Direct observation of minimum-sized amyloid fibrils using solution NMR spectroscopy

It is challenging to investigate the structure and dynamics of amyloid fibrils at the residue and atomic resolution because of their high molecular weight and heterogeneous properties Here, we used solution nuclear magnetic resonance (NMR) spectroscopy to characterize the conformation and flexibility of amyloid fibrils of beta(2)-microglobulin (beta 2m), for which direct observation of solution NMR could not be made Ultrasonication led to fragmentation producing a solution of minimum-sized fibrils with a molecular weight of around 6 MDa In H-1-N-15 heteronuclear single-quantum correlation measurements, five signals, derived from N-terminal residues (i e, Ile1, Gln2, Arg3, Thr4, and Lys6), were newly detected Signal strength decreased with the distance from the N-terminal end Capping experiments with the unlabeled beta 2m monomer indicated that the signals originated from molecules located inside the fibrils Ultrasonication makes the residues with moderate flexibility observable by reducing size of the fibrils Thus, solution NMR measurements of ultrasonicated fibrils will be promising for studying the structure and dynamics of fibrils