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Xu T, Wang Q, Wang Q, Sun L. Mass spectrometry-intensive top-down proteomics: an update on technology advancements and biomedical applications. ANALYTICAL METHODS : ADVANCING METHODS AND APPLICATIONS 2024; 16:4664-4682. [PMID: 38973469 PMCID: PMC11257149 DOI: 10.1039/d4ay00651h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/09/2024] [Accepted: 06/25/2024] [Indexed: 07/09/2024]
Abstract
Proteoforms are all forms of protein molecules from the same gene because of variations at the DNA, RNA, and protein levels, e.g., alternative splicing and post-translational modifications (PTMs). Delineation of proteins in a proteoform-specific manner is crucial for understanding their biological functions. Mass spectrometry (MS)-intensive top-down proteomics (TDP) is promising for comprehensively characterizing intact proteoforms in complex biological systems. It has achieved substantial progress in technological development, including sample preparation, proteoform separations, MS instrumentation, and bioinformatics tools. In a single TDP study, thousands of proteoforms can be identified and quantified from a cell lysate. It has also been applied to various biomedical research to better our understanding of protein function in regulating cellular processes and to discover novel proteoform biomarkers of diseases for early diagnosis and therapeutic development. This review covers the most recent technological development and biomedical applications of MS-intensive TDP.
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Affiliation(s)
- Tian Xu
- Department of Chemistry, Michigan State University, 578 S Shaw Lane, East Lansing, MI 48824, USA.
| | - Qianjie Wang
- Department of Chemistry, Michigan State University, 578 S Shaw Lane, East Lansing, MI 48824, USA.
| | - Qianyi Wang
- Department of Chemistry, Michigan State University, 578 S Shaw Lane, East Lansing, MI 48824, USA.
| | - Liangliang Sun
- Department of Chemistry, Michigan State University, 578 S Shaw Lane, East Lansing, MI 48824, USA.
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2
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Mikawy NN, Rojas Ramírez C, DeFiglia SA, Szot CW, Le J, Lantz C, Wei B, Zenaidee MA, Blakney GT, Nesvizhskii AI, Loo JA, Ruotolo BT, Shabanowitz J, Anderson LC, Håkansson K. Are Internal Fragments Observable in Electron Based Top-Down Mass Spectrometry? Mol Cell Proteomics 2024:100814. [PMID: 39029587 DOI: 10.1016/j.mcpro.2024.100814] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2024] [Revised: 06/26/2024] [Accepted: 07/12/2024] [Indexed: 07/21/2024] Open
Abstract
Protein tandem mass spectrometry (MS/MS) often generates sequence-informative fragments from backbone bond cleavages near the termini. This lack of fragmentation in the protein interior is particularly apparent in native top-down MS. Improved sequence coverage, critical for reliable annotation of posttranslational modifications (PTMs) and sequence variants, may be obtained from internal fragments generated by multiple backbone cleavage events. However, internal fragment assignments can be error prone due to isomeric/isobaric fragments from different parts of a protein sequence. Also, internal fragment generation propensity depends on the chosen MS/MS activation strategy. Here, we examine internal fragment formation in electron capture dissociation (ECD) and electron transfer dissociation (ETD) following native and denaturing MS, as well as liquid chromatography (LC)/MS of several proteins. Experiments were undertaken on multiple instruments, including Q-ToF, Orbitrap, and high-field FT-ICR across four laboratories. ECD was performed at both ultrahigh vacuum and at similar pressure to ETD conditions. Two complementary software packages were used for data analysis. When feasible, ETD-higher-energy collision dissociation (ETD-HCD) MS3 was performed to validate/refute potential internal fragment assignments, including differentiating MS3 fragmentation behavior of radical vs. even-electron primary fragments. We show that, under typical operating conditions, internal fragments cannot be confidently assigned in ECD, nor ETD. On the other hand, such fragments, along with some b-type terminal fragments (not typically observed in ECD/ETD spectra) appear at atypical ECD operating conditions, suggesting they originate from a separate ion-electron activation process. Furthermore, atypical fragment ion types, e.g., x ions, are observed at such conditions as well as upon EThcD, presumably due to vibrational activation of radical z-type ions.
