|Conformational variations in an infectious protein determine prion strain differences.|
Tanaka M, Chien P, Naber N, Cooke R, Weissman JS
Category: prions ¤ Added: Mar 18, 2004 ¤ Rating: ◊◊◊
A remarkable feature of prion biology is the strain phenomenon wherein prion particles apparently composed of the same protein lead to phenotypically distinct transmissible states14. To reconcile the existence of strains with the protein-only hypothesis of prion transmission, it has been proposed that a single protein can misfold into multiple distinct infectious forms, one for each different strain13,5. Several studies have found correlations between strain phenotypes and conformations of prion particles6 10; however, whether such differences cause or are simply a secondary manifestation of prion strains remains unclear, largely due to the difficulty of creating infectious material from pure protein3,5. Here we report a high-efficiency protocol for infecting yeast with the [PSI1] prion using amyloids composed of a recombinant Sup35 fragment (Sup-NM). Using thermal stability and electron paramagnetic resonance spectroscopy, we demonstrate that Sup-NM amyloids formed at different temperatures adopt distinct, stably propagating conformations. Infection of yeast with these different amyloid conformations leads to different [PSI1] strains. These results establish that Sup- NM adopts an infectious conformation before entering the cell fulfilling a key prediction of the prion hypothesis5and directly demonstrate that differences in the conformation of the infectious protein determine prion strain variation.