2D IR Spectroscopy for the Elucidation of the Effects of Stimuli on Peptide Aggregation and Self-Assembly

Peptide self-assembly has been used to template the growth of metallic and semiconductor nanostructures, form hybrid bio-nano conjugated materials, and create stimuli responsive materials. There is considerable interest in using peptide-based self-assembled nanostructures for biomedical applications such as drug delivery and tissue engineering and regeneration. Understanding the external stimuli which affect peptide aggregation is essential for informing the efficient development of designer proteins and peptide-based self-assembling materials. Proteins readily adsorb on the surface of nanoparticles, which can cause secondary structure change that alters native protein function or induces self-assembly into potentially toxic aggregates. We seek to better understand the nanoparticle-protein interaction mechanisms between an amyloidogenic protein indicated in type II diabetes, human islet amyloid polypeptide (hIAPP), and gold nanoparticles. The roles of nanoparticle features such as capping ligand, size, concentration, as well as surface chemistry on interaction mechanism and aggregation kinetics will be studied using two-dimensional infrared (2D IR) spectroscopy with site-specific ¹³C¹⁸O isotope labeling to observe changes in peptide structure with single-residue structural resolution. From these measurements, transition dipole strength can provide more information on the order and stability throughout aggregation at these sites by measuring the extent of delocalization of the amide I’ vibrational mode between peptides. These methods allow for precise characterization of a broad range of peptide-based macrostructures, not just biologically relevant ones. Other stimulated conformational changes often relevant in self-assembling materials, such as pH and temperature, can also be studied at steady state using traditional 2D IR. Steady state analysis; however, does not provide information on the mechanism of assembly or aggregation. To elucidate the mechanisms of these phenomena, we report progress towards transient 2D IR studies of protein structure following a pH jump. This technique can be applied to self-assembling peptide systems to analyze the assembly process and inform efficient design of these systems.