(A) The primary sequence of aS, with its three parts labeled along with Cu(II), Cu(I), and Atox1-Cu(I) interaction sites. The lipid–vesicle interaction part of aS is also indicated. Typically, in cells, the N-terminus is acetylated. (B) Amyloid formation involves primary nucleation, fiber elongation, and secondary processes (such as secondary nucleation and fiber fragmentation). Cu may affect all these steps. It is not known if Cu(II)/Cu(I) can bind to oligomers or preformed fibers directly. It is also not known where (if) the Cu ions end up in the final amyloid structure when added to aggregating monomers. There may also be off-pathway reactions (not indicated in figure). (C) Amyloid fibers visualized by atomic force microscopy (left) and an example of a high-resolution structure of an aS amyloid (pdb: 2N0A), right.