Steric Crowding of the Turn Region Alters the Tertiary Fold of Amyloid-β18-35 and Makes It Soluble.

Aβ self-assembles into parallel cross-β fibrillar aggregates, which is associated with Alzheimer's disease pathology. A central hairpin turn around residues 23-29 is a defining characteristic of Aβ in its aggregated state. Major biophysical properties of Aβ, including this turn, remain unaltered in the central fragment Aβ18-35.