Venoms and Toxins – An Introduction
There was an overwhelming response to my question about writing on venoms and toxins (Ok, only 3 of my fellow bloggers replied: Thinking Sci-Fi, Science on the Land and Regeneration in Nature). They are three of the good ones though and anyway, I had my mind made up about writing on the topic… (:-)…
I will start with an introductory post on toxins and venoms. My eventual goal is to write a series of posts focusing on one toxic organism, the specific toxin or toxins and mechanism of action and any current or potential medical applications. If you wish, please participate in the poll to help me decide what to start with. Of course, we’ll play it by ear… Here we go!
Nature’s Chemical Weapons
“Nature is the best chemist. During the course of evolution, through literally millions of years, a wide variety of organisms have developed substances used for defense against predators, or to become predators themselves. As part of the evolutionary process, chemical structures beneficial for the survival of the organism are conserved; many of these molecules include small organic toxins.”
This is the very first paragraph of my PhD Dissertation; this should tell you how much do I like this topic…
It is truly amazing how many different chemical structures can be the difference between survival and death in the majestic history of life on Earth. When we think about some of the details about the true chemical diversity that we have in nature, it is no wonder that this embarrassment of riches is used by life. For example, plants and microorganisms account for some 500,000 different chemical compounds with various chemical properties and plants alone are thought to produce about a million tons (!) of chemical compounds every year.
Do you think that when you eat a yummy slice of pizza you are just eating fats, carbohydrates and maybe some protein? Think again; say that you like veggies in your pizza. In addition to the normal nutrients that are in there, there is a multiplicity of compounds with various chemical structures. It is compounds like this that are largely responsible for all the flavors, spiciness and general deliciousness of plant-derived foods for example.
Picture credit: whatthehealthmag.wordpress.com and Baldscientist.
Back to the number of compounds, this is just to start with. Some (conservative) estimation of the possible number or possible organic compounds is in the range of 10 to the power of 60.
Yep, this number:
Give or take a couple of zeroes; it really makes no difference. Keep in mind that this is not the number of organic compounds that actually exists; this is an approximate possible number based on what we know about organic chemistry. We are not even including the many different proteins that can also occur in nature; this is another really rich source of biomolecules of which we’ll talk soon…
Before we go on, there is an important detail; the actual purpose of most of these compounds in nature is to avoid being eaten by insects, hence many of those are classified as toxins. Yes, some of these toxins include some of the very same seasonings of the foods you love (:-D)…
It is important to point out that any given toxin needs to be defined in terms of the affected organism (s). For example, let’s go to a particularly nasty example for us humans. Botulinum toxin (BTX), a bacterial compound, is a perfect example. A dose as small as 0.7 ug can kill a grown person. Just how much is 0.7 ug?
Consider a ½ liter bottle of water:
Picture credit: chrispypaul.blogspot.com
Half a liter of water weights exactly 500 grams. Divide this number by 500 and you get 1 gram (a U.S penny weights about 3 grams, I think I’ve said this in another post). To make the long story short, if you divide a gram a millionfold you get a microgram and 70 % of this tiny amount of Botox (yes, that botox!) can kill a human. In other words, a botox lethal dose weights about 0.000000002 (give or take) as much as a normal bottle of water.
To each his / her own and I am not judging, but I cannot think of many reasons why I would allow such a thing to be injected in my body…
The thing is that there are some animals, generally carrion-eaters like vultures, that are highly resistant to this toxin, which essentially means that to them, BTX is no toxin at all. Therefore, it is important to realize that the ecological or evolutionary context of a toxin is also an important consideration. In virtually every case, the toxicity of a compound against humans is a mere byproduct of its “intended” purpose in nature. We are not the prey of a scorpion, but its venom can hurt or even kill us.
That said, what is the difference between toxins and venoms? Well, toxins are usually referred to as single compounds with a defined molecular target (generally a receptor or any other type of protein). In many instances these compounds are passively secreted (very much like perspiration) and require the “cooperation” of the target. For example, a tobacco plant do not chases after the insect that it wants to avoid. Rather, the toxin is actively ingested by the insect upon trying to feed on the plant.
Venoms, on the other hand, are more or less complex cocktails containing several different types of toxins, each of them with potentially different targets. Additionally, venoms are produced in specialized structures called venom sacs (duh!) and are actively injected to the target animal via specialized structures like fangs, stings, the works. Here are some more formal definitions:
Picture credit: Baldscientist.
Also, there is more than one way for an organism of becoming toxic:
In the example above, all of those organisms contain tetrodotoxin (TTX), an especially toxic toxin (see what I did there?).
By the way, did you see the newspiece about how dolphins seem to get high on tetrodotoxin? One of the main sources of TTX is the pufferfish, a delicacy in Japan where it is prepared as Fugu, which is attractive to some people because of the tingling sensation that it elicits when eating it, a sensation caused by (wait for it…) tetrodotoxin! Each year there is a certain number of deaths directly attributable to improperly prepared Fugu.
Incidentally,when many types of organisms in nature seem to use the same toxin as in the picture above, it is generally an indication that these organisms somehow acquire the toxin from the environment, as it would be unlikely (but not impossible) that such a wide variety of organisms evolve the complex biochemical pathways to synthesize a specific toxin. More on this in a future post.
In our wonderful planet virtually every class of organisms from microbes to mammals have at least one poisonous representative. This is not a new phenomenon in nature; it has been happening for a VERY long time:
As far as bigger organisms go, they oftentimes announce their toxic ways by being especially flashy, usually brightly colored:
These guys are a species of poison arrow frog, a coral snake, a blue-ringed octopus (another one that uses TTX) and a cone snail. Remember the Magnificent Conotoxins?
We have seen a rather brief overview of this fascinating topic. There is much more to say and I am looking forward to it. Remember, please let me know what you think and if you wish, participate in the poll to help me decide what to start with!
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If you want to know more
Brodie ED 3rd (2009) Toxins and venoms. Curr Biol 19(20):R931–35.
Larsson J et al., (2005) Expanding the ChemGPS chemical space with natural products. Journal of Natural Products 68: 985-991.
Leippe M et al., (2005) Ancient weapons: the three-dimensional structure of amoebapore A. Trends Parasitol 21(1):5-7.
Mebs D (2001) Toxicity in animals. Trends in evolution? Toxicon 9(1):87-96.
Pagán OR (2005) Synthetic Local Anesthetics as Alleviators of Cocaine Inhibition of the Human Dopamine Transporter. PhD dissertation. Cornell University, Ithaca, NY.