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

BthTX-I, a phospholipase A2-like toxin, is inhibited by the plant cinnamic acid derivative: chlorogenic acid

Snakebite is a significant health concern in tropical and subtropical regions, particularly in Africa, Asia, and Latin America, resulting in more than 2.7 million envenomations and an estimated one hundred thousand fatalities annually. The Bothrops genus is responsible for the majority of snakebite envenomings in Latin America and Caribbean countries. Accidents involving snakes from this genus are characterized by local symptoms that often lead to permanent sequelae and death. However, specific antivenoms exhibit limited effectiveness in inhibiting local tissue damage. Phospholipase A2-like (PLA2-like) toxins emerge as significant contributors to local myotoxicity in accidents involving Bothrops species. As a result, they represent a crucial target for prospective treatments. Some natural and synthetic compounds have shown the ability to reduce or abolish the myotoxic effects of PLA2-like proteins. In this study, we employed a combination approach involving myographic, morphological, biophysical and bioinformatic techniques to investigate the interaction between chlorogenic acid (CGA) and BthTX-I, a PLA2-like toxin. CGA provided a protection of 71.8% on muscle damage in a pre-incubation treatment. Microscale thermophoresis and circular dichroism experiments revealed that CGA interacted with the BthTX-I while preserving its secondary structure. CGA exhibited an affinity to the toxin that ranks among the highest observed for a natural compound. Bioinformatics simulations indicated that CGA inhibitor binds to the toxin's hydrophobic channel in a manner similar to other phenolic compounds previously investigated. These findings suggest that CGA interferes with the allosteric transition of the non-activated toxin, and the stability of the dimeric assembly of its activated state.

Viper Venom Phospholipase A2 Database: The Structural and Functional Anatomy of a Primary Toxin in Envenomation

Viper venom phospholipase A2 enzymes (vvPLA2s) and phospholipase A2-like (PLA2-like) proteins are two of the principal toxins in viper venom that are responsible for the severe myotoxic and neurotoxic effects caused by snakebite envenoming, among other pathologies. As snakebite envenoming is the deadliest neglected tropical disease, a complete understanding of these proteins' properties and their mechanisms of action is urgently needed. Therefore, we created a database comprising information on the holo-form, cofactor-bound 3D structure of 217 vvPLA2 and PLA2-like proteins in their physiologic environment, as well as 79 membrane-bound viper species from 24 genera, which we have made available to the scientific community to accelerate the development of new anti-snakebite drugs. In addition, the analysis of the sequenced, 3D structure of the database proteins reveals essential aspects of the anatomy of the proteins, their toxicity mechanisms, and the conserved binding site areas that may anchor universal interspecific inhibitors. Moreover, it pinpoints hypotheses for the molecular origin of the myotoxicity of the PLA2-like proteins. Altogether, this study provides an understanding of the diversity of these toxins and how they are conserved, and it indicates how to develop broad, interspecies, efficient small-molecule inhibitors to target the toxin's many mechanisms of action.

Lys49 myotoxins, secreted phospholipase A2-like proteins of viperid venoms: A comprehensive review

Muscle necrosis is a potential clinical complication of snakebite envenomings, which in severe cases can lead to functional or physical sequelae such as disability or amputation. Snake venom proteins with the ability to directly damage skeletal muscle fibers are collectively referred to as myotoxins, and include three main types: cytolysins of the "three-finger toxin" protein family expressed in many elapid venoms, the so-called "small" myotoxins found in a number of rattlesnake venoms, and the widespread secreted phospholipase A₂ (sPLA₂) molecules. Among the latter, protein variants that conserve the sPLA₂ structure, but lack such enzymatic activity, have been increasingly found in the venoms of many viperid species. Intriguingly, these sPLA₂-like proteins are able to induce muscle necrosis by a mechanism independent of phospholipid hydrolysis. They are commonly referred to as "Lys49 myotoxins" since they most often present, among other substitutions, the replacement of the otherwise invariant residue Asp49 of sPLA₂s by Lys. This work comprehensively reviews the historical developments and current knowledge towards deciphering the mechanism of action of Lys49 sPLA₂-like myotoxins, and points out main gaps to be filled for a better understanding of these multifaceted snake venom proteins, to hopefully lead to improved treatments for snakebites.

