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Luan M, Hou Z, Zhang B, Ma L, Yuan S, Liu Y, Huang G. Inter-Domain Repulsion of Dumbbell-Shaped Calmodulin during Electrospray Ionization Revealed by Molecular Dynamics Simulations. Anal Chem 2023; 95:8798-8806. [PMID: 37309130 DOI: 10.1021/acs.analchem.2c05630] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
The mechanisms whereby protein ions are released from nanodroplets at the liquid-gas interface have continued to be controversial since electrospray ionization (ESI) mass spectrometry was widely applied in biomolecular structure analysis in solution. Several viable pathways have been proposed and verified for single-domain proteins. However, the ESI mechanism of multi-domain proteins with more complicated and flexible structures remains unclear. Herein, dumbbell-shaped calmodulin was chosen as a multi-domain protein model to perform molecular dynamics simulations to investigate the structural evolution during the ESI process. For [Ca4CAM], the protein followed the classical charge residue model. As the inter-domain electrostatic repulsion increased, the droplet was found to split into two sub-droplets, while stronger-repulsive apo-calmodulin unfolded during the early evaporation stage. We designated this novel ESI mechanism as the domain repulsion model, which provides new mechanistic insights into further exploration of proteins containing more domains. Our results suggest that greater attention should be paid to the effect of domain-domain interactions on structure retention during liquid-gas interface transfer when mass spectrometry is used as the developing technique in gas phase structural biology.
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Affiliation(s)
- Moujun Luan
- Department of Cardiology, The First Affiliated Hospital of USTC, University of Science and Technology of China, Hefei 230001, China
- School of Chemistry and Materials Science, University of Science and Technology of China, Hefei 230026, China
| | - Zhuanghao Hou
- Department of Cardiology, The First Affiliated Hospital of USTC, University of Science and Technology of China, Hefei 230001, China
- School of Chemistry and Materials Science, University of Science and Technology of China, Hefei 230026, China
| | - Buchun Zhang
- Department of Cardiology, The First Affiliated Hospital of USTC, University of Science and Technology of China, Hefei 230001, China
| | - Likun Ma
- Department of Cardiology, The First Affiliated Hospital of USTC, University of Science and Technology of China, Hefei 230001, China
| | - Siming Yuan
- School of Chemistry and Materials Science, University of Science and Technology of China, Hefei 230026, China
- Department of Pharmacy, The First Affiliated Hospital of USTC, University of Science and Technology of China, Hefei 230001, China
| | - Yangzhong Liu
- School of Chemistry and Materials Science, University of Science and Technology of China, Hefei 230026, China
- Department of Pharmacy, The First Affiliated Hospital of USTC, University of Science and Technology of China, Hefei 230001, China
| | - Guangming Huang
- Department of Cardiology, The First Affiliated Hospital of USTC, University of Science and Technology of China, Hefei 230001, China
- School of Chemistry and Materials Science, University of Science and Technology of China, Hefei 230026, China
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Hou Z, Luan M, Zhan L, Wang X, Yuan S, Cao K, Sheng Y, Yin H, Liu Y, Huang G. Native Mass Spectrometry for Peptide–Metal Interaction in Picoliter Cell Lysate. Anal Chem 2022; 94:13829-13833. [DOI: 10.1021/acs.analchem.2c02390] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Zhuanghao Hou
- Department of Cardiology, The First Affiliated Hospital of USTC, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, Anhui 230001, China
- School of Chemistry and Materials Science, University of Science and Technology of China, Hefei, Anhui 230001, China
| | - Moujun Luan
- Department of Cardiology, The First Affiliated Hospital of USTC, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, Anhui 230001, China
- School of Chemistry and Materials Science, University of Science and Technology of China, Hefei, Anhui 230001, China
| | - Liujuan Zhan
- Department of Cardiology, The First Affiliated Hospital of USTC, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, Anhui 230001, China
- School of Chemistry and Materials Science, University of Science and Technology of China, Hefei, Anhui 230001, China
| | - Xinchen Wang
- Department of Cardiology, The First Affiliated Hospital of USTC, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, Anhui 230001, China
- School of Chemistry and Materials Science, University of Science and Technology of China, Hefei, Anhui 230001, China
| | - Siming Yuan
- Department of Cardiology, The First Affiliated Hospital of USTC, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, Anhui 230001, China
- School of Chemistry and Materials Science, University of Science and Technology of China, Hefei, Anhui 230001, China
| | - Kaiming Cao
- Department of Cardiology, The First Affiliated Hospital of USTC, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, Anhui 230001, China
- School of Chemistry and Materials Science, University of Science and Technology of China, Hefei, Anhui 230001, China
| | - Yaping Sheng
- Department of Cardiology, The First Affiliated Hospital of USTC, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, Anhui 230001, China
- School of Chemistry and Materials Science, University of Science and Technology of China, Hefei, Anhui 230001, China
