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

Sialic acid-containing glycans play a role in the activity of snake venom proteases

Structural variability is a feature of snake venom proteins, and glycosylation is a post-translational modification that contributes to the diversification of venom proteomes. Studies by our group have shown that Bothrops venoms are distinctly defined by their glycoprotein content, and that most hybrid/complex N-glycans identified in these venoms contain sialic acid. Considering that metalloproteases and serine proteases are abundant components of Bothrops venoms and essential in the envenomation process, and that these enzymes contain several glycosylation sites, the role of sialic acid in venom proteolytic activity was evaluated. Here we show that removal of sialic acid by treatment of nine Bothrops venoms with neuraminidase (i) altered the pattern of gelatinolysis in zymography of most venoms and reduced the gelatinolytic activity of all venoms, (ii) decreased the proteolytic activity of some venoms on fibrinogen and the clotting activity of human plasma of all venoms, and (iii) altered the proteolysis profile of plasma proteins by B. jararaca venom, suggesting that sialic acid may play a role in the interaction of proteases with their protein substrates. In contrast, the profile of venom amidolytic activity on Bz-Arg-pNA did not change after removal of sialic acid, indicating that this monosaccharide is not essential in N-glycans of serine proteases acting on small substrates. In summary, these results expand the knowledge about the variability of the subproteomes of Bothrops venom proteases, and for the first time point to the importance of carbohydrate chains containing sialic acid in the enzymatic activities of venom proteases relevant in human envenomation.

Two-Dimensional Blue Native/SDS Polyacrylamide Gel Electrophoresis for Analysis of Brazilian Bothrops Snake Venoms

Viperidae snakes are the most important agents of snakebites in Brazil. The protein composition of snake venoms has been frequently analyzed by means of electrophoretic techniques, but the interaction of proteins in venoms has barely been addressed. An electrophoretic technique that has gained prominence to study this type of interaction is blue native polyacrylamide gel electrophoresis (BN-PAGE), which allows for the high-resolution separation of proteins in their native form. These protein complexes can be further discriminated by a second-dimension gel electrophoresis (SDS-PAGE) from lanes cut from BN-PAGE. Once there is no study on the use of bidimensional BN/SDS-PAGE with snake venoms, this study initially standardized the BN/SDS-PAGE technique in order to evaluate protein interactions in Bothrops atrox, Bothrops erythromelas, and Bothrops jararaca snake venoms. Results of BN/SDS-PAGE showed that native protein complexes were present, and that snake venom metalloproteinases and venom serine proteinases maintained their enzymatic activity after BN/SDS-PAGE. C-type lectin-like proteins were identified by Western blotting. Therefore, bidimensional BN/SDS-PAGE proved to be an easy, practical, and efficient method for separating functional venom proteins according to their assemblage in complexes, as well as to analyze their biological activities in further details.

Fibrinogenolysis in Venom-Induced Consumption Coagulopathy after Viperidae Snakebites: A Pilot Study

Envenomations that are caused by Viperidae snakebites are mostly accompanied by venom-induced consumption coagulopathy (VICC) with defibrination. The clinical course of VICC is well described; however, reports about its detailed effects in the hemocoagulation systems of patients are sparse. In this pilot study, we prospectively analyzed the changes in plasma fibrinogen that were caused by the envenomation of six patients by five non-European Viperidae snakes. Western blot analysis was employed and fibrinogen fragments were visualized with the use of specific anti-human fibrinogen antibodies. All of the studied subjects experienced hypo- or afibrinogenemia. The western blot analysis demonstrated fibrinogenolysis of the fibrinogen chains in all of the cases. Fibrinogenolysis was considered to be a predominant cause of defibrination in Crotalus, Echis, and Macrovipera envenomation; while, in the cases of VICC that were caused by Atheris and Calloselasma envenomation, the splitting of the fibrinogen chains was present less significantly.

