Localization of the domains of fibrin involved in binding to platelets.
The molecular basis of platelet-fibrin interactions has been investigated by using synthetic peptides as potential inhibitors of fibrin protofibril and fibrinogen binding to ADP-stimulated platelets, adhesion of fibrin fibers to the platelet surface, and platelet-mediated clot retraction. Synthetic peptides of sequence RGDS and HHLGGAKQAGDV, corresponding to regions of the fibrinogen alpha- and gamma-chains previously identified as platelet recognition sites, inhibited the binding of radiolabelled soluble fibrin oligomers to ADP-stimulated platelets with IC50 values of 10 and 40 microM, respectively. Synthetic GPRP and GHRP, corresponding to the N-terminal tripeptide sequence of the fibrin alpha-chains and the tetrapeptide sequence of the beta-chains, respectively, were minimally effective in blocking soluble fibrin polymer binding to ADP-stimulated platelets. Platelet functions which are unique to the three-dimensional fibrin network were examined by measurements of the extent of adhesion of fluorophore-labelled fibrin to platelets with a microfluorimetric technique and by light scattering measurements of the time course of clot retraction. Inhibition of fibrin-platelet adhesion by RGDS, HHLGGAKQAGDV and GHRP exhibited a similar, linear dependence reaching 1/2 maximum at about 200 microM, suggesting nonspecific effects. GPRP inhibited fibrin assembly but did not appear to have specific effects on fibrin-platelet adhesion. Only RGDS effected clot retraction, causing a 4-6-fold decrease in rate at 230 microM. These results indicate that fibrinogen and fibrin protofibrils, which are obligatory intermediates on the fibrin assembly pathway, share a set of common platelet recognition sites located at specific regions of the alpha- and gamma-chains of the multinodular fibrin(ogen) molecules. The RGDS site is also involved in mediating interactions between the three-dimensional fibrin network and stimulated platelets.
Hantgan
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Department of Biochemistry, Bowman Gray School of Medicine of Wake Forest University, Winston-Salem, NC 27103.
D000595:Amino Acid Sequence; D001665:Binding Sites; D001667:Binding, Competitive; D001792:Blood Platelets / Q000378:metabolism*; D005337:Fibrin / Q000378:metabolism*; D005340:Fibrinogen / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D011956:Receptors, Cell Surface / Q000378:metabolism*; D018000:Receptors, Peptide
D011956:Receptors, Cell Surface; D018000:Receptors, Peptide; C048650:fibrin-fibrinogen degradation products receptor; D005337:Fibrin; D005340:Fibrinogen