Franz Mesmer might have been on to something when he described animal magnetism as an invisible force possessed by all living things – at least, that seems to be the case with these snakes.
A study by Richard Harris and Bryan Fry of the University of Queensland found that snakes may have evolved to resist their own venom by utilising a magnet-like mechanism to “repel” the molecules in their venom from damaging their nerves.
While all snake venom contains toxins, only some are neurotoxins – those that damage nerve tissue and help a venomous snake slow down or kill its prey. They work by disrupting the signals that tell nerves what to do.
“A nerve releases the neurotransmitter acetylcholine that acts as an email telling the muscle to contract,” explains Fry. “The toxins block the binding of acetylcholine to the receptor located on the muscle, thereby preventing these instructions from getting through.”
This happens because neurotoxins have a positive charge and are pulled towards molecules with a negative charge – such as these receptors. This is an electrostatic interaction that pulls the molecules together like a magnet.
But not all snakes experience this.
In a delightful collision of biology, physics and chemistry, the researchers found that some snakes evolved to have a different, positively charged molecule – lysine – in the place of the normal receptor amino acids. This, instead, makes both molecules positively charged and pushes them apart, they show in their paper, published in Proceedings of the Royal Society B.
“In this form of resistance, a mutation occurs where a newly evolved, positively charged amino acid (lysine) replaces one or both of the characteristic negatively charged amino acids in the nerve receptor, thereby repelling the neurotoxins since same-charges repel each other,” says Fry. “An analogy would be like two magnets with the same side facing each other.”
Even more bizarrely and wonderfully, this appeared to be a trait that was picked up in many different snakes in a case of convergent evolution – where species develop a shared trait that has nothing to do with their genetic ancestry.
“We have shown that it has evolved independently on 10 separate occasions,” says Fry. “Eight times within different snakes that are prey for venomous snakes, and two times in venomous snakes as a form of resistance to their own venom.”
Pleasingly, no snakes were harmed in the research process.
“The technology we are using is a really novel approach that allows us to construct artificial nerves, which gives us the flexibility to make all sorts of mutant versions to test structure-activity relationships,” says Fry. “But since it’s animal-free, it’s not only more efficient but more ethical.”
Dr Deborah Devis is a science journalist at The Royal Institution of Australia.
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