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Changes in the platelet membrane glycoprotein IIb.IIIa complex during platelet activation
The Journal of Biological Chemistry
|September 15, 1985
Summary
Platelet activation exposes fibrinogen receptors on activated platelets. A new antibody, PAC-1, specifically binds to this activated glycoprotein IIb.IIIa complex, aiding in platelet research.
Area of Science:
- Hematology
- Immunology
- Molecular Biology
Background:
- Platelet activation leads to fibrinogen receptor expression on platelet surfaces.
- The fibrinogen receptor is located on the glycoprotein IIb.IIIa complex.
- Changes in the glycoprotein IIb.IIIa complex during platelet activation are not fully understood.
Purpose of the Study:
- To characterize a novel monoclonal antibody, PAC-1, that binds to activated platelets.
- To investigate the role of the glycoprotein IIb.IIIa complex in platelet activation and fibrinogen binding.
Main Methods:
- Development and characterization of a murine monoclonal anti-platelet antibody (PAC-1).
- Binding assays using radiolabeled PAC-1 on stimulated and unstimulated platelets.
- Western blot analysis and competitive binding assays with other antibodies.
- Assessment of PAC-1's effect on fibrinogen-mediated platelet aggregation.
Main Results:
- PAC-1 binds to activated platelets with high affinity (Kd = 5 nM) in a Ca2+-dependent manner.
- PAC-1 specifically recognizes the glycoprotein IIb.IIIa complex and does not bind to unstimulated platelets.
- PAC-1 binding is inhibited by calcium chelators and absent in thrombasthenic platelets.
- PAC-1 competitively inhibits fibrinogen binding and blocks fibrinogen-mediated platelet aggregation.
Conclusions:
- PAC-1 recognizes a Ca2+-dependent epitope on the activated glycoprotein IIb.IIIa complex, near the fibrinogen receptor.
- Platelet activation induces a conformational change in the glycoprotein IIb.IIIa complex, exposing both the fibrinogen receptor and the PAC-1 epitope.