Purification and biochemical characterization of atroxase, a nonhemorrhagic fibrinolytic protease from western diamondback rattlesnake venom

Snake Venom Metalloproteinases (SVMPs): A structure-function update

Snake venom metalloproteinases (SVMPs) represent a diverse group of multi-domain proteins with several biological activities such as the ability to induce hemorrhage, proteolytic degradation of fibrinogen and fibrin, induction of apoptosis and inhibition of platelet aggregation. Due to these activities, SVMPs are responsible for many of the well-known pathological phenotypes in snake envenomations caused particularly by species from the Viperidae family and the Crotalinae subfamily. These proteins have been classified based on their size and domain structure into P–I, P-II and P-III classes. Comparatively, members of the P–I SVMPs possess the simplest structures, formed by the catalytic metalloproteinase domain only; the P-II SVMPs are moderately more complex, having the canonical disintegrin domain in addition to the metalloproteinase domain; members of the P-III class are more structurally varied, comprising the metalloproteinase, disintegrin-like, and cysteine-rich domains. Proteolytic cleavage, repeated domain loss and presence of other ancillary domains are responsible for structural diversities in the P-III class. However, studies continue to unveil the relationship between the structure and function of these proteins. In this review, we recovered evidences from literature on the structural peculiarities and functional classification of Snake Venom Metalloproteinases. In addition, we reflect on diversities that exist among each class while taking into account specific and up-to-date class-based activities.

Repurposing Cancer Drugs Batimastat and Marimastat to Inhibit the Activity of a Group I Metalloprotease from the Venom of the Western Diamondback Rattlesnake, Crotalus atrox

Snakebite envenomation causes over 140,000 deaths every year, predominantly in developing countries. As a result, it is one of the most lethal neglected tropical diseases. It is associated with incredibly complex pathophysiology due to the vast number of unique toxins/proteins present in the venoms of diverse snake species found worldwide. Here, we report the purification and functional characteristics of a Group I (PI) metalloprotease (CAMP-2) from the venom of the western diamondback rattlesnake, Crotalus atrox. Its sensitivity to matrix metalloprotease inhibitors (batimastat and marimastat) was established using specific in vitro experiments and in silico molecular docking analysis. CAMP-2 shows high sequence homology to atroxase from the venom of Crotalus atrox and exhibits collagenolytic, fibrinogenolytic and mild haemolytic activities. It exerts a mild inhibitory effect on agonist-induced platelet aggregation in the absence of plasma proteins. Its collagenolytic activity is completely inhibited by batimastat and marimastat. Zinc chloride also inhibits the collagenolytic activity of CAMP-2 by around 75% at 50 μM, while it is partially potentiated by calcium chloride. Molecular docking studies have demonstrated that batimastat and marimastat are able to bind strongly to the active site residues of CAMP-2. This study demonstrates the impact of matrix metalloprotease inhibitors in the modulation of a purified, Group I metalloprotease activities in comparison to the whole venom. By improving our understanding of snake venom metalloproteases and their sensitivity to small molecule inhibitors, we can begin to develop novel and improved treatment strategies for snakebites.

Do Antibiotics Potentiate Proteases in Hemotoxic Snake Venoms?

Antibiotics are often administered with antivenom following snakebite envenomings in order to avoid secondary bacterial infections. However, to this date, no studies have evaluated whether antibiotics may have undesirable potentiating effects on snake venom. Herein, we demonstrate that four commonly used antibiotics affect the enzymatic activities of proteolytic snake venom toxins in two different in vitro assays. Similar findings in vivo could have clinical implications for snakebite management and require further examination.

Cytotoxic effects of Pseudocerastes persicus venom and its HPLC fractions on lung cancer cells

BACKGROUND

Several studies have pointed out that certain snake venoms contain compounds presenting cytotoxic activities that selectively interfere with cancer cell metabolism. In this study, Pseudocerastes persicus venom and its fractions were investigated for their anticancer potential on lung cancer cells.

METHODS

Lung cancer cells (A549) and normal fibroblast cells (Hu02) were treated with the P. persicus venom and its HPLC fractions and the cell cytotoxic effects were analyzed using MTT and lactate dehydrogenase release assays. Apoptosis was determined in venom-treated cell cultures using caspase-3 and caspase-9 assay kits.

RESULTS

The treatment of cells with HPLC fraction 21 (25-35 kDa) of P. persicus venom resulted in high LDH release in normal fibroblast cells and high caspase-3 and caspase-9 activities in lung cancer cells. These results indicate that fraction 21 induces apoptosis in cancer cells, whereas necrosis is predominantly caused by cell death in the normal cells. Fraction 21 at the final concentration of 10 μg/mL killed approximately 60% of lung cancer cells, while in normal fibroblast cells very low cell cytotoxic effect was observed.

CONCLUSION

HPLC fraction 21 at low concentrations displayed promising anticancer properties with apoptosis induction in the lung cancer cells. This fraction may, therefore, be considered a promising candidate for further studies.

Liquid chromatographic nanofractionation with parallel mass spectrometric detection for the screening of plasmin inhibitors and (metallo)proteinases in snake venoms

To better understand envenoming and to facilitate the development of new therapies for snakebite victims, rapid, sensitive, and robust methods for assessing the toxicity of individual venom proteins are required. Metalloproteinases comprise a major protein family responsible for many aspects of venom-induced haemotoxicity including coagulopathy, one of the most devastating effects of snake envenomation, and is characterized by fibrinogen depletion. Snake venoms are also known to contain anti-fibrinolytic agents with therapeutic potential, which makes them a good source of new plasmin inhibitors. The protease plasmin degrades fibrin clots, and changes in its activity can lead to life-threatening levels of fibrinolysis. Here, we present a methodology for the screening of plasmin inhibitors in snake venoms and the simultaneous assessment of general venom protease activity. Venom is first chromatographically separated followed by column effluent collection onto a 384-well plate using nanofractionation. Via a post-column split, mass spectrometry (MS) analysis of the effluent is performed in parallel. The nanofractionated venoms are exposed to a plasmin bioassay, and the resulting bioassay activity chromatograms are correlated to the MS data. To study observed proteolytic activity of venoms in more detail, venom fractions were exposed to variants of the plasmin bioassay in which the assay mixture was enriched with zinc or calcium ions, or the chelating agents EDTA or 1,10-phenanthroline were added. The plasmin activity screening system was applied to snake venoms and successfully detected compounds exhibiting antiplasmin (anti-fibrinolytic) activities in the venom of Daboia russelii, and metal-dependent proteases in the venom of Crotalus basiliscus. Graphical abstract ᅟ.

