Lysine 49 phospholipase A2 proteins

Structural characterization of myotoxic ecarpholin S from Echis carinatus venom

Phospholipase A(2) (PLA(2)), a common toxic component of snake venom, has been implicated in various pharmacological effects. Ecarpholin S, isolated from the venom of the snake Echis carinatus sochureki, is a phospholipase A(2) (PLA(2)) belonging to the Ser(49)-PLA(2) subgroup. It has been characterized as having low enzymatic but potent myotoxic activities. The crystal structures of native ecarpholin S and its complexes with lauric acid, and its inhibitor suramin, were elucidated. This is the first report of the structure of a member of the Ser(49)-PLA(2) subgroup. We also examined interactions of ecarpholin S with phosphatidylglycerol and lauric acid, using surface plasmon resonance, and of suramin with isothermal titration calorimetry. Most Ca(2+)-dependent PLA(2) enzymes have Asp in position 49, which plays a crucial role in Ca(2+) binding. The three-dimensional structure of ecarpholin S reveals a unique conformation of the Ca(2+)-binding loop that is not favorable for Ca(2+) coordination. Furthermore, the endogenously bound fatty acid (lauric acid) in the hydrophobic channel may also interrupt the catalytic cycle. These two observations may account for the low enzymatic activity of ecarpholin S, despite full retention of the catalytic machinery. These observations may also be applicable to other non-Asp(49)-PLA(2) enzymes. The interaction of suramin in its complex with ecarpholin S is quite different from that reported for the Lys(49)-PLA(2)/suramin complex(,) where the interfacial recognition face (i-face), C-terminal region, and N-terminal region of ecarpholin S play important roles. This study provides significant structural and functional insights into the myotoxic activity of ecarpholin S and, in general, of non-Asp(49)-PLA(2) enzymes.

Myotoxic phospholipases A(2) isolated from Bothrops brazili snake venom and synthetic peptides derived from their C-terminal region: cytotoxic effect on microorganism and tumor cells

This paper reports the purification and biochemical/pharmacological characterization of two myotoxic phospholipases A(2) (PLA(2)s) from Bothrops brazili venom, a native snake from Brazil. Both myotoxins (MTX-I and II) were purified by a single chromatographic step on a CM-Sepharose ion-exchange column up to a high purity level, showing M(r) approximately 14,000 for the monomer and 28,000Da for the dimer. The N-terminal and internal peptide amino acid sequences showed similarity with other myotoxic PLA(2)s from snake venoms, MTX-I belonging to Asp49 PLA(2) class, enzymatically active, and MTX-II to Lys49 PLA(2)s, catalytically inactive. Treatment of MTX-I with BPB and EDTA reduced drastically its PLA(2) and anticoagulant activities, corroborating the importance of residue His48 and Ca(2+) ions for the enzymatic catalysis. Both PLA(2)s induced myotoxic activity and dose-time dependent edema similar to other isolated snake venom toxins from Bothrops and Crotalus genus. The results also demonstrated that MTXs and cationic synthetic peptides derived from their 115-129 C-terminal region displayed cytotoxic activity on human T-cell leukemia (JURKAT) lines and microbicidal effects against Escherichia coli, Candida albicans and Leishmania sp. Thus, these PLA(2) proteins and C-terminal synthetic peptides present multifunctional properties that might be of interest in the development of therapeutic strategies against parasites, bacteria and cancer.

An alpha-type phospholipase A(2) inhibitor from Bothrops jararacussu snake plasma: structural and functional characterization

An inhibitory protein that neutralizes the enzymatic, toxic and pharmacological activities of several phospholipases A(2) from Bothrops venoms was isolated from B. jararacussu snake plasma by affinity chromatography using the immobilized myotoxin BthTX-I on Sepharose gel. Biochemical characterization of this inhibitory protein, denominated alphaBjussuMIP, showed it to be an oligomeric glycoprotein with M(r) of 24,000 for the monomeric subunit. Secondary structural analysis by circular dichroism revealed 44% alpha-helix, 18% beta-sheet, 10% beta-turn and 28% random coil structures. Circular dichroism spectroscopy indicated that no significant alterations in the secondary structure of either alphaBjussuMIP or the target protein occur following their interaction. The product from the reaction with reverse transcriptase produced a cDNA fragment of 432 bp that codifies for a mature protein of 144 amino acid residues. The first 21 amino acid residues from the N-terminal and five tryptic peptides were characterized by mass spectrometry of the mature protein and confirmed by the nucleotide sequence. Alignment of alphaBjussuMIP with other snake inhibitors showed a sequence similarity of 73-92% with these alphaPLIs. alphaBjussuMIP was relatively stable within the pH range of 6-12 and temperatures from 0 degrees C to 80 degrees C, even after deglycosylation. The results showed effects against Bothrops phospholipase A(2) activities (enzymatic, edema inducing, myotoxic, cytotoxic and bactericidal), suggesting that alphaBjussuMIP may prove useful in the treatment of snakebite envenomations.

Purification and preliminary crystallographic analysis of a new Lys49-PLA2 from B. Jararacussu

BjVIII is a new myotoxic Lys49-PLA2 isolated from Bothrops jararacussu venom that exhibits atypical effects on human platelet aggregation. To better understand the mode of action of BjVIII, crystallographic studies were initiated. Two crystal forms were obtained, both containing two molecules in the asymmetric unit (ASU). Synchrotron radiation diffraction data were collected to 2.0 A resolution and 1.9 A resolution for crystals belonging to the space group P2(1)2(1)2(1) (a = 48.4 A, b = 65.3 A, c = 84.3 A) and space group P3(1)21 (a = b = 55.7 A, c = 127.9 A), respectively. Refinement is currently in progress and the refined structures are expected to shed light on the unusual platelet aggregation activity observed for BjVIII.

Crystal structure of a novel myotoxic Arg49 phospholipase A2 homolog (zhaoermiatoxin) from Zhaoermia mangshanensis snake venom: insights into Arg49 coordination and the role of Lys122 in the polarization of the C-terminus

The venom of Zhaoermia mangshanensis, encountered solely in Mt Mang in China's Hunan Province, exhibits coagulant, phosphodiesterase, l-amino acid oxidase, kallikrein, phospholipase A2 and myotoxic activities. The catalytically inactive PLA2 homolog referred to as zhaoermiatoxin is highly myotoxic and displays high myonecrotic and edema activities. Zhaoermiatoxin possesses a molecular weight of 13,972Da, consists of 121 amino-acid residues cross-linked by seven disulfide bridges and shares high sequence homology with Lys49-PLA2s from the distantly related Asian pitvipers. However, zhaoermiatoxin possesses an arginine residue at position 49 instead of a lysine, thereby suggesting a secondary Lys49-->Arg substitution which results in a catalytically inactive protein. We have determined the first crystal structure of zhaoermiatoxin, an Arg49-PLA2, from Zhaoermia mangshanensis venom at 2.05 angstroms resolution, which represents a novel member of phospholipase A2 family. In this structure, unlike the Lys49 PLA2s, the C-terminus is well ordered and an unexpected non-polarized state of the putative calcium-binding loop due to the flip of Lys122 towards the bulk solvent is observed. The orientation of the Arg-49 side chain results in a similar binding mode to that observed in the Lys49 PLA2s; however, the guadinidium group is tri-coordinated by carbonyl oxygen atoms of the putative calcium-binding loop, whereas the Nzeta atom of lysine is tetra-coordinated as a result of the different conformation adopted by the putative calcium-binding loop.

