Conformations of gas-phase ions of ubiquitin, cytochrome c, apomyoglobin, and β-lactoglobulin produced from two different solution conformations

Abstract

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 ␣-helices (the "H c " state). Gas-phase ions of ubiquitin, cytochrome c, apomyoglobin, and native and disulfide-reduced ␤-lactoglobulin were formed by electrospray ionization (ESI) of the proteins from the H and H c 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 H c states showed the same cross sections (within ϳ1%). Ions of cytochrome c, apomyoglobin, and native and reduced ␤-lactoglobulin of a given charge state showed no differences in H/D exchange level when produced from the H or H c state. However, ubiquitin ions produced from the H c state consistently exchange fewer (ϳ13%) 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. (J

Differential Mobility Spectrometry-Hydrogen Deuterium Exchange (DMS-HDX) as a Probe of Protein Conformation in Solution

“…Thus, solution conformation, while not necessarily retained through DMS separation, controls the set of gas-phase conformers that become populated. This explanation is consistent with the observations of Wright and co-workers, who reported that proteins retained a 'memory' of their original solution structures through substantial gas-phase manipulations associated with kinetic energy loss cross-sectional measurements [35].…”

Supermetallization of peptides and proteins during electrospray ionization

“…It was demonstrated many times that gas‐phase H/D exchange performed in the high vacuum part of the mass spectrometer produces a multi‐modal isotopic distribution suggesting the existence of different conformations with different H/D exchange rates . It was demonstrated that when MeOD or D 2 O is used as the deuterating agent, then the number of incorporated deuterium atoms decreases with the increase of CS . While when ND 3 is used, higher CS incorporate more deuteriums .…”

Transitions between Elongated Conformations of Ubiquitin [M+11H]11+ Enhance Hydrogen/Deuterium Exchange

“…30 All of these values for the [M+11H] 11+ state are far below the maximum number of possible exchanges (144 plus 11 protons); generally, non-reactive sites on elongated states are interpreted as being protected by secondary structural elements through hydrogen bonding. 32 Additionally, the orientation of charged sites on highly-extended states may not favor efficient exchange because heteroatom sites are not in close proximity to the site of protonation, where the H/D exchange process initiates. 11,12,40 …”