Detection and characterization of large-scale protein conformational transitions in solution using charge-state distribution analysis in ESI-MS.

Ion charge-state distribution analysis in electro-spray ionization mass spectrometry (ESI-MS) is a robust and fast technique for direct detection and characterization of coexisting protein conformations in solution. Compact folded proteins give rise to ESI-generated ions carrying a relatively small number of charges, whereas less compact conformers accommodate upon ESI a larger number of charges depending on the extent of their unfolding. A chemometric approach [1] based upon factor analysis is applied to determine contributions from individual conformers to the overall CSD. Here we present basic guidelines for the use of this MS-based technique: from the preparation of suitable solutions for ESI-MS to the acquisition of reliable MS data and their subsequent analysis.