Neutralization of snake venom phospholipase A2 toxins by aqueous extract of Casearia sylvestris (Flacourtiaceae) in mouse neuromuscular preparation

Aqueous extract of Casearia sylvestris (Flacourtiaceae) has been shown to inhibit enzymatic and biological properties of some Bothrops and Crotalus venoms and their purified phospholipase A(2) (PLA(2)) toxins. In this work we evaluated the influence of C. sylvestris aqueous extract upon neuromuscular blocking and muscle damaging activities of some PLA(2)s (crotoxin from C. durissus terrificus, bothropstoxin-I from B. jararacussu, piratoxin-I from B. pirajai and myotoxin-II from B. moojeni) in mouse phrenic-diaphragm preparations. Crotoxin (0.5 microM) and all other PLA(2) toxins (1.0 microM) induced irreversible and time-dependent blockade of twitches. Except for crotoxin, all PLA(2) toxins induced significant muscle damage indices, assessed by microscopic analysis. Preincubation of bothropstoxin-I, piratoxin-I or myotoxin-II with C. sylvestris extract (1:5 (w/w), 30 min, 37 degrees C) significantly prevented the neuromuscular blockade of preparations exposed to the mixtures for 90 min; the extent of protection ranged from 93% to 97%. The vegetal extract also neutralized the muscle damage (protection of 80-95%). Higher concentration of the C. sylvestris extract (1:10, w/w) was necessary to neutralize by 90% the neuromuscular blockade induced by crotoxin. These findings expanded the spectrum of C. sylvestris antivenom activities, evidencing that it may be a good source of potentially useful PLA(2) inhibitors.

Isolation and functional characterization of a new myotoxic acidic phospholipase A2 from Bothrops pauloensis snake venom

This article reports the purification procedure and the biochemical/functional characterization of Bp-PLA(2), a new myotoxic acidic phospholipase A(2) from Bothrops pauloensis snake venom. It was highly purified through three chromatographic steps (ion-exchange on CM-Sepharose, hydrophobic chromatography on Phenyl-Sepharose and RP-HPLC on a C8 column). Bp-PLA(2) is a single-chain protein of 15.8kDa and pI 4.3. Its N-terminal sequence revealed a high homology with other Asp49 acidic PLA(2)s from snake venoms. Its specific activity was 585.3U/mg. It displayed a high indirect hemolytic activity and inhibited platelet aggregation induced by collagen or ADP. It also induced in vivo edema and myotoxicity. Pretreatment of Bp-PLA(2) with BPB reduced the enzymatic activity, the inhibitory action on platelet aggregation and myotoxicity in vitro. Morphological analyses indicated that Bp-PLA(2) induced an intense edema, with visible leukocyte infiltrate and damaged muscle cells 24h after injection. Acidic myotoxic PLA(2)s from Bothrops snake venoms are still not extensively explored and knowledge of their structural and functional features will contribute for a better understanding of their action mechanism regarding enzymatic and toxic activities.

Crystallization and preliminary X-ray diffraction analysis of a novel Arg49 phospholipase A2 homologue from Zhaoermia mangshanensis venom

Zhaoermiatoxin, an Arg49 phospholipase A2 homologue from Zhaoermia mangshanensis (formerly Trimeresurus mangshanensis, Ermia mangshanensis) venom is a novel member of the PLA2-homologue family that possesses an arginine residue at position 49, probably arising from a secondary Lys49-->Arg substitution that does not alter the catalytic inactivity towards phospholipids. Like other Lys49 PLA2 homologues, zhaoermiatoxin induces oedema and strong myonecrosis without detectable PLA2 catalytic activity. A single crystal with maximum dimensions of 0.2 x 0.2 x 0.5 mm was used for X-ray diffraction data collection to a resolution of 2.05 A using synchrotron radiation and the diffraction pattern was indexed in the hexagonal space group P6(4), with unit-cell parameters a = 72.9, b = 72.9, c = 93.9 A.

Mapping of the structural determinants of artificial and biological membrane damaging activities of a Lys49 phospholipase A2 by scanning alanine mutagenesis

Scanning alanine mutagenesis has been used to study the structural determinants of several activities of bothropstoxin-I (BthTx-I), a lysine 49 Phospholipases A(2) from the venom of Bothrops jararacussu. A total of 31 mutants were generated in the interfacial recognition site and C-terminal loop regions of the protein. The effects of mutagenesis on the in vivo myotoxic activity, the cytolytic activity against cultured C2C12 myoblasts, the bactericidal activity, and the Ca(2+)-independent membrane damaging activity against liposome membranes were compared. Residues 116-119 and 122-125 in the C-terminal loop region are structural determinants for these activities, indicating that membrane permeabilization by the BthTx-I is an important general property in all the measured effects. The structural determinants of myotoxicity and myoblast membrane permeabilization are highly correlated, demonstrating that cultured C2C12 myoblasts are a good model for the myotoxic effect. However, comparison of the structural determinants for all activities revealed several differences in the structural determinants between the effects against myoblast and bacterial membranes, and further differences when compared to the liposome membrane damaging effect. These membrane dependent effects are interpreted to be the consequence of differences in the activation of the membrane bound form of the protein on biological and artificial membranes.

Interfacial surface charge and free accessibility to the PLA2-active site-like region are essential requirements for the activity of Lys49 PLA2 homologues

Lys49 phospholipase A2 homologues are highly myotoxic and cause extensive tissue damage but do not display hydrolytic activity towards natural phospholipids. The binding of heparin, heparin derivatives and polyanionic compounds such as suramin result in partial inhibition (up to 60%) of the myotoxic effects due to a change in the overall charge of the interfacial surface. In vivo experiments demonstrate that polyethylene glycol inhibits more than 90% of the myotoxic effects without exhibiting secondary toxic effects. The crystal structure of bothropstoxin-I complexed with polyethylene glycol reveals that this inhibition is due to steric hindrance of the access to the PLA2-active site-like region. These two inhibitory pathways indicate the roles of the overall surface charge and free accessibility to the PLA2-active site-like region in the functioning of Lys49 phospholipases A2 homologues. Molecular dynamics simulations, small angle X-ray scattering and structural analysis indicate that the oligomeric states both in solution and in the crystalline states of Lys49 phospholipases A2 are principally mediated by hydrophobic contacts formed between the interfacial surfaces. These results provide the framework for the potential application of both clinically approved drugs for the treatment of Viperidae snakebites.

Effects of the myotoxic Lys49 phospholipase A2 from Agkistrodon contortrix laticinctus snake venom on water transport in the toad bladder epithelium: evidence for a role of microtubules and calmodulin

ACLMT is a myotoxic Lys49 phospholipase A2 isolated from the venom of the snake Agkistrodon contortrix laticinctus. We have previously demonstrated that ACLMT affects the water transport in toad bladders through a mechanism partially mediated by an increase in the cytosolic calcium. This study aims to further investigate the sites and mechanisms involved in the effects of ACLMT on water transport in toad bladders by examining the role of microtubules and calmodulin. Water flow across the membrane was gravimetrically measured in bladder sac preparations. ACLMT increased basal water transport and inhibited water transport stimulated by vasopressin. Colchicine and trifluoperazine reduced the effect of the toxin on basal water transport and enhanced it on vasopressin-stimulated water transport. The results suggest that both microtubules and calmodulin may be involved in the effect of ACLMT on basal water transport. On the other hand, the effect of the toxin on vasopressin-stimulated water transport appears to be neither dependent on the microtubules integrity nor directly mediated by calmodulin. This study provides a deeper understanding of the effects of the Lys49 PLA2 myotoxins on membrane permeability, thus contributing to elucidate the toxicity mechanism of these myotoxins on biological tissues.