Panacea within a Pandora's box: the antiparasitic effects of phospholipases A2 (PLA2s) from snake venoms

Parasitic diseases affect millions of individuals worldwide, mainly in low-income regions. There is no cure for most of these diseases, and the treatment relies on drugs that have side effects and lead to drug resistance, emphasizing the urgency to find new treatments. Snake venom has been gaining prominence as a rich source of molecules with antiparasitic potentials, such as phospholipases A₂ (PLA₂s). Here, we compile the findings involving PLA₂s with antiparasitic activities against helminths, Plasmodium, Toxoplasma, and trypanosomatids. We indicate their molecular features, highlighting the possible antiparasitic mechanisms of action of these proteins. We also demonstrate interactions between PLA₂s and some parasite membrane components, shedding light on potential targets for drug design that may provide better treatment for the illnesses caused by parasites.

Isohemigossypolone: Antiophidic properties of a naphthoquinone isolated from Pachira aquatica Aubl

We investigated the antiophidic properties of isohemigossypolone (ISO), a naphthoquinone isolated from the outer bark of the Pachira aquatic Aubl. The inhibition of phospholipase A₂, coagulant, fibrinogenolytic, hemorrhagic and myotoxic activities induced by Bothrops pauloensis venom (Pb) was investigated. For this, we use samples resulting from the incubation of Pb with ISO in different concentrations (1:1, 1:5 and 1:10 w/w), we also evaluated the condition of treatment using ISO after 15 min of venom inoculation. The activities of phospholipase A₂, coagulant, fibrinogenolytic, hemorrhagic and myotoxic induced by the B. pauloensis venom were significantly inhibited when the ISO was pre-incubated with the crude venom. For in vivo neutralization tests, the results were observed even when the ISO was applied after 15 min of inoculation of the venom or metalloprotease (BthMP). Also, to identify the inhibition mechanism, we performed in silico assays, across simulations of molecular coupling and molecular dynamics, it was possible to identify the modes of interaction between ISO and bothropic toxins BmooMPα-I, Jararacussin-I and BNSP-7. The present study shows that naphthoquinone isohemigossypolone isolated from the P. aquatica plant inhibited part of the local and systemic damage caused by venom proteins, demonstrating the pharmacological potential of this compound in neutralizing the harmful effects caused by snakebites.

Antiangiogenic effects of phospholipase A2 Lys49 BnSP-7 from Bothrops pauloensis snake venom on endothelial cells: An in vitro and ex vivo approach

Antiangiogenic strategies are promising tools for cancer treatment and several other disorders. In this sense, phospholipases A₂ (PLA₂s) from snake venom have been described to possess antiangiogenic properties. In this study, we evaluated both in vitro and ex vivo antiangiogenic effects induced by BnSP-7, a Lys49 PLA₂ isolated from Bothrops pauloensis snake venom. BnSP-7 was able to inhibit endothelial cell (HUVEC) proliferation, which was indeed confirmed by a modulation of cell cycle progression. Interestingly, BnSP-7 also inhibited the adhesion and migration of HUVECs and blocked in vitro angiogenesis in a VEGF-dependent manner, an important proangiogenic factor. Finally, BnSP-7 was capable of inhibiting sprouting angiogenic process through an ex vivo aortic ring assay. Taken together, these results indicate that BnSP-7 has potent in vitro and ex vivo antiangiogenic effect.

The allosteric activation mechanism of a phospholipase A2-like toxin from Bothrops jararacussu venom: a dynamic description

The activation process of phospholipase A₂-like (PLA₂-like) toxins is a key step in their molecular mechanism, which involves oligomeric changes leading to the exposure of specific sites. Few studies have focused on the characterization of allosteric activators and the features that distinguish them from inhibitors. Herein, a comprehensive study with the BthTX-I toxin from Bothrops jararacussu venom bound or unbound to α-tocopherol (αT) was carried out. The oligomerization state of BthTX-I bound or unbound to αT in solution was studied and indicated that the toxin is predominantly monomeric but tends to oligomerize when complexed with αT. In silico molecular simulations showed the toxin presents higher conformational changes in the absence of αT, which suggests that it is important to stabilize the structure of the toxin. The transition between the two states (active/inactive) was also studied, showing that only the unbound BthTX-I system could migrate to the inactive state. In contrast, the presence of αT induces the toxin to leave the inactive state, guiding it towards the active state, with more regions exposed to the solvent, particularly its active site. Finally, the structural determinants necessary for a molecule to be an inhibitor or activator were analyzed in light of the obtained results.

