Isolation and Characterization of EMS16, a C-Lectin Type Protein from Echis multisquamatus Venom, a Potent and Selective Inhibitor of the α2β1 Integrin

We have isolated and characterized EMS16, a potent and selective inhibitor of the α2β1 integrin, from Echis multisquamatus venom. It belongs to the family of C-lectin type of proteins (CLPs), and its amino acid sequence is homologous with other members of this protein family occurring in snake venoms. EMS16 (M r ∼ 33K) is a heterodimer composed of two distinct subunits linked by S−S bonds. K562 cells transfected with α2 integrin selectively adhere to immobilized EMS16, but not to two other snake venom-derived CLPs, echicetin and alboaggregin B. EMS16 inhibits adhesion of α2β1-expressing cells to immobilized collagen I at picomolar concentrations, and the platelet/collagen I interaction in solution at nanomolar concentrations. EMS16 inhibits binding of isolated, recombinant I domain of α2 integrin to collagen in an ELISA assay, but not the interaction of isolated I domain of α1 integrin with collagen IV. Studies with monoclonal antibodies suggested that EMS16 binds to the α2 subunit of the integrin. EMS16 inhibits collagen-induced platelet aggregation, but has no effect on aggregation induced by other agonists such as ADP, thromboxane analogue (U46619), TRAP, or convulxin. EMS16 also inhibits collagen-induced, but not convulxin-induced, platelet cytosolic Ca2+ mobilization. In addition, EMS16 inhibits HUVEC migration in collagen I gel. In conclusion, we report a new, potent viper venom-derived inhibitor of α2β1 integrin, which does not belong to the disintegrin family.