Exploring the Utility of Recombinant Snake Venom Serine Protease Toxins as Immunogens for Generating Experimental Snakebite Antivenoms

Snakebite is a neglected tropical disease that causes high rates of global mortality and morbidity. Although snakebite can cause a variety of pathologies in victims, haemotoxic effects are particularly common and are typically characterised by haemorrhage and/or venom-induced consumption coagulopathy. Despite polyclonal antibody-based antivenoms being the mainstay life-saving therapy for snakebite, they are associated with limited cross-snake species efficacy, as there is often extensive toxin variation between snake venoms, including those used as immunogens for antivenom production. This restricts the therapeutic utility of any antivenom to certain geographical regions. In this study, we explored the feasibility of using recombinantly expressed toxins as immunogens to stimulate focused, pathology-specific, antibodies in order to broadly counteract specific toxins associated with snakebite envenoming. Three snake venom serine proteases (SVSP) toxins, sourced from geographically diverse and medically important viper snake venoms, were successfully expressed in HEK293F mammalian cells and used for murine immunisation. Analyses of the resulting antibody responses revealed that ancrod and RVV-V stimulated the strongest immune responses, and that experimental antivenoms directed against these recombinant SVSP toxins, and a mixture of the three different immunogens, extensively recognised and exhibited immunological binding towards a variety of native snake venoms. While the experimental antivenoms showed some reduction in abnormal clotting parameters stimulated by the toxin immunogens and crude venom, specifically reducing the depletion of fibrinogen levels and prolongation of prothrombin times, fibrinogen degradation experiments revealed that they broadly protected against venom- and toxin-induced fibrinogenolytic functional activities. Overall, our findings further strengthen the case for the use of recombinant venom toxins as supplemental immunogens to stimulate focused and desirable antibody responses capable of neutralising venom-induced pathological effects, and therefore potentially circumventing some of the limitations associated with current snakebite therapies.

Neglected Venomous Animals and Toxins: Underrated Biotechnological Tools in Drug Development

Among the vast repertoire of animal toxins and venoms selected by nature and evolution, mankind opted to devote its scientific attention—during the last century—to a restricted group of animals, leaving a myriad of toxic creatures aside. There are several underlying and justifiable reasons for this, which include dealing with the public health problems caused by envenoming by such animals. However, these studies became saturated and gave rise to a whole group of animals that become neglected regarding their venoms and secretions. This repertoire of unexplored toxins and venoms bears biotechnological potential, including the development of new technologies, therapeutic agents and diagnostic tools and must, therefore, be assessed. In this review, we will approach such topics through an interconnected historical and scientific perspective that will bring up the major discoveries and innovations in toxinology, achieved by researchers from the Butantan Institute and others, and describe some of the major research outcomes from the study of these neglected animals.

Fibrinogen-clotting enzyme, pictobin, from Bothrops pictus snake venom. Structural and functional characterization

A thrombin-like enzyme, pictobin, was purified from Bothrops pictus snake venom. It is a 41-kDa monomeric glycoprotein as showed by mass spectrometry and contains approx. 45% carbohydrate by mass which could be removed with N-glycosidase. Pictobin coagulates plasma and fibrinogen, releasing fibrinopeptide A and induces the formation of a friable/porous fibrin network as visualized by SEM. The enzyme promoted platelet aggregation in human PRP and defibrination in mouse model and showed catalytic activity on chromogenic substrates S-2266, S-2366, S-2160 and S-2238. Pictobin interacts with the plasma inhibitor α2-macroglobulin, which blocks its interaction with fibrinogen but not with the small substrate BApNA. Heparin does not affect its enzymatic activity. Pictobin cross reacted with polyvalent bothropic antivenom, and its deglycosylated form reduced its catalytic action and antivenom reaction. In breast and lung cancer cells, pictobin inhibits the fibronectin-stimulated migration. Moreover, it produces strong NADH oxidation, mitochondrial depolarization, ATP decrease and fragmentation of mitochondrial network. These results suggest by first time that a snake venom serinprotease produces mitochondrial dysfunction by affecting mitochondrial dynamics and bioenergetics. Structural model of pictobin reveals a conserved chymotrypsin fold β/β hydrolase. These data indicate that pictobin has therapeutic potential in the treatment of cardiovascular disorders and metastatic disease.

