Purification and properties of a toxin from the sea anemone Condylactis gigantea

Structural foundations of sticholysin functionality

Actinoporins constitute a family of α pore-forming toxins produced by sea anemones. The soluble fold of these proteins consists of a β-sandwich flanked by two α-helices. Actinoporins exert their activity by specifically recognizing sphingomyelin at their target membranes. Once there, they penetrate the membrane with their N-terminal α-helices, a process that leads to the formation of cation-selective pores. These pores kill the target cells by provoking an osmotic shock on them. In this review, we examine the role and relevance of the structural features of actinoporins, down to the residue level. We look at the specific amino acids that play significant roles in the function of actinoporins and their fold. Particular emphasis is given to those residues that display a high degree of conservation across the actinoporin sequences known to date. In light of the latest findings in the field, the membrane requirements for pore formation, the effect of lipid composition, and the process of pore formation are also discussed.

Oligomerization of Sticholysins from Förster Resonance Energy Transfer

Sticholysins are pore-forming toxins produced by sea anemones that are members of the actinoporin family. They exert their activity by forming pores on membranes, provided they have sphingomyelin. To assemble into pores, specific recognition, binding, and oligomerization are required. While recognition and binding have been extensively studied, delving into the oligomerization process and the stoichiometry of the pores has been more difficult. Here, we present evidence that these toxins are capable of oligomerizing in solution and suggesting that the interaction of sticholysin II (StnII) with its isoform sticholysin I (StnI) is stronger than that of StnI with itself. We also show that the stoichiometry of the final, thermodynamically stable StnI pores is, at least, heptameric. Furthermore, our results indicate that this association maintains its oligomerization number when StnII is included, indicating that the stoichiometry of StnII is also of that order, and not tetrameric, as previously thought. These results are compatible with the stoichiometry observed for the crystallized pore of FraC, another very similar actinoporin produced by a different sea anemone species. Our results also indicate that the stoichiometry of actinoporin pores in equilibrium is conserved regardless of the particular composition of a given pore ensemble, which we have shown for mixed sticholysin pores.

Marine Peptides: Bioactivities and Applications

Peptides are important bioactive natural products which are present in many marine species. These marine peptides have high potential nutraceutical and medicinal values because of their broad spectra of bioactivities. Their antimicrobial, antiviral, antitumor, antioxidative, cardioprotective (antihypertensive, antiatherosclerotic and anticoagulant), immunomodulatory, analgesic, anxiolytic anti-diabetic, appetite suppressing and neuroprotective activities have attracted the attention of the pharmaceutical industry, which attempts to design them for use in the treatment or prevention of various diseases. Some marine peptides or their derivatives have high commercial values and had reached the pharmaceutical and nutraceutical markets. A large number of them are already in different phases of the clinical and preclinical pipeline. This review highlights the recent research in marine peptides and the trends and prospects for the future, with special emphasis on nutraceutical and pharmaceutical development into marketed products.

Enzymatic and structural characterization of a basic phospholipase A(2) from the sea anemone Condylactis gigantea

This work aimed at the isolation and structural/functional characterization of a phospholipase A(2) (CgPLA(2)) from the extract of the anemone Condylactis gigantea. CgPLA(2) was isolated with a high purity level through three chromatographic steps, showing pI 8.6 and molecular weights of 14,500 and 29,000 for the monomer and dimer, respectively. CgPLA(2) showed a high catalytic activity upon fluorescent phospholipids inducing no direct hemolytic activity. This enzyme, which is Ca(2+)-dependent, showed a lower stability against temperature and pH variations when compared with snake venom enzymes. The enzymatic activity was significantly reduced or completely abolished after chemical modification of CgPLA(2) with BPB. Its cDNA was then obtained, with 357 base pairs which codified for a mature protein of 119 amino acid residues. A comparative analysis of the primary structure of CgPLA(2) revealed 84%, 61%, 43% and 42% similarity to the PLA(2)s from Adamsia carciniopados, Nematostella vectensis, Vipera russelli russelli and Bothrops jararacussu, respectively.

