1
|
Villacob RA, Feizi N, Beno SC, Solouki T. Collision-Induced Unfolding, Tandem MS, Bottom-up Proteomics, and Interactomics for Identification of Protein Complexes in Native Surface Mass Spectrometry. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2024; 35:13-30. [PMID: 38095581 DOI: 10.1021/jasms.3c00261] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2024]
Abstract
Endogenously occurring salts and nonvolatile matrix components in untreated biological surfaces can suppress protein ionization and promote adduct formation, challenging protein identification. Characterization of labile proteins within biological specimens is particularly demanding because additional purification or sample treatment steps can be time-intensive and can disrupt noncovalent interactions. It is demonstrated that the combined use of collision-induced unfolding, tandem mass spectrometry, and bottom-up proteomics improves protein characterization in native surface mass spectrometry (NSMS). This multiprong analysis is achieved by acquiring NSMS, MS/MS, ion mobility (IM), and bottom-up proteomics data from a single surface extracted sample. The validity of this multiprong approach was confirmed by the successful characterization of nine surface-deposited proteins, with molecular weights ranging from 8 to 147 kDa, in two separate mixtures. Bottom-up proteomics provided a list of proteins to match against observed proteins in NSMS and their detected subunits in tandem MS. The method was applied to characterize endogenous proteins from untreated chicken liver samples. The subcapsular liver sampling for NSMS analysis allowed for the detection of endogenous proteins with molecular weights of up to ∼220 kDa. Moreover, using IM-MS, collision cross sections and collision-induced unfolding pathways of enzymatic proteins and protein complexes of up to 145 kDa were obtained.
Collapse
Affiliation(s)
- Raul A Villacob
- Department of Chemistry and Biochemistry, Baylor University, Waco, Texas 76798, United States
| | - Neda Feizi
- Department of Chemistry and Biochemistry, Baylor University, Waco, Texas 76798, United States
| | - Sarah C Beno
- Department of Chemistry and Biochemistry, Baylor University, Waco, Texas 76798, United States
| | - Touradj Solouki
- Department of Chemistry and Biochemistry, Baylor University, Waco, Texas 76798, United States
| |
Collapse
|
2
|
Davis BTV, Velyvis A, Vahidi S. Fluorinated Ethylamines as Electrospray-Compatible Neutral pH Buffers for Native Mass Spectrometry. Anal Chem 2023; 95:17525-17532. [PMID: 37997939 DOI: 10.1021/acs.analchem.3c02640] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2023]
Abstract
Native electrospray ionization mass spectrometry (ESI-MS) has emerged as a potent tool for examining the native-like structures of macromolecular complexes. Despite its utility, the predominant "buffer" used, ammonium acetate (AmAc) with pKa values of 4.75 for acetic acid and 9.25 for ammonium, provides very little buffering capacity within the physiological pH range of 7.0-7.4. ESI-induced redox reactions alter the pH of the liquid within the ESI capillary. This can result in protein unfolding or weakening of pH-sensitive interactions. Consequently, the discovery of volatile, ESI-compatible buffers, capable of effectively maintaining pH within a physiological range, is of high importance. Here, we demonstrate that 2,2-difluoroethylamine (DFEA) and 2,2,2-trifluoroethylamine (TFEA) offer buffering capacity at physiological pH where AmAc falls short, with pKa values of 7.2 and 5.5 for the conjugate acids of DFEA and TFEA, respectively. Native ESI-MS experiments on model proteins cytochrome c and myoglobin electrosprayed with DFEA and TFEA demonstrated the preservation of noncovalent protein-ligand complexes in the gas phase. Protein stability assays and collision-induced unfolding experiments further showed that neither DFEA nor TFEA destabilized model proteins in solution or in the gas phase. Finally, we demonstrate that multisubunit protein complexes such as alcohol dehydrogenase and concanavalin A can be studied in the presence of DFEA or TFEA using native ESI-MS. Our findings establish DFEA and TFEA as new ESI-compatible neutral pH buffers that promise to bolster the use of native ESI-MS for the analysis of macromolecular complexes, particularly those sensitive to pH fluctuations.
Collapse
Affiliation(s)
- Bradley T V Davis
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| | - Algirdas Velyvis
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| | - Siavash Vahidi
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
| |
Collapse
|
3
|
Götze M, Polewski L, Bechtella L, Pagel K. A 3D-Printed Offline Nano-ESI Source for Bruker MS Instruments. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2023; 34:2403-2406. [PMID: 37602654 PMCID: PMC10557379 DOI: 10.1021/jasms.3c00214] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/07/2023] [Revised: 07/27/2023] [Accepted: 07/31/2023] [Indexed: 08/22/2023]
Abstract
Nanoelectrospray ionization (nano-ESI) is a highly efficient and a widely used technique for the ionization of minute amounts of analyte. Offline nano-ESI sources are convenient for the direct infusion of complex mixtures that suffer from high matrix content and are crucial for the native mass spectrometric analysis of proteins. For Bruker instruments, no such source is readily available. Here we close this gap and present a 3D-printable nano-ESI source for Bruker instruments, which can be assembled by anyone with access to 3D printers. The source can be fitted to any Bruker mass spectrometer with an ionBooster ESI source and only requires minor, reversible changes to the original Bruker hardware. The general utility was demonstrated by recording high-resolution MS spectra of small molecules, intact proteins, as well as complex biological samples in negative and positive ion mode on two different Bruker instruments.
Collapse
Affiliation(s)
- Michael Götze
- Institut für Chemie und Biochemie, Freie Universität Berlin, 14195 Berlin, Germany
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, 14195 Berlin, Germany
| | - Lukasz Polewski
- Institut für Chemie und Biochemie, Freie Universität Berlin, 14195 Berlin, Germany
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, 14195 Berlin, Germany
| | - Leïla Bechtella
- Institut für Chemie und Biochemie, Freie Universität Berlin, 14195 Berlin, Germany
- Fritz-Haber-Institut der Max-Planck-Gesellschaft, 14195 Berlin, Germany
| | | |
Collapse
|
4
|
Villacob RA, Egbejiogu BC, Feizi N, Hogan C, Murray KK, Solouki T. Native Mass Spectrometry and Collision-Induced Unfolding of Laser-Ablated Proteins. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2022; 33:2215-2225. [PMID: 36346890 DOI: 10.1021/jasms.2c00184] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
Infrared laser ablation sample transfer (LAST) was used to collect samples from solid surfaces for mass spectrometry under native spray conditions. Native mass spectrometry was utilized to probe the charge states and collision-induced unfolding (CIU) characteristics of bovine serum albumin (BSA), bovine hemoglobin (BHb), and jack-bean concanavalin A (ConA) via direct injection electrospray, after liquid extraction surface sampling, and after LAST. Each protein was deposited from solution on solid surfaces and laser-ablated for off-line analysis or sampled for online analysis. It was found that the protein ion gas-phase charge-state distributions were comparable for direct infusion, liquid extraction, and laser ablation experiments. Moreover, calculated average collision cross section (CCS) values from direct injection, liquid extraction, and laser ablation experiments were consistent with previously reported literature values. Additionally, an equivalent number of mobility features and conformational turnovers were identified from unfolding pathways from all three methods for all charge states of each protein analyzed in this work. The presented work suggests that laser ablation yields intact proteins (BSA, BHb, and ConA), is compatible with native mass spectrometry, and could be suitable for spatially resolved interrogation of unfolding pathways of proteins.
Collapse
Affiliation(s)
| | | | - Neda Feizi
- Baylor University, Waco, Texas 76706, United States
| | - Cole Hogan
- Baylor University, Waco, Texas 76706, United States
| | - Kermit K Murray
- Louisiana State University, Baton Rouge, Louisiana 70803, United States
| | | |
Collapse
|
5
|
Opening opportunities for K d determination and screening of MHC peptide complexes. Commun Biol 2022; 5:488. [PMID: 35606511 PMCID: PMC9127112 DOI: 10.1038/s42003-022-03366-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2021] [Accepted: 04/13/2022] [Indexed: 01/15/2023] Open
Abstract
An essential element of adaptive immunity is selective binding of peptide antigens by major histocompatibility complex (MHC) class I proteins and their presentation to cytotoxic T lymphocytes. Using native mass spectrometry, we analyze the binding of peptides to an empty disulfide-stabilized HLA-A*02:01 molecule and, due to its unique stability, we determine binding affinities of complexes loaded with truncated or charge-reduced peptides. We find that the two anchor positions can be stabilized independently, and we further analyze the contribution of additional amino acid positions to the binding strength. As a complement to computational prediction tools, our method estimates binding strength of even low-affinity peptides to MHC class I complexes quickly and efficiently. It has huge potential to eliminate binding affinity biases and thus accelerate drug discovery in infectious diseases, autoimmunity, vaccine design, and cancer immunotherapy. The authors present a sensitive and rapid method to determine the binding strength of MHC class 1 peptide complexes using native mass spectrometry.
