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Snake Venom Composition and Variability

Updated on May 12, 2017

Snake Venom Composition Differs Between Taxonomic Families

An Argentine Racer (Philodryas patagoniensis; family Colubridae) produces clear venom while a Prairie Rattlesnake (Crotalus viridis viridis; family Viperidae) produces yellow/gold venom, indicating the presence of LAAO in the viperid's venom.
An Argentine Racer (Philodryas patagoniensis; family Colubridae) produces clear venom while a Prairie Rattlesnake (Crotalus viridis viridis; family Viperidae) produces yellow/gold venom, indicating the presence of LAAO in the viperid's venom.

Compounds Found in Snake Venoms

This article is part of a series about snake venoms. For a complete list of articles in the series, see below.

Here, we are going to explore the major, potentially clinically-relevant, components that have been described in snake venoms thus far and their most common functions. Although snake venoms are primarily made up of proteins (some of which are enzymes) and peptides, they may also contain small organic compounds.

Below is a table listing each type of venom compound, its possible actions [the function of some compounds is still unknown, but is hypothesized ("believed") to act in a certain way] on the body of its prey or a potential predator, and the snake taxonomic family/families that may possess the compound (bear in mind that many of the venom compounds found within snakes of family Atractaspididae have yet to be elucidated). For clarification, family Colubridae refers to many of your common/backyard rear-fanged venomous snakes (please see parts 2-4 of this series for information on rear-fanged snakes if you are unfamiliar with them), such as garter snakes, water snakes, ringneck snakes, and hognose snakes, while family Elapidae includes front-fanged venomous snakes such as cobras, sea snakes, mambas, and coral snakes, and family Viperidae consists of front-fanged venomous snakes such as rattlesnakes, vipers, copperheads, and cottonmouths. Snakes comprising the family Atractaspididae, such as the side-stabbing stiletto snakes, burrowing asps, and mole vipers, can be very confusing as they share a number of fang and venom gland characteristics with the other three venomous snake families and can be either front- or rear-fanged venomous (although they are generally considered front-fanged for a variety of reasons discussed in the other articles in this "Snake Venom" series). Although family Atractaspididae and Colubridae contain some nonvenomous snake species (not possessing fangs or venom), members of families Elapidae and Viperidae are exclusively venomous.

As you can see in the table below, some types of venom compounds exist in a single family of snakes, while others are present in all three families examined here. This observation of shared venom compounds across snake families, combined with the somewhat similar envenomation system of each snake family (please see part 4 of this series), leads us to believe that these snakes shared a common, venomous ancestor. It is because of this that it can be dangerous to "guess" at the venom composition of a particular snake based solely on which family it belongs to (the most common misconception is that elapids, such as cobras, have strictly neurotoxic venom while viperids, such as rattlesnakes, possess strictly hemotoxic venom; these can be fatal assumptions to make). Many of these compounds have overlapping/redundant functions, resulting in the possibility of similar envenomation symptoms in bites from snakes of different families. Now, within each snake family, it is possible for genera (and species) to have venoms that are distinct from one another, giving you a better idea of the likely envenomation symptoms from those snakes.

Although there can be up to 100 distinct compounds (including subtypes and isoforms not represented here) within any one snake's venom, there are snakes that possess less than a dozen different venom components (that's not to say that there is necessarily a direct association between the number of venom components present and toxicity of the venom). Differences in snake venom composition (both presence and abundance of individual compounds) can be found at all taxonomic levels: family, genus, species, and sub-species. There can also be differences in venom composition between snakes belonging to populations in different geographical locations, between individuals within those populations, and between males and females. The venom composition within an individual snake is even subject to change based on its age, diet, environment (including captivity), and season. On rare occasion, venom has also been found to differ between the venom glands of an individual snake.

These phenomena partially explain how/why there are problems with the effectiveness of antivenom, because it can be difficult to account for all of these sources of venom variation in the production of antivenom. Differences in envenomation symptoms can also occur due to the amount of venom injected and how recently the venom gland was "emptied" (venom compounds require time to replenish, with some types being made before others). In addition to the mechanical factors affecting venom injection volume that were discussed in article 2 of this series, there is the conscious factor of how much venom the snake "decides" to inject (with younger snakes exhibiting the same degree of control as older snakes; there is no "learning curve").

