1
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Kempkes LJ, Martens J, Berden G, Houthuijs KJ, Oomens J. Investigation of the position of the radical in z3-ions resulting from electron transfer dissociation using infrared ion spectroscopy. Faraday Discuss 2019; 217:434-452. [DOI: 10.1039/c8fd00202a] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The molecular structures of six open-shell z3-ions resulting from electron transfer dissociation mass spectrometry (ETD MS) were investigated using infrared ion spectroscopy in combination with density functional theory and molecular mechanics/molecular dynamics calculations.
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Affiliation(s)
| | - Jonathan Martens
- Radboud University
- FELIX Laboratory
- 6525 ED Nijmegen
- The Netherlands
| | - Giel Berden
- Radboud University
- FELIX Laboratory
- 6525 ED Nijmegen
- The Netherlands
| | - Kas J. Houthuijs
- Radboud University
- FELIX Laboratory
- 6525 ED Nijmegen
- The Netherlands
| | - Jos Oomens
- Radboud University
- FELIX Laboratory
- 6525 ED Nijmegen
- The Netherlands
- Van’t Hoff Institute for Molecular Sciences
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2
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Kempkes LJM, Martens J, Berden G, Oomens J. w-Type ions formed by electron transfer dissociation of Cys-containing peptides investigated by infrared ion spectroscopy. JOURNAL OF MASS SPECTROMETRY : JMS 2018; 53:1207-1213. [PMID: 30281881 PMCID: PMC6283004 DOI: 10.1002/jms.4298] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/21/2018] [Revised: 08/24/2018] [Accepted: 09/26/2018] [Indexed: 06/08/2023]
Abstract
In mass spectrometry-based peptide sequencing, electron transfer dissociation (ETD) and electron capture dissociation (ECD) have become well-established fragmentation methods complementary to collision-induced dissociation. The dominant fragmentation pathways during ETD and ECD primarily involve the formation of c- and z• -type ions by cleavage of the peptide backbone at the N─Cα bond, although neutral losses from amino acid side chains have also been observed. Residue-specific neutral side chain losses provide useful information when conducting database searching and de novo sequencing. Here, we use a combination of infrared ion spectroscopy and quantum-chemical calculations to assign the structures of two ETD-generated w-type fragment ions. These ions are spontaneously formed from ETD-generated z• -type fragments by neutral loss of 33 Da in peptides containing a cysteine residue. Analysis of the infrared ion spectra confirms that these z• -ions expel a thiol radical (SH• ) and that a vinyl C═C group is formed at the cleavage site. z• -type fragments containing a Cys residue but not at the cleavage site do not spontaneously expel a thiol radical, but only upon additional collisional activation after ETD.
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Affiliation(s)
- Lisanne J. M. Kempkes
- Radboud University, Institute for Molecules and Materials, FELIX LaboratoryNijmegenThe Netherlands
| | - Jonathan Martens
- Radboud University, Institute for Molecules and Materials, FELIX LaboratoryNijmegenThe Netherlands
| | - Giel Berden
- Radboud University, Institute for Molecules and Materials, FELIX LaboratoryNijmegenThe Netherlands
| | - Jos Oomens
- Radboud University, Institute for Molecules and Materials, FELIX LaboratoryNijmegenThe Netherlands
- Van't Hoff Institute for Molecular SciencesUniversity of AmsterdamAmsterdamThe Netherlands
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3
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Chen X, Wang Z, Wong YLE, Wu R, Zhang F, Chan TWD. Electron-ion reaction-based dissociation: A powerful ion activation method for the elucidation of natural product structures. MASS SPECTROMETRY REVIEWS 2018; 37:793-810. [PMID: 29603345 DOI: 10.1002/mas.21563] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/27/2017] [Accepted: 02/12/2018] [Indexed: 05/16/2023]
Abstract
The structural elucidation of natural products (NPs) remains a challenge due to their structurally diversities and unpredictable functionalities, motifs, and scaffolds. Tandem mass spectrometry (MS/MS) is an effective method that assists the full elucidation of complicated NP structures. Ion activation methods play a key role in determining the fragmentation pathways and the structural information obtained from MS/MS. Electron-ion reaction-based dissociation (ExD) methods, including electron capture dissociation (ECD), electron transfer dissociation (ETD), electron-induced dissociation (EID), and electron detachment dissociation (EDD), can induce the breakage of specific chemical bonds and the generation of distinct fragment ions. This review article provides an overview of the mechanisms, instrumentation, and typical applications related to ExD MS/MS in the structural elucidation of NPs, primarly including lipids, oligosaccharides, glycoconjugates, metabolites, and pharmaceutical drugs. This work aims to reveal the capacity and potential of ExD mass spectrometry in analyzing NPs and consequently helping the NP communities to utilize the modern capabilities of MS/MS in the discovery and evaluation of novel NPs.
