1
|
Lan T, Dong Y, Jiang L, Zhang Y, Sui X. Analytical approaches for assessing protein structure in protein-rich food: A comprehensive review. Food Chem X 2024; 22:101365. [PMID: 38623506 PMCID: PMC11016869 DOI: 10.1016/j.fochx.2024.101365] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2023] [Revised: 03/24/2024] [Accepted: 04/05/2024] [Indexed: 04/17/2024] Open
Abstract
This review focuses on changes in nutrition and functional properties of protein-rich foods, primarily attributed to alterations in protein structures. We provide a comprehensive overview and comparison of commonly used laboratory methods for protein structure identification, aiming to offer readers a convenient understanding of these techniques. The review covers a range of detection technologies employed in food protein analysis and conducts an extensive comparison to identify the most suitable method for various proteins. While these techniques offer distinct advantages for protein structure determination, the inherent complexity of food matrices presents ongoing challenges. Further research is necessary to develop and enhance more robust detection methods to improve accuracy in protein conformation and structure analysis.
Collapse
Affiliation(s)
- Tian Lan
- College of Food Science, Northeast Agricultural University, Harbin 150030, China
| | - Yabo Dong
- College of Food Science, Northeast Agricultural University, Harbin 150030, China
| | - Lianzhou Jiang
- College of Food Science, Northeast Agricultural University, Harbin 150030, China
| | - Yan Zhang
- College of Horticulture and Landscape Architecture, Northeast Agricultural University, Harbin 150030, China
| | - Xiaonan Sui
- College of Food Science, Northeast Agricultural University, Harbin 150030, China
| |
Collapse
|
2
|
Takayama M. Transient Conformations Leading to Peptide Fragment Ion [c + 2H] + via Intramolecular Hydrogen Bonding Using MALDI In-source Decay Mass Spectrometry of Serine-, Threonine-, and/or Cysteine-Containing Peptides. Molecules 2023; 28:7700. [PMID: 38067431 PMCID: PMC10708033 DOI: 10.3390/molecules28237700] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2023] [Revised: 11/19/2023] [Accepted: 11/20/2023] [Indexed: 12/18/2023] Open
Abstract
The formation of a peptide fragment ion [c + 2H]+ was examined using ultraviolet matrix-assisted laser desorption/ionization in-source decay mass spectrometry (UV/MALDI-ISD MS). Unusually, an ISD experiment with a hydrogen-abstracting oxidative matrix 4-nitro-1-naphthol (4,1-NNL) resulted in a [c + 2H]+ ion when the analyte peptides contained serine (Ser), threonine (Thr), and/or cysteine (Cys) residues, although the ISD with 4,1-NNL merely resulted in [a]+ and [d]+ ions. The [c + 2H]+ ion observed could be rationalized through intramolecular hydrogen atom transfer (HAT), like a Type-II reaction via a seven-membered conformation involving intramolecular hydrogen bonding (HB) between the active hydrogens (-OH and -SH) of the Ser/Thr/Cys residues and the backbone carbonyl oxygen at the adjacent amino (N)-terminal side residue. The ISD of the Cys-containing peptide resulted in the [c + 2H]+ ions, which originated from cleavage at the backbone N-Cα bonds far from the Cys residue, suggesting that the peptide molecule formed 16- and 22-membered transient conformations in the gas phase. The time-dependent density functional theory (TDDFT) calculations of the model structures of the Ser and Cys residues indicated that the Cys residue did not show a constructive bond interaction between the donor thiol (-SH) and carbonyl oxygen (=CO), while the Ser residue formed a distinct intramolecular HB.
