Conformations of Gas-Phase Ions of Ubiquitin, Cytochrome c, Apomyoglobin, and β-Lactoglobulin Produced from Two Different Solution Conformations

At low pH in solutions of 50% methanol, proteins form expanded denatured states (the “H” state). In 90% methanol, proteins form expanded helical denatured states with artificial α-helices (the “Hc” state). Gas-phase ions of ubiquitin, cytochrome c, apomyoglobin, and native and disulfide-reduced β-lactoglobulin were formed by electrospray ionization (ESI) of the proteins from the H and Hc states in solution. Both states in solution produce the same charge states in ESI. The conformations of the ions were studied with cross section measurements and gas-phase H/D exchange experiments. The cross sections show that the ions retain considerable folded structure. For a given protein and given charge state, ions produced from the H and Hc states showed the same cross sections (within ∼1%). Ions of cytochrome c, apomyoglobin, and native and reduced β-lactoglobulin of a given charge state showed no differences in H/D exchange level when produced from the H or Hc state. However, ubiquitin ions produced from the Hc state consistently exchange fewer (∼13%) hydrogens than ions produced from the H state, suggesting that in this case the gas-phase protein ions retain some memory of their solution conformations.

Graphical AbstractUbiquitin ions produced from two different solution conformations exchange different numbers of hydrogens, suggesting that the gas-phase protein ions retain memory of their solution conformations.Figure optionsDownload high-quality image (126 K)Download as PowerPoint slide