Thromb Haemost 1997; 77(04): 735-740
DOI: 10.1055/s-0038-1656043
Platelets
Schattauer GmbH Stuttgart

Thrombin Interaction with Platelet GPIB: Role of the Heparin Binding Domain

Authors

  • Erica De Candia

    1   The Centro Ricerche Fisiopatologia dell’Emostasi, Istituto di Semeiotica Medica, Università Cattolica S. Cuore, Roma, Italia
  • Raimondo De Cristofaro

    1   The Centro Ricerche Fisiopatologia dell’Emostasi, Istituto di Semeiotica Medica, Università Cattolica S. Cuore, Roma, Italia
  • Lulgi De Marco

    Servizio Immunotrasfusionale e Analisi Cliniche, Centro di Riferimento Oncologico, Aviano, Pordenone, Italia
  • Moreno Mazzucato

    Servizio Immunotrasfusionale e Analisi Cliniche, Centro di Riferimento Oncologico, Aviano, Pordenone, Italia
  • Matilde Picozzi

    1   The Centro Ricerche Fisiopatologia dell’Emostasi, Istituto di Semeiotica Medica, Università Cattolica S. Cuore, Roma, Italia
  • Raffaele Landolfi

    1   The Centro Ricerche Fisiopatologia dell’Emostasi, Istituto di Semeiotica Medica, Università Cattolica S. Cuore, Roma, Italia
Further Information

Publication History

Received 25 June 1996

Accepted after revision 25 November 1996

Publication Date:
11 July 2018 (online)

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Summary

The platelet membrane glycoprotein lb (Gplb) has a high affinity binding site for α-thrombin whose occupancy is thought to positively modulate the thrombin-induced platelet activation. In this study, aimed at further characterizing the thrombin-GpIb interaction, two thrombin anion exosites referred to as “heparin binding site” (HBS) and “fibrino#gen recognition site” (FRS) were investigated as the possible domains involved in Gplb binding. The role of thrombin HBS was explored by performing binding measurements of 125I-α-thrombin to purified glycocalicin (GC), the extracytoplasmic portion of Gplb, in the presence of heparin as well as after chemical modifications of the thrombin heparin binding site (thrombin-HBS phosphopyridoxylation). These studies showed that a) thrombin binding to GC could be competitively inhibited by heparin and b) the equilibrium association constant for thrombin-GC interaction was reduced up to ten-fold by chemical modifications at the HBS. On the other hand, the role of FRS in the thrombin-GC interaction could be excluded by other experiments showing that GC in solution could not influence the interaction of α-thrombin with two substrates which bind to both the catalytic site and the fibrinogen recognition site: 1) the thrombin receptor peptide 38-60 (TR, L38-E60) and 2) the A α-chain of fibrinogen. Altogether these results demonstrated that GC interaction with thrombin involves the enzyme heparin binding site, whereas the fibrinogen recognition site does not play a significant role.