Thursday, April 07, 2005

Evolution of Snake Venom

In related news, it seems that the evolution of snake venom is not so mysterious either:

This study analyzed the origin and evolution of snake venom proteome by means of phylogenetic analysis of the amino acid sequences of the toxins and related nonvenom proteins. The snake toxins were shown to have arisen from recruitment events of genes from within the following protein families: acetylcholinesterase, ADAM (disintegrin/metalloproteinase), AVIT, complement C3, crotasin/ defensin, cystatin, endothelin, factor V, factor X, kallikrein, kunitz-type proteinase inhibitor, LYNX/SLUR, L-amino oxidase, lectin, natriuretic peptide, nerve growth factor, phospholipase A2, SPla/Ryanodine, vascular endothelial growth factor, and whey acidic protein/secretory leukoproteinase inhibitor. Toxin recruitment events were found to have occurred at least 24 times in the evolution of snake venom. Two of these toxin derivations (CRISP and kallikrein toxins) appear to have been actually the result of modifications of existing salivary proteins rather than gene recruitment events. One snake toxin type, the waglerin peptides from Tropidolaemus wagleri (Wagler's Viper), did not have a match with known proteins and may be derived from a uniquely reptilian peptide. All of the snake toxin types still possess the bioactivity of the ancestral proteins in at least some of the toxin isoforms. However, this study revealed that the toxin types, where the ancestral protein was extensively cysteine cross-linked, were the ones that flourished into functionally diverse, novel toxin multigene families.

Sorry about the technical language. That's the abstract of a brief article by Bryan Fry, of the university of Melbourne, Australia. The more approachable version can be found in this article from The New York Times, by Carl Zimmer:

Ultimately, this rush is not what drives Dr. Fry, who is 34. His goal is to decipher the evolution of snake venoms over the past 60 million years. Reconstructing their history will help lead to medical breakthroughs, Dr. Fry believes. For the past 35 years, scientists have been turning snake venoms into drugs. Just this February, Dr. Fry and his colleagues filed a patent for a molecule found in the venom of the inland taipan that may help treat congestive heart failure.

Understanding the evolution of snake venoms will speed up these discoveries immensely, Dr. Fry predicted. “You need a good road map to get your research going,” he said.

And from later in the article:

Dr. Fry has constructed evolutionary trees of these venom genes, and his results indicate that venom actually evolved only once in snakes. It started out being produced at low levels, as illustrated today by garter snakes. Later some lineages evolved a more deadly bite.

“It's been the most important adaptation in the history of snakes,” Dr. Fry argued. The snakes that evolved venom no longer had to rely solely on constriction or other ways of physically subduing their prey. “It's freed them up from having to be big-muscled and slow-moving and killing their prey using constriction,” he said. “They can be light, agile, athletic, and they can occupy any niche from the bottom of the ocean to the top of the tallest tree.”

Dr. Fry's research has also shed light on the origin of venom molecules. A number of researchers have suggested that venom toxins are modified saliva proteins. They point out that ordinary saliva proteins are able to start breaking down food in the mouth. Perhaps some tinkering was all that was necessary to turn them into lethal poisons.

As Dr. Fry reports in the March issue of Genome Research, the DNA of venom genes goes against this idea. He constructed evolutionary trees of 24 venom genes, searching through online databases for their closest relatives among nonvenom genes. In only two cases did he find that venom genes evolved from saliva genes. In almost all the other cases, venom genes evolved from ones that were active outside the venom gland - in the blood, for example, as well as the brain and liver.

The evidence indicates that the evolution of a typical venom gene may begin with the accidental duplication of a gene that is active in another organ. In a process known as gene recruitment, one of these copies then mutates in such a way that it begins producing proteins in the venom gland.

In some cases, these borrowed proteins turn out to be harmful when injected into a snake's prey. Natural selection then favors mutations that make these proteins more lethal.

When I look at what actual biologists do I find them working their tails off to solve actual problems of potential importance to people's day-to-day lives. I find them using evolutionary theory as a tool for guiding them towards research projects that are likely to yield fruit.

