Structure-Based Design of Small Peptide Ligands to Inhibit Early-Stage Protein Aggregation Nucleation

We report a structure-based approach to design peptides that can bind to aggregation-prone, partially folded intermediates (PFI) of insulin, thereby inhibiting early stages of aggregation nucleation. We account for the important role of the modular architecture of protein-protein binding interfaces and tertiary structure heterogeneity of the PFIs in the design of peptide inhibitors. The determination of association hotspots revealed that two interface segments are required to capture majority contribution to insulin homodimer binding energy. The selection of peptides that will have a high probability to inhibit insulin self-association was done on the basis of similarity in binding interface coverage of PFI residues in the peptide-PFI complex and the native-PFI dimer. Data on aggregate growth rate and secondary structure for formulations incubated under amyloidogenic conditions show that designed peptides inhibit insulin aggregation in a concentration-dependent manner. The mechanism of aggregation inhibition was probed by determining the enthalpy of peptide-insulin binding and peptide micellization using isothermal titration calorimetry. Finally, the effect of designed peptides on insulin activity was quantified using a spectrophotometric assay for glucose uptake by HepG2 cells.