Nigexine, a Phospholipase A2 from Cobra Venom with Cytotoxic Properties Not Related to Esterase Activity

A comparison of the venom proteomes and potential therapeutics of 3 African naja subgenera

African cobras (Naja species) represent one of the most encountered medically important snakes in Africa. They are classified as African spitting (Afronaja subgenus) and non-spitting cobras (Uraeus and Boulengerina subgenera) with similar and different characteristics. Snake venom toxins including three-finger toxin (3FTx), phospholipase A2 (PLA2), and snake venom metalloproteinase (SVMP) cause snakebite envenomation leading to morbidity and mortality. The profile of the proteome of African cobra venoms will help to develop safer and more effective antivenoms. The approval of Captopril by the US Food and Drug Administration (FDA) for the treatment of cardiovascular diseases, has led to intensified research towards possible use of venom toxins as therapeutics. In this review, we compare the venom proteome profile of 3 African Naja subgenera. In both Afronaja and Boulengerina subgenera, 3FTx (Afronaja-69.79%; Boulengerina-60.56%) followed by PLA2 (Afronaja-21.15%; Boulengerina-20.21%) dominated the venoms compared to the Uraeus subgenus dominated by 3FTx (84.55%) with little to no PLA2 abundance (0.8%). The venom of subgenus Uraeus was distinct from the other two subgenera by the almost total absence of PLA2, thus indicating little or no contribution of PLA2 in the envenomation caused by Uraeus compared to Afronaja and Boulengerina. Furthermore, we report studies on the experimental testing of African cobra venoms and toxins against diseases including anti-cancer properties.

Dermonecrosis caused by a spitting cobra snakebite results from toxin potentiation and is prevented by the repurposed drug varespladib

Snakebite envenoming is a neglected tropical disease that causes substantial mortality and morbidity globally. The venom of African spitting cobras often causes permanent injury via tissue-destructive dermonecrosis at the bite site, which is ineffectively treated by current antivenoms. To address this therapeutic gap, we identified the etiological venom toxins in Naja nigricollis venom responsible for causing local dermonecrosis. While cytotoxic three-finger toxins were primarily responsible for causing spitting cobra cytotoxicity in cultured keratinocytes, their potentiation by phospholipases A2 toxins was essential to cause dermonecrosis in vivo. This evidence of probable toxin synergism suggests that a single toxin-family inhibiting drug could prevent local envenoming. We show that local injection with the repurposed phospholipase A2-inhibiting drug varespladib significantly prevents local tissue damage caused by several spitting cobra venoms in murine models of envenoming. Our findings therefore provide a therapeutic strategy that may effectively prevent life-changing morbidity caused by snakebite in rural Africa.

Snake venom toxins: Potential anticancer therapeutics

Snake venom contains a cocktail of compounds dominated by proteins and peptides, which make up the toxin. The toxin components of snake venom attack several targets in the human body including the neuromuscular system, kidney and blood coagulation system and cause pathologies. As such, the venom toxins can be managed and used for the treatment of these diseases. In this regard, Captopril used in the treatment of cardiovascular diseases was the first animal venom toxin-based drug approved by the US Food and Drug Administration and the European Medicines Agency. Cancers cause morbidity and mortality worldwide. Due to side effects associated with the current cancer treatments including chemotherapy, radiotherapy, immunotherapy, hormonal therapy and surgery, there is a need to improve the efficacy of current treatments and/or develop novel drugs from natural sources including animal toxin-based drugs. There is a long history of earlier and ongoing studies implicating snake venom toxins as potential anticancer therapies. Here, we review the role of crude snake venoms and toxins including phospholipase A2, L-amino acid oxidase, C-type lectin and disintegrin as potential anticancer agents tested in cancer cell lines and animal tumour models in comparison to normal cell lines. Some of the anti-tumour activities of snake venom toxins include induction of cytotoxicity, apoptosis, cell cycle arrest and inhibition of metastasis, angiogenesis and tumour growth. We thus propose the advancement of multidisciplinary approaches to more pre-clinical and clinical studies for enhanced bioavailability and targeted delivery of snake venom toxin-based anticancer drugs.

Intrageneric cross-reactivity of monospecific rabbit antisera against venoms of the medically most important Naja spp. African snakes

BACKGROUND

Envenomations by African snakes represent a high burden in the sub-Sahara region. The design and fabrication of polyspecific antivenoms with a broader effectiveness, specially tailored for its use in sub-Saharan Africa, require a better understanding of the immunological features of different Naja spp. venoms of highest medical impact in Africa; and to select the most appropriate antigen combinations to generate antivenoms of wider neutralizing scope.

METHODOLOGY/PRINCIPAL FINDINGS

Rabbit-derived monospecific antisera were raised against the venoms of five spitting cobras and six non-spitting cobras. The effects of immunization in the animal model were assessed, as well as the development of antibody titers, as proved by immunochemical assays and neutralization of lethal, phospholipase A2 and dermonecrotic activities. By the end of the immunization schedule, the immunized rabbits showed normal values of all hematological parameters, and no muscle tissue damage was evidenced, although alterations in aspartate aminotransferase (AST) and alkaline phosphatase (ALP) suggested a degree of hepatic damage caused mainly by spitting cobra venoms. Immunologic analyses revealed a considerable extent of cross-reactivity of monospecific antisera against heterologous venoms within the spitting and no-spitting cobras, yet some antisera showed more extensive cross-reactivity than others. The antisera with the widest coverage were those of anti-Naja ashei and anti-N. nigricollis for the spitting cobras, and anti-N. haje and anti-N. senegalensis for the non-spitting cobras.

CONCLUSIONS/SIGNIFICANCE

The methods and study design followed provide a rationale for the selection of the best combination of venoms for generating antivenoms of high cross-reactivity against cobra venoms in sub-Saharan Africa. Results suggest that venoms from N. ashei, N. nigricollis within the spitting cobras, and N. haje and N. senegalensis within the non-spitting cobras, generate antisera with a broader cross-reactivity. These experimental results should be translated to larger animal models used in antivenom elaboration to assess whether these predictions are reproduced.