Iron and carbon monoxide attenuate degradation of plasmatic coagulation by Crotalus atrox venom

Hypofibrinogenemia is an important clinical consequence following envenomation by Crotalus species, usually attenuated or prevented by administration of antivenom. It has been determined that iron and carbon monoxide (CO) enhance fibrinogen as a thrombin substrate, likely secondary to conformational changes in molecular structure. We tested the hypothesis that pretreatment of plasma with iron and CO could attenuate the effects of exposure to Crotalus atrox venom. Human plasma was exposed to 0 to 10 μmol/l ferric chloride (iron source) and 0 to 100 μmol/l CO-releasing molecule-2 (CO source) followed by exposure to 0 to 0.5 μg/ml venom for 5 to 20 min. Changes in coagulation kinetics were determined with thrombelastography. Iron and CO significantly attenuated venom-mediated degradation of plasmatic coagulation in terms of onset time, velocity of clot growth and final clot strength. Further preclinical investigation of iron and CO administration as a 'bridge-to-antivenom' to preserve plasmatic coagulation is justified.

Snake venom metalloproteinases

Recent proteomic analyses of snake venoms show that metalloproteinases represent major components in most of the Crotalid and Viperid venoms. In this chapter we discuss the multiple activities of the SVMPs. In addition to hemorrhagic activity, members of the SVMP family also have fibrin(ogen)olytic activity, act as prothrombin activators, activate blood coagulation factor X, possess apoptotic activity, inhibit platelet aggregation, are pro-inflammatory and inactivate blood serine proteinase inhibitors. Clearly the SVMPs have multiple functions in addition to their well-known hemorrhagic activity. The realization that there are structural variations in the SVMPs and the early studies that led to their classification represents an important event in our understanding of the structural forms of the SVMPs. The SVMPs were subdivided into the P-I, P-II and P-III protein classes. The noticeable characteristic that distinguished the different classes was their size (molecular weight) differences and domain structure: Class I (P-I), the small SVMPs, have molecular masses of 20-30 kDa, contain only a pro domain and the proteinase domain; Class II (P-II), the medium size SVMPs, molecular masses of 30-60 kDa, contain the pro domain, proteinase domain and disintegrin domain; Class III (P-III), the large SVMPs, have molecular masses of 60-100 kDa, contain pro, proteinase, disintegrin-like and cysteine-rich domain structure. Another significant advance in the SVMP field was the characterization of the crystal structure of the first P-I class SVMP. The structures of other P-I SVMPs soon followed and the structures of P-III SVMPs have also been determined. The active site of the metalloproteinase domain has a consensus HEXXHXXGXXHD sequence and a Met-turn. The "Met-turn" structure contains a conserved Met residue that forms a hydrophobic basement for the three zinc-binding histidines in the consensus sequence.

Thermal detoxification of the venom from Daboia russelli russelli of Eastern India with restoration of fibrinolytic activity

The fibrinolytic components of venom have been evaluated for long in the enzymatic treatment of thrombosis. Russell's viper venom has fibrinolytic activity that is associated with hemorrhagic activity. Here it has been investigated whether the crude venom could be detoxified by thermal denaturation retaining fibrinolytic activity. The venom at 0.05 mg/ml in 20 mM K-phosphate, pH 7.5 when exposed to 100 °C for 5 min followed by cooling at 25 °C for 1 h led to its detoxification, while 80-85% of the fibrinolytic activity was recovered. Assessment of toxicity of the renatured venom in mice after injection at 5 fold excess of the lethal dose showed no lethality including hemorrhage, myotoxicity, cytotoxicity and liver toxicity. This simple method for preparation of fibrinolytic component for therapeutic use may be developed.

Comparative study of anticoagulant and procoagulant properties of 28 snake venoms from families Elapidae, Viperidae, and purified Russell's viper venom-factor X activator (RVV-X)

Snake venoms consist of numerous molecules with diverse biological functions used for capturing prey. Each component of venom has a specific target, and alters the biological function of its target. Once these molecules are identified, characterized, and cloned; they could have medical applications. The activated clotting time (ACT) and clot rate were used for screening procoagulant and anticoagulant properties of 28 snake venoms. Crude venoms from Daboia russellii siamensis, Bothrops asper, Bothrops moojeni, and one Crotalus oreganus helleri from Wrightwood, CA, had procoagulant activity. These venoms induced a significant shortening of the ACT and showed a significant increase in the clot rate when compared to the negative control. Factor X activator activity was also measured in 28 venoms, and D. r. siamensis venom was 5-6 times higher than those of B. asper, B. moojeni, and C. o. helleri from Wrightwood County. Russell's viper venom-factor X activator (RVV-X) was purified from D. r. siamensis venom, and then procoagulant activity was evaluated by the ACT and clot rate. Other venoms, Crotalus atrox and two Naja pallida, had anticoagulant activity. A significant increase in the ACT and a significant decrease in the clot rate were observed after the addition of these venoms; therefore, the venoms were considered to have anticoagulant activity. Venoms from the same species did not always have the same ACT and clot rate profiles, but the profiles were an excellent way to identify procoagulant and anticoagulant activities in snake venoms.

Venom variation in hemostasis of the southern Pacific rattlesnake (Crotalus oreganus helleri): isolation of hellerase

Envenomations by the southern Pacific rattlesnake (Crotalus oreganus helleri) are the most common snakebite accidents in southern California. Intraspecies venom variation may lead to unresponsiveness to antivenom therapy. Even in a known species, venom toxins are recognized as diverse in conformity with interpopulational, seasonal, ontogenetic and individual factors. Five venoms of individual C. oreganus helleri located in Riverside and San Bernardino counties of southern California were studied for their variation in their hemostatic activity. The results demonstrated that Riverside 2 and San Bernardino 1 venoms presented the highest lethal activity without hemorrhagic activity. In contrast, San Bernardino 2 and 3 venoms had the highest hemorrhagic and fibrinolytic activities with low lethal and coagulant activities. Riverside 1, Riverside 2 and San Bernardino 1 venoms presented a significant thrombin-like activity. San Bernardino 2 and 3 venoms presented an insignificant thrombin-like activity. In relation to the fibrinolytic activity, San Bernardino 3 venom was the most active on fibrin plates, which was in turn neutralized by metal chelating inhibitors. These results demonstrate the differences amongst C. oreganus helleri venoms from close localities. A metalloproteinase, hellerase, was purified by anionic and cationic exchange chromatographies from San Bernardino 3 venom. Hellerase exhibited the ability to break fibrin clots in vitro, which can be of biomedically importance in the treatment of heart attacks and strokes.

Chemical modification of Art v 1, a major mugwort pollen allergen, by cis-aconitylation and citraconylation

Art v 1 is the major allergen of mugwort (Artemisia vulgaris) pollen, a significant cause of hay fever all over Europe. Specific immunotherapy is the only treatment modality for allergic disease. Application of modified allergens makes the treatment safer and more efficient. In this work, two out of three (citraconic anhydride, cis-aconitic anhydride, 2,3-dimethylmaleic anhydride) tested anhydrides were proven to be suitable for chemical modifications of allergens. Art v 1 was modified by cis-aconitylation and citraconylation in order to obtain derivatives of Art v 1 that may be suitable for further immunological testing. Acylation of Art v 1 gave derivatives (caaArt v 1 and citArt v 1) with about 80 % modified amino groups. The derivatives were in the monomeric form and had dramatically reduced pI values. Both derivatives were relatively stable at neutral pH values, while the acyl groups undergo hydrolysis under acidic conditions. Modification of allergens by cis-aconitylation and citraconylation could be a new tool for obtaining allergoids.