Collapse
|
6
|
Sanders HM, Jovcevski B, Marty MT, Pukala TL. Structural and mechanistic insights into amyloid-β and α-synuclein fibril formation and polyphenol inhibitor efficacy in phospholipid bilayers. FEBS J 2022; 289:215-230. [PMID: 34268903 PMCID: PMC8727495 DOI: 10.1111/febs.16122] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2020] [Revised: 06/11/2021] [Accepted: 07/15/2021] [Indexed: 01/03/2023]
Abstract
Under certain cellular conditions, functional proteins undergo misfolding, leading to a transition into oligomers which precede the formation of amyloid fibrils. Misfolding proteins are associated with neurodegenerative diseases such as Alzheimer's and Parkinson's diseases. While the importance of lipid membranes in misfolding and disease aetiology is broadly accepted, the influence of lipid membranes during therapeutic design has been largely overlooked. This study utilized a biophysical approach to provide mechanistic insights into the effects of two lipid membrane systems (anionic and zwitterionic) on the inhibition of amyloid-β 40 and α-synuclein amyloid formation at the monomer, oligomer and fibril level. Large unilamellar vesicles (LUVs) were shown to increase fibrillization and largely decrease the effectiveness of two well-known polyphenol fibril inhibitors, (-)-epigallocatechin gallate (EGCG) and resveratrol; however, use of immunoblotting and ion mobility mass spectrometry revealed this occurs through varying mechanisms. Oligomeric populations in particular were differentially affected by LUVs in the presence of resveratrol, an elongation phase inhibitor, compared to EGCG, a nucleation targeted inhibitor. Ion mobility mass spectrometry showed EGCG interacts with or induces more compact forms of monomeric protein typical of off-pathway structures; however, binding is reduced in the presence of LUVs, likely due to partitioning in the membrane environment. Competing effects of the lipids and inhibitor, along with reduced inhibitor binding in the presence of LUVs, provide a mechanistic understanding of decreased inhibitor efficacy in a lipid environment. Together, this study highlights that amyloid inhibitor design may be misguided if effects of lipid membrane composition and architecture are not considered during development.
Collapse
Affiliation(s)
- Henry M. Sanders
- Department of Chemistry, School of Physical Sciences, The University of Adelaide, Adelaide, SA 5005, Australia,Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona 85721, United States
| | - Blagojce Jovcevski
- Department of Chemistry, School of Physical Sciences, The University of Adelaide, Adelaide, SA 5005, Australia
| | - Michael T. Marty
- Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona 85721, United States
| | - Tara L. Pukala
- Department of Chemistry, School of Physical Sciences, The University of Adelaide, Adelaide, SA 5005, Australia,Correspondence: Tara L. Pukala: School of Physical Sciences, The University of Adelaide, Adelaide, SA 5005, Australia; ; Tel. +61 8 8313 5497
| |
Collapse
|
7
|
Sever AIM, Yin V, Konermann L. Interrogating the Quaternary Structure of Noncanonical Hemoglobin Complexes by Electrospray Mass Spectrometry and Collision-Induced Dissociation. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2021; 32:270-280. [PMID: 33124417 DOI: 10.1021/jasms.0c00320] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Various activation methods are available for the fragmentation of gaseous protein complexes produced by electrospray ionization (ESI). Such experiments can potentially yield insights into quaternary structure. Collision-induced dissociation (CID) is the most widely used fragmentation technique. Unfortunately, CID of protein complexes is dominated by the ejection of highly charged monomers, a process that does not yield any structural insights. Using hemoglobin (Hb) as a model system, this work examines under what conditions CID generates structurally informative subcomplexes. Native ESI mainly produced tetrameric Hb ions. In addition, "noncanonical" hexameric and octameric complexes were observed. CID of all these species [(αβ)2, (αβ)3, and (αβ)4] predominantly generated highly charged monomers. In addition, we observed hexamer → tetramer + dimer dissociation, implying that hexamers have a tetramer··dimer architecture. Similarly, the observation of octamer → two tetramer dissociation revealed that octamers have a tetramer··tetramer composition. Gas-phase candidate structures of Hb assemblies were produced by molecular dynamics (MD) simulations. Ion mobility spectrometry was used to identify the most likely candidates. Our data reveal that the capability of CID to produce structurally informative subcomplexes depends on the fate of protein-protein interfaces after transfer into the gas phase. Collapse of low affinity interfaces conjoins the corresponding subunits and favors CID via monomer ejection. Structurally informative subcomplexes are formed only if low affinity interfaces do not undergo a major collapse. However, even in these favorable cases CID is still dominated by monomer ejection, requiring careful analysis of the experimental data for the identification of structurally informative subcomplexes.
Collapse
Affiliation(s)
- Alexander I M Sever
- Department of Chemistry, The University of Western Ontario, London, Ontario N6A 5B7, Canada
| | - Victor Yin
- Department of Chemistry, The University of Western Ontario, London, Ontario N6A 5B7, Canada
| | - Lars Konermann
- Department of Chemistry, The University of Western Ontario, London, Ontario N6A 5B7, Canada
| |
Collapse
|
8
|
Liu XR, Zhang MM, Gross ML. Mass Spectrometry-Based Protein Footprinting for Higher-Order Structure Analysis: Fundamentals and Applications. Chem Rev 2020; 120:4355-4454. [PMID: 32319757 PMCID: PMC7531764 DOI: 10.1021/acs.chemrev.9b00815] [Citation(s) in RCA: 130] [Impact Index Per Article: 32.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Proteins adopt different higher-order structures (HOS) to enable their unique biological functions. Understanding the complexities of protein higher-order structures and dynamics requires integrated approaches, where mass spectrometry (MS) is now positioned to play a key role. One of those approaches is protein footprinting. Although the initial demonstration of footprinting was for the HOS determination of protein/nucleic acid binding, the concept was later adapted to MS-based protein HOS analysis, through which different covalent labeling approaches "mark" the solvent accessible surface area (SASA) of proteins to reflect protein HOS. Hydrogen-deuterium exchange (HDX), where deuterium in D2O replaces hydrogen of the backbone amides, is the most common example of footprinting. Its advantage is that the footprint reflects SASA and hydrogen bonding, whereas one drawback is the labeling is reversible. Another example of footprinting is slow irreversible labeling of functional groups on amino acid side chains by targeted reagents with high specificity, probing structural changes at selected sites. A third footprinting approach is by reactions with fast, irreversible labeling species that are highly reactive and footprint broadly several amino acid residue side chains on the time scale of submilliseconds. All of these covalent labeling approaches combine to constitute a problem-solving toolbox that enables mass spectrometry as a valuable tool for HOS elucidation. As there has been a growing need for MS-based protein footprinting in both academia and industry owing to its high throughput capability, prompt availability, and high spatial resolution, we present a summary of the history, descriptions, principles, mechanisms, and applications of these covalent labeling approaches. Moreover, their applications are highlighted according to the biological questions they can answer. This review is intended as a tutorial for MS-based protein HOS elucidation and as a reference for investigators seeking a MS-based tool to address structural questions in protein science.