The secretory phenotypes of envenomed cells: Insights into venom cytotoxicity

Snake envenomation is listed as Category A Neglected Tropical Diseases (NTD) by World Health Organization, indicates a severe public health problem. The global figures for envenomation cases are estimated to be more than 1.8 million annually. Even if the affected victims survive the envenomation, they might suffer from permanent morbidity due to local envenomation. One of the most prominent local envenomation is dermonecrosis. Dermonecrosis is a pathophysiological outcome of envenomation that often causes disability in the victims due to surgical amputations, deformities, contracture, and chronic ulceration. The key venom toxins associated with this local symptom are mainly attributed to substantial levels of enzymatic and non-enzymatic toxins as well as their possible synergistic actions. Despite so, the severity of the local tissue damage is based on macroscopic observation of the bite areas. Furthermore, limited knowledge is known about the key biomarkers involved in the pathogenesis of dermonecrosis. The current immunotherapy with antivenom is also ineffective against dermonecrosis. These local effects eventually end up as sequelae. There is also a global shortage of toxins-targeted therapeutics attributed to inadequate knowledge of the actual molecular mechanisms of cytotoxicity. This chapter discusses the characterization of secretory phenotypes of dermonecrosis as an advanced tool to indicate its severity and pathogenesis in envenomation. Altogether, the secretory phenotypes of envenomed cells and tissues represent the precise characteristics of dermonecrosis caused by venom toxins.

Proteomic characterization of Naja mandalayensis venom

Background

Naja mandalayensis is a spitting cobra from Myanmar. To the best of our knowledge, no studies on this venom composition have been conducted so far. On the other hand, few envenomation descriptions state that it elicits mainly local inflammation in the victims’ eyes, the preferred target of this spiting cobra. Symptoms would typically include burning and painful sensation, conjunctivitis, edema and temporary loss of vision.

Methods

We have performed a liquid-chromatography (C18-RP-HPLC) mass spectrometry (ESI-IT-TOF/MS) based approach in order to biochemically characterize N. mandalayensis venom.

Results

A wide variety of three-finger toxins (cardiotoxins) and metallopeptidases were detected. Less abundant, but still representative, were cysteine-rich secretory proteins, L-amino-acid oxidases, phospholipases A₂, venom 5'-nucleotidase and a serine peptidase inhibitor. Other proteins were present, but were detected in a relatively small concentration.

Conclusion

The present study set the basis for a better comprehension of the envenomation from a molecular perspective and, by increasing the interest and information available for this species, allows future venom comparisons among cobras and their diverse venom proteins.

Cytotoxicity of snake venom enzymatic toxins: phospholipase A2 and l-amino acid oxidase

The phospholipase A2 (PLA2) and l-amino acid oxidase (LAAO) are two major enzymes found in the venoms from most snake species. These enzymes have been structurally and functionally characterised for their pharmacological activities. Both PLA2 and LAAO from different venoms demonstrate considerable cytotoxic effects on cancer cells via induction of apoptosis, cell cycle arrest and suppression of proliferation. These enzymes produce more pronounced cytotoxic effects in cancer cells than normal cells, thus they can be potential sources as chemotherapeutic agents. It is proposed that PLA2 and LAAO contribute to an elevated oxidative stress due to their catalytic actions, for instance, the ability of PLA2 to produce reactive oxygen species during lipolysis and formation of H2O2 from LAAO catalytic activity which consequently lead to cell death. Nonetheless, the cell-death signalling pathways associated with exposure to these enzymatic toxins are not fully elucidated yet. Here in this review, we will discuss the cytotoxic effects of PLA2 and LAAO in relationship to their catalytic mechanisms and the underlying mechanisms of cytotoxic actions.

Micrurus surinamensis Peruvian snake venom: Cytotoxic activity and purification of a C-type lectin protein (Ms-CTL) highly toxic to cardiomyoblast-derived H9c2 cells

Micrurus surinamensis (Cuvier, 1817), popularly known as aquatic coral snake, has a broad geographic distribution in the Rainforest of South America. The purpose of this study was to investigate the cytotoxic effect caused by M. surinamensis venom in H9c2 cardiomyoblast cells and to identify protein components involved in cardiotoxic processes. Venom cardiotoxic potential is evidenced by cell viability reduction in a concentration-dependent manner. We have purified one of venom components responsible for this effect after three chromatographic steps: a cytotoxic 23.461 kDa protein, as determined by mass spectrometry. A 19-residue sequence (DCPSGWSSYEGSCYNFFQR) of the purified protein was deduced by MS/MS and exhibited high homology with N-terminal region of C-type lectin from snake venoms. This protein was named Ms-CTL. Morphologically, H9c2 incubation with Ms-CTL led to a significant cellular retraction and formation of cellular aggregates, as observed by microscopy phase-contrast images. Our results indicate that M. surinamensis venom is highly toxic to H9c2 cardiomyoblast cell and less or not cytotoxic to other cell lines, such as HaCat, VERO and U373. Results presented herein will help understanding the mechanisms that underlie cellular damage and tissue destruction, being useful in the development of alternative therapies against these coral snake bites.

Insights into the antiviral activity of phospholipases A2 (PLA2s) from snake venoms

Viruses are associated with several human diseases that infect a large number of individuals, hence directly affecting global health and economy. Owing to the lack of efficient vaccines, antiviral therapy and emerging resistance strains, many viruses are considered as a potential threat to public health. Therefore, researches have been developed to identify new drug candidates for future treatments. Among them, antiviral research based on natural molecules is a promising approach. Phospholipases A₂ (PLA₂s) isolated from snake venom have shown significant antiviral activity against some viruses such as Dengue virus, Human Immunodeficiency virus, Hepatitis C virus and Yellow fever virus, and have emerged as an attractive alternative strategy for the development of novel antiviral therapy. Thus, this review provides an overview of remarkable findings involving PLA₂s from snake venom that possess antiviral activity, and discusses the mechanisms of action mediated by PLA₂s against different stages of virus replication cycle. Additionally, molecular docking simulations were performed by interacting between phospholipids from Dengue virus envelope and PLA₂s from Bothrops asper snake venom. Studies on snake venom PLA₂s highlight the potential use of these proteins for the development of broad-spectrum antiviral drugs.

