The Arg-Gly-Asp (RGD) recognition site of platelet glycoprotein IIb-IIIa on nonactivated platelets is accessible to high-affinity macromolecules

Y. Tomiyama, T. Tsubakio, R. S. Piotrowicz, Y. Kurata, J. C. Loftus, T. J. Kunicki

Research output: Contribution to journalArticle

69 Scopus citations

Abstract

We have characterized a murine IgG monoclonal antibody, OP-G2, specific for platelet glycoprotein (GP) IIb-IIIa (α(IIb)β3). OP-G2 Fab fragments inhibit fibrinogen-mediated platelet aggregation and competitively inhibit adenosine diphosphate-induced binding of 125I-fibrinogen to washed platelets. OP-G2 binding to GPIIb-IIIa is specifically inhibited by RGD- containing peptides but not the fibrinogen γ-chain carboxyterminal peptide, and OP-G2 Fab fragments, like RGD-containing peptides, alter the conformation of GPIIb-IIIa resulting in the expression of a ligand-induced binding site (LIBS) recognized by PMI-1. OP-G2 fails to bind to the recombinant Cam variant of GPIIb-IIIa (α(IIb)β(3Cam)) wherein an Asp119 to Tyr119 substitution in GPIIIa abrogates the ability to recognize RGD. These data indicate that OP-G2 recognizes an epitope at or in very close proximity to the RGD recognition site of GPIIb-IIIa and that, in every aspect tested, OP- G2 behaves like a macromolecular RGD ligand. Interestingly, two-color flow cytometry shows that OP-G2 IgG can bind to nonactivated platelets. Quantitative binding assays indicate that nonactivated platelets bind approximately 50,000 125I-OP-G2 molecules/platelet. Furthermore, the affinity of OP-G2 for platelets activated with thrombin is roughly fivefold higher (nonactivated, kd = 24.8 nmol/L; activated, kd = 4.9 nmol/L). These results suggest that the RGD recognition site of GPIIb-IIIa is available to macromolecules that contain RGD even on nonactivated platelets, provided that the affinity of the ligand is adequate.

Original languageEnglish (US)
Pages (from-to)2303-2312
Number of pages10
JournalBlood
Volume79
Issue number9
DOIs
StatePublished - 1992

ASJC Scopus subject areas

  • Biochemistry
  • Immunology
  • Hematology
  • Cell Biology

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