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Our main research tools are native mass spectrometry and ion mobility mass spectrometry.

We develop these methods for application to proteins that are challenging to characterise with most techniques. To learn about the types of proteins that we investigate, have a look at our ‘Highlights’ page, which contains some lay descriptions of our recent scientific manuscripts and publications.

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.

Ion Mobility

In an ion mobility experiment, gas phase ions are separated by their shape. The ion mobility cell is filled with an inert buffer gas and as the ions drift through the cell, they collide with the gas. Smaller ions collide less with the gas and so give earlier drift times, whereas larger or more elongated ions collide more and so give later drift times. This method can distinguish between co-existing conformations of a protein, which is incredibly useful when you are measuring the interaction between many molecules and aiming to understand the changes in conformation as a result of the binding interactions.