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Girod M, Arquier D, Helms A, Juetten K, Brodbelt JS, Lemoine J, MacAleese L. Characterization of Phosphorylated Peptides by Electron-Activated and Ultraviolet Dissociation Mass Spectrometry: A Comparative Study with Collision-Induced Dissociation. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2024; 35:1040-1054. [PMID: 38626331 DOI: 10.1021/jasms.4c00048] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/18/2024]
Abstract
Mass-spectrometry-based methods have made significant progress in the characterization of post-translational modifications (PTMs) in peptides and proteins; however, room remains to improve fragmentation methods. Ideal MS/MS methods are expected to simultaneously provide extensive sequence information and localization of PTM sites and retain labile PTM groups. This collection of criteria is difficult to meet, and the various activation methods available today offer different capabilities. In order to examine the specific case of phosphorylation on peptides, we investigate electron transfer dissociation (ETD), electron-activated dissociation (EAD), and 193 nm ultraviolet photodissociation (UVPD) and compare all three methods with classical collision-induced dissociation (CID). EAD and UVPD show extensive backbone fragmentation, comparable in scope to that of CID. These methods provide diverse backbone fragmentation, producing a/x, b/y, and c/z ions with substantial sequence coverages. EAD displays a high retention efficiency of the phosphate modification, attributed to its electron-mediated fragmentation mechanisms, as observed in ETD. UVPD offers reasonable retention efficiency, also allowing localization of the PTM site. EAD experiments were also performed in an LC-MS/MS workflow by analyzing phosphopeptides spiked in human plasma, and spectra allow accurate identification of the modified sites and discrimination of isomers. Based on the overall performance, EAD and 193 nm UVPD offer alternative options to CID and ETD for phosphoproteomics.
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Affiliation(s)
- Marion Girod
- Universite Claude Bernard Lyon 1, CNRS, Institut des Sciences Analytiques, UMR 5280, 5 rue de la Doua, F-69100 Villeurbanne, France
| | - Delphine Arquier
- Universite Claude Bernard Lyon 1, CNRS, Institut des Sciences Analytiques, UMR 5280, 5 rue de la Doua, F-69100 Villeurbanne, France
| | - Amanda Helms
- Department of Chemistry, The University of Texas at Austin, Austin, Texas 78712, United States
| | - Kyle Juetten
- Department of Chemistry, The University of Texas at Austin, Austin, Texas 78712, United States
| | - Jennifer S Brodbelt
- Department of Chemistry, The University of Texas at Austin, Austin, Texas 78712, United States
| | - Jérôme Lemoine
- Universite Claude Bernard Lyon 1, CNRS, Institut des Sciences Analytiques, UMR 5280, 5 rue de la Doua, F-69100 Villeurbanne, France
| | - Luke MacAleese
- Universite Claude Bernard Lyon 1, CNRS, Institut Lumière Matière, UMR5306, F-69100 Villeurbanne, France
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2
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Brodbelt JS, Morrison LJ, Santos I. Ultraviolet Photodissociation Mass Spectrometry for Analysis of Biological Molecules. Chem Rev 2020; 120:3328-3380. [PMID: 31851501 PMCID: PMC7145764 DOI: 10.1021/acs.chemrev.9b00440] [Citation(s) in RCA: 127] [Impact Index Per Article: 31.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
The development of new ion-activation/dissociation methods continues to be one of the most active areas of mass spectrometry owing to the broad applications of tandem mass spectrometry in the identification and structural characterization of molecules. This Review will showcase the impact of ultraviolet photodissociation (UVPD) as a frontier strategy for generating informative fragmentation patterns of ions, especially for biological molecules whose complicated structures, subtle modifications, and large sizes often impede molecular characterization. UVPD energizes ions via absorption of high-energy photons, which allows access to new dissociation pathways relative to more conventional ion-activation methods. Applications of UVPD for the analysis of peptides, proteins, lipids, and other classes of biologically relevant molecules are emphasized in this Review.