SDS-induced oligomerization of Lys49-phospholipase A2 from snake venom

Phospholipase A₂ (PLA₂) is one of the representative toxic components of snake venom. PLA₂s are categorized into several subgroups according to the amino acid at position 49, which comprises either Asp49, Lys49, Arg49 or Ser49. Previous studies suggested that the Lys49-PLA₂ assembles into an extremely stable dimer. Although the behavior on Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) under reducing or non-reducing conditions suggested the presence of intermolecular disulfide bonds, these bonds were not observed in the crystal structure of Lys49-PLA₂. The reason for this discrepancy between the crystal structure and SDS-PAGE of Lys49-PLA₂ remains unknown. In this study, we analyzed a Lys49-PLA₂ homologue from Protobothrops flavoviridis (PflLys49-PLA₂ BPII), by biophysical analyses including X-ray crystallography, SDS-PAGE, native-mass spectrometry, and analytical ultracentrifugation. The results demonstrated that PflLys49-PLA₂ BPII spontaneously oligomerized in the presence of SDS, which is one of the strongest protein denaturants.

PLA2-like proteins myotoxic mechanism: a dynamic model description

Phospholipase A₂-like (PLA₂-like) proteins contribute to the development of muscle necrosis in Viperidae snake bites and are not efficiently neutralized by current antivenom treatments. The toxic mechanisms of PLA₂-like proteins are devoid of catalytic activity and not yet fully understood, although structural and functional experiments suggest a dimeric assembly and that the C-terminal residues are essential to myotoxicity. Herein, we characterized the functional mechanism of bothropic PLA₂-like structures related to global and local measurements using the available models in the Protein Data Bank and normal mode molecular dynamics (NM-MD). Those measurements include: (i) new geometric descriptions between their monomers, based on Euler angles; (ii) characterizations of canonical and non-canonical conformations of the C-terminal residues; (iii) accessibility of the hydrophobic channel; (iv) inspection of ligands; and (v) distance of clustered residues to toxin interface of interaction. Thus, we described the allosteric activation of PLA₂-like proteins and hypothesized that the natural movement between monomers, calculated from NM-MD, is related to their membrane disruption mechanism, which is important for future studies of the inhibition process. These methods and strategies can be applied to other proteins to help understand their mechanisms of action.

Protective effects of green tea and its main constituents against natural and chemical toxins: A comprehensive review

Toxins are natural or chemical poisonous substances with severe side effects on health. Humans are generally exposed by widespread toxic contaminations via air, soil, water, food, fruits and vegetables. Determining a critical antidote agent with extensive effects on different toxins is an ultimate goal for all toxicologists. Traditional medicine is currently perceived as a safe and natural approach against toxins. In this regard, we focused on the protective effects of green tea (Camellia sinensis) and its main components such as catechin, epicatechin, epicatechin gallate, gallocatechin, epigallocatechin and epigallocatechin gallate as a principal source of antioxidants against both natural and chemical toxins. This literate review demonstrates that protective effects of green tea and its constituents were mainly attributed to their anti-oxidative, radical scavenging, chelating, anti-apoptotic properties and modulating inflammatory responses. Although, some studies reveal they have protective effects by increasing toxin metabolism and neutralizing PLA₂, proteases, hyaluronidase and l-amino acid oxidase enzymes.

