Biologically active polypeptides from the tropical sea anemone Radianthus macrodactylus

Designing a Secretory form of RTX-A as an Anticancer Toxin: An In Silico Approach

BACKGROUND

Cancer is a leading cause of death and a significant public health issue worldwide. Standard treatment methods such as chemotherapy, radiotherapy, and surgery are only sometimes effective. Therefore, new therapeutic approaches are needed for cancer treatment. Sea anemone actinoporins are pore-forming toxins (PFTs) with membranolytic activities. RTX-A is a type of PFT that interacts with membrane phospholipids, resulting in pore formation. The synthesis of recombinant proteins in a secretory form has several advantages, including protein solubility and easy purification. In this study, we aimed to discover suitable signal peptides for producing RTX-A in Bacillus subtilis in a secretory form.

METHODS

Signal peptides were selected from the Signal Peptide Web Server. The probability and secretion pathways of the selected signal peptides were evaluated using the SignalP server. ProtParam and Protein-sol were used to predict the physico-chemical properties and solubility. AlgPred was used to predict the allergenicity of RTX-A linked to suitable signal peptides. Non-allergenic, stable, and soluble signal peptides fused to proteins were chosen, and their secondary and tertiary structures were predicted using GOR IV and I-TASSER, respectively. The PROCHECK server performed the validation of 3D structures.

RESULTS

According to bioinformatics analysis, the fusion forms of OSMY_ECOLI and MALE_ECOLI linked to RTX-A were identified as suitable signal peptides. The final proteins with signal peptides were stable, soluble, and non-allergenic for the human body. Moreover, they had appropriate secondary and tertiary structures.

CONCLUSION

The signal above peptides appears ideal for rationalizing secretory and soluble RTX-A. Therefore, the signal peptides found in this study should be further investigated through experimental researches and patents.

Deep-Sea Anemones Are Prospective Source of New Antimicrobial and Cytotoxic Compounds

The peculiarities of the survival and adaptation of deep-sea organisms raise interest in the study of their metabolites as promising drugs. In this work, the hemolytic, cytotoxic, antimicrobial, and enzyme-inhibitory activities of tentacle extracts from five species of sea anemones (Cnidaria, orders Actiniaria and Corallimorpharia) collected near the Kuril and Commander Islands of the Far East of Russia were evaluated for the first time. The extracts of Liponema brevicorne and Actinostola callosa demonstrated maximal hemolytic activity, while high cytotoxic activity against murine splenocytes and Ehrlich carcinoma cells was found in the extract of Actinostola faeculenta. The extracts of Corallimorphus cf. pilatus demonstrated the greatest activity against Ehrlich carcinoma cells but were not toxic to mouse spleen cells. Sea anemones C. cf. pilatus and Stomphia coccinea are promising sources of antimicrobial and antifungal compounds, being active against Gram-positive bacteria Bacillus subtilis, Staphylococcus aureus, and yeast Candida albicans. Moreover, all sea anemones contain α-galactosidase inhibitors. Peptide mass fingerprinting of L. brevicorne and C. cf. pilatus extracts provided a wide range of peptides, predominantly with molecular masses of 4000–5900 Da, which may belong to a known or new structural class of toxins. The obtained data allow concluding that deep-sea anemones are a promising source of compounds for drug discovery.

Design and evaluation of scFv-RTX-A as a novel immunotoxin for breast cancer treatment: an in silico approach