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Affiliation(s)
- Xiangfeng Chen
- Key Laboratory for Applied Technology of Sophisticated Analytical Instruments, Shandong Analysis and Test Centre, Qilu University of Technology (Shandong Academy of Science), Shandong, P.R. China
- Department of Chemistry, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong SAR, P.R. China
| | - Ze Wang
- Department of Chemistry, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong SAR, P.R. China
| | - Y-L Elaine Wong
- Department of Chemistry, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong SAR, P.R. China
| | - Ri Wu
- Department of Chemistry, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong SAR, P.R. China
| | - Feng Zhang
- Chinese Academy of Inspection and Quarantine, Beijing, P. R. China
| | - T-W Dominic Chan
- Department of Chemistry, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong SAR, P.R. China
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4
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Thakkar BS, Svendsen JSM, Engh RA. Density Functional Studies on Secondary Amides: Role of Steric Factors in Cis/Trans Isomerization. Molecules 2018; 23:molecules23102455. [PMID: 30257481 PMCID: PMC6222500 DOI: 10.3390/molecules23102455] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2018] [Revised: 09/21/2018] [Accepted: 09/21/2018] [Indexed: 11/16/2022] Open
Abstract
Cis/trans isomerization of amide bonds is a key step in a wide range of biological and synthetic processes. Occurring through C-N amide bond rotation, it also coincides with the activation of amides in enzymatic hydrolysis. In recently described QM studies of cis/trans isomerization in secondary amides using density functional methods, we highlighted that a peptidic prototype, such as glycylglycine methyl ester, can suitably represent the isomerization and complexities arising out of a larger molecular backbone, and can serve as the primary scaffold for model structures with different substitution patterns in order to assess and compare the steric effect of the substitution patterns. Here, we describe our theoretical assessment of such steric effects using tert-butyl as a representative bulky substitution. We analyze the geometries and relative stabilities of both trans and cis isomers, and effects on the cis/trans isomerization barrier. We also use the additivity principle to calculate absolute steric effects with a gradual increase in bulk. The study establishes that bulky substitutions significantly destabilize cis isomers and also increases the isomerization barrier, thereby synergistically hindering the cis/trans isomerization of secondary amides. These results provide a basis for the rationalization of kinetic and thermodynamic properties of peptides with potential applications in synthetic and medicinal chemistry.
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Affiliation(s)
- Balmukund S Thakkar
- Department of Chemistry, UiT The Arctic University of Norway, N-9037 Tromsø, Norway.
| | | | - Richard A Engh
- Department of Chemistry, UiT The Arctic University of Norway, N-9037 Tromsø, Norway.
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5
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Imaoka N, Houferak C, Murphy MP, Nguyen HTH, Dang A, Tureček F. Spontaneous Isomerization of Peptide Cation Radicals Following Electron Transfer Dissociation Revealed by UV-Vis Photodissociation Action Spectroscopy. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2018; 29:1768-1780. [PMID: 29340957 DOI: 10.1007/s13361-017-1871-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/19/2017] [Revised: 12/06/2017] [Accepted: 12/14/2017] [Indexed: 06/07/2023]
Abstract
Peptide cation radicals of the z-type were produced by electron transfer dissociation (ETD) of peptide dications and studied by UV-Vis photodissociation (UVPD) action spectroscopy. Cation radicals containing the Asp (D), Asn (N), Glu (E), and Gln (Q) residues were found to spontaneously isomerize by hydrogen atom migrations upon ETD. Canonical N-terminal [z4 + H]+● fragment ion-radicals of the R-C●H-CONH- type, initially formed by N-Cα bond cleavage, were found to be minor components of the stable ion fraction. Vibronically broadened UV-Vis absorption spectra were calculated by time-dependent density functional theory for several [●DAAR + H]+ isomers and used to assign structures to the action spectra. The potential energy surface of [●DAAR + H]+ isomers was mapped by ab initio and density functional theory calculations that revealed multiple isomerization pathways by hydrogen atom migrations. The transition-state energies for the isomerizations were found to be lower than the dissociation thresholds, accounting for the isomerization in non-dissociating ions. The facile isomerization in [●XAAR + H]+ ions (X = D, N, E, and Q) was attributed to low-energy intermediates having the radical defect in the side chain that can promote hydrogen migration along backbone Cα positions. A similar side-chain mediated mechanism is suggested for the facile intermolecular hydrogen migration between the c- and [z + H]●-ETD fragments containing Asp, Asn, Glu, and Gln residues. Graphical Abstract ᅟ.
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Affiliation(s)
- Naruaki Imaoka
- Department of Physics, Graduate School of Science, Osaka University, Toyonaka, Osaka, Japan
| | - Camille Houferak
- Department of Chemistry, University of Washington, Box 351700, Seattle, WA, 98195-1700, USA
| | - Megan P Murphy
- Department of Chemistry, University of Washington, Box 351700, Seattle, WA, 98195-1700, USA
| | - Huong T H Nguyen
- Department of Chemistry, University of Washington, Box 351700, Seattle, WA, 98195-1700, USA
| | - Andy Dang
- Department of Chemistry, University of Washington, Box 351700, Seattle, WA, 98195-1700, USA
| | - František Tureček
- Department of Chemistry, University of Washington, Box 351700, Seattle, WA, 98195-1700, USA.
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6
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Nagoshi K, Yamakoshi M, Sakamoto K, Takayama M. Specific Cα-C Bond Cleavage of β-Carbon-Centered Radical Peptides Produced by Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2018; 29:1473-1483. [PMID: 29675742 DOI: 10.1007/s13361-018-1958-2] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/09/2018] [Revised: 03/14/2018] [Accepted: 03/29/2018] [Indexed: 06/08/2023]
Abstract
Radical-driven dissociation (RDD) of hydrogen-deficient peptide ions [M - H + H]·+ has been examined using matrix-assisted laser dissociation/ionization in-source decay mass spectrometry (MALDI-ISD MS) with the hydrogen-abstracting matrices 4-nitro-1-naphthol (4,1-NNL) and 5-nitrosalicylic acid (5-NSA). The preferential fragment ions observed in the ISD spectra include N-terminal [a] + ions and C-terminal [x]+, [y + 2]+, and [w]+ ions which imply that β-carbon (Cβ)-centered radical peptide ions [M - Hβ + H]·+ are predominantly produced in MALDI conditions. RDD reactions from the peptide ions [M - Hβ + H]·+ successfully explains the fact that both [a]+ and [x]+ ions arising from cleavage at the Cα-C bond of the backbone of Gly-Xxx residues are missing from the ISD spectra. Furthermore, the formation of [a]+ ions originating from the cleavage of Cα-C bond of deuterated Ala(d3)-Xxx residues indicates that the [a]+ ions are produced from the peptide ions [M - Hβ + H]·+ generated by deuteron-abstraction from Ala(d3) residues. It is suggested that from the standpoint of hydrogen abstraction via direct interactions between the nitro group of matrix and hydrogen of peptides, the generation of the peptide radical ions [M - Hβ + H]·+ is more favorable than that of the α-carbon (Cα)-centered radical ions [M - Hα + H]·+ and the amide nitrogen-centered radical ions [M - HN + H]·+, while ab initio calculations indicate that the formation of [M - Hα + H]·+ is energetically most favorable. Graphical Abstract ᅟ.
