Proteins and Enzymes

ID #2333

Is it correct that all primary structures are unique and that there are no proteins with similar ones? If so, then how do prions misfold proteins? I read that they misfold the ones with similar primary structures.


It's important to remember that prions are the exception to the rule (and that how they do what they do is not understood yet). 
The primary structure of a protein is its amino acid sequence. It would be incredibly unlikely to find two non-similar proteins containing the exact same amino acid sequence. So, we could say with certainty that two proteins containing the exact same amino acid sequence are really two copies of the same protein. 
The secondary structure of a protein is the alpha helix or beta strand interactions we discussed in class. You should know what is interacting to create these secondary structures and what you would need to do in order to unfold the protein back to its primary structure only. 
If we looked at two proteins with the same amino acid sequence (ie identical primary structure), we would expect to see the exact same secondary structure folding (because as I said previously basically we're looking at two copies of the same type of protein). 
However, if one of the two proteins we're looking at is a prion protein, we would notice that even though it has the same amino acid sequence as the other protein, it doesn't have the same secondary structure (so we might say it's misfolded according to its amino acid sequence). 
But for who knows what reason, prions can even go one step further and misfold proteins that share their same primary sequence even though those proteins were properly folded to begin with. Really crazy huh! 
So, the short answer is, we still do not know how prions misfold proteins.

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