Human epidermal growth factor receptor 2 (HER2) is overexpressed in breast cancer (BC) patients. Hence, immunotherapy is a proper treatment option for HER2-positive BC patients. Accumulating evidence has indicated that immunotoxin therapy is a novel approach to improve the potency of targeted therapy. Immunotoxins are antibodies or antibody fragments coupled with a toxin. We designed an immunotoxin. The physicochemical properties were evaluated using ProtParam servers and secondary structure was examined by PROSO II and GORV. Using I-TASSER, a 3D model was built and refined by GalaxyRefine. The model was validated using PROCHECK and RAMPAGE. To predict immunotoxin allergenicity and mRNA stability, AlgPred server and RNAfold were used. Furthermore, the immunotoxin and HER2 were docked by ZDOCK. The scFv+RTX-A could be a non-allergenic and stable chimeric protein, and the secondary structure of its components did not alter, and this protein had a proper 3D structure that might have stable mRNA structure which could bind to HER2. Given the fact that the designed immunotoxin was a non-allergenic and stable chimeric protein and that it could bind with high affinity to HER2 receptors, we proposed that this chimeric protein could be a useful candidate for HER-2 positive BC patients.

Sea Anemone Heteractis crispa Actinoporin Demonstrates In Vitro Anticancer Activities and Prevents HT-29 Colorectal Cancer Cell Migration

Actinoporins are the most abundant group of sea anemone cytolytic toxins. Their membranolytic activity is of high interest for the development of novel anticancer drugs. However, to date the activity of actinoporins in malignant cells has been poorly studied. Here, we report on recombinant analog of Hct-S3 (rHct-S3), belonging to the combinatory library of Heteractis crispa actinoporins. rHct-S3 exhibited cytotoxic activity against breast MDA-MB-231 (IC₅₀ = 7.3 µM), colorectal HT-29 (IC₅₀ = 6.8 µM), and melanoma SK-MEL-28 (IC₅₀ = 8.3 µM) cancer cells. The actinoporin effectively prevented epidermal growth factor -induced neoplastic transformation of JB6 Cl41 cells by 34% ± 0.2 and decreased colony formation of HT-29 cells by 47% ± 0.9, MDA-MB-231 cells by 37% ± 1.2, and SK-MEL-28 cells by 34% ± 3.6. Moreover, rHct-S3 decreased proliferation and suppressed migration of colorectal carcinoma cells by 31% ± 5.0 and 99% ± 6.4, respectively. The potent anti-migratory activity was proposed to mediate by decreased matrix metalloproteinases-2 and -9 expression. In addition, rHct-S3 induced programmed cell death by cleavage of caspase-3 and poly (ADP-ribose) polymerase, as well as regulation of Bax and Bcl-2. Our results indicate rHct-S3 to be a promising anticancer drug with a high anti-migratory potential.

Multigene Family of Pore-Forming Toxins from Sea Anemone Heteractis crispa

Sea anemones produce pore-forming toxins, actinoporins, which are interesting as tools for cytoplasmic membranes study, as well as being potential therapeutic agents for cancer therapy. This investigation is devoted to structural and functional study of the Heteractis crispa actinoporins diversity. Here, we described a multigene family consisting of 47 representatives expressed in the sea anemone tentacles as prepropeptide-coding transcripts. The phylogenetic analysis revealed that actinoporin clustering is consistent with the division of sea anemones into superfamilies and families. The transcriptomes of both H. crispa and Heteractis magnifica appear to contain a large repertoire of similar genes representing a rapid expansion of the actinoporin family due to gene duplication and sequence divergence. The presence of the most abundant specific group of actinoporins in H. crispa is the major difference between these species. The functional analysis of six recombinant actinoporins revealed that H. crispa actinoporin grouping was consistent with the different hemolytic activity of their representatives. According to molecular modeling data, we assume that the direction of the N-terminal dipole moment tightly reflects the actinoporins' ability to possess hemolytic activity.

