X-Ray fiber and powder diffraction of PrP prion peptides.

A conformational change from the alpha-helical, cellular form of prion to the beta-sheet, scrapie (infectious) form is the central event for prion replication. The folding mechanism underlying this conformational change has not yet been deciphered. Here, we review prion pathology and summarize X-ray fiber and powder diffraction studies on the N-terminal fragments of prion protein and on short sequences that initiate the beta-assembly for various fibrils, including poly(L-alanine) and poly(L-glutamine). We discuss how the quarter-staggered beta-sheet assembly (like in polyalanine) and polar-zipper beta-sheet formation (like in polyglutamine) may be involved in the formation of the scrapie form of prion.