We've all heard of Mad Cow Disease... no not the one that has cows retaliating for the whole cow tipping phenomenon, the one that has everyone scared that if they eat a cow, they are going to go crazy. In case you haven't heard or if you don't know much behind the biology of it, I'll give you a little primer.
Prions are proteins that in their natural state are responsible for... well, we don't know really. A recent Nature article says that we are narrowing down their role...
There is now increasing, albeit patchy, evidence that the process of prion infection might have a vital role in a large number of biological processes—not only in single-celled organisms but also in higher eukaryotes—ranging from adaptation to new environments to the establishment of long-term memory.
...Ok, so it's not narrowed down much.
But anyway the interesting point about these proteins is that when they are folded in the "prion" conformation, they are almost impossible to degrade. Which means they don't go away. Ever. Which is bad in the brain. Even heating to very high temperatures doesn't harm these proteins.
Here is the next really cool thing about prions, well morbidly cool anyway... when a prion protein comes into contact with a native form of the prion protein, the native protein changes conformation and becomes highly stable as well. So not only do prions stick around, but they make others just like them.
And the scary thing about this kind of protein is that a lot of animals have them. Sheep have them, the disease they cause is scrapies. Cows have them, that disease is actually called bovine spongiform encephalitis (BSE). And humans get it, one form of it is called Crutzfeld-Jacob disease. The worst part about it is if we were to eat a cow that had BSE, those prion proteins could start interacting with our normal proteins and give us the human form of the disease.
Recently, a group has produced genetically engineered cows - over a dozen of them - that don't have the message for this protein (December's Nature Biotechnology). Which means they can't get the disease. These cows are almost 2 years old now and... At over 20 months of age, the cattle are clinically, physiologically, histopathologically, immunologically and reproductively normal.
So, I'm left with a nagging question... What the heck is this protein for?
6 comments:
Prions are probably just out to make copies of themselves, and it looks like they're doing an awfully good job of it. Plus they're virtually indestructible. What more can you ask?
In terms of a physiological role for the native cellular prion protein (PrPC), this protein has been shown to protect cells against oxidative stress (J. Biol. Chem. Vol. 280, pp. 35914-35921, 2005). Reactive oxygen species cause cleavage of PrPC at the end of of the copper-binding octapeptide repeats, a process termed beta-cleavage. Cells expressing mutated forms of PrPC (instead of wild-type PrPC) were more susceptible to oxidative stress, exhibited reduced viability, decreased glutathione peroxidase activity and higher levels of intracellular free radicals. The authors concluded that beta-cleavage of the native form of PrPC is an early and critical event in the protection of cells from oxidative stress.
Terri,
I haven't been keeping up - is there a causal connection between BSE & Creutzfeldt-Jakob, or is this based on small sample statistics?
Kuru is also a bit like BSE.
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