Evaluation of Cyanea capillata Sting Management Protocols Using Ex Vivo and In Vitro Envenomation Models

Lion's mane jellyfish (Cyanea capillata) stings cause severe pain and can lead to dangerous systemic effects, including Irukandji-like syndrome. As is the case for most cnidarian stings, recommended medical protocols in response to such stings lack rigorous scientific support. In this study, we sought to evaluate potential first aid care protocols using previously described envenomation models that allow for direct measurements of venom activity. We found that seawater rinsing, the most commonly recommended method of tentacle removal for this species, induced significant increases in venom delivery, while rinsing with vinegar or Sting No More® Spray did not. Post-sting temperature treatments affected sting severity, with 40 min of hot-pack treatment reducing lysis of sheep's blood (in agar plates), a direct representation of venom load, by over 90%. Ice pack treatment had no effect on sting severity. These results indicate that sting management protocols for Cyanea need to be revised immediately to discontinue rinsing with seawater and include the use of heat treatment.

Membrane-active peptides from marine organisms--antimicrobials, cell-penetrating peptides and peptide toxins: applications and prospects

Marine organisms are known to be a rich and unique source of bioactive compounds as they are exposed to extreme conditions in the oceans. The present study is an attempt to briefly describe some of the important membrane-active peptides (MAPs) such as antimicrobial peptides (AMPs), cell-penetrating peptides (CPPs) and peptide toxins from marine organisms. Since both AMPs and CPPs play a role in membrane perturbation and exhibit interchangeable role, they can speculatively fall under the broad umbrella of MAPs. The study focuses on the structural and functional characteristics of different classes of marine MAPs. Further, AMPs are considered as a potential remedy to antibiotic resistance acquired by several pathogens. Peptides from marine organisms show novel post-translational modifications such as cysteine knots, halogenation and histidino-alanine bridge that enable these peptides to withstand harsh marine environmental conditions. These unusual modifications of AMPs from marine organisms are expected to increase their half-life in living systems, contributing to their increased bioavailability and stability when administered as drug in in vivo systems. Apart from AMPs, marine toxins with membrane-perturbing properties could be essentially investigated for their cytotoxic effect on various pathogens and their cell-penetrating activity across various mammalian cells. The current review will help in identifying the MAPs from marine organisms with crucial post-translational modifications that can be used as template for designing novel therapeutic agents and drug-delivery vehicles for treatment of human diseases.

Synergistic Action of Actinoporin Isoforms from the Same Sea Anemone Species Assembled into Functionally Active Heteropores

Among the toxic polypeptides secreted in the venom of sea anemones, actinoporins are the pore-forming toxins whose toxic activity relies on the formation of oligomeric pores within biological membranes. Intriguingly, actinoporins appear as multigene families that give rise to many protein isoforms in the same individual displaying high sequence identities but large functional differences. However, the evolutionary advantage of producing such similar isotoxins is not fully understood. Here, using sticholysins I and II (StnI and StnII) from the sea anemone Stichodactyla helianthus, it is shown that actinoporin isoforms can potentiate each other's activity. Through hemolysis and calcein releasing assays, it is revealed that mixtures of StnI and StnII are more lytic than equivalent preparations of the corresponding isolated isoforms. It is then proposed that this synergy is due to the assembly of heteropores because (i) StnI and StnII can be chemically cross-linked at the membrane and (ii) the affinity of sticholysin mixtures for the membrane is increased with respect to any of them acting in isolation, as revealed by isothermal titration calorimetry experiments. These results help us understand the multigene nature of actinoporins and may be extended to other families of toxins that require oligomerization to exert toxicity.

Heated Debates: Hot-Water Immersion or Ice Packs as First Aid for Cnidarian Envenomations?

Cnidarian envenomations are an important public health problem, responsible for more deaths than shark attacks annually. For this reason, optimization of first-aid care is essential. According to the published literature, cnidarian venoms and toxins are heat labile at temperatures safe for human application, which supports the use of hot-water immersion of the sting area(s). However, ice packs are often recommended and used by emergency personnel. After conducting a systematic review of the evidence for the use of heat or ice in the treatment of cnidarian envenomations, we conclude that the majority of studies to date support the use of hot-water immersion for pain relief and improved health outcomes.

