Cloning of Complementary and Genomic DNAs Encoding Echotoxins, Proteinaceous Toxins from the Salivary Gland of Marine Gastropod Monoplex echo

Pore-forming moss protein bryoporin is structurally and mechanistically related to actinoporins from evolutionarily distant cnidarians

Pore-forming proteins perforate lipid membranes and consequently affect their integrity and cell fitness. Therefore, it is not surprising that many of these proteins from bacteria, fungi, or certain animals act as toxins. While pore-forming proteins have also been found in plants, there is little information on their molecular structure and mode of action. Bryoporin is a protein from the moss Physcomitrium patens, and its corresponding gene was found to be upregulated by various abiotic stresses, especially dehydration, as well as upon fungal infection. Based on the amino acid sequence, it was suggested that bryoporin was related to the actinoporin family of pore-forming proteins, originally discovered in sea anemones. Here, we provide the first detailed structural and functional analysis of this plant cytolysin. The crystal structure of the monomeric bryoporin is highly similar to those of actinoporins. Our cryo-EM analysis of its pores showed an actinoporin-like octameric structure, thereby revealing a close kinship of proteins from evolutionarily distant organisms. This was further confirmed by our observation of bryoporin's preferential binding to and formation of pores in membranes containing animal sphingolipids, such as sphingomyelin and ceramide phosphoethanolamine; however, its binding affinity was weaker than that of actinoporin equinatoxin II. We determined bryoporin did not bind to major sphingolipids found in fungi or plants, and its membrane-binding and pore-forming activity were enhanced by various sterols. Our results suggest that bryoporin could represent a part of the moss defense arsenal, acting as a pore-forming toxin against membranes of potential animal pathogens, parasites, or predators.

Tetramine in the Salivary Glands of Marine Carnivorous Snails: Analysis, Distribution, and Toxicological Aspects

Focusing on tetramine, tetramethylammonium ion, contained in the salivary glands of marine carnivorous snails, this paper gives an overview of analytical methods, distribution in marine snails, and toxicological aspects. Some Neptunea snails have often caused food poisoning in North Atlantic and Northeast Asia regions, especially in Japan. The toxin of both N. arthritica and N. antiqua was first proven to be tetramine in 1960. Subsequent research on marine snail tetramine has progressed with the development of analytical methods. Of the various methods developed, the LC/ESI-MS method is most recommended for tetramine analysis in terms of sensitivity, specificity, and versatility. Accumulated data show that tetramine is ubiquitously contained at high concentrations (usually several mg/g) in the salivary glands of Neptunea snails. Tetramine is also found in the muscle and viscera of Neptunea snails and even in the salivary gland of marine snails other than Neptunea species, although mostly at low levels (below 0.1 mg/g). Interestingly, the major toxin in the salivary glands of Fusitriton oregonensis and Hemifusus tuba is distinguishable from tetramine. In tetramine poisoning, diverse symptoms attributable to the ganglion-blocking action of tetramine, such as visual disturbance, headache, dizziness, abdominal pain, and nausea, develop within 30 min after ingestion of snails because of rapid absorption of tetramine from the gastrointestinal tract. The symptoms are generally mild and subside in a short time (within 24 at most) because of rapid excretion through the kidney. However, it should be kept in mind that tetramine poisoning can be severe in patients with kidney dysfunction, as shown by two recent case reports. Finally, given the diffusion of tetramine from the salivary gland to the muscle during boiling and thawing of snails, removal of salivary glands from live snails is essential to avoid tetramine poisoning.

Multiomics analysis of the giant triton snail salivary gland, a crown-of-thorns starfish predator

The giant triton snail (Charonia tritonis) is one of the few natural predators of the adult Crown-of-Thorns starfish (COTS), a corallivore that has been damaging to many reefs in the Indo-Pacific. Charonia species have large salivary glands (SGs) that are suspected to produce either a venom and/or sulphuric acid which can immobilize their prey and neutralize the intrinsic toxic properties of COTS. To date, there is little information on the types of toxins produced by tritons. In this paper, the predatory behaviour of the C. tritonis is described. Then, the C. tritonis SG, which itself is made up of an anterior lobe (AL) and posterior lobe (PL), was analyzed using an integrated transcriptomics and proteomics approach, to identify putative toxin- and feeding-related proteins. A de novo transcriptome database and in silico protein analysis predicts that ~3800 proteins have features consistent with being secreted. A gland-specific proteomics analysis confirmed the presence of numerous SG-AL and SG-PL proteins, including those with similarity to cysteine-rich venom proteins. Sulfuric acid biosynthesis enzymes were identified, specific to the SG-PL. Our analysis of the C. tritonis SG (AL and PL) has provided a deeper insight into the biomolecular toolkit used for predation and feeding by C. tritonis.

The Transcriptome of the Zoanthid Protopalythoa variabilis (Cnidaria, Anthozoa) Predicts a Basal Repertoire of Toxin-like and Venom-Auxiliary Polypeptides

Protopalythoa is a zoanthid that, together with thousands of predominantly marine species, such as hydra, jellyfish, and sea anemones, composes the oldest eumetazoan phylum, i.e., the Cnidaria. Some of these species, such as sea wasps and sea anemones, are highly venomous organisms that can produce deadly toxins for preying, for defense or for territorial disputes. Despite the fact that hundreds of organic and polypeptide toxins have been characterized from sea anemones and jellyfish, practically nothing is known about the toxin repertoire in zoanthids. Here, based on a transcriptome analysis of the zoanthid Protopalythoa variabilis, numerous predicted polypeptides with canonical venom protein features are identified. These polypeptides comprise putative proteins from different toxin families: neurotoxic peptides, hemostatic and hemorrhagic toxins, membrane-active (pore-forming) proteins, protease inhibitors, mixed-function venom enzymes, and venom auxiliary proteins. The synthesis and functional analysis of two of these predicted toxin products, one related to the ShK/Aurelin family and the other to a recently discovered anthozoan toxin, displayed potent in vivo neurotoxicity that impaired swimming in larval zebrafish. Altogether, the complex array of venom-related transcripts that are identified in P. variabilis, some of which are first reported in Cnidaria, provides novel insight into the toxin distribution among species and might contribute to the understanding of composition and evolution of venom polypeptides in toxiferous animals.

Detection and some properties of a high molecular weight toxin in the hypobranchial gland of strawberry conch Strombus luhuanus

The extract from the hypobranchial gland of strawberry conch Strombus luhuanus was found to be lethal to mice. There were no marked regional and seasonal variations in toxicity although a considerable individual variation was recognized. The toxin was thermostable and extractable with aqueous solvents but not with organic solvents. Behaviors in dialysis, ultrafiltration and column chromatography on various adsorbents suggested that the toxin is a high molecular weight acidic substance of 400-500 k.

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.