The mechanism of activation of human prothrombin by an activator isolated from Dispholidus typus venom

The sweet side of venom: Glycosylated prothrombin activating metalloproteases from Dispholidus typus (boomslang) and Thelotornis mossambicanus (twig snake)

Dispholidus typus and Thelotornis mossambicanus are closely related rear-fanged colubrid snakes that both possess strongly procoagulant venoms. However, despite similarities in overall venom biochemistry and resulting clinical manifestations, the underlying venom composition differs significantly between the two species. As a result, the only available antivenom-which is a monovalent antivenom for D. typus-has minimal cross reactivity with T. mossambicanus and is not a clinically viable option. It was hypothesised that this lack of cross reactivity is due to the additional large metalloprotease protein within T. mossambicanus venom, which may also be responsible for faster coagulation times. In this study, we found that T. mossambicanus venom is a more powerful activator of prothrombin than that of D. typus and that the SVMP transcripts from T. mossambicanus form a clade with those from D. typus. The sequences from D. typus and T. mossambicanus were highly similar in length, with the calculated molecular weights of the T. mossambicanus transcripts being significantly less than the molecular weights of some isoforms on the 1D SDS-PAGE gels. Analyses utilising degylcosylating enzymes revealed that T. mossambicanus SVMPs are glycosylated during post-translational modification, but that this does not lead to the different molecular weight bands observed in 1D SDS-PAGE gels. However, differences in glycosylation patterns may still explain some of the difference between the enzymatic activities and neutralization by antivenom that have been observed in these venoms. The results of this study provide new information regarding the treatment options for patients envenomated by T. mossambicanus as well as the evolution of these dangerous snakes.

The use of Dispholidus typus venom in elucidating the cause of a low prothrombin index

A simple and rapid in vitro test was devised to detect the presence of the prothrombin precursor molecule circulating in the plasma of 55 out of 56 patients receiving oral vitamin K antagonists and in 4 out of 5 patients with obstructive jaundice, using either Dispholidus typus or Echis carinatus venoms. The absence of the molecule from the plasma of jaundiced patients was suggestive of hepatocellular rather than obstructive jaundice. The test is based on the clotting of aluminium hydroxide gel adsorbed plasma by the venoms. It is more sensitive and easier to perform than measuring antigenic prothrombin levels.

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.

The action of Lonomia achelous caterpillars venom on human factor V

The bleeding syndrome produced by contact with the Lonomia achelous caterpillars is characterized by a decrease of fibrinogen, factor XIII, plasminogen, and factor V with normal platelets. In this study, we report the effect of crude hemolymph and some semipurified chromatographic fractions on human factor V. Incubation of factor V with crude hemolymph resulted in an increase in procoagulant activity, followed by a subsequent decline in factor V activity. Identical results were obtained with fraction I, whereas with fraction II there was only a decrease in activity reaching its minimum at 30 minutes. fraction III did not modify the activity of factor V. All concentrations of fraction I tested produced an initial rise and subsequent fall in activity. However, at lower relative concentrations of fraction I, more sustained increases in activity were observed. The activator and inactivator activities present in fraction I show differences in temperature and pH stability, susceptibility to different inhibitors, and in SDS/PAGE pattern. The factor V activator is a thermostable protein, with maximum activity at acid pH and is inhibited by o-phenantroline, EDTA, and EGTA, while the factor V inactivator is thermolabile, presents maximum activity at basic pH, precipitates at pH 5.0, and is completely inhibited by iodoacetic acid and TLCK. It is partially blocked by diisopropyl fluorophosphate, phenylmethylsulfonyl fluoride, and p-chloromercuribenzoic acid. These results suggest that the activator should be a metallo-proteinase, while the inactivator is a serine or cysteine proteinase with a serine, histidine, or cysteine residue in the active site.

