PPIB and Parkinson disease: Other toxic amyloid-forming proteins also adopt an antiparallel β-sheet conformation, such as the amyloid-β peptide involved in Alzheimer’s disease, and α-synuclein related to Parkinson’s disease (Cerf et al., 2009; Celej et al., 2012), suggesting that the antiparallel β-sheet is a signature of amyloid toxicity.