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Affiliation(s)
- Keishiro Nagoshi
- Mass Spectrometry Laboratory, Graduate School in Nanobioscience, Yokohama City University, 22-2 Seto, Kanazawa-ku, Yokohama, 236-0027, Japan
| | - Mariko Yamakoshi
- Mass Spectrometry Laboratory, Graduate School in Nanobioscience, Yokohama City University, 22-2 Seto, Kanazawa-ku, Yokohama, 236-0027, Japan
| | - Kenya Sakamoto
- Mass Spectrometry Laboratory, Graduate School in Nanobioscience, Yokohama City University, 22-2 Seto, Kanazawa-ku, Yokohama, 236-0027, Japan
| | - Mitsuo Takayama
- Mass Spectrometry Laboratory, Graduate School in Nanobioscience, Yokohama City University, 22-2 Seto, Kanazawa-ku, Yokohama, 236-0027, Japan.
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7
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Thakkar BS, Svendsen JSM, Engh RA. Cis/Trans Isomerization in Secondary Amides: Reaction Paths, Nitrogen Inversion, and Relevance to Peptidic Systems. J Phys Chem A 2017; 121:6830-6837. [DOI: 10.1021/acs.jpca.7b05584] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Balmukund S. Thakkar
- Department of Chemistry, UiT The Arctic University of Norway, Tromsø-9037, Norway
| | | | - Richard A. Engh
- Department of Chemistry, UiT The Arctic University of Norway, Tromsø-9037, Norway
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8
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Nguyen HTH, Tureček F. Near-UV Photodissociation of Tryptic Peptide Cation Radicals. Scope and Effects of Amino Acid Residues and Radical Sites. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2017; 28:1333-1344. [PMID: 28155086 DOI: 10.1007/s13361-016-1586-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/23/2016] [Revised: 12/20/2016] [Accepted: 12/21/2016] [Indexed: 06/06/2023]
Abstract
Peptide cation-radical fragment ions of the z-type, [●AXAR+], [●AXAK+], and [●XAR+], where X = A, C, D, E, F, G, H, K, L, M, N, P, Y, and W, were generated by electron transfer dissociation of peptide dications and investigated by MS3-near-ultraviolet photodissociation (UVPD) at 355 nm. Laser-pulse dependence measurements indicated that the ion populations were homogeneous for most X residues except phenylalanine. UVPD resulted in dissociations of backbone CO─NH bonds that were accompanied by hydrogen atom transfer, producing fragment ions of the [yn]+ type. Compared with collision-induced dissociation, UVPD yielded less side-chain dissociations even for residues that are sensitive to radical-induced side-chain bond cleavages. The backbone dissociations are triggered by transitions to second (B) excited electronic states in the peptide ion R-CH●-CONH- chromophores that are resonant with the 355-nm photon energy. Electron promotion increases the polarity of the B excited states, R-CH+-C●(O-)NH-, and steers the reaction to proceed by transfer of protons from proximate acidic Cα and amide nitrogen positions. Graphical Abstract ᅟ.
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Affiliation(s)
- Huong T H Nguyen
- Department of Chemistry, University of Washington, Bagley Hall, Box 351700, Seattle, WA, 98195-1700, USA
| | - František Tureček
- Department of Chemistry, University of Washington, Bagley Hall, Box 351700, Seattle, WA, 98195-1700, USA.
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9
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Nguyen HTH, Andrikopoulos PC, Bím D, Rulíšek L, Dang A, Tureček F. Radical Reactions Affecting Polar Groups in Threonine Peptide Ions. J Phys Chem B 2017; 121:6557-6569. [DOI: 10.1021/acs.jpcb.7b04661] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Affiliation(s)
- Huong T. H. Nguyen
- Department
of Chemistry, University of Washington, Bagley Hall, Box
351700, Seattle, Washington 98195-1700, United States
| | - Prokopis C. Andrikopoulos
- Institute
of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo nám 2, 16610 Prague, Czech Republic
| | - Daniel Bím
- Institute
of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo nám 2, 16610 Prague, Czech Republic
| | - Lubomír Rulíšek
- Institute
of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Flemingovo nám 2, 16610 Prague, Czech Republic
| | - Andy Dang
- Department
of Chemistry, University of Washington, Bagley Hall, Box
351700, Seattle, Washington 98195-1700, United States
| | - František Tureček
- Department
of Chemistry, University of Washington, Bagley Hall, Box
351700, Seattle, Washington 98195-1700, United States
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10
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Qi Y, Volmer DA. Electron-based fragmentation methods in mass spectrometry: An overview. MASS SPECTROMETRY REVIEWS 2017; 36:4-15. [PMID: 26445267 DOI: 10.1002/mas.21482] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/10/2015] [Revised: 07/03/2015] [Accepted: 07/03/2015] [Indexed: 05/21/2023]
Abstract
Tandem mass spectrometry (MS/MS) provides detailed information for structural characterization of biomolecules. The combination of electron capture dissociation (ECD) techniques with Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) often provides unique ion-electron reactions and fragmentation channels in MS/MS. ECD is often a complimentary, sometimes even a superior tool to conventional MS/MS techniques. This article is aimed at providing a short overview of ECD-based fragmentation techniques (ExD) and optimization of ECD experiments for FTICR mass analyzers. Most importantly, it is meant to pique the interest of potential users for this exciting research field. © 2015 Wiley Periodicals, Inc. Mass Spec Rev 36:4-15, 2017.