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Affiliation(s)
- Jennifer S. Brodbelt
- Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, United States
| | - Lindsay J. Morrison
- Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, United States
| | - Inês Santos
- Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, United States
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3
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Cotham VC, McGee WM, Brodbelt JS. Modulation of Phosphopeptide Fragmentation via Dual Spray Ion/Ion Reactions Using a Sulfonate-Incorporating Reagent. Anal Chem 2016; 88:8158-65. [PMID: 27467576 DOI: 10.1021/acs.analchem.6b01901] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
The labile nature of phosphoryl groups has presented a long-standing challenge for the characterization of protein phosphorylation via conventional mass spectrometry-based bottom-up proteomics methods. Collision-induced dissociation (CID) causes preferential cleavage of the phospho-ester bond of peptides, particularly under conditions of low proton mobility, and results in the suppression of sequence-informative fragmentation that often prohibits phosphosite determination. In the present study, the fragmentation patterns of phosphopeptides are improved through ion/ion-mediated peptide derivatization with 4-formyl-1,3-benezenedisulfonic acid (FBDSA) anions using a dual spray reactor. This approach exploits the strong electrostatic interactions between the sulfonate moieties of FBDSA and basic sites to facilitate gas-phase bioconjugation and to reduce charge sequestration and increase the yield of phosphate-retaining sequence ions upon CID. Moreover, comparative CID fragmentation analysis between unmodified phosphopeptides and those modified online with FBDSA or in solution via carbamylation and 4-sulfophenyl isothiocyanate (SPITC) provided evidence for sulfonate interference with charge-directed mechanisms that result in preferential phosphate elimination. Our results indicate the prominence of charge-directed neighboring group participation reactions involved in phosphate neutral loss, and the implementation of ion/ion reactions in a dual spray reactor setup provides a means to disrupt the interactions by competing hydrogen-bonding interactions between sulfonate groups and the side chains of basic residues.
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Affiliation(s)
- Victoria C Cotham
- Department of Chemistry, The University of Texas at Austin , Austin, Texas 78712, United States
| | - William M McGee
- Department of Chemistry, The University of Texas at Austin , Austin, Texas 78712, United States
| | - Jennifer S Brodbelt
- Department of Chemistry, The University of Texas at Austin , Austin, Texas 78712, United States
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Robinson MR, Taliaferro JM, Dalby KN, Brodbelt JS. 193 nm Ultraviolet Photodissociation Mass Spectrometry for Phosphopeptide Characterization in the Positive and Negative Ion Modes. J Proteome Res 2016; 15:2739-48. [PMID: 27425180 DOI: 10.1021/acs.jproteome.6b00289] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Advances in liquid chromatography tandem mass spectrometry (LC-MS/MS) have permitted phosphoproteomic analysis on a grand scale, but ongoing challenges specifically associated with confident phosphate localization continue to motivate the development of new fragmentation techniques. In the present study, ultraviolet photodissociation (UVPD) at 193 nm is evaluated for the characterization of phosphopeptides in both positive and negative ion modes. Compared to the more standard higher energy collisional dissociation (HCD), UVPD provided more extensive fragmentation with improved phosphate retention on product ions. Negative mode UVPD showed particular merit for detecting and sequencing highly acidic phosphopeptides from alpha and beta casein, but was not as robust for larger scale analysis because of lower ionization efficiencies in the negative mode. HeLa and HCC70 cell lysates were analyzed by both UVPD and HCD. While HCD identified more phosphopeptides and proteins compared to UVPD, the unique matches from UVPD analysis could be combined with the HCD data set to improve the overall depth of coverage compared to either method alone.
