Characterization of a ligand-attenuated binding site on glycoprotein IIb/IIIa

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Characterization of Glycoproteins with the Immunoglobulin Fold by X-Ray Crystallography and Biophysical Techniques
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Characterization of Glycoproteins with the Immunoglobulin Fold by X-Ray Crystallography and Biophysical Techniques

Published on: July 5, 2018

Martin J Quinn1, John Fullard, Steven Kerrigan

  • 1Centre for Cardiovascular Science, The Royal College of Surgeons in Ireland, Dublin, Ireland.

Thrombosis and Haemostasis
|November 13, 2002
PubMed

We describe an epitope on the platelet integrin, GPIIb/IIIa, identified by the monoclonal antibody, 4F8, which is attenuated by small-molecule GPIIb/IIIa ligands. 4F8 did not bind to the ligand binding pocket as it did not compete with a radiolabelled antagonist, (3)H-SC-52012. This indicates that the 4F8 epitope behaves as a ligand-attenuated binding site (LABS). Ligand-induced attenuation of 4F8 was an active process as it was prevented by pretreating platelets with cytochalasin D and reduced by prostaglandin E(1) or inhibition of protein kinase C. Disappearance of the epitope was required for full platelet activation as 4F8 prevented platelet aggregation without inhibiting fibrinogen binding. These results suggest a model where disappearance of the 4F8 epitope is a secondary event required for full "outside-in" signaling through GPIIb/IIIa.

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