Interspecific and intraspecific venom enzymatic variation among cobras (Naja sp. and Ophiophagus hannah)

The genera Ophiophagus and Naja comprise part of a clade of snakes referred to as cobras, dangerously venomous front-fanged snakes in the family Elapidae responsible for significant human mortality and morbidity throughout Asia and Africa. We evaluated venom enzyme variation for eleven cobra species and three N. kaouthia populations using SDS-PAGE venom fingerprinting and numerous enzyme assays. Acetylcholinesterase and PLA₂ activities were the most variable between species, and PLA₂ activity was significantly different between Malaysian and Thailand N. kaouthia populations. Venom metalloproteinase activity was low and significantly different among most species, but levels were identical for N. kaouthia populations; minor variation in venom L-amino acid oxidase and phosphodiesterase activities were seen between cobra species. Naja siamensis venom lacked the α-fibrinogenolytic activity common to other cobra venoms. In addition, venom from N. siamensis had no detectable metalloproteinase activity and exhibited an SDS-PAGE profile with reduced abundance of higher mass proteins. Venom profiles from spitting cobras (N. siamensis, N. pallida, and N. mossambica) exhibited similar reductions in higher mass proteins, suggesting the evolution of venoms of reduced complexity and decreased enzymatic activity among spitting cobras. Generally, the venom proteomes of cobras show highly abundant three-finger toxin diversity, followed by large quantities of PLA₂s. However, PLA₂ bands and activity were very reduced for N. haje, N. annulifera and N. nivea. Venom compositionalenzy analysis provides insight into the evolution, diversification and distribution of different venom phenotypes that complements venomic data, and this information is critical for the development of effective antivenoms and snakebite treatment.

Phospholipase A2 from krait Bungarus fasciatus venom induces human cancer cell death in vitro

Background

Snake venoms are the complex mixtures of different compounds manifesting a wide array of biological activities. The venoms of kraits (genus Bungarus, family Elapidae) induce mainly neurological symptoms; however, these venoms show a cytotoxicity against cancer cells as well. This study was conducted to identify in Bungarus fasciatus venom an active compound(s) exerting cytotoxic effects toward MCF7 human breast cancer cells and A549 human lung cancer cells.

Methods

The crude venom of B. fasciatus was separated by gel-filtration on Superdex HR 75 column and reversed phase HPLC on C18 column. The fractions obtained were screened for cytotoxic effect against MCF7, A549, and HK2 cell lines using colorimetric assay with the tetrazolium dye MTT- 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide. The primary structure of active protein was established by ultra high resolution LC-MS/MS. The molecular mechanism of the isolated protein action on MCF7 cells was elucidated by flow cytometry.

Results

MTT cell viability assays of cancer cells incubated with fractions isolated from B. fasciatus venom revealed a protein with molecular mass of about 13 kDa possessing significant cytotoxicity. This protein manifested the dose and time dependent cytotoxicity for MCF7 and A549 cell lines while showed no toxic effect on human normal kidney HK2 cells. In MCF7, flow cytometry analysis revealed a decrease in the proportion of Ki-67 positive cells. As Ki-67 protein is a cellular marker for proliferation, its decline indicates the reduction in the proliferation of MCF7 cells treated with the protein. Flow cytometry analysis of MCF7 cells stained with propidium iodide and Annexin V conjugated with allophycocyanin showed that a probable mechanism of cell death is apoptosis. Mass spectrometric studies showed that the cytotoxic protein was phospholipase A₂. The amino acid sequence of this enzyme earlier was deduced from cloned cDNA, and in this work it was isolated from the venom as a protein for the first time. It is also the first krait phospholipase A₂ manifesting the cytotoxicity for cancer cells.

Exploring the structural and functional aspects of the phospholipase A2 from Naja spp

Naja spp. venom is a natural source of active compounds with therapeutic application potential. Phospholipase A₂ (PLA₂) is abundant in the venom of Naja spp. and can perform neurotoxicity, cytotoxicity, cardiotoxicity, and hematological disorders. The PLA₂s from Naja spp. venoms are Asp 49 isoenzymes with the exception of PLA₂ Cys 49 from Naja sagittifera. When looking at the functional aspects, the neurotoxicity occurs by PLA₂ called β-toxins that have affinity for phosphatidylcholine in nerve endings and synaptosomes membranes, and by α-toxins that block the nicotinic acetylcholine receptors in the neuromuscular junctions. In addition, these neurotoxins may inhibit K⁺ and Ca⁺⁺ channels or even interfere with the Na⁺/K⁺/ATPase enzyme. The disturbance in the membrane fluidity also results in inhibition of the release of acetylcholine. The PLA₂ can act as anticoagulants or procoagulant. The cytotoxicity exerted by PLA₂s result from changes in the cardiomyocyte membranes, triggering cardiac failure and hemolysis. The antibacterial activity, however, is the result of alterations that decrease the stability of the lipid bilayer. Thus, the understanding of the structural and functional aspects of PLA₂s can contribute to studies on the toxic and therapeutic mechanisms involved in the envenomation by Naja spp. and in the treatment of pathologies.

Malaysian Cobra Venom: A Potential Source of Anti-Cancer Therapeutic Agents

Cancer is a deadly disease and there is an urgent need for the development of effective and safe therapeutic agents to treat it. Snake venom is a complex mixture of bioactive proteins that represents an attractive source of novel and naturally-derived anticancer agents. Malaysia is one of the world’s most biodiverse countries and is home to various venomous snake species, including cobras. Naja kaouthia, Naja sumatrana, and Ophiophagus hannah are three of the most common cobra species in Malaysia and are of medical importance. Over the past decades, snake venom has been identified as a potential source of therapeutic agents, including anti-cancer agents. This present review highlights the potential anticancer activity of the venom and purified venom protein of N. kaouthia, N. sumatrana, and O. hannah. In conclusion, this review highlights the important role of the venom from Malaysian cobras as an important resource that researchers can exploit to further investigate its potential in cancer treatment.

Cytotoxic and pro-apoptotic action of MjTX-I, a phospholipase A2 isolated from Bothrops moojeni snake venom, towards leukemic cells

Background

Chronic myeloid leukemia (CML) is a BCR-ABL1⁺ myeloproliferative neoplasm marked by increased myeloproliferation and presence of leukemic cells resistant to apoptosis. The current first-line therapy for CML is administration of the tyrosine kinase inhibitors imatinib mesylate, dasatinib or nilotinib. Although effective to treat CML, some patients have become resistant to this therapy, leading to disease progression and death. Thus, the discovery of new compounds to improve CML therapy is still challenging. Here we addressed whether MjTX-I, a phospholipase A₂ isolated from Bothrops moojeni snake venom, affects the viability of imatinib mesylate-resistant Bcr-Abl⁺ cell lines.