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Affiliation(s)
- Michelle R Robinson
- Department of Chemistry, and ‡Division of Chemical Biology and Medicinal Chemistry College of Pharmacy, The University of Texas Austin, Texas 78712, United States
| | - Juliana M Taliaferro
- Department of Chemistry, and ‡Division of Chemical Biology and Medicinal Chemistry College of Pharmacy, The University of Texas Austin, Texas 78712, United States
| | - Kevin N Dalby
- Department of Chemistry, and ‡Division of Chemical Biology and Medicinal Chemistry College of Pharmacy, The University of Texas Austin, Texas 78712, United States
| | - Jennifer S Brodbelt
- Department of Chemistry, and ‡Division of Chemical Biology and Medicinal Chemistry College of Pharmacy, The University of Texas Austin, Texas 78712, United States
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5
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Robotham SA, Brodbelt JS. Comparison of Ultraviolet Photodissociation and Collision Induced Dissociation of Adrenocorticotropic Hormone Peptides. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2015; 26:1570-9. [PMID: 26122515 DOI: 10.1007/s13361-015-1186-y] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/09/2015] [Revised: 04/19/2015] [Accepted: 05/10/2015] [Indexed: 05/16/2023]
Abstract
In an effort to better characterize the fragmentation pathways promoted by ultraviolet photoexcitation in comparison to collision induced dissociation (CID), six adrenocorticotropic hormone (ACTH) peptides in a range of charge states were subjected to 266 nm ultraviolet photodissociation (UVPD), 193 nm UVPD, and CID. Similar fragment ions and distributions were observed for 266 nm UVPD and 193 nm UVPD for all peptides investigated. While both UVPD and CID led to preferential cleavage of the Y-S bond for all ACTH peptides [except ACTH (1-39)], UVPD was far less dependent on charge state and location of basic sites for the production of C-terminal and N-terminal ions. For ACTH (1-16), ACTH (1-17), ACTH (1-24), and ACTH (1-39), changes in the distributions of fragment ion types (a, b, c, x, y, z, and collectively N-terminal ions versus C-terminal ions) showed only minor changes upon UVPD for all charge states. In contrast, CID displayed significant changes in the fragment ion type distributions as a function of charge state, an outcome consistent with the dependence on the number and location of mobile protons that is not prominent for UVPD. Sequence coverages obtained by UVPD showed less dependence on charge state than those determined by CID, with the latter showing a consistent decrease in coverage as charge state increased.
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Affiliation(s)
- Scott A Robotham
- Department of Chemistry, University of Texas, Austin, TX, 78712, USA
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Greer SM, Parker WR, Brodbelt JS. Impact of Protease on Ultraviolet Photodissociation Mass Spectrometry for Bottom-up Proteomics. J Proteome Res 2015; 14:2626-32. [DOI: 10.1021/acs.jproteome.5b00165] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Sylvester M. Greer
- Department of Chemistry, University of Texas at Austin, 105
East 24th Street, Austin, Texas 78712, United States
| | - W. Ryan Parker
- Department of Chemistry, University of Texas at Austin, 105
East 24th Street, Austin, Texas 78712, United States
| | - Jennifer S. Brodbelt
- Department of Chemistry, University of Texas at Austin, 105
East 24th Street, Austin, Texas 78712, United States
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Brodbelt JS. Photodissociation mass spectrometry: new tools for characterization of biological molecules. Chem Soc Rev 2014; 43:2757-83. [PMID: 24481009 PMCID: PMC3966968 DOI: 10.1039/c3cs60444f] [Citation(s) in RCA: 232] [Impact Index Per Article: 23.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Photodissociation mass spectrometry combines the ability to activate and fragment ions using photons with the sensitive detection of the resulting product ions by mass spectrometry. This combination affords a versatile tool for characterization of biological molecules. The scope and breadth of photodissociation mass spectrometry have increased substantially over the past decade as new research groups have entered the field and developed a number of innovative applications that illustrate the ability of photodissociation to produce rich fragmentation patterns, to cleave bonds selectively, and to target specific molecules based on incorporation of chromophores. This review focuses on many of the key developments in photodissociation mass spectrometry over the past decade with a particular emphasis on its applications to biological molecules.