| | - Hao Yin
- Mass Spectrometry Lab, Instruments Center for Physical Science, University of Science and Technology of China, Hefei, Anhui 230001, China
| | - Yangzhong Liu
- Department of Cardiology, The First Affiliated Hospital of USTC, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, Anhui 230001, China
- School of Chemistry and Materials Science, University of Science and Technology of China, Hefei, Anhui 230001, China
| | - Guangming Huang
- Department of Cardiology, The First Affiliated Hospital of USTC, Division of Life Sciences and Medicine, University of Science and Technology of China, Hefei, Anhui 230001, China
- School of Chemistry and Materials Science, University of Science and Technology of China, Hefei, Anhui 230001, China
- National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui 230001, China
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Dias HJ, Crevelin EJ, Palaretti V, Vessecchi R, Crotti AEM. Electrospray ionization tandem mass spectrometry of deprotonated dihydrobenzofuran neolignans. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2021; 35:e8990. [PMID: 33119941 DOI: 10.1002/rcm.8990] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/10/2020] [Revised: 10/21/2020] [Accepted: 10/24/2020] [Indexed: 06/11/2023]
Abstract
RATIONALE Although dihydrobenzofuran neolignans (DBNs) display a wide diversity of biological activities, the identification of their in vivo metabolites using liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS) remains a challenge to be overcome. Recently, ESI-MS/MS data of protonated DBNs have been reported, but they were shown to be limited due to the scarcity of diagnostic ions. METHODS The gas-phase fragmentation pathways of a series of biologically active synthetic benzofuran neolignans (BNs) and DBNs were elucidated by means of negative ESI accurate-mass tandem and sequential mass spectrometry, and thermochemical data estimated using computational chemistry and the B3LYP/6-31+G(d,p) model. RESULTS Deprotonated DBNs produced more diagnostic product ions than the corresponding protonated molecules. Moreover, a series of odd-electron product ions (radical anions) were detected, which has not been reported for protonated DBNs. Direct C2 H3 O2 • elimination from the precursor ion (deprotonated molecule) only occurred for the BNs and can help to distinguish these compounds from the DBNs. The mechanism through which the [M - H - CH3 OH]- ion is formed is strongly dependent on specific structural features. CONCLUSIONS The negative ion mode provides much more information than the positive ion mode (at least one diagnostic product ion was detected for all the analyzed compounds) and does not require the use of additives to produce the precursor ions (deprotonated molecules).
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Affiliation(s)
- Herbert J Dias
- Departamento de Química, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, SP, Brazil
| | - Eduardo J Crevelin
- Departamento de Química, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, SP, Brazil
| | - Vinicius Palaretti
- Departamento de Química, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, SP, Brazil
| | - Ricardo Vessecchi
- Departamento de Química, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, SP, Brazil
| | - Antônio E M Crotti
- Departamento de Química, Faculdade de Filosofia, Ciências e Letras de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, SP, Brazil
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Lipstein N, Göth M, Piotrowski C, Pagel K, Sinz A, Jahn O. Presynaptic Calmodulin targets: lessons from structural proteomics. Expert Rev Proteomics 2017; 14:223-242. [DOI: 10.1080/14789450.2017.1275966] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Affiliation(s)
- Noa Lipstein
- Department of Molecular Neurobiology, Max-Planck-Institute of Experimental Medicine, Göttingen, Germany
| | - Melanie Göth
- Institute of Chemistry and Biochemistry, Free University Berlin, Berlin & Fritz Haber Institute of the Max-Planck-Society, Berlin, Germany
| | - Christine Piotrowski
- Department of Pharmaceutical Chemistry & Bioanalytics, Institute of Pharmacy, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany
| | - Kevin Pagel
- Institute of Chemistry and Biochemistry, Free University Berlin, Berlin & Fritz Haber Institute of the Max-Planck-Society, Berlin, Germany
| | - Andrea Sinz
- Department of Pharmaceutical Chemistry & Bioanalytics, Institute of Pharmacy, Martin Luther University Halle-Wittenberg, Halle (Saale), Germany
| | - Olaf Jahn
- Proteomics Group, Max-Planck-Institute of Experimental Medicine, Göttingen, Germany
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Abstract
The identification of endogenous proteins as well as their binding to metal ions in living cells is determined by combining pulsed electrophoretic separations with nanoelectrospray ionization followed by mass spectrometric detection. This approach avoids problems resulting from the complicated cellular environment. In this manner, we demonstrate the rapid identification (300 ms or less) of intact proteins from living E. coli cells including the complexation of calmodulin with calcium ion. The latter showed different binding states from those observed in in vitro studies. These observations also reveal in vitro measurements do not necessarily represent the actual situation in living cells. We conclude that the attempted in situ measurement of intracellular proteins with minimal sampling processes should be preferred.