Surface loops of trypsin-like serine proteases as determinants of function

Trypsin and chymotrypsin-like serine proteases from family S1 (clan PA) constitute the largest protease group in humans and more generally in vertebrates. The prototypes chymotrypsin, trypsin and elastase represent simple digestive proteases in the gut, where they cleave nearly any protein. Multidomain trypsin-like proteases are key players in the tightly controlled blood coagulation and complement systems, as well as related proteases that are secreted from diverse immune cells. Some serine proteases are expressed in nearly all tissues and fluids of the human body, such as the human kallikreins and kallikrein-related peptidases with specialization for often unique substrates and accurate timing of activity. HtrA and membrane-anchored serine proteases fulfill important physiological tasks with emerging roles in cancer. The high diversity of all family members, which share the tandem β-barrel architecture of the chymotrypsin-fold in the catalytic domain, is conferred by the large differences of eight surface loops, surrounding the active site. The length of these loops alters with insertions and deletions, resulting in remarkably different three-dimensional arrangements. In addition, metal binding sites for Na+, Ca2+ and Zn2+ serve as regulatory elements, as do N-glycosylation sites. Depending on the individual tasks of the protease, the surface loops determine substrate specificity, control the turnover and allow regulation of activation, activity and degradation by other proteins, which are often serine proteases themselves. Most intriguingly, in some serine proteases, the surface loops interact as allosteric network, partially tuned by protein co-factors. Knowledge of these subtle and complicated molecular motions may allow nowadays for new and specific pharmaceutical or medical approaches.

Purification and Biochemical Characterization of TsMS 3 and TsMS 4: Neuropeptide-Degrading Metallopeptidases in the Tityus serrulatus Venom

Although omics studies have indicated presence of proteases on the Tityus serrulatus venom (TsV), little is known about the function of these molecules. The TsV contains metalloproteases that cleave a series of human neuropeptides, including the dynorphin A (1-13) and the members of neuropeptide Y family. Aiming to isolate the proteases responsible for this activity, the metalloserrulase 3 and 4 (TsMS 3 and TsMS 4) were purified after two chromatographic steps and identified by mass spectrometry analysis. The biochemical parameters (pH, temperature and cation effects) were determined for both proteases, and the catalytic parameters (K_m, k_cat, cleavage sites) of TsMS 4 over fluorescent substrate were obtained. The metalloserrulases have a high preference for cleaving neuropeptides but presented different primary specificities. For example, the Leu-enkephalin released from dynorphin A (1-13) hydrolysis was exclusively performed by TsMS 3. Neutralization assays using Butantan Institute antivenoms show that both metalloserrulases were well blocked. Although TsMS 3 and TsMS 4 were previously described through cDNA library studies using the venom gland, this is the first time that both these toxins were purified. Thus, this study represents a step further in understanding the mechanism of scorpion venom metalloproteases, which may act as possible neuropeptidases in the envenomation process.

New Insights on Moojase, a Thrombin-Like Serine Protease from Bothrops moojeni Snake Venom

Snake venom serine proteases (SVSPs) are enzymes that are capable of interfering in various parts of the blood coagulation cascade, which makes them interesting candidates for the development of new therapeutic drugs. Herein, we isolated and characterized Moojase, a potent coagulant enzyme from Bothrops moojeni snake venom. The toxin was isolated from the crude venom using a two-step chromatographic procedure. Moojase is a glycoprotein with N-linked glycans, molecular mass of 30.3 kDa and acidic character (pI 5.80⁻6.88). Sequencing of Moojase indicated that it is an isoform of Batroxobin. Moojase was able to clot platelet-poor plasma and fibrinogen solutions in a dose-dependent manner, indicating thrombin-like properties. Moojase also rapidly induced the proteolysis of the Aα chains of human fibrinogen, followed by the degradation of the Bβ chains after extended periods of incubation, and these effects were inhibited by PMSF, SDS and DTT, but not by benzamidine or EDTA. RP-HPLC analysis of its fibrinogenolysis confirmed the main generation of fibrinopeptide A. Moojase also induced the fibrinolysis of fibrin clots formed in vitro, and the aggregation of washed platelets, as well as significant amidolytic activity on substrates for thrombin, plasma kallikrein, factor Xia, and factor XIIa. Furthermore, thermofluor analyses and the esterase activity of Moojase demonstrated its very high stability at different pH buffers and temperatures. Thus, studies such as this for Moojase should increase knowledge on SVSPs, allowing their bioprospection as valuable prototypes in the development of new drugs, or as biotechnological tools.

