Biophysical Insights into Amyloid Formation by Islet Amyloid Polypeptide

Abstract

Amyloid deposition has been implicated to play a role in the pathology of over 40 human diseases including Alzheimer's, Parkinson's, type 2 diabetes and systemic amyloidosis, to name a few. All amyloid fibrils are characterized by a cross &beta-pleated sheet structure with interstrand hydrogen bonds running parallel to the long axis of the fibril. Islet amyloid polypeptide (IAPP) is a 37-residue peptide hormone that is the major proteinaceous component of pancreatic islet amyloid deposition that develops during type 2 diabetes. These deposits have been shown to play a role in the decrease of islet mass and &beta-cell apoptosis, which are typical pathologies developed during type 2 diabetes. The aggregation process of how IAPP goes from an unstructured monomer to an ordered peptide aggregate with significant &beta-sheet secondary structure is highly complex and involves a number of transient species that are highly dynamic and metastable. This research provides insights into the biophysical mechanisms and environmental components that can enhance amyloid assembly by IAPP using chemical, biophysical and kinetic methods. My work included the development of a new method to synthesize IAPP via microwave solid-phase peptide synthesis; the examination of the role of aromatic amino acids in IAPP via a triple mutant in which the three aromatic amino acids were substituted with leucines; probing the nature lag phase species populated during amyloid formation via the unnatural fluorescent amino acid, p-cyanophenylalanine; and the study of the effects of ionic strength and ion composition on amyloid formation by IAPP. These studies aim to provide a better understanding of the intrinsic factors inherent to IAPP, as well as extrinsic environmental factors, that can decrease the stability of monomeric IAPP and induce amyloid formation.