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Konermann L, Liu Z, Haidar Y, Willans MJ, Bainbridge NA. On the Chemistry of Aqueous Ammonium Acetate Droplets during Native Electrospray Ionization Mass Spectrometry. Anal Chem 2023; 95:13957-13966. [PMID: 37669319 DOI: 10.1021/acs.analchem.3c02546] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/07/2023]
Abstract
Ammonium acetate (NH4Ac) is a widely used solvent additive in native electrospray ionization (ESI) mass spectrometry. NH4Ac can undergo proton transfer to form ammonia and acetic acid (NH4+ + Ac- → NH3 + HAc). The volatility of these products ensures that electrosprayed ions are free of undesired adducts. NH4Ac dissolution in water yields pH 7, providing "physiological" conditions. However, NH4Ac is not a buffer at pH 7 because NH4+ and Ac- are not a conjugate acid/base pair (Konermann, L. J. Am. Soc. Mass Spectrom. 2017, 28, 1827-1835.). In native ESI, it is desirable that analytes experience physiological conditions not only in bulk solution but also while they reside in ESI droplets. Little is known about the internal milieu of NH4Ac-containing ESI droplets. The current work explored the acid/base chemistry of such droplets, starting from a pH 7 analyte solution. We used a two-pronged approach involving evaporation experiments on bulk solutions under ESI-mimicking conditions, as well as molecular dynamics simulations using a newly developed algorithm that allows for proton transfer. Our results reveal that during droplet formation at the tip of the Taylor cone, electrolytically generated protons get neutralized by Ac-, making NH4+ the net charge carriers in the weakly acidic nascent droplets. During the subsequent evaporation, the droplets lose water as well as NH3 and HAc that were generated by proton transfer. NH3 departs more quickly because of its greater volatility, causing the accumulation of HAc. Together with residual Ac-, these HAc molecules form an acetate buffer that stabilizes the average droplet pH at 5.4 ± 0.1, as governed by the Henderson-Hasselbalch equation. The remarkable success of native ESI investigations in the literature implies that this pH drop by ∼1.6 units relative to the initially neutral analyte solution can be tolerated by most biomolecular analytes on the short time scale of the ESI process.
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Affiliation(s)
- Lars Konermann
- Department of Chemistry, The University of Western Ontario, London, Ontario N6A 5B7, Canada
| | - Zeyuan Liu
- Department of Chemistry, The University of Western Ontario, London, Ontario N6A 5B7, Canada
| | - Yousef Haidar
- Department of Chemistry, The University of Western Ontario, London, Ontario N6A 5B7, Canada
| | - Mathew J Willans
- Department of Chemistry, The University of Western Ontario, London, Ontario N6A 5B7, Canada
| | - Nicholas A Bainbridge
- Department of Chemistry, The University of Western Ontario, London, Ontario N6A 5B7, Canada
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Du C, Cleary SP, Kostelic MM, Jones BJ, Kafader JO, Wysocki VH. Combining Surface-Induced Dissociation and Charge Detection Mass Spectrometry to Reveal the Native Topology of Heterogeneous Protein Complexes. Anal Chem 2023; 95:13889-13896. [PMID: 37672632 PMCID: PMC10874503 DOI: 10.1021/acs.analchem.3c02185] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/08/2023]
Abstract
Charge detection mass spectrometry (CDMS) enables the direct mass measurement of heterogeneous samples on the megadalton scale, as the charge state for a single ion is determined simultaneously with the mass-to-charge ratio (m/z). Surface-induced dissociation (SID) is an effective activation method to dissociate non-intertwined, non-covalent protein complexes without extensive gas-phase restructuring, producing various subcomplexes reflective of the native protein topology. Here, we demonstrate that using CDMS after SID on an Orbitrap platform offers subunit connectivity, topology, proteoform information, and relative interfacial strengths of the intact macromolecular assemblies. SID dissects the capsids (∼3.7 MDa) of adeno-associated viruses (AAVs) into trimer-containing fragments (3mer, 6mer, 9mer, 15mer, etc.) that can be detected by the individual ion mass spectrometry (I2MS) approach on Orbitrap instruments. SID coupled to CDMS provides unique structural insights into heterogeneous assemblies that are not readily obtained by traditional MS measurements.
