Phosphorylation is one the most studied and important post translational modifications. Nano electrospray mass spectrometry coupled with traveling wave (T-Wave)-based ion mobility has been used to filter for phosphorylated peptides in tryptic protein digests. T-Wave parameters have been optimized to maximize the separation between phosphorylated and non-phosphorylated peptides. A method to calibrate the T-Wave device, to provide estimates of collision cross sections, is presented, and these estimates are in excellent agreement with values obtained on drift cell instrumentation. Phosphorylated peptides have smaller cross sections which enables their separation from non-phosphorylated peptides of the same m/z. Post-mobility fragmentation is used to obtain the primary sequence for peptides of interest. This approach is shown to have potential as an additional screen for phosphorylated peptides, where up to 40% of observed peptides can be eliminated from the study.

The three-dimensional conformation of a protein is central to its biological function. The characterisation of aspects of three-dimensional protein structure by mass spectrometry is an area of much interest as the gas-phase conformation, in many instances, can be related to that of the solution phase. Travelling wave ion mobility mass spectrometry (TWIMS) was used to investigate the biological significance of gas-phase protein structure. Protein standards were analysed by TWIMS under denaturing and near-physiological solvent conditions and cross-sections estimated for the charge states observed. Estimates of collision cross-sections were obtained with reference to known standards with published cross-sections. Estimated cross-sections were compared with values from published X-ray crystallography and nuclear magnetic resonance (NMR) spectroscopy structures. The cross-section measured by ion mobility mass spectrometry varies with charge state, allowing the unfolding transition of proteins in the gas phase to be studied. Cross-sections estimated experimentally for proteins studied, for charge states most indicative of native structure, are in good agreement with measurements calculated from published X-ray and NMR structures. The relative stability of gas-phase structures has been investigated, for the proteins studied, based on their change in cross-section with increase in charge. These results illustrate that the TWIMS approach can provide data on three-dimensional protein structures of biological relevance.

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