Figure 7.

This model describes the formation of protofibrils and type I and type II fibrils from filaments. The model posits that two filaments intertwine to form a protofibril. Two protofibrils pack against each other, as shown, to form a type I fibril, in which the average height of the fibril is less than twice the average protofibril height. Based on the filament and protofibril dimensions, the model predicts a maximum height (diameter) for type I fibrils of 9.1 nm, which is in good agreement with the observed value, 8.8 ± 0.4 nm. The model also predicts that the type II fibrils are made of three filaments.