Cryo-EM structure and inhibitor design of human IAPP (amylin) fibrils

Abstract

Human islet amyloid polypeptide (hIAPP, or amylin) is a 37 amino acid hormone secreted by pancreatic islet {beta}-cells. Aggregation of hIAPP into amyloid fibrils is found in more than 90% of Type-II Diabetes (T2D) patients and is considered to be associated with T2D pathology. Although different models have been proposed, the high resolution structure of hIAPP fibrils is unknown. Here we report the cryo-EM structure of recombinant full-length hIAPP fibrils. The fibril is composed of two symmetrically-related protofilaments with ordered residues 14-37 that meet at a 14-residue central hydrophobic core. Our hIAPP fibril structure (i) supports the previous hypothesis that residues 20-29, especially 23-29 are the primary amyloid core of hIAPP, (ii) suggests a molecular mechanism for the action of the hIAPP hereditary mutation S20G, (iii) explains why the 6 residue substitutions in rodent IAPP prevent aggregation, and (iv) suggests possible regions responsible for the observed hIAPP cross-seeding with {beta}-amyloid. Furthermore, we performed structure-based inhibitor design to generate potential hIAPP aggregation inhibitors via a capping strategy. Four of the designed candidates delay hIAPP aggregation in vitro, providing a starting point for the development of T2D therapeutics and proof-of-concept that the capping strategy can be used on full-length cryo-EM fibril structures.