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Affiliation(s)
- Chen Du
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210, United States
- Resource for Native MS Guided Structural Biology, The Ohio State University, Columbus, Ohio 43210, United States
| | - Sean P Cleary
- Resource for Native MS Guided Structural Biology, The Ohio State University, Columbus, Ohio 43210, United States
| | - Marius M Kostelic
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210, United States
- Resource for Native MS Guided Structural Biology, The Ohio State University, Columbus, Ohio 43210, United States
| | - Benjamin J Jones
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210, United States
- Resource for Native MS Guided Structural Biology, The Ohio State University, Columbus, Ohio 43210, United States
| | - Jared O Kafader
- Departments of Chemistry, Molecular Biosciences, The Chemistry of Life Processes Institute, The Proteomics Center of Excellence at Northwestern University, Evanston, Illinois 60208, United States
| | - Vicki H Wysocki
- Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210, United States
- Resource for Native MS Guided Structural Biology, The Ohio State University, Columbus, Ohio 43210, United States
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Abstract
Native mass spectrometry (nMS) is evolving into a workhorse for structural biology. The plethora of online and offline preparation, separation, and purification methods as well as numerous ionization techniques combined with powerful new hybrid ion mobility and mass spectrometry systems has illustrated the great potential of nMS for structural biology. Fundamental to the progression of nMS has been the development of novel activation methods for dissociating proteins and protein complexes to deduce primary, secondary, tertiary, and quaternary structure through the combined use of multiple MS/MS technologies. This review highlights the key features and advantages of surface collisions (surface-induced dissociation, SID) for probing the connectivity of subunits within protein and nucleoprotein complexes and, in particular, for solving protein structure in conjunction with complementary techniques such as cryo-EM and computational modeling. Several case studies highlight the significant role SID, and more generally nMS, will play in structural elucidation of biological assemblies in the future as the technology becomes more widely adopted. Cases are presented where SID agrees with solved crystal or cryoEM structures or provides connectivity maps that are otherwise inaccessible by "gold standard" structural biology techniques.
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Affiliation(s)
- Dalton T. Snyder
- Resource for Native Mass Spectrometry Guided Structural Biology, The Ohio State University, Columbus, OH 43210
| | - Sophie R. Harvey
- Resource for Native Mass Spectrometry Guided Structural Biology, The Ohio State University, Columbus, OH 43210,Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210
| | - Vicki H. Wysocki
- Resource for Native Mass Spectrometry Guided Structural Biology, The Ohio State University, Columbus, OH 43210,Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH 43210,Corresponding author:
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Szkoda BE, Di Capua A, Shaffer J, Behrman EJ, Wysocki VH, Gopalan V. Characterization of a Salmonella transcription factor-DNA complex and identification of the inducer by native mass spectrometry. J Mol Biol 2022. [PMID: 35176290 PMCID: PMC8977229 DOI: 10.1016/j.jmb.2022.167480] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2021] [Revised: 01/29/2022] [Accepted: 01/31/2022] [Indexed: 11/21/2022]
Abstract
FraR, a transcriptional repressor, was postulated to regulate the metabolism of the Amadori compound fructose-asparagine (F-Asn) in the foodborne pathogen Salmonella enterica. Here, the DNA- and inducer-binding affinities and stoichiometries of FraR were determined and cross-validated by electrophoretic mobility-shift assays (EMSAs) and online buffer exchange coupled to native mass spectrometry (OBE-nMS). We demonstrate the utility of OBE-nMS to characterize protein and protein-DNA complexes that are not amenable to offline exchange into volatile buffers. OBE-nMS complemented EMSAs by revealing that FraR binds to the operator DNA as a dimer and by establishing 6-phosphofructose-aspartate as the inducer that weakens DNA binding by FraR. These results provide insights into how FraR regulates the expression of F-Asn-catabolizing enzymes and add to our understanding of the intricate bacterial circuitry that dictates utilization of diverse nutrients.