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Affiliation(s)
- Gongyu Li
- Department of Chemistry, School of Chemistry and Materials Science, University of Science and Technology of China , Hefei, Anhui 230026, P. R. China
| | - Siming Yuan
- Department of Chemistry, School of Chemistry and Materials Science, University of Science and Technology of China , Hefei, Anhui 230026, P. R. China
| | - Yang Pan
- National Synchrotron Radiation Laboratory, University of Science and Technology of China , Hefei, Anhui 230029, P. R. China
| | - Yangzhong Liu
- Department of Chemistry, School of Chemistry and Materials Science, University of Science and Technology of China , Hefei, Anhui 230026, P. R. China
| | - Guangming Huang
- Department of Chemistry, School of Chemistry and Materials Science, University of Science and Technology of China , Hefei, Anhui 230026, P. R. China
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Ma L, Wang Z, Liu S, Song F, Liu Z, Liu S. Screening calmodulin-binding ligands using intensity-fading matrix-assisted laser desorption/ionization mass spectrometry. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2013; 27:1527-1534. [PMID: 23722687 DOI: 10.1002/rcm.6594] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/10/2013] [Revised: 04/07/2013] [Accepted: 04/07/2013] [Indexed: 06/02/2023]
Abstract
RATIONALE Calmodulin (CaM) plays an important role in the regulation of metabolism, cytoskeleton and cell proliferation. CaM antagonists are a class of drugs that can bind to CaM and modulate the interactions between CaM and their target biological processes. Screening new calmodulin antagonists and developing novel methods for detecting calmodulin ligands are important for developing novel anti-cancer drugs that bind specifically to CaM. METHODS An intensity-fading matrix-assisted laser desorption/ionization mass spectrometry (IF-MALDI-MS) method for screening calmodulin ligands was established, with the non-binding drug propranolol as the internal control. The experimental sample was prepared by mixing the positive ligand trifluoperazine (or chlorpromazine), propranolol and Ca(2+)-CaM. The control sample was treated in the same way without the addition of CaM. The experimental and control samples were both analyzed by MALDI-MS. Based on the relative intensity fading (IF) of the ligand to propranolol, the MS conditions were optimized and then used to study the binding of eight alkaloids and calmodulin. Competitive experiments were performed in a similar way by adding two drugs to compare their binding affinities with calmodulin. RESULTS The matrix 2,6-dihydroxyacetophenone (DHAP) was suitable for detecting calmodulin ligands. Compared with propranolol, the relative intensities of six free drugs (berbamine, tetrandrine, papaverine, reserpine, brucine and tetrahydropalmatine) clearly faded after the addition of calmodulin, indicating that they can bind with CaM. The other two alkaloids (strychnine and piperine) had no or weak interaction with the target protein. Based on the data from the competitive binding experiments, the binding affinities of five drugs to calmodulin were obtained in the order: tetrandrine > trifluoperazine > berbamine > chlorpromazine > imipramine. CONCLUSIONS The IF-MALDI-MS method was successfully applied to screen novel calmodulin agents at both qualitative and semiquantitative levels. The new ligands may be novel leads for CaM antagonists.