Oligomerization inhibits Legionella pneumophila PlaB phospholipase A activity

The intracellularly replicating lung pathogen Legionella pneumophila consists of an extraordinary variety of phospholipases, including at least 15 different phospholipases A (PLA). Among them, PlaB, the first characterized member of a novel lipase family, is a hemolytic virulence factor that exhibits the most prominent PLA activity in L. pneumophila. We analyzed here protein oligomerization, the importance of oligomerization for activity, addressed further essential regions for activity within the PlaB C terminus, and the significance of PlaB-derived lipolytic activity for L. pneumophila intracellular replication. We determined by means of analytical ultracentrifugation and small angle x-ray scattering analysis that PlaB forms homodimers and homotetramers. The C-terminal 5, 10, or 15 amino acids, although the individual regions contributed to PLA activity, were not essential for protein tetramerization. Infection of mouse macrophages with L. pneumophila wild type, plaB knock-out mutant, and plaB complementing or various mutated plaB-harboring strains showed that catalytic activity of PlaB promotes intracellular replication. We observed that PlaB was most active in the lower nanomolar concentration range but not at or only at a low level at concentration above 0.1 μm where it exists in a dimer/tetramer equilibrium. We therefore conclude that PlaB is a virulence factor that, on the one hand, assembles in inactive tetramers at micromolar concentrations. On the other hand, oligomer dissociation at nanomolar concentrations activates PLA activity. Our data highlight the first example of concentration-dependent phospholipase inactivation by tetramerization, which may protect the bacterium from internal PLA activity, but enzyme dissociation may allow its activation after export.

Molecular cloning and pharmacological properties of an acidic PLA2 from Bothrops pauloensis snake venom

In this work, we describe the molecular cloning and pharmacological properties of an acidic phospholipase A(2) (PLA(2)) isolated from Bothrops pauloensis snake venom. This enzyme, denominated BpPLA(2)-TXI, was purified by four chromatographic steps and represents 2.4% of the total snake venom protein content. BpPLA(2)-TXI is a monomeric protein with a molecular mass of 13.6 kDa, as demonstrated by Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF) analysis and its theoretical isoelectric point was 4.98. BpPLA(2)-TXI was catalytically active and showed some pharmacological effects such as inhibition of platelet aggregation induced by collagen or ADP and also induced edema and myotoxicity. BpPLA(2)-TXI displayed low cytotoxicity on TG-180 (CCRF S 180 II) and Ovarian Carcinoma (OVCAR-3), whereas no cytotoxicity was found in regard to MEF (Mouse Embryonic Fibroblast) and Sarcoma 180 (TIB-66). The N-terminal sequence of forty-eight amino acid residues was determined by Edman degradation. In addition, the complete primary structure of 122 amino acids was deduced by cDNA from the total RNA of the venom gland using specific primers, and it was significantly similar to other acidic D49 PLA(2)s. The phylogenetic analyses showed that BpPLA(2)-TXI forms a group with other acidic D49 PLA(2)s from the gender Bothrops, which are characterized by a catalytic activity associated with anti-platelet effects.

Structural and phylogenetic studies with MjTX-I reveal a multi-oligomeric toxin--a novel feature in Lys49-PLA2s protein class

The mortality caused by snakebites is more damaging than many tropical diseases, such as dengue haemorrhagic fever, cholera, leishmaniasis, schistosomiasis and Chagas disease. For this reason, snakebite envenoming adversely affects health services of tropical and subtropical countries and is recognized as a neglected disease by the World Health Organization. One of the main components of snake venoms is the Lys49-phospholipases A₂, which is catalytically inactive but possesses other toxic and pharmacological activities. Preliminary studies with MjTX-I from Bothrops moojeni snake venom revealed intriguing new structural and functional characteristics compared to other bothropic Lys49-PLA₂s. We present in this article a comprehensive study with MjTX-I using several techniques, including crystallography, small angle X-ray scattering, analytical size-exclusion chromatography, dynamic light scattering, myographic studies, bioinformatics and molecular phylogenetic analyses.Based in all these experiments we demonstrated that MjTX-I is probably a unique Lys49-PLA₂, which may adopt different oligomeric forms depending on the physical-chemical environment. Furthermore, we showed that its myotoxic activity is dramatically low compared to other Lys49-PLA₂s, probably due to the novel oligomeric conformations and important mutations in the C-terminal region of the protein. The phylogenetic analysis also showed that this toxin is clearly distinct from other bothropic Lys49-PLA₂s, in conformity with the peculiar oligomeric characteristics of MjTX-I and possible emergence of new functionalities inresponse to environmental changes and adaptation to new preys.

