Conformational footprinting of proteins using a combination of top-down electron transfer dissociation and ion mobility

In recent years native mass spectrometry has been increasingly employed to study protein structure. As such a thorough understanding of the effect of the gas-phase on protein structure is becoming increasingly important. We show how a combination of top-down ETD and ion mobility can be used to probe the gas-phase structure of heterogeneous protein ensembles. By applying collisional activation to the non-covalently bound ETD products after IM separation, the peptide fragments can be released while maintaining the conformational information of the protein ion. We studied the unknown gas-phase structures of the measles virus (MeV) phosphoprotein X domain (P XD ), which shows a wide range of different conformations in the gas-phase. We then generated structural models by state-of-the-art gas-phase steered molecular dynamics, which we verified using restraints from ion mobility and the fragment patterns observed. Our findings illustrate the applicability of ETD for obtaining conformational specific structural information on heterogeneous protein ensembles.