Late-fibrin(ogen) fragment E modulates human alpha-thrombin specificity.
Fibrinogen contains at least two independent sites having demonstrable affinity for alpha-thrombin. One of these two sites, located in the fibrin E domain, binds to structures within the anion-binding exosite of alpha-thrombin. Taking advantage of its solubility, we have used late-fibrin(ogen) fragment E in competition experiments to examine its effect on alpha-thrombin specificity. We show that fragment E modulates alpha-thrombin enzymic activity towards small synthetic substrates, suggesting that fibrin-thrombin interaction might induce subtle changes in the conformation near the catalytic center of the enzyme. In addition, fragment E behaved as a competitive inhibitor of alpha-thrombin-catalyzed fibrinopeptide-A cleavage (Ki = 5.2 +/- 1.3 microM), indicating that alpha-thrombin interaction with the fibrin moiety of fibrinogen makes a major contribution to the efficacy of fibrinogen hydrolysis. Fragment E inhibited alpha-thrombin-induced serotonin release by platelets (concentration required to obtain 50% inhibition, IC50 = 10 microM) and alpha-thrombin binding to GPIb. Fragment E competitively inhibited alpha-thrombin binding to thrombomodulin (Ki = 18.3 +/- 0.8 microM) but did not inhibit protein-C activation in the absence of thrombomodulin. The data are consistent with the proposal that fibrin, platelet GPIb and thrombomodulin bind to overlapping, but probably non-identical sites, while protein C binds to an independent site on alpha-thrombin.
Laboratoire de Recherche sur l'Hémostase et la Thrombose, Faculté Xavier Bichat, Paris, France.
M C
MC
Bouton
M
M
Jandrot-Perrus
A
A
Bezeaud
M C
MC
Guillin
D000595:Amino Acid Sequence; D001665:Binding Sites; D005338:Fibrin Fibrinogen Degradation Products / Q000494:pharmacology*; D006801:Humans; D008969:Molecular Sequence Data; D010974:Platelet Aggregation / Q000187:drug effects; D011486:Protein C / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000378:metabolism; D018179:Receptors, Thrombin; D013917:Thrombin / Q000378:metabolism* / Q000494:pharmacology
D005338:Fibrin Fibrinogen Degradation Products; D011486:Protein C; D011956:Receptors, Cell Surface; D018179:Receptors, Thrombin; C018543:fibrinogen fragment E; D013917:Thrombin