A protein in our saliva shares an origin with snake venom

Some snakes, lizards and even mammals have venomous bites despite these lineages being separated by 300 million years of evolution. Scientists recently traced the origin of a class of these toxins, called kallikrein serine proteases, to a salivary protein found in a common ancestor of venomous snakes and non-venomous mammals. 

The research provides strong evidence for the idea that venom evolved from genes with potential for toxicity that existed in the ancestors of both snakes and mammals. 

Study co-first author Agneesh Barua is a PhD student at Okinawa Institute of Science and Technology (OIST).

“Venoms are cocktails of toxic proteins that have evolved across the whole animal kingdom, typically as a method of killing or immobilizing prey,” said Barua.

“The oral venom systems found in snakes are particularly complex, and the origin of their venoms is still unclear.”

In previous research, Barua and his colleagues found that regulatory genes for saliva glands in mammals and venom glands in snakes are similar in their pattern of activity, suggesting a similar foundation for the two. 

“In that paper, we hypothesized that in the ancestor of snakes and mammals, there was a common group of genes that had a toxic potential,” said Barua.

“Snakes and mammals then took different evolutionary paths, with snake lineages evolving diverse and increasingly toxic concoctions, while in mammals, venom did evolve, but to a much lesser degree. But what we wanted to know is whether the toxins within mammal and snake venom evolved from a common ancestral gene.”

Early in the research, scientists found that there is a similarity between the biochemistry of Kallikrein serine proteases found in snake venoms and those found in mammal saliva. It was not known, however, whether the two were evolutionarily related. In fact, many serine proteases are similar.  

“This is really strong evidence for our hypothesis that venom evolved from a common group of genes in an ancestor that had a toxic potential,” said Barua. “But the most surprising thing was that non-toxic salivary kallikreins, like those found in humans and mice, also evolved from the same ancestral gene.”

The results of the study show that the line between venomous and non-venomous mammals is not as clear cut as once thought. 

The study is published in the journal BMC Biology.

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By Zach Fitzner, Earth.com Staff Writer