Inactivation of phospholipase A2 and metalloproteinase fromCrotalus atrox venom by direct current

To achieve our aim of understanding the interactions between direct current and enzymes in solution, we exposed reconstituted Crotalus atrox venom to direct electric current by immersing two platinum thread electrodes connected to a voltage generator (between 0 and 8 V) into a reaction mixture for a few seconds. Then, we assayed the residual activity of phospholipases A(2) (PLA(2)),metalloproteinases, and phosphodiesterases, abundant in crotaline snake venoms and relevant in the pathophysiology of envenomation, characterized by hemorrhage, pain, and tissue damage. C. atrox venom phospholipase A(2) and metalloproteinases were consistently and irreversibly inactivated by direct current (between 0 and 0.7 mA) exposure. In contrast, C. atrox venom phosphodiesterases were not affected. Total protein content and temperature of the sample remained the same. Secretory pancreatic phospholipase A(2), homologue to snake venom phospholipases A(2), was also inactivated by direct current treatment. In order to understand the structural reasoning behind PLA(2) inactivation, circular dichroism measurements were conducted on homogeneous commercial pancreatic phospholipase A(2), and it was found that the enzyme undergoes structural alterations upon direct current exposure.

Structural and Functional Properties of Cr 5, a New Lys49 Phospholipase A2 Homologue Isolated from the Venom of the Snake Calloselasma rhodostoma

Cr 5 PLA(2) homologous (K49) was isolated from Calloselasma rhodostoma venom in only one chromatographic step in reverse phase HPLC (RP-HPLC) (on mu-Bondapack C-18). A molecular mass of 13.965 Da was determined by MALDI-TOF mass spectrometry. The amino acid composition showed that Cr 5 had a high content of Lys, Tyr, Gly, Pro, and 14 half-Cys residues, typical residues of a basic PLA(2). The complete amino acid sequence of Cr 5 PLA(2) contains 120 residues, resulting in a calculated pI value of 5.55. This sequence shows high identity values when compared to other K49 PLA(2)s isolated from the venoms of viperid snakes. Lower identity is observed in comparison to D49 PLA(2)s. The sequence found was SLVELGKMIL QETGKNPAKS YGAYGCNCGV LGRHKPKDAT DRCCFVHKCC YKKLTGCDPK KDRYSYSWKD KTIVCGENNP CLKEMCECDK AVAICLRENL DTYNKKYRYL KPFCKKADDC. In mice, Cr 5 induced myonecrosis and edema upon intramuscular and intravenous injections, respectively. The LD(50) of Cr 5 was 0.070 mg/kg of the animal weight, by intracerebroventricular (i.c.v.) route. In vitro, the toxin caused rapid cytolytic effect upon mouse skeletal muscle myoblasts in culture. The isolation of this PLA(2) and the combined structural and functional information obtained classify Cr 5 as a new member of the K49 PLA(2) family, since it presents typical features from such proteins.

Expression of recombinant human antibody fragments capable of inhibiting the phospholipase and myotoxic activities of Bothrops jararacussu venom

Phospholipases A(2) are components of Bothrops venoms responsible for disruption of cell membrane integrity via hydrolysis of its phospholipids. This study used a large nonimmune human scFv library named Griffin.1 (MRC, Cambridge, UK) for selection of recombinant antibodies against antigens present in Bothrops jararacussu venom and identification of specific antibodies able to inhibit phospholipase activity. Four clones were identified as capable of inhibiting this activity in vitro. These clones were able to reduce in vivo the myotoxic activity of BthTX-I and BthTX-II PLA(2), but had no effect on the in vitro anticoagulant activity of BthTX-II. This work shows the potential of using recombinant scFv libraries in the search for antibodies that neutralize relevant venom components.

The effect of the myotoxic Lys49 phospholipase A(2) from Agkistrodon contortrix laticinctus snake venom on Na+/K+ -ATPase activity of toad bladders

ACLMT is a myotoxic Lys49 phospholipase A(2) isolated from the venom of the snake Agkistrodon contortrix laticinctus. We have previously shown that ACLMT increases baseline water transport and partially inhibits vasopressin-stimulated water transport across toad bladders due to an increase in cytosolic calcium. However, these evidences provide insufficient insight into the mechanisms involved in the effects of ACLMT on membrane permeability. In an attempt to better understand such mechanisms, the current study aimed to investigate whether the Na(+)/K(+)-ATPase activity of isolated toad bladders can be affected by the ACLMT and the synthetic peptide from its C-terminal region. The toxin significantly decreased the Na(+)/K(+)-ATPase, while the peptide did not alter it. These findings suggest that the effects of ACLMT on membrane permeability may be due to the inhibition of the Na(+)/K(+)-ATPase activity, and that the C-terminal region may not play a relevant role in this effect. This study contributes toward a better understanding of the mechanisms involved in the toxicity of the snake venom Lys49 PLA(2) myotoxins on biological tissues.

Bothrops moojeni myotoxin-II, a Lys49-phospholipase A2 homologue: an example of function versatility of snake venom proteins

MjTX-II, a myotoxic phospholipase A(2) (PLA(2)) homologue from Bothrops moojeni venom, was functionally and structurally characterized. The MjTX-II characterization included: (i) functional characterization (antitumoral, antimicrobial and antiparasitic effects); (ii) effects of structural modifications by 4-bromophenacyl bromide (BPB), cyanogen bromide (CNBr), acetic anhydride and 2-nitrobenzenesulphonyl fluoride (NBSF); (iii) enzymatic characterization: inhibition by low molecular weight heparin and EDTA; and (iv) molecular characterization: cDNA sequence and molecular structure prediction. The results demonstrated that MjTX-II displayed antimicrobial activity by growth inhibition against Escherichia coli and Candida albicans, antitumoral activity against Erlich ascitic tumor (EAT), human breast adenocarcinoma (SK-BR-3) and human T leukemia cells (JURKAT) and antiparasitic effects against Schistosoma mansoni and Leishmania spp., which makes MjTX-II a promising molecular model for future therapeutic applications, as well as other multifunctional homologous Lys49-PLA(2)s or even derived peptides. This work provides useful insights into the structural determinants of the action of Lys49-PLA(2) homologues and, together with additional strategies, supports the concept of the presence of others "bioactive sites" distinct from the catalytic site in snake venom myotoxic PLA(2)s.

Calcium plays a key role in the effects induced by a snake venom Lys49 phospholipase A2 homologue on a lymphoblastoid cell line

A catalytically-inactive Lys49 phospholipase A2 homologue from the venom of the snake Bothrops asper induces diverse effects (necrosis, apoptosis and proliferation) in a lymphoblastoid cell line, depending on the toxin concentration. The increments in cytosolic Ca2+ levels induced by this toxin in this cell line were assessed. At high toxin concentration (100 microg/mL) the toxin induces drastic disruption of the plasma membrane, associated with a prominent Ca2+ influx and necrosis. Previous incubation of the cells with the chelating agent EGTA or with ruthenium red, an inhibitor of the uniporter mitochondrial Ca2+ transport, greatly reduced necrosis. At a toxin concentration of 12.5 microg/mL, apoptosis is the predominant response, being associated with lower increments in cytosolic Ca2+. This effect was inhibited by preincubation with ruthenium red and the cytosolic Ca2+ chelator BAPTA-AM. The proliferative response, which occurs at a low toxin concentration (0.5 microg/mL), is associated with a small and oscillatory increment in cytosolic Ca2+. It was inhibited by EGTA, ruthenium red and BAPTA-AM, by inhibitors of the endoplasmic reticulum Ca2+ -ATPase (SERCA) and by blockade of the ryanodine receptor. It is concluded that necrosis and apoptosis induced by this toxin are associated with increments in cytosolic Ca2+ levels following plasma membrane perturbation, together with the involvement of mitochondria. The cellular proliferative response depends on a limited Ca2+ influx through the plasma membrane, being associated with a concerted functional unit constituted by SERCA, the ryanodine receptor and mitochondria, which regulate the observed oscillations in cytosolic Ca2+ concentration.

