Pharmacological effects of two cytolysins isolated from the sea anemone Stichodactyla helianthus

Functional and Structural Variation among Sticholysins, Pore-Forming Proteins from the Sea Anemone Stichodactyla helianthus

Venoms constitute complex mixtures of many different molecules arising from evolution in processes driven by continuous prey-predator interactions. One of the most common compounds in these venomous cocktails are pore-forming proteins, a family of toxins whose activity relies on the disruption of the plasmatic membranes by forming pores. The venom of sea anemones, belonging to the oldest lineage of venomous animals, contains a large amount of a characteristic group of pore-forming proteins known as actinoporins. They bind specifically to sphingomyelin-containing membranes and suffer a conformational metamorphosis that drives them to make pores. This event usually leads cells to death by osmotic shock. Sticholysins are the actinoporins produced by Stichodactyla helianthus. Three different isotoxins are known: Sticholysins I, II, and III. They share very similar amino acid sequence and three-dimensional structure but display different behavior in terms of lytic activity and ability to interact with cholesterol, an important lipid component of vertebrate membranes. In addition, sticholysins can act in synergy when exerting their toxin action. The subtle, but important, molecular nuances that explain their different behavior are described and discussed throughout the text. Improving our knowledge about sticholysins behavior is important for eventually developing them into biotechnological tools.

Identification of unusual peptides with new Cys frameworks in the venom of the cold-water sea anemone Cnidopus japonicus

Sea anemones (Actiniaria) are intensely popular objects of study in venomics. Order Actiniaria includes more than 1,000 species, thus presenting almost unlimited opportunities for the discovery of novel biologically active molecules. The venoms of cold-water sea anemones are studied far less than the venoms of tropical sea anemones. In this work, we analysed the molecular venom composition of the cold-water sea anemone Cnidopus japonicus. Two sets of NGS data from two species revealed molecules belonging to a variety of structural classes, including neurotoxins, toxin-like molecules, linear polypeptides (Cys-free), enzymes, and cytolytics. High-throughput proteomic analyses identified 27 compounds that were present in the venoms. Some of the toxin-like polypeptides exhibited novel Cys frameworks. To characterise their function in the venom, we heterologously expressed 3 polypeptides with unusual Cys frameworks (designated CjTL7, CjTL8, and AnmTx Cj 1c-1) in E. coli. Toxicity tests revealed that the CjTL8 polypeptide displays strong crustacean-specific toxicity, while AnmTx Cj 1c-1 is toxic to both crustaceans and insects. Thus, an improved NGS data analysis algorithm assisted in the identification of toxins with unusual Cys frameworks showing no homology according to BLAST. Our study shows the advantage of combining omics analysis with functional tests for active polypeptide discovery.

Molecular Diversity and Gene Evolution of the Venom Arsenal of Terebridae Predatory Marine Snails

Venom peptides from predatory organisms are a resource for investigating evolutionary processes such as adaptive radiation or diversification, and exemplify promising targets for biomedical drug development. Terebridae are an understudied lineage of conoidean snails, which also includes cone snails and turrids. Characterization of cone snail venom peptides, conotoxins, has revealed a cocktail of bioactive compounds used to investigate physiological cellular function, predator-prey interactions, and to develop novel therapeutics. However, venom diversity of other conoidean snails remains poorly understood. The present research applies a venomics approach to characterize novel terebrid venom peptides, teretoxins, from the venom gland transcriptomes of Triplostephanus anilis and Terebra subulata. Next-generation sequencing and de novo assembly identified 139 putative teretoxins that were analyzed for the presence of canonical peptide features as identified in conotoxins. To meet the challenges of de novo assembly, multiple approaches for cross validation of findings were performed to achieve reliable assemblies of venom duct transcriptomes and to obtain a robust portrait of Terebridae venom. Phylogenetic methodology was used to identify 14 teretoxin gene superfamilies for the first time, 13 of which are unique to the Terebridae. Additionally, basic local algorithm search tool homology-based searches to venom-related genes and posttranslational modification enzymes identified a convergence of certain venom proteins, such as actinoporin, commonly found in venoms. This research provides novel insights into venom evolution and recruitment in Conoidean predatory marine snails and identifies a plethora of terebrid venom peptides that can be used to investigate fundamental questions pertaining to gene evolution.

A Polychaete's powerful punch: venom gland transcriptomics of Glycera reveals a complex cocktail of toxin homologs

Glycerids are marine annelids commonly known as bloodworms. Bloodworms have an eversible proboscis adorned with jaws connected to venom glands. Bloodworms prey on invertebrates, and it is known that the venom glands produce compounds that can induce toxic effects in animals. Yet, none of these putative toxins has been characterized on a molecular basis. Here we present the transcriptomic profiles of the venom glands of three species of bloodworm, Glycera dibranchiata, Glycera fallax and Glycera tridactyla, as well as the body tissue of G. tridactyla. The venom glands express a complex mixture of transcripts coding for putative toxin precursors. These transcripts represent 20 known toxin classes that have been convergently recruited into animal venoms, as well as transcripts potentially coding for Glycera-specific toxins. The toxins represent five functional categories: Pore-forming and membrane-disrupting toxins, neurotoxins, protease inhibitors, other enzymes, and CAP domain toxins. Many of the transcripts coding for putative Glycera toxins belong to classes that have been widely recruited into venoms, but some are homologs of toxins previously only known from the venoms of scorpaeniform fish and monotremes (stonustoxin-like toxin), turrid gastropods (turripeptide-like peptides), and sea anemones (gigantoxin I-like neurotoxin). This complex mixture of toxin homologs suggests that bloodworms employ venom while predating on macroscopic prey, casting doubt on the previously widespread opinion that G. dibranchiata is a detritivore. Our results further show that researchers should be aware that different assembly methods, as well as different methods of homology prediction, can influence the transcriptomic profiling of venom glands.

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.