Collapse
Affiliation(s)
- Mitsuo Takayama
- Graduate School in Nanobioscience, Yokohama City University, 22-2 Seto, Kanazawa-ku, Yokohama 236-0027, Japan
| |
Collapse
|
3
|
Asakawa D, Hosokai T, Nakayama Y. Experimental and Theoretical Investigation of MALDI In-Source Decay of Peptides with a Reducing Matrix: What Is the Initial Fragmentation Step? JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2022; 33:1011-1021. [PMID: 35587880 DOI: 10.1021/jasms.2c00066] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Matrix-assisted laser desorption/ionization in-source decay (MALDI-ISD) with a reducing matrix is believed to be initiated by hydrogen transfer from the matrix to the peptide. Several new matrices have recently been developed to achieve more efficient MALDI-ISD. In particular, the use of matrices containing aniline groups facilitates MALDI-ISD to a greater extent than that of matrices containing phenol groups, although the N-H bond in aniline is stronger than the O-H bond in phenol. In this study, photoelectron yield spectroscopy of matrix solids revealed that conversion of the phenol group to the aniline group decreased the ionization energy of the matrix solids. Crucially, the use of a matrix with lower ionization energy has been found to result in efficient cleavage at N-Cα and disulfide bonds by MALDI-ISD. Therefore, electron association with the peptide rather than the fragmentation mechanism involving hydrogen atom attachment is proposed as the initial step of the MALDI-ISD process. In this mechanism, electron transfer from the reducing matrix to the peptide produces a peptide anion radical, which provides either a [cn + H]/[zm]• or [an]•/[ym + H] fragment pair. Fragmentation of the peptide anion radical strongly depends on the gas-phase acidity of the matrix used. Subsequently, the resultant fragments/radicals underwent a reaction in the MALDI plume, producing observable even-electron ions. Consequently, MALDI-ISD fragments are observed as both positive and negative ions, even though MALDI-ISD with a reducing matrix involves fragmentation of peptide anion radicals. The proposed mechanism is suitable for obtaining a better understanding of the MALDI-ISD process.
Collapse
Affiliation(s)
- Daiki Asakawa
- National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan
| | - Takuya Hosokai
- National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan
- Department of Pure and Applied Chemistry, Tokyo University of Science, Noda, Chiba 278-8510, Japan
| | - Yasuo Nakayama
- National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 2, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan
- Department of Pure and Applied Chemistry; Division of Colloid and Interface Science; Research Group for Advanced Energy Conversion, Tokyo University of Science, Noda 278-8510, Japan
| |
Collapse
|
4
|
Lu Q, Xu Z, You X, Ma S, Zenobi R. Atmospheric Pressure Mass Spectrometry Imaging Using Laser Ablation, Followed by Dielectric Barrier Discharge Ionization. Anal Chem 2021; 93:6232-6238. [PMID: 33826303 DOI: 10.1021/acs.analchem.1c00549] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Mass spectrometry imaging (MSI) has become a powerful tool in diverse fields, for example, life science, biomaterials, and catalysis, for its ability of in situ and real-time visualization of the location of chemical compounds in samples. Although laser ablation (LA) achieves high spatial resolution in MSI, the ion yield can be very low. We therefore combined an LA system with an ambient ion source for post-ionization and an atmospheric pressure (AP) inlet mass spectrometer to construct a novel AP-MSI platform. A dielectric barrier discharge ionization (DBDI) source is operated in the "active sampling capillary" configuration, can be coupled to any mass spectrometer with an AP interface, and possesses high ion transmission efficiency. This study presents some application examples based on LA-DBDI, a low-cost and flexible strategy for AP-MSI, which does not require any sample pretreatment, and we show MS imaging of endogenous species in a traditional Chinese herbal medicine and of a drug molecule in zebra fish tissue, with a lateral resolution of ≈20 μm.