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Affiliation(s)
- Lei Ma
- Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun Center of Mass Spectrometry, Changchun, PR China
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7
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Pan J, Konermann L. Calcium-Induced Structural Transitions of the Calmodulin−Melittin System Studied by Electrospray Mass Spectrometry: Conformational Subpopulations and Metal-Unsaturated Intermediates. Biochemistry 2010; 49:3477-86. [DOI: 10.1021/bi100261c] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Affiliation(s)
- Jingxi Pan
- Department of Chemistry, The University of Western Ontario, London, Ontario N6A 5B7, Canada
| | - Lars Konermann
- Department of Chemistry, The University of Western Ontario, London, Ontario N6A 5B7, Canada
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8
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Chekmeneva E, Díaz-Cruz JM, Ariño C, Esteban M. Study of the Hg2+ binding with chelation therapy agents by differential pulse voltammetry on rotating Au-disk electrode and electrospray ionization mass-spectrometry. Anal Chim Acta 2009; 653:77-85. [DOI: 10.1016/j.aca.2009.08.041] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2009] [Revised: 08/14/2009] [Accepted: 08/28/2009] [Indexed: 10/20/2022]
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9
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Pan J, Xu K, Yang X, Choy WY, Konermann L. Solution-Phase Chelators for Suppressing Nonspecific Protein−Metal Interactions in Electrospray Mass Spectrometry. Anal Chem 2009; 81:5008-15. [DOI: 10.1021/ac900423x] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Affiliation(s)
- Jingxi Pan
- Departments of Chemistry and Biochemistry, The University of Western Ontario, London, Ontario, N6A 5B7, Canada, State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116012, People’s Republic of China, and School of Pharmaceutical Sciences and National Research Laboratories of Natural and Biomimetic Drugs, Peking University, Beijing 100083, People’s Republic of China
| | - Kun Xu
- Departments of Chemistry and Biochemistry, The University of Western Ontario, London, Ontario, N6A 5B7, Canada, State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116012, People’s Republic of China, and School of Pharmaceutical Sciences and National Research Laboratories of Natural and Biomimetic Drugs, Peking University, Beijing 100083, People’s Republic of China
| | - Xiaoda Yang
- Departments of Chemistry and Biochemistry, The University of Western Ontario, London, Ontario, N6A 5B7, Canada, State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116012, People’s Republic of China, and School of Pharmaceutical Sciences and National Research Laboratories of Natural and Biomimetic Drugs, Peking University, Beijing 100083, People’s Republic of China
| | - Wing-Yiu Choy
- Departments of Chemistry and Biochemistry, The University of Western Ontario, London, Ontario, N6A 5B7, Canada, State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116012, People’s Republic of China, and School of Pharmaceutical Sciences and National Research Laboratories of Natural and Biomimetic Drugs, Peking University, Beijing 100083, People’s Republic of China
| | - Lars Konermann
- Departments of Chemistry and Biochemistry, The University of Western Ontario, London, Ontario, N6A 5B7, Canada, State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116012, People’s Republic of China, and School of Pharmaceutical Sciences and National Research Laboratories of Natural and Biomimetic Drugs, Peking University, Beijing 100083, People’s Republic of China
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Pukala TL, Urathamakul T, Watt SJ, Beck JL, Jackway RJ, Bowie JH. Binding studies of nNOS-active amphibian peptides and Ca2+ calmodulin, using negative ion electrospray ionisation mass spectrometry. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2008; 22:3501-3509. [PMID: 18853393 DOI: 10.1002/rcm.3757] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
Amphibian peptides which inhibit the formation of nitric oxide by neuronal nitric oxide synthase (nNOS) do so by binding to the protein cofactor, Ca2+calmodulin (Ca2+CaM). Complex formation between active peptides and Ca2+CaM has been demonstrated by negative ion electrospray ionisation mass spectrometry using an aqueous ammonium acetate buffer system. In all cases studied, the assemblies are formed with a 1:1:4 calmodulin/peptide/Ca2+ stoichiometry. In contrast, the complex involving the 20-residue binding domain of the plasma Ca2+ pump C20W (LRRGQILWFRGLNRIQTQIK-OH) with CaM has been shown by previous two-dimensional nuclear magnetic resonance (2D NMR) studies to involve complexation of the C-terminal end of CaM. Under identical conditions to those used for the amphibian peptide study, the ESI complex between C20W and CaM shows specific 1:1:2 stoichiometry. Since complex formation with the studied amphibian peptides requires Ca2+CaM to contain its full complement of four Ca2+ ions, this indicates that the amphibian peptides require both ends of the CaM to effect complex formation. Charge-state analysis and an H/D exchange experiment (with caerin 1.8) suggest that complexation involves Ca2+CaM undergoing a conformational change to a more compact structure.
