The hemorrhagin catrocollastatin inhibits collagen-induced platelet aggregation by binding to collagen via its disintegrin-like domain

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.

Collagen-induced secretion-dependent phase of platelet aggregation is inhibited by the snake venom metalloproteinase jararhagin

Jararhagin, a 52 kDa metalloproteinase from Bothrops jararaca snake venom, belongs to the family of enzymes with an N-terminal Zn2+-containing enzymatic domain, a disintegrin-like domain and a cysteine-rich C-terminal domain. Both jararhagin and jararhagin C, a 28 kDa-protein from the same venom identical to the disintegrin-like domain of jararhagin, inhibit collagen-induced platelet aggregation. In this study, jararhagin and synthetic linear peptides based on the disintegrin-like domain of jararhagin overlapping with the RGD sequence of venom disintegrins, were shown for the first time to inhibit the release of 5-hydroxytryptamine (5-HT) from platelets preloaded with [14C]5-HT and stimulated with collagen. The normal phosphorylation of the 21-kDa myosin light chain (p21) in response to the stimulation indicated that jararhagin and the peptides did not interfere with platelet shape change. The selective inhibition of the secretion-dependent phase of the platelet response to collagen by the enzyme and its peptides was confirmed by the defective phosphorylation of pleckstrin, a 47-kDa platelet protein (p47) involved in dense granule secretion.

Cloning of a disintegrin metalloproteinase that processes precursor tumour-necrosis factor-alpha

Tumour-necrosis factor-alpha (TNF-alpha) is a cytokine that contributes to a variety of inflammatory disease states. The protein exists as a membrane-bound precursor of relative molecular mass 26K which can be processed by a TNF-alpha-converting enzyme (TACE), to generate secreted 17K mature TNF-alpha. We have purified TACE and cloned its complementary DNA. TACE is a membrane-bound disintegrin metalloproteinase. Structural comparisons with other disintegrin-containing enzymes indicate that TACE is unique, with noteable sequence identity to MADM, an enzyme implicated in myelin degradation, and to KUZ, a Drosophila homologue of MADM important for neuronal development. The expression of recombinant TACE (rTACE) results in the production of functional enzyme that correctly processes precursor TNF-alpha to the mature form. The rTACE provides a readily available source of enzyme to help in the search for new anti-inflammatory agents that target the final processing stage of TNF-alpha production.

Inhibition of collagen-induced platelet aggregation as the result of cleavage of alpha 2 beta 1-integrin by the snake venom metalloproteinase jararhagin

Jararhagin is a high-molecular-mass (52 kDa) haemorrhagic metalloproteinase from Bothrops jararaca venom and a member of the metalloproteinase/disintegrin/cysteine-rich protein family. The disintegrin domain of jararhagin has been implicated in the inhibition of platelet responses to collagen by a mechanism that is not entirely known. The present investigation demonstrates that both active and 1,10-phenanthroline-inactivated jararhagin inhibit platelet aggregation by collagen with an IC50 of 40 and 140 nM respectively. The apparently higher inhibitory effect of the active enzyme clearly indicates that, in addition to the disintegrin region, the metalloproteinase domain of jararhagin also participates in this inhibition. As collagen interacts with platelets via alpha 2 beta 1-integrin, we investigated the effects of jararhagin on this integrin using selected function-blocking monoclonal antibodies against both of its subunits. Flow cytometry of platelets treated with native jararhagin and immunoprecipitation of platelet surface glycoproteins from lysates after jararhagin treatment showed an apparently selective reduction of alpha 2 beta 1-integrin immunoreactivity with both anti-alpha 2 and anti-beta 1 monoclonal antibodies. The loss of immunoreactivity was not due to integrin internalization, since it also took place in cytochalasin D-treated platelets. Here we show that jararhagin cleaved isolated alpha 2 beta 1-integrin resulting in the generation of a 115 kDa beta 1 fragment. We therefore propose that the inhibition by jararhagin of platelet response to collagen is mediated through the binding of jararhagin to platelet alpha 2-subunit via the disintegrin domain, followed by proteolysis of the beta 1-subunit with loss of the integrin structure (conformation) necessary for the binding of macromolecular ligands.

ADAMs and cell fusion

Members of the ADAM family (membrane proteins with a disintegrin and metalloprotease domain) have been implicated in several cell-interactive events, including cell-cell fusion. Recent evidence implicates three ADAMs, fertilin-alpha, fertilin-beta, and meltrin-alpha, in sperm-egg fusion and myoblast fusion. In light of the large number and wide tissue distribution of the ADAMs, they may also participate in other cell-cell fusion events. As ADAMs are also found in both vertebrates and invertebrates, some features of cell-cell fusion reactions may be conserved throughout the animal kingdom.