Sequence and biological activity of catrocollastatin-C: a disintegrin-like/cysteine-rich two-domain protein from Crotalus atrox venom.

In this study we report on the isolation and biological characterization of a 23.6-kDa protein from the venom of the western diamondback rattlesnake, Crotalus atrox. Primary structural analysis shows the protein to be composed of a spacer/disintegrin-like domain and a cysteine-rich domain. The sequence is identical to the same carboxy-terminal domains found in the C. atrox metalloproteinase, catrocollastatin, and hence we termed the protein catrocollastatin-C. We estimate that catrocollastatin-C represents at least 0.5% of the total protein in C. atrox venom. The protein is an inhibitor of collagen-stimulated but not ADP-stimulated platelet aggregation. Reduction and alkylation of catrocollastatin-C causes a loss of platelet aggregation inhibitor activity. A synthetic, cyclic peptide designed from the catrocollastatin-C disintegrin-like domain has potent platelet aggregation inhibitory activity. This suggests that the corresponding region in the disintegrin-like domain of the protein is at least partially responsible for the inhibition of platelet aggregation previously reported for the protein. These studies underscore the biochemical and functional complexity of crotalid snake venoms due to differential proteolytic processing of precursor proteins and how the processed precursor fragments may contribute to the observed pathological effects of the venom.