Exploring the coral snake venom proteome

Abstract

The current study examined the venoms of two groups of coral snakes; Old World coral snakes that reside in parts of Asia, and the New World coral snakes that are endemic to North and South America. The species of interest were Micrurus fulvius, Micrurus tener, Micrurus spixii, Micrurus pyrrhocryptus and Micruroides euryxanthus as representatives of the New World coral snakes and Calliophis bivirgata as the representative for the Old World coral snakes. Symptoms following envenoming by coral snakes are typically neurotoxic. In the present study, the relative neurotoxic potential of venoms from Old and New World coral snakes was examined. The data indicated that the rank order of in vitro neurotoxicity of New World coral snakes was: M. tener > M. spixii ≥ M. pyrrhocryptus > Micruroides euryxanthus > M. fulvius in order of most potent to least potent. Moreover, the venoms were characterized as possessing post-synaptic neurotoxicity, indicating that their site of action is on the nicotinic receptors on the motor end plate. Studies on the venom of C. bivirgata revealed that the venom was unique in comparison to New World coral snakes. A novel three finger toxin (3FTx), δ-elapitoxin-Cb1a, was isolated from the venom and was found to impair sodium channel function, a feature similar to that of toxins from scorpion and spider venoms, and not previously identified in snake venom. Subsequent testing using Coralmyn® antivenom revealed that the antivenom was effective in neutralizing the neurotoxic effects of M. fulvius venom but ineffective against the venoms of M. tener, M. spixii, M. pyrrhocryptus, Micruroides euryxanthus and C. bivirgata. The findings of the M. tener antivenom study were surprising given that past studies have demonstrated the effectiveness of Coralmyn® against M. tener venom in a whole animal model. Pre-incubation of tetrodotoxin, a sodium channel blocker, was effective in neutralising the effects of C. bivirgata venom, further substantiating the effect of the venom on sodium channels. Proteomic analysis of the venoms revealed differences in protein composition between Old World and New World coral snakes, in addition to identifying differences between species of Micrurus based on geographical location (North cf. South America). The data suggests that North American coral snakes possess phospholipase A2-predominant venoms and their counterparts in South America contain predominantly 3FTx venoms. The venom of C. bivirgata was shown to be heavily skewed to proteins of lower molecular weight, in contrast to the venoms of the New World coral snakes. These findings suggest that geographical location may influence the evolution of venom composition. Phylogenetic analysis of Micrurus spp. and C. bivirgata 3FTx revealed a multitude of toxins that were not closely related to any previously characterized toxins. Toxin sequences identified from the venom glands of M. fulvius and M. tener were not closely related to any known α-neurotoxins which suggests that the neurotoxicity is 3FTx-independent. Overall, the results of this study provide important insights into the venoms of both Old and New World coral snake venoms, in addition to identifying potential factors that influence the evolution of venom composition.