Bothrops protease A, a unique highly glycosylated serine proteinase, is a potent, specific fibrinogenolytic agent

BACKGROUND

The hemostatic system is the major target of snake venom serine proteinases (SVSPs) that act on substrates of the coagulation, fibrinolytic and kallikrein-kinin systems. Bothrops protease A (BPA), the most glycosylated SVSP, is a non-coagulant, thermostable enzyme. A cDNA encoding BPA showed that the protein has a calculated molecular mass of 25 409 Da, implying that approximately 62% of its molecular mass as assessed by sodium dodecylsulfate polyacrylamide gel electrophoresis (67 kDa) is due to carbohydrate moieties.

RESULTS

Here we show that BPA is a potent fibrinogenolytic agent in vitro, as it readily degraded human and rat fibrinogen at a very low enzyme concentration. Partially N-deglycosylated BPA (p-N-d-BPA) generated similar fibrinogen products, but with enhanced fibrinogenolytic activity. In vivo, injection of 0.75 nmoles of BPA in rats completely avoided thrombus formation induced by stasis in the vena cava, or by endothelium injury in the jugular vein. Moreover, it decreased the fibrinogen plasma level and prolonged the recalcification time. Cleavage of fibrinogen in human and rat plasma was observed with native BPA and p-N-d-BPA by electrophoresis followed by western blot using an anti-fibrinogen antibody. BPA did not cause unspecific degradation of plasma proteins and did not cleave isolated albumin, vitronectin and fibronectin at the same concentration used with fibrinogen. Serine proteinase inhibitors failed to inhibit BPA, probably due to steric hindrance caused by its huge carbohydrate moieties.

CONCLUSIONS

To the best of our knowledge, this investigation underscores a new, thermostable, specific defibrinogenating agent that may have an application in the prevention of thrombus formation.

Characterization of a fibrinolytic enzyme (ussurenase) from Agkistrodon blomhoffii ussurensis snake venom: Insights into the effects of Ca2+ on function and structure

Fibrino(geno)lytic enzymes from snake venoms have been identified as high quality therapeutic agents for treatment of blood clots and strokes. They act on fibrinogen and fibrin, leading to defibrinogenation of blood, lysis of fibrin, and a consequent decrease in blood viscosity. In this work, a fibrinolytic enzyme (ussurenase) from China Agkistrodon blomhoffii Ussurensis snake venom, was purified to homogeneity, identified as a stable 23,367.8 Da monomeric protein, and was identified as a new kind of snake venom metalloproteinase. Ussurenase reacts optimally with fibrin clots at pH 7.5-8.3 and a temperature of 33-41 degrees C. Although many fibrinolytic enzymes are known to be zinc-dependent, measurements from inductively coupled plasma-atomic emission spectroscopy (ICP-AES) reveal that ussurenase is a Ca2+-containing protein with a molar ratio of 1:1 ([Ca2+]:[enzyme]). Ca2+ is crucial to the fibrin clot hydrolysis by ussurenase but also plays an important role in maintaining the structural integrity of the enzyme. The addition of Ca2+ to the apoenzyme induces a conformational change making the environments surrounding the Trp residues of the enzyme more hydrophobic. The presence of Ca2+ also increases the structural stability of ussurenase, so that higher concentrations of the denaturant guanidine hydrochloride are required to denature the native ussurenase compared to the apo-form. UV absorption and CD spectroscopy experiments show that Ca2+ increases the thermostability and changes the secondary structure of ussurenase. All these data suggest that Ca2+ is crucial for the correct folding and activity of ussurenase.

Releasing or expression modulating mediator involved in hemostasis by Berythractivase and Jararhagin (SVMPs)

PIII snake venom metalloproteases (SVMPs) are structurally related to ADAMs (a disintegrin and metalloprotease human family of proteins). Berythractivase and Jararhagin are PIII SVMPs with 69% homology with different hemostatic properties. In order to clarify these differences and further characterize the biological effects of these proteins, we compared the effect of both proteases on human umbilical vein endothelial cell (HUVEC) for evaluating the release and modulation of coagulation and fibrinolysis mechanisms as well as the expression of their correlated genes. We found that both proteins increase the von Willebrand factor liberation, but did not modulate gene expression. Berythractivase, differently from Jararhagin increased the expression of tissue factor. Our results showed that both SVMPs (Berythractivase and Jararhagin) activate HUVEC releasing or modulating mediators involved in hemostasis. Meanwhile, we can suggest through the up-regulation of TF gene that the studied SVMP acts in a specific manner, suggesting that Jararhagin has preferentially a local action, while Berythractivase can be assumed as a systemic pro-coagulant protein with activity on the surface of HUVECs.

Inflammatory effects of BaP1 a metalloproteinase isolated from Bothrops asper snake venom: leukocyte recruitment and release of cytokines

The inflammatory events induced by BaP1, a 22.7 kDa metalloproteinase isolated from Bothrops asper snake venom, were studied. BaP1 i.p. injection in mice induced a marked inflammatory cell infiltrate into peritoneal cavity of animals with predominance of neutrophils in the early phase followed by mononuclear cells in the late period. Inhibition of enzymatic activity of BaP1 by chelation with EDTA resulted in a drastic reduction of this effect. In addition, BaP1 induced a significant increase of blood neutrophil numbers before its accumulation in peritoneal cavity, thus suggesting a stimulatory action of BaP1 on mechanisms of cell mobilization from bone marrow reserve compartments. A reduction in the number of neutrophils was observed in the exudate when antibodies against LECAM-1, CD18 and LFA-1 were used, suggesting the involvement of these adhesion molecules in the effects of BaP1. In contrast, there was no effect with antibodies against ICAM-1 and PECAM-1. Moreover, a conspicuous increment in the levels of IL-1 and TNF-alpha, but not of LTB4, was observed in peritoneal washes collected from mice injected with BaP1. It is concluded that BaP1 induces in vivo a marked leukocyte influx, which parallels an increased number of these cells in the blood, and is associated to the expression of specific leukocyte adhesion molecules and release of chemotactic inflammatory cytokines. Since BaP1 is a P-I class metalloproteinase, these results indicate that the proteolytic domain of metalloproteinases per se can trigger specific inflammatory events.

Sex-based individual variation of snake venom proteome among eighteen Bothrops jararaca siblings

Variation of venom proteome is relevant to basic research, to management of envenoming, and to studies on the evolution of poisonous snakes. In this study, we explored the venom proteomes of eighteen Bothrops jararaca specimens of a single litter born and raised in laboratory. Using electrophoretic techniques and various protocols for measuring the proteolytic activities of these venoms we have detected individual variability and highlighted sex-specific proteomic similarities and differences among sibling snakes. SDS-polyacrylamide gel electrophoresis under non-reducing conditions showed protein bands of approximately 100 kDa specific of male venoms. 2D-electrophoresis showed regions with varying spot complexity between pooled female and male venoms as well as spots that were gender specific. Gelatin zymography showed that female venoms contained proteinases of approximately 25 kDa absent from male venoms. Female venoms were more active than male venoms in degrading fibrinogen whereas on fibrin no significant differences were detected. Among various chromogenic peptide substrates tested, male venoms showed higher amidolytic activity than female venoms on D-Val-Leu-Lys-pNA and D-Phe-Pip-Arg-pNA. Taken together, these results show sex-based differences in the venom proteome of sibling snakes of a single litter raised under controlled conditions which seem to be genetically inherited and imposed by evolutionary forces.