A new toxin from the sea anemone Condylactis gigantea with effect on sodium channel inactivation

A new peptide toxin exhibiting a molecular weight of 5043Da (av.) and comprising 47 amino acid residues was isolated from the sea anemone Condylactis gigantea. Purification of the peptide was achieved by a multistep chromatographic procedure monitoring its strong paralytic activity on crustacea (LD(50) approx. 1microg/kg). Complete sequence analysis of the toxic peptide revealed the isolation of a new member of type I sea anemone sodium channel toxins containing the typical pattern of the six cysteine residues. From 11kg of wet starting material, approximately 1g of the peptide toxin was isolated. The physiological action of the new toxin from C. gigantea CgNa was investigated on sodium currents of rat dorsal root ganglion neurons in culture using whole-cell patch clamp technique (n=60). Under current clamp condition (CgNa) increased action potential duration. This effect is due to slowing down of the TTX-S sodium current inactivation, without modifying the activation process. CgNa prolonged the cardiac action potential duration and enhanced contractile force albeit at 100-fold higher concentrations than the Anemonia sulcata toxin ATXII. The action on sodium channel inactivation and on cardiac excitation-contraction coupling resemble previous results with compounds obtained from this and other sea anemones [Shapiro, B.I., 1968. Purification of a toxin from tentacles of the anemone C. gigantea. Toxicon 5, 253-259; Pelhate, M., Zlotkin, E., 1982. Actions of insect toxin and other toxins derived from the venom of scorpion Androtonus australis on isolated giant axons of the cockroach Periplaneta americana. J. Exp. Biol. 97, 67-77; Salgado, V., Kem, W., 1992. Actions of three structurally distinct sea anemone toxins on crustacean and insect sodium channels. Toxicon 30, 1365-1381; Bruhn, T., Schaller, C., Schulze, C., Sanchez-Rodriquez, J., Dannmeier, C., Ravens, U., Heubach, J.F., Eckhardt, K., Schmidtmayer, J., Schmidt, H., Aneiros, A., Wachter, E., Béress, L., 2001. Isolation and characterization of 5 neurotoxic and cardiotoxic polypeptides from the sea anemone Anthopleura elegantissima. Toxicon, 39, 693-702]. Comprehensive analysis of the purified active fractions suggests that CgNa may represent the main peptide toxin of this sea anemone species.

Equinatoxins, pore-forming proteins from the sea anemone Actinia equina, belong to a multigene family

The multigene family of equinatoxins, pore-forming proteins from sea anemone Actinia equina, has been studied at the protein and gene levels. We report the cDNA sequence of a new, sphingomyelin inhibited equinatoxin, EqtIV. The N-terminal sequences of natural Eqt I and III were also determined, confirming two isoforms of EqtI, differing at position 13. The number of Eqt genes determined by Southern blot hybridization was found to be more than five, indicating that Eqts belong to a multigene family.

Mechanism of action of equinatoxin II, a cytolysin from the sea anemone Actinia equina L. belonging to the family of actinoporins

Actinia equina equinatoxin II (EqT-II) is a representative of a family of pore-forming, basic, polypeptide toxins from sea anemones, now called actinoporins. This family comprises at least 27 members, which are all hemolytic at rather low concentrations. Red blood cell (RBC) hemolysis by EqT-II is the result of a colloid-osmotic shock caused by the opening of toxin-induced pores. Using osmotic protectants of different size the functional radius of the lesion was estimated to be approximately 1.1 nm. These pores are most probably constituted by oligomeric aggregates of cytolysin molecules, whose presence on the membrane of lysed RBC was directly demonstrated by polyacrylamide gel electrophoresis (PAGE) after covalent cross-linking. EqT-II is active also against a variety of mammalian cells including leukocytes, platelets and cardiomiocytes. An increased permeability of the plasma membrane after Eq-II attack is compatible with the notion that the toxin forms pores also on these cells. Eq-II permeabilises even purely lipidic model membranes, suggesting a protein receptor is not necessary. Using calcein-loaded unilamellar vesicles (UVs) comprised of phosphatydylcholine (PC) mixed with other lipids we observed that the rate and extent of permeabilization greatly increases when sphingomyelin (SM) or the ganglioside GM1 were introduced, particularly in the case of large UVs (which are more sensitive to the toxin than small UVs). PAGE indicated that the increased effect of Eq-II on SM containing vesicles is due to an increased level of toxin binding to such vesicles. The formation of cation-selective channels by EqT-II was directly demonstrated using planar lipid membranes where the toxin induced discrete increases of the film conductivity. The conductance of the channel was consistent with the estimated size of the lesion formed in RBC. Several factors can affect toxin activity: serum, low pH, low ionic strength and multivalent cations are potent inhibitors. pH Dependence is bell shaped, optimum activity being between pH 8 and 9. Similarly the action of Ca2+ is also bivalent: up to a concentration of approximately 2 mM it stimulates hemolysis, but above this concentration it inhibits (with 50% inhibition occurring at approximately 10 mM). When the known amino acid sequences of actinoporins are examined a common trait emerges; the presence of a well conserved, amphiphilic, putative alpha-helix at the N-terminus, which might be involved in the insertion of EqT-II in lipid membranes.