Collapse
Affiliation(s)
- Qiao Lu
- Department of Chemistry and the MOE Key Laboratory of Spectrochemical Analysis & Instrumentation, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China
| | - Zhouyi Xu
- Department of Chemistry and the MOE Key Laboratory of Spectrochemical Analysis & Instrumentation, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China
| | - Xue You
- Department of Chemistry and the MOE Key Laboratory of Spectrochemical Analysis & Instrumentation, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China
| | - Siyuan Ma
- Department of Chemistry and the MOE Key Laboratory of Spectrochemical Analysis & Instrumentation, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China
| | - Renato Zenobi
- Department of Chemistry and the MOE Key Laboratory of Spectrochemical Analysis & Instrumentation, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China.,Department of Chemistry and Applied Biosciences, ETH Zurich, CH-8093 Zurich , Switzerland
| |
Collapse
|
5
|
Asakawa D. Cooperative dissociation of peptide backbones and side-chains during matrix-assisted laser desorption/ionization in-source decay mediated by hydrogen abstraction. JOURNAL OF MASS SPECTROMETRY : JMS 2021; 56:e4530. [PMID: 32469146 DOI: 10.1002/jms.4530] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/04/2020] [Revised: 03/19/2020] [Accepted: 04/13/2020] [Indexed: 06/11/2023]
Abstract
Matrix-assisted laser desorption/ionization in-source decay (MALDI-ISD) causes the selective cleavage of Cα -C peptide bonds when an oxidizing matrix is used, and the fragmentation involves the hydrogen abstraction from a peptide by a matrix. The hydrogen abstraction from either an amide nitrogen or β-carbon atom has been proposed to be the initial step leading to the Cα -C bond cleavage. In this regard, the production of [a]+ fragments originated upon bond cleavage at the C-terminal side of phenylglycine residues strongly suggested that that the Cα -C bond cleavage occurred through a nitrogen-centered radical intermediate and that the fragmentation through a β-carbon-centered radical intermediate can be ruled out from the MALDI-ISD process, because phenylglycine residues do not contain β-carbon atoms. The Cα -C bond cleavage of such nitrogen-centered radical initially produced an [a]•/[x - H] fragment pair, and then the [a]• radical either reacted with the matrix or underwent loss of the side-chain, leading to [a - H] or [d - H] fragment. The Cα -C bond cleavage at the C-terminal side of phenylglycine and phenylalanine residues only generated [a]+ fragments, whereas that of homophenylalanine and S-methylated cysteine residues provided both [a]+ and [d]+ fragments. The yield of [d]+ fragments was dependent on the chemical stability of the resultant radicals formed upon side-chain loss. MALDI-ISD produced [M - H + matrix]+ , [M - 16 + H]+ , [M - 32 + H]+ , and [d]+ fragments, when the analyte peptide contained a methionine residue. These fragments were formed upon abstraction of a hydrogen atom from the side-chain of a methionine residue and its subsequent reaction with the matrix. The oxidation of methionine residues suppressed the hydrogen abstraction from their side-chain.
Collapse
Affiliation(s)
- Daiki Asakawa
- National Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki, Japan
| |
Collapse
|
6
|
Asakawa D. Ultraviolet-Laser-Induced Electron Transfer from Peptides to an Oxidizing Matrix: Study of the First Step of MALDI In-Source Decay Mass Spectrometry. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2020; 31:1918-1926. [PMID: 32687357 DOI: 10.1021/jasms.0c00186] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Although the N-H bond in peptide backbones is stronger than the C-H bond, hydrogen abstraction from the amide nitrogen is considered to be the initial step in the Cα-C bond cleavage of peptide backbones by matrix-assisted laser desorption/ionization in-source decay (MALDI-ISD) when using an oxidizing matrix. MALDI-ISD induces Cα-C bond cleavage in most amino acid residues, whereas the N-terminal sides of proline (Pro) residues preferentially undergo peptide bond cleavage, which cannot be explained by the previously proposed mechanism involving hydrogen abstraction from peptides. To explain the whole MALDI-ISD process, electron abstraction from peptides by the oxidizing matrix is proposed as the initial step in the MALDI-ISD process. The electron abstraction occurs from either nitrogen or oxygen in the peptide backbone and induces the cleavage of both Cα-C and N-H bonds in most amino acid residues, except for those on the N-terminal sides of Pro residues. Electron abstraction from the Pro residues induces the cleavage of both peptide and Cα-C bonds, which is consistent with MALDI-ISD experimental results. The electron transfer from the peptide to the oxidizing matrix occurs simultaneously with the formation of matrix ions, which is considered to be the initial ion formation process in MALDI. The resultant peptide radical cation produces protonated and neutral molecules/radicals, which undergo subsequent ion-molecule reactions in the MALDI plume, finally yielding the ions that are observed in MALDI-ISD spectrum. As a result, the fragment ions formed by MALDI-ISD are observed as both positive and negative ions.