Enzymological characterization of FII(a), a fibrinolytic enzyme from Agkistrodon acutus venom

AIM

To study the enzymological characterization of a fibrinolytic enzyme (FII(a)) from Agkistrodon acutus venom.

METHODS

The fibrinogenolytic effect and the influences of several protease inhibitors, chelating agents, and metal ions on fibrinogenolytic activity were visualized by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The metal content of FII(a) was determined by atomic absorption spectroscopy.

RESULTS

After incubation with FII(a) (0.25 g/L), Aalpha-, Bbeta- and gamma-chains of fibrinogen disappeared within 5 min, 30 min, and 8 h , respectively. The molecular weights of major degradation products were 45,000 and 41,000, which were different from those bands produced by plasmin. The fibrinogenolytic activity of FIIa was strongly inhibited by ethylenediamine tetraacetic acid (EDTA), ethyleneglycol tetraacetic acid (EGTA), dithiothreitol and cysteine, but not by phenylmethyl-sulfonyl fluoride and soybean trypsin inhibitor. Zinc (3171+/-25 mg/kg), potassium (489+/-17 mg/kg) and calcium (319+/-13 mg/kg) were found in FIIa. Zn2+, Ca2+ and Mg2+ could recover the fibrinogenolytic activity of FIIa, which was inhibited by EDTA. Only Ca2+ could recover the fibrinogenolytic activity inhibited by EGTA.

CONCLUSION

FIIa can degrade the Aalpha-, Bbeta- and gamma-chains of fibrinogen. FII(a) is a metalloproteinase, and Zn2+, Ca2+, and disulfide bonds are necessary for its fibrinogenolytic activity.

Snake venom fibrin(ogen)olytic enzymes

Snake venoms contain a number of serine and metalloproteinases and included among these are the fibrin(ogen)olytic proteinases. Some years ago it was postulated that the fibrin(ogen)olytic enzymes may be clinically useful. Over the past 150 years a substantial body of literature has been generated on the identification and characterization of fibrin(ogen)olytic enzymes from a broad spectrum of snake species. In this review we describe the two different classes of fibrin(ogen)olytic enzymes isolated from snake venom and we summarize a number of studies aimed at characterizing the purified enzymes and/or their derivatives. Two distinct classes of venom fibrin(ogen)olytic enzymes have been previously identified, the metalloproteinases and serine proteinases. These two classes of proteinases differ in their mechanism of action and they target different amino acid sequences in fibrin(ogen), but each perform the same role in nature. When a snake envenomates its prey it needs a mechanism to facilitate the spread of the toxic components throughout the circulation. Fibrin(ogen)olytic enzymes break down fibrin rich clots and help to prevent further clot formation by their action on fibrinogen. This characteristic feature has led to development of fibrin(ogen)olytic snake venom enzymes as potential clinical agents to treat occlusive thrombi. Fibrolase, a fibrinolytic metalloproteinase isolated from Agkistrodon contortrix contortrix venom and the serine beta-fibrinogenolytic proteinase from Vipera lebetina have been chosen as representative enzymes from the two classes, and their biochemical and physiochemical properties will be described in detail. Finally, the characterization and development of alfimeprase, a recombinant fibrinolytic enzyme derived from fibrolase, as a clinical agent is described citing the progression from the laboratory bench to its current status as having successfully completed Phase II clinical trials.

Inflammatory effects of snake venom metalloproteinases

Metalloproteinases are abundant enzymes in crotaline and viperine snake venoms. They are relevant in the pathophysiology of envenomation, being responsible for local and systemic hemorrhage frequently observed in the victims. Snake venom metalloproteinases (SVMP) are zinc-dependent enzymes of varying molecular weights having multidomain organization. Some SVMP comprise only the proteinase domain, whereas others also contain a disintegrin-like domain, cysteine-rich, and lectin domains. They have strong structural similarities with both mammalian matrix metalloproteinases (MMP) and members of ADAMs (a disintegrin and metalloproteinase) group. Besides hemorrhage, snake venom metalloproteinase induce local myonecrosis, skin damage, and inflammatory reaction in experimental models. Local inflammation is an important characteristic of snakebite envenomations inflicted by viperine and crotaline snake species. Thus, in the recent years there is a growing effort to understand the mechanisms responsible for SVMP-induced inflammatory reaction and the structural determinants of this effect. This short review focuses the inflammatory effects evoked by SVMP.

Structural considerations of the snake venom metalloproteinases, key members of the M12 reprolysin family of metalloproteinases

The importance of proteinases in the pathologies associated with Viperid envenoming has long been appreciated. Over the past 40 years substantial research has clearly implicated metalloproteinases in the venom (snake venom metalloproteinases; SVMPs) as playing key roles in the development of such symptoms as hemorrhage, edema, hypotension, hypovolemia, inflammation and necrosis. In spite of this wealth of information there are still many unresolved questions pertaining to the structural basis for the various SVMPS giving rise to the diversity of activities. In this short review we will not attempt to provide an exhaustive collation of structural studies on the SVMPs; however, we will give a brief outline of the structural classification of the SVMPs; as well as relate them to the other members of the reprolysin family of metalloproteinases, the ADAMs. The information put forth in the text does not allow specific conclusions to be drawn on the structural basis for SVMP functional diversity, but it is our goal that it will allow for the development of testable hypotheses that can be experimentally pursued. What the reader will observe is that there are very interesting structural features displayed by the various SVMP classes and subclasses that provide insight into their functional characteristics.

Duvernoy's gland secretion of Philodryas patagoniensis from the northeast of Argentina: its effects on blood coagulation

