Impact of limited oxidation on protein ion mobility and structure of importance to footprinting by radical probe mass spectrometry

The effect of hydroxyl radical induced oxidation on the collision cross-sections of hen egg lysozyme and bovine ubiquitin was investigated by travelling wave ion mobility mass spectrometry for the first time. The oxidized ions of lysozyme and ubiquitin share common collision cross-sections with their unoxidized counterparts suggesting that they share common structures that were unaffected by limited oxidation. In the case of bovine ubiquitin, two distinct conformers were detected for the protein in its unoxidized and oxidized states though no change in the levels of each was observed upon oxidation. This supports the validity of Radical Probe Mass Spectrometry (RP-MS) using an electrical discharge source for protein footprinting experiments. Travelling wave ion mobility mass spectrometry has been used for the first time to confirm that limited oxidation does not have an impact on the global structure of proteins.