Reptile venom is a lethal brew of chemicals that snakes use to immobilize and digest their prey. Its bites are dangerous to humans, but medical researchers have developed antivenoms that save lives.
Several three-finger toxin peptides have been isolated from snake venom, including the a-bungarotoxin from the krait Bungarus multicinctus. These peptides show a high binding affinity to mAChR.
The elapids (Elapidae) are a family of venomous snakes that is characterized by a pair of front-mounted hollow fangs in the upper jaw connected to venom glands. They are endemic to tropical and sub-tropical regions around the world with terrestrial forms in Asia, Africa, Australia, and the Americas and marine forms in the Indian and Pacific Oceans. They can be recognized by a threat display of rearing upwards while spreading the neck-flap. Most have a round pupils and are slender and agile. The most venomous members of the elapids are the cobras and king cobras.
Their venoms contain neurotoxic components for immobilizing prey and defense, mainly PLA2 and three finger toxins (3FTx). Some species also possess cardiotoxins that cause heart dysfunction and cytotoxins that destroy cells. They have a high risk of bites and are among the most feared of all snakes, with a substantial number of fatal snake bites occurring each year.
Unlike vipers, which typically hunt birds and reptiles, elapids generally ambush their prey. Their diets are diverse, with many consuming small terrestrial vertebrates such as mice and rats, frogs, lizards, and birds, while others prefer specific taxa such as the southern African black mamba, Dendroaspis polylepis, which is particular to arid grasslands. The partially marine sea kraits and the fully marine coral snakes eat fish, squid, and fish egg masses.
Colubrids are the largest snake family and many of its species are technically venomous. Despite this, their venoms are much less well characterized than those of the front-fanged snakes. This is due to the fact that they are often less studied, and researchers use different methods. This has resulted in a patchwork of toxin sequences from different studies, limiting our understanding of the overall structure and evolution of venom proteins.
Nevertheless, many colubrids have rear fangs that are capable of injecting significant amounts of venom. These are derived from a special gland called the Duvernoy’s gland, which is homologous to the true venom gland of elapids and vipers. The saliva produced by this gland is deposited into the area of the posterior maxillary teeth. This enables the snake to squirt its toxic compounds into the mouth of prey or humans that are captured.
The venom of the Venezuelan opisthoglyphous colubrid Leptodeira bakeri is an example of this. Crude venom showed several toxic activities, including hemorrhagic effects and neurotoxicity. Partial sequencing of the venom revealed that its proteins were composed of five distinct clusters with different affinities for serine proteases, such as phospholipase A2. While type I PLA2 is a common component of the venoms of front-fanged snakes and some members of the ophidids, it does not appear to be a major component in the opisthoglyphous colubrids.
Viper (family Viperidae) snakes are characterized by long, hollow fangs that inject venom into prey. They also have a very short maxillary bone that can rotate to allow the fangs to lie flat against the roof of the mouth when not in use. Viper venoms contain many proteins, including neurotoxic components that paralyze the nervous system and inhibit muscle contractions, and proteolytic enzymes that break down proteins, nucleic acids, lipids, and other molecules in prey items. In addition, many of these venoms are able to stimulate the innate immune system and may promote thromboinflammation.
The venom of Vipera latastei contains a procoagulant component that activates blood clotting factor VIII by binding to its activation site. This compound, called ecamulin, was isolated and purified in 1991; it is a member of the hemostatic family of peptides that have been shown to be effective in animal models of thrombosis. The molecule was later renamed multactivase, reflecting its multiple functions in blood coagulation.
Although vipers can inspire loathing and fear in humans, they are not normally predators of people and the rare venomous attacks that do occur usually result from aggression or carelessness. However, vipers play a vital ecological role by controlling populations of agricultural and household pests. They also defend themselves with a powerful bite that can kill or cripple prey. Unlike other snakes, their jaws close on impact and the venom glands are anchored in a fixed position in the back of the upper jaws.
A spitting cobra can forcibly eject its venom as a spray up to 2.5 metres away. This behaviour is an effective defence against crocodiles and large birds. It also allows snakes to escape dogs that would otherwise attack them. It has been described as “genius.”
But what motivates the spitting cobra to forcibly fire its venom at predators from a distance? To answer this question, scientists compared the venoms of 17 spitting and nonspitting snakes. They found that the venoms of the spitting cobras had evolved to produce more agonising effects than those of their nonspitting relatives.
The researchers speculate that this may have helped the snakes avoid being stomped on by hoofed mammals like buffaloes and zebras, which are hard to hit with a stream of venom. The team also tested whether increasing the agonising effect of a snake’s venom could encourage it to use its venom to ward off predators at long range.
Bangor University MSc students studying on the only zoology with herpetology course in the UK had the opportunity to contribute to this international research project. They were responsible for generating DNA sequences to generate the phylogeny, or evolutionary family tree, of cobras, which allowed the study to trace the evolution of venom adaptations.
The findings were published in the journal Nature Communications.