Prions Speed Evolution

Usually, we think of prions as nasty little things, which do only harm.  They cause Mad Cow disease, and variant Creutzfeldt-Jakob disease (vCJD).  Now we find that they serve a useful purpose, in at least one instance; this is reported in today's news@Nature.com:


Prions speed evolution
Published online: 16 August 2004;  | doi:10.1038/news040816-1
Helen Pearson
Sloppy proteins may help organisms adapt.

Prions, the twisted proteins usually linked to disease, could help organisms adapt to tough situations by subtly altering the proteins manufactured by a cell. The discovery backs the idea that proteins as well as DNA are vital in driving evolution. [...]

But scientists studying yeast (Saccharomyces cerevisiae) have found that, in some cases, infectious prions may have an important role. In a colony of yeast cells, some cells carry the 'normal' type of the protein, whereas others harbour the infectious form, which accumulates into clumps and is passed from one cell to another.

But scientists studying yeast (Saccharomyces cerevisiae) have found that, in some cases, infectious prions may have an important role. In a colony of yeast cells, some cells carry the 'normal' type of the protein, whereas others harbour the infectious form, which accumulates into clumps and is passed from one cell to another.

Four years ago, Susan Lindquist and Heather True of the Whitehead Institute in Cambridge, Massachusetts, showed that this yeast prion can change the way that cells behave. In their infectious form, the prions sometimes helped the yeast to adapt, changing their rates of survival when they were grown in various nutrients or temperatures.

Now Lindquist and her colleagues have worked out how the prions do this. In its non-infectious form, the protein normally helps to read and convert the DNA code into other proteins. But in its infectious form, the prion stops working. This means that many proteins are manufactured slightly sloppily.

The team believes that prions may therefore offer a speedy way for yeast to evolve, because those cells with the infectious prion churn out a whole range of slightly altered proteins. Normally this is bad news for the yeast, but when the cells find themselves in a tough spot, one or two of them may grow better in the new conditions as a result, and so help the colony to survive.

The significance of this is more theoretical than practical at this point, since no one really cares about yeast.  But, anything that advances our knowledge of prions is welcome.  Although it is not yet obvious that there could be a clinical application for this discovery, it is possible that a better understanding of the behavior of prions could lead to some kind of treatment. 

In addition, anything that advances our understanding of the molecular mechanisms of evolution is welcome.  In this case, we see a way that an organism can speed up the process of evolution in times of duress.  This is another example of a new discovery that simply reinforces the overall Theory of Evolution.  There are those who are waiting for that one great discovery that will blow the Theory apart.  I guess they simply will have to keep waiting. 

If the Nature article does not satiate your curiosity about this subject, there is a little more detail available here, at Eureka Alert.  More information about Dr. Lindquist's work with prions and yeast is available here (Are We as Crazy as Mad Cows?), at MITworld