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Affiliation(s)
- Yulin Qi
- Institute of Bioanalytical Chemistry, Saarland University, Campus B2.2, Saarbrücken, 66123, Germany
| | - Dietrich A Volmer
- Institute of Bioanalytical Chemistry, Saarland University, Campus B2.2, Saarbrücken, 66123, Germany
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11
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Viglino E, Lai CK, Mu X, Chu IK, Tureček F. Ground and Excited-Electronic-State Dissociations of Hydrogen-Rich and Hydrogen-Deficient Tyrosine Peptide Cation Radicals. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2016; 27:1454-1467. [PMID: 27278824 DOI: 10.1007/s13361-016-1425-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2016] [Revised: 05/10/2016] [Accepted: 05/20/2016] [Indexed: 06/06/2023]
Abstract
We report a comprehensive study of collision-induced dissociation (CID) and near-UV photodissociation (UVPD) of a series of tyrosine-containing peptide cation radicals of the hydrogen-rich and hydrogen-deficient types. Stable, long-lived, hydrogen-rich peptide cation radicals, such as [AAAYR + 2H](+●) and several of its sequence and homology variants, were generated by electron transfer dissociation (ETD) of peptide-crown-ether complexes, and their CID-MS(3) dissociations were found to be dramatically different from those upon ETD of the respective peptide dications. All of the hydrogen-rich peptide cation radicals contained major (77%-94%) fractions of species having radical chromophores created by ETD that underwent photodissociation at 355 nm. Analysis of the CID and UVPD spectra pointed to arginine guanidinium radicals as the major components of the hydrogen-rich peptide cation radical population. Hydrogen-deficient peptide cation radicals were generated by intramolecular electron transfer in Cu(II)(2,2':6',2″-terpyridine) complexes and shown to contain chromophores absorbing at 355 nm and undergoing photodissociation. The CID and UVPD spectra showed major differences in fragmentation for [AAAYR](+●) that diminished as the Tyr residue was moved along the peptide chain. UVPD was found to be superior to CID in localizing Cα-radical positions in peptide cation radical intermediates. Graphical Abstract ᅟ.
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Affiliation(s)
- Emilie Viglino
- Department of Chemistry, University of Washington, Bagley Hall, Box 351700, Seattle, WA, 981915-1700, USA
| | - Cheuk Kuen Lai
- Department of Chemistry, University of Hong Kong, Pokfulam Road, Hong Kong, China
| | - Xiaoyan Mu
- Department of Chemistry, University of Hong Kong, Pokfulam Road, Hong Kong, China
| | - Ivan K Chu
- Department of Chemistry, University of Hong Kong, Pokfulam Road, Hong Kong, China.
| | - František Tureček
- Department of Chemistry, University of Washington, Bagley Hall, Box 351700, Seattle, WA, 981915-1700, USA.
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12
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Shaffer CJ, Martens J, Marek A, Oomens J, Tureček F. Photoleucine Survives Backbone Cleavage by Electron Transfer Dissociation. A Near-UV Photodissociation and Infrared Multiphoton Dissociation Action Spectroscopy Study. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2016; 27:1176-1185. [PMID: 27059977 DOI: 10.1007/s13361-016-1390-4] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/15/2016] [Revised: 03/15/2016] [Accepted: 03/16/2016] [Indexed: 06/05/2023]
Abstract
We report a combined experimental and computational study aimed at elucidating the structure of N-terminal fragment ions of the c type produced by electron transfer dissociation of photo-leucine (L*) peptide ions GL*GGKX. The c 4 ion from GL*GGK is found to retain an intact diazirine ring that undergoes selective photodissociation at 355 nm, followed by backbone cleavage. Infrared multiphoton dissociation action spectra point to the absence in the c 4 ion of a diazoalkane group that could be produced by thermal isomerization of vibrationally hot ions. The c 4 ion from ETD of GL*GGK is assigned an amide structure by a close match of the IRMPD action spectrum and calculated IR absorption. The energetics and kinetics of c 4 ion dissociations are discussed. Graphical Abstract ᅟ.
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Affiliation(s)
| | - Jonathan Martens
- FELIX Laboratory, Radboud University Nijmegen, Institute for Molecules and Materials, Toernooiveld 7c, 6525ED, Nijmegen, The Netherlands
| | - Aleš Marek
- Department of Chemistry, University of Washington, Seattle, WA, 98195-1700, USA
- Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Prague, Czech Republic
| | - Jos Oomens
- FELIX Laboratory, Radboud University Nijmegen, Institute for Molecules and Materials, Toernooiveld 7c, 6525ED, Nijmegen, The Netherlands
- van't Hoff Institute for Molecular Sciences, University of Amsterdam, 1098XH, Amsterdam, Science Park 908, The Netherlands
| | - František Tureček
- Department of Chemistry, University of Washington, Seattle, WA, 98195-1700, USA.
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13
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Martens J, Grzetic J, Berden G, Oomens J. Structural identification of electron transfer dissociation products in mass spectrometry using infrared ion spectroscopy. Nat Commun 2016; 7:11754. [PMID: 27277826 PMCID: PMC4906228 DOI: 10.1038/ncomms11754] [Citation(s) in RCA: 71] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2015] [Accepted: 04/27/2016] [Indexed: 12/04/2022] Open
Abstract
Tandem mass spectrometry occupies a principle place among modern analytical methods and drives many developments in the ‘omics' sciences. Electron attachment induced dissociation methods, as alternatives for collision-induced dissociation have profoundly influenced the field of proteomics, enabling among others the top-down sequencing of entire proteins and the analysis of post-translational modifications. The technique, however, produces more complex mass spectra and its radical-driven reaction mechanisms remain incompletely understood. Here we demonstrate the facile structural characterization of electron transfer dissociation generated peptide fragments by infrared ion spectroscopy using the tunable free-electron laser FELIX, aiding the elucidation of the underlying dissociation mechanisms. We apply this method to verify and revise previously proposed product ion structures for an often studied model tryptic peptide, [AlaAlaHisAlaArg+2H]2+. Comparing experiment with theory reveals that structures that would be assigned using only theoretical thermodynamic considerations often do not correspond to the experimentally sampled species. Mass spectrometry is a leading method used for sequencing peptides and proteins by fragmentation followed by analysis of the sequence fragments. Here, the authors use infrared spectroscopy to characterize the structures of peptide fragments formed during electron transfer dissociation.