Pore-forming toxins: Properties, diversity, and uses as tools to image sphingomyelin and ceramide phosphoethanolamine

Pore-forming toxins (PFTs) represent a unique class of highly specific lipid-binding proteins. The cytotoxicity of these compounds has been overcome through crystallographic structure and mutation studies, facilitating the development of non-toxic lipid probes. As a consequence, non-toxic PFTs have been utilized as highly specific probes to visualize the diversity and dynamics of lipid nanostructures in living and fixed cells. This review is focused on the application of PFTs and their non-toxic analogs as tools to visualize sphingomyelin and ceramide phosphoethanolamine, two major phosphosphingolipids in mammalian and insect cells, respectively. This article is part of a Special Issue entitled: Pore-Forming Toxins edited by Mauro Dalla Serra and Franco Gambale.

New Kunitz-Type HCRG Polypeptides from the Sea Anemone Heteractis crispa

Sea anemones are a rich source of Kunitz-type polypeptides that possess not only protease inhibitor activity, but also Kv channels toxicity, analgesic, antihistamine, and anti-inflammatory activities. Two Kunitz-type inhibitors belonging to a new Heteractis crispa RG (HCRG) polypeptide subfamily have been isolated from the sea anemone Heteractis crispa. The amino acid sequences of HCRG1 and HCRG2 identified using the Edman degradation method share up to 95% of their identity with the representatives of the HCGS polypeptide multigene subfamily derived from H. crispa cDNA. Polypeptides are characterized by positively charged Arg at the N-terminus as well as P1 Lys residue at their canonical binding loop, identical to those of bovine pancreatic trypsin inhibitor (BPTI). These polypeptides are shown by our current evidence to be more potent inhibitors of trypsin than the known representatives of the HCGS subfamily with P1Thr. The kinetic and thermodynamic characteristics of the intermolecular interactions between inhibitors and serine proteases were determined by the surface plasmon resonance (SPR) method. Residues functionally important for polypeptide binding to trypsin were revealed using molecular modeling methods. Furthermore, HCRG1 and HCRG2 possess anti-inflammatory activity, reducing tumor necrosis factor-α (TNF-α) and interleukin 6 (IL-6) secretions, as well as proIL-1β expression in lipopolysaccharide (LPS)-activated macrophages. However, there was no effect on nitric oxide (NO) generation.

The effect of cholesterol on the long-range network of interactions established among sea anemone Sticholysin II residues at the water-membrane interface

Actinoporins are α-pore forming proteins with therapeutic potential, produced by sea anemones. Sticholysin II (StnII) from Stichodactyla helianthus is one of its most extensively characterized members. These proteins remain stably folded in water, but upon interaction with lipid bilayers, they oligomerize to form a pore. This event is triggered by the presence of sphingomyelin (SM), but cholesterol (Chol) facilitates pore formation. Membrane attachment and pore formation require changes involving long-distance rearrangements of residues located at the protein-membrane interface. The influence of Chol on membrane recognition, oligomerization, and/or pore formation is now studied using StnII variants, which are characterized in terms of their ability to interact with model membranes in the presence or absence of Chol. The results obtained frame Chol not only as an important partner for SM for functional membrane recognition but also as a molecule which significantly reduces the structural requirements for the mentioned conformational rearrangements to occur. However, given that the DOPC:SM:Chol vesicles employed display phase coexistence and have domain boundaries, the observed effects could be also due to the presence of these different phases on the membrane. In addition, it is also shown that the Arg51 guanidinium group is strictly required for membrane recognition, independently of the presence of Chol.

