Cloning of subunits of convulxin, a collagen-like platelet-aggregating protein from Crotalus durissus terrificus venom

Abstract

Convulxin (CVX) is a potent platelet-aggregating glycoprotein from the venom of the snake Crotalus durissus terrificus. It consists of two subunits, α and β, joined by disulphide bridges in a hexameric structure. A cDNA library from venom gland was constructed in the vector pT3T7. The cloned cDNAs encoding the two chains of CVX were sequenced. Both are preceded by an identical 23-amino acid peptide signal sequence and encode sequences of 135 amino acids for the α chain and 125 amino acids for the β chain. These polypeptides include a carbohydrate-recognition domain (CRD) in which some of the specific amino acids required for binding Ca2+ and galactose or mannose are absent. The presence of such a domain means that CVX can be included in the family of C-type lectins along with other snake venom proteins, although it is not a true lectin. Assuming that the localization of intracatenary disulphide bridges of each CVX chain is similar to that of the CRD and that an intercatenary bridge between the α and β chains is similar to that of the C-type lectin botrocetin, we postulate the existence of an additional intercatenary bridge, which explains the tridimeric structure (αβ)3 of CVX.