Snake venom components in medicine: From the symbolic rod of Asclepius to tangible medical research and application

Both mythologically and logically, snakes have always fascinated man. Snakes have attracted both awe and fear not only because of the elegant movement of their limbless bodies, but also because of the potency of their deadly venoms. Practically, in 2017, the world health organization (WHO) listed snake envenomation as a high priority neglected disease, as snakes inflict up to 2.7 million poisonous bites, around 100.000 casualties, and about three times as many invalidities on man. The venoms of poisonous snakes are a cocktail of potent compounds which specifically and avidly target numerous essential molecules with high efficacy. The individual effects of all venom toxins integrate into lethal dysfunctions of almost any organ system. It is this efficacy and specificity of each venom component, which after analysis of its structure and activity may serve as a potential lead structure for chemical imitation. Such toxin mimetics may help in influencing a specific body function pharmaceutically for the sake of man's health. In this review article, we will give some examples of snake venom components which have spurred the development of novel pharmaceutical compounds. Moreover, we will provide examples where such snake toxin-derived mimetics are in clinical use, trials, or consideration for further pharmaceutical exploitation, especially in the fields of hemostasis, thrombosis, coagulation, and metastasis. Thus, it becomes clear why a snake captured its symbolic place at the Asclepius rod with good reason still nowadays.

BjSP, a novel serine protease from Bothrops jararaca snake venom that degrades fibrinogen without forming fibrin clots

Snake venom serine proteases (SVSPs) are commonly described as capable of affecting hemostasis by interacting with several coagulation system components. In this study, we describe the isolation and characterization of BjSP from Bothrops jararaca snake venom, a serine protease with distinctive properties. This enzyme was isolated by three consecutive chromatographic steps and showed acidic character (pI 4.4), molecular mass of 28 kDa and N-carbohydrate content around 10%. Its partial amino acid sequence presented 100% identity to a serine protease cDNA clone previously identified from B. jararaca venom gland, but not yet isolated or characterized. BjSP was significantly inhibited by specific serine protease inhibitors and showed high stability at different pH values and temperatures. The enzyme displayed no effects on washed platelets, but was able to degrade fibrin clots in vitro and also the Aα and Bβ chains of fibrinogen differently from thrombin, forming additional fibrinopeptides derived from the Bβ chain, which should be related to its inability to coagulate fibrinogen solutions or platelet-poor plasma. In the mapping of catalytic subsites, the protease showed high hydrolytic specificity for tyrosine, especially in subsite S1. Additionally, its amidolytic activity on different chromogenic substrates suggests possible effects on other factors of the coagulation cascade. In conclusion, BjSP is a serine protease that acts nonspecifically on fibrinogen, generating different Bβ fibrinopeptides and thus not forming fibrin clots. Its distinguished properties in comparison to most SVSPs stimulate further studies in an attempt to validate its potential as a defibrinogenating agent.

Agkihpin, a Distinct SVTLE from the Venom of Gloydius halys Pallas: Purification, Characterization and Structure-Activity Determination

Blood clots produced by snake-venom thrombin-like enzymes (SVTLEs) are cleared rapidly, which makes SVTLEs attractive as potential candidates for antithrombotic therapy. We isolated a SVTLE, agkihpin, from the venom of Gloydius halys Pallas. Agkihpin was confirmed to a single-chain TLE with molecular mass of 25.5 kD, pI of 7.43, optimal pH of 8.0 (hydrolyzing TAME), linked carbohydrate absent, and weak fibrinogen clotting activity. It was also found that (i) G. halys might be the latest species in SVTLEs phylogenetic tree; (ii) different level of conservation was shown among the SVTLEs from the Viperidae snakes. Some of those site may account for different activities exhibited by those SVTLEs, especially position 181, at which a fibrinogenolytic activity increase was found when a basic and larger amino acid substituted by a neutral and smaller one; (iii) an extra α-helix constructed with a 'Pro + acidic amino acid + aromatic amino acid' pattern was found in the SVTLEs from Gloydius and Agkistrodon snakes, although it does not necessarily imply an effect on the fibrinogenolytic activity of the SVTLEs. This study provided some new insight into the activity of SVTLE.

