Investigating the Effects of Dehydration on the Conformational Preferences of Biomolecules during the Final Stages of Electrospray Ionization
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Electrospray ionization (ESI) combined with ion mobility-mass spectrometry (IMMS) provides a means to directly measure the three-dimensional shape(s) of intact biomolecular ions allowing for the structural investigation of biologically-important systems. Studies of gas-phase biomolecules remove the complicating effects of solute-solvent interactions, but understanding the conformational preferences of ions as they transition from solution to the gas phase is of critical importance to the development of “native” mass spectrometry. A number of recent studies utilizing ESI have demonstrated that gas-phase peptide and protein ions can retain memory of their solution-phase counterparts. However, the preservation of native structures is dependent on an ensemble of stabilizing interactions, specifically the interplay between inter- and intramolecular interactions that afford stability to ions. Cryogenic ion mobility-mass spectrometry takes advantage of the freeze-drying capabilities of ESI and a cold IM drift cell (80 K) to preserve extensively solvated ions of the type [M + xH]^x+ (H2O)n, where n can vary from zero to several hundred. This affords an experimental approach for tracking the structural evolution of hydrated biomolecules en route to forming solvent-free gas-phase ions. Studies of small ions, including protonated water clusters and alkyl diammonium cations, reveal structural transitions associated with the development of the H-bond network of water molecules surrounding the charge carrier(s). When extended to larger peptide ions, results show that water networks are highly dependent on the charge-carrying species within the cluster. Studies on the neuropeptide substance P illustrate the ability to elucidate information about heterogeneous ion populations. Results showed that a kinetically-trapped conformer was stabilized by a combination of solvation and specific intramolecular interactions. However, upon desolvation, the kinetically-trapped conformer rearranges to form a thermodynamically-favored gas-phase ion conformation. Finally, extension of this approach to larger biomolecules revealed a water-mediated protein-binding event associated with dehydration of ubiquitin ions. Cryo-IM-MS adds a new dimension to studies of biomolecules in the ability to monitor snapshots of the structural evolution of ions during the transition from solution to gas phase, and provides insight into the intricate interplay between competing effects that dictate conformational preferences.
Servage, Kelly Anne (2016). Investigating the Effects of Dehydration on the Conformational Preferences of Biomolecules during the Final Stages of Electrospray Ionization. Doctoral dissertation, Texas A & M University. Available electronically from