Electron microscopy was employed to characterize the morphologies of the fibril samples that we prepared from the small peptides, amylin 20 ). Full-length amylin forms two different fibril species, where the predominate species that we observe exhibits a straight, unbranched morphology for both sample 1 and 2. In contrast, the minor population of fibrils in our TEM imaging experiments for both sample 1 and 2 adopt twisted rope-like morphologies (Figure ,f and S1e,f).