Seeding-dependent propagation and maturation of amyloid fibril conformation.

Recent studies of amyloid fibrils have focused on the presence of multiple amyloid forms even with one protein and their propagation by seeding, leading to conformational memory. To establish the structural basis of these critical features of amyloid fibrils, we used the amyloidogenic fragment Ser20-Lys41 (K3) of beta2-microglobulin, a protein responsible for dialysis-related amyloidosis. In 20% (v/v) 2,2,2-trifluoroethanol and 10 mM HCl (pH approximately 2), K3 peptide formed two types of amyloid-like fibrils, f218 and f210, differing in the amount of beta-sheet as measured by circular dichroism spectroscopy and Fourier transform infrared spectroscopy. Atomic force microscopy showed that the fibril with a larger amount of beta-sheet (f210) is thinner and longer. Both fibrils were reproduced by seeding, showing the template-dependent propagation of a fibril's conformation. However, upon repeated self-seeding, f218 fibrils were gradually transformed into f210 fibrils, revealing the conformational maturation. The observed maturation can be explained fully by a competitive propagation of two fibrils. The maturation of amyloid fibrils might play a role during the development of amyloidosis.