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Affiliation(s)
- Neven N Mikawy
- Department of Chemistry, University of Michigan, Ann Arbor, MI 48109-1055, United States; Department of Pharmaceutical Analytical Chemistry, Faculty of Pharmacy, Ain-Shams University, Cairo, Egypt
| | - Carolina Rojas Ramírez
- Department of Chemistry, University of Michigan, Ann Arbor, MI 48109-1055, United States; Department of Pathology, University of Michigan, Ann Arbor, MI 48109-5602, United States
| | - Steven A DeFiglia
- Department of Chemistry, University of Michigan, Ann Arbor, MI 48109-1055, United States
| | - Carson W Szot
- Department of Chemistry, University of Michigan, Ann Arbor, MI 48109-1055, United States
| | - Jessie Le
- Department of Chemistry and Biochemistry, University of California-Los Angeles, Los Angeles, CA 90095, United States
| | - Carter Lantz
- Department of Chemistry and Biochemistry, University of California-Los Angeles, Los Angeles, CA 90095, United States
| | - Benqian Wei
- Department of Chemistry and Biochemistry, University of California-Los Angeles, Los Angeles, CA 90095, United States
| | - Muhammad A Zenaidee
- Australian Proteome Analysis Facility, Macquarie University, Sydney, NSW, 2109, Australia
| | - Greg T Blakney
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, United States
| | - Alexey I Nesvizhskii
- Department of Pathology, University of Michigan, Ann Arbor, MI 48109-5602, United States; Department of Computational Medicine and Bioinformatics, University of Michigan, Ann Arbor, MI 48109-2218, United States
| | - Joseph A Loo
- Department of Chemistry and Biochemistry, University of California-Los Angeles, Los Angeles, CA 90095, United States
| | - Brandon T Ruotolo
- Department of Chemistry, University of Michigan, Ann Arbor, MI 48109-1055, United States
| | - Jeffrey Shabanowitz
- Department of Chemistry, University of Virginia, Charlottesville, VA 22904, United States
| | - Lissa C Anderson
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, United States
| | - Kristina Håkansson
- Department of Chemistry, University of Michigan, Ann Arbor, MI 48109-1055, United States.
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3
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Escobar EE, Yang W, Lanzillotti MB, Juetten KJ, Shields S, Siegel D, Zhang YJ, Brodbelt JS. Tracking Inhibition of Human Small C-Terminal Domain Phosphatase 1 Using 193 nm Ultraviolet Photodissociation Mass Spectrometry. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2024; 35:1330-1341. [PMID: 38662915 DOI: 10.1021/jasms.4c00098] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2024]
Abstract
Working in tandem with kinases via a dynamic interplay of phosphorylation and dephosphorylation of proteins, phosphatases regulate many cellular processes and thus represent compelling therapeutic targets. Here we leverage ultraviolet photodissociation to shed light on the binding characteristics of two covalent phosphatase inhibitors, T65 and rabeprazole, and their respective interactions with the human small C-terminal domain phosphatase 1 (SCP1) and its single-point mutant C181A, in which a nonreactive alanine replaces one key reactive cysteine. Top-down MS/MS analysis is used to localize the binding of T65 and rabeprazole on the two proteins and estimate the relative reactivities of each cysteine residue.