Molecular cloning of novel serine proteases and phospholipases A2 from green pit viper (Trimeresurus albolabris) venom gland cDNA library

Green pit viper (Trimeresurus albolabris) is the most common venomous snake responsible for bites in Bangkok. It causes local edema and systemic hypofibrinogenemia resulted from the thrombin-like, as well as the fibrinolytic effects of the venom. However, the amino acid sequences of these venom proteins have never been reported. In this study, we have cloned five novel serine proteases from the Thai T. albolabris venom gland cDNA library. They were all closely homologous to the corresponding serine proteases from Chinese green viper (Trimeresurus stejnegeri), suggesting the evolutionary proximity of the two species. In addition, their functional activities could be deduced. There were predicted to be two thrombin-like enzymes (GPV-TL1 and GPV-TL-2), two isoforms of a fibrinogenolytic enzyme (albofibrase) and a plasminogen activator (GPV-PA), suggesting that defibrination syndrome in patients is a combination of these enzymatic effects. By multiple sequence alignment, no conserved residue or motif responsible for distinct functions of snake venom serine proteases could be observed. Moreover, one Lys 49 and one Asn 49 phospholipase A2 (PLA2) genes were cloned. Lys 49 PLA2 was predicted to devoid of catalytic activity, but showed a carboxy terminal cytotoxic region. No Asp 49 PLA2 was found in 150 clones screened. This explains the marked limb edema but no hemolysis in patients. These novel serine proteases have potentials to be therapeutic anti-thrombotic and thrombolytic agents in the future.

Biochemical and enzymatic characterization of two basic Asp49 phospholipase A2 isoforms from Lachesis muta muta (Surucucu) venom

Two basic phospholipase A2 (PLA2) isoforms were isolated from Lachesis muta muta snake venom and partially characterized. The venom was fractionated by molecular exclusion chromatography in ammonium bicarbonate buffer followed by reverse-phase HPLC on a C-18 mu-Bondapack column and RP-HPLC on a C-8 column. From liquid chromatography-electrospray ionization/mass spectrometry, the molecular mass of the two isoforms LmTX-I and LmTX-II was respectively measured as 14,245.4 and 14,186.2 Da. The pI was respectively estimated to be 8.7 and 8.6 for LmTX-I and LmTX-II, as determined by two-dimensional electrophoresis. The two proteins were sequenced and differentiated from each other by a single amino acid substitution, Arg65 (LmTX-I)-->Pro65 (LmTX-II). The amino acid sequence showed a high degree of homology between PLA2 isoforms from Lachesis muta muta and other PLA2 snake venoms. LmTX-I and LmTX-II had PLA2 activity in the presence of a synthetic substrate and showed a minimum sigmoidal behaviour; with maximal activity at pH 8.0 and 35-45 degrees C. Full PLA2 activity required Ca2+ and was respectively inhibited by Cu2+ and Zn2+ in the presence and absence of Ca2+. Crotapotin from Crotalus durissus cascavella rattlesnake venom significantly inhibited (P<0.05) the enzymatic activity of LmTX-I, suggesting that the binding site for crotapotin in this PLA2 was similar to another in the basic PLA2 of the crotoxin complex from C. durissus cascavella venom.

Activation of cellular functions in macrophages by venom secretory Asp-49 and Lys-49 phospholipases A2

The in vitro effects of myotoxin III (MT-III), an Asp-49 catalytically-active phospholipase A(2), and myotoxin II (MT-II), a catalytically-inactive Lys-49 variant, isolated from Bothrops asper snake venom, on phagocytosis and production of hydrogen peroxide (H(2)O(2)) by thioglycollate-elicited macrophages were investigated. MT-II and MT-III were cytotoxic to mouse peritoneal macrophages at concentrations higher than 25 microg/ml. At non-cytotoxic concentrations, MT-II stimulated Fcgamma, complement, mannose and beta-glucan receptors-mediated phagocytosis, whereas MT-III stimulated only the mannose and beta-glucan receptors-mediated phagocytosis. Moreover, both myotoxins induced the release of H(2)O(2) by thioglycollate-elicited macrophages, MT-III being the most potent stimulator. MT-II induced the release of H(2)O(2) only at a concentration of 3.2 microg/ml (130% increment) while MT-III induced this effect at all concentrations tested (0.5-2.5 microg/ml; average of 206% increment). It is concluded that, at non-cytotoxic concentrations, MT-II and MT-III activate defense mechanisms in macrophages up regulating phagocytosis, mainly via mannose and beta-glucan receptors, and the respiratory burst.

Crystallization and preliminary X-ray diffraction analysis of myotoxin I, a Lys49-phospholipase A2 from Bothrops moojeni

A new myotoxic Lys49-phospholipase A2 isolated from Bothrops moojeni snake venom has been crystallized. The crystals diffracted to 2.18 A resolution using a synchrotron-radiation source and belong to space group C2. The unit-cell parameters are a = 56.8, b = 125.0, c = 64.7 A, beta = 105.5 degrees. Preliminary analysis indicates the presence of four molecules in the asymmetric unit. This may suggest a new quaternary structure for this Lys49-phospholipase A2 in contrast to the dimeric and monomeric structures solved so far for this class of proteins.

A Lys49 phospholipase A(2) homologue from Bothrops asper snake venom induces proliferation, apoptosis and necrosis in a lymphoblastoid cell line

Lys49 phospholipase A(2) homologues are abundant in viperid snake venoms. These proteins have substitutions at the calcium-binding loop and catalytic center which render them enzymatically inactive; however, they display a series of toxic activities, particularly cytotoxicity upon various cell lines in vitro. In this study we explored whether myotoxin II (MT-II), a Lys49 phospholipase A(2) homologue from the venom of the snake Bothrops asper, is capable of inducing various effects in a single cell type, using the lymphoblastoid B cell line CRL-8062 as a model. Cells were incubated with varying concentrations of MT-II for 24 and 48 h, time intervals that are more prolonged than the usual incubation times previously used in the characterization of this toxin. Results indicate that MT-II induces proliferation at low concentrations (0.5-5.0 microg/mL). Apoptosis was predominant at higher toxin levels (5-25 microg/mL), whereas necrosis, associated with overt plasma membrane disruption, occurred at concentrations > or =25 microg/mL, and was the predominant effect at higher MT-II concentrations (50 microg/mL). It is concluded that a single phospholipase A(2) homologue can induce markedly different effects on a single cell line, depending on the concentration used, an observation that may have implications for the action of this type of venom component in vivo.

Influence of temperature upon paralyzing and myotoxic effects of bothropstoxin-I on mouse neuromuscular preparations

Bothropstoxin-I (BthTX-I), from B. jararacussu venom, is a phospholipase A2 (PLA2) homologue devoid of enzymatic activity. Besides inducing severe myonecrosis, BthTX-I promotes paralysis of both directly and indirectly evoked contractions in isolated neuromuscular preparations. We applied an experimental paradigm in order to characterize the steps involved in the toxic effects of BthTX-I on mouse neuromuscular junction. Myotoxicity was assessed by microscopic analysis of extensor digitorum longus muscles; paralyzing activity was evaluated through the recording of isolated contractions indirectly evoked in phrenic-diaphragm preparations. After 90 min at 35 degrees C, BthTX-I induced complete and irreversible paralysis, and damaged 30.3+/-2.7% of muscle fibers. In contrast, no effect was observed when tissues were incubated with BthTX-I at 10 degrees C for 60 min and subsequently washed with toxin-free solution and maintained at 35 degrees C. These results indicate that the binding of BthTX-I to the cellular tissue surface is very weak at low temperature and that an additional factor is necessary. However, when tissues were submitted to BthTX-I (10 degrees C for 60 min), and the temperature was elevated to 35 degrees C, omitting the washing step, it was observed muscle paralysis and damage in 39.04+/-4.2% of muscle fibers. These results indicate that a temperature-dependent step is necessary for BthTX-I to promote both its myotoxic and paralyzing activities.

