PRNP and Alzheimer disease: The PHF purified from AD subjects and the PHF digested with proteinase K were specific selectors of the dominant ß-sheet secondary structure associated with tau toxic oligomers (Figs 3 and 4)10, 25, 26, 30, 34, 35, while the deer recombinant PrP served as an example of aggregation through ß-sheet dominant motifs similar to that found in oligomeric PrPRes25, 30.