Evolution of an Ancient Venom: Novel Family of Cnidarian Toxins and the Common Evolutionary Origin of Na & K Neurotoxins in Sea Anemone
Mahdokht Jouiaei, Kartik Sunagar, Aya Federman Gross, Holger Scheib, Paul F. Alewood, Yehu Moran, Bryan G. Fry
Take a look at our paper in MBE where we show that Cndarian toxins remain conserved despite their long evolutionary history and that Potassium ion-channel targeting toxins have evolved from the Sodium ion-channel targeting toxins in Actinioidea (sea anemone)
Despite Cnidaria (sea anemones, corals, jellyfish, and hydroids) being the oldest venomous animal lineage, structure–function relationships, phyletic distributions, and the molecular evolutionary regimes of toxins encoded by these intriguing animals are poorly understood. Hence, we have comprehensively elucidated the phylogenetic and molecular evolutionary histories of pharmacologically characterized cnidarian toxin families, including peptide neurotoxins (voltage-gated Na+ and K+ channel-targeting toxins: NaTxs and KTxs, respectively), pore-forming toxins (actinoporins, aerolysin-related toxins, and jellyfish toxins), and the newly discovered small cysteine-rich peptides (SCRiPs). We show that despite long evolutionary histories, most cnidarian toxins remain conserved under the strong influence of negative selection—a finding that is in striking contrast to the rapid evolution of toxin families in evolutionarily younger lineages, such as cone snails and advanced snakes. In contrast to the previous suggestions that implicated SCRiPs in the biomineralization process in corals, we demonstrate that they are potent neurotoxins that are likely involved in the envenoming function, and thus represent the first family of neurotoxins from corals. We also demonstrate the common evolutionary origin of type III KTxs and NaTxs in sea anemones. We show that type III KTxs have evolved from NaTxs under the regime of positive selection, and likely represent a unique evolutionary innovation of the Actinioidea lineage. We report a correlation between the accumulation of episodically adaptive sites and the emergence of novel pharmacological activities in this rapidly evolving neurotoxic clade.