Low-frequency Raman spectra of amyloid fibrils.

We report on how low-frequency Raman measurements can be used as a facile tool to investigate the supramolecular structure of amyloid fibrils. We investigate the low-frequency Raman spectra (<500 cm-1) of six different amyloid fibrils exhibiting parallel β-sheet structures prepared from amyloid-β1-40, amylin, amyloid-β25-35, and amylin20-29 peptides. We propose band assignments using a combination of semi-empirical tight-binding calculations and insights gleaned from previously published studies on model polypeptides in β-sheet conformations. We discuss how low-frequency Raman modes can be used to probe the interactions, packing, and ordering of strands and side chains within fibril β-sheets to gain insights into their supramolecular structures.