Structural changes in platelet glycoprotein IIb/IIIa by plasmin: determinants and functional consequences.
Plasmin exposure modulates platelet aggregation responses, but a direct effect of plasmin on the platelet fibrinogen receptor, glycoprotein IIb/IIIa (GPIIb/IIIa), has never been conclusively shown in a plasma milieu. To examine this issue, we incubated platelets in platelet-rich plasma with plasmin and measured the effect of this treatment on platelet aggregation, fibrinogen binding, and the structural integrity of GPIIb/IIIa. Plasmin treatment reduced maximal reversible fibrinogen binding in a dose-dependent fashion, and this reduction in binding was accompanied by a correlative reduction in the maximal rate of aggregation. Immunoblots performed with polyclonal antibodies against GPIIb/IIIa showed that GPIIIa had been cleaved by plasmin, but this cleavage was detected only after subsequent degradation of the solubilized GPIIb/IIIa with Staphylococcus aureus V8 (Glu-C) endoprotease. Peptide sequence analysis showed that cleavage occurred at the lys444-pro445 bond in the first cysteine-rich repeat domain of GPIIIa a unique proteolytic event observed only in the presence of plasma fibrinogen. These observations suggest that plasmin modifies GPIIIa by a unique proteolytic event in plasma that is dependent on fibrinogen binding and, consequently, is accompanied by significant reductions in fibrinogen binding and aggregation response.
Pasche
B
B
Cardiology Divisions, Brigham and Women's Hospital, Boston, MA 02115.
Ouimet
H
H
Francis
S
S
Loscalzo
J
J
D000595:Amino Acid Sequence; D004305:Dose-Response Relationship, Drug; D005338:Fibrin Fibrinogen Degradation Products / Q000032:analysis; D005340:Fibrinogen / Q000378:metabolism; D005341:Fibrinolysin / Q000494:pharmacology*; D006801:Humans; D015151:Immunoblotting; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000032:analysis; D015539:Platelet Activation / Q000187:drug effects; D010974:Platelet Aggregation / Q000187:drug effects; D010980:Platelet Membrane Glycoproteins / Q000187:drug effects* / Q000378:metabolism
D005338:Fibrin Fibrinogen Degradation Products; D010446:Peptide Fragments; D010980:Platelet Membrane Glycoproteins; D005340:Fibrinogen; D005341:Fibrinolysin