Echicetin, a heterodimeric protein from the venom of Echis carinatus, binds to platelet glycoprotein Ib (GPIb) and so inhibits platelet aggregation or agglutination induced by various platelet agonists acting via GPIb. The amino acid sequence of the β subunit of echicetin has been reported and found to belong to the recently identified snake venom subclass of the C-type lectin protein family. Echicetin α and β subunits were purified. N-terminal sequence analysis provided direct evidence that the protein purified was echicetin. The paper presents the complete amino acid sequence of the α subunit and computer models of the α and β subunits. The sequence of α echicetin is highly similar to the α and β chains of various heterodimeric and homodimeric C-type lectins. Neither of the fully reduced and alkylated α or β subunits of echicetin inhibited the platelet agglutination induced by von Willebrand factor–ristocetin or α-thrombin. Earlier reports about the inhibitory activity of reduced and alkylated echicetin β subunit might have been due to partial reduction of the protein.

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