Duvernoy's gland secretion of Philodryas patagoniensis exhibits high hemorrhagic activity, containing enzymes that are able to degrade the vascular wall. In this work we aim to determine if the secretion can also affect the hemostatic system by causing changes in blood coagulation. Procoagulant and coagulant activities were evaluated on plasma and fibrinogen, respectively. The delay in the thrombin clotting time of fibrinogen previously incubated with the secretion was also determined. Specific hydrolysis of fibrinogen and fibrin incubated with the secretion at different time intervals was shown by electrophoresis on polyacrylamide gel. To determine the structural characteristics of the enzymes degrading fibrinogen and fibrin, secretion were incubated in the presence of 45 mM Na(2)EDTA, 40 mM Benzamidine, and/or 2 mM PMSF before the incubation with fibrinogen or fibrin, respectively. The effect in vivo was investigated in adult male rats injected with different dose of secretion, aliquots of blood were withdrawn at different time intervals, and the fibrinogen concentration was determined. Duvernoy's gland secretion of P. patagoniensis did not clot plasma or fibrinogen. It exhibited a potent fibrinogenolytic activity degrading the Aalpha-chain faster than the Bbeta-chain, whereas gamma-chain was resistant. This latter corresponded with a strong delay in the thrombin clotting time of fibrinogen (4 mg/ml) pre-incubated with the secretion, being 9.53 microg the amount of protein from Duvernoy's gland secretion that increased the thrombin clotting time from 20 to 60 s. In vivo, the loss of rat plasma fibrinogen was proportional to the amount of secretion injected. The secretion also hydrolyzed fibrin degrading the alpha-monomer. Inhibition studies with Na(2)EDTA, Benzamidine, and/or PMSF showed that metalloproteinases and serinoproteinases are the main enzymes responsible for the hydrolyzing activity on fibrinogen and fibrin. All these results demonstrate that Duvernoy's gland secretion of P. patagoniensis possesses enzymes able to hydrolyze plasma components playing a relevant role in the blood coagulation. These hydrolyzing activities and those acting on the wall of blood vessels let the secretion exhibit a high hemorrhagic activity, which may result in permanent sequelae or even cause the death of the victims bitten by this colubrid snake.

Isolation of anticoagulant from the venom of tick, Boophilus calcaratus, from Uzbekistan

Boophilus calcaratus is a tick found in Central Asia and a common parasite to domestic animals. Venom from this tick was fractionated by two-step column chromatography, Sephadex G-75, and DEAE-Sephadex A-25. The homogeneity of the anticoagulant was examined by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The purified component is named calcaratin and has a molecular weight of 14,500. The effect of the purified anticoagulant component (calcaratin) on various sites of the blood coagulation cascade scheme was examined and compared with crude venom. The chromogenic substrates S-2238 (H-D-Phe-Pip-Arg-pNA 2HCl) for thrombin and S-2765 (N-alpha-Z-D-Arg-Gly-Arg-pNA 2HCl) for factor Xa were also investigated. Activated partial clotting times were all prolonged, suggesting the anticoagulation nature of the purified component and crude venom. Prolongation of fibrinogen clotting time (FCT) is highly suggestive of the antithrombin property of the purified component and its original venom.

The effect of post-translational modifications on the hemorrhagic activity of snake venom metalloproteinases

Metalloproteinases (MPs) are Zn(+)-dependent endoproteolytic enzymes, abundant in crotalid and viperid snake venoms. Most snake venom metalloproteinases (svMPs) are active on extracellular matrix components and this effect is thought to result in bleeding as a consequence of the basement membrane disruption in capillaries. Jararhagin and ACLH are hemorrhagic svMPs from Bothrops jararaca and Agkistrodon contortrix laticinctus venom, respectively. Both enzymes demonstrate proteolytic activity on fibrinogen and fibronectin and jararhagin inhibits collagen-induced platelet aggregation in vitro. This work describes the expression, purification and successful refolding of the recombinant ACLH zymogen (rPRO-ACLH) as well as the catalytic domain of jararhagin (rCDJARA). The heterologous proteins were produced in E. coli, an in vivo expression system that does not make post-translational modifications. The recombinant refolded proteins did not show any hemorrhagic activity in mice skin, as well as the native deglycosylated jararhagin and ACLH. However, they preserved their proteolytic activity on fibrinogen and fibronectin. It seems that the hemorrhagic properties of these hemorrhagins are dependent on post-translational modifications, whereas their proteolytic activity is not dependent on such modifications.

Biological characterization of glutaraldehyde-modified Parietaria judaica pollen extracts

BACKGROUND

Allergoids are widely used in specific immunotherapy (SIT) for the treatment of IgE-mediated allergic diseases, but all techniques for standardization of conventional allergic extracts may not be appropriate for standardization of a glutaraldehyde (GA)-modified extract because of the unique characteristics of these extracts.

OBJECTIVE

To assess an accurate methodology for standardization of chemically modified extracts.

METHODS

GA-modified extracts from Parietaria judaica pollen were purified by diafiltration. Biochemical properties were investigated by determination of amino groups, chromatography, and SDS-PAGE. The IgE-binding activity was determined by skin prick test, enzyme allergosorbent test inhibition, basophil activation, and histamine release tests. Peripheral blood mononuclear cells (PBMCs) from P. judaica pollen-allergic subjects were stimulated with either native or allergoid extracts, and proliferation was measured.

RESULTS

Biochemical data indicated a high degree of allergen polymerization resulting in extract components higher than 100 kDa. IgE-binding activity, both in vivo and in vitro, was reduced by more than 99.8%. Both allergen and allergoid induced PBMC proliferation and synthesis of blocking IgG antibodies at similar rates. Moreover, no evidence of introduction of new determinants by chemical modification was found.

CONCLUSIONS

The preparation of GA-modified extracts by diafiltration is faster and more reliable than previous chromatographic methods. These modified extracts have drastically reduced their allergenicity while maintaining their immunogenicity, and therefore they can be used in safer and shortened schedules of SIT.

Expression, refolding, and in vitro activation of a recombinant snake venom pro-metalloprotease

Metalloproteases comprise a family of Zn(2+)-endopeptidases that degrade most components of the extracellular matrix. Snake venoms are rich sources of metalloproteases, which also digest fibrinogen as well as fibrin, and in some cases, induce hemorrhage. A few low-molecular weight snake venom metalloproteases (svMPs) have been described as being devoid of hemorrhagic activity, but they have strong direct-acting fibrinolytic activity. This property could be very helpful in thrombosis therapy. ACLF is a fibrinolytic, non-hemorrhagic metalloprotease from the venom of the North American snake Agkistrodon contortrix laticinctus. We have developed an expression system for production of a recombinant pro-ACLF from a clone (ACLPREF) isolated from a venom gland cDNA library. The coding region including both the pro-enzyme domain and the mature protein domain was amplified by PCR and subcloned into the pET28a vector and the new plasmid was used to transform BL21(DE3) Escherichia coli cells. Culture of the transformants at 37 degrees C led to the overexpression of an insoluble 48kDa protein after induction with 1.0mM IPTG. The expressed protein was recovered from inclusion bodies with 6M buffered urea and purified by affinity chromatography under denaturing conditions. After dithiothreitol treatment, protein refolding was performed by gradual removal of the denaturing agent by dialysis. The pro-enzyme underwent auto-activation during refolding and it was active on fibrinogen and on a synthetic substrate. To control the activation step, the denaturing agent was rapidly removed to keep the protein in an unprocessed form, followed by later addition of Ca(2+) and Zn(2+) ions. This allowed controlling the enzyme activation, when it is needed.