Prothrombin and factor X activator activities in the venoms of Viperidae snakes

A Ca(2+)-dependent prothrombin activator, carinactivase-1 (CA-1), was previously found in the venom of Echis carinatus leucogaster. In the present study, the activities of CA-1-like enzymes were screened in the venoms of various Viperidae snakes. The addition of 1 mM Ca2+ ions to the venoms of only Echis snakes in Viperidae produced considerably high prothrombin activator activity, indicating that only the Echis snake venoms contain not only the Ca(2+)-independent prothrombin activator, ecarin, but also Ca(2+)-dependent activator(s). CA-1-like activators and ecarin in the venom of each Echis snake were efficiently separated by Blue Sepharose column chromatography. The venoms of the various Viperidae snakes were also examined for factor X activator activity. The venoms of genera Daboia, Vipera, Cerastes, Echis, Calloselasma and Bothrops contained factor X activator activity in the presence of Ca2+ ions. Cerastes cerastes and Calloselasma rhodostoma venoms also had Ca(2+)-independent factor X activator activity.

Structural and functional properties of snake venom prothrombin activators

In this review we have summarized the current knowledge about the prothrombin activating principles present in the venom of a large number of different snake species. It appears that snake venom prothrombin activators can be classified into four different groups based on their structural properties and on their functional properties in prothrombin activation. Group I activators efficiently convert prothrombin into meizothrombin and their activity is not influenced by the non-enzymatic cofactors of the prothrombinase complex (CaCl2, factor Va and phospholipid). Group II and III activators can cleave both peptide bonds in prothrombin necessary to convert prothrombin into thrombin. The prothrombin-converting activity of Group II activators is strongly stimulated by phospholipids and factor Va in the presence of CaCl2, whereas the activity of group III activators is only stimulated by CaCl2 and phospholipid. Group IV consists of snake venom proteases which do not convert prothrombin into enzymatically active products but cleave peptide bonds in prothrombin, resulting in the formation of inactive precursor forms of thrombin.

Activation of human prothrombin by the venom of Lonomia achelous (Cramer) caterpillars

In this paper, we demonstrated that the procoagulant action of Lonomia achelous (Cramer) is due in part to a component that activates prothrombin. The activation by crude venom and Fractions obtained by gel filtration on Sephadex G-75 is not dependent of phospholipid, Ca++ or Factor V. The activation of prothrombin by Fraction I is greatly stimulated by Factor V in the presence of phospholipid and Ca++; in presence of SBTI, we found that the Fraction I and Factor Xa act in a similar manner. These results suggest that the Fraction I is a Factor Xa - like prothrombin activator.

Procoagulant activities in venoms from central Asian snakes

The venoms from central Asian snakes (Echis carinatus, Echis multisquamatus, Vipera ursini, Vipera lebetina, Agkistrodon halys halys and Naja naja oxiana) contain several enzymes with amidolytic- and procoagulant activity. We have characterized the activities and the mol. wts of the venom enzymes that are able to convert a number of commercially available chromogenic substrates for activated coagulation factors. The chromogenic substrate cleavage patterns obtained for the crude venoms may be helpful tools in the further identification of venom fractions and venom enzymes with procoagulant activity. The crude venoms were also tested for their ability to clot fibrinogen, to lyse fibrin polymers and to activate the coagulation factors prothrombin, factor X and factor V. The products of venom-catalyzed coagulation factor activation were structurally characterized by SDS gel electrophoresis and were compared with activated coagulation factors that are generated under physiological conditions.

Effects of snake venoms on hemostasis

Proteins found in venoms, especially of the Viperidae snake family, exert, often with a narrow specificity, activating, inactivating, or other converting effects on different components of the hemostatic and fibrinolytic systems, respectively. Some purified snake venom proteins have become valuable tools in basic research and in diagnostic procedures in hemostaseology. "Procoagulant" as well as "anticoagulant" venom components have been identified in in vitro test systems. "Procoagulant" snake venom components may cause in vivo, upon massive application as in the case of snake-bite of small prey animals, intravascular coagulation leading to circulatory arrest and rapid death. Smaller doses of procoagulant venom components applied to large organisms as in the case of snake-bite accidents in humans, may cause a consumption coagulopathy with localized or generalized bleeding. Highly purified, specific fibrinogen coagulant venom proteinases are used in human medicine to produce therapeutic defibrinogenation. These practically nontoxic venom enzymes may act synergistically with other components aggravating their toxic effects.