Collapse
Affiliation(s)
| | | | - Michael L. Gross
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO, USA, 63130
| |
Collapse
|
9
|
Development of hypoallergenic variants of the major horse allergen Equ c 1 for immunotherapy by rational structure based engineering. Sci Rep 2019; 9:20148. [PMID: 31882906 PMCID: PMC6934807 DOI: 10.1038/s41598-019-56812-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2019] [Accepted: 12/10/2019] [Indexed: 11/25/2022] Open
Abstract
The use of recombinant allergens is a promising approach in allergen-specific immunotherapy (AIT). Considerable limitation, however, has been the ability of recombinant allergens to activate effector cells leading to allergic reactions. Recombinant hypoallergens with preserved protein folding and capacity to induce protective IgG antibodies binding effectively to the native allergen upon sensitization would be beneficial for safer AIT. In this study, hypoallergen variants of the major horse allergen Equ c 1 were designed by introducing one point mutation on the putative IgE epitope region and two mutations on the monomer-monomer interface of Equ c 1 dimer. The recombinant Equ c 1 wild type and the variants were produced and purified to homogeneity, characterized by size-exclusion ultra-high performance liquid chromatography and ultra-high resolution mass spectrometry. The IgE-binding profiles were analyzed by a competitive immunoassay and the biological activity by a histamine release assay using sera from horse allergic individuals. Two Equ c 1 variants, Triple 2 (V47K + V110E + F112K) and Triple 3 (E21Y + V110E + F112K) showed lower allergen-specific IgE-binding capacity and decreased capability to release histamine from basophils in vitro when using sera from six allergic individuals. Triple 3 showed higher reduction than Triple 2 in IgE-binding (5.5 fold) and in histamine release (15.7 fold) compared to wild type Equ c 1. Mutations designed on the putative IgE epitope region and monomer-monomer interface of Equ c 1 resulted in decreased dimerization, a lower IgE-binding capacity and a reduced triggering of an allergic response in vitro.
Collapse
|
10
|
Muralidharan M, Mitra A, Maity D, Pal D, Mandal AK. Structural analysis of glutathionyl hemoglobin using native mass spectrometry. J Struct Biol 2019; 208:107386. [PMID: 31518635 DOI: 10.1016/j.jsb.2019.09.003] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2019] [Revised: 09/05/2019] [Accepted: 09/07/2019] [Indexed: 01/18/2023]
Abstract
Glutathionylation is an example of reversible post-translation modification of proteins where free and accessible cysteine residues of proteins undergo thiol-disulfide exchange with oxidized glutathione (GSSG). In general, glutathionylation occurs under the condition of elevated oxidative stress in vivo. In human hemoglobin, Cys93 residue of β globin chain was found to undergo this oxidative modification. Glutathionyl hemoglobin (GSHb) was reported to act as a biomarker of oxidative stress under several clinical conditions such as chronic renal failure, iron deficiency anemia, hyperlipidemia, diabetes mellitus, Friedreich's ataxia, atherosclerosis. Previously we showed that the functional abnormality associated with six-fold tighter oxygen binding of GSHb supposedly attributed to the conformational transition of the deoxy state of GSHb towards oxy hemoglobin like conformation. In the present study, we investigated the structural integrity and overall architecture of the quaternary structure of GSHb using native mass spectrometry and ion mobility mass spectrometry platforms. The dissociation equilibrium constants of both tetramer/dimer (Kd1) and dimer/monomer equilibrium (Kd2) was observed to increase by 1.91 folds and 3.64 folds respectively. However, the collision cross-section area of the tetrameric hemoglobin molecule remained unchanged upon glutathionylation. The molecular dynamics simulation data of normal human hemoglobin and GSHb was employed to support our experimental findings.
Collapse
Affiliation(s)
- Monita Muralidharan
- Clinical Proteomics Unit, Division of Molecular Medicine, St. John's Research Institute, 100 ft Road, Koramangala, Bangalore 560034, India
| | - Amrita Mitra
- Clinical Proteomics Unit, Division of Molecular Medicine, St. John's Research Institute, 100 ft Road, Koramangala, Bangalore 560034, India
| | - Dibyajyoti Maity
- IISc Mathematics Initiative, Indian Institute of Science, Bangalore 560012, India
| | - Debnath Pal
- Bioinformatics Centre, Department of Computational & Data Sciences, Indian Institute of Science, Bangalore 560012, India
| | - Amit Kumar Mandal
- Clinical Proteomics Unit, Division of Molecular Medicine, St. John's Research Institute, 100 ft Road, Koramangala, Bangalore 560034, India.
| |
Collapse
|
11
|
Rahman MM, Wu D, Chingin K, Xu W, Chen H. High ohmic resistor hyphenated gel loading tip nano-electrospray ionization source for mini mass spectrometer. Talanta 2019; 202:59-66. [PMID: 31171225 DOI: 10.1016/j.talanta.2019.04.052] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2019] [Revised: 04/16/2019] [Accepted: 04/19/2019] [Indexed: 10/27/2022]
Abstract
The deployment of mini mass spectrometers on the field strongly demands efficient ionization sources that are easy-to-operate. Nano-electrospray (nESI) ion source has been widely used in the field of chemistry, biology, medicine, pharmaceutical industry, clinical assessment and forensic science. In this study, a high ohmic resistor hyphenated gel loading tip nESI source was coupled with our home developed mini mass spectrometer. This ionization source has the advantages of simple-in-design, disposable and low-in-cost, therefore it could be frequently used for analysis of aqueous samples without leading to cross contamination. Performances of the gel loading tip nESI emitter were similar to pulled glass capillary, and highly compatible for the analysis of biomolecule in aqueous solution. Different peptide and small molecules have been confirmed with a continuous atmospheric pressure-interfaced (CAPI) mini mass spectrometer. The corona discharge, which was usually observed at nESI emitter tip under high aqueous solvent conditions, resulting in low ion intensity, has been successfully quenched using a 10 GΩ resistor in both a pulled glass capillary and a gel loading tip as nESI emitter in this study. Compared with conventional ESI, the metal wire assisted gel loading tip facilitated loading and direct analysis of biological samples without sample pretreatment.
Collapse
Affiliation(s)
- Md Matiur Rahman
- Jiangxi Key Laboratory for Mass Spectrometry and Instrumentation, East China University of Technology, Nanchang, 330013, China.
| | - Debo Wu
- Jiangxi Key Laboratory for Mass Spectrometry and Instrumentation, East China University of Technology, Nanchang, 330013, China
| | - Konstantin Chingin
- Jiangxi Key Laboratory for Mass Spectrometry and Instrumentation, East China University of Technology, Nanchang, 330013, China
| | - Wei Xu
- College of Information of Science, Shenzhen University, Shenzhen, 518060, China; School of Life Science, Beijing Institute of Technology, Beijing, 100081, China.
| | - Huanwen Chen
- Jiangxi Key Laboratory for Mass Spectrometry and Instrumentation, East China University of Technology, Nanchang, 330013, China
| |
Collapse
|
12
|
Mitra A, Mandal AK. Conjugation of para-benzoquinone of Cigarette Smoke with Human Hemoglobin Leads to Unstable Tetramer and Reduced Cooperative Oxygen Binding. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2018; 29:2048-2058. [PMID: 29967937 DOI: 10.1007/s13361-018-2011-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/20/2018] [Revised: 05/27/2018] [Accepted: 06/12/2018] [Indexed: 06/08/2023]
Abstract
Besides multiple life-threatening diseases like lung cancer and cardiovascular disease, cigarette smoking is known to produce hypoxia, a state of inadequate oxygen supply to tissues. Hypoxia plays a pivotal role in the development of chronic obstructive pulmonary disease. Smoking during pregnancy imposes risk for the unborn child. In addition to carbon monoxide, conjugation of para-benzoquinone (pBQ), derived from cigarette smoke, with human hemoglobin (HbA) was also reported to contribute in hypoxia. In fact, conjugation of pBQ is more alarming than carbon monoxide as it is an irreversible covalent modification. In the present study, the functional assay of Hb-pBQ, performed through oxygen equilibrium curve, showed a significant decrease in both P50 and cooperativity. However, the structural changes associated with the observed functional perturbation of the hemoglobin conjugate (Hb-pBQ) are unknown to date. Enhanced sensitivity and high resolution of nano-ESI mass spectrometry platform have enabled to investigate the native structure of oligomers of hemoglobin in a single scan. The structural integrity of Hb-pBQ measured through the dissociation equilibrium constants (Kd) indicated that compared to HbA, Kd of tetramer-dimer and dimer-monomer equilibria were increased by 4.98- and 64.3-folds, respectively. Using isotope exchange mass spectrometry, we observed perturbations in the inter-subunit interactions of deoxy and oxy states of Hb-pBQ. However, the three-dimensional architecture of Hb-pBQ, monitored through collision cross-sectional area, did not show any change. We propose that the significant destabilization of the functionally active structure of hemoglobin upon conjugation with pBQ results in tighter oxygen binding that leads to hypoxia. Graphical Abstract ᅟ.
