Snake venom proteins acting on hemostasis

The venoms of Viperidae and Crotalidae snakes are a rich source of proteins with activity against various factors involved in coagulation and fibrinolysis. These proteins are very specific for their molecular targets, resistant to physiological inhibitors and stable in vitro and in vivo. They have therefore proved to be useful for diagnostic tests. Based on sequence similarities, these snake venom proteins have been classified into various families, such as serine proteinases, metalloproteinases, C-type lectins, disintegrins and phospholipases A(2). The various members of a given family, although structurally similar, act selectively on different blood coagulation factors. This opens up the possibility of characterizing the structural elements involved in target molecule recognition. Thus, snake venom proteins provide excellent models for studies of structure-function relationships.     

Snake venom proteins in hemostasis: new results

Biological features of venomous snakes as well as biochemical properties and actions of their venoms which serve for prey acquisition, indicate the vertebrates' haemostasis system as a vulnerable target for snake venom actions. Components exerting a specific, either stimulating or inactivating effect on basal membrane or endothelial cells of the vascular wall, on platelets, on almost every step of plasma coagulation or fibrinolysis respectively, have been isolated and purified from snake venoms. Snake venom proteins acting with a defined specificity on cellular or plasmatic components of the human haemostatic system are being used in coagulation and aggregation tests, in photometric assays in conjunction with chromogenic substrates as well as in immunological systems as biochemical tools for research and diagnostic purposes.     

清栓酶治疗儿童脑动脉炎和脑血栓形成31例

用清栓酶治疗儿童脑动脉炎和脑血栓形成３１例,其中急性期２２例、恢复期５例、后遗症期４例,有效率分别为９Ｏ．９％、８０．０％和８７．１％．总有效率为８７．１％。脑动脉炎可导致血小板聚集性增高、血管闭塞和血栓形成,清栓酶可降低血小板聚集性,具有扩张血管,溶解血栓之作用,故可以使临床表现得以好转。     

Snake venom cardiotoxin induces G-actin polymerization

Snake venom cardiotoxin showed the ability to induce polymerization of G-actin from rabbit skeletal muscle in a low ionic strength buffer composed of 0.2 mM CaCl2/0.2 mM ATP/0.5 mM mercaptoethanol/2.0 mM Tris-HCl, pH 8.0. The activity was enhanced greatly when 0.4 mM MgCl2 was present in the buffer and could be inhibited if G-actin was preincubated with deoxyribonuclease I. Furthermore, the DNAase could also partially depolymerize actin polymer previously formed by the interaction of G-actin with the toxin.     

Snake venom alpha-neurotoxins and other 'three-finger' proteins.

The review is mainly devoted to snake venom alpha-neurotoxins which target different muscle-type and neuronal nicotinic acetylcholine receptors. The primary and spatial structures of other snake venom proteins as well as mammalian proteins of the Ly-6 family, which structurally resemble the 'three-finger' snake proteins, are also briefly discussed. The main emphasis is placed on recent data characterizing the alpha-neurotoxin interactions with nicotinic acetylcholine receptors.     

Snake venom phosphodiesterase: A zinc metalloenzyme

Snake venom phosphodiesterase fromCrotalus adamanteus can be purified by blue sepharose chromatography followed by gel exclusion chromatography on Sephadex G-100. The enzyme is judged to be homogeneous by SDS gel electrophoresis. Atomic absorption spectrometry indicates a stoichiometry of 1.07 g-atom of zinc per mole of purified enzyme. The enzyme is inhibited by a wide variety of structurally different metal binding agents, e.g., 1,10-phenanthroline, thioglycolic acid,l-cysteine, 8-hydroxy-5-quinoline sulfonic acid, EDTA, and dipicolinic acid. The results of both the chelator inhibition and the atomic absorption analysis indicate that snake venom phosphodiesterase is a zinc metalloenzyme. Snake venom phosphodiesterase shares a number of mechanistic features in common with the nucleotidyl transferases. All of these enzymes contain zinc, are activated by magnesium, and catalyze α-β phosphoryl bond cleavage. Mechanistic studies of phosphodiesterase may therefore be helpful in understanding the mechanism of the hydrolytic step catalyzed by all of these enzymes.     

Snake venom hyaluronidase: a therapeutic target

The diffusion of toxins from the site of a bite into the circulation is essential for successful envenomation. Degradation of hyaluronic acid in the extracellular matrix (ECM) by venom hyaluronidase is a key factor in this diffusion. Hyaluronidase not only increases the potency of other toxins but also damages the local tissue. In spite of its important role, little attention has been paid to this enzyme. Hyaluronidase exists in various isoforms and generates a wide range of hyaluronic acid degradation products. This suggests that beyond its role as a spreading factor venom hyaluronidase deserves to be explored as a possible therapeutic target for inhibiting the systemic distribution of venom and also for minimizing local tissue destruction at the site of the bite.     

