Design and Characterization of Peptide Modulators of IAPP-Membrane Binding

Abstract

Type II Diabetes (T2D) is characterized by the formation of pancreatic amyloid deposits of the peptide hormone islet amyloid polypeptide (IAPP). Recent evidence suggests that α-helical oligomeric species of IAPP formed en route to, or independently of, amyloid formation may be cytotoxic to β-islet cells of the pancreas and play a role in the pathogenesis of T2D. These α-helical oligomers interact with anionic lipid bilayers, and may cooperatively and transiently convert to leakage-competent oligomers that disrupt the bilayer [Last, Rhoades & Miranker (2011) PNAS 108:9460]. We used Rosetta modeling software and Monte Carlo simulations to rationally design short peptides to selectively bind one of two early intermediate dimer structures of IAPP proposed from single-molecule fluorescence experiments: one hypothesized to lead to the formation of leakage-competent oligomers, and one hypothesized to inhibit such formation. Here we describe the computational design as well as the in vitro characterization of six candidate peptides. Half of the peptides were predicted to preferentially bind a dimer of IAPP believed to lead to leakage-competent oligomers, and half were targeted to a dimer not believed to lead to leakage-competent oligomers. We characterized the short peptides by measuring their effects on IAPP-induced leakage across DOPG liposomes at various concentrations. As another metric for interactions between IAPP and these short peptides, we also performed isothermal titration calorimetry on the binding of the short peptides with IAPP. The methods utilized here could serve useful in studying the mechanism of amyloid formation, and in the development of specific peptide binding partners targeting other proteins.