Prions Challenge the Definition of Life

[n2doc]

Earlier this year, scientists from the Scripps Research Institute showed for the first time that 'lifeless' organic substances with no genetic material — prions similar to those believed responsible for Mad Cow disease and similar, rare conditions in humans — are capable of evolving just like higher forms of life, a discovery that could reshape the definition of life and have revolutionary impacts on how certain diseases are treated."

Natural selection is incredibly useful: it's resulted in everything alive so far, including us, it works to improve it all even now. The scientists at the Scripps Research Institute have shown that you don't even need to be alive to evolve, with prion protein populations enjoying natural selection.

A prion is a chunk of protein, which doesn't sound like much because people don't appreciate how complex those things can be. Large proteins are to chemistry what War and Peace is to the alphabet: incredibly long and stuffed with more data than the human mind knows what to do with. Even the shape encodes information, and amazingly that's the aspect attacked by infectious prions – they're transmitted shapes, twisting healthy prions into catalytic carriers of their own twisted form.
Normal prions, including the ones in your brain, are water-soluble. Which is good because you're mostly water. In prion problems like Creutzfeld-Jakob disease, an 'infected' prion has been folded into a lower energy but non-water-soluble configuration, the exact same chemicals simply arranged in a different way – which alters its chemical properties. This becomes a tiny grain in your brain which triggers the same shift in shape in other prions, building a growing chunk of protein inside your skull. With predictably disastrous results.

What Professor Charles Weissmann and colleagues of the Department of Infectology have shown is that these shapes can evolve and adapt like lifeforms with DNA. As they 'replicate' by triggering shifts in other host prions there are an array of minor errors and changes, and in different conditions the best-suited shapes survive and multiply faster. It turns out that “things better suited to replicating in an environment will replicate better in that environment” is a tautology, not a controversial theory.

-Luke McKinney
http://www.dailygalaxy.com/my_weblog/2010/12/prions-challenge-the-definition-of-life-todays-most-popular.html

[txlibdem]

1. Mmmm, Prions. I like my Mad Cow medium-rare, please!

Just kidding, I gag if my meat isn't completely cooked. I never go out to a steak restaurant because the cook gets insulted when I send my plate back or ask up front to cut it into medallions so it can be fully cooked. Well done is well done.

[snagglepuss]

3. Heat does not kill prions which is why it is critical to for slaughter houses

to be vigilant however given the gross negligence witnessed in slaughter houses new cases of BSE will continue to surface. The only thing consumers can do to protect themselves is not eat any ground meat products as BSE is found in brain and spinal cord tissue and often slaughter houses are very sloppy about insuring those tissues stay out of ground meat.

If you want risk free hamburger, grind your own meat.

[qazplm]

4. yeah i generally only eat steak

I rarely eat burgers anymore but in all honesty, that's mostly because I'm getting too fat. :)

Thankfully, prions are still extremely rare in our food supply comparatively but sooner or later that could change.

[txlibdem]

6. Remember the old A-1 Steak Sauce commercials?

The guy was putting A-1 on his hamburger and said, "What is Hamburger? Is it chopped ham? No! It's chopped steak!"

[Jim__]

2. Wikipedia has a pretty good description of some ideas about how prions replicate

The first hypothesis that tried to explain how prions replicate in a protein-only manner was the heterodimer model.<27> This model assumed that a single PrP^Sc molecule binds to a single PrP^C molecule and catalyzes its conversion into PrP^Sc. The two PrP^Sc molecules then come apart and can go on to convert more PrP^C. However, Manfred Eigen showed that since PrP^C has a very low rate of spontaneous conversion into PrP^Sc, the heterodimer model requires PrP^Sc to be an extraordinarily effective catalyst, increasing the rate of the conversion reaction by a factor of around 10^15.<28> What is more, despite considerable effort, infectious monomeric PrP^Sc has never been isolated. Theory and experiments both suggest that PrP^Sc exists only in aggregated forms such as amyloid, and that prion replication involves cooperativity.

An alternative model assumes that PrP^Sc exists only as fibrils, and that fibril ends bind PrP^C and convert it into PrP^Sc. If this were all, then the quantity of prions would increase linearly, forming ever longer fibrils. But exponential growth of both PrP^Sc and of the quantity of infectious particles is observed during prion disease.<29><30><31> This can be explained by taking into account fibril breakage.<32> A mathematical solution for the exponential growth rate resulting from the combination of fibril growth and fibril breakage has been found.<7> The exponential growth rate depends largely on the square root of the PrP^C concentration.<7> The incubation period is determined by the exponential growth rate, and in vivo data on prion diseases in transgenic mice match this prediction.<7> The same square root dependence is also seen in vitro in experiments with a variety of different amyloid proteins.<33>

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[PetrusMonsFormicarum]

5. These arsenic microbes do too.

Back in 2001 I referred to prions as "The Ancient Enemy". I guess we should be grateful that life (according to the current definition, rapidly being undermined as it is) evolves at a faster rate than prions, although I fear that prions, like sharks, don't have the need to evolve: they already do what they are supposed to, and do it well.