Inflammatory events induced by Lys-49 and Asp-49 phospholipases A2 isolated from Bothrops asper snake venom: role of catalytic activity

The inflammatory events induced in the peritoneal cavity of mice by two PLA2s isolated from Bothrops asper snake venom were investigated. MT-III, an Asp-49 catalytically active enzyme and MT-II, a catalytically inactive Lys-49 variant induced increase in vascular permeability. Inhibition of enzymatic activity of MT-III with p-bromophenacyl bromide reduced this effect. MT-III induced a larger neutrophil infiltrate than MT-II. This activity was significantly reduced after inhibition of catalytic activity. Reduction in the number of neutrophils was observed when antibodies against L-selectin, CD18 or LFA-1 were used, suggesting the involvement of these adhesion molecules in the effects of both PLA2s. There was no effect with antibodies against ICAM-1 and PECAM-1. Increase in the levels of LTB4 and TXA2, as well as of IL-1, IL-6 and TNF-alpha, were observed in the peritoneal exudates induced by MT-III. MT-II did not enhance levels of eicosanoids but increased those of cytokines. It is concluded that both PLA2s induce inflammatory events in this model. Since MT-III exerts a stronger proinflammatory effect, the enzymatic phospholipid hydrolysis may be relevant for these phenomena. However, the fact that MT-II induced inflammation suggests that molecular regions distinct from the catalytic site elicit inflammatory events perhaps by interacting with specific cell membrane acceptors.

Inhibition of the myotoxic activity of Bothrops jararacussu venom and its two major myotoxins, BthTX-I and BthTX-II, by the aqueous extract of Tabernaemontana catharinensis A. DC. (Apocynaceae)

Partial neutralization of the myotoxic effect of Bothrops jararacussu venom (BV) and two of its myotoxins [bothropstoxin-I (BthTX-I), catalytically inactive, and II (BthTX-II), showing low PLA2 activity], by the lyophilized aqueous extract of Tabernaemontana catharinensis (AE), was studied in rat isolated soleus muscle preparations (in vitro) and through i.m. injection in the gastrocnemius muscle (in vivo) by determination of creatine kinase (CK) activity and histopathological analysis. Incubation of soleus muscle for 1 h with BV or toxins (20 microg/ml) plus AE (400 microg/ml) added immediately after BV, BthTX-I or BthTX-II reduced CK levels by 53%, 37% and 56%, respectively. The myonecrotic effects of BV (20 microg/ml) upon soleus muscle was reduced 24%, 35% and 36% when AE (400 microg/ml) was added 1 h after BV and CK was evaluated 30 min, 1 and 2 h later, respectively. For BthTX-I these values were 46%, 48% and 47%, while for BthTX-II no inhibitory effect was detected. Histological analysis of soleus muscle after incubation with AE (400 microg/ml, 1 h) did not reveal any change in muscle fibers, but severe necrosis induced by BV or toxins (20 microg/ml) was clearly in evidence, and decreased significantly when soleus muscle was protected by AE. This protection was also observed when AE was administered 1 h after BV or BthTX-I, but not after BthTX-II. AE did not inhibit the catalytic PLA2 activity of BthTX-II or BV and did not change the PAGE pattern of BV, BthTX-I or BthTX-II. In vivo assays were performed in 100-g rats and maximal CK release was attained at a dose of 100 microg of BV, 3 h after injection. AE was not effective when injected 20 s after BV or toxins. However, injecting BV or toxins (100 microg), which were pre-incubated with AE (2 mg) caused an inhibition of 57%, 59% and 51%, respectively, with zero time pre-incubation, but was less effective with 1 h pre-incubation. This plant represents a potential source of promising myotoxin inhibitors.

Bitis gabonica (Gaboon viper) snake venom gland: toward a catalog for the full-length transcripts (cDNA) and proteins

The venom gland of the snake Bitis gabonica (Gaboon viper) was used for the first time to construct a unidirectional cDNA phage library followed by high-throughput sequencing and bioinformatic analysis. Hundreds of cDNAs were obtained and clustered into contigs. We found mostly novel full-length cDNA coding for metalloproteases (P-II and P-III classes), Lys49-phospholipase A2, serine proteases with essential mutations in the active site, Kunitz protease inhibitors, several C-type lectins, bradykinin-potentiating peptide, vascular endothelial growth factor, nucleotidases and nucleases, nerve growth factor, and L-amino acid oxidases. Two new members of the recently described short coding region family of disintegrin, displaying RGD and MLD motifs are reported. In addition, we have identified for the first time a cytokine-like molecule and a multi-Kunitz protease inhibitor in snake venoms. The CLUSTAL alignment and the unrooted cladograms for selected families of B. gabonica venom proteins are also presented. A significant number of sequences were devoid of database matches, suggesting that their biologic function remains to be identified. This paper also reports the N-terminus of the 15 most abundant venom proteins and the sequences matching their corresponding transcripts. The electronic version of this manuscript, available on request, contains spreadsheets with hyperlinks to FASTA-formatted files for each contig and the best match to the GenBank and Conserved Domain Databases, in addition to CLUSTAL alignments of each contig. We have thus generated a comprehensive catalog of the B. gabonica venom gland, containing for each secreted protein: (i) the predicted molecular weight, (ii) the predicted isoelectric point, (iii) the accession number, and (iv) the putative function. The role of these molecules is discussed in the context of the envenomation caused by the Gaboon viper.

Crystal structure of an acidic platelet aggregation inhibitor and hypotensive phospholipase A2 in the monomeric and dimeric states: insights into its oligomeric state

Phospholipases A2 belong to the superfamily of proteins which hydrolyzes the sn-2 acyl groups of membrane phospholipids to release arachidonic acid and lysophospholipids. An acidic phospholipase A2 isolated from Bothrops jararacussu snake venom presents a high catalytic, platelet aggregation inhibition and hypotensive activities. This protein was crystallized in two oligomeric states: monomeric and dimeric. The crystal structures were solved at 1.79 and 1.90 angstroms resolution, respectively, for the two states. It was identified a Na+ ion at the center of Ca2+-binding site of the monomeric form. A novel dimeric conformation with the active sites exposed to the solvent was observed. Conformational states of the molecule may be due to the physicochemical conditions used in the crystallization experiments. We suggest dimeric state is one found in vivo.

The Presynaptic Activity of Bothropstoxin-I, a Myotoxin from Bothrops jararacussu Snake Venom

Bothropstoxin-I from Bothrops jararacussu snake venom is a lysine-49 phospholipase A(2) with myotoxic and neurotoxic activities. In this study, we used mouse phrenic nerve-diaphragm preparations in the absence and presence of manganese (Mn(2+)), a presynaptic blocker, to investigate a possible presynaptic action of bothropstoxin-I. At concentrations of 0.9 mM and 1.8 mM, Mn(2+) produced 50% neuromuscular blockade in less than 4 min., which was spontaneously reversible at the lower concentration. Bothropstoxin-I (1.4 microM) irreversibly inhibited neuromuscular blockade by 50% in 31+/-4 min. (mean+/-S.E.M., n = 9). Pretreating preparations with 0.9 mM Mn(2+) prevented the blockade by bothropstoxin-I. When added after bothropstoxin-I, Mn(2+) produced its characteristic blockade and, after washing, the twitch tension returned to pre-Mn(2+) levels, indicating that bothropstoxin-I caused irreversible damage before the addition of Mn(2+). Electrophysiological measurements showed that a concentration of bothropstoxin-I (0.35 microM), which did not produce neuromuscular blockade, caused the appearance of giant miniature end-plate potentials with no change in the membrane resting potential but increased the quantal content. Preparations preincubated with Mn(2+) (0.9 mM, 30 min.) were protected against the depolarizing action of bothropstoxin-I (0.7 microM). These results show that, in addition to its well-known myotoxic effect, bothropstoxin-I also has a presynaptic action.