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Affiliation(s)
- Tara L Pukala
- Department of Chemistry, The University of Adelaide, South Australia, 5005, Australia
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11
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Goulding AM, Rahimi Y, Shrestha S, Deo SK. Dual Function Labeling of Biomolecules Based on DsRed-Monomer. Bioconjug Chem 2008; 19:2113-9. [DOI: 10.1021/bc800147k] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Affiliation(s)
- A. M. Goulding
- Department of Chemistry and Chemical Biology, Indiana University Purdue University Indianapolis, Indianapolis, Indiana 46202
| | - Y. Rahimi
- Department of Chemistry and Chemical Biology, Indiana University Purdue University Indianapolis, Indianapolis, Indiana 46202
| | - S. Shrestha
- Department of Chemistry and Chemical Biology, Indiana University Purdue University Indianapolis, Indianapolis, Indiana 46202
| | - S. K. Deo
- Department of Chemistry and Chemical Biology, Indiana University Purdue University Indianapolis, Indianapolis, Indiana 46202
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12
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Watt SJ, Sheil MM, Beck JL, Prosselkov P, Otting G, Dixon NE. Effect of protein stabilization on charge state distribution in positive- and negative-ion electrospray ionization mass spectra. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2007; 18:1605-11. [PMID: 17629493 DOI: 10.1016/j.jasms.2007.06.004] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/21/2007] [Revised: 05/28/2007] [Accepted: 06/05/2007] [Indexed: 05/16/2023]
Abstract
Changes in protein conformation are thought to alter charge state distributions observed in electrospray ionization mass spectra (ESI-MS) of proteins. In most cases, this has been demonstrated by unfolding proteins through acidification of the solution. This methodology changes the properties of the solvent so that changes in the ESI-MS charge envelopes from conformational changes are difficult to separate from the effects of changing solvent on the ionization process. A novel strategy is presented enabling comparison of ESI mass spectra of a folded and partially unfolded protein of the same amino acid sequence subjected to the same experimental protocols and conditions. The N-terminal domain of the Escherichia coli DnaB protein was cyclized by in vivo formation of an amide bond between its N- and C-termini. The properties of this stabilized protein were compared with its linear counterpart. When the linear form was unfolded by decreasing pH, a charge envelope at lower m/z appeared consistent with the presence of a population of unfolded protein. This was observed in both positive-ion and negative-ion ESI mass spectra. Under the same conditions, this low m/z envelope was not present in the ESI mass spectrum of the stable cyclized form. The effects of changing the desolvation temperature in the ionization source of the Q-TOF mass spectrometer were also investigated. Increasing the desolvation temperature had little effect on positive-ion ESI mass spectra, but in negative-ion spectra, a charge envelope at lower m/z appeared, consistent with an increase in the abundance of unfolded protein molecules.
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Affiliation(s)
- Stephen J Watt
- Chemistry Department, University of Wollongong, New South Wales, Australia
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13
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Murphy PW, Rowland EE, Byers DM. Electrospray ionization mass spectra of acyl carrier protein are insensitive to its solution phase conformation. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2007; 18:1525-32. [PMID: 17604643 DOI: 10.1016/j.jasms.2007.05.012] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/15/2007] [Revised: 05/21/2007] [Accepted: 05/23/2007] [Indexed: 05/16/2023]
Abstract
Electrospray ionization mass spectrometry (ESI-MS) can be used to monitor conformational changes of proteins in solution based on the charge state distribution (CSD) of the corresponding gas-phase ions, although relatively few studies of acidic proteins have been reported. Here, we have compared the CSD and solution structure of recombinant Vibrio harveyi acyl carrier protein (rACP), a small acidic protein whose secondary and tertiary structure can be manipulated by pH, fatty acylation, and site-directed mutagenesis. Circular dichroism and intrinsic fluorescence demonstrated that apo-rACP adopts a folded helical conformation in aqueous solution below pH 6 or in 50% acetonitrile/0.1% formic acid, but is unfolded at neutral and basic pH values. A rACP mutant, in which seven conserved acidic residues were replaced with their corresponding neutral amides, was folded over the entire pH range of 5 to 9. However, under the same solvent conditions, both wild type and mutant ACPs exhibited similar CSDs (6(+)-9(+) species) at all pH values. Covalent attachment of myristic acid to the phosphopantetheine prosthetic group of rACP, which is known to stabilize a folded conformation in solution, also had little influence on its CSD in either positive or negative ion modes. Overall, our results are consistent with ACP as a "natively unfolded" protein in a dynamic conformational equilibrium, which allows access to (de)protonation events during the electrospray process.
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Affiliation(s)
- Peter W Murphy
- Atlantic Research Centre, Department of Pediatrics, Halifax, Nova Scotia, Canada
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14
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Mathur S, Badertscher M, Scott M, Zenobi R. Critical evaluation of mass spectrometric measurement of dissociation constants: accuracy and cross-validation against surface plasmon resonance and circular dichroism for the calmodulin–melittin system. Phys Chem Chem Phys 2007; 9:6187-98. [DOI: 10.1039/b707946j] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
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