Collapse
Affiliation(s)
- Amrita Mitra
- Clinical Proteomics Unit, Division of Molecular Medicine, St. John's Research Institute, St. John's National Academy of Health Sciences, 100ft Road, Koramangala, Bangalore, 560034, India
| | - Amit Kumar Mandal
- Clinical Proteomics Unit, Division of Molecular Medicine, St. John's Research Institute, St. John's National Academy of Health Sciences, 100ft Road, Koramangala, Bangalore, 560034, India.
| |
Collapse
|
13
|
Rahman MM, Chen LC. Analytical characteristics of nano-electrospray operated under super-atmospheric pressure. Anal Chim Acta 2018; 1021:78-84. [DOI: 10.1016/j.aca.2018.03.026] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2018] [Revised: 03/08/2018] [Accepted: 03/10/2018] [Indexed: 10/17/2022]
|
14
|
Root K, Wittwer Y, Barylyuk K, Anders U, Zenobi R. Insight into Signal Response of Protein Ions in Native ESI-MS from the Analysis of Model Mixtures of Covalently Linked Protein Oligomers. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2017; 28:1863-1875. [PMID: 28593376 DOI: 10.1007/s13361-017-1690-3] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/09/2016] [Revised: 04/12/2017] [Accepted: 04/13/2017] [Indexed: 05/28/2023]
Abstract
Native ESI-MS is increasingly used for quantitative analysis of biomolecular interactions. In such analyses, peak intensity ratios measured in mass spectra are treated as abundance ratios of the respective molecules in solution. While signal intensities of similar-size analytes, such as a protein and its complex with a small molecule, can be directly compared, significant distortions of the peak ratio due to unequal signal response of analytes impede the application of this approach for large oligomeric biomolecular complexes. We use a model system based on concatenated maltose binding protein units (MBPn, n = 1, 2, 3) to systematically study the behavior of protein mixtures in ESI-MS. The MBP concatamers differ from each other only by their mass while the chemical composition and other properties remain identical. We used native ESI-MS to analyze model mixtures of MBP oligomers, including equimolar mixtures of two proteins, as well as binary mixtures containing different fractions of the individual components. Pronounced deviation from a linear dependence of the signal intensity with concentration was observed for all binary mixtures investigated. While equimolar mixtures showed linear signal dependence at low concentrations, distinct ion suppression was observed above 20 μM. We systematically studied factors that are most often used in the literature to explain the origin of suppression effects. Implications of this effect for quantifying protein-protein binding affinity by native ESI-MS are discussed in general and demonstrated for an example of an anti-MBP antibody with its ligand, MBP. Graphical Abstract ᅟ.
Collapse
Affiliation(s)
- Katharina Root
- Department of Chemistry and Applied Biosciences, ETH Zurich, Zurich, Switzerland
| | - Yves Wittwer
- Department of Chemistry and Applied Biosciences, ETH Zurich, Zurich, Switzerland
| | - Konstantin Barylyuk
- Department of Chemistry and Applied Biosciences, ETH Zurich, Zurich, Switzerland
- Department of Biochemistry, University of Cambridge, Cambridge, UK
| | - Ulrike Anders
- Department of Chemistry and Applied Biosciences, ETH Zurich, Zurich, Switzerland
| | - Renato Zenobi
- Department of Chemistry and Applied Biosciences, ETH Zurich, Zurich, Switzerland.
| |
Collapse
|
15
|
Niu S, Kim BC, Fierke CA, Ruotolo BT. Ion Mobility-Mass Spectrometry Reveals Evidence of Specific Complex Formation between Human Histone Deacetylase 8 and Poly-r(C)-binding Protein 1. INTERNATIONAL JOURNAL OF MASS SPECTROMETRY 2017; 420:9-15. [PMID: 28983190 PMCID: PMC5624731 DOI: 10.1016/j.ijms.2016.12.017] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Histone deacetylase 8, part of a broad class of proteins responsible for regulating transcription and many other cellular processes and directly linked to a host of human disease through its mis-function, has been canonically described as a zinc-based mettalo-enzyme for many years. Recent evidence, however, has linked this protein to iron incorporation, loaded through transient interactions with the poly r(C)-binding protein 1, a metallo-chaperone and storage protein. In this report, we construct and deploy an electrospray-mass spectrometry based assay aimed at quantifying the interaction strength between these two weakly-associated proteins, as well as the zinc and iron associated form of the histone deacetylase. Despite challenges derived from artifact protein complexes derived from the electrospray process, we use carefully-constructed positive and negative control experiments, along with detailed measurements of protein ionization efficiency to validate our dissociation constant measurements for protein dimers in this size range. Furthermore, our data strongly support that complexes between histone deacetylase 8 and poly r(C)-binding protein 1 are specific, and that they are equally strong when both zinc and iron-loaded proteins are involved, or perhaps mildly promoted in the latter case, suggesting an in vivo role for the non-canonical, iron-incorporated histone deacetylase.
Collapse
|
16
|
Rautenbach M, Vlok NM, Eyéghé-Bickong HA, van der Merwe MJ, Stander MA. An Electrospray Ionization Mass Spectrometry Study on the "In Vacuo" Hetero-Oligomers Formed by the Antimicrobial Peptides, Surfactin and Gramicidin S. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2017; 28:1623-1637. [PMID: 28560564 DOI: 10.1007/s13361-017-1685-0] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/07/2016] [Revised: 04/08/2017] [Accepted: 04/11/2017] [Indexed: 06/07/2023]
Abstract
It was previously observed that the lipopeptide surfactants in surfactin (Srf) have an antagonistic action towards the highly potent antimicrobial cyclodecapeptide, gramicidin S (GS). This study reports on some of the molecular aspects of the antagonism as investigated through complementary electrospray ionization mass spectrometry techniques. We were able to detect stable 1:1 and 2:1 hetero-oligomers in a mixture of surfactin and gramicidin S. The noncovalent interaction between GS and Srf, with the proposed equilibrium: GS~Srf↔GS+Srf correlated to apparent K d values of 6-9 μM in gas-phase and 1 μM in aqueous solution. The apparent K d values decreased with a longer incubation time and indicated a slow oligomerization equilibrium. Furthermore, the low μM K dapp values of GS~Srf↔GS+Srf fell within the biological concentration range and related to the 2- to 3-fold increase in [GS] needed for bacterial growth inhibition in the presence of Srf. Competition studies indicated that neither Na+ nor Ca2+ had a major effect on the stability of preformed heterodimers and that GS in fact out-competed Ca2+ and Na+ from Srf. Traveling wave ion mobility mass spectrometry revealed near symmetrical peaks of the heterodimers correlating to a compact dimer conformation that depend on specific interactions. Collision-induced dissociation studies indicated that the peptide interaction is most probably between one Orn residue in GS and the Asp residue, but not the Glu residue in Srf. We propose that flanking hydrophobic residues in both peptides stabilize the antagonistic and inactive peptide hetero-oligomers and shield the specific polar interactions in an aqueous environment. Graphical Abstract ᅟ.
Collapse
Affiliation(s)
- Marina Rautenbach
- BIOPEP® Peptide Group, University of Stellenbosch, Stellenbosch, 7602, Republic of South Africa.
- Department of Biochemistry, University of Stellenbosch, Stellenbosch, 7602, Republic of South Africa.
| | - N Maré Vlok
- BIOPEP® Peptide Group, University of Stellenbosch, Stellenbosch, 7602, Republic of South Africa
- Department of Biochemistry, University of Stellenbosch, Stellenbosch, 7602, Republic of South Africa
| | - Hans A Eyéghé-Bickong
- BIOPEP® Peptide Group, University of Stellenbosch, Stellenbosch, 7602, Republic of South Africa
- Department of Biochemistry, University of Stellenbosch, Stellenbosch, 7602, Republic of South Africa
| | - Marthinus J van der Merwe
- Department of Biochemistry, University of Stellenbosch, Stellenbosch, 7602, Republic of South Africa
- LCMS Central Analytical Facility, University of Stellenbosch, Stellenbosch, 7602, Republic of South Africa
| | - Marietjie A Stander
- Department of Biochemistry, University of Stellenbosch, Stellenbosch, 7602, Republic of South Africa
- LCMS Central Analytical Facility, University of Stellenbosch, Stellenbosch, 7602, Republic of South Africa
| |
Collapse
|
17
|
Seetoh WG, Abell C. Disrupting the Constitutive, Homodimeric Protein-Protein Interface in CK2β Using a Biophysical Fragment-Based Approach. J Am Chem Soc 2016; 138:14303-14311. [PMID: 27726344 PMCID: PMC5257173 DOI: 10.1021/jacs.6b07440] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
![]()
Identifying small molecules that
induce the disruption of constitutive
protein–protein interfaces is a challenging objective. Here,
a targeted biophysical screening cascade was employed to specifically
identify small molecules that could disrupt the constitutive, homodimeric
protein–protein interface within CK2β. This approach
could potentially be applied to achieve subunit disassembly of other
homo-oligomeric proteins as a means of modulating protein function.
