Abstract
A critical role of the hormone islet amyloid polypeptide (IAPP) is vividly discussed for Type 2 Diabetes (T2D), where amyloid deposits in pancreatic islets consisting of fibrillar IAPP have been associated with beta cell loss. Here, we applied cryo-electron microscopy to elucidate the structure of IAPP fibrils prepared at physiological pH and reconstructed densities of three dominant polymorphs. An atomic model of the main polymorph comprising residues 13 – 37 in a density map of 4.2 Å resolution reveals two S-shaped, intertwined protofilaments. The segment 21-NNFGAIL-27, which is essential for IAPP amyloidogenicity, forms the protofilament interface together with tyrosine 37 and the amidated C-terminus. The main IAPP fibril polymorph resembles polymorphs of the Alzheimer disease (AD)-associated amyloid-β peptide (Aβ), which is striking in light of the epidemiological link between T2D and AD and reports on IAPP-Aβ cross-seeding in vivo. The results structurally link the early-onset T2D IAPP genetic polymorphism S20G with the early-onset AD Arctic mutation E22G of Aβ, rationalize previous data on IAPP fibrils, help to elucidate mechanisms of amyloid formation and toxicity, and support the design of fibril growth inhibitors as well as imaging probes for early detection of IAPP fibrils.
