Mass-spectometry tools for the investigation of structural disorder and conformational transitions in proteins

Electrospray-ionization mass spectrometry has recently developed into a central tool of structural biology, which allows the investigation of the structure and the dynamics of protein conformations and protein assemblies. This contribution describes the principles of the main experimental approaches that have been applied to the study of intrinsically disordered proteins and describes some recent example from the literature. In particular, we distinguish between methods that are based on maintenance of non-covalent interactions under electrospray conditions, such as charge-state distribution analysis and ion mobility, from methods based on isotope exchange, in which the protein can be denatured or even digested before mass-spectrometry analysis. All together, these methods offer useful structural information, which is complementary to that gained by other biophysical techniques. Particularly interesting is the possibility to directly monitor distinct conformers in complex mixtures, free from averaging over the molecular population. Although this is a very young field, the examples discussed in this chapter illustrate the contribution that mass-spectrometry methods can give to the structural characterization of intrinsically disordered proteins in the absence and in the presence of interactors