Collapse
Affiliation(s)
- Daiki Asakawa
- National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568, Japan
| |
Collapse
|
7
|
Asakawa D. General Mechanism of C α-C Peptide Backbone Bond Cleavage in Matrix-Assisted Laser Desorption/Ionization In-Source Decay Mediated by Hydrogen Abstraction. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2019; 30:1491-1502. [PMID: 31147890 DOI: 10.1007/s13361-019-02214-6] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/05/2019] [Revised: 04/02/2019] [Accepted: 04/02/2019] [Indexed: 06/09/2023]
Abstract
Nitrogen-centered and β-carbon-centered hydrogen-deficient peptide radicals are considered to be intermediates in the matrix-assisted laser desorption/ionization in-source decay (MALDI-ISD)-induced Cα-C bond cleavage of peptide backbones when using an oxidizing matrix. To understand the general mechanism of Cα-C bond cleavage by MALDI-ISD, I study the fragmentation of model peptides and investigate the fragment formation pathways using calculations with density functional theory and transition state theory. The calculations indicate that the nitrogen-centered radical immediately undergoes Cα-C bond cleavage, leading to the formation of an a•/x fragment pair. In contrast, the dissociation of the β-carbon-centered radical is kinetically feasible under MALDI-ISD conditions, leading to the formation of an a/x• fragment pair. To discriminate these processes, I focus on the yield of d fragments, which originate from a• radicals through radical-induced side-chain loss, not from a fragments. The Cα-C bond cleavage on the C-terminal side of the carbamidomethylated cysteine residue is found to produce d fragments instead of a fragments. According to the calculation of the rate constant, the corresponding fragmentation occurs within 1 ns. The intense signal arising from d fragments and the lack of or weak signal from a fragments strongly suggest that the Cα-C bond cleavage occurs through a nitrogen-centered radical intermediate. In addition to the side-chain loss, the resulting a• radical undergoes hydrogen atom abstraction by the matrix. The results for a deuterium-labeled peptide indicate that the matrix abstracts a hydrogen atom from either the amide nitrogen or the β-carbon.
Collapse
Affiliation(s)
- Daiki Asakawa
- National Metrology Institute of Japan (NMIJ), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki, Japan.
| |
Collapse
|
8
|
He H, Wen Y, Guo Z, Li P, Liu Z. Efficient Mass Spectrometric Dissection of Glycans via Gold Nanoparticle-Assisted in-Source Cation Adduction Dissociation. Anal Chem 2019; 91:8390-8397. [PMID: 31180200 DOI: 10.1021/acs.analchem.9b01217] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Structural identification of glycans is important but remains challenging, for which tandem mass spectrometry has evolved as an indispensable tool. However, it requires additional complex hardware and extra time for ion extraction. Herein, we report a straightforward approach called gold nanoparticles (AuNPs)-assisted in-source cation adduction dissociation (isCAD) for efficient mass spectrometry (MS) dissection of glycans. Although AuNPs have been employed as an inorganic matrix for MALDI MS, this is the first report of AuNP-induced fragmentation. In this approach, AuNPs were employed as an energy absorber for laser ionization as well as a trigger for fragmentation, while residual or deliberately added sodium ions acted as a cationizing agent. The addition of sodium ions induced intensive fragmentation, but the addition of protons suppressed the fragmentation, allowing for facile tuning of the degree of fragmentation. In addition, it was found that larger oligosaccharides and glycans were much easier to fragment as compared with their smaller counterparts, and the use of high-concentration AuNPs effectively suppressed the degree of fragmentation and thereby provided abundant molecular ions. Without any extra hardware and ion extraction, this approach provides a straightforward, cost-efficient and tunable fragmentation for efficient MS dissection of saccharides, including monosaccharides, oligosaccharides, and glycans. Thus, it opens new access to efficient MS dissection of glycans.
