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The intricate patterns and beautiful colors of cone shells never fail to attract the attention of collectors. In the Enlightenment Gallery of the British Museum in London you can spot a little old box full of shells. This is a part of collection brought to Europe in 1771 by Joseph Banks, the scientist from the famous Endeavour voyage, the first Pacific expedition of Captain James Cook. Many items now look dull and grey (the colors have faded after so many years) but the cone shells are still some of the brightest in the box.
The shells of cone snails from this box were the first representative of several snail species common around the Pacific. In general, cone snails are not rare (apart from those few most beautifully decorated and over-harvested species) and can be found in the most tropical waters of the world’s oceans.
Snail Venom and Medicine
Cone snails are now much more popular among scientists than ever before. In the last 30 years, thousands of research articles about them were published. And the number is growing fast. But it’s not their color and decorations that make researchers excited these days. It’s their venom. The venom of these seemingly innocent snails is packed with biologically active components that might be useful for treating the diseases and conditions as different as epilepsy and cancer.
Cone snails are predators. They hunt for small fish using a venom-filled harpoon tooth. Toxins in the venom paralyze, stun or immediately kill the unfortunate prey. Since cone shells are slow moving animals, the effect of venom must be immediate. If prey swim away by just a couple of meters after stinging, the snail might never have a chance to consume its meal.
Rich pharmacopeia of snail venom
Each cone snail species has around 100-200 venom components in its repertoire, mostly so called conopeptides. Conopeptides are relatively short protein molecules consisting of 10-30 amino acids. The repertoire of these peptides in each species is distinctly different – there is hardly any overlap between two different types of cone snail. Taking into account that there are around 500-700 species of cone snail currently known, we can expect to discover between 50,000 and 140,000 different conopeptides.
The variety of these peptides is explained by two factors. The first reason is the variety of prey. Cone snails do not hunt for just one specific kind of fish, they are opportunistic predators. Different prey species have differing sensitivities to the components of venom. Also, cone snails use venom to protect themselves from crabs, mollusc-eating fishes and drilling snails capable of turning the dining table around.
The second reason for the variety and diversity of protein is their co-operative mode of action. Cone snail peptides work so fast because they work together. The groups of peptides in the venom aim at different biochemical targets with the intention to achieve the same desirable physiological end point. Some researchers compare this action to the combination therapy which is used to treat diseases like HIV and cancer: each individual component is not sufficient, but the use of a whole combination may help to achieve the effect. Some fish-hunting cone snails use the combination of peptides which scientists call “the lightning strike cabal”. They hyper-activate the neurons which allow the extremely rapid immobilization of prey resulting in the tetanus paralysis. Another group of snails use a different peptide combination which make the prey quiescent and sedated (the “nirvana cabal”).