Complete amino acid sequence and identification of the platelet glycoprotein Ib-binding site of jararaca GPIb-BP, a snake venom protein isolated from Bothrops jararaca.

Jararaca GPIb-BP, a snake venom protein composed of alpha and beta subunits purified from Bothrops jararaca, binds to platelet glycoprotein (GP)Ib and functions as a receptor blocker for von Willebrand factor binding to GPIb (Fujimura, Y., Ikeda, Y., Miura, S., Yoshida, E., Shima, H., Nishida, S., Suzuki, M., Titani, K., Taniuchi, Y., and Kawasaki, T. (1995) Thromb. Haemostasis 74, 743-750). We present here the entire 142- and 123-residue amino acid sequence of the respective alpha and beta subunits and also demonstrate that the platelet GPIb-binding site resides on the beta and not on the alpha subunit based on an enzyme-linked immunosorbent assay using biotin-labeled jararaca GPIb-BP and competing ligands. Sequences of the alpha and beta subunits were determined by analysis of the intact S-pyridylethylated proteins and their peptides generated by digestion with Achromobacter protease I, Staphyloccocus aureus V8 protease, pepsin, endoproteinase Asp-N, or L-1-tosylamino-2-phenylethyl chloromethyl ketone-trypsin. A 38-39% identity of amino acid sequence between the alpha and beta subunits of jararaca GPIb-BP was observed, as well as a high degree of sequence identities (38-64%) with the respective subunits of botrocetin (Usami, Y., Fujimura, Y., Suzuki, M., Ozeki, Y., Nishio, K., Fukui, H., and Titani, K (1993) Proc. Natl. Acad. Sci. U. S. A. 90, 928-932) and the beta-chain of echicetin (Peng, M., Holt, J. C., and Niewiarowski, S. (1994) Biochem. Biophys. Res. Commun. 205, 68-72).