Structural and functional characterization of myotoxin I, a Lys49 phospholipase A2 homologue from the venom of the snake Bothrops atrox

A new myotoxin was isolated from the venom of Bothrops atrox from Colombia. B. atrox myotoxin I is a homodimer, with a subunit molecular mass of 13,826, and a pI of 8.9. Its complete nucleotide sequence was obtained by cDNA cloning, indicating a mature product of 122 residues that belongs to the family of Lys49 phospholipase A(2) (PLA(2)) homologues, a subgroup of catalytically inactive proteins within the group IIA. Accordingly, the toxin was devoid of phospholipase and anticoagulant activities, in vitro. In mice, it induced conspicuous local myonecrosis, edema, and a systemic interleukin-6 response. In vitro, it was cytolytic upon myoblasts, and weakly bactericidal. The toxin showed highest homology with other Lys49 PLA(2)s, both in its primary and three-dimensional modeled structure, although with an evident difference in the C-terminal region. Unlike Lys49 proteins of American crotalids having 121 residues, this toxin presents an insertion (Asn) between positions 118 and 119. Despite several substitutions within the C-terminal region 115-129 between B. atrox myotoxin I and B. asper myotoxin II, antibodies against synthetic peptide 115-129 of the latter were strongly cross-reactive to the former, indicating the antigenic conservation of this site, known to be critical for the membrane-damaging activities of Lys49 myotoxins.

Bactericidal and neurotoxic activities of two myotoxic phospholipases A2 from Bothrops neuwiedi pauloensis snake venom

Two basic myotoxic PLA(2)s, namely BnpTX-I and II, were isolated from Bothrops neuwiedi pauloensis snake venom through three chromatographic steps: ion-exchange chromatography on CM-Sepharose, gel filtration on Sephadex G-50 and reverse phase HPLC on a C18 column. Both PLA(2)s showed a M(r) around 14,000 for the monomer and 28,000 for the dimer (as estimated by SDS-PAGE), pI approximately 7.8 and approximately 121 amino acid residues cross-linked by seven disulfide bonds. The N-terminal sequences revealed significant homology with Asp49 basic myotoxic PLA(2)s from other snake venoms. The catalytic and anticoagulant activities of BnpTX-I were higher than those of BnpTX-II. Both were able to induce cytotoxicity in vitro, as well as, myotoxicity, edema and lethality in mice. BnpTX-I also induced neurotoxic effect on mouse neuromuscular preparations and bactericidal activity on Eschericia coli and Staphylococcus aureus. After chemical modification of BnpTX-I with BPB or incubation with EDTA or Mn(2+) ions, the catalytic activity was completely abolished, while the toxic and pharmacological activities were partially reduced. Interaction with heparin inhibited the cytotoxic and bactericidal effects. Anti-BthTX-I, anti-BthTX-II and anti-115-129-C terminal antibodies strongly recognize both BnpTX-I and II. It is shown that the neurotoxic effect induced by B. neuwiedi pauloensis venom is due to the presence of myotoxic PLA(2)s. The data also corroborate the hypothesis of a partial dissociation between toxic and enzymatic domains. In addition, BnpTX-I displays a heparin binding C-terminal region, which is probably responsible for the cytotoxic and bactericidal effects.

Most cited papers in Toxicon

Citation of a published work is one of the parameters considered in the analysis of relevance and importance of scientific contributions. In 2002, for the first time the Impact Factor of Toxicon has risen above 2.0, placing it at the 17th position among 76 journals in the 'toxicology' field. The aim of this article was to identify the most cited articles in Toxicon, that have contributed to the steady increase of its Impact Factor. The number of citations, complete reference and type of all documents appearing in Toxicon in the period 1963-2003 were retrieved from the ISI Web-of-Science homepage. The documents retrieved were sorted by the number of citations received. A 'citation index', defined as the number of citations divided by the number of years since publication, was calculated for each document. It was clearly seen that reviews in Toxicon received 4.4-fold more citations than articles. Unexpectedly, it was found that recent papers were proportionally more cited than old ones. A decrease in the proportion of papers dealing on 'snake*' through out the period and the broadened range of subjects of the most cited papers recently published in Toxicon reflects an increased 'visibility' in other fields of toxinology. Research on plant toxins gained its own space in Toxicon with newer publications showing high citation indexes. It can be postulated that these facts helped to increase Toxicon's Impact Factor from 1.248 in 1999 to 2.003 in 2002. With the increased number of issues in Toxicon as well as publications of subject-dedicated volumes containing mostly reviews, the Impact Factor of Toxicon is expected to keep rising in the near future.

Effect of a recombinant Lys49PLA2 myotoxin and Lys49PLA2-derived synthetic peptides from Agkistrodon species on membrane permeability to water

The aim of this work was to study the effect of recombinant ACL myotoxin, a Lys49PLA2 from Agkistrodon contortrix laticinctus snake venom and Lys49PLA2-derived synthetic peptides corresponding to the region 115-129 of venom of the two different Agkistrodon species on water permeability in the toad urinary bladder. The water flow through the membrane was measured gravimetrically in bag preparations of the bladder. The addition of recombinant ACL myotoxin-MBP (maltose binding protein) fusion protein (10 nM) to the bathing solution significantly increased (above 60%) the water transport compared with the control hemibladders. The addition of the Lys49PLA2-derived synthetic peptides in several concentrations to the bathing solution did not affect the water transport across membrane. These results suggest that the ACL myotoxin effect on water transport is not related to the cytotoxic C-terminal region.

Effects of a myotoxic Asp49 phospholipase A2 (ACL-I PLA2) isolated from Agkistrodon contortrix laticinctus snake venom on water transport in the isolated toad urinary bladder

An Asp49 PLA2 (ACL-I PLA2) was purified from the venom of Agkistrodon contortrix laticinctus by gel filtration and cation-exchange chromatography. It has a relative molecular mass of 14,000, and its N-terminal sequence has more than 65% of identity with other snake venom PLA2s. ACL-I PLA2 injected into the Tibialis anterior muscle of rats and mice at doses of 0.3 and 1.6 mg/kg, respectively, induced muscle fiber necrosis, cellular infiltration and edema 3 and 48 h after injection. The effect of the purified enzyme on water permeability was tested in the isolated toad urinary bladder. Water flow through the membrane was measured gravimetrically in bag preparations of the bladder. ACL-I PLA2 (20 nM) did not significantly alter the water permeability in the bladder preparations, whereas ACL myotoxin (ACLMT), a Lys49 PLA2 isolated from the same venom, at similar concentration significantly increased (81%) the water permeability. However, both toxins inhibited the AVP-stimulated water permeability. These results strongly suggest that PLA2 activity is not involved in the ACLMT effect on water transport and the effect of ACL-I PLA2 myotoxin on membrane permeability is mediated by mechanisms that are different in comparison to ACLMT.

Effects of the Ga-As laser irradiation on myonecrosis caused by Bothrops Moojeni snake venom

BACKGROUND AND OBJECTIVES

Viper snake envenoming induces in the victims systemic coagulopathy, and severe local tissue damage such as edema, hemorrhage, intense pain, and myonecrosis. Serumtherapy and other first-aid managements are ineffective in neutralizing these local effects. The effects of the gallium-arsenide (Ga-As) laser irradiation on mice gastrocnemius injected intramuscularly (i.m.) with Bothrops moojeni snake venom were investigated.