Protease inhibitors from marine venomous animals and their counterparts in terrestrial venomous animals

The Kunitz-type protease inhibitors are the best-characterized family of serine protease inhibitors, probably due to their abundance in several organisms. These inhibitors consist of a chain of ~60 amino acid residues stabilized by three disulfide bridges, and was first observed in the bovine pancreatic trypsin inhibitor (BPTI)-like protease inhibitors, which strongly inhibit trypsin and chymotrypsin. In this review we present the protease inhibitors (PIs) described to date from marine venomous animals, such as from sea anemone extracts and Conus venom, as well as their counterparts in terrestrial venomous animals, such as snakes, scorpions, spiders, Anurans, and Hymenopterans. More emphasis was given to the Kunitz-type inhibitors, once they are found in all these organisms. Their biological sources, specificity against different proteases, and other molecular blanks (being also K⁺ channel blockers) are presented, followed by their molecular diversity. Whereas sea anemone, snakes and other venomous animals present mainly Kunitz-type inhibitors, PIs from Anurans present the major variety in structure length and number of Cys residues, with at least six distinguishable classes. A representative alignment of PIs from these venomous animals shows that, despite eventual differences in Cys assignment, the key-residues for the protease inhibitory activity in all of them occupy similar positions in primary sequence. The key-residues for the K⁺ channel blocking activity was also compared.

Combining multidimensional liquid chromatography and MALDI-TOF-MS for the fingerprint analysis of secreted peptides from the unexplored sea anemone species Phymanthus crucifer

Sea anemones are sources of biologically active proteins and peptides. However, up to date few peptidomic studies of these organisms are known; therefore most species and their peptide diversity remain unexplored. Contrasting to previous venom peptidomic works on sea anemones and other venomous animals, in the present study we combined pH gradient ion-exchange chromatography with gel filtration and reversed-phase chromatography, allowing the separation of the 1-10 kDa polypeptides from the secretion of the unexplored sea anemone Phymanthus crucifer (Cnidaria/Phymanthidae). This multidimensional chromatographic approach followed by MALDI-TOF-MS detection generated a peptide fingerprint comprising 504 different molecular mass values from acidic and basic peptides, being the largest number estimated for a sea anemone exudate. The peptide population within the 2.0-3.5 kDa mass range showed the highest frequency whereas the main biomarkers comprised acidic and basic peptides with molecular masses within 2.5-6.9 kDa, in contrast to the homogeneous group of 4-5 kDa biomarkers found in sea anemones such as B. granulifera and B. cangicum (Cnidaria/Actiniidae). Our study shows that sea anemone peptide fingerprinting can be greatly improved by including pH gradient ion-exchange chromatography into the multidimensional separation approach, complemented by MALDI-TOF-MS detection. This strategy allowed us to find the most abundant and unprecedented diversity of secreted components from a sea anemone exudate, indicating that the search for novel biologically active peptides from these organisms has much greater potential than previously predicted.

[Conformational stability of serine proteinase inhibitor from the sea anemone Heteractis crispa]

The influence of different environmental values of the pH and temperature on the spatial organization of serine proteinase inhibitor from the sea anemone Heteractis crispa (=Radianthus macrodactylus) on the level of tertiary and secondary structure was studied by CD spectroscopy. The molecule InhVJ was shown to possess a high conformational thermo- and pH-stability. We determined the point of conformational thermotransition of polypeptide (70 degrees C) after which the molecule gets denaturational stable state with conservation of 80% proteinase inhibitory activity. The significant partial reversible changes of molecule spatial organization were established to occur at the level of tertiary structure in the process of acid-base titration in the range of pH 11.0-13.0. This can be explained by of ionization of tyrosine residues. The molecule InhVJ is conformationally stable at the low pH values (2.0). The quenching of tyrosine residues by acrylamide showed that two of these residues are accessible to the quencher in full, while the third part is available.