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Robotham SA, Kluwe C, Cannon JR, Ellington A, Brodbelt JS. De novo sequencing of peptides using selective 351 nm ultraviolet photodissociation mass spectrometry. Anal Chem 2013; 85:9832-8. [PMID: 24050806 DOI: 10.1021/ac402309h] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Although in silico database search methods remain more popular for shotgun proteomics methods, de novo sequencing offers the ability to identify peptides derived from proteins lacking sequenced genomes and ones with subtle splice variants or truncations. Ultraviolet photodissociation (UVPD) of peptides derivatized by selective attachment of a chromophore at the N-terminus generates a characteristic series of y ions. The UVPD spectra of the chromophore-labeled peptides are simplified and thus amenable to de novo sequencing. This method resulted in an observed sequence coverage of 79% for cytochrome C (eight peptides), 47% for β-lactoglobulin (five peptides), 25% for carbonic anhydrase (six peptides), and 51% for bovine serum albumin (33 peptides). This strategy also allowed differentiation of proteins with high sequence homology as evidenced by de novo sequencing of two variants of green fluorescent protein.
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Affiliation(s)
- Scott A Robotham
- Department of Chemistry, University of Texas , Austin, Texas 78712, United States
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Frese CK, Zhou H, Taus T, Altelaar AFM, Mechtler K, Heck AJR, Mohammed S. Unambiguous phosphosite localization using electron-transfer/higher-energy collision dissociation (EThcD). J Proteome Res 2013; 12:1520-5. [PMID: 23347405 PMCID: PMC3588588 DOI: 10.1021/pr301130k] [Citation(s) in RCA: 131] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
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We recently introduced a novel scheme combining electron-transfer
and higher-energy collision dissociation (termed EThcD), for improved
peptide ion fragmentation and identification. We reasoned that phosphosite
localization, one of the major hurdles in high-throughput phosphoproteomics,
could also highly benefit from the generation of such EThcD spectra.
Here, we systematically assessed the impact on phosphosite localization
utilizing EThcD in comparison to methods employing either ETD or HCD,
respectively, using a defined synthetic phosphopeptide mixture and
also using a larger data set of Ti4+-IMAC enriched phosphopeptides
from a tryptic human cell line digest. In combination with a modified
version of phosphoRS, we observed that in the majority of cases EThcD
generated richer and more confidently identified spectra, resulting
in superior phosphosite localization scores. Our data demonstrates
the distinctive potential of EThcD for PTM localization, also beyond
protein phosphorylation.
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Affiliation(s)
- Christian K Frese
- Biomolecular Mass Spectrometry and Proteomics, Bijvoet Center for Biomolecular Research and Utrecht Institute for Pharmaceutical Sciences, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
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Shaw JB, Madsen JA, Xu H, Brodbelt JS. Systematic comparison of ultraviolet photodissociation and electron transfer dissociation for peptide anion characterization. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2012; 23:1707-15. [PMID: 22895858 PMCID: PMC4460832 DOI: 10.1007/s13361-012-0424-9] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/18/2012] [Revised: 05/19/2012] [Accepted: 05/20/2012] [Indexed: 05/10/2023]
Abstract
Ultraviolet photodissociation at 193 nm (UVPD) and negative electron transfer dissociation (NETD) were compared to establish their utility for characterizing acidic proteomes with respect to sequence coverage distributions (a measure of product ion signals across the peptide backbone), sequence coverage percentages, backbone cleavage preferences, and fragmentation differences relative to precursor charge state. UVPD yielded significantly more diagnostic information compared with NETD for lower charge states (n ≤ 2), but both methods were comparable for higher charged species. While UVPD often generated a more heterogeneous array of sequence-specific products (b-, y-, c-, z-, Y-, d-, and w-type ions in addition to a- and x- type ions), NETD usually created simpler sets of a/x-type ions. LC-MS/UVPD and LC-MS/NETD analysis of protein digests utilizing high pH mobile phases coupled with automated database searching via modified versions of the MassMatrix algorithm was undertaken. UVPD generally outperformed NETD in stand-alone searches due to its ability to efficiently sequence both lower and higher charge states with rapid activation times. However, when combined with traditional positive mode CID, both methods yielded complementary information with significantly increased sequence coverage percentages and unique peptide identifications over that of just CID alone.
