Comprehensive Peptide Ion Structure Studies Using Ion Mobility Techniques: Part 3. Relating Solution-Phase to Gas-Phase Structures

Kondalaji, Samaneh Ghassabi; Khakinejad, Mahdiar; Valentine, Stephen J.

doi:10.1007/s13361-018-1996-9

Cited by 24 publications

(33 citation statements)

References 68 publications

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“…An increasing area of interest in biological mass spectrometry is the characterization of biomolecular structure. − To evaluate the potential of cVSSI plus voltage for structure characterization, experiments have been conducted for molecules for which it has been proposed that native MS allows the preservation of solution structure in the gas phase . The first study involves the examination of the globular protein ubiquitin which was examined in both positive and negative ion mode.…”

Section: Resultsmentioning

confidence: 99%

Facile Improvement of Negative Ion Mode Electrospray Ionization Using Capillary Vibrating Sharp-Edge Spray Ionization

Attanayake

Valentine

2020

Anal. Chem.

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Electrospray Ionization (ESI) is often affected by corona discharge when spraying 100% aqueous solutions as the voltage that induces discharge can be well below the onset voltage of ESI. As a result, it is especially challenging to perform native mass spectrometry in negative ion mode where 100% aqueous solution is preferred. Here we report a simple instrumentation method to improve the performance of ESI in negative ion mode based on capillary vibrating sharp-edge spray ionization (cVSSI). By attaching a fused silica capillary emitter to a vibrating glass slide, improved signal quality is achieved for various analytes in aqueous solutions over applying ESI alone. Compared to commercial ESI sources using nebulization gas to reduce discharge, 10-100 fold enhancement in signal intensity and 3-10 fold improvement in S/N are achieved for various kinds of molecules including DNA, peptides, proteins, and oligosaccharides. Finally, the new method demonstrates utility for native mass spectrometry analysis of proteins and G-quadruplex DNA. The present method is expected to have great potential to be adopted by the scientific community because of its improved analytical performance, simplicity, and low cost.

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Section: Resultsmentioning

confidence: 99%

Facile Improvement of Negative Ion Mode Electrospray Ionization Using Capillary Vibrating Sharp-Edge Spray Ionization

Attanayake

Valentine

2020

Anal. Chem.

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“…21,28,32,41 For example, it has become possible to obtain atomistic insights into the IEM ejection of small ions. 19,21,42,43 Simulations on compact folded proteins, 21,44 nucleic acid duplexes, 45 and peptides 46,47 revealed CRM behavior, while unfolded proteins were shown to follow the CEM. 21 Those MD studies provided strong support for the viability of the three ESI mechanisms depicted in Figure 1A,C,D.…”

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Formation of Gaseous Proteins via the Ion Evaporation Model (IEM) in Electrospray Mass Spectrometry

Aliyari

Konermann

2020

Anal. Chem.

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The mechanisms whereby protein ions are released into the gas phase from charged droplets during electrospray ionization (ESI) continue to be controversial. Several pathways have been proposed. For native ESI the charged residue model (CRM) is favored; it entails the liberation of proteins via solvent evaporation to dryness. Unfolded proteins likely follow the chain ejection model (CEM), which involves the gradual expulsion of stretched-out chains from the droplet. According to the ion evaporation model (IEM) ions undergo electrostatically driven desorption from the droplet surface. The IEM is well supported for small precharged species such as Na+. However, it is unclear whether proteins can show IEM behavior as well. We examined this question using molecular dynamics (MD) simulations, mass spectrometry (MS), and ion mobility spectrometry (IMS) in positive ion mode. Ubiquitin was chosen as the model protein because of its structural stability which allows the protein charge in solution to be controlled via pH adjustment without changing the protein conformation. MD simulations on small ESI droplets (3 nm radius) showed CRM behavior regardless of the protein charge in solution. Surprisingly, many MD runs on larger droplets (5.5 nm radius) culminated in IEM ejection of ubiquitin, as long as the protein carried a sufficiently large positive solution charge. MD simulations predicted that nonspecific salt adducts are less prevalent for IEM-generated protein ions than for CRM products. This prediction was confirmed experimentally. Also, collision cross sections of MD structures were in good agreement with IMS data. Overall, this work reveals that the CRM, CEM, and IEM all represent viable pathways for generating gaseous protein ions during ESI. The IEM is favored for proteins that are tightly folded and highly charged in solution and for droplets in a suitable size regime.

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“…Using ESI-IMS-MS and molecular dynamics (MD) simulations, the current work scrutinizes the mechanism of denatured supercharging ESI. MD simulations have addressed many ESI-related questions in recent years, − including protein ion formation under conditions (i), ,, (ii), and (iii) . However, this approach has not yet been extended to denatured supercharging ESI (scenario iv).…”

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Mechanism of Electrospray Supercharging for Unfolded Proteins: Solvent-Mediated Stabilization of Protonated Sites During Chain Ejection

2019

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Proteins that are unfolded in solution produce higher charge states during electrospray ionization (ESI) than their natively folded counterparts. Protein charge states can be further increased by the addition of supercharging agents (SCAs) such as sulfolane. The mechanism whereby these supercharged [M + zH] z+ ions are formed under unfolded conditions remains unclear. Here we employed a combination of mass spectrometry (MS), ion mobility spectrometry (IMS), and molecular dynamics (MD) simulations for probing the ESI mechanism under denatured supercharging conditions. ESI of acid-unfolded apo-myoglobin (aMb) in the presence of sulfolane produced charge states around 27+, all the way to fully protonated (33+) aMb. MD simulations of aMb 27+ to 33+ in Rayleigh-charged water/sulfolane droplets culminated in electrostatically driven protein expulsion, consistent with the chain ejection model (CEM). The electrostatically stretched conformations predicted by these simulations were in agreement with IMS experiments. The CEM involves partitioning of mobile H + between the droplet and the departing protein. Our results imply that supercharging of unfolded proteins is caused by residual sulfolane that stabilizes protonated sites on the protruding chains, thereby promoting H + retention on the protein. The stabilization of charged sites is due to charge−dipole interactions mediated by the large dipole moment and the low volatility of sulfolane. Support for this mechanism comes from the experimental observation of sulfolane adducts on the most highly charged ions, a phenomenon previously noted by Venter (J. Am. Soc. Mass Spectrom. 2012, 23, 489−497). The "CEM supercharging model" proposed here for unfolded proteins is distinct from the charge trapping mechanism believed to be operative during native ESI supercharging.

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Comprehensive Peptide Ion Structure Studies Using Ion Mobility Techniques: Part 3. Relating Solution-Phase to Gas-Phase Structures

Cited by 24 publications

References 68 publications

Facile Improvement of Negative Ion Mode Electrospray Ionization Using Capillary Vibrating Sharp-Edge Spray Ionization

Facile Improvement of Negative Ion Mode Electrospray Ionization Using Capillary Vibrating Sharp-Edge Spray Ionization

Formation of Gaseous Proteins via the Ion Evaporation Model (IEM) in Electrospray Mass Spectrometry

Mechanism of Electrospray Supercharging for Unfolded Proteins: Solvent-Mediated Stabilization of Protonated Sites During Chain Ejection

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