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Affiliation(s)
| | | | | | | | | | - Dionicio Siegel
- Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, 9500 Gilman Drive 0741, La Jolla, California 92093, United States
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4
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Zhu Y, Liu Z, Liu J, Zhao H, Feng R, Shu K, Wang F, Chang C. Panda-UV Unlocks Deeper Protein Characterization with Internal Fragments in Ultraviolet Photodissociation Mass Spectrometry. Anal Chem 2024; 96:8474-8483. [PMID: 38739687 PMCID: PMC11140674 DOI: 10.1021/acs.analchem.4c00253] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2024] [Revised: 05/06/2024] [Accepted: 05/06/2024] [Indexed: 05/16/2024]
Abstract
Ultraviolet photodissociation (UVPD) mass spectrometry unlocks insights into the protein structure and sequence through fragmentation patterns. While N- and C-terminal fragments are traditionally relied upon, this work highlights the critical role of internal fragments in achieving near-complete sequencing of protein. Previous limitations of internal fragment utilization, owing to their abundance and potential for random matching, are addressed here with the development of Panda-UV, a novel software tool combining spectral calibration, and Pearson correlation coefficient scoring for confident fragment assignment. Panda-UV showcases its power through comprehensive benchmarks on three model proteins. The inclusion of internal fragments boosts identified fragment numbers by 26% and enhances average protein sequence coverage to a remarkable 93% for intact proteins, unlocking the hidden region of the largest protein carbonic anhydrase II in model proteins. Notably, an average of 65% of internal fragments can be identified in multiple replicates, demonstrating the high confidence of the fragments Panda-UV provided. Finally, the sequence coverages of mAb subunits can be increased up to 86% and the complementary determining regions (CDRs) are nearly completely sequenced in a single experiment. The source codes of Panda-UV are available at https://github.com/PHOENIXcenter/Panda-UV.
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Affiliation(s)
- Yinlong Zhu
- Chongqing
Key Laboratory on Big Data for Bio Intelligence, Chongqing University of Posts and Telecommunications, Chongqing 400065, China
- State
Key Laboratory of Medical Proteomics, Beijing
Proteome Research Center, National Center for Protein Sciences (Beijing),
Beijing Institute of Lifeomics, Beijing 102206, China
- CAS
Key Laboratory of Separation Sciences for Analytical Chemistry, Dalian
Institute of Chemical Physics, Chinese Academy
of Sciences, Dalian 116023, China
| | - Zheyi Liu
- CAS
Key Laboratory of Separation Sciences for Analytical Chemistry, Dalian
Institute of Chemical Physics, Chinese Academy
of Sciences, Dalian 116023, China
- State
Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of
Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China
- University
of Chinese Academy of Sciences, Beijing 100049, China
| | - Jialiang Liu
- CAS
Key Laboratory of Separation Sciences for Analytical Chemistry, Dalian
Institute of Chemical Physics, Chinese Academy
of Sciences, Dalian 116023, China
- State
Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of
Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China
- School of
Pharmacy, China Medical University, Shenyang 110122, China
| | - Heng Zhao
- CAS
Key Laboratory of Separation Sciences for Analytical Chemistry, Dalian
Institute of Chemical Physics, Chinese Academy
of Sciences, Dalian 116023, China
- State
Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of
Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China
| | - Rui Feng
- State
Key Laboratory of Medical Proteomics, Beijing
Proteome Research Center, National Center for Protein Sciences (Beijing),
Beijing Institute of Lifeomics, Beijing 102206, China
| | - Kunxian Shu
- Chongqing
Key Laboratory on Big Data for Bio Intelligence, Chongqing University of Posts and Telecommunications, Chongqing 400065, China
| | - Fangjun Wang
- CAS
Key Laboratory of Separation Sciences for Analytical Chemistry, Dalian
Institute of Chemical Physics, Chinese Academy
of Sciences, Dalian 116023, China
- State
Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of
Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China
- University
of Chinese Academy of Sciences, Beijing 100049, China
| | - Cheng Chang
- State
Key Laboratory of Medical Proteomics, Beijing
Proteome Research Center, National Center for Protein Sciences (Beijing),
Beijing Institute of Lifeomics, Beijing 102206, China
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5