Collapse
Affiliation(s)
- Wei-Guang Seetoh
- Department of Chemistry, University of Cambridge , Lensfield Road, Cambridge, CB2 1EW, United Kingdom
| | - Chris Abell
- Department of Chemistry, University of Cambridge , Lensfield Road, Cambridge, CB2 1EW, United Kingdom
| |
Collapse
|
18
|
Sun Y, Vahidi S, Sowole MA, Konermann L. Protein Structural Studies by Traveling Wave Ion Mobility Spectrometry: A Critical Look at Electrospray Sources and Calibration Issues. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2016; 27:31-40. [PMID: 26369778 DOI: 10.1007/s13361-015-1244-5] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/20/2015] [Revised: 07/27/2015] [Accepted: 07/29/2015] [Indexed: 06/05/2023]
Abstract
The question whether electrosprayed protein ions retain solution-like conformations continues to be a matter of debate. One way to address this issue involves comparisons of collision cross sections (Ω) measured by ion mobility spectrometry (IMS) with Ω values calculated for candidate structures. Many investigations in this area employ traveling wave IMS (TWIMS). It is often implied that nanoESI is more conducive for the retention of solution structure than regular ESI. Focusing on ubiquitin, cytochrome c, myoglobin, and hemoglobin, we demonstrate that Ω values and collisional unfolding profiles are virtually indistinguishable under both conditions. These findings suggest that gas-phase structures and ion internal energies are independent of the type of electrospray source. We also note that TWIMS calibration can be challenging because differences in the extent of collisional activation relative to drift tube reference data may lead to ambiguous peak assignments. It is demonstrated that this problem can be circumvented by employing collisionally heated calibrant ions. Overall, our data are consistent with the view that exposure of native proteins to electrospray conditions can generate kinetically trapped ions that retain solution-like structures on the millisecond time scale of TWIMS experiments. ᅟ
Collapse
Affiliation(s)
- Yu Sun
- Department of Chemistry, The University of Western Ontario, London, ON, N6A 5B7, Canada
| | - Siavash Vahidi
- Department of Chemistry, The University of Western Ontario, London, ON, N6A 5B7, Canada
| | - Modupeola A Sowole
- Department of Chemistry, The University of Western Ontario, London, ON, N6A 5B7, Canada
| | - Lars Konermann
- Department of Chemistry, The University of Western Ontario, London, ON, N6A 5B7, Canada.
| |
Collapse
|
19
|
Pujol-Pina R, Vilaprinyó-Pascual S, Mazzucato R, Arcella A, Vilaseca M, Orozco M, Carulla N. SDS-PAGE analysis of Aβ oligomers is disserving research into Alzheimer´s disease: appealing for ESI-IM-MS. Sci Rep 2015; 5:14809. [PMID: 26450154 PMCID: PMC4598734 DOI: 10.1038/srep14809] [Citation(s) in RCA: 85] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2015] [Accepted: 09/09/2015] [Indexed: 12/20/2022] Open
Abstract
The characterization of amyloid-beta peptide (Aβ) oligomer forms and structures is crucial to the advancement in the field of Alzheimer´s disease (AD). Here we report a critical evaluation of two methods used for this purpose, namely sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), extensively used in the field, and ion mobility coupled to electrospray ionization mass spectrometry (ESI-IM-MS), an emerging technique with great potential for oligomer characterization. To evaluate their performance, we first obtained pure cross-linked Aβ40 and Aβ42 oligomers of well-defined order. Analysis of these samples by SDS-PAGE revealed that SDS affects the oligomerization state of Aβ42 oligomers, thus providing flawed information on their order and distribution. In contrast, ESI-IM-MS provided accurate information, while also reported on the chemical nature and on the structure of the oligomers. Our findings have important implications as they challenge scientific paradigms in the AD field built upon SDS-PAGE characterization of Aβ oligomer samples.
Collapse
Affiliation(s)
- Rosa Pujol-Pina
- Institute for Research in Biomedicine (IRB Barcelona), Baldiri Reixac 10, Barcelona 08028, Spain
| | | | - Roberta Mazzucato
- Institute for Research in Biomedicine (IRB Barcelona), Baldiri Reixac 10, Barcelona 08028, Spain
| | - Annalisa Arcella
- Joint IRB-BSC Research Program in Computational Biology, Institute for Research in Biomedicine (IRB Barcelona), Baldiri Reixac 10, Barcelona 08028, Spain
| | - Marta Vilaseca
- Mass Spectrometry Core Facility, Institute for Research in Biomedicine (IRB Barcelona), Baldiri Reixac 10, Barcelona 08028, Spain
| | - Modesto Orozco
- Joint IRB-BSC Research Program in Computational Biology, Institute for Research in Biomedicine (IRB Barcelona), Baldiri Reixac 10, Barcelona 08028, Spain.,Department of Biochemistry and Molecular Biology, University of Barcelona, Diagonal 647, Barcelona 08028, Spain
| | - Natàlia Carulla
- Institute for Research in Biomedicine (IRB Barcelona), Baldiri Reixac 10, Barcelona 08028, Spain
| |
Collapse
|
20
|
Abstract
Lipocalins are one of the most important groups of inhalant animal allergens. The analysis of structural features of these proteins is important to get insights into their allergenicity. We have determined two different dimeric crystal structures for bovine dander lipocalin Bos d 2, which was earlier described as a monomeric allergen. The crystal structure analysis of all other determined lipocalin allergens also revealed oligomeric structures which broadly utilize inherent structural features of the β-sheet in dimer formation. According to the moderate size of monomer-monomer interfaces, most of these dimers would be transient in solution. Native mass spectrometry was employed to characterize quantitatively transient dimerization of two lipocalin allergens, Bos d 2 and Bos d 5, in solution.
Collapse
|
21
|
Domínguez-Vega E, Haselberg R, Somsen GW, de Jong GJ. Simultaneous Assessment of Protein Heterogeneity and Affinity by Capillary Electrophoresis–Mass Spectrometry. Anal Chem 2015. [DOI: 10.1021/acs.analchem.5b01701] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Affiliation(s)
- E. Domínguez-Vega
- Division
of BioAnalytical Chemistry, VU University Amsterdam, de Boelelaan
1083, 1081 HV Amsterdam, The Netherlands
| | - R. Haselberg
- Division
of BioAnalytical Chemistry, VU University Amsterdam, de Boelelaan
1083, 1081 HV Amsterdam, The Netherlands
| | - G. W. Somsen
- Division
of BioAnalytical Chemistry, VU University Amsterdam, de Boelelaan
1083, 1081 HV Amsterdam, The Netherlands
| | - G. J. de Jong
- Biomolecular
Analysis, Utrecht University, P.O. Box 80082, 3508 TB Utrecht, The Netherlands
| |
Collapse
|
22
|
Zhang J, Reza Malmirchegini G, Clubb RTCT, Loo JA. Native top-down mass spectrometry for the structural characterization of human hemoglobin. EUROPEAN JOURNAL OF MASS SPECTROMETRY (CHICHESTER, ENGLAND) 2015; 21:221-31. [PMID: 26307702 PMCID: PMC4731028 DOI: 10.1255/ejms.1340] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
Native mass spectrometry (MS) has become an invaluable tool for the characterization of proteins and noncovalent protein complexes under near physiological solution conditions. Here we report the structural characterization of human hemoglobin (Hb), a 64 kDa oxygen-transporting protein complex, by high resolution native top-down MS using electrospray ionization and a 15-Tesla Fourier transform ion cyclotron resonance mass spectrometer. Native MS preserves the noncovalent interactions between the globin subunits, and electron capture dissociation (ECD) produces fragments directly from the intact Hb complex without dissociating the subunits. Using activated ion ECD, we observe the gradual unfolding process of the Hb complex in the gas phase. Without protein ion activation, the native Hb shows very limited ECD fragmentation from the N-termini, suggesting a tightly packed structure of the native complex and therefore a low fragmentation efficiency. Precursor ion activation allows a steady increase in N-terminal fragment ions, while the C-terminal fragments remain limited (38 c ions and four z ions on the α chain; 36 c ions and two z ions on the β chain). This ECD fragmentation pattern suggests that upon activation, the Hb complex starts to unfold from the N-termini of both subunits, whereas the C-terminal regions and therefore the potential regions involved in the subunit binding interactions remain intact. ECD-MS of the Hb dimer shows similar fragmentation patterns as the Hb tetramer, providing further evidence for the hypothesized unfolding process of the Hb complex in the gas phase. Native top-down ECD-MS allows efficient probing of the Hb complex structure and the subunit binding interactions in the gas phase. It may provide a fast and effective means to probe the structure of novel protein complexes that are intractable to traditional structural characterization tools.
