title: Isolating Protein Charge State Reduction in Electrospray Droplets Using Femtosecond Laser Vaporization.
abstract: Charge state distributions are measured using mass spectrometry for both native and denatured cytochrome c and myoglobin after laser vaporization from the solution state into an electrospray (ES) plume consisting of a series of solution additives differing in gas-phase basicity. The charge distribution depends on both the pH of the protein solution prior to laser vaporization and the gas-phase basicity of the solution additive employed in the ES solvent. Cytochrome c (myoglobin) prepared in solutions with pH of 7.0, 2.6, and 2.3 resulted in the average charge state distribution (Zavg) of 7.0 ± 0.1 (8.2 ± 0.1), 9.7 ± 0.2 (14.5 ± 0.3), and 11.6 ± 0.3 (16.4 ± 0.1), respectively, in ammonium formate ES solvent. The charge distribution shifted from higher charge states to lower charge states when the ES solvent contained amines additives with higher gas-phase basicity. In the case of triethyl ammonium formate, Zavgof cytochrome c (myoglobin) prepared in solutions with pH of 7.0, 2.6, and 2.3 decreased to 4.9 (5.7), 7.4 ± 0.2 (9.6 ± 0.3), and 7.9 ± 0.3 (9.8 ± 0.2), respectively. The detection of a charge state distribution corresponding to folded protein after laser vaporized, acid-denatured protein interacts with the ES solvent containing ammonium formate, ammonium acetate, triethyl ammonium formate, and triethyl ammonium acetate suggests that at least a part of protein population folds within the electrospray droplet on a millisecond timescale. Graphical Abstract ᅟ.
authors.affiliation: Department of Chemistry and Center for Advanced Photonics Research, Temple University, Philadelphia, PA, 19122, USA.
authors.forename: Santosh
authors.initials: S
authors.lastname: Karki
authors.affiliation: Department of Chemistry and Center for Advanced Photonics Research, Temple University, Philadelphia, PA, 19122, USA.
authors.forename: Habiballah
authors.initials: H
authors.lastname: Sistani
authors.affiliation: Department of Chemistry and Center for Advanced Photonics Research, Temple University, Philadelphia, PA, 19122, USA.
authors.forename: Jieutonne J
authors.initials: JJ
authors.lastname: Archer
authors.affiliation: Department of Chemistry and Center for Advanced Photonics Research, Temple University, Philadelphia, PA, 19122, USA.
authors.forename: Fengjian
authors.initials: F
authors.lastname: Shi
authors.affiliation: Department of Chemistry and Center for Advanced Photonics Research, Temple University, Philadelphia, PA, 19122, USA. rjlevis@temple.edu.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Levis
keywords: Charge state distribution; Electrospray ionization; Femtosecond laser vaporization; Protein conformation