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Wei B, Lantz C, Loo RRO, Campuzano IDG, Loo JA. Internal Fragments Enhance Middle-Down Mass Spectrometry Structural Characterization of Monoclonal Antibodies and Antibody-Drug Conjugates. Anal Chem 2024; 96:2491-2499. [PMID: 38294207 PMCID: PMC11001303 DOI: 10.1021/acs.analchem.3c04526] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2024]
Abstract
Monoclonal antibodies (mAbs) and antibody-drug conjugates (ADCs) are important large biotherapeutics (∼150 kDa) and high structural complexity that require extensive sequence and structure characterization. Middle-down mass spectrometry (MD-MS) is an emerging technique that sequences and maps subunits larger than those released by trypsinolysis. It avoids potentially introducing artifactual modifications that may occur in bottom-up MS while achieving higher sequence coverage compared to top-down MS. However, returning complete sequence information by MD-MS is still challenging. Here, we show that assigning internal fragments in direct infusion MD-MS of a mAb and an ADC substantially improves their structural characterization. For MD-MS of the reduced NIST mAb, including internal fragments recovers nearly 100% of the sequence by accessing the middle sequence region that is inaccessible by terminal fragments. The identification of important glycosylations can also be improved after the inclusion of internal fragments. For the reduced lysine-linked IgG1-DM1 ADC, we show that considering internal fragments increases the DM1 conjugation sites coverage to 80%, comparable to the reported 83% coverage achieved by peptide mapping on the same ADC (Luo et al. Anal. Chem. 2016, 88, 695-702). This study expands our work on the application of internal fragment assignments in top-down MS of mAbs and ADCs and can be extended to other heterogeneous therapeutic molecules such as multispecifics and fusion proteins for more widespread applications.
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Affiliation(s)
- Benqian Wei
- Department of Chemistry and Biochemistry, University of California Los Angeles-Los Angeles, CA, USA
| | - Carter Lantz
- Department of Chemistry and Biochemistry, University of California Los Angeles-Los Angeles, CA, USA
| | - Rachel R. Ogorzalek Loo
- Department of Chemistry and Biochemistry, University of California Los Angeles-Los Angeles, CA, USA
- UCLA-DOE Institute, University of California-Los Angeles, Los Angeles, CA, USA
- Molecular Biology Institute, University of California-Los Angeles, Los Angeles, CA, USA
| | - Iain D. G. Campuzano
- Center for Research Acceleration by Digital Innovation, Molecular Analytics, Amgen Research, Thousand Oaks, CA, USA
| | - Joseph A. Loo
- Department of Chemistry and Biochemistry, University of California Los Angeles-Los Angeles, CA, USA
- Department of Biological Chemistry, University of California-Los Angeles, Los Angeles, CA, USA
- UCLA-DOE Institute, University of California-Los Angeles, Los Angeles, CA, USA
- Molecular Biology Institute, University of California-Los Angeles, Los Angeles, CA, USA
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Dunham SD, Brodbelt JS. Enhancing Top-Down Analysis of Proteins by Combining Ultraviolet Photodissociation (UVPD), Proton-Transfer Charge Reduction (PTCR), and Gas-Phase Fractionation to Alleviate the Impact of Nondissociated Precursor Ions. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2024; 35:255-265. [PMID: 38150423 DOI: 10.1021/jasms.3c00351] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2023]
Abstract
Recent advances in top-down mass spectrometry strategies continue to improve the analysis of intact proteins. 193 nm ultraviolet photodissociation (UVPD) is one method well-suited for top-down analysis. UVPD is often performed using relatively low photon flux in order to limit multiple-generation dissociation of fragment ions and maximize sequence coverage. Consequently, a large portion of the precursor ion survives the UVPD process, dominates the spectrum, and may impede identification of fragment ions. Here, we explore the isolation of subpopulations of fragment ions lower and higher than the precursor ion after UVPD as a means to eliminate the impact of the surviving precursor ion on the detection of low abundance fragment ions. This gas-phase fractionation method improved sequence coverage harvested from fragment ions found in the m/z regions lower and higher than the precursor by an average factor of 1.3 and 2.3, respectively. Combining this gas-phase fractionation method with proton transfer charge reduction (PTCR) further increased the sequence coverage obtained from these m/z regions by another factor of 1.3 and 1.4, respectively. Implementing a post-UVPD fractionation + PTCR strategy with six fractionation events resulted in a sequence coverage of 75% for enolase, the highest reported for 193 nm UVPD.
