Coupling desorption electrospray ionization with ion mobility/mass spectrometry for analysis of protein structure:: Evidence for desorption of folded and denatured states

A desorption electrospray ionization (DESI) source has been coupled to an ion mobility time-of-flight mass spectrometer for the analysis of proteins. Analysis of solid-phase horse heart cytochrome c and chicken egg white lysozyme proteins with different DESI solvents and conditions shows similar mass spectra and charge state distributions to those formed when using electrospray to analyze these proteins in solution. The ion mobility data show evidence for compact ion structures [when the surface is exposed to a spray that favors retention of "nativelike" structures (50:50 water:methanol)] or elongated structures [when the surface is exposed to a spray that favors "denatured" structures (49:49:2 water: methanol:acetic acid)]. The results suggest that the DESI experiment is somewhat gentler than ESI and under appropriate conditions, it is possible to preserve structural information throughout the DESI process. Mechanisms that are consistent with these results are discussed.