Combined snake venomics and venom gland transcriptomic analysis of Bothropoides pauloensis

Unraveling the repertoire of venom toxins of Bothropoides pauloensis was assessed by snake venomics and venom gland transcriptomic surveys. Both approaches yielded converging overall figures, pointing to metalloproteinases (~37%), PLA(2)s (26-32%), and vasoactive (bradykinin-potentiating) peptides (12-17%) as the major toxin classes. The high occurrence of SVMPs, PLA(2) molecules, vasoactive peptides, along with serine proteinases, explains the local and systemic effects observed in envenomations by B. pauloensis. Minor (<3%) C-type lectin, serine proteinase, L-amino acid oxidase, nerve growth factor, and CRISP molecules were also identified in the transcriptome and the proteome. Low abundance (0.3%) EST singletons coding for vascular endothelial growth factor (svVEGF), ohanin, hyaluronidase, and 5' nucleotidase were found only in the venom gland cDNA library. At the molecular level, the transcriptomic and proteomic datasets display low compositional concordance. In particular, although there is good agreement between transcriptome and proteome in the identity of BPPs, PLA(2) molecules and L-amino acid oxidase, both datasets strongly depart in their C-type lectin and SVMP complements. These data support the view that venom composition is influenced by transcriptional and translational mechanisms and emphasize the value of combining proteomic and transcriptomic approaches to acquire a more complete understanding of the toxinological profile and natural history of the snake venom.

Crystallization and preliminary X-ray diffraction studies of BmooPLA2-I, a platelet-aggregation inhibitor and hypotensive phospholipase A2 from Bothrops moojeni venom

Phospholipases A(2) (PLA(2)s) are enzymes that cause the liberation of fatty acids and lysophospholipids by the hydrolysis of membrane phospholipids. In addition to their catalytic action, a wide variety of pharmacological activities have been described for snake-venom PLA(2)s. BmooPLA(2)-I is an acidic, nontoxic and catalytic PLA(2) isolated from Bothrops moojeni snake venom which exhibits an inhibitory effect on platelet aggregation, an immediate decrease in blood pressure, inducing oedema at a low concentration, and an effective bactericidal effect. BmooPLA(2)-I has been crystallized and X-ray diffraction data have been collected to 1.6 Å resolution using a synchrotron-radiation source. The crystals belonged to space group C222(1), with unit-cell parameters a = 39.7, b = 53.2, c = 89.2 Å. The molecular-replacement solution of BmooPLA(2)-I indicated a monomeric conformation, which is in agreement with nondenaturing electrophoresis and dynamic light-scattering experiments. A comparative study of this enzyme with the acidic PLA(2) from B. jararacussu (BthA-I) and other toxic and nontoxic PLA(2)s may provide important insights into the functional aspects of this class of proteins.

Crystal structure of Bn IV in complex with myristic acid: a Lys49 myotoxic phospholipase A₂ from Bothrops neuwiedi venom

The LYS49-PLA₂s myotoxins have attracted attention as models for the induction of myonecrosis by a catalytically independent mechanism of action. Structural studies and biological activities have demonstrated that the myotoxic activity of LYS49-PLA₂ is independent of the catalytic activity site. The myotoxic effect is conventionally thought to be to due to the C-terminal region 111-121, which plays an effective role in membrane damage. In the present study, Bn IV LYS49-PLA₂ was isolated from Bothrops neuwiedi snake venom in complex with myristic acid (CH₃(CH₂)₁₂COOH) and its overall structure was refined at 2.2 Å resolution. The Bn IV crystals belong to monoclinic space group P2₁ and contain a dimer in the asymmetric unit. The unit cell parameters are a = 38.8, b = 70.4, c = 44.0 Å. The biological assembly is a "conventional dimer" and the results confirm that dimer formation is not relevant to the myotoxic activity. Electron density map analysis of the Bn IV structure shows clearly the presence of myristic acid in catalytic site. The relevant structural features for myotoxic activity are located in the C-terminal region and the Bn IV C-terminal residues NKKYRY are a probable heparin binding domain. These findings indicate that the mechanism of interaction between Bn IV and muscle cell membranes is through some kind of cell signal transduction mediated by heparin complexes.

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.

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.

