The flight of macromolecular complexes in a mass spectrometer.

The discovery that conditions can be found such that non-covalent macromolecular complexes can survive the transition from solution to gas phase and remain intact during their flight in a mass spectrometer is an intriguing observation. While the nature of the interaction between the components, either ionic, hydrophobic or van der Waals, undoubtedly has an effect on the stability of these gas phase species, the role of small molecules in conferring additional stability is often overlooked. Here we review historical aspects of the development of mass spectrometry for macromolecular complexes with particular focus on the role of small molecules in stabilizing gas-phase complexes. Moreover, we demonstrate how the dissociation of small molecules from subunits within a macromolecular complex can be used to probe the topological arrangement. Overall, therefore, we show that mass spectrometry used in this way is capable of addressing features of the energy landscape not readily accessed by traditional structural biology approaches.