Effects of a high molecular weight toxin from the sea anemone Condylactis gigantea on cholinergic responses

1. The effects of a high molecular weight toxin isolated from the sea anemone Condylactis gigantea (Condytoxina 2) on the cholinergic responses were studied in two different preparations: identified cells of a land snail and enzymatically dissociated mice sensory neurons. These neurons were studied using intracellular recording and concentration clamp techniques respectively. 2. The toxin produces a concentration-dependent dual effect on the cholinergic responses in both preparations. Thus the application of the toxin at concentrations up to 25 nmol/l produces a reversible block of the response whereas higher doses potentiates it. 3. These results suggest that Condytoxina 2 contains an active compound(s) with the capacity to bind to the nicotinic acetylcholine receptor of excitable cells in both snail and mice neurons. During this action complex allosteric interactions among the binding sites could occur.

Polypeptide cytolytic toxins from sea anemones (Actiniaria)

Biochemical and biological properties of 30 cytolytic polypeptide toxins isolated from 18 species of sea anemones (Actiniaria) are presented and classified into three groups according to their molecular mass, isoelectric points and the molecular mechanism of action. Phospholipase A2-like toxins (30 kDa) from Aiptasia pallida are dissimilar to acidic metridiolysin (80 kDa) from Metridium senile and the group of about 27 predominantly basic toxins, having a molecular mass of 16-20 or 10 kDa, inhibited by sphingomyelin. They are lethal for both invertebrates and vertebrates, cardiotoxic, cytolytic and cytotoxic. Pharmacological activities, cytotoxic and cytolytic properties are mediated, at least in part, by forming pores in lipid membranes. Channels, 1-2 nm in diameter, formed in planar lipid membranes are cation selective and rectified. The mechanisms and some characteristics of ion channel formation by the toxins in the cells as well as in artificial lipid membranes are summarized and discussed in view of the structure-function studies of the toxins. Putative biological roles of toxins, based on their channel-forming activity, in the capture and killing of prey, digestion, repelling of predators and intraspecific spatial competition are suggested.

Biochemical and pharmacological studies of the mechanism of action of tenebrosin-C, a cardiac stimulatory and haemolytic protein from the sea anemone, Actinia tenebrosa

Tenebrosin-C is a protein of mol. wt 19,500 that displays potent cardiac stimulatory and haemolytic activities. Its haemolytic activity is inhibited by sphingomyelin but not phosphatidylcholine, and is not affected by Ca2+. The positive inotropic effect of tenebrosin-C on isolated guinea pig right atria is inhibited by the cyclooxygenase blockers indomethacin and aspirin, the lipoxygenase blocker and leukotriene antagonist RG5901, and the phospholipase A2 inhibitor mepacrine. This activity of tenebrosin-C therefore appears to be due to stimulation of the release of arachidonic acid and subsequent formation of prostaglandins and leukotrienes. Phospholipase A2-like activity was found with some tenebrosin-C preparations, but did not correlate with their positive inotropic or haemolytic activities and was too weak to account for either of these effects. Treatment of tenebrosin-C with various proteases in order to obtain active fragments showed that the protein is remarkably resistant to proteolysis.

Chemical modification of equinatoxin II, a lethal and cytolytic toxin from the sea anemone Actinia equina L

The role of arginine and tyrosine in cytolytic properties of equinatoxin II, isolated from the sea anemone Actinia equina L., was studied by means of chemical modifications. The toxin was modified with 2,3 butanedione and tetranitromethane, respectively. The extent of modification and physico-chemical properties of the modified proteins were checked with amino acid analysis, isoelectric focusing and circular dichroic spectra. Extensive treatment of the toxin with 2,3 butanedione modified seven arginines and also two tyrosines, with resulting loss of hemolytic activity. Modification of two out of nine arginine residues resulted in a 25% loss of hemolytic activity, whereas nitration of three out of ten tyrosines decreased hemolytic activity by 95%. The nitrated toxin had at least a 30-fold higher i.v. LD50 than the native toxin. None of the modifications significantly affected the secondary structure of the toxin as revealed by the CD spectra. It is concluded that tyrosine residues are involved in both lethal and cytolytic activity, while the role of arginine residues is not evident because of the non-specific alteration of tyrosine residues with 2,3 butanedione.

