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 sub units purified from Bothrops jararaca, binds to platelet glycoprotein (GP)Ib and functions as a receptor blocker for von Willebrand factor b inding 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 entir e 142- and 123-residue amino acid sequences of the respective alpha an d beta subunits and also demonstrate that the platelet GPIb-binding si te 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 deter mined by analysis of the intact S-pyridylethylated proteins and their peptides generated by digestion with Achromobacter protease I, Staphyl occocus aureus V8 protease, pepsin, endoproteinase Asp-N, or L-1-tosyl amino-2-phenylethyl chloromethyl ketone-trypsin. A 38-39% identity of amino acid sequence between the alpha and beta subunits of jararaca GP Ib-BP was observed, as well as a high degree of sequence identities (3 8-64%) with the respective subunits of botrocetin (Usami, Y., Fujimura , Y., Suzuki, M., Ozeki, Y., Nishio, K., Fukui, H., and Titani, K (199 3) Pr oc. 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).