CONVULXIN, A POTENT PLATELET-AGGREGATING PROTEIN FROM CROTALUS-DURISSUS-TERRIFICUS VENOM, SPECIFICALLY BINDS TO PLATELETS

Convulxin, a very potent aggregating protein from rattlesnake venom, w as purified by a new procedure and its heterodimeric structure alpha(3 ) beta(3) was confirmed. The polypeptide N-terminal sequences of convu lxin subunits were determined by Edman degradation. They are very simi lar and appear homologous to botrocetin from Bothrops jararaca venom a nd to rattlesnake lectin from Crotalus atrox venom, both being classif ied among the C-type lectin family. The binding of I-125-labelled conv ulxin to blood platelets has also been analysed under equilibrium cond itions, These studies indicated that convulxin binds to platelets with a high affinity (K-d = 30 pM) on a small number of binding sites (100 0 binding sites per cell). The high-affinity binding of convulxin appe ars specific to platelets, since it is not observed on other cell type s such as neutrophils and erythrocytes. Also, the high-affinity bindin g of convulxin to membranes platelet is not inhibited by alpha-thrombi n, fibrinogen, collagen, laminin binding inhibitor, RGDS peptide, aden osine diphosphate, platelet-activating factor-acether, serotonin or ep inephrine. This, together with the recent observation that platelet ac tivation by convulxin is partially mediated by phospholipase C and inv olves other mechanisms as well, indicates that convulxin may interact with a specific platelet acceptor (receptor) protein which has yet to be characterized. (C) 1997 Elsevier Science Ltd.