Expression of a new serine protease from Crotalus durissus collilineatus venom in Pichia pastoris and functional comparison with the native enzyme

Snake venom serine proteases (SVSPs) act primarily on plasma proteins related to blood clotting and are considered promising for the treatment of several hemostatic disorders. We report the heterologous expression of a serine protease from Crotalus durissus collilineatus, named collinein-1, in Pichia pastoris, as well as the enzymatic comparative characterization of the toxin in native and recombinant forms. The complementary DNA (cDNA) encoding collinein-1 was amplified from cDNA library of C. d. collilineatus venom gland and cloned into the pPICZαA vector. The recombinant plasmid was used to transform cells of KM71H P. pastoris. Heterologous expression was induced by methanol and yielded 56 mg of recombinant collinein-1 (rCollinein-1) per liter of culture. The native collinein-1 was purified from C. d. collilineatus venom, and its identity was confirmed by amino acid sequencing. The native and recombinant enzymes showed similar effects upon bovine fibrinogen by releasing preferentially fibrinopeptide A. Although both enzymes have induced plasma coagulation, native Colinein-1 has shown higher coagulant activity. The serine proteases were able to hydrolyze the chromogenic substrates S-2222, S-2238, and S2302. Both enzymes showed high stability on different pH and temperature, and their esterase activities were inhibited in the presence of Zn2+ and Cu2+. The serine proteases showed similar k cat/K m values in enzyme kinetics assays, suggesting no significant differences in efficiency of these proteins to hydrolyze the substrate. These results demonstrated that rCollinein-1 was expressed with functional integrity on the evaluated parameters. The success in producing a functionally active recombinant SVSP may generate perspectives to their future therapeutic applications.

Bothrops jararaca envenomation: Pathogenesis of hemostatic disturbances and intravascular hemolysis

To attain fully functional biological activity, vitamin-K dependent coagulation factors (VKDCF) are γ-carboxylated prior to secretion from liver. Warfarin impairs the γ-carboxylation, and consequently their physiological function. Bothrops jararaca snake venom (BjV) contains several activators of blood coagulation, especially procoagulant enzymes (prothrombin and factor X activators) and thrombin-like enzymes. In order to clarify the relative contribution of prothrombin and factor X activators to the hemostatic disturbances occurring during experimental B. jararaca envenomation, warfarin was used to deplete VKDCF, prior to BjV administration. Male Wistar rats were pretreated with saline (Sal) or warfarin (War) and inoculated subsequently with BjV or saline, thus forming four groups: Sal + Sal (negative control), Sal + BjV (positive control), War + Sal (warfarinization control), and War + BjV. Three hours after inoculation, prothrombin and factor X levels fell 40% and 50%, respectively; levels of both factors decreased more than 97% in the War + Sal and War + BjV groups. Platelet counts dropped 93% and 76% in Sal + BjV and War + BjV, respectively, and plasma fibrinogen levels decreased 86% exclusively in Sal + BjV. After 6 and 24 h, platelet counts and fibrinogen levels increased progressively. A dramatic augmentation in plasma hemoglobin levels and the presence of schizocytes and microcytes in the Sal + BjV group indicated the development of intravascular hemolysis, which was prevented by warfarin pretreatment. Our findings show that intravascular thrombin generation has the foremost role in the pathogenesis of coagulopathy and intravascular hemolysis, but not in the development of thrombocytopenia, in B. jararaca envenomation in rats; in addition, fibrinogenases (metalloproteinases) may contribute to coagulopathy more than thrombin-like enzymes.

Effects of single N-glycosylation site knockout on folding and defibrinogenating activities of acutobin recombinants from HEK293T

