Cryo-EM Analysis of the Effect of Seeding with Brain-derived Aβ Amyloid Fibrils

•This study examines the effect of seeding with ex vivo Aβ amyloid fibrils on the fibril morphology in vitro.•Seeded fibrils are right-hand twisted and show a peptide fold that corresponds to the one in the seeds.•The twist and peptide fold of seeded fibrils differ from unseeded fibrils.•Upon multiple rounds of seeding, the propagation of the seed structure loses efficiency and de novo nucleated fibril structures emerge.•These findings imply a competition between seed extension and de novo nucleation in seeded samples.