Characterising Functional Venom Profiles of Anthozoans and Medusozoans within Their Ecological Context.

This review examines the current state of knowledge regarding toxins from anthozoans (sea anemones, coral, zoanthids, corallimorphs, sea pens and tube anemones). We provide an overview of venom from phylum Cnidaria and review the diversity of venom composition between the two major clades (Medusozoa and Anthozoa). We highlight that the functional and ecological context of venom has implications for the temporal and spatial expression of protein and peptide toxins within class Anthozoa. Understanding the nuances in the regulation of venom arsenals has been made possible by recent advances in analytical technologies that allow characterisation of the spatial distributions of toxins. Furthermore, anthozoans are unique in that ecological roles can be assigned using tissue expression data, thereby circumventing some of the challenges related to pharmacological screening.

Stichodactyla helianthus' de novo transcriptome assembly: Discovery of a new actinoporin isoform.

Transcriptomic profiling of venom producing tissues from different animals is an effective approach for discovering new toxins useful in biotechnological and pharmaceutical applications, as well in evolutionary comparative studies of venomous animals. Stichodactyla helianthus is a Caribbean sea anemone which produces actinoporins as part of its toxic venom. This family of pore forming toxins is multigenic and at least two different isoforms, encoded by separate genes, are produced by S. helianthus. These isoforms, sticholysins I and II, share 93% amino acid identity but differ in their pore forming activity and act synergistically. This observation suggests that other actinoporin isoforms, if present in the venomous mixture, could offer an advantageous strategy to modulate whole venom activity. Using high-throughput sequencing we generated a de novo transcriptome of S. helianthus and determined the relative expression of assembled transcripts using RNA-Seq to better characterize components of this species' venom, focusing on actinoporin diversity. Applying this approach, we have discovered at least one new actinoporin variant from S. helianthus in addition to several other putative venom components.

Modulation of neuronal sodium channels by the sea anemone peptide BDS-I.

Blood-depressing substance I (BDS-I), a 43 amino-acid peptide from sea anemone venom, is used as a specific inhibitor of Kv3-family potassium channels. We found that BDS-I acts with even higher potency to modulate specific types of voltage-dependent sodium channels. In rat dorsal root ganglion (DRG) neurons, 3 µM BDS-I strongly enhanced tetrodotoxin (TTX)-sensitive sodium current but weakly inhibited TTX-resistant sodium current. In rat superior cervical ganglion (SCG) neurons, which express only TTX-sensitive sodium current, BDS-I enhanced current elicited by small depolarizations and slowed decay of currents at all voltages (EC(50) ∼ 300 nM). BDS-I acted with exceptionally high potency and efficacy on cloned human Nav1.7 channels, slowing inactivation by 6-fold, with an EC(50) of approximately 3 nM. BDS-I also slowed inactivation of sodium currents in N1E-115 neuroblastoma cells (mainly from Nav1.3 channels), with an EC(50) ∼ 600 nM. In hippocampal CA3 pyramidal neurons (mouse) and cerebellar Purkinje neurons (mouse and rat), BDS-I had only small effects on current decay (slowing inactivation by 20-50%), suggesting relatively weak sensitivity of Nav1.1 and Nav1.6 channels. The biggest effect of BDS-I in central neurons was to enhance resurgent current in Purkinje neurons, an effect reflected in enhancement of sodium current during the repolarization phase of Purkinje neuron action potentials. Overall, these results show that BDS-I acts to modulate sodium channel gating in a manner similar to previously known neurotoxin receptor site 3 anemone toxins but with different isoform sensitivity. Most notably, BDS-I acts with very high potency on human Nav1.7 channels.

Actinoporins from the sea anemones, tropical Radianthus macrodactylus and northern Oulactis orientalis: Comparative analysis of structure-function relationships.

Actinoporins Or-A and Or-G from the northern sea anemone Oulactis orientalis and actinoporins RTX-A and RTX-SII from the tropical sea anemone Radianthus macrodactylus (=Heteractis crispa) were compared with each other and with some known actinoporins. In this work the complete amino acid sequence of RTX-SII was determined by molecular biology methods. The following differences were revealed in functionally significant regions of Radianthus, Oulactis, and some other actinoporins: (i) tryptophan is substituted for leucine in the position equivalent to Trp112 in the POC binding site of EqtII; (ii) 13 and 5 residues are truncated in N-terminal regions of Or-A and Or-G, respectively. A possible role of these structural differences in specific regions of the actinoporin sequence was analyzed. Some differences in hydrophobicity parameters, distribution of charged residues, and length of actinoporins' N-terminus apparently cause considerable differences in their hemolytic activities. Homology models of Radianthus and Oulactis actinoporin monomers were generated using crystal structures of equinatoxin II from Actinia equina and sticholysin II from Stichodactyla helianthus as templates. The current data on actinoporin structures and activities, coupled with results of our earlier differential scanning calorimetric and electrophoretic experiments with RTX-A-modified erythrocyte ghosts (Shnyrov et al., 1992), suggests that the exposed RGD motif located near the POC binding site can interact with membrane integrin(s).

In vivo effects of cnidarian toxins and venoms.

Cnidarians (Coelenterates), a very old and diverse animal phylum, possess a wide variety of biologically active substances that can be considered as toxins. Anthozoan toxins can be classified into two chemically very different groups, namely polypeptide toxins isolated from sea anemones and diterpenes isolated from octocorals. Cubozoan and scyphozoan protein toxins have been the most elusive cnidarian toxins to investigate - despite a tremendous effort in the past few decades, very few of these large, relatively unstable protein toxins were isolated, but recently this has been achieved for cubozoan venoms. Hydrozoans mainly contain large proteins with physiological mechanisms of action similar to the sea anemone and jellyfish pore-forming toxins. This article will focus on the in vivo physiological effects of cnidarian toxins and venoms; their actions at the cellular level will only be considered to understand their actions at the organ and whole animal levels. An understanding of mechanisms underlying the in vivo toxic effects will facilitate the development of more effective treatments of cnidarian envenomations.