How Do 'Killer Snails' Kill Their Victims? - Science Friday

Cone snail venom is like a cup of fruit cocktail–it is actually a mix of several different kinds of venom! The venom of each cone snail species contains several different venoms in the form of peptides–small proteins usually between 10-30 amino acids in length. The venom of each cone snail species contains a unique mix of these venom peptides–also called “conotoxins”–that have evolved over many generations to be effective against the prey, predators, and competitors specific to its niche.

An individual peptide is a three-dimensional structure made out of a string of amino acids strung together like Christmas lights. The string of peptides bends and folds itself into a tangled mass with a very specific shape. The snail’s own genetic code determines the order of amino acids in a conotoxin, which influence the ultimate 3D structure of the conotoxin peptide. Because the amino acid sequence ultimately dictates the three-dimensional shape of the resulting peptide, different sequences of amino acids form peptides with different shapes. The unique shapes of cone snail venom peptides, determine how and where that particular venom works within the body of prey.

The more peptides of different shapes there are in a cone snail’s venom cocktail, the more venom components it has at its disposal for poisoning prey.

Most proteins, peptides included, exhibit four styles or “orders” of structure: Primary, secondary, tertiary, and quaternary structures. In the following activity, you will be modeling the primary structure of conotoxins–their amino acid sequences–with beads. You will also model one example of tertiary structure–in this case the covalent bonds between cysteines–called disulfide bridges.

Disulfide bridges are just one of the many amino-acid interactions that give a peptide its 3D shape. In addition, the position and number of these bridges are particularly valuable for predicting how a venom peptide affects the nervous system of prey and can also provide hints about how they might be used for medicinal purposes in humans.