Model for the growth mechanism of fibrillar oligomers.

<p>Elongation of protofilaments and thickening to protofilament pairs can occur in the following steps: (1) aggregation of monomers forming small protofilaments; (2) and (3) elongation of protofilaments along the longitudinal growth axis; (4) fragmentation of large protofilaments into small protofilaments; (5) merging of two small protofilaments leading to a small protofilament pair; (6) addition of monomers elongating small protofilament pairs; (7) merging of two medium protofilaments leading to a medium protofilament pair; (8) addition of monomers elongating medium protofilament pairs; and (9) downstream aggregation of A via elongation of large protofilament pairs to fibrils and plaques.