Acutobin, the α-fibrinogenase from Deinagkistrodon acutus venom, contains four N-glycosylation sites with disialylated complex-typed glycans. Here, we explore the functional roles of each of the N-glycan by site-directed mutagenesis. The wild-type (ATB-wt) and single glycan-knockout mutants of recombinant acutobin were prepared from HEK293T, demonstrating that mutations at Asn(77), Asn(81) and Asn(100) impaired the folding while the S79A mutant and various Asn(229)-deglycosylated mutants were correctly folded. Based on homology modeling of acutobin and multiple sequence alignment with various venom thrombin-like enzymes, the importance of a hydrophilic environment at each glycosylation site to the enzyme folding could be rationalized. Remarkably, all the mutants showed similar catalytic activities for the chromogenic substrate and similar thermal stabilities as ATB-wt, suggesting that the glycan knockout did not affect the gross conformation and stability of the active sites. Although SDS-PAGE analyses revealed that ATB-wt and the D229-mutant degraded all human fibrinogen subunits faster but less specifically in vitro as compared with other mutants that cleaved only the α-subunit, ATB-wt and D229-mutant were not able to release fibrinogen-peptide A and thus coagulated human plasma slower than the other mutants did. In the mice model, the defibrinogenating effect of ATB-wt was stronger and lasting-longer than those of all the mutants. Taken together, all the glycans contribute to the pharmacokinetics of acutobin and ATB-wt in vivo, and the microenvironment around the Asn(229)-glycan appears to regulate the fibrinogen-chain specificity of acutobin while the N-glycans at positions 77, 81 and 100 are crucial for its folding.

Fibrin(ogen)olytic and platelet modulating activity of a novel protease from the Echis multisquamatis snake venom

The variety of enzymes including serine proteases that possess fibrin(ogen)olytic and platelet modulating activity have been discovered in different snake venoms. In our work the fibrin(ogen)olytic and platelet modulating activity of a new protease from Echis multisquamatis snake venom was studied. It was shown that purified enzyme cleaved the ВβR42-A43 bond of fibrinogen during first contact with the substrate following much slower hydrolysis of C-terminus of fibrinogen Aα-chain. Protease hydrolysed fibrin clot too, but at much slower rate and cleaved both C-terminus of Aα-chain and ВβR42-A43 bond of Bβ-chain simultaneously. Preincubation of fibrinogen with protease dramatically elongated thrombin clotting time and the clot formed from a mixture of native fibrinogen and fibrinogen desВβ(1-42)2 digested by plasmin much faster than a native fibrin clot. The protease did not activate platelets nor cause changes in their shape and granularity, but it reduced platelets aggregation induced by ADP.

Correlation between the glycan variations and defibrinogenating activities of acutobin and its recombinant glycoforms

Acutobin isolated from Deinagkistrodon acutus venom has been used to prevent or treat stroke in patients. This defibrinogenating serine protease is a 39 kDa glycoprotein containing terminal disialyl-capped N-glycans. After sialidase treatment, the enzyme showed similar catalytic activities toward chromogenic substrate, and cleaved the Aα chain of fibrinogen as efficiently as the native acutobin did. However, the level of fibrinogen degradation products in mice after i.p.-injection of desialylated-acutobin was significantly lower than the level after acutobin injection, suggesting that the disialyl moieties may improve or prolong the half-life of acutobin. Two recombinant enzymes with identical protein structures and similar amidolytic activities to those of native acutobin were expressed from HEK293T and SW1353 cells and designated as HKATB and SWATB, respectively. Mass spectrometric profiling showed that their glycans differed from those of acutobin. In contrast to acutobin, HKATB cleaved not only the Aα chain but also the Bβ and γ chains of human fibrinogens, while SWATB showed a reduced α-fibrinogenase activity. Non-denaturing deglycosylation of these proteases by peptide N-glycosidase F significantly reduced their fibrinogenolytic activities and thermal stabilities. The in vivo defibrinogenating effect of HKATB was inferior to that of acutobin in mice. Taken together, our results suggest that the conjugated glycans of acutobin are involved in its interaction with fibrinogen, and that the selection of cells optimally expressing efficient glycoforms and further glycosylation engineering are desirable before a recombinant product can replace the native enzyme for clinical use.

The crude skin secretion of the pepper frog Leptodactylus labyrinthicus is rich in metallo and serine peptidases

