anticoagulants; D046911:Macromolecular Substances; D010446:Peptide Fragments; D011486:Protein C; D018180:Thrombomodulin; D002268:Carboxypeptidases; D025901:Carboxypeptidase B2; D013917:Thrombin