The behavior of sea anemone actinoporins at the water-membrane interface

Actinoporins constitute a group of small and basic α-pore forming toxins produced by sea anemones. They display high sequence identity and appear as multigene families. They show a singular behaviour at the water-membrane interface: In aqueous solution, actinoporins remain stably folded but, upon interaction with lipid bilayers, become integral membrane structures. These membranes contain sphingomyelin, display phase coexistence, or both. The water soluble structures of the actinoporins equinatoxin II (EqtII) and sticholysin II (StnII) are known in detail. The crystalline structure of a fragaceatoxin C (FraC) nonamer has been also determined. The three proteins fold as a β-sandwich motif flanked by two α-helices, one of them at the N-terminal end. Four regions seem to be especially important: A cluster of aromatic residues, a phosphocholine binding site, an array of basic amino acids, and the N-terminal α-helix. Initial binding of the soluble monomers to the membrane is accomplished by the cluster of aromatic amino acids, the array of basic residues, and the phosphocholine binding site. Then, the N-terminal α-helix detaches from the β-sandwich, extends, and lies parallel to the membrane. Simultaneously, oligomerization occurs. Finally, the extended N-terminal α-helix penetrates the membrane to build a toroidal pore. This model has been however recently challenged by the cryo-EM reconstruction of FraC bound to phospholipid vesicles. Actinoporins structural fold appears across all eukaryotic kingdoms in other functionally unrelated proteins. Many of these proteins neither bind to lipid membranes nor induce cell lysis. Finally, studies focusing on the therapeutic potential of actinoporins also abound.

Molecular characterization on the genome structure of hemolysin toxin isoforms isolated from sea anemone Actineria villosa and Phyllodiscus semoni

We recently identified the existence of new isoforms of Avt-I (from sea anemone Actineria villosa) and Pstx20 (from sea anemone Phyllodiscus semoni) hemolytic toxins, and named them Avt-II and Pst-I. Avt-II and Pst-I differ in length by 14 and 7 bp, respectively, as compared to their corresponding isoform genes. Both newly found isoform genes have the coding regions with the identical length of 1033 bp. The restriction fragment length polymorphism analysis with endonuclease HphI was able to clearly distinguish between the two Avt isoforms, but not Pstx isoforms, and based on the densitometric analysis of DNA bands, it indicated that relative expression levels of Avt-I and Avt-II genes were 18.3% and 81.7%, respectively. PCR amplification of the two Avt isoform genes using the genomic DNA as template indicated the existence of two introns within each toxin isoform gene. The first intron with the identical 242 bp in length for both Avt isoform was found within the 5'-untranslated region, and the second intron with lengths of 654 bp and 661 bp in Avt-I and Avt-II isoforms, respectively, was found within the signal sequence coding region. This is for the first time to identify the existence of introns within hemolysin genes of sea anemone. Having several unique characteristics that have identified only for a new member of actinoporin family of A. villosa and P. semoni, e.g., strong toxicity and genes with introns, it is plausible to speculate that these toxins have a unique genetic evolutionary linage differed from that for other sea anemone hemolytic toxins.

The anticancer effects of actinoporin RTX-A from the sea anemone Heteractis crispa (=Radianthus macrodactylus)

Four isoforms of actinoporins were isolated in 2002-2004 from the tropical sea anemone Heteractis crispa (=Radianthus macrodactylus). Their potent hemolytic activities and effects on Ehrlich ascites carcinoma bearing mice were also studied. In this study, the individual actinoporin (RTX-A) demonstrated potential cancer-preventive activity at extremely low and non-cytotoxic concentrations. The substance suppressed the malignant transformation of mouse JB6 P(+) Cl41 cells stimulated by epidermal growth factor (EGF) in soft agar with the inhibition of number of the colonies C(50) (INCC(50))=0.034 nM. Actinoporin RTX-A also was shown to inhibit the phenotype expression of HeLa human cancer cells with an INCC(50)=0.03 nM. The cytotoxic effect of RTX-A against JB6 P(+) Cl41 cells and HeLa, THP-1, MDA-MB-231, and SNU-C4 human tumor cell lines was high (IC(50)=0.57, 2.26, 1.11, 30.0 and 4.66 nM), but significantly less than their capacity to suppress tumor cell colony formation or phenotype expression. RTX-A also induced apoptosis and inhibited basal AP-1, NF-kappaB, and p53-dependent transcriptional activity in JB6 Cl41 cells. These results confirmed that actinoporin RTX-A from H. crispa, at least partially, might exhibit cancer-preventive and anticancer cytotoxic properties through the induction of p53-independent apoptosis and inhibition of the oncogenic AP-1 and NF-kappaB nuclear factors activity.

