Thromb Haemost 1993; 69(05): 490-495
DOI: 10.1055/s-0038-1651639
Original Article
Platelets
Schattauer GmbH Stuttgart

Effects of Hybrid Peptide Analogs to Receptor Recognition Domains on α- and γ-Chains of Human Fibrinogen on Fibrinogen Binding to Platelets

Authors

  • Hiroshi Mohri

    The First Department of Internal Medicine, Yokohama City University School of Medicine, Yokohama, Japan
  • Takao Ohkubo

    The First Department of Internal Medicine, Yokohama City University School of Medicine, Yokohama, Japan
Further Information

Publication History

Received 07 September 1992

Accepted after revision 21 December 1992

Publication Date:
25 July 2018 (online)

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Summary

We synthesized a series of hybrid peptides that correspond to the γ-chain dodecapeptide (400-411), variable numbers of glycine residues, and the RGDS peptide [Y-HHLGGAK-QAGDV(G) n RGDS] to investigate the relationship of these receptor recognition domains of fibrinogen to platelet membrane glycoprotein IIb/IIIa. The tetrapeptide RGDS, the GRGDSPA peptide and the dodecapeptide inhibited binding of fibrinogen to GPIIb/IIIa by 50% (IC50) at concentrations of 17 ± 1.6 μM, 15 ± 2.1 μM, and 87 ± 6.8 μM, respectively. The inhibitory effect of hybrid peptides increased as the number of glycine residues increased, plateauing with 9-11 glycine residues in hybrid peptide analogs, which had an IC50 of 0.68 ± 0.14 μM. These hybrid peptides completely inhibited the binding of fibrinogen to activated platelets when used in sufficient concentrations. The peptide Y-HHLGGAKQAGDV(G)9RGDS blocked ADP-induced aggregation in citrated platelet-rich plasma with IC50 of 3.5 ± 0.6 μM. When the peptide Y-HHLGGAK-QAGDV(G)9RGDS was labeled with 125I to quantify its binding to platelets, maximal binding was observed within 30 min. The binding sites of the hybrid peptide were 43,600 molecules/platelet (K d = 3.1 ± 0.5 × 10-7 M) to stimulated platelets and 12,500 molecules/platelet (K d = 1.4 ± 0.2 × 10-7 M) to nonstimulated platelets. The hybrid peptides had the same binding affinity to platelets as fibrinogen and inhibited platelet function. Moreover, anti-GPIIb/IIIa antibody inhibited the binding of the labeled hybrid peptide to stimulated platelets. These results indicate that in the native fibrinogen molecule the presence of both RGD sequence or γ-chain domain at optimal distances increased the binding affinity to GPIIb/IIIa. These domains may be the source of hybrid peptide, expanding a new class of platelet inhibitors that act at membrane receptors for adhesive proteins.