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Affiliation(s)
- Jonathan Martens
- Radboud University, Institute for Molecules and Materials, FELIX Laboratory, Toernooiveld 7c, 6525ED Nijmegen, The Netherlands
| | - Josipa Grzetic
- Radboud University, Institute for Molecules and Materials, FELIX Laboratory, Toernooiveld 7c, 6525ED Nijmegen, The Netherlands
| | - Giel Berden
- Radboud University, Institute for Molecules and Materials, FELIX Laboratory, Toernooiveld 7c, 6525ED Nijmegen, The Netherlands
| | - Jos Oomens
- Radboud University, Institute for Molecules and Materials, FELIX Laboratory, Toernooiveld 7c, 6525ED Nijmegen, The Netherlands.,Van 't Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 908, 1098XH Amsterdam, The Netherlands
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14
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Abstract
UV photodissociation (UVPD) action spectroscopy is reported to provide a sensitive tool for the detection of radical sites in gas-phase peptide ions. UVPD action spectra of peptide cation radicals of the z-type generated by electron-transfer dissociation point to the presence of multiple structures formed as a result of spontaneous isomerizations by hydrogen atom migration. N-terminal Cα radicals are identified as the dominant components, but the content of isomers differing in the radical defect position in the backbone or side chain depends on the nature of the aromatic residue with phenylalanine being more prone to isomerization than tryptophan. These results illustrate that spontaneous hydrogen atom migrations can occur in peptide cation-radicals upon electron-transfer dissociation.
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Affiliation(s)
- Huong T H Nguyen
- Department of Chemistry, University of Washington , Bagley Hall, Box 351700, Seattle, Washington 981195-1700, United States
| | - Christopher J Shaffer
- Department of Chemistry, University of Washington , Bagley Hall, Box 351700, Seattle, Washington 981195-1700, United States
| | - Robert Pepin
- Department of Chemistry, University of Washington , Bagley Hall, Box 351700, Seattle, Washington 981195-1700, United States
| | - František Tureček
- Department of Chemistry, University of Washington , Bagley Hall, Box 351700, Seattle, Washington 981195-1700, United States
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15
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Tang WK, Leong CP, Hao Q, Siu CK. Theoretical examination of competitive β-radical-induced cleavages of N–Cα and Cα–C bonds of peptides. CAN J CHEM 2015. [DOI: 10.1139/cjc-2015-0208] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Selective cleavages of N–Cα and Cα–C bonds of β-radical tautomers of amino acid residues in radical peptides have been examined theoretically by means of the density functional theory at the M06-2X/6-311++G(d,p) level. The majority of the bond cleavages are homolytic via β-scission. Their energy barriers depend largely on the ability of the radical being stabilized in the transition structures and the availability of a mobile proton in the vicinity of the β-radical center. The N–Cα bond is less favorably cleaved than the Cα–C bond (except Ser and Thr) for systems without a mobile proton. It is because, firstly, the homolytic cleavage is less favorable for the more polar N–Cα bond than for the less polar Cα–C bond. Secondly, a less stable σ-radical localized on the amide nitrogen atom of the incipient N-terminal fragment is formed for the former, while a more stable radical delocalized in a π*(CO)-like orbital of the incipient C-terminal fragment is formed for the latter. In the presence of a mobile proton N-terminal to the β-radical center, some degrees of heterolytic cleavage character, as preferred by the polar N–Cα bond, are observed. Consequently, its barrier is reduced. If the mobile proton is located at the C-terminal amide oxygen of the β-radical center, the Cα–C bond cleavage will be significantly suppressed. It is because the radical in the incipient C-terminal fragment becomes more localized as a σ-radical on the carbon atom of its protonated amide group. With basic amino acid residues, the Cα–C bond cleavage can be reactivated. Heterolytic cleavage of the polar N–Cα bond can be largely facilitated if a mobile proton N-terminal to the β-radical center is available and the radical in the incipient C-terminal fragment is sufficiently stabilized, for instance, by the aromatic side chain of Trp and Tyr. Therefore, cleavages of the N–Cα bond induced by the β-radical tautomer of Trp and Tyr are often preferred as compared with cleavages of the Cα–C bond in peptide radical cations containing mobile protons.