When I look at what ID folks do, I see them desperately trying to make a virtue out of ignorance. I see people who make no attempt to do any sort of actual science based on ID, and who devote their lives to tearing down the work of others. They do this solely because their weak faith in God can only be maintained by finding scientific gaps for Him to fill. Pathetic.


At 3:38 PM, Anonymous Anonymous said...

The evidence indicates that the evolution of a typical venom gene may begin with the accidental duplication of a gene that is active in another organ. In a process known as gene recruitment, one of these copies then mutates in such a way that it begins producing proteins in the venom gland.

But that's impossible because then you would have an increase in information, which we all know can't happen because Ken Ham says so. ;-)

At 9:57 PM, Blogger itisnt said...

Nice article. A simple mechanism for venom evolution that makes sense, with many of the stages backed up with evidence. Exactly the kind of thing to add to the arsenal. I will probably use this on the next anti-evolutionist I find spouting off on a random forum.

Of course I can almost predict the kind of reply I will get:

"But the evolution of snake venom is actually a decrease in information because snake venom kills people which isn't a good thing!"


"So this venom gene came from a gene in the liver, but where did that come from? If you don't know that then the evolution of venom obviously didn't happen"


"So what? The genes in the liver and the venom just look similar. This is more evidence of a designer reusing parts. Intelligent Design predicts this [and would predict any other possible reality too]"


"Yes but you know they found man tracks alongside dinosaurs - explain that!"


"but everyone knows that mutations just harm organisms as proved at chernobyl."

It can be quite entertaining trying to predict an anti-evolutionists repsonse to your answers. I never guess correctly, they always come up with something amusingly original and fustrating.

At 1:31 PM, Anonymous Anonymous said...

"...desperately trying to make a virtue out of ignorance."

That really was brilliant. Maybe it's been said before, in different ways...but that was the first time I've seen it. I will be paraphrasing you for years to come in discussions with certain people I know. Many thanks.

At 8:26 PM, Anonymous Dr. Bryan Grieg Fry said...

I've just discovered this site and I've had a good trawl through the various areas.

Perhaps I've been locked away in the lab too much, or out in the field enjoying nature, or maybe we just do things differently here in Australia but I must say I was absolutely shocked when I started reading about the amount of anti-evolution legislation being pushed in the US, specifically the absolutely incomprehensible 'intelligent design' being advocated as an alternative to evolution in school teaching.

I am absolutely dumbfounded that the believe in god is actually increasing! The entire idea of a supernatural being was put in place long ago to explain natural phenomena for which an obvious explanation was lacking (e.g. start with the volcano god and go from there).

The idea of a finite existance is an awful concept to have to come to terms with but hey, thats life (pun fully intended). If someone needs to believe in god as an emotional security blanket in order to get through the day, no worries. However, don't try to push this illogical drivel on anyone else. I must say that I find the rise of religious fundamentalism to be troubling.


At 8:31 AM, Anonymous Anonymous said...

Did hemotoxic venom or neurotoxic venom evolve first?

At 6:29 PM, Anonymous Anonymous said...

I came across your work when disputing the claims of a creationist - it was a great help. But please don't sneer about those people who have faith. I myself am a Christian who believes in the Creator God and I know that one of the biggest barriers to the general acceptance of evolution is the athiest baggage unfairly dumped on it. Maybe one day you'll be able to see that too. I hope so.

At 8:15 AM, Blogger Bac Pham said...

Some animals are very sensitive to snake venom, like birds, others not, like mongooses that consume venomous snakes and some species, like snake eating snakes (king cobra, king snakes), 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. Ultimately, the aggressiveness is important on appreciating the danger posed by a snake species, and most Elapids and Viperids are both aggressive and highly satisfactionOrthopedic Dog Beds

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So this venom gene came from a gene in the liver

At 8:22 AM, Blogger Unknown said...

We got us two different events that we need to take into consideration
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At 7:26 PM, Anonymous Anonymous said...

For an atheist to claim that he or she knows without a doubt that God does not exist, is to claim that he or she has examined every single shred of evidence that ever has or ever will exist and that he or she in fact, knows everything.

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