Protective effect of melatonin against the inflammatory response elicited by crude venom from isolated nematocysts of Pelagia noctiluca (Cnidaria, Scyphozoa)

Melatonin (N-acetyl-5-methoxytryptamine) is an efficient free radical scavenger and antioxidant, both in vitro and in vivo. The role of melatonin as an immunomodulator is, in some cases, contradictory. In this study we have investigated the therapeutic efficacy of melatonin in rats subjected to Pelagia noctiluca crude venom (of the familia Pelaguiidae; and genus Pelagia) induced acute paw inflammation. In particular, injection of the venom into the paw of rats elicited an acute inflammatory response characterized by accumulation of fluid containing a large number of polymorphonuclear neutrophils in the paw and subsequent lipid peroxidation. Furthermore, the venom promoted an expression of iNOS, nitrotyrosine and the activation of the nuclear enzyme poly (ADP-ribose) polymerase as determined by immunohistochemical analysis of paw tissues. Administration of melatonin 30 min, 1 and 6 hr after the challenge with the venom, caused a significant reduction in all the parameters of inflammation measured. Thus, based on these findings we propose that melatonin may be useful a treatment of local acute inflammation induced by P. noctiluca crude venom.

Marine natural products

This review covers the literature published in 2006 for marine natural products, with 758 citations (534 for the period January to December 2006) referring to compounds isolated from marine microorganisms and phytoplankton, green algae, brown algae, red algae, sponges, cnidaria, bryozoans, molluscs, tunicates and echinoderms. The emphasis is on new compounds (779 for 2006), together with their relevant biological activities, source organisms and country of origin. Biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included.

Amino acid sequence of RTX-A's isoform actinoporin from the sea anemone, Radianthus macrodactylus

The amino acid sequence of actinoporin RTX-A (175 aa) from the sea anemone Radianthus macrodactylus was determined by sequencing of clones obtained via amplification of cDNA. It was established that RTX-A possessed high homology with HmgIII from Heteractis magnifica (87%) and StI, StII from Stichodactyla helianthus (84 and 87%, respectively). The analysis of structural and functional relationships within RTX-A was carried out. The some disagreement concerning to significant role of several amino acid residues for actinoporins exhibition of hemolytic activity was found.

Isolation and biological characterization of neurotoxic compounds from the sea anemone Lebrunia danae (Duchassaing and Michelotti, 1860)

This paper describes two neurotoxic proteins obtained from the Caribbean sea anemone Lebrunia danae. To assess the neurotoxic activity of the venom of L. danae, several bioassays were carried out, and to evaluate the effect of the toxin, Median Lethal Doses (LD(50)) were determined in vivo using sea crabs (Ocypode quadrata) and Artemia salina nauplii with the crude extract of the proportion of 2.82 mg/m. The proteins with neurotoxic effects were isolated using low-pressure liquid chromatography. The fractions containing the neurotoxic activity were analyzed by SDS-PAGE and showed protein bands with an apparent molecular weight of 62.50 kDa (LdNt1) and 58 kDa (LdNt2). To demonstrate that these proteins were indeed responsible for the neurotoxic activity observed, we injected a small fraction of the purified protein into the third walking leg of a crab and observed the typical convulsions, paralysis and death provoked by neurotoxins. Hemolytic activity was also tested for 0.238 mg of crude extract; the hemolytic value was 39.5, 49.6 and 50.1% for cow, sheep and pig erythrocytes, respectively.

