How some cone snails use insulin to hunt

Above, a Conus snail eats a fish. (Credit: "Conus sp." by David Burdick/NOAA)

The world’s most venomous cone snails use a cocktail of fast-acting toxins to subdue and capture fish—and the mix includes a form of insulin.

The type of insulin used by Conus geographus and Conus tulipa drugs the fish into a coma, allowing the snail to close in on its prey.

“This snail insulin is different from other insulins because it is smaller in size and contains chemical modifications that may have evolved to enhance its ability to rapidly induce hypoglycemia in prey,” says Professor Ray Norton of the Monash Institute for Pharmaceutical Science (MIPS) at Monash University.

“It should prove useful as a tool to probe the systems used by the human body to control blood sugar and energy metabolism.”

Custom venom blends

Found in tropical marine waters, each species of cone snail makes a distinct repertoire of venom compounds, mixtures that have evolved to target particular prey.

When the cone snail releases the venom into the water, its prey—generally schools of fish—become disoriented and stop moving. This lets the snail stick out an expandable mouth-like part, which slowly advances and engulfs the fish.

“Cone snails are very slow moving predators, but they’ve made up for this by producing a vast array of fast-acting toxins that target the nervous systems of their prey,” says Norton.

“What’s really interesting is that they use a unique form of insulin. Found in the venom of these snails in large quantities, it’s very unlikely that it is being used for any other purpose than as a weapon.”

Blood glucose ‘plummets’

Scientists searched the gene sequences coding for all of the proteins expressed in the venom gland of cone snails and found two sequences that looked like insulin.

These insulin genes were more highly expressed in the venom gland than genes for some of the known venom toxins. Researchers have thought that adding insulin to the mix of venom toxins has allowed the predatory cone snails to disable entire schools of swimming fish.

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To test the theory, scientists created a synthetic form of the cone snail insulin. Assays with fish confirm that it causes blood glucose levels to plummet.

Norton says no other animal is known to use insulin in this way, although it is likely that other examples will be found now in light of the new study.

“Our findings underscore the amazing diversity of strategies used by venomous animals to capture their prey or protect themselves from predators,” he says.

“Animal venoms have already yielded several therapeutics that are used in human medicine, and the ongoing exploration of these venoms is likely to produce even more.”

The study involved scientists from MIPS, the University of Utah, New York University and the Copenhagen Biocenter. They report their findings in the Proceedings of the National Academy of Sciences.

Source: Monash University