Collapse
Affiliation(s)
- Hui He
- State Key Laboratory of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering , Nanjing University , Nanjing 210023 , China
| | - Yanrong Wen
- State Key Laboratory of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering , Nanjing University , Nanjing 210023 , China
| | - Zhanchen Guo
- State Key Laboratory of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering , Nanjing University , Nanjing 210023 , China
| | - Pengfei Li
- State Key Laboratory of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering , Nanjing University , Nanjing 210023 , China
| | - Zhen Liu
- State Key Laboratory of Analytical Chemistry for Life Science, School of Chemistry and Chemical Engineering , Nanjing University , Nanjing 210023 , China
| |
Collapse
|
9
|
Lee S, Ahmed A, Kim S. Solvent composition dependent signal reduction of molecular ions generated from aromatic compounds in (+) atmospheric pressure photoionization mass spectrometry. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2018; 32:973-980. [PMID: 29600539 DOI: 10.1002/rcm.8127] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/02/2018] [Revised: 03/14/2018] [Accepted: 03/16/2018] [Indexed: 06/08/2023]
Abstract
RATIONALE The ionization process is essential for successful mass spectrometric (MS) analysis because of its influence on selectivity and sensitivity. In particular, certain solvents reduce the ionization of the analyte, thereby reducing the overall sensitivity in atmospheric pressure photoionization (APPI). Since the sensitivity varies greatly depending on the solvents, a fundamental understanding of the mechanism is required. METHODS Standard solutions were analyzed using a (+)-APPI Q Exactive ion trap mass spectrometer (Thermo Scientific). Each solution was infused directly into the APPI source at a flow rate of 100 μL/min and the APPI source temperature was 300°C. Other operating mass spectrometric parameters were maintained under the same conditions. Quantum mechanical calculations were carried out using the Gaussian 09 suite program. RESULTS Density functional theory was used to calculate the reaction enthalpies (∆H) of the reactions between toluene and other solvents. The experimental and theoretical results showed good agreement. The abundances of analyte ions were well correlated with the calculated ∆H values. Therefore, the results strongly support the suggested signal reduction mechanism. In addition, linear correlations between the abundance of toluene and analyte molecular ions were observed, which also supports the suggested mechanism. CONCLUSIONS A solvent composition dependent signal reduction mechanism was suggested and evaluated for the (+)-APPI-MS analysis of polyaromatic hydrocarbons (PAHs) generating mainly molecular ions. Overall, the evidence provided in this work suggests that reactions between solvent cluster(s) and toluene molecular ions are responsible for the observed reductions in signal.
Collapse
Affiliation(s)
- Seulgidaun Lee
- Department of Chemistry, Kyungpook National University, Daegu, 702-701, Republic of Korea
| | - Arif Ahmed
- Department of Chemistry, Kyungpook National University, Daegu, 702-701, Republic of Korea
| | - Sunghwan Kim
- Department of Chemistry, Kyungpook National University, Daegu, 702-701, Republic of Korea
- Department of Chemistry, Green Nano Center, Daegu, 702-701, Republic of Korea
| |
Collapse
|
10
|
Calvano CD, Monopoli A, Cataldi TRI, Palmisano F. MALDI matrices for low molecular weight compounds: an endless story? Anal Bioanal Chem 2018; 410:4015-4038. [DOI: 10.1007/s00216-018-1014-x] [Citation(s) in RCA: 97] [Impact Index Per Article: 16.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2017] [Revised: 02/27/2018] [Accepted: 03/08/2018] [Indexed: 10/17/2022]
|
11
|
Lai YH, Wang YS. Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry: Mechanistic Studies and Methods for Improving the Structural Identification of Carbohydrates. Mass Spectrom (Tokyo) 2017; 6:S0072. [PMID: 28959517 PMCID: PMC5610957 DOI: 10.5702/massspectrometry.s0072] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2017] [Accepted: 08/03/2017] [Indexed: 12/21/2022] Open
Abstract
Although matrix-assisted laser desorption/ionization (MALDI) mass spectrometry is one of the most widely used soft ionization methods for biomolecules, the lack of detailed understanding of ionization mechanisms restricts its application in the analysis of carbohydrates. Structural identification of carbohydrates achieved by MALDI mass spectrometry helps us to gain insights into biological functions and pathogenesis of disease. In this review, we highlight mechanistic details of MALDI, including both ionization and desorption. Strategies to improve the ion yield of carbohydrates are also reviewed. Furthermore, commonly used fragmentation methods to identify the structure are discussed.