Purification and characterization of a prothrombin-activating protease from Nephila clavata

We report upon the purification and characterization of a novel prothrombin-activating enzyme from the body fluid (total homogenates of isolated digestive tract without eggs, spinnerets and silk glands) of the spider, Nephila clavata by a combination of acetone fractionation, ion exchange, and Soybean trypsin inhibitor-Sepharose chromatography. Analysis of the purified enzyme with SDS-PAGE and gel filtration revealed a single polypeptide chain with an apparent molecular weight of 24kDa. The proteolytic activity of the enzyme was stable up to 50 degrees C, however, it became unstable over 55 degrees C. The enzyme had an optimum pH of 8, and Ca(2+) was not required for the enzyme activity. According to inhibition profiles obtained with several serine protease inhibitors such as PMSF and benzamidine, the purified protease is a member of the serine proteases. Bz-Ile-Glu(gamma-OR)- Gly-Arg-pNA and Z-Arg-Gly-Arg-pNA which are known as substrates for factor Xa, were hydrolyzed favorably by the enzyme. And the Nephila protease could produce thrombin from prothrombin at nM range, and form the turbid ring using fibrinogen-agarose plate. The results obtained confirmed that the purified protease is a potent prothrombin-activating activity belonging to the family of serine protease.

Purification and biochemical characterization of F II(a), a fibrinolytic enzyme from Agkistrodon acutus venom

A fibrinolytic enzyme, F II(a), was isolated from Agkistrodon acutus venom by ion-exchange chromatography and gel filtration. F II(a) consisted of a single polypeptide chain with a molecular weight of 26,000 and an isoelectric point of 4.6. F II(a) was shown to solubilize fibrin and fibrinogen. F II(a) cleaved, primarily, the alpha chain of fibrinogen and fibrin followed by the beta chain, while the gamma chain was minimally affected. Thus, the enzyme was an alpha,beta-fibrinogenase. The cleavage pattern of fibrinogen clearly varied from plasmin cleavage of the same molecule. In vivo, F II(a) had no influence on the rat's tissue-type plasminogen activator and plasminogen activator inhibitor-1 activities in plasma. At the dosage of 5mg/kg, histological examination of heart, liver and lung tissue showed no hemorrhage. F II(a) is an enzyme that hydrolyzed fibrin directly without hemorrhagic activity.

Snake venoms

Snake venoms are complex mixtures containing many different biologically active proteins and peptides. A number of these proteins act on components of the haemostatic system in humans. The paper focuses on those venom constituents that affect the blood coagulation pathway, endothelial cells and platelets. Several highly purified venom enzymes have been used clinically as anticoagulants, and other venom proteins are being used in preclinical research to investigate their possible therapeutic potential. Haemostatically active components are distributed widely in the venom of many different snake species. In no case are all the components described below found in any single venom. Venom components can be grouped into several categories depending on their haemostatic effect. The following haemostatically active components are discussed in this chapter: enzymes that cause fibrinogen coagulation: enzymes that degrade fibrin(ogen); plasminogen activator; prothrombin activators; factor V activator; factor X activator; anticoagulant activities: enzymes with haemorrhagic activity; platelet aggregation inducers: and platelet aggregation inhibitors.

Haemorrhagic protein of Russell's viper venom with fibrinolytic and esterolytic activities

A haemorrhagic toxin specifically active on skin and muscle at the site of introduction in mice has been purified from Vipera russelli russelli (Indian subspecies of Russell's viper) venom by CM-Sephadex C-50 ion exchange chromatography and size exclusion (SE)-HPLC. This toxic protein also has strong fibrinolytic and arginine esterolytic activities. The purified preparation was a single polypeptide chain of molecular weight 73,000, as revealed by SDS-PAGE and SE-HPLC under native and denatured conditions. It has been named as VRR-73. Atomic absorption spectrometry indicated the existence of Mg(2+) in a mol per mol ratio. Antiserum was effective in neutralizing haemorrhage when administered immediately following VRR-73 but was ineffective in inhibiting fibrinolytic and esterolytic activities. On the other hand phenylmethyl sulphonyl fluoride and EDTA inhibited fibrinolysis and esterolysis but did not affect haemorrhage. Thermal denaturation of VRR-73, after exposure at 100 degrees C for 10 min, led to inactivation of all of its activities. Fibrinolytic and esterolytic activities, but not the haemorrhagic activity, were slowly regained after cooling at 25 degrees C. Thus the two pathological activities of VRR-73 appear to be associated with two different regions of the molecule.

Structural and functional characterization of neuwiedase, a nonhemorrhagic fibrin(ogen)olytic metalloprotease from Bothrops neuwiedi snake venom

A fibrino(geno)lytic nonhemorrhagic metalloprotease (neuwiedase) was purified from Bothrops neuwiedi snake venom by a single chromatographic step procedure on a CM-Sepharose column. Neuwiedase represented 4.5% (w/w) of the crude desiccated venom, with an approximate Mr of 20,000 and pI 5.9. As regards the amino acid composition, neuwiedase showed similarities with other metalloproteases, with high proportions of Asx, Glx, Leu, and Ser. Atomic absorption spectroscopy showed that one mole of Zn2+ and one mole of Ca2+ were present per mole of protein. The cDNA encoding neuwiedase was isolated by RT-PCR from venom gland RNA, using oligonucleotides based on the partially determined amino-acid sequences of this metalloprotease. The full sequence contained approximately 594 bp, which codified the 198 amino acid residues with an estimated molecular weight of 22,375. Comparison of the nucleotide and amino acid sequences of neuwiedase with those of other snake venom metalloproteases showed a high level of sequential similarity. Neuwiedase has two highly conserved characteristics sequences H142E143XXH146XXG149XXH152 and C164I165M166. The three-dimensional structure of neuwiedase was modeled based on the crystal structure of Crotalus adamanteus Adamalysin II. This model revealed that the zinc binding site region showed a high structural similarity with other metalloproteases. The proteolyitc specificity, using the Bbeta-chain of oxidized insulin as substrate, was shown to be directed to the Ala14-Leu15 and Tyr16-Leu17 peptide bonds which were preferentially hydrolyzed. Neuwiedase is a Aalpha,Bbeta fibrinogenase. Its activity upon the Aalpha chain of fibrinogen was detected within 15 min of incubation. The optimal temperature and pH for the degradation of both Aalpha and Bbeta chains were 37 degrees C and 7.4-8.0, respectively. This activity was inhibited by EDTA and 1,10-phenantroline. Neuwiedase also showed proteolytic activity upon fibrin and some components of the extracellular matrix. However, it did not show TAME esterase activity and was not able to inhibit platelet aggregation.

