A fibrinolytic snake venom metalloproteinase, mutalysin-II, with antiplatelet activity and targeting capability toward glycoprotein GPIbα and glycoprotein GPVI.

Glycoprotein (GP)Ib that binds von Willebrand factor (vWF) and glycoprotein (GP)VI, that binds collagen play a significant role in platelet activation and aggregation, and are potential targets for antithrombotic treatment. They are targeted by snake venom proteinases. The effect of a such proteinase, mutalysin-II, on platelet aggregation was examined using washed human platelets and platelet-rich plasma. Its proteolytic activity on vWF, on its binding partner GPIbα, and on GPVI was analyzed by SDS-PAGE, and immunodetection with the corresponding antibodies after blotting. Dose- and time-dependently, mutalysin-II inhibits aggregation of washed platelets induced by vWF plus ristocetin and by convulxin, but with no significant effect on platelet-rich-plasma. Furthermore, mutalysin-II cleaves vWF into low molecular mass multimers of vWF and a rvWF-A1 domain to realease a ∼27-kDa fragment detectable by SDS-PAGE and blotting with mouse anti-rvWF-A1-domain IgG. Moreover, GPVI was cut by mutalysin-II into a soluble ∼55-kDa ectodomain and a fragment of ∼35-kDa. Thus, mutalysin-II inhibits vWF-induced platelet aggregation via cleavage of bound vWF-A1, and its receptor GPIbα. The additional cleavage of, GPVI, blocks collagen-induced platelets. Our data highlight mutalysin-II as an interesting platelet-directed tool targeting vWF-GPIbα binding and particularly GPVI. Thus, it might be suited for antithrombotic therapy as its combined inactivation of two receptors does not significantly compromise hemostasis, but shows high efficacy and safety. Studies are needed to further develop and demonstrate its potential benefits.