Cone Snails Jolt Fish Into Insulin Shock

Some cone snails slogging through the ocean have an unexpected compound in their arsenal of chemical weapons—an unusual version of the peptide hormone insulin. Conus geographus and C. tulipa release specialized insulin into the water as part of a chemical weapons cocktail, Baldomero M. Olivera and Helena Safavi-Hemami of the University of Utah and coworkers report (Proc. Natl. Acad. Sci. USA 2015, DOI: 10.1073/pnas.1423857112). This cocktail, which they have labeled the “nirvana cabal,” shuts down the sensory circuits of small fish, making them easy prey for cone snails, which engulf the fish with their billowy mouths. The insulin depletes glucose in the fish’s blood and sends them into hypoglycemic shock. The snail venom insulin is structurally more similar to insulin produced by the fish than it is to the insulin the snail produces for its own metabolism. The venom insulin contains posttranslational modifications, such as hydroxyproline and γ-carboxyglutamate, which are characteristic of peptide neurotoxins called conotoxins produced by cone snails. In addition, the venom insulin, which is the shortest insulin molecule yet discovered, may act faster than other types of insulin, the researchers speculate.