Good Amyloid, Bad Amyloid—What’s the Difference?

Amyloids have had some bad press. From Alzheimer to Parkinson, Huntington to Creutzfeldt-Jakob, amyloids are best known for their role in causing some very serious human diseases. The usual story is that the structure of a perfectly respectable, neatly folded (and usually soluble) protein is disrupted in some way, making it refold into a new "cross-beta" structure that predisposes multiple copies of that protein to tile together into a massive insoluble fibrous deposit. The trigger may be a mutation, an unusual cleavage pattern, a post-translational modification, or even (in the case of a class of amyloids called prions) infection by a ready-formed amyloid, but the end point tends to be the same-insoluble protein, cognitive problems, and eventual neurodegeneration.