title: Proteolysis of platelet glycoprotein Ib by plasmin is facilitated by plasmin lysine-binding regions.
abstract: We have characterized the effects of plasmin on glycoprotein Ib (GpIb), a platelet membrane receptor for von Willebrand factor (vWF), and on glycocalicin, a fragment of the alpha chain of GpIb that contains the vWF-binding region. The addition of 4.5 X 10(-7) mol/L plasmin to washed platelets caused a time-dependent decrease in ristocetin-induced, vWF-dependent platelet agglutination. epsilon-Aminocaproic acid (EACA) inhibited plasmin release of glycocalicin-related antigen from washed platelets and preserved vWF-dependent platelet agglutination, thus indicating that the lysine-binding sites on plasmin facilitated its degradation of GpIb. To demonstrate a direct interaction between plasmin and the vWF-binding region of GpIb we incubated purified glycocalicin with plasmin. Plasmin degraded the glycocalicin into two small carbohydrate-poor peptides and into a larger carbohydrate-rich fragment. EACA was able to inhibit plasmin-mediated degradation of glycocalicin in a concentration-dependent fashion. These studies indicated that plasmin degradation of GpIb was due to a direct interaction between plasmin and GpIb and that this effect was mediated by the lysine-binding region of the plasmin molecule.
mesh_terms: D000614:Aminocaproates / Q000494:pharmacology; D001665:Binding Sites; D001792:Blood Platelets / Q000378:metabolism*; D005341:Fibrinolysin / Q000378:metabolism*; D006801:Humans; D008239:Lysine / Q000378:metabolism; D010974:Platelet Aggregation; D019038:Platelet Glycoprotein GPIb-IX Complex; D010980:Platelet Membrane Glycoproteins / Q000378:metabolism*; D012310:Ristocetin / Q000378:metabolism; D014841:von Willebrand Factor / Q000378:metabolism
chemical_list: D000614:Aminocaproates; D019038:Platelet Glycoprotein GPIb-IX Complex; D010980:Platelet Membrane Glycoproteins; C023592:glycocalicin; D014841:von Willebrand Factor; D012310:Ristocetin; D005341:Fibrinolysin; D008239:Lysine