Beyond DNA! Prions Point to a New Form of Evolution in Nature (VIDEO)



In 2010 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 (image below) 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 showed 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.

More recently, researchers at MIT (see video below) have discovered that prion molecules can clamp onto DNA and prevent some parts of the sequence from being read, leading to genetic changes through a process that is known as epigenetics vs the standard view is that new traits can only evolve if DNA itself changes in some way by mutating the genetic code. Susan Lindquist at the Whitehead Institute for Biomedical Research at MIT, first discovered this process, which she calls "combinatorial evolution", in 2004, while studying lab-grown Baker's yeast.

"We've been saying this is really cool and a way of producing new traits for years, but other people have said it's a disease of lab yeast," she says. Yeast breaks the mould. In challenging conditions, it can instantly churn out hundreds of brand-new and potentially lifesaving proteins from its DNA, all without changing the genes in any way. Instead, yeast alters the way genes are read. The tiny fungi convert a special type of protein called Sup35 into a prion.

Sup35 normally plays an important role in the protein production line. It makes sure that the ribosomes within cells, in which the proteins are built, start and stop reading an RNA strand at just the right points to generate a certain protein. When Sup35 transforms into a prion, it no longer performs that role. With this quality control missing, the entire gene sequence is read as it spools through the ribosome.

This generates new proteins from sections of RNA that are usually ignored . The result is that the yeast generates a brew of brand-new proteins without changing its DNA . Within that mix of new proteins could be some that are crucial for survival.

Lindquist has proved sceptics in the scientific community wrong by demonstrating beyond doubt that the same process at work in 255 of 700 natural yeasts she and her colleagues have studied. Lindquist grew the yeast in hostile oxygen-depleted or abnormally acidic environments, for example, and then exposed the survivors to a chemical that destroys prions. Many colonies withered, showing that the prions were responsible for their competitive edge. The prions are passed down in mating, so daughter cells will also make the same suite of survivor proteins.

"First and foremost it's an adaptive strategy," says Lindquist. "It's a great way of acquiring new [physical traits]." Lindquist says that it is even possible for the production of the new proteins to become "hard-wired" into the genome, through mutation in the genetic code, although she has yet to see this happen.

It remains uncertain, however, whether combinatorial evolution is a quirk of yeast biology or a more general fact of life, but researchers are hoping that prions play an important role in natural evolution.

The Daily Galaxy via, newscientist, and

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