Methods

We examined the cytotoxic and pro-apoptotic effect of MjTX-I in K562-S and K562-R Bcr-Abl⁺ cells and in the non-tumor HEK-293 cell line and peripheral blood mononuclear cells, using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and the hypotonic fluorescent solution methods, associated with detection of caspases 3, 8, and 9 activation and poly (ADP-ribose) polymerase (PARP) cleavage. We also analyzed the MjTX-I potential to modulate the expression of apoptosis-related genes in K562-S and K562-R cells.

Results

MjTX-I decreased the viability of K562-S and K562-R cells by 60 to 65%, without affecting the viability of the non-tumor cells, i.e. it exerted selective cytotoxicity towards Bcr-Abl⁺ cell lines. In leukemic cell lines, the toxin induced apoptosis, activated caspases 3, 8, and 9, cleaved PARP, downregulated expression of the anti-apoptotic gene BCL-2, and upregulated expression of the pro-apoptotic gene BAD.

Conclusion

The antitumor effect of MjTX-I is associated with its potential to induce apoptosis and cytotoxicity in Bcr-Abl positive cell lines sensitive and resistant to imatinib mesylate, indicating that MjTX-I is a promising candidate drug to upgrade the CML therapy.

Cytotoxic and inflammatory potential of a phospholipase A2 from Bothrops jararaca snake venom

Background

Snake venom phospholipases A₂ (PLA₂s) have been reported to induce myotoxic, neurotoxic, hemolytic, edematogenic, cytotoxic and proinflammatory effects. This work aimed at the isolation and functional characterization of a PLA₂ isolated from Bothrops jararaca venom, named BJ-PLA₂-I.

Methods and Results

For its purification, three consecutive chromatographic steps were used (Sephacryl S-200, Source 15Q and Mono Q 5/50 GL). BJ-PLA₂-I showed acidic characteristics, with pI~ 4.4 and molecular mass of 14.2 kDa. Sequencing resulted in 60 amino acid residues that showed high similarity to other Bothrops PLA₂s, including 100% identity with BJ-PLA₂, an Asp49 PLA₂ previously isolated from B. jararaca venom. Being an Asp49 PLA₂, BJ-PLA₂-I showed high catalytic activity, and also inhibitory effects on the ADP-induced platelet aggregation. Its inflammatory characterization showed that BJ-PLA₂-I was able to promote leukocyte migration in mice at different concentrations (5, 10 and 20 μg/mL) and also at different response periods (2, 4 and 24 h), mainly by stimulating neutrophil infiltration. Furthermore, increased levels of total proteins, IL-6, IL-1β and PGE₂ were observed in the inflammatory exudate induced by BJ-PLA₂-I, while nitric oxide, TNF-α, IL-10 and LTB₄ levels were not significantly altered. This toxin was also evaluated for its cytotoxic potential on normal (PBMC) and tumor cell lines (HL-60 and HepG2). Overall, BJ-PLA₂-I (2.5–160 μg/mL) promoted low cytotoxicity, with cell viabilities mostly varying between 70 and 80% and significant values obtained for HL-60 and PBMC only at the highest concentrations of the toxin evaluated.

Conclusions

BJ-PLA₂-I was characterized as an acidic Asp49 PLA₂ that induces acute local inflammation and low cytotoxicity. These results should contribute to elucidate the action mechanisms of snake venom PLA₂s.

Antitumoral activity of snake venom proteins: new trends in cancer therapy

For more than half a century, cytotoxic agents have been investigated as a possible treatment for cancer. Research on animal venoms has revealed their high toxicity on tissues and cell cultures, both normal and tumoral. Snake venoms show the highest cytotoxic potential, since ophidian accidents cause a large amount of tissue damage, suggesting a promising utilization of these venoms or their components as antitumoral agents. Over the last few years, we have studied the effects of snake venoms and their isolated enzymes on tumor cell cultures. Some in vivo assays showed antineoplastic activity against induced tumors in mice. In human beings, both the crude venom and isolated enzymes revealed antitumor activities in preliminary assays, with measurable clinical responses in the advanced treatment phase. These enzymes include metalloproteases (MP), disintegrins, L-amino acid oxidases (LAAOs), C-type lectins, and phospholipases A2 (PLA2s). Their mechanisms of action include direct toxic action (PLA2s), free radical generation (LAAOs), apoptosis induction (PLA2s, MP, and LAAOs), and antiangiogenesis (disintegrins and lectins). Higher cytotoxic and cytostatic activities upon tumor cells than normal cells suggest the possibility for clinical applications. Further studies should be conducted to ensure the efficacy and safety of different snake venom compounds for cancer drug development.

Structural basis for functional diversity of animal toxins

The diversity of biological functions that are exerted by toxins from snake and scorpion venoms is associated with a limited number of structural frameworks. At present, one predominant basic fold has been observed among scorpion toxins whereas six folds have been found among snake toxins. Most toxin folds have the capacity to accept multiple insertions, deletions and mutations and to exert various recognition functions. We suggest that such folds may serve as guides to engineer new protein functions.

Recent progress on phospholipases: different sources, assay methods, industrial potential and pathogenicity

Significant studies on phospholipases optimization, characterization, physiological role and industrial potential have been conducted worldwide. Some of them have been directed for biotechnological advances such as gene discovery and functional enhancement by protein engineering. Others reported phospholipases as virulence factor and major cause of pathophysiological effects. A general overview on phospholipase is needed for the identification of new reliable and efficient phospholipase, which would be potentially used in number of industrial and medical applications. Phospholipases catalyse the hydrolysis of one or more ester and phosphodiester bonds of glycerophospholipids. They vary in site of action on phospholipid which can be used industrially for modification/production of new phospholipids. Catalytically active phospholipase mainly use phosphatidylcholine as major substrate, but they can also show specificity with other phospholipids. Several accurate phospholipase assay methods are known, but a rapid and reliable method for high-throughput screening is still a challenge for efficient supply of superior phospholipases and their practical applications. Major application of phospholipase is in industries like oil refinery, health food manufacturing, dairy, cosmetics etc. All types of phospholipases can be involved as virulence factor. They can also be used as diagnostic markers for microbial infection. The importance of phospholipase in virulence is proven and inhibitors of the enzyme can be used as candidate for preventing the associated disease.

