Transmissible Spongiform Encephalopathies, or prion diseases are the result of proteins trying to fold properly but getting it wrong. When proteins get it wrong in mammals it can lead to horrible diseases such as Kuru which causes people to slowly loose motor function and die while completely aware in their minds.
What’s interesting about infectious prion proteins that we have not already talked about is that they can sometimes be beneficial. For example cells containing yeast prions when exposed to certain unsavory conditions can actually fare better than their prion-free siblings. This suggests that the ability to adopt an advantageous prion form may result from positive evolutionary selection in fungi.
Good for you fungi!
Too bad when prions fold improperly in humans they cause the protein to go berserk and kill the host.