Excerpt from a letter to a friend:
Scrapie is a disease associated with alot of neurodegenerative diseases in mammals. Here's a table:
|Chronic wasting disease|
|Cattle||Bovine spongiform encephalopathy|
Creutzfeldt-Jakob disease (CJD)
Gerstmann-Straussler-Sheinker Syndrome (GSS)
Fatal familial insomnia
The interesting thing about this disease is that it is transmissible but there is no viral component that has been identified. It seems to spread from association or exposure, and even (or especially) through cannibalistic practices. Needless to say, you wouldn't want to eat the brain of someone with Kuru, even under peer pressure. The main idea so far is that transmission occurs via a protein. There is a protein that is in the nervous system of all of us mammals that appears to be able to misfold. The misfolded protein aggregates and forms amyloid plaques in the brain, just like in Alzheimer's Disease. The normal function of the protein is unknown and the gene for the protein can be removed from mice and the mice develop normally, so it doesn't appear to be essential. Furthermore, removal of the gene makes these mice no longer susceptible to scrapie infection! Ok so the interesting part is that infectivity follows the misfolded protein. If this protein is purified and given to healthy animals (usually by injection into the brain), they get sick after a well defined incubation time. The anomaly is the following: A gene is a sequence in the DNA that specifies the sequence of amino acids to make a protein. The main idea in the protein folding field is that the sequence of a protein determines the three dimensional shape a protein will assume once it is made. Yet healthy animals and sick animals contain the same scrapie protein (by sequence). If the protein is purified from healthy animals and from sick animals and compared, it has the same sequence of amino acids, but a different shape. The "bad" shaped protein seems to be able to convert the other cellular proteins with it's sequence from the normal shape into the bad shape. Thus, once one has been exposed to the protein with the "bad" shape, the "bad" shape is taken on by one's normal cellular scrapie protein, and the sickness and infection are propagated. This is a highly unusual method of disease propagation that raises many questions. Indeed it hasn't been definitively proven yet, and people have been looking for a viral component for years. I'm proposing experiments to address looking at sequence elements that are important for the three dimensional structure of the protein, both its toxic and normal structure, especially I'd like to ask how much of the protein can be manipulated before it loses infectivity so those portions of it can be narrowed down for further study. Protein folding is quite an up and coming field. Since a protein is a linear sequence of amino acids stuck together like popcorn on a string that folds up into a particular shape, you might think of a piece of freshly cooked spaghetti and what it would look like if you dropped it on the floor. The slides at quite a few seminars these days show pictures that look alot like what you might see. The integrity of that squiggly curled up shape seems to be one of the key determinants to life and consciousness as we know it. Did you ever realize that pasta could be so profound?