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Affiliation(s)
- Sean D Dunham
- Department of Chemistry, University of Texas, Austin, Texas 787812, United States
| | - Jennifer S Brodbelt
- Department of Chemistry, University of Texas, Austin, Texas 787812, United States
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Beaumal C, Deslignière E, Diemer H, Carapito C, Cianférani S, Hernandez-Alba O. Improved characterization of trastuzumab deruxtecan with PTCR and internal fragments implemented in middle-down MS workflows. Anal Bioanal Chem 2024; 416:519-532. [PMID: 38008785 DOI: 10.1007/s00216-023-05059-x] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2023] [Revised: 11/13/2023] [Accepted: 11/14/2023] [Indexed: 11/28/2023]
Abstract
Antibody-drug conjugates (ADCs) are highly complex proteins mainly due to the structural microvariability of the mAb, along with the additional heterogeneity afforded by the bioconjugation process. Top-down (TD) and middle-down (MD) strategies allow the straightforward fragmentation of proteins to elucidate the conjugated amino acid residues. Nevertheless, these spectra are very crowded with multiple overlapping and unassigned ion fragments. Here we report on the use of dedicated software (ClipsMS) and application of proton transfer charge reduction (PTCR), to respectively expand the fragment ion search space to internal fragments and improve the separation of overlapping fragment ions for a more comprehensive characterization of a recently approved ADC, trastuzumab deruxtecan (T-DXd). Subunit fragmentation allowed between 70 and 90% of sequence coverage to be obtained. Upon addition of internal fragment assignment, the three subunits were fully sequenced, although internal fragments did not contribute significantly to the localization of the payloads. Finally, the use of PTCR after subunit fragmentation provided a moderate sequence coverage increase between 2 and 13%. The reaction efficiently decluttered the fragmentation spectra allowing increasing the number of fragment ions characteristic of the conjugation site by 1.5- to 2.5-fold. Altogether, these results show the interest in the implementation of internal fragment ion searches and more particularly the use of PTCR reactions to increase the number of signature ions to elucidate the conjugation sites and enhance the overall sequence coverage of ADCs, making this approach particularly appealing for its implementation in R&D laboratories.
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Affiliation(s)
- Corentin Beaumal
- Laboratoire de Spectrométrie de Masse Bio Organique, IPHC UMR 7178, CNRS, Université de Strasbourg, 67087, Strasbourg, France
- Infrastructure Nationale de Protéomique ProFI - FR2048, Strasbourg, France
| | - Evolène Deslignière
- Laboratoire de Spectrométrie de Masse Bio Organique, IPHC UMR 7178, CNRS, Université de Strasbourg, 67087, Strasbourg, France
- Infrastructure Nationale de Protéomique ProFI - FR2048, Strasbourg, France
| | - Hélène Diemer
- Laboratoire de Spectrométrie de Masse Bio Organique, IPHC UMR 7178, CNRS, Université de Strasbourg, 67087, Strasbourg, France
- Infrastructure Nationale de Protéomique ProFI - FR2048, Strasbourg, France
| | - Christine Carapito
- Laboratoire de Spectrométrie de Masse Bio Organique, IPHC UMR 7178, CNRS, Université de Strasbourg, 67087, Strasbourg, France
- Infrastructure Nationale de Protéomique ProFI - FR2048, Strasbourg, France
| | - Sarah Cianférani
- Laboratoire de Spectrométrie de Masse Bio Organique, IPHC UMR 7178, CNRS, Université de Strasbourg, 67087, Strasbourg, France
- Infrastructure Nationale de Protéomique ProFI - FR2048, Strasbourg, France
| | - Oscar Hernandez-Alba
- Laboratoire de Spectrométrie de Masse Bio Organique, IPHC UMR 7178, CNRS, Université de Strasbourg, 67087, Strasbourg, France.
- Infrastructure Nationale de Protéomique ProFI - FR2048, Strasbourg, France.
