|MadSci Network: Biochemistry|
Hi Hector, Prions are a very interesting topic because there is still a lot of debate over whether a protein can initiate changes in other proteins to cause disease or if these proteins are just manifestations of another underlying process. Anyway, prions are known to be responsible for diseases such as Bovine Spongiform Encephalitis(mad-cow), Creutzfeldt- Jakob disease, and Scrapies. What essentially happens is that an animal eats something that contains the prion from a similar animal. This prion is acid, heat, UV, and other denaturing agent resistant due to it's very hearty tertiary structure(which I will get to in a minute). It somehow finds normal precursor proteins, called PrP for short, and converts them to Prions. These guys then accumulate in tissue, the effects of which especially apparant when it involves the brain because neurological symptoms arise like Mad-cow disease. Tertiary structure as you may know has to do with folding of a protein into a 3-D shape. This shape depends on things like primary stucture(amino acid sequence) and secondary structure (alpha helix aka twists and beta pleated sheets aka turns) as well as the type of environment it is in(water, lipid). What makes a protein hardy is the number of crosslinks it has, especially by cysteine residues that form disulfide bonds. Let's take curly hair for example. It has a lots of disulfide bonds that hold the structure of all those proteins in their normal shape. It is fairly resistant to heat(barring the extreme) and such, but when we add something like beta-mercaptoethanol the disulfide bonds break and we can straighten the hair out. Other factors like hydrophobic regions also aid to hold tertiary structure and unless you remove the insulting environmental water those regions of the protein will do their best to exlude water through electrochemical interactions. Prions are just very good at resisting all those insulting factors that would otherwise denature it. It is a little more complex than what I have said above, but that is the basic idea. For more, and better, information on prions I suggest you check out this article found in the journal called PNAS (or Proceedings of the National Acadamy of Science). It is by Stanley B. Prusiner who is at the forefront of prion research. It is an overview of prions, with a lot of technical info but I am sure that you'll have a better understanding of these interesting proteins after reading this. You can find it in Vol. 95, Issue 23, pages 13363- 13383, November 10, 1998. It is simply titled Prions. Good reading. Mark Sullivan
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