Conformational Stability and Hemolytic Activity of Actinoporin RTX-SII from the Sea Anemone Radianthus macrodactylus

The spatial organization of actinoporin RTX-SII from the sea anemone Radianthus macrodactylus on the level of tertiary and secondary structures was studied by UV and CD spectroscopy and intrinsic protein fluorescence. The specific and molar extinction coefficients of RTX-SII were determined. The percentages of canonical secondary structures of actinoporin were calculated. The tertiary structure of the polypeptide is well developed and its secondary structure is highly ordered and contains about 50% antiparallel folded beta-sheets. The irreversible thermal denaturation of RTX-SII was studied by CD spectroscopy; a conformational transition occurs at 53 degrees C. Above this temperature irreversible conformational changes are observed in the secondary and tertiary structures. This is accompanied by redistribution of the content of regular and distorted forms of beta-sheet and also by increase in the content of an unordered form. It is suggested that an intermediate is formed in the process of thermal denaturation. Acid-base titration of RTX-SII results in irreversible conformational changes at pH below 2.0 and above 12.0. As shown by intrinsic protein fluorescence, tyrosine residues of RTX-SII make a fundamental contribution to emission, and the total fluorescence depends more on temperature and ionic strength of the solution than tryptophan fluorescence. The data on conformational stability of actinoporin are correlated with data on its hemolytic activity. Activity of RTX-SII significantly decreases at increased temperature and slightly decreases at low pH. Hemolytic activity drastically increases at high pH. Increase in the actinoporin activity at pH above 10 seems to be caused by ionization of the molecule.

Cytotoxicity of the nematocyst venom from the sea anemone Aiptasia mutabilis

Crude extracts of the coelenterate Aiptasia mutabilis (Anthozoa, Aiptasiidae) nematocysts have been tested for their cytotoxicity of Vero and HEp-2 cells monolayers. The results indicate that the nematocyte venom contains one or more toxins with an extremely powerful cytolytic activity. An extract containing the equivalent of as little as 0.6 nematocysts/microL is sufficient to induce significant cellular necrosis, and IC50 can be estimated to be ca. 2 nematocysts/microL on Vero cells. These values are 1-2 orders of magnitude lower than those reported so far for other sea anemone venoms. The extreme potency is accompanied by poor stability of the venom that is readily inactivated by moderate heat and by buffers at non-neutral pH values. The extract is unstable even when kept for short times at 4 degrees C, or after storage at -20 degrees C. Separation of crude venom by affinity chromatography on ConA-Sepharose allowed us to identify two main components with molecular masses of 95 and 31 kDa, respectively, as responsible for the cytolytic properties of A. mutabilis nematocyst extract.

Isolation, properties and partial amino acid sequence of a new actinoporin from the sea anemone Radianthus macrodactylus

A new cytolytic toxin, actinoporin RTX-S II, was isolated from the sea anemone Radianthus macrodactylus with a high degree of purity by a combination of gel filtration, ion-exchange and reverse-phase chromatography. RTX-S II has molecular mass of 19,280 Da and isoelectric point of 10.0. The hemolytic activity of RTX-S II is inhibited by sphingomyelin. RTX-S II had an LD(50) of 70 mg/kg, and is lacking in phospholipase activity. The amino acid composition of this protein contains a high amount of basic and non-polar amino acids and no cysteine. The N-terminal sequence of RTX-S II was determined. The partial amino acid sequence (141 aa) of RTX-S II was deduced based on the cDNA sequence obtained with two oligonucleotides encoding the N-terminal portion of RTX-S II and the internal conserved cytolysin peptide by PCR. A comparison of the RTX-S II cDNA sequence and the rtx-s II gene obtained with the same PCR primers indicates that they are 100% identical at the nucleotide level. It shows that no introns are present in the corresponding region of the rtx-s II gene. Multiple alignments of RTX-S II with known sequences of actinoporins show that RTX-S II is highly homologous to magnificalysin II from Heteractis magnifica. The predicted secondary structure of RTX-S II is predominantly anti-parallel beta-structure, which is in good agreement with experimental data obtained from other sea anemones-actinoporins.