In situ analysis of intact proteins by ion mobility mass spectrometry

We describe ion mobility mass spectrometry techniques for the in situ analysis of intact proteins, i.e., the analysis of proteins directly from their biological environment. The benefits of in situ analysis include those associated more broadly with analysis of intact proteins, e.g., retention of connectivity between post-translational modifications and direct determination of amino acid substitutions, and those associated with surface sampling, e.g., retention of spatial information. Sampling techniques include liquid extraction surface analysis, continuous-flow liquid-microjunction surface sampling, desorption electrospray ionisation and matrix assisted laser desorption/ionisation. Direct surface sampling is beset by the challenge of inherent sample complexity, a challenge which can be addressed through integration of ion mobility spectrometry. To date, travelling wave ion mobility spectrometry and high field asymmetric waveform ion mobility spectrometry have been applied to the area of in situ analysis of proteins. In the case of travelling wave ion mobility spectrometry, information relating to tertiary or quaternary structure can also be obtained.