Solvent‐induced conformational changes of polypeptides probed by electrospray‐ionization mass spectrometry

Loo, Joseph A.; Loo, Rachel R. Ogorzalek; Udseth, Harold R.; Edmonds, Charles G.; Smith, Richard D.

doi:10.1002/rcm.1290050303

Cited by 300 publications

(269 citation statements)

References 22 publications

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“…ESI-MS conditions can be mild enough that proteins retain their native conformations and enzyme-substrate complexes or subunit interactions can be observed (Ganem et al, 1991a(Ganem et al, , 1991bKatta & Chait, 1991b;Baca & Kent, 1992;Ganguly et al, 1992;Drummond et al, 1993;Goodlett et al, 1993;Light-Wahl et al, 1993aLoo et al, 1993aLoo et al, , 1993bOgorzalek Loo et al, 1993). A number of investigators have taken advantage of the dramatic increase in charge state observed when some proteins are denatured to probe protein structure (Katta & Chait, 1991aLeBlanc et al, 1991;Loo et al, 1991Loo et al, , 1993b Mirzaet al, 1993). The applicability of mass spectrometry to biological problems would be greatly enhanced and expanded if methodologies were developed to analyze surfactant-containing protein solutions.…”

Section: Introductionmentioning

confidence: 99%

Surfactant effects on protein structure examined by electrospray ionization mass spectrometry

1994

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Electrospray ionization mass spectrometry (ESI-MS) has proven to be a useful tool for examining noncovalent complexes between proteins and a variety of ligands. It has also been used to distinguish between denatured and refolded forms of proteins. Surfactants are frequently employed to enhance solubilization or to modify the tertiary or quaternary structure of proteins, but are usually considered incompatible with mass spectrometry. A broad range of ionic, nonionic, and zwitterionic surfactants was examined to characterize their effects on ESI-MS and on protein structure under ESI-MS conditions. Solution conditions studied include 4% acetic acid/50% acetonitrile/46% H 2 0 and 100% aqueous. Of the surfactants examined, the nonionic saccharides, such as n-dodecyl-P-D-glucopyranoside, at 0.1 Vo to 0.01% (w/v) concentrations, performed best, with limited interference from chemical background and adduct formation. Under the experimental conditions used, ESI-MS performance in the presence of surfactants was found to be unrelated to critical micelle concentration. It is demonstrated that surfactants can affect both the tertiary and quaternary structures of proteins under conditions used for ESI-MS. However, several of the surfactants caused significant shifts in the charge-state distributions, which appeared to be independent of conformational effects. These observations suggest that surfactants, used in conjunction with ESI-MS, can be useful for protein structure studies, if care is used in the interpretation of the results.Keywords: conformation; denaturation; detergent; electrospray; mass spectrometry; surfactant Surfactants play a significant role in protein chemistry with primary applications ranging from solubilization and stabilization of proteins to disaggregation of protein complexes and denaturation (Neugebauer, 1990(Neugebauer, , 1992Bollag & Edelstein, 1991). Some surfactants can disrupt protein higher order structure, whereas others are used as aids in protein refolding. They are employed in both gel and capillary electrophoresis and enhance protein and peptide recoveries from synthetic membranes employed in electroblotting and in electroelution of proteins from gels (Fernandez et al., 1994). Membrane-bound proteins, in particular, require surfactant treatment for solubilization. Abbreviotiom: CMC, critical micelle concentration; ESI, electrospray ionization; ESI-MS, electrospray ionization mass spectrometry; MALDI, matrix-assisted laser desorption/ionization; NP40, Nonidet P a , CHAPS, 3-(3-cholamidopropyl)dimethylammonio-I-propane sulfonate; CTAB, cetyl trimethylammonium bromide; LDAO, laurel dimethylamine oxide; n-dodecyl glucoside, n-dodecyl-0-D-glucopyranoside; n-hexylglucoside, n-hexyl-0-D-glucopyranoside; octyl glucoside, octyl-fl-D-glucopyranoside; octyl thioglucoside, I-S-octyl-fi-~-thioglucopyranoside.Matrix-assisted laser desorption/ionization or electrospray ionization have demonstrated molecular weight determinations for proteins greater than 100 kDa (Fenn et al., 1989;Smith et al., 19...

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Section: Introductionmentioning

confidence: 99%

Surfactant effects on protein structure examined by electrospray ionization mass spectrometry

1994

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“…Indeed, it was not long after the acceptance of ESI MS as a tool for measuring masses of macromolecular ions that observations were made linking the dramatic changes of ionic charge state distributions to protein denaturation in solution [6,7]. These observations brought about the realization of the potential of ESI MS as a means of probing protein higher order structure and detecting large-scale conformational transitions in solution.…”

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Do ionic charges in ESI MS provide useful information on macromolecular structure?