Primary Snake Venom Compounds of Concern to Humans

Type of Compound
Action on the Body
Snake Family
Acetylcholinesterases (AChE)
believed to cause tetanic paralysis
Colubridae, Elapidae
Arginine esterases
believed to predigest prey
Viperidae
Bradykinin-potentiating peptides (BPP)
pain, hypotension, immobilize prey
Viperidae
C-type lectins
modulate platelet activity, prevent clotting
Viperidae
Cysteine-rich secretory proteins (CRiSP)
believed to induce hypothermia, immobilize prey
Colubridae, Elapidae, Viperidae
Disintegrins
inhibit platelet activity, promote hemorrhaging
Viperidae
Hyaluronidases
increase interstitial fluidity, aiding the dissemination of venom from the bite site
Elapidae, Viperidae
L-amino acid oxidases (LAAO)
cell damage/apoptosis
Elapidae, Viperidae
Metalloproteinases (MPr)
hemorrhage, myonecrosis, believed to predigest prey
Atractaspididae, Colubridae, Elapidae, Viperidae
Myotoxins
myonecrosis, analgesia, immobilize prey
Viperidae
Nerve growth factors
believed to cause cell apoptosis
Elapidae, Viperidae
Phosphodiesterases (PDE)
believed to cause hypotension, shock
Colubridae, Elapidae, Viperidae
Phospholipase A2's (PLA2)
myotoxicity, myonecrosis, damage to cell membranes
Colubridae, Elapidae, Viperidae
PLA2-based presynaptic neurotoxins
immobilize prey
Elapidae, Viperidae
Prothrombin activators
disseminated intravascular coagulation (DIC: small clots form throughout body, leading to uncontrolled bleeding), which can be fatal
Elapidae
Purines and pyrimidines
believed to cause hypotension, paralysis, apoptosis, necrosis, immobilization of prey
Elapidae, Viperidae
Sarafotoxins
myocardial ischemia (reduced blood flow to heart), increase blood pressure, disturb heart rhythm
Atractaspididae
Serine proteases
hemostasis disruption, hypotension, immobilize prey
Colubridae, Viperidae
Three-finger toxins (3FTx)
rapid immobilization of prey, paralysis, death
Colubridae, Elapidae
The information in this table is modified from: Mackessy, S.P., 2009. Handbook of Venoms and Toxins of Reptiles. CRC Press/Taylor & Francis Group, Boca Raton, FL.

Venom Variation Between Venom Glands

A Prairie Rattlesnake (Crotalus viridis viridis), expressing white venom from its right fang and yellow venom from its left fang, indicating a much higher level of LAAO in the venom coming from the left venom gland.
A Prairie Rattlesnake (Crotalus viridis viridis), expressing white venom from its right fang and yellow venom from its left fang, indicating a much higher level of LAAO in the venom coming from the left venom gland.

Substrate Specificity of Venom Compounds

This compares the "general" proteinase activity of some metalloproteinases against structural proteins to the highly specific activity of some three-finger toxins against acetylcholine receptors.
This compares the "general" proteinase activity of some metalloproteinases against structural proteins to the highly specific activity of some three-finger toxins against acetylcholine receptors.

Substrate/Prey Specificity

As you read through the table above, I'm sure you came to realize that while some types of venom compounds produced very distinct envenomation symptoms, others presented a broad range of biological effects. The reasoning for this is that each individual venom compound (as well as every one of its subtypes) possesses its own degree of target (substrate) specificity. Try thinking about it this way: each venom compound is a key that can only open certain locks. Some venom compounds are similar to skeleton keys (able to open several kinds of locks), while other venom compounds are only capable of opening a single kind of lock (with many venom compounds that are in between the two extremes).