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Harvey SR, O’Neale C, Schey KL, Wysocki VH. Native Mass Spectrometry and Surface Induced Dissociation Provide Insight into the Post-Translational Modifications of Tetrameric AQP0 Isolated from Bovine Eye Lens. Anal Chem 2022; 94:1515-1519. [PMID: 35015511 PMCID: PMC9161558 DOI: 10.1021/acs.analchem.1c04322] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Aquaporin-0 (AQP0) is a tetrameric membrane protein and the most abundant membrane protein in the eye lens. Interestingly, there is little to no cellular turnover once mature lens fiber cells are formed, and hence, age-related modifications accumulate with time. While bottom-up mass spectrometry-based approaches can provide identification of post-translational modifications, they cannot provide information on how these modifications coexist in a single chain or complex. Native mass spectrometry, however, enables the transfer of the intact complex into the gas-phase allowing modifications to be identified at the tetramer level. Here, we present the use of native mass spectrometry and surface-induced dissociation to study the post-translational modifications of AQP0 isolated and purified from bovine eye lens, existing as multiple forms due to the different modification states naturally present.
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Affiliation(s)
- Sophie R Harvey
- Department of Chemistry and Biochemistry and Resource for Native Mass Spectrometry Guided Structural Biology, The Ohio State University, Columbus, OH 43210
| | - Carla O’Neale
- Vanderbilt University Department of Biochemistry and Mass Spectrometry Research Center, Nashville, TN 37240
| | - Kevin L Schey
- Vanderbilt University Department of Biochemistry and Mass Spectrometry Research Center, Nashville, TN 37240
| | - Vicki H Wysocki
- Department of Chemistry and Biochemistry and Resource for Native Mass Spectrometry Guided Structural Biology, The Ohio State University, Columbus, OH 43210,
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Harvey SR, Ben-Nissan G, Sharon M, Wysocki VH. Surface-Induced Dissociation for Protein Complex Characterization. Methods Mol Biol 2022; 2500:211-37. [PMID: 35657596 DOI: 10.1007/978-1-0716-2325-1_15] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Native mass spectrometry (nMS) enables intact non-covalent complexes to be studied in the gas phase. nMS can provide information on composition, stoichiometry, topology, and, when coupled with surface-induced dissociation (SID), subunit connectivity. Here we describe the characterization of protein complexes by nMS and SID. Substructural information obtained using this method is consistent with the solved complex structure, when a structure exists. This provides confidence that the method can also be used to obtain substructural information for unknowns, providing insight into subunit connectivity and arrangements. High-energy SID can also provide information on proteoforms present. Previously SID has been limited to a few in-house modified instruments and here we focus on SID implemented within an in-house-modified Q Exactive UHMR. However, SID is currently commercially available within the Waters Select Series Cyclic IMS instrument. Projects are underway that involve the NIH-funded native MS resource (nativems.osu.edu), instrument vendors, and third-party vendors, with the hope of bringing the technology to more platforms and labs in the near future. Currently, nMS resource staff can perform SID experiments for interested research groups.
