I understand that prions are misfolded in a way that’s smaller and more spatially efficient than the normal proteins that brain tissue is made out of, and the spread of these smaller proteins causes the tissue to shrink and literally grow holes. What I don’t understand is why the proteins in an infected brain “want” to copy the improper fold pattern – they aren’t sentient, they can’t notice the pattern and think “Why didn’t I try folding like this before, it’s so much more efficient”. If proteins “want” to fold a certain way because of a physical property, what was stopping them from folding that way in the first place? What is it about the introduction of a prion that makes healthy nerve tissue “get the idea” to fold that way?
In: Biology
So proteins fold in a way determined by their amino acid structure, but there are multiple possible ways this can happen. The classic way to imagine this is a series of valleys of different depths. The depth of the valley corresponds to how energetically favourable that conformation is, and the mountains between represent the energy cost it takes to change conformation.
Prion proteins are one specific protein, and they only change their own kind, just to clarify. The misfolded conformation is a deeper valley so to speak, and they can bump other proteins of their kind over the mountain to get there. How they do that mechanically I don’t exactly know.
There are proteins called chaperones which assist in protein folding. They are the reason some proteins are in a shallow valley instead of a deep one, because the chaperone helps them get there, and once they are in the valley they don’t climb the mountain on their own. Prions can kick them over and this is the cause of the problem.
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