Investigating protein conformational ensembles by native mass spectrometry and complementary biophysical techniques—the case of α-synuclein

One of the challenges of modern structural biology is to account for protein structural dynamics. Intrinsically disordered proteins (IDPs), which do not fold spontaneously into a defined conformation, existing, instead, as highly heterogeneous conformational ensembles, provide an extreme and challenging example of protein dynamics. Native mass spectrometry (nMS) allows dissecting the molecular population in its main conformational components of different compactness, assessing structural parameters, covalent modifications, and binding states for each resolved species. This review summarizes the work performed by our research group in investigating the conformational states of human α-synuclein (α-syn), an IDP involved in Parkinson’s disease (PD) and other neurodegenerative conditions, by applying nMS. This case study is taken as an example, highlighting the complementarity of nMS to other biophysical techniques, such as circular dichroism (CD), Fourier-transform infrared (FTIR) spectroscopy, nuclear magnetic resonance (NMR), atomic force microscopy (AFM), and molecular-dynamics (MD) simulations. This multi-technological approach is useful in analyzing the response of α-syn conformational ensembles to covalent modifications and noncovalent interactions with metal ions, small ligands, and other proteins.