Snake venom metalloproteinases: their role in the pathogenesis of local tissue damage

The biochemical characteristics of hemorrhagic metalloproteinases isolated from snake venoms are reviewed, together with their role in the pathogenesis of the local tissue damage characteristic of crotaline and viperine snake envenomations. Venom metalloproteinases differ in their domain structure. Some enzymes comprise only the metalloproteinase domain, others have disintegrin-like and high cysteine domains and others present, besides these domains, an additional lectin-like subunit. All of them are zinc-dependent enzymes with highly similar zinc binding environments. Some metalloproteinases induce hemorrhage by directly affecting mostly capillary blood vessels. It is suggested that hemorrhagic enzymes cleave, in a highly selective fashion, key peptide bonds of basement membrane components, thereby affecting the interaction between basement membrane and endothelial cells. As a consequence, these cells undergo a series of morphological and functional alterations in vivo, probably associated with biophysical hemodynamic factors such as tangential fluid shear stress. Eventually, gaps are formed in endothelial cells through which extravasation occurs. In addition to hemorrhage, venom metalloproteinases induce skeletal muscle damage, myonecrosis, which seems to be secondary to the ischemia that ensues in muscle tissue as a consequence of bleeding and reduced perfusion. Microvessel disruption by metalloproteinases also impairs skeletal muscle regeneration, being therefore responsible of fibrosis and permanent tissue loss after snakebites. Moreover, venom metalloproteinases participate in the degradation of extracellular matrix components and play a relevant role in the prominent local inflammatory response that characterizes snakebite envenomations, since they induce edema, activate endogenous matrix metalloproteinases (MMPs) and are capable of releasing TNF-alpha from its membrane-bound precursor. Owing to their protagonic role in the pathogenesis of local tissue damage, snake venom metalloproteinases constitute relevant targets for natural and synthetic inhibitors which may complement antivenoms in the neutralization of these effects.

Expression, refolding, and activity of a recombinant nonhemorrhagic snake venom metalloprotease

Snake venoms are rich sources of proteases that strongly affect the vascular system, by promoting blood coagulation, hemorrhage, and fibrinolysis. Hemorrhagic activity is mostly due to the enzymatic action of metalloproteases on capillary basement membrane components, such as collagen IV, laminin, and fibronectin. A few low-molecular-weight snake venom metalloproteases (svMP) have been described as being devoid of hemorrhagic activity, but they have strong direct-acting fibrinolytic activity that could be very helpful in thrombosis therapy. We have developed an expression system for production of a recombinant svMP from a cDNA (ACLPREF) coding for a small metalloprotease (ACLF) with three disulfide bonds from an Agkistrodon contortrix laticinctus (broad-banded copperhead) venom gland cDNA library. The mature protein-coding region was amplified by PCR and subcloned into the pET28a vector, and the resulting plasmid was used to transform BL21(DE3) Escherichia coli cells. Culture of the transformants at either 37 or 20 degrees C led to the overexpression of an insoluble and inactive 30-kDa protein after 1.0 mM IPTG induction. The expressed protein (rACLF) was recovered from inclusion bodies with 6 M buffered urea solution and purified on a nickel-Sepharose column followed by gel filtration chromatography, both under denaturing conditions. After treatment with dithiothreitol, protein refolding was performed by gradual removal of the denaturing agent by dialysis. The refolded recombinant protein was active in fibrin-agarose plates. The purified protein achieved a conformation similar to that of the native enzyme as judged by circular dichroism analysis.

Hannahpep: A novel fibrinolytic peptide from the Indian King Cobra (Ophiophagus hannah) venom

A novel fibrinolytic peptide (Hannahpep) was isolated and purified from the venom of the Indian King Cobra (Ophiophagus hannah) by thin-layer chromatography followed by reverse-phase high-performance liquid chromatography. The MW of the peptide was found to be 610 Da and the amino acid sequence of Hannahpep was determined to be Arg, His, Ala, Arg, His, Asp. Hannahpep produced defibrinogenating activity in male albino mice. It exhibited significant fibrinolytic and fibrinogenolytic activity in vitro. Hannahpep showed plasma-anticlotting activity. However, it lacked hemolytic, hemorrhagic, or phospholipase activity. This peptide may have possible therapeutic application in the management of thrombosis or occlusion of a blood vessel.

A fibrinolytic enzyme from a marine green alga, Codium latum

A fibrinolytic enzyme was isolated from a marine green alga, Codium latum, and designated C. latum protease (CLP). It also had fibrinogenolytic activity, hydrolyzing A alpha, B beta and gamma chains with preference in this order. As CLP hydrolyzed oxidized insulin B chain at position Arg22-Gly23, and the peptide map of lysozyme digested with CLP was similar to that with trypsin, CLP would be expected to have a high substrate specificity, similar to that of trypsin. Protease activity peaked at pH 10, and was completely inhibited by diisopropyl fluorophosphate (DFP). Therefore, we conclude that CLP is a trypsin-like serine protease.

Lebetase, an alpha(beta)-fibrin(ogen)olytic metalloproteinase of Vipera lebetina snake venom, is inhibited by human alpha-macroglobulins

The effects of the plasma proteinase inhibitors alpha(2)-macroglobulin (alpha(2)M) and the alpha(2)M-related pregnancy zone protein (PZP) were evaluated towards the metalloproteinase lebetase, isolated from Vipera lebetina venom. We demonstrate that lebetase interacts with both inhibitors. Cleavage of alpha(2)M by lebetase resulted in the formation of 90-kDa fragments, and covalent complexes of alpha(2)M with lebetase were observed. The proteolytic activity of lebetase against fibrinogen and azocasein could be inhibited by alpha(2)M. Cleavage of PZP also resulted in the formation of 90-kDa fragments, and complexes of both dimer and tetramer forms of PZP with lebetase were detected. The amino acid sequence identification of the sites of specific proteolysis of alpha(2)M and PZP demonstrate that the cleavage sites are within the bait regions of both proteins. Lebetase I cleaves between Arg(696)-Leu(697), which is one of the most common cleavage sites in alpha(2)M by proteinases. The other two cleavage sites in alpha(2)M by lebetase are Gly(679)-Leu(680) and His(694)-Ala(695). The cleavage between Pro(689)-Gln(690) is the only cleavage site identified in PZP. In that lebetase is an anticoagulation agent in vivo, we propose that the interaction of lebetase with alpha(2)M may suggest a reduced fibrin(ogen)olytic activity of lebetase in human.

Screening for fibrinolytic activity in eight Viperid venoms

Snake venoms contain direct-acting fibrinolytic metalloproteinases (MMP) that could have important applications in medicine. Fibrinolytic enzymes isolated from venom can induce in vitro clot lysis by directly acting on a fibrin clot. The most ideal fibrinolytic enzyme would have high affinity for clots, dissolve clots directly without causing hemorrhage, and would not be neutralized in vivo by endogenous metalloproteinase inhibitors. The purpose of this study was to compare DEAE/HPLC venom profiles from Viperid snakes and identify fractions that contain fibrinolytic activity with no hemorrhagic activity and are not neutralized by animal sera. The sera selected were from four (Virginia opossum, Gray woodrat, Mexican ground squirrel, and Hispid cottonrat) animals known to neutralize hemorrhagic activity in snake venoms. Nineteen fractions from the Viperid venoms had fibrinolytic activity. Agkistrodon venom fractions contained the highest specific fibrinolytic activities. A. piscivorus leucostoma fraction 4 contained a high specific fibrinolytic activity, no hemorrhagic activity, and the fibrinolytic activity was not neutralized by the proteinase inhibitors of the four animal sera. A. contortrix laticinctus fraction 1 also had a high specific fibrinolytic activity and no hemorrhagic activity. However, the fibrinolytic activity was neutralized by Didelphis virginiana (Virginia opossum) serum.

