Tokaracetin, a new platelet antagonist that binds to platelet glycoprotein Ib and inhibits von Willebrand factor-dependent shear-induced platelet aggregation

T. Kawasaki, Y. Taniuchi, N. Hisanichi, Y. Fujimura, M. Suzuki, K. Titani, Y. Sakai, S. Kaku, N. Satoh, T. Takenaka, M. Handa, Y. Sawai

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Abstract

A new platelet antagonist, tokaracetin, was isolated from the venom of Trimeresurus tokarensis by ion-exchange chromatography, heparin-Sepharose chromatography and hydrophobic HPLC. The purified protein showed an apparent molecular mass on SDS/PAGE of 28.9 kDa under non-reducing conditions. On reduction, 16.1 and 15.4 kDa subunits were observed, suggesting that the molecule is a heterodimer. Tokaracetin inhibited the binding of 125I-labelled bovine von Willebrand factor (vWF) and 125I-labelled human vWF in the presence of botrocetin to fixed human platelets. It did not block ADP-, collagen- or thrombin receptor agonist peptide-induced platelet aggregation in human platelet-rich plasma (PRP), or induce platelet agglutination in PRP. On reduction, tokaracetin lost its inhibitory activity on the agglutination of fixed human platelets by bovine vWF. 125I-Tokaracetin specifically bound to washed human platelets with high affinity (K(d) 3.9 ± 1.4 nM) at 47440 ± 2780 binding sites per platelet. Binding of tokaracetin to fixed human platelets was reversible, and was inhibited by monoclonal antibody GUR83-35, which is directed against the N-terminal vWF-binding domain of human glycoprotein Ib (GPIb). Tokaracetin completely inhibited vWF-dependent shear-induced platelet aggregation in PRP at 3 μg/ml. The N-terminal amino acid sequences of tokaracetin subunits showed a high degree of identity with those of alboaggregin-B. These results suggest that this new platelet antagonist may be a useful tool in the development of specific inhibitors of the vWF-GPIb interaction.

Original languageEnglish
Pages (from-to)947-953
Number of pages7
JournalBiochemical Journal
Volume308
Issue number3
DOIs
Publication statusPublished - 1995 Jan 1

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ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

Cite this

Kawasaki, T., Taniuchi, Y., Hisanichi, N., Fujimura, Y., Suzuki, M., Titani, K., Sakai, Y., Kaku, S., Satoh, N., Takenaka, T., Handa, M., & Sawai, Y. (1995). Tokaracetin, a new platelet antagonist that binds to platelet glycoprotein Ib and inhibits von Willebrand factor-dependent shear-induced platelet aggregation. Biochemical Journal, 308(3), 947-953. https://doi.org/10.1042/bj3080947