Native mass spectrometry
In our native mass spectrometry (nMS) experiments, the protein or protein complex is first prepared in an ammonium acetate solution which allows it to be in its native conformation. We then use nanoelectrospray ionisation (nESI) to transfer the sample from solution into the gas phase. nESI is a very soft ionisation technique, requiring low voltages, and allows proteins to retain their 3-dimensional conformation as the solvent evaporates. This produces protein ions with a discrete number of charges, and the mass-to-charge ratio (m/z) of these ions can then be measured.
The mass informs on the intact mass of any non-covalent complexes that are formed, making nMS a useful tool for measuring protein-protein, protein-drug or protein-DNA/RNA complexes. nMS can also be used to investigate DNA and the complexes it forms with drugs.
Additionally, the number of charges that the proteins carry can also inform on their conformation, providing information on the range of shapes they exist in. Compact conformations have a low number of charge states, as there’s a limited surface area available for protonation. Unfolded proteins have a larger surface area which can accommodate more protons, so have a higher charge state. Intrinsically disordered proteins, which are a key area of research in the group, exist in a wide range of conformations and hence display a wide charge state distribution.

A folded/ globular protein, as shown above, will display low charge states

An unfolded protein will display higher charge states. IDPs exist in many conformations so display a wide charge state distribution.

Mixtures of proteins or protein complexes can be analysed, since each species will present a distinct signal.