On-Pathway Oligomer of Human Islet Amyloid Polypeptide Induced and Stabilized by Mechanical Rotation during Magic Angle Spinning Nuclear Magnetic Resonance

Intermediates along the fibrillation pathway are generally considered to be the toxic species responsible for the pathologies of amyloid diseases. However, structural studies of these species have been hampered by heterogeneity and poor stability under standard aqueous conditions. Here, we report a novel methodology for producing stable, on-pathway oligomers of the human type-2 diabetes-associated islet amyloid polypeptide (hIAPP or amylin) using the mechanical forces associated with magic angle spinning (MAS). The species were a heterogeneous mixture of globular and short rod-like species with significant β-sheet content and the capability of seeding hIAPP fibrillation. We used MAS nuclear magnetic resonance to demonstrate that the nature of the species was sensitive to sample conditions, including peptide concentration, ionic strength, and buffer. The methodology should be suitable for studies of other aggregating systems.