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Affiliation(s)
- Jared B. Shaw
- Department of Chemistry and Biochemistry, The University of Texas at Austin, 1 University Station A5300, Austin, TX, USA 78712
| | - James A. Madsen
- Department of Chemistry and Biochemistry, The University of Texas at Austin, 1 University Station A5300, Austin, TX, USA 78712
| | - Hua Xu
- Center for Proteomics and Bioinformatics, Case Western Reserve University, 10900 Euclid Avenue, BRB 9 Floor, Cleveland, OH, USA 44106
| | - Jennifer S. Brodbelt
- Department of Chemistry and Biochemistry, The University of Texas at Austin, 1 University Station A5300, Austin, TX, USA 78712
- Correspondence to:
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Palumbo AM, Smith SA, Kalcic CL, Dantus M, Stemmer PM, Reid GE. Tandem mass spectrometry strategies for phosphoproteome analysis. MASS SPECTROMETRY REVIEWS 2011; 30:600-25. [PMID: 21294150 DOI: 10.1002/mas.20310] [Citation(s) in RCA: 103] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Protein phosphorylation is involved in nearly all essential biochemical pathways and the deregulation of phosphorylation events has been associated with the onset of numerous diseases. A multitude of tandem mass spectrometry (MS/MS) and multistage MS/MS (i.e., MS(n) ) strategies have been developed in recent years and have been applied toward comprehensive phosphoproteomic analysis, based on the interrogation of proteolytically derived phosphopeptides. However, the utility of each of these MS/MS and MS(n) approaches for phosphopeptide identification and characterization, including phosphorylation site localization, is critically dependant on the properties of the precursor ion (e.g., polarity and charge state), the specific ion activation method that is employed, and the underlying gas-phase ion chemistries, mechanisms and other factors that influence the gas-phase fragmentation behavior of phosphopeptide ions. This review therefore provides an overview of recent studies aimed at developing an improved understanding of these issues, and highlights the advantages and limitations of both established (e.g., CID) and newly maturing (e.g., ECD, ETD, photodissociation, etc.) yet complementary, ion activation techniques. This understanding is expected to facilitate the continued refinement of existing MS/MS strategies, and the development of novel MS/MS techniques for phosphopeptide analysis, with great promise in providing new insights into the role of protein phosphorylation on normal biological function, and in the onset and progression of disease. © 2011 Wiley Periodicals, Inc., Mass Spec Rev 30:600-625, 2011.
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Affiliation(s)
- Amanda M Palumbo
- Department of Chemistry, Michigan State University, East Lansing, USA
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Brodbelt JS. Shedding light on the frontier of photodissociation. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2011; 22:197-206. [PMID: 21472579 DOI: 10.1007/s13361-010-0023-6] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/17/2010] [Revised: 10/11/2010] [Accepted: 10/13/2010] [Indexed: 05/30/2023]
Abstract
The development of new ion activation/dissociation methods is motivated by the need for more versatile ways to characterize structures of ions, especially in the growing arena of biological mass spectrometry in which better tools for determining sequences, modifications, interactions, and conformations of biopolymers are essential. Although most agree that collision-induced dissociation (CID) remains the gold standard for ion activation/dissociation, recent inroads in electron- and photon-based activation methods have cemented their role as outstanding alternatives. This article will focus on the impact of photodissociation, including its strengths and drawbacks as an analytical tool, and its potential for further development in the next decade. Moreover, the discussion will emphasize photodissociation in quadrupole ion traps, because that platform has been used for one of the greatest arrays of new applications over the past decade.
