Interaction of von Willebrand factor with platelets activated by thrombin or a synthetic 7-amino acid peptide derived from the cleaved thrombin receptor.
Thrombin and the 7-mer agonist peptide from its receptor (SFLLRNP) were compared for their ability to promote the binding of vWF to platelets. Identical Ca(2+)-dependence and kinetics of activation were observed. Studies of inhibition of the binding by a series of monoclonal antibodies to GPIb, GPIIb/IIIa and vWF and experiments performed using platelets from patients with Glanzmann thrombasthenia or Bernard-Soulier syndrome enabled to identify GPIIb/IIIa as the receptor of vWF. Binding isotherms of vWF in the presence of an excess of either agonist yielded a similar number of binding sites but an apparent dissociation constant slightly but consistently higher with the 7-mer peptide than with thrombin. The latter point was confirmed by studying the binding of limiting amounts of vWF to platelets as a function of the agonist concentration. The lower affinity in the presence of 7-mer peptide was not corrected by adding increasing amounts of FPR-thrombin, a derivative with irreversibly blocked active site but retaining the binding properties of the active enzyme. Conversely, the higher affinity observed with thrombin was decreased when platelets were treated with Serratia protease which selectively cleaved GPIb but did not affect the function of the thrombin receptor and GPIIb/IIa. Our data thus suggest that both the 7-mer peptide and thrombin are able to induce the assembly of functional GPIIb/IIIa.(ABSTRACT TRUNCATED AT 250 WORDS)
Minckes
O
O
INSERM U. 143, Institut de Pathologie Cellulaire, Hôpital de Bicêtre, le Kremlin-Bicêtre, France.
Freyssinet
J M
JM
Rouault
C
C
Pavirani
A
A
Rasmussen
U
U
Boyer-Neumann
C
C
Meyer
D
D
Girma
J P
JP
D001606:Bernard-Soulier Syndrome / Q000473:pathology; D001792:Blood Platelets / Q000378:metabolism*; D004347:Drug Interactions; D006801:Humans; D010446:Peptide Fragments / Q000494:pharmacology*; D011485:Protein Binding / Q000187:drug effects; D018179:Receptors, Thrombin / Q000378:metabolism*; D013915:Thrombasthenia / Q000473:pathology; D013917:Thrombin / Q000494:pharmacology*; D014841:von Willebrand Factor / Q000378:metabolism*
D010446:Peptide Fragments; D018179:Receptors, Thrombin; D014841:von Willebrand Factor; D013917:Thrombin