RGD-independent binding of Russell's Viper venom Kunitz-type protease inhibitors to platelet GPIIb/IIIa receptor.

This study elucidates the platelet-modulating properties of two snake venom Kunitz-type serine protease inhibitors, Rusvikunin and Rusvikunin-II, from Russell's Viper venom, their native and reconstituted complexes, and two synthetic custom peptides (developed from the platelet-binding region of Rusvikunin-II) against mammalian platelet-rich plasma (PRP) and washed platelets. The Rusvikunins and their complexes demonstrated concentration-dependent deaggregation and aggregation of washed platelets independent of von Willebrand factor and/or fibrinogen requirement. At lower concentrations they abolished collagen and ADP-induced platelet aggregation, but at higher concentrations, they progressively decreased the inhibition of ADP-induced aggregation and potentiated the effect of collagen on PRP. Rusvikunin complex/Rusvikunin-II bound to and induced RGD-independent aggregation of α-chymotrypsin-treated platelets. Molecular docking studies suggested interaction of Rusvikunin-II and custom peptides with platelet GPIIb/IIIa receptor, which was validated by spectrofluorometry analysis and ELISA. This study reports, for the first time, an RGD-independent binding of a snake venom component to the platelet GPIIb/IIIa receptor.