INN-toxin, a highly lethal peptide from the venom of Indian cobra (Naja naja) venom-Isolation, characterization and pharmacological actions

A novel toxic polypeptide, INN-toxin, is purified from the venom of Naja naja using combination of gel-permeation and ion-exchange chromatography. It has a molecular mass of 6951.6Da as determined by MALDI-TOF/MS and the N-terminal sequence of LKXNKLVPLF. It showed both neurotoxic as well as cytotoxic activities. INN-toxin is lethal to mice with a LD(50) of 1.2mg/kg body weight. IgY raised in chicks against basic peptide pool neutralized the toxicity of INN-toxin. INN-toxin did not inhibit cholinesterase activity. It is toxic to Ehrlich ascites tumor (EAT) cells, but it is not toxic to leukocyte culture. The toxin appears to be specific in its mode of action. Interaction of N-bromosuccinamide (NBS) with the peptide resulted in the modification of tryptophan residues and loss of lethal toxicity of INN-toxin.

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.

Isolation and characterization of "Reprotoxin", a novel protein complex from Daboia russelii snake venom

In snake venoms, non-covalent protein-protein interaction leads to protein complexes with synergistic and, at times, distinct pharmacological activities. Here we describe a new protein complex containing phospholipaseA(2) (PLA(2)), protease, and a trypsin inhibitor. It is isolated from the venom of Daboia russelii by gel permeation chromatography, on a Sephadex G-75 column. This 44.6 kDa complex exhibits only phospholipase A(2) activity. In the presence of 8M urea it is well resolved into protease (29.1 kDa), PLA(2) (13 kDa), and trypsin inhibitor (6.5 kDa) peaks. The complex showed an LD(50) of 5.06 mg/kg body weight in mice. It inhibited the frequency of spontaneous release of neurotransmitter in hippocampal neurons. It also caused peritoneal bleeding, and edema in the mouse foot pads. Interestingly, the complex caused degeneration of both the germ cells and the mouse Leydig cells of mouse testis. A significant reduction in both the diameter of the seminiferous tubules and height of the seminiferous epithelia were observed following intraperitoneal injection of the sub-lethal dose (3 mg/kg body weight). This effect of the toxin is supported by the increase in the activities of acid and alkaline phosphatases and the nitric oxide content in the testes, and a decrease in the ATPase activity. Because of its potent organ atrophic effects on the reproductive organs, the toxin is named "Reprotoxin". This is the first report demonstrating toxicity to the reproductive system by a toxin isolated from snake venom.

Crystal structure of Natratoxin, a novel snake secreted phospholipaseA2 neurotoxin from Naja atra venom inhibiting A-type K+ currents

Snake secreted phospholipasesA2 (sPLA2s) are widely used as pharmacological tools to investigate their role in diverse pathophysiological processes. Some members of snake venom sPLA2s have been found to block voltage-activated K(+) channels (K(v) channels). However, most studies involved in their effects on ion channels were indirectly performed on motor nerve terminals while few studies were directly done on native neurons. Here, a novel snake sPLA2 peptide neurotoxin, Natratoxin, composed of 119 amino acid residues and purified from Naja atra venom was reported. It was characterized using whole-cell patch-clamp in acutely dissociated rat dorsal root ganglion (DRG) neurons. It was found to effectively inhibit A-type K(+) currents and cause alterations of channel gating characters, such as the shifts of steady-state activation and inactivation curves to hyperpolarization direction and changes of V(1/2) and slope factor. Therefore, Natratoxin was suggested to be a gating modifier of K(v) channel. In addition, this inhibitory effect was found to be independent of its enzymatic activity. These results suggested that the toxin enacted its inhibitory effect by binding to K(v) channel. To further elucidate the structural basis for this electrophysiological phenomenon, we determined the crystal structure of Natratoxin at 2.2 A resolution by molecular replacement method and refined to an R-factor of 0.190. The observed overall fold has a different structural organization from other K(+) channel inhibitors in animal toxins. Compared with other K(v) channel inhibitors, a similar putative functional surface in its C-terminal was revealed to contribute to protein-protein interaction in such a blocking effect. Our results demonstrated that the spatial distribution of key amino acid residues matters most in the recognition of this toxin towards its channel target rather than its type of fold.

Cytotoxic l-amino acid oxidase from Bothrops moojeni: Biochemical and functional characterization

An L-amino acid oxidase isolated from Bothrops moojeni snake venom (BmooLAAO-I) was purified to a high degree using sequential CM-Sepharose ion-exchange and phenyl-Sepharose chromatography. When analyzed by mass spectrometry, the purified BmooLAAO-I presented a molecular weight of 64,889 and 130,779 under denaturing and nondenaturing conditions, respectively. BmooLAAO-I is a homodimeric acidic glycoprotein with a pI approximately 4.7, and the N-terminal sequence shows close structural similarity to other snake venom LAAOs. This enzyme was inactivated by freezing or low pH, and secondary structural analysis by circular dichroism revealed 48% alpha-helix, 20% beta-sheet, 12% beta-turn, and 20% random coil structures. BmooLAAO-I exhibited bactericidal, antitumoral, trypanocidal, edematogenic, and platelet-aggregating activities. All of these effects were inhibited by catalase, suggesting that these biological effects are mediated by the production of H(2)O(2). BmooLAAO-I induced typical apoptotic DNA fragmentation in HL-60 cells, which was also inhibited by catalase. These results point to the potential use of BmooLAAO-I as a therapeutic agent for treatment of diseases in which induction of H(2)O(2) production can be beneficial.

Antimicrobial properties of a non-toxic glycoprotein (WSG) from Withania somnifera (Ashwagandha)

A monomeric glycoprotein with a molecular mass of 28 kDa in SDS-PAGE was isolated from the Withania somnifera root tubers. The protein designated WSG (Withania somnifera glycoprotein) demonstrated potent antimicrobial activity against the phytopathogenic fungi and bacteria tested. Antifungal effect has been demonstrated in that WSG exerts a fungistastic effect by inhibiting spore germination and hyphal growth in the tested fungi. WSG showed potent antifungal activity against Aspergillus flavus, Fusarium oxysporum, F. verticilloides and antibacterial activity against Clvibacter michiganensis subsp. michiganensis. WSG is an acidic, non-toxic (trypsin-chymotrypsin) protease inhibitor. These results encourage further studies of WSG as a potential therapeutic agent for its antifungal activity.

