How Similar Are the Snake Venoms?

There's no venomous creature to trigger more dread in humans than snakes. And for a good reason, even if just about 200 out 2,900 species are traumatogenic for humans. Their venom is devastating. Some venoms are neurotoxic and paralyze the muscles. The victim dies of suffocation and heart attack. All cobras and their relatives (mambas, kraits, coral snakes, venomous Australian snakes, sea snakes) have extremely potent neurotoxic venom, but neurotoxic venom can also be found in some rattlesnakes, moccasins and pitless vipers. Some venoms, like that of the cobra, produce anaphylactic shock.

Other venoms act like a powerful digesting juice, producing necrosis and hemorrhage. Most vipers (pit or pitless) possess a powerful venom of this type and with their huge fangs can introduce large amounts of venom into the wounds. The bushmaster (Lachesis muta), a pit viper from tropical America produces general necrosis, generalized internal hemorrhage and external hemorrhage through all the orifices.

Sea snake's venom provokes elimination of mioglobin (muscle protein) through the kidney and necrosis into the muscles, but these snakes are not known to have ever bitten a person.

Some animals are very sensitive to snake venom, such as birds, whereas others are not, like mongooses that consume venomous snakes and some species, like snake eating snakes (king cobra, king snakes), that are totally immune to snake venom. Many snakes have venom specialized for their prey, like an aquatic Colubrid, Fordonia, whose venom is toxic only for the crabs.

Now, a research published in the on-line journal BMC Molecular Biology shows that venoms from various snake families are more similar than previously believed. The research was made on the desert Massasauga Rattlesnake (Sistrurus catenatus edwardsii), a North American pit viper.

The research team made a cDNA library of the snake's toxins with 576 tagged sequences. Many toxins from the cocktail represented by the venom had already been known, but there were also three-finger toxin-like transcripts. This type of toxins was believed to be typical just for Elapidae snakes (cobras and relatives). The researchers also spotted a new gene generated by the fusion of two individual toxin genes, an evolutionary mechanism not previously known in the snake venom evolution. Usually, new toxins emerge through gene duplication and subsequent neofunctionalization by mutations.

"In addition to gene duplication, exon shuffling or transcriptional splicing may also contribute to generating the diversity of toxins and toxin isoforms observed among snake venoms", said Pahari.

The library method came out with new toxins and even new types of toxins, previously missed because they could be found in small amounts in the venom. These low level toxins reveal that snake venoms are in fact much more similar than previously believed.

Snake venoms are just complex cocktails of active proteins and peptides, which vary a lot even within snake families.

"Such a diversity of toxins provides a gold mine of bioactive polypeptides, which could aid the development of novel therapeutic agents", said co-author R. Manjunatha Kini, from the National University of Singapore.