Abstract
A potent platelet aggregation inhibitor in the venom of Crotalus viridis snake was purified to homogeneity by gel filtration chromatography and reverse phase high-performance liquid chromatography. This purified principle, named crotavirin, is a single-chain polypeptide with a mol. wt of 9200 as estimated by SDS-polyacrylamide gel electrophoresis. It inhibited the aggregation of human washed platelets induced by collagen, thrombin and thomboxane analogue (U46619) with a similar IC 50 (~ 1.0 μg/ml, 0.11 μM). The binding of fluorescein isothiocyanate-conjugated crotavirin to platelets was abolished in the presence of divalent cation chelator, EDTA, indicating that divalent cation is essential for crotavirin's binding. A monoclonal antibody, 7E3, raised against platelet glycoprotein IIb-IIIa complex blocked the binding of fluorescein isothiocyanate-conjugated crotavirin to platelets, whereas the other monoclonal antibody against glycoprotein IIb-IIIa, 10E5, had no inhibitory effect. In addition, crotavirin inhibited in a concentration-dependent manner the binding of fluorescein isothiocyanate-conjugated rhodostomin, a member of the disintegrin family, to platelets. Its binding to platelets was blocked by disintegrins e.g. trigramin and rhodostomin. It is concluded that crotavirin is a potent platelet aggregation inhibitor, which acts specifically on an epitope of glycoprotein IIb-IIIa, leading to the blockade of fibrinogen binding to glycoprotein IIb-IIIa and eventually the blockade of platelet aggregation.
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