Peptidases are ubiquitous enzymes involved in diverse biological processes. Fragments from bioactive peptides have been found in skin secretions from frogs, and their presence suggests processing by peptidases. Thus, the aim of this work was to characterize the peptidase activity present in the skin secretion of Leptodactylus labyrinthicus. Zymography revealed the presence of three bands of gelatinase activity of approximately 60 kDa, 66 kDa, and 80 kDa, which the first two were calcium-dependent. These three bands were inhibited either by ethylenediaminetetraacetic acid (EDTA) and phenathroline; thus, they were characterized as metallopeptidases. Furthermore, the proteolytic enzymes identified were active only at pH 6.0-10.0, and their activity increased in the presence of CHAPS or NaCl. Experiments with fluorogenic substrates incubated with skin secretions identified aminopeptidase activity, with cleavage after leucine, proline, and alanine residues. This activity was directly proportional to the protein concentration, and it was inhibited in the presence of metallo and serine peptidase inhibitors. Besides, the optimal pH for substrate cleavage was determined to be 7.0-8.0. The results of the in gel activity assay showed that all substrates were hydrolyzed by a 45 kDa peptidase. Gly-Pro-AMC was also cleaved by a peptidase greater than 97 kDa. The data suggest the presence of dipeptidyl peptidases (DPPs) and metallopeptidases; however, further research is necessary. In conclusion, our work will help to elucidate the implication of these enzymatic activities in the processing of the bioactive peptides present in frog venom, expanding the knowledge of amphibian biology.

Biochemical and pharmacological properties of a new thrombin-like serine protease (Russelobin) from the venom of Russell's Viper (Daboia russelii russelii) and assessment of its therapeutic potential

BACKGROUND

Snake venoms are rich sources of bioactive molecules, and several venom-derived proteins have entered clinical trials for use in ischemic disorders; however, late-stage failure of a recent drug candidate due to low in vivo efficacy demonstrated the need for new sources of fibrinogenolytic drug candidates.

METHODS

A 51.3kDa thrombin-like serine protease (Russelobin) purified from the venom of Russell's Viper (Daboia russelii russelii) was subjected to extensive biochemical characterization, including N-terminal sequencing, substrate specificity, kinetic and inhibitor assays, glycosylation analysis and stability assays. Toxicity and pathology analyses were conducted in NSA mice.

RESULTS

Russelobin has extensive N-terminus identity with a beta-fibrinogenase-like serine proteinase precursor from Daboia russelii siamensis venom, a mass of 51.3kDa and contains extensive N-linked oligosaccharides. Serine protease inhibitors and heparin significantly decreased activity, with much lower inhibition by DTT, antithrombin-III and α2-macroglobulin. Russelobin preferentially released FPA and slowly released FPB from human fibrinogen, forming a labile fibrin clot readily hydrolyzed by plasmin. The partially deglycosylated enzyme showed significantly lower activity toward fibrinogen and less resistance against neutralization by plasma α2MG and antithrombin-III. Russelobin was non-cytotoxic, non-lethal and produced no histopathologies in mice, and it demonstrated in vivo dose-dependent defibrinogenating activity.

CONCLUSIONS

Russelobin is an A/B fibrinogenase with high specificity toward fibrinogen, both in vitro and in vivo. Extensive glycosylation appears to protect the molecule against endogenous protease inhibitors, prolonging its in vivo efficacy.

GENERAL SIGNIFICANCE

Due to its low toxicity, stability and activity as a defibrinogenating agent, Russelobin shows high potential for cardiovascular drug development.

Coagulant thrombin-like enzyme (barnettobin) from Bothrops barnetti venom: molecular sequence analysis of its cDNA and biochemical properties

The thrombin-like enzyme from Bothrops barnetti named barnettobin was purified. We report some biochemical features of barnettobin including the complete amino acid sequence that was deduced from the cDNA. Snake venom serine proteases affect several steps of human hemostasis ranging from the blood coagulation cascade to platelet function. Barnettobin is a monomeric glycoprotein of 52 kDa as shown by reducing SDS-PAGE, and contains approx. 52% carbohydrate by mass which could be removed by N-glycosidase. The complete amino acid sequence was deduced from the cDNA sequence. Its sequence contains a single chain of 233 amino acid including three N-glycosylation sites. The sequence exhibits significant homology with those of mammalian serine proteases e.g. thrombin and with homologous TLEs. Its specific coagulant activity was 251.7 NIH thrombin units/mg, releasing fibrinopeptide A from human fibrinogen and showed defibrinogenating effect in mouse. Both coagulant and amidolytic activities were inhibited by PMSF. N-deglycosylation impaired its temperature and pH stability. Its cDNA sequence with 750 bp encodes a protein of 233 residues. Indications that carbohydrate moieties may play a role in the interaction with substrates are presented. Barnettobin is a new defibrinogenating agent which may provide an opportunity for the development of new types of anti-thrombotic drugs.

