How to Get Insight into Amyloid Structure and Formation from Infrared Spectroscopy.

There is an enormous amount of interest in the structures and formation mechanisms of amyloid fibers. In this Perspective, we review the most common structural motifs of amyloid fibers and discuss how infrared spectroscopy and isotope labeling can be used to identify their structures and aggregation kinetics. We present three specific strategies, site-specific labeling to obtain residue-by-residue structural information, isotope dilution of uniformly labeled proteins for identifying structural folds and protein mixtures, and expressed protein ligation for studying the domain structures of large proteins. For each of these methods, vibrational couplings are the source of the identifying features in the infrared spectrum. Examples are provided using the proteins hIAPP, Aβ, polyglutamine, and γD-crystallin. We focus on FTIR spectroscopy but also describe new observables made possible by 2D IR spectroscopy.