The figure above is a simplified 2-D diagram illustrating these two extremes, using a metalloproteinase as an example of a skeleton key (able to bind to and act on several kinds of structural proteins) and a three-finger toxin as an example of a key that only fits one kind of lock (only capable of binding to and acting on acetylcholine receptors). Therefore, metalloproteinases can be thought of as possessing a low target specificity, while three-finger toxins can be considered as having a high substrate specificity. If we expand upon this further, we come to the concept of taxon-specific venom compounds, with "taxon" referring to taxonomy. This namely applies to higher levels of taxonomic organization (suborder and above) and typically involves toxins that are only capable of acting on certain "kinds" of animals. For example, a particular 3FTx (irditoxin) is highly toxic towards birds and lizards, but harmless towards mammals. These "taxon-specific" mechanisms tend to be associated with the preferred prey of the snakes, which is why they are often referred to as being "prey-specific" toxins.

The genes responsible for encoding snake venom compounds are subject to accelerated segment switch in exons to alter targeting (ASSET), which is a form of accelerated evolution meant to encourage the creation of new venom compounds with novel functions and targets (helping explain how/why snake venoms can be so variable). This phenomenon could partially explain the observation that front-fanged snakes often possess venoms that are fairly toxic towards humans, whereas rear-fanged snakes frequently produce mild envenomation symptoms in people [with the exception of the Boomslang (Dispholidus typus) and Twig Snake (genus Thelotornis), among a few others].

You may take the quiz below to test your knowledge of snake venom composition/variability before moving onto the next article, which explores the utility of snake venom research. You can also check out the video below, which gives an excellent example of the in-vivo effects of (principally) one particular type of venom compound: myotoxin. If you would like to learn more about the composition of snake venoms, please see the Amazon link below for a very useful book resource. If you have further questions about snakes that are not addressed by this article on snake venom composition (or any other articles in this snake venom series), please see my article, FAQs About Snakes.

Example of a Dangerous Rear-fanged Snake

A Twig Snake (Thelotornis capensis) holding a Green Anole (Anolis carolinensis) in its mouth such that it can effectively envenomate it.  This snake is among the few rear-fanged snake species that pose a real threat to humans.
A Twig Snake (Thelotornis capensis) holding a Green Anole (Anolis carolinensis) in its mouth such that it can effectively envenomate it. This snake is among the few rear-fanged snake species that pose a real threat to humans.

Disclaimer

This article is intended to educate people ranging from snake experts to laymen about the composition of snake venoms. This information contains generalizations and by no means encompasses all exceptions to the most common "rules" presented here. This information comes from my personal experience/knowledge as well as various primary (journal articles) and secondary (books) literature sources (and can be made available upon request). All pictures and videos, unless specifically noted otherwise, are my property and may not be used in any form, to any degree, without my express permission (please send email inquiries to christopher.j.rex@gmail.com).

I wholly believe feedback can be a useful tool for helping make the world a better place, so I welcome any (positive or negative) that you might feel compelled to offer. But, before actually leaving feedback, please consider the following two points: 1. Please mention in your positive comments what you thought was done well, and mention in your negative comments how the article can be altered to better suit your needs/expectations; 2. If you intend on criticizing "missing" information that you feel would be relevant to this article, please be sure you read through all of the others in this Snake Venom series first in order to see if your concerns are addressed elsewhere.

If you enjoyed this article and would like to find out how you can help support snake venom research examining the pharmaceutical potential of various snake venom compounds, please check out my profile. Thank you for reading!

An Example of Myotoxic Effects: Tetanic Paralysis

Handbook of Venoms and Toxins of Reptiles
Handbook of Venoms and Toxins of Reptiles

This book provides the most up-to-date, comprehensive coverage on the venom composition of both front- and rear-fanged snakes.

 

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      ChristopherJRex 2 years ago from Fort Wayne, IN

      Zannatul Sakina: I'm glad this information could help! Thanks for reading!

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      Zannatul Sakina 2 years ago

      it's really helpful for my research

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      ChristopherJRex 4 years ago from Fort Wayne, IN

      R.S.: I'm glad that you appreciated the article! Thanks!

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      R.S. 4 years ago

      it is so useful to know more information of snake venom

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