Neuromuscular and phospholipase activities of venoms from three subspecies of Bothrops neuwiedi (B. n. goyazensis, B. n. paranaensis and B. n. diporus)

The Bothrops neuwiedi (Neuwied's lancehead) species complex consists of a variety of subspecies with a wide distribution in South America. In this work, we compared the neuromuscular blockade caused by venoms from three subspecies (B. n. goyazensis, B. n. paranaensis and B. n. diporus) of this complex using chick biventer cervicis (BC) and mouse phrenic nerve-diaphragm (PND) preparations and investigated their phospholipase A2 (PLA2) activities and electrophoretic profiles. The order of potency of PLA2 activity was B. n. diporus>B. n. paranaensis>B. n. goyazensis. In BC preparations, B. n. goyazensis venom (50 microg/mL) was significantly (p<0.05) more active than B. n. paranaensis and B. n. diporus venoms, which did not produce a significant blockade at this time interval; after 120 min, B. n. goyazensis, B. n. paranaensis and B. n. diporus venoms (100 microg/mL) produced blockades of 57.4+/-5%, 30+/-3% and 17.4+/-7% (n=3-6 each), respectively. The three venoms inhibited contractures in response to ACh, indicating interference with postsynaptic neurotransmission. Only B. n. goyazensis and B. n. paranaensis venoms caused a long-lasting, concentration-dependent muscle contracture prior to blockade. In PND preparations, all of the venoms blocked the twitch-tension responses within 45-100 min, indicating that these preparations were more sensitive than avian preparations. There was a correlation between PLA2 activity and the time for 50% blockade in PND but not in BC preparations. SDS-PAGE showed quantitative rather than qualitative differences among the venoms. These results indicate that the venoms of the three subspecies had similar profiles of neuromuscular activity, although the relationship with PLA2 activity varied with the preparation used.

Purification, sequencing and structural analysis of two acidic phospholipases A2 from the venom of Bothrops insularis (jararaca ilhoa)

Bothrops snake venoms contain a variety of phospholipases (PLA(2)), some of which are myotoxic. In this work, we used reverse-phase HPLC and mass spectrometry to purify and sequence two PLA(2) from the venom of Bothrops insularis. The two enzymes, designated here as BinTX-I and BinTx-II, were acidic (pI 5.05 and 4.49) Asp49 PLA(2), with molecular masses of 13,975 and 13,788, respectively. The amino acid sequence and molecular mass of BinTX-I were identical to those of a PLA(2) previously isolated from this venom (PA2_BOTIN, SwissProt accession number ) while those of BinTX-II indicated that this was a new enzyme. Multiple sequence alignments with other Bothrops PLA(2) showed that the amino acids His48, Asp49, Tyr52 and Asp99, which are important for enzymatic activity, were fully conserved, as were the 14 cysteine residues involved in disulfide bond formation, in addition to various other residues. A phylogenetic analysis showed that BinTX-I and BinTX-II grouped with other acidic Asp49 PLA(2) from Bothrops venoms, and computer modeling indicated that these enzymes had the characteristic structure of bothropic PLA(2) that consisted of three alpha-helices, a beta-wing, a short helix and a calcium-binding loop. BinTX-I (30 microg/paw) produced mouse hind paw edema that was maximal after 1h compared to after 3h with venom (10 and 100 microg/paw); in both cases, the edema decreased after 6h. BinTX-1 and venom (40 microg/ml each) produced time-dependent neuromuscular blockade in chick biventer cervicis preparations that reached 40% and 95%, respectively, after 120 min. BinTX-I also produced muscle fiber damage and an elevation in CK, as also seen with venom. These results indicate that BinTX-I contributes to the neuromuscular activity and tissue damage caused by B. insularis venom in vitro and in vivo.

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.

Preliminary X-ray crystallographic studies of BthTX-II, a myotoxic Asp49-phospholipase A2 with low catalytic activity from Bothrops jararacussu venom

For the first time, a complete X-ray diffraction data set has been collected from a myotoxic Asp49-phospholipase A2 (Asp49-PLA2) with low catalytic activity (BthTX-II from Bothrops jararacussu venom) and a molecular-replacement solution has been obtained with a dimer in the asymmetric unit. The quaternary structure of BthTX-II resembles the myotoxin Asp49-PLA2 PrTX-III (piratoxin III from B. pirajai venom) and all non-catalytic and myotoxic dimeric Lys49-PLA2s. In contrast, the oligomeric structure of BthTX-II is different from the highly catalytic and non-myotoxic BthA-I (acidic PLA2 from B. jararacussu). Thus, comparison between these structures should add insight into the catalytic and myotoxic activities of bothropic PLA2s.