Collapse
|
12
|
Lou X, van Dongen JLJ, Milroy LG, Meijer EW. Generation of gas-phase ions from charged clusters: an important ionization step causing suppression of matrix and analyte ions in matrix-assisted laser desorption/ionization mass spectrometry. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2016; 30:2628-2634. [PMID: 27643391 DOI: 10.1002/rcm.7741] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/09/2016] [Revised: 09/02/2016] [Accepted: 09/14/2016] [Indexed: 06/06/2023]
Abstract
RATIONALE Ionization in matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is a very complicated process. It has been reported that quaternary ammonium salts show extremely strong matrix and analyte suppression effects which cannot satisfactorily be explained by charge transfer reactions. Further investigation of the reasons causing these effects can be useful to improve our understanding of the MALDI process. METHODS The dried-droplet and modified thin-layer methods were used as sample preparation methods. In the dried-droplet method, analytes were co-crystallized with matrix, whereas in the modified thin-layer method analytes were deposited on the surface of matrix crystals. Model compounds, tetrabutylammonium iodide ([N(Bu)4 ]I), cesium iodide (CsI), trihexylamine (THA) and polyethylene glycol 600 (PEG 600), were selected as the test analytes given their ability to generate exclusively pre-formed ions, protonated ions and metal ion adducts respectively in MALDI. RESULTS The strong matrix suppression effect (MSE) observed using the dried-droplet method might disappear using the modified thin-layer method, which suggests that the incorporation of analytes in matrix crystals contributes to the MSE. By depositing analytes on the matrix surface instead of incorporating in the matrix crystals, the competition for evaporation/ionization from charged matrix/analyte clusters could be weakened resulting in reduced MSE. Further supporting evidence for this inference was found by studying the analyte suppression effect using the same two sample deposition methods. CONCLUSIONS By comparing differences between the mass spectra obtained via the two sample preparation methods, we present evidence suggesting that the generation of gas-phase ions from charged matrix/analyte clusters may induce significant suppression of matrix and analyte ions. The results suggest that the generation of gas-phase ions from charged matrix/analyte clusters is an important ionization step in MALDI-MS. Copyright © 2016 John Wiley & Sons, Ltd.