Kaltashov

Abzalimov

2008

J. Am. Soc. Mass Spectrom.

154

190

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Multiple charging is an intrinsic feature of electrospray ionization (ESI) of macromolecules. While multiple factors influence the appearance of protein ion charge state distributions in ESI mass spectra, physical dimensions of protein molecules in solution are the major determinants of the extent of multiple charging. This article reviews the information that can be obtained by analyzing ionic charge state distributions in ESI MS, as well as potential pitfalls and limitations of this powerful technique. We also discuss future areas of growth with particular emphasis on applications in structural biology, biotechnology (protein-polymer conjugates), and nanomedicine. (J Am Soc Mass Spectrom 2008, 19, 1239 -1246 [2][3][4] preceded the triumphant entry of this ionization technique into the mainstream of biological mass spectrometry by some time. One particular feature of ESI that seemed to be a major impediment for its application to macromolecules was multiple charging, a phenomenon that seemingly complicated the appearance of mass spectra by crowding them with multiple ion peaks corresponding to the same analyte. Although ionic species carrying more than one elementary charge are not uncommon in mass spectra of macromolecular ions generated by means of fast atom bombardment (FAB) or matrix-assisted laser desorption/ionization (MALDI), they typically account for only a small fraction of the overall signal. Furthermore, typical ionic charge density (defined here as the average number of charges per unit mass) is much lower for the macromolecular ions produced by FAB and MALDI compared with ions generated by ESI. Charge reduction strategies via ion-molecular reactions in the gas phase provided an opportunity to simplify ESI mass spectra of polypeptides by eliminating peaks of multiply charged ions. However, it was the realization that multiple charging is an intrinsic property of ESI process and must be dealt with using mathematical tools, that made it a practical tool for the analysis of macromolecules [5].In retrospect, it seems almost ironic that the multiple charging of macromolecules in ESI MS is now viewed not as a liability, but an extremely valuable asset, which provides a new important dimension to the analysis of biopolymers. Indeed, it was not long after the acceptance of ESI MS as a tool for measuring masses of macromolecular ions that observations were made linking the dramatic changes of ionic charge state distributions to protein denaturation in solution [6,7]. These observations brought about the realization of the potential of ESI MS as a means of probing protein higher order structure and detecting large-scale conformational transitions in solution.Natively folded proteins by definition have stable, compact cores sequestered from the solvent and undergo ESI to produce ions carrying a relatively small number of charges. This is because the compact shape of a tightly folded polypeptide chain in solution does not allow the accommodation of a significant number of protons on their surface upon transit...

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“…One outstanding challenge in ESI mass spectrometry is to accurately predict the observed charge state distribution of a large molecule, given its primary structure, the composition of the solvent system from which the ions are formed, instrumental conditions, etc. Several factors have been shown to influence the observed charge state distribution, including molecular conformation [4][5][6], acid-base chemistry both in solution and in the gas phase [7][8][9][10][11], solvent composition [8], instrumental factors, etc. Several models have been proposed to qualitatively account for some of these effects [12][13][14][15].…”

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confidence: 99%

“…Loo et al [6] found that charge state distributions correlate with the denaturing capacities of different solvents.…”

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Effects of solvent on the maximum charge state and charge state distribution of protein ions produced by electrospray ionization

Iavarone

Jurchen

Williams

2000

J. Am. Soc. Mass Spectrom.

171

199

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The effects of solvent composition on both the maximum charge states and charge state distributions of analyte ions formed by electrospray ionization were investigated using a quadrupole mass spectrometer. The charge state distributions of cytochrome c and myoglobin, formed from 47%/50%/ 3% water/solvent/acetic acid solutions, shift to lower charge (higher m/z) when the 50% solvent fraction is changed from water to methanol, to acetonitrile, to isopropanol. This is also the order of increasing gas-phase basicities of these solvents, although other physical properties of these solvents may also play a role. The effect is relatively small for these solvents, possibly due to their limited concentration inside the electrospray interface. In contrast, the addition of even small amounts of diethylamine (<0.4%) results in dramatic shifts to lower charge, presumably due to preferential proton transfer from the higher charge state ions to diethylamine. These results clearly show that the maximum charge states and charge state distributions of ions formed by electrospray ionization are influenced by solvents that are more volatile than water. Addition of even small amounts of two solvents that are less volatile than water, ethylene glycol and 2-methoxyethanol, also results in preferential deprotonation of higher charge state ions of small peptides, but these solvents actually produce an enhancement in the higher charge state ions for both cytochrome c and myoglobin. For instruments that have capabilities that improve with lower m/z, this effect could be taken advantage of to improve the performance of an analysis.Electrospray ionization (ESI) [1] is well recognized as a soft ionization method for producing gas-phase ions of large biopolymers, such as oligonucleotides, proteins, and even noncovalent biomolecular complexes [2]. In combination with mass spectrometry, molecular masses of large molecules can be measured with unprecedented accuracy [3]. The multiple charging of large analyte ions that occurs with ESI has the advantage that the masses of very large molecules can be measured using mass spectrometers with upper mass-to-charge limits. One outstanding challenge in ESI mass spectrometry is to accurately predict the observed charge state distribution of a large molecule, given its primary structure, the composition of the solvent system from which the ions are formed, instrumental conditions, etc. Several factors have been shown to influence the observed charge state distribution, including molecular conformation [4][5][6], acid-base chemistry both in solution and in the gas phase [7][8][9][10][11], solvent composition [8], instrumental factors, etc. Several models have been proposed to qualitatively account for some of these effects [12][13][14][15]. A general conclusion from several studies is that the electrospray charge state distributions of proteins formed from denaturing solution conditions are shifted to higher charge states (lower m/z) than those formed from solutions in which the protein has signific...

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Solvent‐induced conformational changes of polypeptides probed by electrospray‐ionization mass spectrometry

Cited by 300 publications

References 22 publications

Surfactant effects on protein structure examined by electrospray ionization mass spectrometry

Surfactant effects on protein structure examined by electrospray ionization mass spectrometry

Do ionic charges in ESI MS provide useful information on macromolecular structure?

Effects of solvent on the maximum charge state and charge state distribution of protein ions produced by electrospray ionization

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