Collapse
Affiliation(s)
| | | | - Robert T Clubb T Clubb
- Department of Chemistry and Biochemistry, UCLA/DOE Institute of Genomics and Proteomics, University of California, Los Angeles, California, 90095, United States.
| | - Joseph A Loo
- De partment of Chemistry and Biochemistry, Department of Biological Chemistry, David Geffen School of Medicine, UCLA/DOE Institute of Genomics and Proteomics, University of California, Los Angeles, California, 90095, United States.
| |
Collapse
|
23
|
Liu Y, Lord H, Maciążek-Jurczyk M, Jolly S, Hussain MA, Pawliszyn J. Development of an immunoaffinity solid phase microextraction method for the identification of penicillin binding protein 2a. J Chromatogr A 2014; 1364:64-73. [DOI: 10.1016/j.chroma.2014.08.042] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2014] [Revised: 07/22/2014] [Accepted: 08/11/2014] [Indexed: 10/24/2022]
|
24
|
Zinck N, Stark AK, Wilson DJ, Sharon M. An improved rapid mixing device for time-resolved electrospray mass spectrometry measurements. ChemistryOpen 2014; 3:109-14. [PMID: 25050229 PMCID: PMC4101726 DOI: 10.1002/open.201402002] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2014] [Indexed: 12/12/2022] Open
Abstract
Time series data can provide valuable insight into the complexity of biological reactions. Such information can be obtained by mass-spectrometry-based approaches that measure pre-steady-state kinetics. These methods are based on a mixing device that rapidly mixes the reactants prior to the on-line mass measurement of the transient intermediate steps. Here, we describe an improved continuous-flow mixing apparatus for real-time electrospray mass spectrometry measurements. Our setup was designed to minimize metal–solution interfaces and provide a sheath flow of nitrogen gas for generating stable and continuous spray that consequently enhances the signal-to-noise ratio. Moreover, the device was planned to enable easy mounting onto a mass spectrometer replacing the commercial electrospray ionization source. We demonstrate the performance of our apparatus by monitoring the unfolding reaction of cytochrome C, yielding improved signal-to-noise ratio and reduced experimental repeat errors.
Collapse
Affiliation(s)
- Nicholas Zinck
- Department of Chemistry, York University Toronto, ON M3J 1P3 (Canada)
| | - Ann-Kathrin Stark
- Department of Biological Chemistry, Weizmann Institute of Science 76100 Rehovot (Israel) E-mail:
| | - Derek J Wilson
- Department of Chemistry, York University Toronto, ON M3J 1P3 (Canada)
| | - Michal Sharon
- Department of Biological Chemistry, Weizmann Institute of Science 76100 Rehovot (Israel) E-mail:
| |
Collapse
|
25
|
Niemi MH, Rytkönen-Nissinen M, Jänis J, Virtanen T, Rouvinen J. Structural aspects of dog allergies: the crystal structure of a dog dander allergen Can f 4. Mol Immunol 2014; 61:7-15. [PMID: 24859823 DOI: 10.1016/j.molimm.2014.04.003] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2014] [Revised: 04/10/2014] [Accepted: 04/14/2014] [Indexed: 10/25/2022]
Abstract
Four out of six officially recognized dog allergens are members of the lipocalin protein family. So far, a three-dimensional structure has been determined for only one dog allergen, Can f 2, which is a lipocalin protein. We present here the crystal structure of a second lipocalin allergen from dog, a variant of Can f 4. Moreover, we have compared and analyzed the structures of these two weakly homologous (amino acid identity 21%) dog allergens. The size and the amino acid composition of the ligand-binding pocket indicate that Can f 4 is capable of binding only relatively small hydrophobic molecules which are different from those that Can f 2 is able to bind. The crystal structure of Can f 4 contained both monomeric and dimeric forms of the allergen, suggesting that Can f 4 is able to form transient (weak) dimers. The existence of transient dimers in solution was confirmed by use of native mass spectrometry. The dimeric structure of Can f 4 is formed when the ends of four β-strands are packed against the same strands from the second monomer. The residues in the interface are mainly hydrophobic and the formation of the dimer is similar to the major horse allergen Equ c 1. Interestingly, the crystal structure of dog Can f 2 has been reported to show a different type of dimer formation. The capability of these allergens to form dimers may be important for the development of immediate allergic reaction (mast cell activation) because oligomeric allergens can effectively present multivalent epitopes.
Collapse
Affiliation(s)
- Merja H Niemi
- Department of Chemistry and Biocenter Kuopio, University of Eastern Finland, PO Box 111, 80101 Joensuu, Finland
| | - Marja Rytkönen-Nissinen
- Department of Clinical Microbiology, Institute of Clinical Medicine and Biocenter Kuopio, University of Eastern Finland, PO Box 1627, 70211 Kuopio, Finland; Institute of Dentistry, School of Medicine, University of Eastern Finland, PO Box 1627, 70211 Kuopio, Finland
| | - Janne Jänis
- Department of Chemistry and Biocenter Kuopio, University of Eastern Finland, PO Box 111, 80101 Joensuu, Finland
| | - Tuomas Virtanen
- Department of Clinical Microbiology, Institute of Clinical Medicine and Biocenter Kuopio, University of Eastern Finland, PO Box 1627, 70211 Kuopio, Finland
| | - Juha Rouvinen
- Department of Chemistry and Biocenter Kuopio, University of Eastern Finland, PO Box 111, 80101 Joensuu, Finland.
| |
Collapse
|
26
|
Liu J, Konermann L. Cation-induced stabilization of protein complexes in the gas phase: mechanistic insights from hemoglobin dissociation studies. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2014; 25:595-603. [PMID: 24452299 DOI: 10.1007/s13361-013-0814-7] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/24/2013] [Revised: 12/13/2013] [Accepted: 12/14/2013] [Indexed: 06/03/2023]
Abstract
Collision-induced dissociation (CID) of electrosprayed protein complexes usually involves asymmetric charge partitioning, where a single unfolded chain gets ejected that carries a disproportionately large fraction of charge. Using hemoglobin (Hb) tetramers as model system, we confirm earlier reports that bound metal ions can stabilize protein complexes under CID conditions. We examine the mechanism underlying this effect. Nonvolatile salts cause extensive adduct formation. Significant stabilization was observed for Mg(2+) and Ca(2+), whereas K(+), Rb(+), and Cs(+) had no effect. Precursor ion selection was used to examine Hb subpopulations with well-defined metal binding levels. K(+), Rb(+), and Cs(+)-adducted tetramers eject monomers that carry roughly one-quarter of the metal ions that were bound to the precursor. This demonstrates that charge migration during CID is exclusively due to proton transfer, not metal ion transfer. Also, replacement of highly mobile charge carriers (protons) with less mobile species (metal ions) does not exert a stabilizing influence under the conditions used here. Interestingly, Hb carrying stabilizing ions (Mg(2+) and Ca(2+)) generates monomeric CID products that are metal depleted. This effect is attributed to a combination of two factors: (1) Me(2+) binding stabilizes Hb via formation of chelation bridges (e.g., R-COO(-) Me(2+) (-)OOC-R); the more Me(2+) a subunit contains the more stable it is. (2) More than ~90% of the tetramers contain at least one subunit with a below-average number of Me(2+). The prevalence of monomeric CID products with depleted Me(2+) levels is caused by the tendency of these low metal-containing subunits to undergo preferential unfolding/ejection.
Collapse
Affiliation(s)
- JiangJiang Liu
- Department of Chemistry, The University of Western Ontario, London, ON, N6A 5B7, Canada
| | | |
Collapse
|
27
|
Abstract
In recent years, HDX-MS (hydrogen–deuterium exchange coupled to MS) on biomolecules has evolved from a niche technique to a powerful method in the investigation of protein dynamics. Protein kinases, in particular, represent an area of active study using this technique owing to their well-characterized protein structures and their relevance to diseases such as cancer, immune disorders and neurodegenerative defects. In the present review, we describe how HDX-MS has revealed important dynamic properties of protein kinases and provided insight into the mechanisms of drug binding.
