Fig 4.

Schematic illustration showing how the peptides might associate to form the ribbons observed by EM. Protofilaments ≈41 Å wide and ≈21 Å high consist of four antiparallel β-sheets of indefinite length running parallel to the axis of the protofilament. β-sheets are organized into two β-sandwiches, where the face-to-face distance between β-sheets is 10.0 and the distance between the faces that pair β-sandwiches is 12.1 Å. The strands of the β-sheets are continuously H-bonded in the direction of the long axis of the fibril, nontwisted with respect to each other and oriented perpendicularly to the plane formed by the fibrillar ribbon. The termini of the β-strands are solvent-exposed.