Collapse
Affiliation(s)
- Xianwen Lou
- Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600, MB, Eindhoven, The Netherlands
| | - Joost L J van Dongen
- Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600, MB, Eindhoven, The Netherlands
| | - Lech-Gustav Milroy
- Laboratory of Chemical Biology, Department of Biomedical Engineering, Eindhoven University of Technology, P.O. Box 513, 5600, MB, Eindhoven, The Netherlands
- Institute of Complex Molecular Systems (ICMS), Eindhoven University of Technology, P.O. Box 513, 5600, MB, Eindhoven, The Netherlands
| | - E W Meijer
- Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, P.O. Box 513, 5600, MB, Eindhoven, The Netherlands
- Institute of Complex Molecular Systems (ICMS), Eindhoven University of Technology, P.O. Box 513, 5600, MB, Eindhoven, The Netherlands
| |
Collapse
|
13
|
Mikhailov VA, Liko I, Mize TH, Bush MF, Benesch JLP, Robinson CV. Infrared Laser Activation of Soluble and Membrane Protein Assemblies in the Gas Phase. Anal Chem 2016; 88:7060-7. [PMID: 27328020 DOI: 10.1021/acs.analchem.6b00645] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Collision-induced dissociation (CID) is the dominant method for probing intact macromolecular complexes in the gas phase by means of mass spectrometry (MS). The energy obtained from collisional activation is dependent on the charge state of the ion and the pressures and potentials within the instrument: these factors limit CID capability. Activation by infrared (IR) laser radiation offers an attractive alternative as the radiation energy absorbed by the ions is charge-state-independent and the intensity and time scale of activation is controlled by a laser source external to the mass spectrometer. Here we implement and apply IR activation, in different irradiation regimes, to study both soluble and membrane protein assemblies. We show that IR activation using high-intensity pulsed lasers is faster than collisional and radiative cooling and requires much lower energy than continuous IR irradiation. We demonstrate that IR activation is an effective means for studying membrane protein assemblies, and liberate an intact V-type ATPase complex from detergent micelles, a result that cannot be achieved by means of CID using standard collision energies. Notably, we find that IR activation can be sufficiently soft to retain specific lipids bound to the complex. We further demonstrate that, by applying a combination of collisional activation, mass selection, and IR activation of the liberated complex, we can elucidate subunit stoichiometry and the masses of specifically bound lipids in a single MS experiment.
Collapse
Affiliation(s)
- Victor A Mikhailov
- Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford , Oxford, OX1 3QZ, United Kingdom
| | - Idlir Liko
- Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford , Oxford, OX1 3QZ, United Kingdom
| | - Todd H Mize
- Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford , Oxford, OX1 3QZ, United Kingdom
| | - Matthew F Bush
- Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford , Oxford, OX1 3QZ, United Kingdom
| | - Justin L P Benesch
- Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford , Oxford, OX1 3QZ, United Kingdom
| | - Carol V Robinson
- Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford , Oxford, OX1 3QZ, United Kingdom
| |
Collapse
|
14
|
Takayama M. MALDI In-Source Decay of Protein: The Mechanism of c-Ion Formation. ACTA ACUST UNITED AC 2016; 5:A0044. [PMID: 27162707 DOI: 10.5702/massspectrometry.a0044] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2016] [Accepted: 02/22/2016] [Indexed: 02/05/2023]
Abstract
The in-source decay (ISD) phenomenon, the fragmentation at an N-Cα bond of a peptide backbone that occurs within several tens of nanoseconds in the ion-source in matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS), is discussed from the standpoints of the discovery and early publications dealing with MALDI-ISD, the formation of c-ions in energy-sudden desorption/ionization methods, the formation of radical species in a MALDI, model construction for ISD, and matrix materials that are suitable for use in MALDI-ISD. The formation of c-ions derived from peptides and proteins in MALDI-ISD can be rationalized by a mechanism involving intermolecular hydrogen transfer, denoted as the "Takayama's model" by De Pauw's group (Anal. Chem. 79: 8678-8685, 2007). It should be emphasized that the model for MALDI-ISD was constructed on the basis of X-ray crystallography and scanning probe microscopy (SPM) analyses of matrix crystals, as well as the use of isotopically-labelled peptides.