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.

A predominant role for hydrogen bonding in the stability of the homodimer of bothropstoxin-I, A lysine 49-phospholipase A2

Bothropstoxin-I (BthTx-I) is a homodimeric Lys49-phospholipase A(2) isolated from Bothrops jararacussu venom which damages liposome membranes via a Ca(2+)-independent mechanism. The Glu12/Trp77/Lys80 triad at the dimer interface forms extensive intermolecular hydrogen bonds and hydrophobic contacts, and equilibrium chemical denaturation was used to evaluate the effect on homodimer stability of site-directed mutagenesis of these residues. Changes in the intrinsic fluorescence anisotropy and farUV circular dichroism signals were analyzed using a two-step unfolding model of the BthTx-I dimer to estimate the Gibbs free energy changes of transitions between the dimer and native monomer and between the native and denatured monomers. Whereas the Trp77His, Trp77Gln and Glu12Gln mutants showed native-like dimer stabilities, the Trp77Phe, Lys80Met and Lys80Gly mutants showed significantly reduced K(d) values. A reduced dimer stability is correlated with a decrease in the Ca(2+)-independent membrane damaging activity as monitored by the release of a liposome entrapped fluorescent marker. Although the membrane damaging activity of the monomer is fivefold less than the dimer, the myotoxic activity was unaffected, indicating that these two effects are not correlated. These data suggest that the BthTx-I dimer is predominantly stabilized by hydrogen bonding interactions, and highlight the importance of the homodimeric form for efficient Ca(2+)-independent membrane damage.

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.

Myotoxic and cytolytic activities of dimeric Lys49 phospholipase A2 homologues are reduced, but not abolished, by a pH-induced dissociation

Lys49 phospholipase A2 (PLA2) homologues are myotoxic proteins devoid of catalytic activity. Their toxic determinants map to the C-terminal region 115-129, which plays an effector role in membrane damage. The dimeric state was reported to be essential for a Lys49 PLA2 which lost its liposome-disrupting activity after dissociating into monomers at pH 5.0. This study, evaluated the effects of a pH-induced dissociation on the toxicity of four Lys49 PLA2s, using biological targets instead. Both their cytolytic and myotoxic activities were lower at pH 5.0 than at pH 7.2. However, in contrast with experiments using artificial bilayers, toxic effects upon biological targets were not abolished at pH 5.0. Importantly, C-terminal synthetic peptides of two Lys49 PLA2s also showed lower cytolytic action at pH 5.0 than at pH 7.2, indicating that factors other than the dimeric/monomeric state of the proteins may also be involved in these differences of toxicity. Results support the view that the dimeric state of Lys49 PLA2s could play an enhancing, although not essential role, in their C-terminal region-mediated mechanism of myotoxicity.

Structural insights for fatty acid binding in a Lys49-phospholipase A2: crystal structure of myotoxin II from Bothrops moojeni complexed with stearic acid

The crystal structure of dimeric Lys49-phospholipase A2 myotoxin-II from Bothrops moojeni (MjTX-II) co-crystallized with stearic acid (C(18)H(36)O(2)) has been determined at a resolution of 1.8 A. The electron density maps permitted the unambiguous inclusion of six stearic acid molecules in the refinement. Two stearic acid molecules could be located in the substrate-binding cleft of each monomer in positions, which favor the interaction of their carboxyl groups with active site residues. The way of binding of stearic acids to this Lys49-PLA(2)s is analogous to phospholipids and transition state analogues to catalytically active PLA(2)s. Two additional stearic acid molecules were located at the dimer interface region, defining a hitherto unidentified acyl-binding site on the protein surface. The strictly conserved Lys122 for Lys49-PLA(2)s may play a fundamental role for stabilization of legend-protein complex. The comparison of MjTX-II/satiric acid complex with other Lys-PLA(2)s structures whose putative fatty acids were located at their active site is also analysed. Molecular details of the stearic acid/protein interactions provide insights to binding in group I/II PLA(2)s, and to the possible interactions of Lys49-PLA(2)s with target membranes.

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.

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.