Binding of von Willebrand factor (vWF) to platelet glycoprotein (GP) Ib-IX-V mediates platelet activation in the early stage of thrombus formation. Kistomin, a snake venom metalloproteinase (SVMP) purified from venom of Calloselasma rhodostoma, has been shown to inhibit vWF-induced platelet aggregation. However, its action mechanism, structure-function relationship, and in vivo antithrombotic effects are still largely unknown. In the present study, cDNA encoding kistomin precursor was cloned and revealed that kistomin is a P-I class SVMP with only a proteinase domain. Further analysis indicated that kistomin specifically inhibited vWF-induced platelet aggregation through binding and cleavage of platelet GPIb␣ and vWF. Cleavage of platelet GPIb␣ by kistomin resulted in release of 45-and 130-kDa soluble fragments, indicating that kistomin cleaves GPIb␣ at two distinct sites. In parallel, cleavage of vWF by kistomin also resulted in the formation of low-molecular-mass multimers of vWF. In ex vivo and in vivo studies, kistomin cleaved platelet GPIb␣ in whole blood. Moreover, GPIb␣ agonist-induced platelet aggregation ex vivo was inhibited, and tail-bleeding time was prolonged in mice administered kistomin intravenously. Kistomin's in vivo antithrombotic effect was also evidenced by prolonging the occlusion time in mesenteric microvessels of mice. In conclusion, kistomin, a P-I class metalloproteinase, has a relative specificity for GPIb␣ and vWF and its proteolytic activity on GPIb␣-vWF is responsible for its antithrombotic activity both in vitro and in vivo. Kistomin can be useful as a tool for studying metalloproteinase-substrate interactions and has a potential being developed as an antithrombotic agent.
impaired collagen-induced platelet aggregation ex vivo through matrix metalloproteinase-dependent GPVI shedding. J Thromb Haemost 2008; 6: 669-76.Summary. Background: C-type lectin proteins (CLPs) have diverse targets including platelet GPIb, GPVI and integrin a 2 b 1 , and affect platelet function in a various way. In this study, we characterized a huge, heterodimeric venom protein, trowaglerix, which belongs to the CLP family. Methods: We purified a potent platelet-aggregation inducer, trowaglerix, from the crude venom of Tropidolaemus wagleri. Biotinylated trowaglerix was used for binding assays, and immunoblotting was used to investigate the signal transduction involved. Results: Two distinct subunits of trowaglerix with similar masses of around 16 kDa were eluted by high-performance liquid chromatography after reduction and alkylation. Trowaglerix induced platelet aggregation of washed human platelets and platelet-rich plasma (PRP) in a concentration-dependent manner. Biotinylated trowaglerix specifically bound to platelet membrane GPVI, but not to GPIb or a 2 integrin. Treatment with trowaglerix induced GPVI loss in human platelets in vitro and impaired the platelet aggregation of mouse PRP ex vivo in response to collagen but not in response to adenosine diphosphate (ADP). However, GM6001, a matrix metalloproteinase (MMP) inhibitor, inhibited trowaglerix-induced GPVI cleavage and restored the platelet responsiveness of PRP to collagen. Conclusions: Trowaglerix activates platelets through specific binding to GPVI, leading to kinases-dependent exposure of functional a IIb b 3 and platelet aggregation, and also induces MMPdependent GPVI shedding from platelets.
To cite this article: Hsu CC, Wu WB, Huang TF. A snake venom metalloproteinase, kistomin, cleaves platelet glycoprotein VI and impairs platelet functions. J Thromb Haemost 2008; 6: 1578-85.Summary. Background and objectives: Injuries to the vessel wall and subsequent exposure of the matrix of the subendothelial layer resulted in thrombus formation. Platelet glycoprotein (GP) Ib and VI play a crucial role in matrixinduced activation and aggregation of platelets. Methods and results: In the present study, we reported that the GPIbcleaving snake venom metalloproteinase (SVMP), kistomin, inhibited collagen-induced platelet aggregation. Moreover, kistomin inhibited platelet aggregation induced by convulxin (CVX, a GPVI agonist) and a GPVI-specific antibody in a concentration and time-dependent manner. Kistomin treatment decreased platelet GPVI but not integrin a2b1 and aIIbb3, accompanied with the formation of GPVI cleavage fragments, as determined by flow cytometric and Western blot analyses. In addition, intact platelet GPVI and recombinant GPVI were digested by kistomin to release 25-and 35-kDa fragments, suggesting that kistomin cleaved GPVI near the mucin-like region. We designed four synthetic peptides ranging from Leu 180 to Asn 249 as the substrates for kistomin and found that kistomin cleaved these synthetic peptides at FSE TT, as analyzed by MALDI-TOF-MS. In addition, GPVI-specific antibody-induced tyrosine kinase phosphorylation in platelets was reduced after kistomin pretreatment, and platelet adhesion to collagen but not to fibrinogen was attenuated by kistomin. Conclusions: We provided here the first evidence that a P-I snake venom metalloproteinase, kistomin, inhibits the interaction between collagen and platelet GPVI through its proteolytic activity on GPVI, thus providing an alternative strategy for developing new anti-thrombotic agents.
Snake venoms affect blood coagulation and platelet function in a complex manner. However, two classes of venom proteins, snaclecs and disintegrins have been shown to specifically target receptors including GPIb, α2β1, GPVI, CLEC-2 and integrins αIIbβ3, αvβ3, α5β1 expressed on platelets, endothelial cells, phagocytes, tumor cells, thus affecting cell-matrices and cell-cell interactions. Here, we focus on disintegrins, a class of low molecular mass Arg-Gly-Asp(RGD)/Lys-Gly-Asp(KGD)-containing, cysteine-rich polypeptide derived from various viper snake venoms. This review describes the potential applications of disintegrins in field of integrin-related diseases, especially arterial thrombosis, angiogenesis, tumor progression and septic inflammation. In addition, a novel RGD-containing disintegrin TMV-7 is being developed as a safer antithrombotic agent with minimal side effects, such as thrombocytopenia and bleeding.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.