Charge-Induced Unzipping of Isolated Proteins to a Defined Secondary Structure

Retention of Native Protein Structures in the Absence of Solvent: A Coupled Ion Mobility and Spectroscopic Study

Can the structures of small to medium‐sized proteins be conserved after transfer from the solution phase to the gas phase? A large number of studies have been devoted to this topic, however the answer has not been unambiguously determined to date. A clarification of this problem is important since it would allow very sensitive native mass spectrometry techniques to be used to address problems relevant to structural biology. A combination of ion‐mobility mass spectrometry with infrared spectroscopy was used to investigate the secondary and tertiary structure of proteins carefully transferred from solution to the gas phase. The two proteins investigated are myoglobin and β‐lactoglobulin, which are prototypical examples of helical and β‐sheet proteins, respectively. The results show that for low charge states under gentle conditions, aspects of the native secondary and tertiary structure can be conserved.

Charge-Induced Unzipping of Isolated Proteins to a Defined Secondary Structure

Here we present a combined experimental and theoretical study on the secondary structure of isolated proteins as a function of charge state. In infrared spectra of the proteins ubiquitin and cytochrome c, amide I (C=O stretch) and amide II (N-H bend) bands can be found at positions that are typical for condensed-phase proteins. For high charge states a new band appears, substantially red-shifted from the amide II band observed at lower charge states. The observations are interpreted in terms of Coulomb-driven transitions in secondary structures from mostly helical to extended C5 -type hydrogen-bonded structures. Support for this interpretation comes from simple energy considerations as well as from quantum chemical calculations on model peptides. This transition in secondary structure is most likely universal for isolated proteins that occur in mass spectrometric experiments.

Gas-phase microsolvation of ubiquitin: investigation of crown ether complexation sites using ion mobility-mass spectrometry

The influence of side chain to backbone interactions on the gas-phase structure of ubiquitin and ubiquitin lysine-to-arginine mutants was analysed.