Figure 6.
Two different models of amyloid polymerization. (A) Proposed proceeding of amyloidogenesis followed by HET-s(218-289). The soluble random coil monomer is subjected to a slow nucleation process (k1) and the nucleus formed is barely detectable. A rapid elongation then takes place (k2) by addition of unfolded monomers in a sort of template-assisted β-sheet structuration. The protofibril grew with the addition of soluble monomers, and then formed more complex and twisted fibers and bundles. (B) M8 amyloid followed a different pathway of aggregation. The soluble random coil form of M8 was only observed at pH 2.0. At pH 7.4, the process of polymerization started instantly (k3) by forming antiparallel β-sheet species. These species assembled into 10-nm-diameter oligomers and then into short fibers (∼10 × 100 nm).