Isolation and characterization of three lethal and hemolytic toxins from the sea anemone Actinia equina L

Lethal and hemolytic toxins were purified by acetone precipitation, Sephadex G-50, CM-cellulose and CM-Sephadex column chromatography from the tentacles and bodies of the sea anemone Actinia equina. The isolated toxins, with a mol. wt of 19,000 determined by SDS-polyacrylamide gel electrophoresis, differed only slightly in amino acid composition and had a high tryptophan content. The isoelectric points were estimated to be 9.8 for equinatoxin I and 10.5 for equinatoxins II and III. The pure toxins exhibited high lethal potency; the acute i.v. LD50 in mice of equinatoxins I, II and III were 23, 35 and 83 micrograms/kg, respectively. The sigmoidal time course of hemolysis is characteristic of toxins.

Isolation and characterization of a lethal hemolysin in the sea anemone Parasicyonis actinostoloides

Four species of sea anemones in the coastal waters of Japan were surveyed for hemolysins. Powerful hemolysins were detected in Parasicyonis actinostoloides and Anthopleura japonica, whereas extracts of A. fuscoviridis showed much weaker hemolytic activity and those of of Haliplanella luciae no activity. Among the animal erythrocytes tested sheep were most sensitive to the hemolysins of the three positive species. The major hemolysin (parasitoxin) in whole bodies of P. actinostoloides was isolated by ion exchange chromatography, gel filtration and chromatofocusing. In addition to hemolytic activity (119900 HU/mg) it exhibited lethal activity in mice (LD50 65 micrograms/kg, i.v.) and fish Oryzias latipes (approximate minimum lethal concentration 1.5 micrograms/ml). Parasitoxin was slightly basic (pI 7.9) in nature and its amino acid composition was characterized by the absence of half-cystine. The molecular weight was 19,000 by SDS-polyacrylamide gel electrophoresis or 17,000 by sedimentation equilibrium, indicating that parasitoxin has no subunit structure.

Properties of a cytolytic toxin from the sea anemone, Stoichactis kenti

A cytolytic toxin (kentin) from the Indo-Pacific sea anemone, Stoichactis kenti, was purified to near homogeneity. The toxin is a basic polypeptide of molecular weight approximately 18,000. It broadly resembles cytotoxins from Stoichactis helianthus (helianthin), as well as similar toxins from a number of other anemones, namely Condylactis, Epiactis, Actinia, Pseudactinia, Tealia, Anthopleura, Radianthus and Gyrostoma. The amino acid composition of kentin shows considerable resemblance to that of helianthin, but there are also several significant differences. Neutralization tests indicate that kentin and helianthin are immunologically related but distinguishable. In contrast, no immunological relatedness was found between helianthin and cytolytic toxins from Condylactis gigantea and Epiactis prolifera.

Isolation and partial characterization of a lethal sea nettle (Chrysaora quinquecirrha) mesenteric toxin

A protein lethal to mice was isolated from the sea nettle (Chrysaora quinquecirrha) mesenteric tentacle nematocysts by immunochromatography. The partially purified protein was also toxic to spontaneously beating cultural chick cardiocytes but was not hemolytic to rat erythrocytes. On sodium dodecyl sulfate polyacrylamide gels, the mesenteric protein consisted of three bands with apparent molecular weights of 175,000, 160,000 and 108,000. The three protein bands yielded similar peptide maps when subjected to limited proteolysis.

Purification and properties of a toxin from the South African sea anemone, Pseudactinia varia

A comparison was made of the hemolytic potency of aqueous extracts prepared from five species of intertidal sea anemones from the coast of South Africa. The active agent in an extract of Pseudactinia varia was purified by ammonium sulfate precipitation, gel permeation chromatography and isoelectric focusing. The hemolytic toxin, termed variolysin, is a protein having a molecular weight of 19,500 and an isoelectric pH of 9.8. It retained appreciable activity after heating to 70 degrees for 40 min. Amino acid analysis revealed that it lacked methionine and cysteine. Its hemolytic activity was inhibited by sphingomyelin. The properties of variolysin show that it is broadly similar to cytolytic toxins isolated from a number of other anthozoans.