Structural analysis of intrinsically unstructured proteins using Raman optical activity

A major obstacle in the structural analysis of intrinsically unstructured proteins (IUPs), at least from a classical biological perspective, is precisely that: lack of structure. While the dynamic nature of IUPs makes crystallographic studies virtually impossible, even solution based NMR studies of this group of proteins are difficult, due to the fast, fluid changes in back bone torsion angles. When faced with the lack of well-defined tertiary fold and fast dynamics in IUPs, it arguably may even be redundant to attempt to isolate one single, true " structure " of an IUP. Even so, due to the role of IUPs in age related diseases, it is imperative to develop quick, solution based methods for structurally charac-terising different IUP species, in order to distinguish native IUP " motifs " from their misfolded counterparts. Here, Raman optical activity (ROA) spectroscopy is presented as one such method. While experimental ROA has shown great promise as a tool in structural biology, until recently, the purely empirical nature of ROA studies made detailed structural analysis very difficult. Using state-of-the-art computational approaches, libraries of predicted ROA spectra of model peptides adopting any perceivable structural motifs can be constructed. With these, it is possible to redefine the description of " structure " in proteins, by detailed comparison between experimental ROA spectra of IUPs (or well ordered proteins for that matter) and the predicted ROA libraries, potentially superseding the need for classical structural analysis.