Collapse
|
28
|
Barylyuk K, Gülbakan B, Xie X, Zenobi R. DNA oligonucleotides: a model system with tunable binding strength to study monomer-dimer equilibria with electrospray ionization-mass spectrometry. Anal Chem 2013; 85:11902-12. [PMID: 24274465 DOI: 10.1021/ac402669e] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Electrospray ionization (ESI) is increasingly used to measure binding strengths, but it is not always clear whether the ESI process introduces artifacts. Here we propose a model monomer-dimer equilibrium system based on DNA oligonucleotides to systematically explore biomolecular self-association with the ESI-mass spectrometry (MS) titration method. The oligonucleotides are designed to be self-complementary and have the same chemical composition and mass, allowing for equal ionization probability, ion transmission, and detection efficiency in ESI-MS. The only difference is the binding strength, which is determined by the nucleotide sequence and can be tuned to cover a range of dissociation constant values. This experimental design allows one to focus on the impact of ESI on the chemical equilibrium and to avoid the other typical sources of variation in ESI-MS signal responses, which yields a direct comparison of samples with different binding strengths. For a set of seven model DNA oligonucleotides, the monomer-dimer binding equilibrium was probed with the ESI-MS titration method in both positive and negative ion modes. A mathematical model describing the dependence of the monomer-to-dimer peak intensity ratio on the DNA concentration was proposed and used to extract apparent Kd values and the fraction of DNA duplex that irreversibly dissociates in the gas phase. The Kd values determined via ESI-MS titration were compared to those determined in solution with isothermal titration calorimetry and equilibrium thermal denaturation methods and were found to be significantly lower. The observed discrepancy was attributed to a greater electrospray response of dimers relative to that of monomers.
Collapse
Affiliation(s)
- Konstantin Barylyuk
- Department of Chemistry and Applied Biosciences, ETH Zurich , Wolfgang-Pauli-Strasse 10, 8093 Zurich, Switzerland
| | | | | | | |
Collapse
|
29
|
Sowole MA, Konermann L. Comparative analysis of oxy-hemoglobin and aquomet-hemoglobin by hydrogen/deuterium exchange mass spectrometry. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2013; 24:997-1005. [PMID: 23666601 DOI: 10.1007/s13361-013-0647-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/09/2013] [Revised: 04/12/2013] [Accepted: 04/14/2013] [Indexed: 06/02/2023]
Abstract
The function of hemoglobin (Hb) as oxygen transporter is mediated by reversible O2 binding to Fe(2+) heme in each of the α and β subunits. X-ray crystallography revealed different subunit arrangements in oxy-Hb and deoxy-Hb. The deoxy state is stabilized by additional contacts, causing a rigidification that results in strong protection against hydrogen/deuterium exchange (HDX). Aquomet-Hb is a dysfunctional degradation product with four water-bound Fe(3+) centers. Heme release from aquomet-Hb is relatively facile, triggering oxidative damage of membrane lipids. Aquomet-Hb crystallizes in virtually the same conformation as oxy-Hb. Hence, it is commonly implied that the solution-phase properties of aquomet-Hb should resemble those of the oxy state. This work compares the structural dynamics of oxy-Hb and aquomet-Hb by HDX mass spectrometry (MS). It is found that the aquomet state exhibits a solution-phase structure that is significantly more dynamic, as manifested by elevated HDX levels. These enhanced dynamics affect the aquomet α and β subunits in a different fashion. The latter undergoes global destabilization, whereas the former shows elevated HDX levels only in the heme binding region. It is proposed that these enhanced dynamics play a role in facilitating heme release from aquomet-Hb. Our findings should be of particular interest to the MS community because oxy-Hb and aquomet-Hb serve as widely used test analytes for probing the relationship between biomolecular structure in solution and in the gas phase. We are not aware of any prior comparative HDX/MS experiments on oxy-Hb and aquomet-Hb.
Collapse
Affiliation(s)
- Modupeola A Sowole
- Department of Chemistry, The University of Western Ontario, London, Ontario, N6A 5B7, Canada
| | | |
Collapse
|
30
|
Hedges JB, Vahidi S, Yue X, Konermann L. Effects of Ammonium Bicarbonate on the Electrospray Mass Spectra of Proteins: Evidence for Bubble-Induced Unfolding. Anal Chem 2013; 85:6469-76. [DOI: 10.1021/ac401020s] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Affiliation(s)
- Jason B. Hedges
- Department of Chemistry, The University of Western Ontario, London, Ontario, N6A 5B7, Canada
| | - Siavash Vahidi
- Department of Chemistry, The University of Western Ontario, London, Ontario, N6A 5B7, Canada
| | - Xuanfeng Yue
- Department of Chemistry, The University of Western Ontario, London, Ontario, N6A 5B7, Canada
| | - Lars Konermann
- Department of Chemistry, The University of Western Ontario, London, Ontario, N6A 5B7, Canada
| |
Collapse
|
31
|
Liu J, Konermann L. Assembly of Hemoglobin from Denatured Monomeric Subunits: Heme Ligation Effects and Off-Pathway Intermediates Studied by Electrospray Mass Spectrometry. Biochemistry 2013; 52:1717-24. [DOI: 10.1021/bi301693g] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Affiliation(s)
- Jiangjiang Liu
- Department of Chemistry, The University of Western Ontario, London, Ontario N6A 5B7, Canada
| | - Lars Konermann
- Department of Chemistry, The University of Western Ontario, London, Ontario N6A 5B7, Canada
| |
Collapse
|
32
|
Konermann L, Ahadi E, Rodriguez AD, Vahidi S. Unraveling the Mechanism of Electrospray Ionization. Anal Chem 2012; 85:2-9. [DOI: 10.1021/ac302789c] [Citation(s) in RCA: 359] [Impact Index Per Article: 29.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Affiliation(s)
- Lars Konermann
- Department
of Chemistry, The University of Western Ontario, London, Ontario, N6A 5B7 Canada
| | - Elias Ahadi
- Department
of Chemistry, The University of Western Ontario, London, Ontario, N6A 5B7 Canada
| | - Antony D. Rodriguez
- Department
of Chemistry, The University of Western Ontario, London, Ontario, N6A 5B7 Canada
| | - Siavash Vahidi
- Department
of Chemistry, The University of Western Ontario, London, Ontario, N6A 5B7 Canada
| |
Collapse
|
33
|
Spirig T, Malmirchegini GR, Zhang J, Robson SA, Sjodt M, Liu M, Krishna Kumar K, Dickson CF, Gell DA, Lei B, Loo JA, Clubb RT. Staphylococcus aureus uses a novel multidomain receptor to break apart human hemoglobin and steal its heme. J Biol Chem 2012; 288:1065-78. [PMID: 23132864 DOI: 10.1074/jbc.m112.419119] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Staphylococcus aureus is a leading cause of life-threatening infections in the United States. It requires iron to grow, which must be actively procured from its host to successfully mount an infection. Heme-iron within hemoglobin (Hb) is the most abundant source of iron in the human body and is captured by S. aureus using two closely related receptors, IsdH and IsdB. Here we demonstrate that each receptor captures heme using two conserved near iron transporter (NEAT) domains that function synergistically. NMR studies of the 39-kDa conserved unit from IsdH (IsdH(N2N3), Ala(326)-Asp(660)) reveals that it adopts an elongated dumbbell-shaped structure in which its NEAT domains are properly positioned by a helical linker domain, whose three-dimensional structure is determined here in detail. Electrospray ionization mass spectrometry and heme transfer measurements indicate that IsdH(N2N3) extracts heme from Hb via an ordered process in which the receptor promotes heme release by inducing steric strain that dissociates the Hb tetramer. Other clinically significant Gram-positive pathogens capture Hb using receptors that contain multiple NEAT domains, suggesting that they use a conserved mechanism.
