Interaction of thrombospondin with platelet glycoproteins GPIa-IIa and GPIIb-IIIa.
The interaction of human thrombospondin (TSP) with GPIa-IIa and GPIIb-IIIa was studied. The binding for both proteins became time-independent after 60 min. A 7-fold excess concentration of unlabelled GPIa-IIa added either initially, or after time-dependent binding, resulted in a 50% inhibition of GPIa-IIa bound to TSP. GPIa-IIa and GPIIb-IIIa specifically bound TSP since: (a) the binding of GPIIb-IIIa to TSP was dependent on the presence of 1 mM MgCl2 and 1 mM CaCl2, whereas binding of GPIa-IIa was ion-independent. (b) The binding was saturable, with dissociation constants of 0.69 +/- 0.17 microM and 3.77 +/- 1.02 microM for GPIa-IIa and GPIIb-IIIa respectively. (c) GPIIb-IIIa and GPIa-IIa did not significantly bind to BSA. (d) GPIIb-IIIa bound fibrinogen ion-specifically, whereas little or no binding of GPIa-IIa was detectable. (e) Both GPIIb-IIIa and GPIa-IIa bound collagen in an ion-independent manner. (f) GPIIb-IIIa did not compete with GPIa-IIa for binding to TSP. (g) Binding of GPIa-IIa to TSP was inhibited with anti-(GPIa-IIa) (6F1), whereas mouse IgG and anti-(GPIIb-IIIa) (AP-2) had no effect. (h) The interaction of GPIa-IIa with TSP is 5.5-fold more favourable than that of GPIIb-IIIa suggesting that GPIa-IIa may be a preferred binding protein for TSP-mediated platelet adhesion.
Kowalska
M A
MA
Department of Medicine, Medical College of Pennsylvania, Philadelphia 19129.
Tuszynski
G P
GP
D000911:Antibodies, Monoclonal / Q000494:pharmacology; D001667:Binding, Competitive; D002122:Calcium Chloride / Q000494:pharmacology; D003094:Collagen / Q000378:metabolism; D005340:Fibrinogen / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D015636:Magnesium Chloride / Q000494:pharmacology; D008562:Membrane Glycoproteins / Q000378:metabolism*; D010980:Platelet Membrane Glycoproteins / Q000276:immunology / Q000378:metabolism*; D019699:Thrombospondins
D000911:Antibodies, Monoclonal; D008562:Membrane Glycoproteins; D010980:Platelet Membrane Glycoproteins; D019699:Thrombospondins; D015636:Magnesium Chloride; D005340:Fibrinogen; D003094:Collagen; D002122:Calcium Chloride