 studies of yeast and mammalian prions introduced the idea that the protein aggregates can exist in multiple stable conformations that can be propagated by seeding . these conformational states ( aka strains ) were shown to have distinct physical ( secondary structure , stability ) and biological ( cytotoxicity , infectivity ) properties . for mammalian prions 
 they were also tied to differences in disease pathology and incubation time . 
 it was later shown that this phenomenon is not limited to prion proteins , and distinct conformational states of amyloid fibrils and oligomers derived from a variety of proteins can be propagated both in vitro and in vivo . moreover , in some cases these conformations were preserved even when propagated into a protein with a different sequence . 
 there is now an increasing body of evidence that strain phenomenon is a generic feature of protein aggregation , and characteristic features of amyloid strains can be transmitted between unrelated sequences . 
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