Prion peptide fragment that shares many physiochemical features with PrPSc. Exhibits neurotoxicity caused by amplification of PrPC-associated signaling responses and induces NF-κB-mediated apoptosis in the mouse neuroblastoma cell line N2a. Forms β-sheet-rich, insoluble, protease-resistant fibrils and is used as a model to study prion diseases in vitro.