The rhodocetin αβ subunit targets GPIb and inhibits von Willebrand factor induced platelet activation

Rhodocetin, a heterotetrameric snake C-type lectin from Calloselasma rhodostoma is a specific antagonist of α2β1 integrin. Its γδ subunit is responsible for binding to α2β1 integrin. In this study we show that the rhodocetin αβ subunit can bind to platelet glycoprotein GPIb. Binding of the rhodocetin αβ subunit does not depend on divalent cations. When added to washed human platelets the rhodocetin αβ subunit effectively inhibits platelet aggregation induced by von Willebrand factor plus ristocetin. In contrast, it does not affect collagen-induced platelet activation. By itself the rhodocetin αβ subunit does not induce any changes when added to washed platelets or platelet-rich plasma. However, rhodocetin αβ, after biotinylation and cross-linkage with avidin induces small platelet agglutination but not aggregation. These agglutinated platelets change their pattern of protein tyrosine phosphorylation slightly as kinase p72SYK but not p125FAK is phosphorylated.