by Vivienne Baillie Gerritsen

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Nature has found many ways to ward off predators. Flowers give off scents. Lions use a roar. Some protozoans shoot out harpoon-shaped spikes on their surface and snakes spit venom. Venom is composed of a cocktail of substances, one of which is the poison which will either frighten off the predator – because of the pain which has been inflicted on it – or simply kill it by way of muscular paralysis for instance.

One such poison is neurotoxin. Neurotoxins are used by many organisms, from bees to scorpions and pufferfish to spiders. Snakes harbour a variety of neurotoxins in their venom. Cobratoxin is one and is discharged by the monocled cobra. Its structure is characteristic of the alpha-neurotoxins which look like three erect fingers with the general aspect of a protein which is giving someone the finger.

Cobratoxin binds to acetylcholine receptors. Acetylcholine receptors are located in neuromuscular junctions and, once activated, they cause muscles to contract. When cobratoxin binds to acetylcholine receptors, it blocks their actions thereby bringing on muscle paralysis.

For the past thirty years, neurotoxins have been used extensively to identify different acetylcholine receptors. The identification of such receptors can be very informative in the study of chronic illnesses such as multiple sclerosis for instance – for which cobratoxin could have a therapeutic effect. Time will tell. Is it not intriguing, though, that the structure of a protein used as a means of defense – such as cobratoxin – should echo the human gesture used to insult a fellowman?

UniProt cross references
Alpha-cobratoxin, Naja kaouthia (Monocled cobra) P01391
Protein Spotlight (ISSN 1424-4721) is a monthly review written by the Swiss-Prot team of the SIB Swiss Institute of Bioinformatics. Spotlight articles describe a specific protein or family of proteins on an informal tone. Follow us: Subscribe · Twitter · Facebook