Ionic Charge Manipulation Using Solution and Gas-Phase Chemistry to Facilitate Analysis of Highly Heterogeneous Protein Complexes in Native Mass Spectrometry

Ionic signal in native MS typically populates high m/z regions of mass spectra, which frequently extend beyond the precursor ion isolation limits of most commercial mass spectrometers. An approach explored in this work relies on adding supercharging reagents to protein solutions as a means of increasing the extent of multiple charging of non-covalent complexes in ESI MS without compromising their integrity. This shifts the ionic signal down the m/z scale to the region where ion selection and isolation can be readily accomplished, followed by limited charge reduction of the isolated ionic population. The feasibility of the new approach is demonstrated using non-covalent complexes formed by hemoglobin with structurally heterogeneous haptoglobin.