STUDY DESIGN/MATERIALS AND METHODS

Macroscopical, histopatological, and myonecrosis quantification through serum creatine kinase (CK) evaluation was done at 3, 12, and 24 hours (two, five, and eight irradiation sessions, 4 J/cm(2), 1 minute 32 seconds per period, respectively), were done after the venom or saline injection, and in venom-unirradiated mice.

RESULTS

In unirradiated gastrocnemius, the venom induced massive hemorrhage, vascular congestion, time-progressing myonecrosis, edema, abundant inflammatory infiltrate, and high CK serum levels. Ga-As irradiation significantly decreased the amount of myonecrosis in all the periods tested (P < 0.05).

CONCLUSIONS

The laser treatment significantly inhibited the ability of B. moojeni venom to rapidly disrupt the integrity of the plasma membrane.

Skeletal muscle degeneration induced by venom phospholipases A2: insights into the mechanisms of local and systemic myotoxicity

Local and systemic skeletal muscle degeneration is a common consequence of envenomations due to snakebites and mass bee attacks. Phospholipases A2 (PLA2) are important myotoxic components in these venoms, inducing a similar pattern of degenerative events in muscle cells. Myotoxic PLA2s bind to acceptors in the plasma membrane, which might be lipids or proteins and which may differ in their affinity for the PLA2s. Upon binding, myotoxic PLA2s disrupt the integrity of the plasma membrane by catalytically dependent or independent mechanisms, provoking a pronounced Ca2+ influx which, in turn, initiates a complex series of degenerative events associated with hypercontraction, activation of calpains and cytosolic Ca(2+)-dependent PLA2s, and mitochondrial Ca2+ overload. Cell culture models of cytotoxicity indicate that some myotoxic PLA2s affect differentiated myotubes in a rather selective fashion, whereas others display a broad cytolytic effect. A model is presented to explain the difference between PLA2s that induce predominantly local myonecrosis and those inducing both local and systemic myotoxicity. The former bind not only to muscle cells, but also to other cell types, thereby precluding a systemic distribution of these PLA2s and their action on distant muscles. In contrast, PLA2s that bind muscle cells in a more selective way are not sequestered by non-specific interactions with other cells and, consequently, are systemically distributed and reach muscle cells in other locations.

Chemical modifications of phospholipases A2 from snake venoms: effects on catalytic and pharmacological properties

Phospholipases A2 (PLA2s) constitute major components of snake venoms and have been extensively investigated not only because they are very abundant in these venoms but mainly because they display a wide range of biological effects, including neurotoxic, myotoxic, cytotoxic, edema-inducing, artificial membrane disrupting, anti-coagulant, platelet aggregation inhibiting, hypotensive, bactericidal, anti-HIV, anti-tumoral, anti-malarial and anti-parasitic. Due to this functional diversity, these structurally similar proteins aroused the interest of many researchers as molecular models for study of structure-function relationships. One of the main experimental strategies used for the study of myotoxic PLA2s is the traditional chemical modification of specific amino acid residues (His, Met, Lys, Tyr, Trp and others) and examination of the consequent effects upon the enzymatic, toxic and pharmacological activities. This line of research has provided useful insights into the structural determinants of the action of these enzymes and, together with additional strategies, supports the concept of the presence of 'pharmacological sites' distinct from the catalytic site in snake venom myotoxic PLA2s.

Inflammatory effects of snake venom myotoxic phospholipases A2

Snake venom phospholipases A2 (PLA2) show a remarkable functional diversity. Among their toxic activities, some display the ability to cause rapid necrosis of skeletal muscle fibers, thus being myotoxic PLA2s. Besides myotoxicity, these enzymes evoke conspicuous inflammatory and nociceptive events in experimental models. Local inflammation and pain are important characteristics of snakebite envenomations inflicted by viperid and crotalid species, whose venoms are rich sources of myotoxic PLA2s. Since the discovery that mammalian PLA2 is a key enzyme in the release of arachidonic acid, the substrate for the synthesis of several lipid inflammatory mediators, much interest has been focused on this enzyme in the context of inflammation. The mechanisms involved in the proinflammatory action of secretory PLA2s are being actively investigated, and part of the knowledge on secretory PLA2 effects has been gained by using snake venom PLA2s as tools, due to their high structural homology with human secretory PLA2s. The inflammatory events evoked by PLA2s are primarily associated with enzymatic activity and to the release of arachidonic acid metabolites. However, catalytically inactive Lys49 PLA2s trigger inflammatory and nociceptive responses comparable to those of their catalytically active counterparts, thereby evidencing that these proteins promote inflammation and pain by mechanisms not related to phospholipid hydrolysis nor to mobilization of arachidonic acid. These studies have provided a boost to the research in this field and various approaches have been used to identify the amino acid residues and the specific sites of interaction of myotoxic PLA2s with cell membranes potentially involved in the PLA2-induced inflammatory and nociceptive effects. This work reviews the proinflammatory and nociceptive effects evoked by myotoxic PLA2s and their mechanisms of action.

Alkylation of myotoxic phospholipases A2 in Bothrops moojeni venom: a promising approach to an enhanced antivenom production

Bothrops moojeni crude venom (MjCV) and its two major toxins, namely myotoxin I (MjTX-I) and myotoxin II (MjTX-II) were alkylated by p-bromophenacyl bromide (BPB). After alkylation the i.p. LD(50) (mice) of MjCV and MjTX-I/II increased from 6.0 to 15.7mg/kg and from 8.0 to 45.0mg/kg, respectively. In addition, doses of 5x LD(50) of alkylated MjTX-I did not cause a single death in mice and no myonecrosis was detected for the alkylated toxins, although both proteins still induced edema. Antibodies to native and modified crude venom or myotoxins cross-reacted with 12 purified class II myotoxic phospholipases A(2) found in snake venoms of the genus Bothrops. Myotoxic PLA(2)s from class I and class III were not recognized by the above antibodies. These results suggest that the overall antigenic structure is conserved among class II myotoxic PLA(2)s, despite differences in their amino acid sequences. Anti-MjTX-I-BPB and anti-MjTX-II-BPB rabbit serum, obtained against the modified myotoxins, were apparently more efficient than those obtained against the native myotoxins. In neutralization experiments, pre-incubation of crude venom or isolated myotoxins with antibodies raised against the native or modified toxins inhibited their PLA(2) and myotoxic activities. Therefore, alkylation of His48 by BPB strongly reduces the local tissue damage induced by B. moojeni venom or isolated myotoxins while retaining antigenicity, which suggests a promising procedure for an enhanced antiophidian serum production for practical purposes.

Antagonism of myotoxic and paralyzing activities of bothropstoxin-I by suramin

Polyanionic substances are known to inhibit the myotoxic effects of some crotalide snake venoms. Bothropstoxin-I (BthTX-I), a basic Lys49 phospholipase (PLA2) homologue from Bothrops jararacussu venom, besides inducing muscle damage, also promotes the blockade of both directly and indirectly evoked contractions in mouse neuromuscular preparation. In this work, we evaluated the ability of suramin, a polysulfonated naphtylurea derivative, to antagonize the myotoxic and the paralyzing activities of BthTX-I on mice neuromuscular junction in vitro. Myotoxicity was assessed by light and electronic microscopic analysis of extensor digitorum longus (EDL) muscles; paralyzing activity was evaluated through the recording of both directly and indirectly evoked contractions of phrenic-diaphragm (PD) preparations. BthTX-I (1 microM) alone, or pre-incubated with suramin (10 microM) at 37 degrees C for 15 min was added to the preparations for 120 min. BthTX-I induced histological alterations typical of myonecrosis in 14.6 +/- 1.0% of EDL muscle fibers. In addition, BthTX-I blocked 50% of both directly and indirectly evoked contractions in PD preparations in 72.1 +/- 9.1 and 21.1 +/- 2.0 min, respectively. Pre-incubation with suramin abolished both the muscle-damaging and muscle-paralyzing activities of BthTX-I. Since suramin is a polyanionic substance, we suggested that its effects result from the formation of inactive acid-base complexes with BthTX-I.

