ADP-dependent common receptor mechanism for binding of von Willebrand factor and fibrinogen to human platelets.

Publisher Website
Google Scholar
Abstract
Human von Willebrand factor (vWF) and fibrinogen are adhesive plasma glycoproteins essential for formation of a platelet hemostatic plug. The role of ADP and fibrinogen in binding of vWF to platelets in vitro was investigated. Binding of 125I-labeled vWF to human platelets separated from plasma proteins and treated with ADP was specific, and time and concentration dependent, reaching equilibrium at 20 min and approaching saturation at 12 .mu.g/ml. The binding was inhibited by EDTA and by prostaglandin I2, a known activator of platelet adenylate cyclase. A purine nucleotide affinity analog, 5''-p-fluorosulfonylbenzoyl adenosine (FSBA), which covalently modifies the ADP binding sites on the human platelet membrane, prevented binding of vWF induced with ADP, as well as with human thrombin and with ionophore A23187, agents known to cause platelet ADP secretion. By comparison, FSBA did not inhibit binding of vWF induced by ristocetin, indicating that the ristocetin mechanism is not dependent on ADP. Human fibrinogen inhibited in a competitive manner the ADP-induced binding of 125I-labeled vWF (9 .mu.g/ml) with an IC50 [median inhibitory concentration] of 25 .mu.g/ml. Conversely, unlabeled vWF inhibited ADP-induced binding of 125I-labeled fibrinogen (60 .mu.g/ml) with an IC50 of 16 .mu.g/ml. A synthetic dodecapeptide (MW, 1188), analogous with the specific platelet receptor recognition site of human fibrinogen .gamma. chain (.gamma.400-411), inhibited binding of both 125I-labeled vWF and 125I-labeled vWF to ristocetin-treated platelets. vWF and fibrinogen have a common receptor mechanism for their interaction with human platelets that is dependent on ADP occupancy of its binding sites and is recognized by the sequence of 12 amino acid residues at the carboxyl terminus of the human fibrinogen .gamma. chain.