Structural changes in platelet glycoprotein IIb/IIIa by plasmin:
determinants and functional consequences
B Pasche, H Ouimet, S Francis and J Loscalzo
Cardiology Divisions, Brigham and Women's Hospital, Boston, MA 02115.
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.
Volume 83,
Issue 2,
pp. 404-414,
01/15/1994
Copyright © 1994 by The American Society of Hematology