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Snyder DT, Jones BJ, Lin YF, Cooper-Shepherd DA, Hewitt D, Wildgoose J, Brown JM, Langridge JI, Wysocki VH. Surface-induced dissociation of protein complexes on a cyclic ion mobility spectrometer. Analyst 2021; 146:6861-6873. [PMID: 34632987 PMCID: PMC8574189 DOI: 10.1039/d1an01407b] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
We describe the implementation of a simple three-electrode surface-induced dissociation (SID) cell on a cyclic ion mobility spectrometer (cIMS) and demonstrate the utility of multipass mobility separations for resolving multiple conformations of protein complexes generated during collision-induced and surface-induced unfolding (CIU & SIU) experiments. In addition to CIU and SIU, SID of protein complexes is readily accomplished within the native instrument software and with no additional external power supplies by entering a single SID collision energy, a simplification in user experience compared to prior implementations. A set of cyclic homomeric protein complexes and a heterohexamer with known CID and SID behavior were analyzed to investigate mass and mobility resolution improvements, the latter of which improved by 20-50% (median: 33%) compared to a linear travelling wave device. Multiple passes of intact complexes, or their SID fragments, increased the mobility resolution by an average of 15% per pass, with the racetrack effect being observed after ∼3 or 4 passes, depending on the drift time spread of the analytes. Even with modest improvements to apparent mobility resolving power, multipass experiments were particularly useful for separating conformations produced from CIU and SIU experiments. We illustrate several examples where either (1) multipass experiments revealed multiple overlapping conformations previously unobserved or obscured due to limited mobility resolution, or (2) CIU or SIU conformations that appeared 'native' in a single pass experiment were actually slightly compacted or expanded, with the change only being measurable through multipass experiments. The work conducted here, the first utilization of multipass cyclic ion mobility for CIU, SIU, and SID of protein assemblies and a demonstration of a wholly integrated SIU/SID workflow, paves the way for widespread adoption of SID technology for native mass spectrometry and also improves our understanding of gas-phase protein complex CIU and SIU conformationomes.
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Affiliation(s)
- Dalton T Snyder
- Resource for Native MS Guided Structural Biology, The Ohio State University, Columbus, OH, USA 43210
| | - Benjamin J Jones
- Resource for Native MS Guided Structural Biology, The Ohio State University, Columbus, OH, USA 43210.,Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH, USA 43210.
| | - Yu-Fu Lin
- Resource for Native MS Guided Structural Biology, The Ohio State University, Columbus, OH, USA 43210.,Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH, USA 43210.
| | | | - Darren Hewitt
- Waters Corporation, Stamford Avenue, Altrincham Road, Wilmslow SK9 4AX, UK
| | - Jason Wildgoose
- Waters Corporation, Stamford Avenue, Altrincham Road, Wilmslow SK9 4AX, UK
| | - Jeffery M Brown
- Waters Corporation, Stamford Avenue, Altrincham Road, Wilmslow SK9 4AX, UK
| | - James I Langridge
- Waters Corporation, Stamford Avenue, Altrincham Road, Wilmslow SK9 4AX, UK
| | - Vicki H Wysocki
- Resource for Native MS Guided Structural Biology, The Ohio State University, Columbus, OH, USA 43210.,Department of Chemistry and Biochemistry, The Ohio State University, Columbus, OH, USA 43210.
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Abstract
Native mass spectrometry (MS) is aimed at preserving and determining the native structure, composition, and stoichiometry of biomolecules and their complexes from solution after they are transferred into the gas phase. Major improvements in native MS instrumentation and experimental methods over the past few decades have led to a concomitant increase in the complexity and heterogeneity of samples that can be analyzed, including protein-ligand complexes, protein complexes with multiple coexisting stoichiometries, and membrane protein-lipid assemblies. Heterogeneous features of these biomolecular samples can be important for understanding structure and function. However, sample heterogeneity can make assignment of ion mass, charge, composition, and structure very challenging due to the overlap of tens or even hundreds of peaks in the mass spectrum. In this review, we cover data analysis, experimental, and instrumental advances and strategies aimed at solving this problem, with an in-depth discussion of theoretical and practical aspects of the use of available deconvolution algorithms and tools. We also reflect upon current challenges and provide a view of the future of this exciting field.
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Affiliation(s)
- Amber D Rolland
- Department of Chemistry and Biochemistry, University of Oregon, Eugene, Oregon 97403-1253, United States
| | - James S Prell
- Department of Chemistry and Biochemistry, University of Oregon, Eugene, Oregon 97403-1253, United States.,Materials Science Institute, University of Oregon, Eugene, Oregon 97403-1252, United States
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