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Affiliation(s)
- Jennifer S Brodbelt
- Department of Chemistry and Biochemistry, University of Texas, Austin, TX 78712, USA.
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Madsen JA, Boutz DR, Brodbelt JS. Ultrafast ultraviolet photodissociation at 193 nm and its applicability to proteomic workflows. J Proteome Res 2010; 9:4205-14. [PMID: 20578723 DOI: 10.1021/pr100515x] [Citation(s) in RCA: 96] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Ultraviolet photodissociation (UVPD) at 193 nm was implemented on a linear ion trap mass spectrometer for high-throughput proteomic workflows. Upon irradiation by a single 5 ns laser pulse, efficient photodissociation of tryptic peptides was achieved with production of a, b, c, x, y, and z sequence ions, in addition to immonium ions and v and w side-chain loss ions. The factors that influence the UVPD mass spectra and subsequent in silico database searching via SEQUEST were evaluated. Peptide sequence aromaticity and the precursor charge state were found to influence photodissociation efficiency more so than the number of amide chromophores, and the ion trap q-value and number of laser pulses significantly affected the number and abundances of diagnostic product ions (e.g., sequence and immonium ions). Also, photoionization background subtraction was shown to dramatically improve SEQUEST results, especially when peptide signals were low. A liquid chromatography-mass spectrometry (LC-MS)/UVPD strategy was implemented and yielded comparable or better results relative to LC-MS/collision induced dissociation (CID) for analysis of proteolyzed bovine serum albumin and lysed human HT-1080 cytosolic fibrosarcoma cells.
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Affiliation(s)
- James A Madsen
- Department of Chemistry and Biochemistry, The University of Texas at Austin, 1 University Station A5300, Austin, Texas 78712, USA
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Smith SA, Kalcic CL, Safran KA, Stemmer PM, Dantus M, Reid GE. Enhanced characterization of singly protonated phosphopeptide ions by femtosecond laser-induced ionization/dissociation tandem mass spectrometry (fs-LID-MS/MS). JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2010; 21:2031-2040. [PMID: 20888783 DOI: 10.1016/j.jasms.2010.08.016] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/26/2010] [Revised: 08/22/2010] [Accepted: 08/23/2010] [Indexed: 05/29/2023]
Abstract
To develop an improved understanding of the regulatory role that post-translational modifications (PTMs) involving phosphorylation play in the maintenance of normal cellular function, tandem mass spectrometry (MS/MS) strategies coupled with ion activation techniques such as collision-induced dissociation (CID) and electron-transfer dissociation (ETD) are typically employed to identify the presence and site-specific locations of the phosphate moieties within a given phosphoprotein of interest. However, the ability of these techniques to obtain sufficient structural information for unambiguous phosphopeptide identification and characterization is highly dependent on the ion activation method employed and the properties of the precursor ion that is subjected to dissociation. Herein, we describe the application of a recently developed alternative ion activation technique for phosphopeptide analysis, termed femtosecond laser-induced ionization/dissociation (fs-LID). In contrast to CID and ETD, fs-LID is shown to be particularly suited to the analysis of singly protonated phosphopeptide ions, yielding a wide range of product ions including a, b, c, x, y, and z sequence ions, as well as ions that are potentially diagnostic of the positions of phosphorylation (e.g., 'a(n)+1-98'). Importantly, the lack of phosphate moiety losses or phosphate group 'scrambling' provides unambiguous information for sequence identification and phosphorylation site characterization. Therefore, fs-LID-MS/MS can serve as a complementary technique to established methodologies for phosphoproteomic analysis.
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Affiliation(s)
- Scott A Smith
- Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, USA
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