Venom from spiders of the genus Hippasa: biochemical and pharmacological studies

The venoms from female spiders of the genus Hippasa namely H. partita, H. agelenoides and H. lycosina are compared for biochemical and pharmacological properties. SDS-PAGE pattern revealed varied protein composition. Marked variability is seen with casein hydrolyzing enzymes in SDS-PAGE zymogram. H. partita venom was the only venom that hydrolyzed gelatin while the other two venoms did not. The venoms shared similar hyaluronidase activity, showing a single activity band in SDS-PAGE zymogram. The PLA2 activity varied as H. partita>H. agelenoides>H. lycosina venoms. Marked differences were noted in the ability to induce edema, cytotoxicity, myotoxicity and neurotoxicity, while hemorrhage was associated exclusively with H. partita venom.

Biochemical and functional characterization of an L-amino acid oxidase isolated from Bothrops pirajai snake venom

In this work we describe the isolation of a new l-amino acid oxidase (LAAO) referred to as BpirLAAO-I from Bothrops pirajai snake venom, which was highly purified using a combination of molecular exclusion, affinity, and hydrophobic chromatography steps. BpirLAAO-I homodimeric acid glycoprotein (approximate Mr and pI of 130,000 and 4.9, respectively) displays high specificity toward hydrophobic/aromatic amino acids, while deglycosylation does not alter its enzymatic activity. The N-terminal LAAO sequence of its first 49 amino acids presented a high similarity between a amino acid sequence with other LAAOs from: Bothrops spp., Crotalus spp., Calloselasma rhodostoma, Agkistrodon spp., Trimeresurus spp., Pseudechis australis, Oxyuranus scutellatus, and Notechis scutatus. BpirLAAO-I induces time-dependent platelet aggregation, mouse paw edema, cytotoxic activity against Escherichia coli, Pseudomonas aeruginosa, Leishmania sp., and tumor cells, and also a typical fago (M13mp18) DNA fragmentation. Platelet aggregation, leishmanicidal and antitumoral activities were reduced by catalase. Thus, BpirLAAO-I is a multifunctional protein with promising biotechnological and medical applications.

Neurotoxicity and other pharmacological activities of the snake venom phospholipase A2 OS2: the N-terminal region is more important than enzymatic activity

Several snake venom secreted phospholipases A2 (sPLA2s) including OS2 exert a variety of pharmacological effects ranging from central neurotoxicity to anti-HIV activity by mechanisms that are not yet fully understood. To conclusively address the role of enzymatic activity and map the key structural elements of OS2 responsible for its pharmacological properties, we have prepared single point OS2 mutants at the catalytic site and large chimeras between OS2 and OS1, a homologous but nontoxic sPLA2. Most importantly, we found that the enzymatic activity of the active site mutant H48Q is 500-fold lower than that of the wild-type protein, while central neurotoxicity is only 16-fold lower, providing convincing evidence that catalytic activity is at most a minor factor that determines central neurotoxicity. The chimera approach has identified the N-terminal region (residues 1-22) of OS2, but not the central one (residues 58-89), as crucial for both enzymatic activity and pharmacological effects. The C-terminal region of OS2 (residues 102-119) was found to be critical for enzymatic activity, but not for central neurotoxicity and anti-HIV activity, allowing us to further dissociate enzymatic activity and pharmacological effects. Finally, direct binding studies with the C-terminal chimera, which poorly binds to phospholipids while it is still neurotoxic, led to the identification of a subset of brain N-type receptors which may be directly involved in central neurotoxicity.

A neurotoxic phospholipase A2 variant: Isolation and characterization from eastern regional Indian cobra (Naja naja) venom

CM-Sephadex C-25 column chromatography profile of Indian cobra (Naja naja) venom from eastern region showed a distinct and a dominant phospholipase peak, peak-10, while it was not seen in either southern or western venom samples. Peak-10 was subjected to CM-Sephadex C-25 and Sephadex G-50 column chromatography to isolate NN-X-PLA(2). NN-X-PLA(2) is a single chain protein with the relative molecular weight of 10kDa by SDS-PAGE. It was toxic to mice with an LD(50) value 0.098 mg/kg body weight (i.p.) and the mice exhibited acute neurotoxic symptoms. Upon indirect stimulation, it inhibited the twitching of frog's gastrocnemius muscle in a dose dependent manner. NN-X-PLA(2) was weakly anticoagulant and devoid of cytotoxicity, myotoxicity, hemorrhage, edema inducing, and directlytic activities and effects on platelet aggregation process. Upon chemical modification independently with p-bromophenacyl bromide and acetic anhydride, NN-X-PLA(2) lost both enzymatic and toxic properties.

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.

Molecular cloning of two toxic phospholipases A2 from the crown-of-thorns starfish Acanthaster planci venom

The full-length cDNAs encoding two toxic phospholipases A2 (AP-PLA2-I and -II) from the crown-of-thorns starfish Acanthaster planci venom were individually cloned by RT-PCR, 3'RACE and 5'RACE. In common with both AP-PLA2s, the precursor protein is composed of a signal peptide, a propeptide and a mature protein (136 and 135 residues for AP-PLA2-I and -II, respectively). The four motifs (Ca2+-binding loop, Ca2+-binding site, active site and catalytic network) characteristic of groups I and II PLA2s are well conserved in both AP-PLA2s. In addition to this, the presence of the elapid and pancreatic loops and the involvement of a propeptide in the precursors suggested that AP-PLA2s are highly analogous to the group IB PLA2s. However, when compared to the amino acid sequence of bovine pancreatic PLA2, the representative group IB PLA2, AP-PLA2s require some amino acid insertions and deletions in the region 76-100, as previously observed for the starfish Asterina pectinifera PLA2s. Furthermore, the phylogenetic tree made clearly demonstrated that AP-PLA2s and A. pectinifera PLA2s are distinguishable from the group IB PLA2s as well as other PLA2s, being classified into a new group.