Effects of ACL myotoxin, a Lys49 phospholipase A2 from Agkistrodon contortrix laticinctus snake venom, on water transport in the isolated toad urinary bladder

ACL myotoxin (ACLMT) is a Lys49 phospholipase A(2)-like protein isolated from the venom of the snake Agkistrodon contortrix laticinctus. The aim of this work was to study the effect of ACLMT on water transport in the toad bladder. Water flow through the membrane was measured gravimetrically in bag preparations of the bladder. ACLMT (20 nM) increased the baseline water flow and partially inhibited arginine-vasopressin (AVP), 8-chlorophenylthio-cAMP (8-CPT-cAMP) and forskolin-stimulated water flow. The effect of ACLMT on baseline or AVP-stimulated water flow was prevented by lanthanum (0.1 mM) indicating that the effect of ACLMT on water transport may be mediated through an increase in intracellular calcium. The effect of ACLMT on baseline water flow was also prevented by nifedipine (0.1 mM) indicating the participation of exogenous calcium in this effect. Carbachol (0.1 mM) has been shown to enhance baseline water flow while inhibiting AVP-stimulated water flow. The effects of ACLMT and carbachol on baseline water flow and AVP-stimulated water flow were not additive, suggesting that both agents alter water transport by a similar mechanism. Indomethacin (10 microM) reduced the effect of ACLMT on forskolin-stimulated water flow, suggesting an increase in prostaglandin biosynthesis. These results suggest that the effects of ACLMT on water transport may be mediated by increasing intracellular calcium and stimulation prostaglandin biosynthesis.

An overview of lysine-49 phospholipase A2 myotoxins from crotalid snake venoms and their structural determinants of myotoxic action

In 1984, the first venom phospholipase A2 (PLA2) with a lysine substituting for the highly conserved aspartate 49 was discovered, in the North American crotalid snake Agkistrodon p. piscivorus [J. Biol. Chem. 259 (1984) 13839]. Ten years later, the first mapping of a 'toxic region' on a Lys49 PLA2 was reported, in Bothrops asper myotoxin II [J. Biol. Chem. 269 (1994) 29867]. After a further decade of research on the Lys49 PLA2s, a better understanding of their structural determinants of toxicity and mode of action is rapidly emerging, with myotoxic effector sites identified at the C-terminal region in at least four proteins: B. asper myotoxin II, A. p. piscivorus K49 PLA2, A. c. laticinctus ACL myotoxin, and B. jararacussu bothropstoxin I. Although important features still remain to be established, their toxic mode of action has now been understood in its more general concepts, and a consistent working hypothesis can be experimentally supported. It is proposed that all the toxic activities of Lys49 PLA2s are related to their ability to destabilize natural (eukaryotic and prokaryotic) and artificial membranes, using a cationic/hydrophobic effector site located at their C-terminal loop. This review summarizes the general properties of the Lys49 PLA2 myotoxins, emphasizing the development of current concepts and hypotheses concerning the molecular basis of their toxic activities.

A structure based model for liposome disruption and the role of catalytic activity in myotoxic phospholipase A2s

Venom phospholipase A2s (PLA2s) display a wide spectrum of pharmacological activities and, based on the wealth of biochemical and structural data currently available for PLA2s, mechanistic models can now be inferred to account for some of these activities. A structural model is presented for the role played by the distribution of surface electrostatic potential in the ability of myotoxic D49/K49 PLA2s to disrupt multilamellar vesicles containing negatively charged natural and non-hydrolyzable phospholipids. Structural evidence is provided for the ability of K49 PLA2s to bind phospholipid analogues and for the existence of catalytic activity in K49 PLA2s. The importance of the existence of catalytic activity of D49 and K49 PLA2s in myotoxicity is presented.

Crystal structures of BnSP-7 and BnSP-6, two Lys49-phospholipases A2: quaternary structure and inhibition mechanism insights

Phospholipases A(2) are components of Bothrops venoms responsible for disruption of cell membrane integrity via hydrolysis of its phospholipids. A class of PLA(2)-like proteins has been described which despite PLA(2) activity on artificial substrate, due to a D49K mutation, is still highly myonecrotic. This work reports the X-ray structure determination of two Lys49-PLA(2)s from Bothrops neuwiedi pauloensis (BnSP-7 and BnSP-6) and, for the first time, the comparison of eight dimeric Lys49-PLA(2)s. This comparison reveals that there are not just two ("open" and "closed") but at least six different conformations. The binding of fatty acid observed in three recent Lys49-PLA(2) structures seems to be independent of their quaternary conformation. Cys29 polarization by Lys122 is not significant for BnSP-7 and BnSP-6 or other structures not bound by fatty acids. These structures may be in an "active" state when nothing is bound to them and the Lys122/Cys29 interactions are weak or absent.

The crystal structure of a novel, inactive, lysine 49 PLA2 from Agkistrodon acutus venom: an ultrahigh resolution, AB initio structure determination

The crystal structure of acutohaemolysin, a lysine 49 phospholipase A2 protein with 1010 non-hydrogen protein atoms and 232 water molecules, has been determined ab initio using the program SnB at an ultrahigh resolution of 0.8 A. The lack of catalytic activity appears to be related to the presence of Phe102, which prevents the access of substrate to the active site. The substitution of tryptophan for leucine at residue 10 interferes with dimer formation and may be responsible for the additional loss of hemolytic activity. The ultrahigh resolution of the experimental diffraction data permits alternative conformations to be modeled for disordered residues, many hydrogen atoms to be located, the protonation of the Nepsilon2 atom in the catalytic residue His48 to be observed experimentally, and the density of the bonding electrons to be analyzed in detail.

Myotoxicity induced by an acidic Asp-49 phospholipase A(2) isolated from Lachesis muta snake venom. Comparison with lysophosphatidylcholine

In a previous report we showed that Lachesis muta crude venom displays potent indirect hemolytic activity and myotoxicity when injected into mice. Then, a phospholipase A(2) (PLA(2)) (LM-PLA(2)-I) responsible for these activities was isolated. More recently, a catalytically active isoenzyme (LM-PLA(2)-II) with molecular mass of 18 kDa and isoeletric point at pH 5.4 was isolated from the same snake venom. LM-PLA(2)-II inhibited ADP- and collagen-induced platelet aggregation as well as induced a potent paw edema reaction in rats. Here we show that LM-PLA(2)-II induced myotoxic effects both in vitro characterized by an increase on the rate of creatine kinase (CK) release from isolated mice extensor digitorum longus (EDL) muscles and in vivo by increasing plasma CK activity of injected mice. Histological analysis showed an intense damage in muscle cells injected with LM-PLA(2)-II. It was also shown that exogenous lysophosphatidylcholine (lyso-pc) behaved as a typical myotoxin damaging muscle cells, producing myonecrosis characterized by local infiltration of inflammatory cells similarly to that observed for LM-PLA(2)-II. Hemorrhage and lethal effects were not observed neither with LM-PLA(2)-II nor lyso-pc. As previously observed for other biological activities, pretreatment of LM-PLA(2)-II with p-bromophenacyl bromide (p-BPB) or acetic anhydride abolished all the enzyme's actions. The data confirms that biological activities displayed by LM-PLA(2)-II, including the myotoxic effects reported here, are all dependent on its enzymatic activity where the product formed (lyso-pc) may play an important function on such myotoxicity.