Characterization of the local tissue damage induced by LHF-II, a metalloproteinase with weak hemorrhagic activity isolated from Lachesis muta muta snake venom

Local tissue damage induced by LHF-II, a 22-kDa hemorrhagic metalloproteinase from Lachesis muta venom was studied. Intravital microscopy experiments evidenced hemorrhagic events 2 min after LHF-II application onto cremaster muscle, characterized by microhemorrhages in capillary vessels and venules. However, histological analysis showed only mild hemorrhage in the gastrocnemius muscle. LHF-II degraded laminin, fibronectin and type IV collagen upon incubation in vitro, but was not cytotoxic to capillary endothelial cells in culture. Intramuscular injection of LHF-II induced a mild myonecrosis, with early small increments in plasma creatine kinase activity. It also induced edema in the mouse footpad at doses where hemorrhage is absent. Injection of LHF-II induced the synthesis of matrix metalloproteinases evidenced in muscle homogenates and in exudate samples. It is concluded that LHF-II has weak hemorrhagic and myotoxic activities, and that its role in the pathogenesis of L. muta-induced local tissue damage is associated with edema formation and degradation of extracellular matrix components, either directly or by activation of endogenous matrix metalloproteinases.

Purification and characterization of brevinase, a heterogeneous two-chain fibrinolytic enzyme from the venom of Korean snake, Agkistrodon blomhoffii brevicaudus

A fibrinolytic enzyme, designated as brevinase, was purified from the venom of Korean snake, Agkistrodon blomhoffii brevicaudus. Brevinase cleaved both the Aalpha- and Bbeta-chains of fibrinogen but did not affect the gamma-chain. It showed beta-fibrinogenase activity devoid of fibrinogen clotting and caseinolytic activity. The fibrinolytic activity was completely inhibited by PMSF, DFP, Pefabloc, and DTT, indicating brevinase is a serine protease requiring disulfide bridge(s) for its activity. It kept 80% of the initial activity after heating at 100 degrees C for 3 min, showed an equal maximum activity in the pH range from 5.5 to 8.5, and was inactivated by Zn(2+). Brevinase consists of two polypeptide chains of 16.5 and 17 kDa linked by disulfide bridge(s). The N-terminal amino acid sequences of 16.5 and 17 kDa chains showed homology to the N-terminal and the internal (central region) amino acid sequences of single-chain fibrinolytic enzymes in snake venom, respectively.

Snake venoms and the hemostatic system

Snake venoms are complex mixtures containing many different biologically active proteins and peptides. A number of these proteins interact with components of the human hemostatic system. This review is focused on those venom constituents which affect the blood coagulation pathway, endothelial cells, and platelets. Only highly purified and well characterized snake venom proteins will be discussed in this review. Hemostatically active components are distributed widely in the venom of many different snake species, particularly from pit viper, viper and elapid venoms. The venom components can be grouped into a number of different categories depending on their hemostatic action. The following groups are discussed in this review: (i) enzymes that clot fibrinogen; (ii) enzymes that degrade fibrin(ogen); (iii) plasminogen activators; (iv) prothrombin activators; (v) factor V activators; (vi) factor X activators; (vii) anticoagulant activities including inhibitors of prothrombinase complex formation, inhibitors of thrombin, phospholipases, and protein C activators; (viii) enzymes with hemorrhagic activity; (ix) enzymes that degrade plasma serine proteinase inhibitors; (x) platelet aggregation inducers including direct acting enzymes, direct acting non-enzymatic components, and agents that require a cofactor; (xi) platelet aggregation inhibitors including: alpha-fibrinogenases, 5'-nucleotidases, phospholipases, and disintegrins. Although many snake venoms contain a number of hemostatically active components, it is safe to say that no single venom contains all the hemostatically active components described here. Several venom enzymes have been used clinically as anticoagulants and other venom components are being used in pre-clinical research to examine their possible therapeutic potential. The disintegrins are an interesting group of peptides that contain a cell adhesion recognition motif, Arg-Gly-Asp (RGD), in the carboxy-terminal half of their amino acid sequence. These agents act as fibrinogen receptor (integrin GPIIb/IIIa) antagonists. Since this integrin is believed to serve as the final common pathway leading to the formation of platelet-platelet bridges and platelet aggregation, blockage of this integrin leads to inhibition of platelet aggregation regardless of the stimulating agent. Clinical trials suggest that platelet GPIIb/IIIa blockade is an effective therapy for the thrombotic events and restenosis frequently accompanying cardiovascular and cerebrovascular disease. Therefore, because of their clinical poten tial, a large number of disintegrins have been isolated and characterized.

Purification from Bothrops lanceolatus (fer de lance) venom of a fibrino(geno)lytic enzyme with esterolytic activity

Bothrops lanceolatus venom has high caseinolytic, phospholipasic, esterolytic and hemorrhagic activities. In spite of having no coagulant effect on plasma, this venom contains a thrombin-like enzyme. Using gel filtration and ion-exchange chromatographies, we have purified an esterolytic fraction (F-II-1a) from this venom with a protein yield of 4% and a 58% recovery in enzyme activity. SDS-PAGE in the presence of beta-mercaptoethanol showed that the enzyme is a single chain polypeptide with a MW=38,100. Immunodiffusion and immunoelectrophoresis of fraction F-II-1a against serum from horses immunized with B. lanceolatus venom and against rabbit antiserum prepared using fraction F-II-1a both showed a single immunoprecipitin line. The Km and Vmax values for TAME hydrolysis were 0.85 mM and 38.6 micromol/min/mg, respectively. The esterolytic activity was completely inhibited by PMSF (10 mM) but not by EDTA (20 mM). Fraction F-II-1a hydrolyzed the alpha and beta chains of fibrinogen. Degradation of the alpha chain occurred within 10 min while that of the beta-chain was slower. The enzyme had no effect on the gamma-chain even after 4 h of hydrolysis.

Biochemical characterization of lebetase, a direct-acting fibrinolytic enzyme from Vipera lebetina snake venom

Lebetase, the fibrinolytic enzyme isolated from Vipera lebetina (Levantine viper) snake venom is a metalloenzyme that contains one mole of Zn2+ and one mole of Ca2+ per mole of protein. Lebetase is inhibited by dithiothreitol, suggesting that disulfide bonds are necessary for holding the structure. Vipera lebetina venom contains several isoforms of lebetase in the interval of pI 4.6-5.4. Two lebetase fractions I (pI of the main component 5.0) and II (pI of the main component 5.3) degrade fibrin and fibrinogen by hydrolysis of the alpha and beta chains. The molecular weights of the cleavage products produced by the two different lebetase fractions are identical. The metal ions, Cd2+, Cu2+, Co2+, inhibit fibrinolytic and caseinolytic activity of lebetase I and II. Using mass spectrometry we characterized differences in molecular masses of lebetase I and II (22719 Da and 22912 Da). Vipera lebetina venom from a single snake contains mainly one form of lebetase. Lebetase I is more stable at low pH than lebetase II. The lebetases I and II inhibit platelet aggregation induced by ADP in a dose-dependent manner.