Ca2+-mediated association of glycoprotein G (thrombinsensitive protein, thrombospondin) with human platelets.
Washed human platelets suspended in buffers containing either 1.8 mM Ca2+ and 0.49 mM Mg2+ or 1 mM EDTA were treated with human alpha-thrombin to induce secretion. Glycoprotein G, a major glycoprotein in alpha-granules, was quantitatively secreted from platelets activated in the EDTA-containing buffer but remained with the platelet in the presence of Ca2+ and Mg2+. Addition of Ca2+ to the platelets that were activated in the presence of EDTA caused glycoprotein G to bind to platelets. To determine if glycoprotein G is expressed on the membrane surface of the activated platelet, platelets were rapidly labeled by a method employing lactoperoxidase-catalyzed iodination. Although glycoprotein G was barely detected on the surface of unstimulated platelets, labveling 1 min after thrombin treatment showed that glycoprotein G rapidly became one of the prominent surface proteins. These findings show that an alpha-granule protein, glycoprotein G, is one of the major glycoproteins on the membrane surface of thrombin-activated platelets and that its binding is dependent on divalent cations.
D000328:Adult; D001792:Blood Platelets / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology*; D004492:Edetic Acid / Q000494:pharmacology; D006023:Glycoproteins / Q000097:blood*; D006801:Humans; D008274:Magnesium / Q000494:pharmacology; D008970:Molecular Weight; D010974:Platelet Aggregation; D011485:Protein Binding; D013917:Thrombin; D019699:Thrombospondins
D006023:Glycoproteins; D019699:Thrombospondins; D004492:Edetic Acid; D013917:Thrombin; D008274:Magnesium; D002118:Calcium