Biochemical characterization and comparative analysis of two distinct serine proteases from Bothrops pirajai snake venom

This study reports the isolation and biochemical characterization of two different serine proteases from Bothrops pirajai snake venom, thus providing a comparative analysis of the enzymes. The isolation process consisted of three consecutive chromatographic steps (Sephacryl S-200, Benzamidine Sepharose and C2/C18), resulting in two serine proteases, named BpirSP27 and BpirSP41 after their molecular masses by mass spectrometry (27,121 and 40,639 Da, respectively). Estimation by SDS-PAGE under denaturing conditions showed that, when deglycosylated with PNGase F, BpirSP27 and BpirSP41 had their molecular masses reduced by approximately 15 and 42%, respectively. Both are acidic enzymes, with pI of approximately 4.7 for BpirSP27 and 3.7 for BpirSP41, and their N-terminal amino acid sequences showed 57% identity to each other, with high similarity to the sequences of other snake venom serine proteases (SVSPs). The enzymes showed different actions on bovine fibrinogen, with BpirSP27 acting preferentially on the Bβ chain and BpirSP41 on both Aα and Bβ chains. The two serine proteases were also able to degrade fibrin and blood clots in vitro depending on the doses and incubation periods, with higher results for BpirSP41. Both enzymes coagulated the human plasma in a dose-dependent manner, and BpirSP41 showed a higher coagulant potential, with minimum coagulant dose (MCD) of ∼3.5 μg versus 20 μg for BpirSP27. The enzymes were capable of hydrolyzing different chromogenic substrates, including S-2238 for thrombin-like enzymes, but only BpirSP27 acted on the substrate S-2251 for plasmin. They also showed high stability against variations of temperature and pH, but their activities were significantly reduced after preincubation with Cu(2+) ion and specific serine protease inhibitors. In addition, BpirSP27 induced aggregation of washed platelets to a greater extent than BpirSP41. The results showed significant structural and functional differences between B. pirajai serine proteases, providing interesting insights into the structure-function relationship of SVSPs.

An unusual family of glycosylated peptides isolated from Dendroaspis angusticeps venom and characterized by combination of collision induced and electron transfer dissociation

This study describes the structural characterization of a totally new family of peptides from the venom of the snake green mamba (Dendroaspis angusticeps). Interestingly, these peptides differ in several points from other already known mamba toxins. First of all, they exhibit very small molecular masses, ranging from 1.3 to 2.4 kDa. The molecular mass of classical mamba toxins is in the range of 7 to 25 kDa. Second, the new peptides do not contain disulfide bonds, a post-translational modification commonly encountered in animal toxins. The third difference is the very high proportion of proline residues in the sequence accounting for about one-third of the sequence. Finally, these new peptides reveal a carbohydrate moiety, indicating a glycosylation in the sequence. The last two features have made the structural characterization of the new peptides by mass spectrometry a real analytical challenge. Peptides were characterized by a combined use of MALDI- TOF/TOF and nanoESI-IT-ETD experiments to determine not only the peptide sequence but also the composition and the position of the carbohydrate moiety. Anyway, such small glycosylated and proline-rich toxins are totally different from any other known snake peptide and form, as a consequence, a new family of peptides.

The Anopheles gambiae adult midgut peritrophic matrix proteome

Malaria is a devastating disease. For transmission to occur, Plasmodium, the causative agent of malaria, must complete a complex developmental cycle in its mosquito vector. Thus, the mosquito is a potential target for disease control. Plasmodium ookinetes, which develop within the mosquito midgut, must first cross the midgut's peritrophic matrix (PM), a thick extracellular sheath that completely surrounds the blood meal. The PM poses a partial, natural barrier against parasite invasion of the midgut and it is speculated that modifications to the PM may lead to a complete barrier to infection. However, such strategies require thorough characterization of the structure of the PM. Here, we describe for the first time, the complete PM proteome of the main malaria vector, Anopheles gambiae. Altogether, 209 proteins were identified by mass spectrometry. Among them were nine new chitin-binding peritrophic matrix proteins, expanding the list from three to twelve peritrophins. Lastly, we provide a model for the putative interactions among the proteins identified in this study.