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Affiliation(s)
- Wai-Kit Tang
- Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon Tong, Hong Kong SAR, P.R. China
- Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon Tong, Hong Kong SAR, P.R. China
| | - Chun-Ping Leong
- Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon Tong, Hong Kong SAR, P.R. China
- Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon Tong, Hong Kong SAR, P.R. China
| | - Qiang Hao
- Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon Tong, Hong Kong SAR, P.R. China
- Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon Tong, Hong Kong SAR, P.R. China
| | - Chi-Kit Siu
- Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon Tong, Hong Kong SAR, P.R. China
- Department of Biology and Chemistry, City University of Hong Kong, 83 Tat Chee Avenue, Kowloon Tong, Hong Kong SAR, P.R. China
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16
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Tureček F. Benchmarking Electronic Excitation Energies and Transitions in Peptide Radicals. J Phys Chem A 2015; 119:10101-11. [DOI: 10.1021/acs.jpca.5b06235] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- František Tureček
- Department of Chemistry, University of Washington, Bagley Hall,
Box 351700, Seattle, Washington 98195-1700, United States
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17
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Shaffer CJ, Marek A, Nguyen HTH, Tureček F. Combining Near-UV Photodissociation with Electron Transfer. Reduction of the Diazirine Ring in a Photomethionine-Labeled Peptide Ion. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2015; 26:1367-1381. [PMID: 25904063 DOI: 10.1007/s13361-015-1139-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2015] [Revised: 02/26/2015] [Accepted: 03/12/2015] [Indexed: 06/04/2023]
Abstract
Electron transfer dissociation of peptide ions with the diazirine-containing residue photomethionine (M*) results in side-chain dissociations by loss of C3H7N2 radicals in addition to standard backbone cleavages. The side-chain dissociations are particularly prominent upon activation of long-lived, charge-reduced, cation radicals (GM*GGR + 2H)(+•). Investigation of these cation radicals by near-UV photodissociation and collisional activation revealed different fragmentation products and mechanisms resulting from these ion activation modes. The dissociations observed for photomethionine were dramatically different from those previously reported for the lower homologue photoleucine; here, a difference by a single methylene group in the side chain had a large effect on the chemistries of the cation radicals upon ETD and further activation. ETD intermediates and products were probed by tandem 355-nm UV photodissociation-collision induced dissociation and found to contain chromophores that resulted from electron attachment to the diazirine ring. The nature of the newly formed chromophores and ion energetics and kinetics were investigated by electron structure calculations combining ab initio and density functional theory methods and Rice-Ramsperger-Kassel-Marcus (RRKM) theory. The dramatic difference between the dissociations of L* and M* containing peptide cation radicals is explained by electronic effects that play a role in stabilizing critical reaction intermediates and steer the dissociations into kinetically favored reaction channels. In addition, a new alternating UVPD-ETD-UVPD MS(4) experiment is introduced and utilized for ion structure elucidation.
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Affiliation(s)
- Christopher J Shaffer
- Department of Chemistry, University of Washington, Bagley Hall, Box 351700, Seattle, WA, 98195-1700, USA
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18
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Marek A, Shaffer CJ, Pepin R, Slováková K, Laszlo KJ, Bush MF, Tureček F. Electron transfer reduction of the diazirine ring in gas-phase peptide ions. On the peculiar loss of [NH4O] from photoleucine. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2015; 26:415-431. [PMID: 25515220 DOI: 10.1007/s13361-014-1047-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/18/2014] [Revised: 10/22/2014] [Accepted: 11/02/2014] [Indexed: 06/04/2023]
Abstract
Electron transfer to gas-phase peptide ions with diazirine-containing amino acid residue photoleucine (L*) triggers diazirine ring reduction followed by cascades of residue-specific radical reactions. Upon electron transfer, substantial fractions of (GL*GGR +2H)(+[Symbol: see text]) cation-radicals undergo elimination of [NH(4)O] radicals and N(2)H(2) molecules from the side chain. The side-chain dissociations are particularly prominent on collisional activation of long-lived (GL*GGR +2H)(+[Symbol: see text]) cation-radicals formed by electron transfer dissociation of noncovalent peptide-18-crown-6-ether ion complexes. The ion dissociation products were characterized by multistage tandem mass spectrometry (MS(n)) and ion mobility measurements. The elimination of [NH(4)O] was elucidated with the help of (2)H, (15) N, and (18)O-labeled peptide ions and found to specifically involve the amide oxygen of the N-terminal residue. The structures, energies, and electronic states of the peptide radical species were elucidated by a combination of near-UV photodissociation experiments and electron structure calculations combining ab initio and density functional theory methods. Electron transfer reaching the ground electronic states of charge reduced (GL*GGR +2H)(+[Symbol: see text]) cation-radicals was found to reduce the diazirine ring. In contrast, backbone N - Cα bond dissociations that represent a 60%-75% majority of all dissociations because of electron transfer are predicted to occur from excited electronic states.
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Affiliation(s)
- Aleš Marek
- Department of Chemistry, Bagley Hall, University of Washington, Seattle, WA, 98195-1700, USA
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19
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Nguyen HTH, Shaffer CJ, Ledvina AR, Coon JJ, Tureček F. Serine effects on collision-induced dissociation and photodissociation of peptide cation radicals of the z+• -type. INTERNATIONAL JOURNAL OF MASS SPECTROMETRY 2015; 378:20-30. [PMID: 26005367 PMCID: PMC4437545 DOI: 10.1016/j.ijms.2014.06.028] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
The serine residue displays specific effects on the dissociations of peptide fragment cation-radicals of the z+• type which are produced by electron transfer dissociation. Energy-resolved collision-induced dissociation (ER-CID), time-resolved infrared multiphoton dissociation (TR-IRMPD), and single-photon UV photodissociation at 355 nm revealed several competitive dissociation pathways consisting of loss of OH radical, water, and backbone cleavages occurring at N-terminal and C-terminal positions relative to the serine residue. The activation modes using slow-heating and UV photon absorption resulted in different relative intensities of fragment ions. This indicated that the dissociations proceeded through several channels with different energy-dependent kinetics. The experimental data were interpreted with the help of electron structure calculations that provided fully optimized structures and relative energies for cis and trans amide isomers of the z4+• ions as well as isomerization, dissociation, and transition state energies. UV photon absorption by the z4+• ions was due to Cα-radical amide groups created by ETD that provided a new chromophore absorbing at 355 nm.
