Widespread Evolution of Molecular Resistance to Snake Venom α-Neurotoxins in Vertebrates.

Muzaffar A Khan,Harald Kerkkamp,Michael K Richardson,Merijn A G De Bakker,Bryan G Fry,Jory Van Thiel,R Manjunatha Kini,Dušan Kordiš,Roel Wouters,Daniel Dashevsky,Bianca Op Den Brouw,Freek J Vonk,Jawad Nazir

doi:10.3390/toxins12100638

Abstract

Venomous snakes are important subjects of study in evolution, ecology, and biomedicine. Many venomous snakes have alpha-neurotoxins (α-neurotoxins) in their venom. These toxins bind the alpha-1 nicotinic acetylcholine receptor (nAChR) at the neuromuscular junction, causing paralysis and asphyxia. Several venomous snakes and their predators have evolved resistance to α-neurotoxins. The resistance is conferred by steric hindrance from N-glycosylated asparagines at amino acids 187 or 189, by an arginine at position 187 that has been hypothesized to either electrostatically repulse positively charged neurotoxins or sterically interfere with α-neurotoxin binding, or proline replacements at positions 194 or 197 of the nAChR ligand-binding domain to inhibit α-neurotoxin binding through structural changes in the receptor. Here, we analyzed this domain in 148 vertebrate species, and assessed its amino acid sequences for resistance-associated mutations. Of these sequences, 89 were sequenced de novo. We find widespread convergent evolution of the N-glycosylation form of resistance in several taxa including venomous snakes and their lizard prey, but not in the snake-eating birds studied. We also document new lineages with the arginine form of inhibition. Using an in vivo assay in four species, we provide further evidence that N-glycosylation mutations reduce the toxicity of cobra venom. The nAChR is of crucial importance for normal neuromuscular function and is highly conserved throughout the vertebrates as a result. Our research shows that the evolution of α-neurotoxins in snakes may well have prompted arms races and mutations to this ancient receptor across a wide range of sympatric vertebrates. These findings underscore the inter-connectedness of the biosphere and the ripple effects that one adaption can have across global ecosystems.

Highlights

Venoms have evolved independently in multiple animal lineages [1,2]
We sequenced de novo the nicotinic acetylcholine receptor (nAChR) ligand binding domain of 89 vertebrate species and obtained sequences for a further 59 species from The National Center for Biotechnology Information (NCBI; Supplementary Table S1)
Selected sites inferred under posterior probability (PP) > 0.95 were found (172, 177, 181, 187, 194, and 206)

Summary

Introduction

Venoms have evolved independently in multiple animal lineages [1,2]. When a venomous animal injects venom into a target animal (an event called ’envenomation’), venom toxins disrupt physiological processes, causing pain, incapacitation, or death. The snake α-neurotoxins are members of the three-finger toxin (3FTx) family [7,8,9,10,11] and are major components of venoms from the families Elapidae and Colubridae [12,13,14,15,16,17] Venomous snakes in these families are of considerable scientific interest, not least because they are responsible for numerous human fatalities [18], and because species possessing them—such as Boiga irregularis (the brown tree snake)—can cause ecological destruction as invasive species owing in part to the effectiveness of these toxins [19]

Methods

Results

Conclusion