Structural and functional characterization of a prothrombin activator from the venom of Bothrops neuwiedi

A prothrombin activator from the venom of Bothrops neuwiedi was purified by gel filtration on Sephadex G-100, ion-exchange chromatography on DEAE-Sephacel and affinity chromatography on a Zn2+-chelate column. The overall purification was about 200-fold, which indicates that the prothrombin activator comprises about 0.5% of the crude venom. The venom activator is a single-chain protein with an apparent molecular weight of 60 kDa. It readily activated bovine prothrombin with a Km of 38 microM and a Vmax of 120 mumol prothrombin activated per min per mg of venom activator. Venom-catalyzed prothrombin activation was not accelerated by the so-called accessory components of the prothrombinase complex, phospholipids plus Ca2+ and Factor Va. Gel-electrophoretic analysis of prothrombin activation indicated that the venom activator only cleaved the Arg-323-Ile-324 bond of bovine prothrombin, since meizothrombin was the only product of prothrombin activation. The activator did not hydrolyze commercially available p-nitroanilide substrates and its prothrombin-converting activity was not inhibited by benzamidine, phenylmethylsulfonyl fluoride, dansyl-Glu-Gly-Arg-chloromethyl ketone and soy-bean trypsin inhibitor. However, chelating agents such as EDTA, EGTA and o-phenanthroline rapidly destroyed the enzymatic activity of the venom activator. The activity of chelator-treated venom activator could be partially restored by the addition of an excess CaCl2. These results indicate that the venom activator remarkably differs from Factor Xa and that the enzyme is not a serine proteinase, but likely belongs to the metalloproteinases. The structural and functional properties of the venom prothrombin activator from B. neuwiedi are similar to those reported for the venom activator from Echis carinatus.

Quantitation of prothrombin activation products in human urine

Urine samples obtained from 37 normal individuals have been screened for the presence of prothrombin activation products using radioimmunoassays developed for fragment 1, fragment 2 and prothrombin derivatives bearing the thrombin region. The cross-reacting materials detected in urine were isolated by affinity chromatography on insolubilized antibodies, and analysed by SDS polyacrylamide gel electrophoresis. The only prothrombin derivatives detected were fragment 1 (37/37) and fragment 2 (22/37). The mean values of daily urinary fragment 1 and fragment 2 excretion were respectively 13.4 nM and 1.5 nM. The excretion of prothrombin derivatives has been quantitated in 14 normal pregnant women, during the third trimester of gestation. The mean values of urinary excretion were 47.2 nM per day for fragment 1 (P less than 0.005) and 6.4 nM per day for fragment 2 (P less than 0.05). The significant increase in fragment 1 and fragment 2 excretion observed in a condition known to be associated with the so-called hypercoagulable state suggest that the measurement of prothrombin derivatives in urine could be a useful tool for the non-invasive detection of thromboembolic diseases or prethrombotic states.

The action of Echis carinatus venom on the blood coagulation system. Demonstration of an activator of factor X

It is shown that Echis carinatus venom activates both coagulation factor II and coagulation factor X. The activation of both proenzymes by the venom is Ca++-dependent; phospholipids are not necessary. The activation of factor II by the venom is a slow process and, in the absence of factor X, the clotting activity towards fibrinogen is generated only very slowly. Because Echis carinatus venom clots plasma readily, we postulate that under conditions where the prothrombinase complex can be formed from the factor X activated by the venom it is this complex, rather than the venom itself, that is responsible for the major part of the thrombin formation.

Purification and properties of an activating enzyme of blood clotting factor X from the venom of Cerastes cerastes

An activator of blood coagulation factor X was found in the venom of the horned viper Cerastes cerastes, and was purified by gel filtration, ion-exchange chromatography and chromatofocussing. The activator is a protein composed of a heavy and a light polypeptide chain linked by disulfide bonds. Two subforms of the activator were found. Both contained a heavy chain of Mr 58000 and are distinguished from each other by the presence of two different light chains of Mr 17700 and 15000. The activator appears to cleave the bond in the factor X molecule that is also cleaved by factor IXa. Factor X activation by the activator is strongly stimulated by Ca2+. The kinetic parameters for the activation reaction have been determined. A Km for factor X of 19.2 nM and a Vmax of 0.11 pmol of Xa/min per ng venom were found.