Caterpillar venom toxin genes borrowed from bacteria

What is it about?

Asp caterpillars produce a pain-inducing venom to defend themselves from predators, but previously almost nothing has been known about where they are produced, what toxins they contain, or how they work. In this article we use a range of complementary techniques to elucidate how the venom system functions. Among the many peptides and proteins in the venom, we found that a group of proteins we dubbed megalysins are responsible for the strong pain and swelling induced by the venom. These megalysins belong a family called aerolysins, which are toxins produced by bacteria that punch holes in cells. The structures of the megalysins we discovered in this study suggest they work in a similar way to cause pain. Remarkably, analysis of the evolution of megalysins show that this a gene encoding this type of toxin was transferred from a bacterium to the ancestors of butterflies and moths hundreds of millions of years ago, was retained for some unknown non-venom function, and then was recruited to act as a venom toxin by asp caterpillars. This kind of gene transfer between species is known as horizontal gene transfer, and this is one of a handful of examples of how it has contributed to venom evolution.

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Photo by PROJETO CAFÉ GATO-MOURISCO on Unsplash

Photo by PROJETO CAFÉ GATO-MOURISCO on Unsplash

Why is it important?

This study adds to our understanding of how venom toxins evolve, highlighting horizontal gene transfer as an important, if rare, mechanism. It also adds to our understanding of caterpillar defense systems, which are highly diverse and sophisticated. Venoms are increasingly recognized as a source of novel molecules for use in medicine and industry, and our study adds to the pool of resources that might be adopted in biotechnology. The molecular nature of insect venoms, and caterpillar venoms in particular, represents a knowledge gap that this paper contributes to filling.

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