Protease resistance of amyloid fibrils implies the proteolytic selection of disease-associated fibril morphologies.

Several studies recently showed that fibrils from patient or animal tissue were structurally different from formed fibrils from the same polypeptide chain. Analysis of serum amyloid A (SAA) and Aβ-derived amyloid fibrils additionally revealed that fibrils were more protease stable than fibrils. These observations gave rise to the proteolytic selection hypothesis that suggested that disease-associated amyloid fibrils were selected inside the body by their ability to resist endogenous clearance mechanisms. We here show, for more than twenty different fibril samples, that fibrils are more protease stable than fibrils. These data support the idea of a proteolytic selection of pathogenic amyloid fibril morphologies and help to explain why only few amino acid sequences lead to amyloid diseases, although many, if not all, polypeptide chains can form amyloid fibrils .