Collapse
Affiliation(s)
- Thomas Spirig
- Department of Chemistry and Biochemistry and the UCLA-Department of Energy Institute for Genomics and Proteomics, UCLA, Los Angeles, California 90095, USA
| | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
34
|
Hyung SJ, Ruotolo BT. Integrating mass spectrometry of intact protein complexes into structural proteomics. Proteomics 2012; 12:1547-64. [PMID: 22611037 DOI: 10.1002/pmic.201100520] [Citation(s) in RCA: 75] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
MS analysis of intact protein complexes has emerged as an established technology for assessing the composition and connectivity within dynamic, heterogeneous multiprotein complexes at low concentrations and in the context of mixtures. As this technology continues to move forward, one of the main challenges is to integrate the information content of such intact protein complex measurements with other MS approaches in structural biology. Methods such as H/D exchange, oxidative foot-printing, chemical cross-linking, affinity purification, and ion mobility separation add complementary information that allows access to every level of protein structure and organization. Here, we survey the structural information that can be retrieved by such experiments, demonstrate the applicability of integrative MS approaches in structural proteomics, and look to the future to explore upcoming innovations in this rapidly advancing area.
Collapse
Affiliation(s)
- Suk-Joon Hyung
- Department of Chemistry, University of Michigan, Ann Arbor, MI 48109, USA
| | | |
Collapse
|
35
|
Hilton GR, Benesch JLP. Two decades of studying non-covalent biomolecular assemblies by means of electrospray ionization mass spectrometry. J R Soc Interface 2012; 9:801-16. [PMID: 22319100 PMCID: PMC3306659 DOI: 10.1098/rsif.2011.0823] [Citation(s) in RCA: 112] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2011] [Accepted: 01/16/2012] [Indexed: 12/31/2022] Open
Abstract
Mass spectrometry (MS) is a recognized approach for characterizing proteins and the complexes they assemble into. This application of a long-established physico-chemical tool to the frontiers of structural biology has stemmed from experiments performed in the early 1990s. While initial studies focused on the elucidation of stoichiometry by means of simple mass determination, developments in MS technology and methodology now allow researchers to address questions of shape, inter-subunit connectivity and protein dynamics. Here, we chart the remarkable rise of MS and its application to biomolecular complexes over the last two decades.
Collapse
Affiliation(s)
| | - Justin L. P. Benesch
- Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX3 1QZ, UK
| |
Collapse
|
36
|
Sokratous K, Roach LV, Channing D, Strachan J, Long J, Searle MS, Layfield R, Oldham NJ. Probing Affinity and Ubiquitin Linkage Selectivity of Ubiquitin-Binding Domains Using Mass Spectrometry. J Am Chem Soc 2012; 134:6416-24. [DOI: 10.1021/ja300749d] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Affiliation(s)
- Kleitos Sokratous
- School of Chemistry, University of Nottingham, University Park NG7 2RD,
U.K
| | - Lucy V. Roach
- School of Chemistry, University of Nottingham, University Park NG7 2RD,
U.K
| | - Debora Channing
- School of Biomedical
Sciences,
Queen’s Medical Centre, University of Nottingham, Nottingham NG7 2UH, U.K
| | - Joanna Strachan
- School of Biomedical
Sciences,
Queen’s Medical Centre, University of Nottingham, Nottingham NG7 2UH, U.K
| | - Jed Long
- Centre for Biomolecular Sciences,
School of Chemistry, University Park, University of Nottingham, Nottingham NG7 2RD, U.K
| | - Mark S. Searle
- Centre for Biomolecular Sciences,
School of Chemistry, University Park, University of Nottingham, Nottingham NG7 2RD, U.K
| | - Robert Layfield
- School of Biomedical
Sciences,
Queen’s Medical Centre, University of Nottingham, Nottingham NG7 2UH, U.K
| | - Neil J. Oldham
- School of Chemistry, University of Nottingham, University Park NG7 2RD,
U.K
| |
Collapse
|
37
|
Linking structural change with functional regulation—insights from mass spectrometry. Curr Opin Struct Biol 2012; 22:44-51. [DOI: 10.1016/j.sbi.2011.12.003] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2011] [Accepted: 12/27/2011] [Indexed: 12/20/2022]
|
38
|
Mädler S, Barylyuk K, Boeri Erba E, Nieckarz RJ, Zenobi R. Compelling advantages of negative ion mode detection in high-mass MALDI-MS for homomeric protein complexes. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2012; 23:213-224. [PMID: 22131225 DOI: 10.1007/s13361-011-0274-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/05/2011] [Revised: 10/04/2011] [Accepted: 10/08/2011] [Indexed: 05/31/2023]
Abstract
Chemical cross-linking in combination with high-mass MALDI mass spectrometry allows for the rapid identification of interactions and determination of the complex stoichiometry of noncovalent protein-protein interactions. As the molecular weight of these complexes increases, the fraction of multiply charged species typically increases. In the case of homomeric complexes, signals from multiply charged multimers overlap with singly charged subunits. Remarkably, spectra recorded in negative ion mode show lower abundances of multiply charged species, lower background, higher reproducibility, and, thus, overall cleaner spectra compared with positive ion mode spectra. In this work, a dedicated high-mass detector was applied for measuring high-mass proteins (up to 200 kDa) by negative ion mode MALDI-MS. The influences of sample preparation and instrumental parameters were carefully investigated. Relative signal integrals of multiply charged anions were relatively independent of any of the examined parameters and could thus be approximated easily for the spectra of cross-linked complexes. For example, the fraction of doubly charged anions signals overlapping with the signals of singly charged subunits could be more precisely estimated than in positive ion mode. Sinapinic acid was found to be an excellent matrix for the analysis of proteins and cross-linked protein complexes in both ion modes. Our results suggest that negative ion mode data of chemically cross-linked protein complexes are complementary to positive ion mode data and can in some cases represent the solution phase situation better than positive ion mode.
Collapse
Affiliation(s)
- Stefanie Mädler
- Department of Chemistry and Applied Biosciences, ETH Zurich, 8093 Zurich, Switzerland
| | | | | | | | | |
Collapse
|
39
|
Boeri Erba E, Barylyuk K, Yang Y, Zenobi R. Quantifying Protein–Protein Interactions Within Noncovalent Complexes Using Electrospray Ionization Mass Spectrometry. Anal Chem 2011; 83:9251-9. [DOI: 10.1021/ac201576e] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Affiliation(s)
- Elisabetta Boeri Erba
- Department of Chemistry and Applied Biosciences, ETH Zurich, CH-8093 Zurich, Switzerland
| | - Konstantin Barylyuk
- Department of Chemistry and Applied Biosciences, ETH Zurich, CH-8093 Zurich, Switzerland
| | - Yang Yang
- Department of Chemistry and Applied Biosciences, ETH Zurich, CH-8093 Zurich, Switzerland
| | - Renato Zenobi
- Department of Chemistry and Applied Biosciences, ETH Zurich, CH-8093 Zurich, Switzerland
| |
Collapse
|
40
|
Sciuto SV, Liu J, Konermann L. An electrostatic charge partitioning model for the dissociation of protein complexes in the gas phase. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2011; 22:1679-1689. [PMID: 21952881 DOI: 10.1007/s13361-011-0205-x] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/23/2011] [Revised: 06/27/2011] [Accepted: 06/28/2011] [Indexed: 05/31/2023]
Abstract
Electrosprayed multi-protein complexes can be dissociated by collisional activation in the gas phase. Typically, these processes follow a mechanism whereby a single subunit gets ejected with a disproportionately high amount of charge relative to its mass. This asymmetric behavior suggests that the departing subunit undergoes some degree of unfolding prior to being separated from the residual complex. These structural changes occur concomitantly with charge (proton) transfer towards the subunit that is being unraveled. Charge accumulation takes place up to the point where the subunit loses physical contact with the residual complex. This work develops a simple electrostatic model for studying the relationship between conformational changes and charge enrichment during collisional activation. Folded subunits are described as spheres that carry continuum surface charge. The unfolded chain is envisioned as random coil bead string. Simulations are guided by the principle that the system will adopt the charge configuration with the lowest potential energy for any backbone conformation. A finite-difference gradient algorithm is used to determine the charge on each subunit throughout the dissociation process. Both dimeric and tetrameric protein complexes are investigated. The model reproduces the occurrence of asymmetric charge partitioning for dissociation events that are preceded by subunit unfolding. Quantitative comparisons of experimental MS/MS data with model predictions yield estimates of the structural changes that occur during collisional activation. Our findings suggest that subunit separation can occur over a wide range of scission point structures that correspond to different degrees of unfolding.
Collapse
Affiliation(s)
- Stephen V Sciuto
- Department of Chemistry, The University of Western Ontario, London, Ontario, N6A 5B7, Canada
| | | | | |
Collapse
|