Determination of the Amino Acid Sequence of a New Phospholipase A2 (MIDCA1) Isolated from Micrurus dumerilii carinicauda Venom

A new Phospholipase A(2) (PLA(2)) from Micrurus dumerilii carinicauda venom was isolated and its primary structure determined. This new PLA(2) showed a low enzymatic activity when compared with other PLA(2)s and it is moderately basic with an isoelectric point of 8.0. Its amino acid sequence showed the presence of 120 amino acid residues and its sequence was: NLIQFLNMIQCTTPGREPLVAFANYGCYCGRGGSGTPVDELDRCCQVHDNCYDTAKKVFGCSPYFTMYSYDCSEGKLTCKDNNTKCKAAVCNCDRTAALCFAKAPYNDKNYKIDLTKRCQ. The structural model of MIDCA1, when compared with other strong neurotoxic PLA(2)s, such as Naja naja, showed significant differences in the beta-wing and neurotoxic sites, despite the high level of amino acid sequence similarity. These observations indicate a dissociation between the biological and catalytic activity of this new PLA(2), supporting the view that other regions of the protein are involved in the biological effects.

Cobra cardiotoxin and phospholipase A2 as GAG-binding toxins: on the path from structure to cardiotoxicity and inflammation

Glycosaminoglycans (GAGs) represent the sulfated carbohydrate moieties of proteoglycans which occur abundantly in tissues of the cardiovascular system. Many proteins bind specifically to GAGs and perform an important role in inflammation, cell proliferation, and blood coagulation processes. Recently, in vitro GAG-binding studies of cardiotoxins (CTXs) and basic phospholipase A(2) (PLA(2)) from cobra venom established the toxins as two new families of GAG-binding proteins. In particular, discontinuous basic residues in beta-sheet CTXs may form a cationic cradle suitable for heparin binding, as in the case of fibronectin module III-13. The binding specificity of beta-sheet proteins to different GAGs can be further enhanced by involving other cationic clusters near the flexible loop of the molecule. Since the three-dimensional structures of many CTXs and PLA(2) are available, these two toxins may serve as models for the elucidation of the molecular recognition of GAG-binding proteins and also as polypeptide templates for further improvement of the binding specificity suitable for future biomedical application. Research along the line of GAG-guided toxicity of cobra venom components may help us to understand the functional role of GAGs and the action mechanism of cobra venom components in the cardiovascular system.

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.

Functional expression and characterization of a recombinant phospholipase A2 from sea snake Lapemis hardwickii as a soluble protein in E. coli

Three full-length phospholipase A(2) (PLA(2)) cDNAs from sea snake Lapemis hardwickii venom were cloned and sequenced in our previous study. In order to investigate their biological functions, we established a fusion expression system for PLA(2)-9 in E. coli. The open reading frame encoding mature peptide of PLA(2)-9 was subcloned into the vector pTRX. The Trx-PLA(2)-9 fusion protein was expressed as a soluble protein by IPTG induction at 23 degrees C. The fusion protein was purified with metal-chelate affinity chromatography and then cleaved by enterokinase. The mature recombinant PLA(2)-9 was further purified by ion-exchange chromatography and a final yield of approximately 2.5mg pure PLA(2)-9 from 1l of bacteria culture was obtained. The catalytic activity of recombinant PLA(2)-9 (rPLA(2)-9) was measured and found to be similar to native enzyme. As the Austrelaps superbus PLA(2), which shares 90% nucleotide sequence similarity to PLA(2)-9, the rPLA(2)-9 displayed the anti-platelet aggregation effect. Site-directed mutagenesis of the two conserved residues, His-48 and Asp-49, resulted in the loss of catalytic activity, however did not affect the inhibition effect of platelet aggregation suggesting that these two activities of sea snake PLA(2)-9 may be dissociated.

Purification and characterization of an anticoagulant phospholipase A(2) from Indian monocled cobra (Naja kaouthia) venom

An anticoagulant, non-toxic phospholipase A(2) was isolated from the venom of Indian monocled cobra (Naja kaouthia) by a combination of ion-exchange chromatography on CM-Sephadex C-50 and gel filtration on Sephadex G-50. This purified protein named NK-PLA(2)-I, had a subunit molecular mass of 13.6 kDa and migrated as a dimer under non-reduced condition in SDS-PAGE. NK-PLA(2)-I was a highly thermostable protein requiring basic pH optima for its catalytic activity and showed preferential hydrolysis of phosphotidylcholine. This protein exhibited higher anticoagulant, indirect hemolysis, liver and heart tissue damaging activity but exerted less toxicity, direct hemolysis, edema and lung tissue damaging activity as compared to whole venom. Treatment of NK-PLA(2)-I with rho-BPB, TPCK, PMSF, antivenom and heating had almost equal effect on PLA(2), and other pharmacological properties except in vitro tissue damaging activity. Current investigation provides a fairly good indication that NK-PLA(2)-I induces various pharmacological effects by mechanisms, which are either dependent or independent of its catalytic activity.

Purification and characterization of a glycoprotein inhibitor of toxic phospholipase from Withania somnifera

A phospholipase inhibitor (WSG) has been purified from Withania somnifera using gel-filtration and ion-exchange chromatographies. The WSG is an acidic glycoprotein. Its molecular mass as determined by SDS-PAGE was 27kDa. It neutralized the enzyme activity and pharmacological properties such as cytotoxicity, edema, and myotoxicity of a multi-toxic Indian cobra venom phospholipase (NNXIa-PLA) but failed to neutralize the neurotoxicity. The glycan part of the molecule does not appear to be involved in any of the pharmacological properties studied. The results suggest that the neutralization of the pharmacological effects of the toxic phospholipase is brought about by inhibition of the enzyme activity by formation of a complex between the WSG and the toxic phospholipase. We report the purification and characterization of a glycoprotein phospholipase A inhibitor from Withania somnifera, medicinal plant.

Isolation and characterization of a novel postsynaptic/cytotoxic neurotoxin from Daboia russelli russelli venom

A postsynaptic neurotoxin was purified from Daboia russelli russelli venom using gel filtration, ion-exchange chromatography and reverse-phase high-performance liquid chromatography. The N-terminal sequence, molecular mass and pharmacological activities of the neurotoxin/cytotoxin indicate that it is a short-chain neurotoxin like that found in Elapid venom. This is the first report on the presence of such a postsynaptic neurotoxin from D. r. russelli venom.