Collapse
Affiliation(s)
- Mitsuo Takayama
- Mass Spectrometry Laboratory, Graduate School of Nanobioscience, Yokohama City University
| |
Collapse
|
15
|
Moskovets E. Ghost peaks observed after atmospheric pressure matrix-assisted laser desorption/ionization experiments may disclose new ionization mechanism of matrix-assisted hypersonic velocity impact ionization. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2015; 29:1501-12. [PMID: 26212165 PMCID: PMC4518465 DOI: 10.1002/rcm.7248] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/06/2015] [Revised: 05/28/2015] [Accepted: 06/09/2015] [Indexed: 05/12/2023]
Abstract
RATIONALE Understanding the mechanisms of matrix-assisted laser desorption/ionization (MALDI) promises improvements in the sensitivity and specificity of many established applications in the field of mass spectrometry. This paper reports a serendipitous observation of a significant ion yield in a post-ionization experiment conducted after the sample had been removed from a standard atmospheric pressure (AP)-MALDI source. This post-ionization is interpreted in terms of collisions of microparticles moving with a hypersonic velocity into a solid surface. Calculations show that the thermal energy released during such collisions is close to that absorbed by the top matrix layer in traditional MALDI. The microparticles, containing both the matrix and analytes, could be detached from a film produced inside the inlet capillary during the sample ablation and accelerated by the flow rushing through the capillary. These observations contribute some new perspective to ion formation in both laser and laser-less matrix-assisted ionization. METHODS An AP-MALDI ion source hyphenated with a three-stage high-pressure ion funnel system was utilized for peptide mass analysis. After the laser had been turned off and the MALDI sample removed, ions were detected during a gradual reduction of the background pressure in the first funnel. The constant-rate pressure reduction led to the reproducible appearance of different singly and doubly charged peptide peaks in mass spectra taken a few seconds after the end of the MALDI analysis of a dried-droplet spot. RESULTS The ion yield as well as the mass range of ions observed with a significant delay after a completion of the primary MALDI analysis depended primarily on the background pressure inside the first funnel. The production of ions in this post-ionization step was exclusively observed during the pressure drop. A lower matrix background and significant increase in relative yield of double-protonated ions are reported. CONCLUSIONS The observations were partially consistent with a model of the supersonic jet from the inlet capillary accelerating detached particles to kinetic energies suitable for matrix-assisted hypersonic-velocity impact ionization.
Collapse
Affiliation(s)
- Eugene Moskovets
- MassTech Inc., 6992 Columbia Gateway Dr., Columbia MD, USA, Phone: 443-539-0139
| |
Collapse
|
16
|
Leurs U, Mistarz UH, Rand KD. Getting to the core of protein pharmaceuticals--Comprehensive structure analysis by mass spectrometry. Eur J Pharm Biopharm 2015; 93:95-109. [PMID: 25791210 DOI: 10.1016/j.ejpb.2015.03.012] [Citation(s) in RCA: 48] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2014] [Revised: 02/27/2015] [Accepted: 03/02/2015] [Indexed: 01/19/2023]
Abstract
Protein pharmaceuticals are the fastest growing class of novel therapeutic agents, and have been a major research and development focus in the (bio)pharmaceutical industry. Due to their large size and structural diversity, biopharmaceuticals represent a formidable challenge regarding analysis and characterization compared to traditional small molecule drugs. Any changes to the primary, secondary, tertiary or quaternary structure of a protein can potentially impact its function, efficacy and safety. The analysis and characterization of (structural) protein heterogeneity is therefore of utmost importance. Mass spectrometry has evolved as a powerful tool for the characterization of both primary and higher order structures of protein pharmaceuticals. Furthermore, the chemical and physical stability of protein drugs, as well as their pharmacokinetics are nowadays routinely determined by mass spectrometry. Here we review current techniques in primary, secondary and tertiary structure analysis of proteins by mass spectrometry. An overview of established top-down and bottom-up protein analyses will be given, and in particular the use of advanced technologies such as hydrogen/deuterium exchange mass spectrometry (HDX-MS) for higher-order structure analysis will be discussed. Modification and degradation pathways of protein drugs and their detection by mass spectrometry will be described, as well as the growing use of mass spectrometry to assist protein design and biopharmaceutical development.
Collapse
Affiliation(s)
- Ulrike Leurs
- Department of Pharmacy, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen, Denmark
| | - Ulrik H Mistarz
- Department of Pharmacy, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen, Denmark
| | - Kasper D Rand
- Department of Pharmacy, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen, Denmark.
| |
Collapse
|