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Affiliation(s)
- Huong T H Nguyen
- Department of Chemistry, Bagley Hall, Box 351700, University of Washington, Seattle, WA, 98195-1700
| | - Christopher J Shaffer
- Department of Chemistry, Bagley Hall, Box 351700, University of Washington, Seattle, WA, 98195-1700
| | - Aaron R Ledvina
- Department of Chemistry, University of Wisconsin, Madison, WI, USA
| | - Joshua J Coon
- Department of Chemistry, University of Wisconsin, Madison, WI, USA ; Department of Biomolecular Chemistry, University of Wisconsin, Madison, WI, USA
| | - František Tureček
- Department of Chemistry, Bagley Hall, Box 351700, University of Washington, Seattle, WA, 98195-1700
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20
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Ledvina AR, Coon JJ, Tureček F. Competitive Hydrogen Atom Migrations Accompanying Cascade Dissociations of Peptide Cation-Radicals of the z+• Type. INTERNATIONAL JOURNAL OF MASS SPECTROMETRY 2015; 377:44-53. [PMID: 25844055 PMCID: PMC4380023 DOI: 10.1016/j.ijms.2014.02.015] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
We report a combined experimental and computational study of energy-resolved collision-induced dissociation (ER-CID) and time-resolved infrared multiphoton dissociation (TR-IRMPD) of z4 ions prepared by electron transfer dissociation of peptide (Ala-Ala-Asn-Ala-Arg + 2H)2+ ions. The z4 cation-radicals, •ANAR+, undergo competitive dissociations by backbone cleavage and loss of a CONH2 radical from the Asn side chain. The backbone cleavage proceeds by radical-assisted dissociation of the Asn Cα-CO bond, forming an x2 ion intermediate which rapidly dissociates by HNCO elimination to yield a stable z2 fragment ion, •AR+. The ER-CID and TR-IRMPD data were consistent with the consecutive nature of the backbone dissociation but showed different branching ratios for the two major fragmentations. The ER-CID data showed branching ratios 0.6-1.0 for the side-chain and backbone cleavages whereas the TR-IRMPD data showed an earlier onset for the latter dissociation. Computational analysis of the potential energy surface with density functional theory and ab initio calculations was carried out to provide structures and energies for the reactant ions as well as several intermediates, products, and transition states. Dissociation pathways for cis and trans amide conformers were distinguished and their energies were evaluated. The threshold dissociation energies for the backbone and side-chain dissociations were similar in accordance with the experimental ER-CID branching ratio. The TR-IRMPD data were interpreted by different absorbances of intermediates produced by hydrogen atom migrations along the dissociation pathways.
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Affiliation(s)
- Aaron R Ledvina
- Department of Chemistry, University of Wisconsin, Madison, WI, USA
| | - Joshua J Coon
- Department of Chemistry, University of Wisconsin, Madison, WI, USA ; Department of Biomolecular Chemistry, University of Wisconsin, Madison, WI, USA
| | - František Tureček
- Department of Chemistry, Bagley Hall, Box 351700, University of Washington, Seattle, WA 98195-1700, USA
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21
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Riffet V, Jacquemin D, Cauët E, Frison G. Benchmarking DFT and TD-DFT Functionals for the Ground and Excited States of Hydrogen-Rich Peptide Radicals. J Chem Theory Comput 2014; 10:3308-18. [DOI: 10.1021/ct5004912] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Vanessa Riffet
- Laboratoire
de Chimie Moléculaire, Département de Chimie, Ecole
polytechnique and CNRS, 91128 Palaiseau cedex, France
| | - Denis Jacquemin
- Laboratoire
CEISAM, UMR CNRS 6230, Université de Nantes, 2 rue de la
Houssinière - BP 92208, 44322 Nantes cedex 3, France
- Institut Universitaire
de France, 103 bd Saint-Michel, F-75005 Paris Cedex 05, France
| | - Emilie Cauët
- Service
de Chimie quantique et Photophysique, Université Libre de Bruxelles, CP160/09, 50 av. F.D. Roosevelt, 1050 Bruxelles, Belgium
| | - Gilles Frison
- Laboratoire
de Chimie Moléculaire, Département de Chimie, Ecole
polytechnique and CNRS, 91128 Palaiseau cedex, France
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22
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Bogdanov B, Zhao X, Robinson DB, Ren J. Electron capture dissociation studies of the fragmentation patterns of doubly protonated and mixed protonated-sodiated peptoids. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2014; 25:1202-1216. [PMID: 24845348 DOI: 10.1007/s13361-014-0869-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/21/2013] [Revised: 02/09/2014] [Accepted: 02/14/2014] [Indexed: 06/03/2023]
Abstract
The fragmentation patterns of a group of doubly protonated ([P + 2H](2+)) and mixed protonated-sodiated ([P + H + Na](2+)) peptide-mimicking oligomers, known as peptoids, have been studied using electron capturing dissociation (ECD) tandem mass spectrometry techniques. For all the peptoids studied, the primary backbone fragmentation occurred at the N-Cα bonds. The N-terminal fragment ions, the C-ions (protonated) and the C'-ions (sodiated) were observed universally for all the peptoids regardless of the types of charge carrier. The C-terminal ions varied depending on the type of charge carrier. The doubly protonated peptoids with at least one basic residue located at a position other than the N-terminus fragmented by producing the Z(•)-series of ions. In addition, most doubly protonated peptoids also produced the Y-series of ions with notable abundances. The mixed protonated-sodiated peptoids fragmented by yielding the Z(•)'-series of ions in addition to the C'-series. Chelation between the sodium cation and the amide groups of the peptoid chain might be an important factor that could stabilize both the N-terminal and the C-terminal fragment ions. Regardless of the types of the charge carrier, one notable fragmentation for all the peptoids was the elimination of a benzylic radical from the odd-electron positive ions of the protonated peptoids ([P + 2H](•+)) and the sodiated peptoids ([P + H + Na](•+)). The study showed potential utility of using the ECD technique for sequencing of peptoid libraries generated by combinatorial chemistry.