A non-toxic anticoagulant metalloprotease: purification and characterization from Indian cobra (Naja naja naja) venom

A non-toxic potent anticoagulant metalloprotease NN-PF(3) has been purified to homogeneity from the Indian cobra (Naja naja naja) venom through a combination of column chromatography and electrophoresis. NN-PF(3) is a single chain protein with a molecular weight of 68 kDa by SDS-PAGE. It hydrolysed casein, gelatin, haemoglobin and bovine fibrinogen, but did not hydrolyse bovine serum albumin or synthetic substrates such as TAME, BAEE and BAPNA. EDTA, EGTA and cyanide inhibited the enzymatic activity while 1,10-phenanthroline, PMSF, leupetin and pepstatin did not show any effect. NN-PF(3) is a metalloprotease containing Ca(2+) and Zn(2+) at a molar ratio of 1:1.2 and 1:0.4, respectively, as revealed by atomic absorption spectroscopy. NN-PF(3) was non-lethal up to an i.p. dose of 15 mg/kg body weight of mice and is devoid of myotoxicity, cytotoxicity and haemorrhagic activity. It is weakly oedematic, but strongly anticoagulant in property and the effect observed was both dose and time dependent.

Bee venom phospholipase A2 induces stage-specific growth arrest of the intraerythrocytic Plasmodium falciparum via modifications of human serum components

Secreted phospholipases A(2) (sPLA(2)s) from snake and insect venoms and from mammalian pancreas are structurally related enzymes that have been associated with several toxic, pathological, or physiological processes. We addressed the issue of whether toxic sPLA(2)s might exert specific effects on the Plasmodium falciparum intraerythrocytic development. We showed that both toxic and non-toxic sPLA(2)s are lethal to P. falciparum grown in vitro, with large discrepancies between respective IC(50) values; IC(50) values from toxic PLA(2)s ranged from 1.1 to 200 pm, and IC(50) values from non-toxic PLA(2)s ranged from 0.14 to 1 microm. Analysis of the molecular mechanisms responsible for cytotoxicity of bee venom PLA(2) (toxic) and hog pancreas PLA(2) (non-toxic) demonstrated that, in both cases, enzymatic hydrolysis of serum phospholipids present in the culture medium was responsible for parasite growth arrest. However, bee PLA(2)-lipolyzed serum induced stage-specific inhibition of P. falciparum development, whereas hog PLA(2)-lipolyzed serum killed parasites at either stage. Sensitivity to bee PLA(2)-treated serum appeared restricted to the 19-26-h period of the 48 h parasite cycle. Analysis of the respective role of the different lipoprotein classes as substrates of bee PLA(2) showed that enzyme treatment of high density lipoproteins, low density lipoproteins, and very low density lipoproteins/chylomicrons fractions induces cytotoxicity of either fraction. In conclusion, our results demonstrate that toxic and non-toxic PLA(2)s 1) are cytotoxic to P. falciparum via hydrolysis of lipoprotein phospholipids and 2) display different killing processes presumably involving lipoprotein by-products recognizing different targets on the infected red blood cell.

cDNA cloning and sequencing of phospholipase A2 from the pyloric ceca of the starfish Asterina pectinifera

Three cDNA from the pyloric ceca of the starfish Asterina pectinifera, (namely, cDNA 1, 2, and 3), encoding phospholipase A2 (PLA2), were isolated and sequenced. These cDNAs were composed of 415 bp with an open reading frame of 414 bp at nucleotide positions 1-414, which encodes 138 amino acids including N-terminal Met derived from the PCR primer. The amino acid sequence deduced from the cDNA 1 was completely consistent with the sequence determined with the starfish PLA2 protein, while those deduced from cDNA 2 and cDNA 3 differed at one and twelve amino acid residual positions, respectively, from the sequence of the PLA2 protein, suggesting the presence of multiple forms in the starfish PLA2. All of the sequences deduced from cDNA 1, 2, and 3 required two amino acid deletions in pancreatic loop region, and sixteen insertions and three deletions in beta-wing region when aligned with the sequence of mammalian pancreatic PLA2. In phylogenetic tree, the starfish PLA2 should be classified into an independent group, but hardly to the established groups IA and IB. The characteristic structure in the pancreatic loop and beta-wing regions may account for the specific properties of the starfish PLA2, e.g. the higher activity and characteristic substrate specificity compared with commercially available PLA2 from porcine pancreas.

Purification and characterization of a platelet aggregation inhibitor acidic phospholipase A2 from Indian saw-scaled viper (Echis carinatus) venom

An acidic phospholipase A2 (EC-I-PLA2) has been purified from the Indian saw-scaled viper (Echis carinatus) venom through a combination of column chromatography and electrophoresis. EC-I-PLA2 has a molecular weight of 16000 by SDS-PAGE. It was focussed between pH 4.2 and 4.8 by isoelectro focussing. EC-I-PLA2 was non-lethal to mice and devoid of neurotoxicity, myotoxicity, anticoagulant activity and cytotoxicity. It induced mild oedema in the foot pads of mice. The purified PLA2 inhibited ADP, collagen and epinephrine induced human platelet aggregation and the inhibition was both dose and time dependent.

Secreted phospholipases A(2), a new class of HIV inhibitors that block virus entry into host cells

Mammalian and venom secreted phospholipases A(2) (sPLA(2)s) have been associated with a variety of biological effects. Here we show that several sPLA(2)s protect human primary blood leukocytes from the replication of various macrophage and T cell-tropic HIV-1 strains. Inhibition by sPLA(2)s results neither from a virucidal effect nor from a cytotoxic effect on host cells, but it involves a more specific mechanism. sPLA(2)s have no effect on virus binding to cells nor on syncytia formation, but they prevent the intracellular release of the viral capsid protein, suggesting that sPLA(2)s block viral entry into cells before virion uncoating and independently of the coreceptor usage. Various inhibitors and catalytic products of sPLA(2) have no effect on HIV-1 infection, suggesting that sPLA(2) catalytic activity is not involved in the antiviral effect. Instead, the antiviral activity appears to involve a specific interaction of sPLA(2)s to host cells. Indeed, of 11 sPLA(2)s from venom and mammalian tissues assayed, 4 venom sPLA(2)s were found to be very potent HIV-1 inhibitors (ID(50) < 1 nM) and also to bind specifically to host cells with high affinities (K(0.5) < 1 nM). Although mammalian pancreatic group IB and inflammatory-type group IIA sPLA(2)s were inactive against HIV-1 replication, our results could be of physiological interest, as novel sPLA(2)s are being characterized in humans.