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Castel J, Delaux S, Hernandez-Alba O, Cianférani S. Recent advances in structural mass spectrometry methods in the context of biosimilarity assessment: from sequence heterogeneities to higher order structures. J Pharm Biomed Anal 2023; 236:115696. [PMID: 37713983 DOI: 10.1016/j.jpba.2023.115696] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2023] [Revised: 08/31/2023] [Accepted: 09/01/2023] [Indexed: 09/17/2023]
Abstract
Biotherapeutics and their biosimilar versions have been flourishing in the biopharmaceutical market for several years. Structural and functional characterization is needed to achieve analytical biosimilarity through the assessment of critical quality attributes as required by regulatory authorities. The role of analytical strategies, particularly mass spectrometry-based methods, is pivotal to gathering valuable information for the in-depth characterization of biotherapeutics and biosimilarity assessment. Structural mass spectrometry methods (native MS, HDX-MS, top-down MS, etc.) provide information ranging from primary sequence assessment to higher order structure evaluation. This review focuses on recent developments and applications in structural mass spectrometry for biotherapeutic and biosimilar characterization.
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Affiliation(s)
- Jérôme Castel
- Laboratoire de Spectrométrie de Masse Bio-Organique, IPHC UMR 7178, Université de Strasbourg, CNRS, Strasbourg 67087, France; Infrastructure Nationale de Protéomique ProFI, FR2048 CNRS CEA, Strasbourg 67087, France
| | - Sarah Delaux
- Laboratoire de Spectrométrie de Masse Bio-Organique, IPHC UMR 7178, Université de Strasbourg, CNRS, Strasbourg 67087, France; Infrastructure Nationale de Protéomique ProFI, FR2048 CNRS CEA, Strasbourg 67087, France
| | - Oscar Hernandez-Alba
- Laboratoire de Spectrométrie de Masse Bio-Organique, IPHC UMR 7178, Université de Strasbourg, CNRS, Strasbourg 67087, France; Infrastructure Nationale de Protéomique ProFI, FR2048 CNRS CEA, Strasbourg 67087, France
| | - Sarah Cianférani
- Laboratoire de Spectrométrie de Masse Bio-Organique, IPHC UMR 7178, Université de Strasbourg, CNRS, Strasbourg 67087, France; Infrastructure Nationale de Protéomique ProFI, FR2048 CNRS CEA, Strasbourg 67087, France.
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Walker JN, Lam R, Brodbelt JS. Enhanced Characterization of Histones Using 193 nm Ultraviolet Photodissociation and Proton Transfer Charge Reduction. Anal Chem 2023; 95:5985-5993. [PMID: 36989418 DOI: 10.1021/acs.analchem.2c05765] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/31/2023]
Abstract
Top-down characterization of histones, proteins that are critical participants in an array of DNA-dependent processes, offers the potential to examine the relationship between histone structure and mechanisms of genetic regulation. Mapping patterns of post-translational modifications (PTMs) of histones requires extensive backbone cleavages to bracket the sites of mass shifts corresponding to specific PTMs. Ultraviolet photodissociation (UVPD) causes substantial fragmentation of proteins, which is well-suited for PTM localization, but the resulting spectra are congested with fragment ions that may have overlapping isotopic distributions that confound deconvolution. Gas-phase proton transfer charge reduction (PTCR) decreases the charge states of highly charged ions, thus alleviating this congestion and facilitating the identification of additional sequence-determining and PTM-localizing fragment ions. By integrating UVPD with PTCR for histone proteoform analyses, sequence coverages up to 91% were achieved for calf thymus histone H4 containing acetylation marks at the N-terminus and Lys12 as well as a dimethylation at Arg3. UVPD-PTCR exhibited large gains in characterization for other histones, such as histone H2A, increasing the sequence coverage from 59 to 77% for monoacetylated H2A.
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Affiliation(s)
- Jada N Walker
- Department of Chemistry, The University of Texas at Austin, Austin, Texas 78712, United States
| | - Raymond Lam
- 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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