Snake venom composition may change according to the victim

A snake's intended prey might affect the type and evolution of toxins in their venom, research published in the online open access journal BMC Evolutionary Biology shows.

In snakes, venom composition varies both between species and within a particular species. Land snakes feed on a range of animals and birds, so scientists think that these snakes need a diverse array of toxins in their venom. Sea snakes, on the other hand, tend to have a more restricted diet, feeding only on fish. The toxins in these snakes have now been shown to be less diverse than those in terrestrial snakes.

Professor R Manjunatha Kini and colleagues from the National University of Singapore examined two kinds of sea snakes. They constructed complementary DNA libraries from the venom glands of the reptiles, representing only the stretches of DNA that code for venom gland proteins, and studied two types of protein toxins. The three-finger toxins (3FTx) and the phospholipase A2 (PLA2) enzymes are the main components of sea snake venom.

Although the sea snakes studied lived in very different aquatic environments, the toxins examined were similar in both and the genes encoding the toxins were highly conserved. By contrast, the same toxins in land snakes and sea kraits (which fall between land and sea snakes) showed much greater diversity. The researchers suggest that the toxin genes in sea snakes have remained relatively unchanged because of sea snakes share the same kind of feeding behaviour and diet.

"We examine toxin genes of snakes to identify new toxins, some of which will be useful in developing new therapeutic strategies to treat human diseases," says Prof Kini from the Department of Biological Sciences, National University of Singapore. "A new anticoagulant or a hypotensive toxin may help us develop new cardiovascular drugs to block unwanted clot formation or to lower the blood pressure."

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