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Affiliation(s)
- Bogdan Bogdanov
- Department of Chemistry, University of the Pacific, Stockton, CA, 95211, USA
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23
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Mädler S, Kai-Chi Lau J, Williams D, Wang Y, Saminathan IS, Zhao J, Siu KWM, Hopkinson AC. Fragmentation of Peptide Radical Cations Containing a Tyrosine or Tryptophan Residue: Structural Features That Favor Formation of [x(n–1) + H]•+ and [z(n–1) + H]•+ Ions. J Phys Chem B 2014; 118:6123-33. [DOI: 10.1021/jp5030087] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Affiliation(s)
- Stefanie Mädler
- Department
of Chemistry and Centre for Research in Mass Spectrometry, York University, 4700 Keele Street, Toronto, Ontario Canada M3J 1P3
| | - Justin Kai-Chi Lau
- Department
of Chemistry and Centre for Research in Mass Spectrometry, York University, 4700 Keele Street, Toronto, Ontario Canada M3J 1P3
- Department
of Chemistry, University of Windsor, 401 Sunset Avenue, Windsor, Ontario Canada N9B 3P4
| | - Declan Williams
- Department
of Chemistry and Centre for Research in Mass Spectrometry, York University, 4700 Keele Street, Toronto, Ontario Canada M3J 1P3
| | - Yating Wang
- Department
of Chemistry and Centre for Research in Mass Spectrometry, York University, 4700 Keele Street, Toronto, Ontario Canada M3J 1P3
| | - Irine S. Saminathan
- Department
of Chemistry and Centre for Research in Mass Spectrometry, York University, 4700 Keele Street, Toronto, Ontario Canada M3J 1P3
| | - Junfang Zhao
- Department
of Chemistry and Centre for Research in Mass Spectrometry, York University, 4700 Keele Street, Toronto, Ontario Canada M3J 1P3
| | - K. W. Michael Siu
- Department
of Chemistry and Centre for Research in Mass Spectrometry, York University, 4700 Keele Street, Toronto, Ontario Canada M3J 1P3
- Department
of Chemistry, University of Windsor, 401 Sunset Avenue, Windsor, Ontario Canada N9B 3P4
| | - Alan C. Hopkinson
- Department
of Chemistry and Centre for Research in Mass Spectrometry, York University, 4700 Keele Street, Toronto, Ontario Canada M3J 1P3
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24
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Mu X, Song T, Xu M, Lai CK, Siu CK, Laskin J, Chu IK. Discovery and mechanistic studies of facile N-terminal Cα-C bond cleavages in the dissociation of tyrosine-containing peptide radical cations. J Phys Chem B 2014; 118:4273-81. [PMID: 24678922 DOI: 10.1021/jp410525f] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Fascinating N-terminal Cα-C bond cleavages in a series of nonbasic tyrosine-containing peptide radical cations have been observed under low-energy collision-induced dissociation (CID), leading to the generation of rarely observed x-type radical fragments, with significant abundances. CID experiments of the radical cations of the alanyltyrosylglycine tripeptide and its analogues suggested that the N-terminal Cα-C bond cleavage, yielding its [x2 + H](•+) radical cation, does not involve an N-terminal α-carbon-centered radical. Theoretical examination of a prototypical radical cation of the alanyltyrosine dipeptide, using density functional theory calculations, suggested that direct N-terminal Cα-C bond cleavage could produce an ion-molecule complex formed between the incipient a1(+) and x1(•) fragments. Subsequent proton transfer from the iminium nitrogen atom in a1(+) to the acyl carbon atom in x1(•) results in the observable [x1 + H](•+). The barriers against this novel Cα-C bond cleavage and the competitive N-Cα bond cleavage, forming the complementary [c1 + 2H](+)/[z1 - H](•+) ion pair, are similar (ca. 16 kcal mol(-1)). Rice-Ramsperger-Kassel-Marcus modeling revealed that [x1 + H](•+) and [c1 + 2H](+) species are formed with comparable rates, in agreement with energy-resolved CID experiments for [AY](•+).
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Affiliation(s)
- Xiaoyan Mu
- Department of Chemistry, The University of Hong Kong , Hong Kong, China
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25
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Marek A, Pepin R, Peng B, Laszlo KJ, Bush MF, Tureček F. Electron transfer dissociation of photolabeled peptides. Backbone cleavages compete with diazirine ring rearrangements. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2013; 24:1641-1653. [PMID: 23633016 DOI: 10.1007/s13361-013-0630-0] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/28/2012] [Revised: 03/25/2013] [Accepted: 03/25/2013] [Indexed: 06/02/2023]
Abstract
Gas-phase conformations and electron transfer dissociations of pentapeptide ions containing the photo-Leu residue (L*) were studied. Exhaustive conformational search including molecular dynamics force-field, semi-empirical, ab initio, and density functional theory calculations established that the photo-Leu residue did not alter the gas-phase conformations of (GL*GGK + 2H)(2+) and (GL*GGK-NH2 + H)(+) ions, which showed the same conformer energy ranking as the unmodified Leu-containing ions. This finding is significant in that it simplifies conformational analysis of photo-labeled peptide ions. Electron transfer dissociation mass spectra of (GL*GGK + 2H)(2+), (GL*GGK-NH2 + 2H)(2+),(GL*GGKK + 2H)(2+), (GL*GLK + 2H)(2+), and (GL*LGK + 2H)(2+) showed 16 %-21 % fragment ions originating by radical rearrangements and cleavages in the diazirine ring. These side-chain dissociations resulted in eliminations of N2H3, N2H4, [N2H5], and [NH4O] neutral fragments and were particularly abundant in long-lived charge-reduced cation-radicals. Deuterium labeling established that the neutral hydrazine molecules mainly contained two exchangeable and two nonexchangeable hydrogen atoms from the peptide and underwent further H/D exchange in an ion-molecule complex. Electron structure calculations on the charge-reduced ions indicated that the unpaired electron was delocalized between the diazirine and amide π* electronic systems in the low electronic states of the cation-radicals. The diazirine moiety in GL*GGK-NH2was calculated to have an intrinsic electron affinity of 1.5 eV, which was further increased by the Coulomb effect of the peptide positive charge. Mechanisms are proposed for the unusual elimination of hydrazine from the photo-labeled peptide ions.
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Affiliation(s)
- Aleš Marek
- Department of Chemistry, Bagley Hall, University of Washington, Seattle, WA, USA
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26
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Affiliation(s)
- František Tureček
- Department of Chemistry, Bagley Hall, University of Washington , Seattle, Washington 98195-1700, United States
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