Snake venom components and their cross-reactivity: a review

Snake venoms are complex mixtures of organic and inorganic compounds, many of which display biological activity. It has been demonstrated that antisera raised against whole venom or a single purified venom protein from one species of snake will react with proteins in the venom of other species. This cross-reactivity between species may have applications in determining snake phylogeny, but recent studies on the variation of venom components within a species make these evolutionary conclusions questionable.     

Snake venom metalloproteases--structure and function of catalytic and disintegrin domains

Snake venoms are relevant sources of toxins that have evolved towards the engineering of highly active compounds. In the last years, research efforts have produced great advance in their understanding and uses. Metalloproteases with disintegrin domains are among the most abundant toxins in many Viperidae snake venoms. This review will focus on the structure, function and possible applications of the metalloprotease and disintegrin domains.     

Quantitative trait locus analysis for hemostasis and thrombosis

Susceptibility to thrombosis varies in human populations as well as many in inbred mouse strains. The objective of this study was to characterize the genetic control of thrombotic risk on three chromosomes. Previously, utilizing a tail-bleeding/rebleeding assay as a surrogate of hemostasis and thrombosis function, three mouse chromosome substitution strains (CSS) (B6-Chr5^A/J, Chr11^A/J _, Chr17^A/J) were identified (Hmtb1, Hmtb2, Hmtb3). The tail-bleeding/rebleeding assay is widely used and distinguishes mice with genetic defects in blood clot formation or dissolution. In the present study, quantitative trait locus (QTL) analysis revealed a significant locus for rebleeding (clot stability) time (time between cessation of initial bleeding and start of the second bleeding) on chromosome 5, suggestive loci for bleeding time (time between start of bleeding and cessation of bleeding) also on chromosomes 5, and two suggestive loci for clot stability on chromosome 17 and one on chromosome 11. The three CSS and the parent A/J had elevated clot stability time. There was no interaction of genes on chromosome 11 with genes on chromosome 5 or chromosome 17. On chromosome 17, twenty-three candidate genes were identified in synteny with previously identified loci for thrombotic risk on human chromosome 18. Thus, we have identified new QTLs and candidate genes not previously known to influence thrombotic risk. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Role of platelets in hemostasis and thrombosis.

Platelets are central to both normal hemostasis and abnormal thrombotic states along with the vessel wall, coagulation elements, and blood flow. The platelets play a pivotal role in the reaction that occurs after vessel injury, during which platelets first adhere to the vessel wall, undergo a release reaction and then aggregate, probably as a result of the materials released from platelets. These processes can be studied by a series of in vitro tests which form the basis of our knowledge of platelets in hemostasis. While the hemostatic plug is usually microscopic in size, this same plug (platelet thrombus) may contribute to the pathogenesis of several arterial diseases such as transient ischemic attacks, sudden blindness, sudden cardiac death and acute respiratory death syndrome. Careful microscopic examinations have shown that platelet aggregates may be found in the microcirculation which could affect vital structures such as the conduction system of the heart. Both anatomic and therapeutic evidence evidence suggests that platelets play a role in venous thrombosis. Recent evidence suggests increased levels of materials known to be released from platelets in patients with both arterial and venous thrombi along with increased platelet coagulant activities in patients with venous thrombosis.     

Sequence and phylogenetic analysis of viper venom serine proteases

Snakebites are a major neglected tropical disease responsible for as many as 95000 deaths every year worldwide. Viper venomserine proteases disrupt haemostasis of prey and victims by affecting various stages of the blood coagulation system. A betterunderstanding of their sequence, structure, function and phylogenetic relationships will improve the knowledge on thepathological conditions and aid in the development of novel therapeutics for treating snakebites. A large dataset for all availableviper venom serine proteases was developed and analysed to study various features of these enzymes. Despite the large number ofvenom serine protease sequences available, only a small proportion of these have been functionally characterised. Although, theyshare some of the common features such as a C-terminal extension, GWG motif and disulphide linkages, they vary widely betweeneach other in features such as isoelectric points, potential N-glycosylation sites and functional characteristics. Some of the serineproteases contain substitutions for one or more of the critical residues in catalytic triad or primary specificity pockets. Phylogeneticanalysis clustered all the sequences in three major groups. The sequences with substitutions in catalytic triad or specificity pocketclustered together in separate groups. Our study provides the most complete information on viper venom serine proteases to dateand improves the current knowledge on the sequence, structure, function and phylogenetic relationships of these enzymes. Thiscollective analysis of venom serine proteases will help in understanding the complexity of envenomation and potential therapeuticavenues.     

The role of tissue factor in thrombosis and hemostasis

The tissue factor (TF) is one of the most important regulators of arterial thrombosis. Because arterial thrombosis is the pathophysiologic background of acute coronary syndrome, the possible impact of blocking the arterial thrombosis on its onset is a challenging problem. The investigations of TF brought a new concept of "cell-based coagulation model" which highlighted the question of blood-borne TF as a source of TF in circulating blood. In this review we summarize essential information on the pathophysiology, molecular structure, expression and distribution of TF and we propose a novel concept of blood-borne TF, suggesting the possibilities of inhibition of the coagulation cascade with newly synthetized drugs.