1
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Benzenberg LR, Katzberger P, Wu R, Metternich JB, Riniker S, Zenobi R. Probing the Stability of a β-Hairpin Scaffold after Desolvation. J Phys Chem Lett 2024; 15:5041-5046. [PMID: 38700091 DOI: 10.1021/acs.jpclett.4c00920] [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: 05/05/2024]
Abstract
Probing the structural characteristics of biomolecular ions in the gas phase following native mass spectrometry (nMS) is of great interest, because noncovalent interactions, and thus native fold features, are believed to be largely retained upon desolvation. However, the conformation usually depends heavily on the charge state of the species investigated. In this study, we combine transition metal ion Förster resonance energy transfer (tmFRET) and ion mobility-mass spectrometry (IM-MS) with molecular dynamics (MD) simulations to interrogate the β-hairpin structure of GB1p in vacuo. Fluorescence lifetime values and collisional cross sections suggest an unfolding of the β-hairpin motif for higher charge states. MD simulations are consistent with experimental constraints, yet intriguingly provide an alternative structural interpretation: preservation of the β-hairpin is not only predicted for 2+ but also for 4+ charged species, which is unexpected given the substantial Coulomb repulsion for small secondary structure scaffolds.
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Affiliation(s)
- Lukas R Benzenberg
- Laboratory of Organic Chemistry, Department of Chemistry and Applied Biosciences ETH Zurich, Vladimir-Prelog-Weg 3, CH-8093 Zurich, Switzerland
| | - Paul Katzberger
- Institute of Molecular Physical Science, Department of Chemistry and Applied Biosciences ETH Zurich, Vladimir-Prelog-Weg 2, CH-8093 Zurich, Switzerland
| | - Ri Wu
- Laboratory of Organic Chemistry, Department of Chemistry and Applied Biosciences ETH Zurich, Vladimir-Prelog-Weg 3, CH-8093 Zurich, Switzerland
| | - Jonas B Metternich
- Laboratory of Organic Chemistry, Department of Chemistry and Applied Biosciences ETH Zurich, Vladimir-Prelog-Weg 3, CH-8093 Zurich, Switzerland
| | - Sereina Riniker
- Institute of Molecular Physical Science, Department of Chemistry and Applied Biosciences ETH Zurich, Vladimir-Prelog-Weg 2, CH-8093 Zurich, Switzerland
| | - Renato Zenobi
- Laboratory of Organic Chemistry, Department of Chemistry and Applied Biosciences ETH Zurich, Vladimir-Prelog-Weg 3, CH-8093 Zurich, Switzerland
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2
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Langeland J, Lindkvist TT, Kjær C, Nielsen SB. Gas-phase Förster resonance energy transfer in mass-selected and trapped ions. MASS SPECTROMETRY REVIEWS 2024; 43:477-499. [PMID: 36514825 DOI: 10.1002/mas.21828] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/02/2022] [Revised: 10/21/2022] [Accepted: 11/25/2022] [Indexed: 06/17/2023]
Abstract
Förster Resonance Energy transfer (FRET) is a nonradiative process that may occur from an electronically excited donor to an acceptor when the emission spectrum of the donor overlaps with the absorption spectrum of the acceptor. FRET experiments have been done in the gas phase based on specially designed mass-spectroscopy setups with the goal to obtain structural information on biomolecular ions labeled with a FRET pair (i.e., donor and acceptor dyes) and to shed light on the energy-transfer process itself. Ions are accumulated in a radio-frequency ion trap or a Penning trap where mass selection of those of interest takes place, followed by photoexcitation. Gas-phase FRET is identified from detection of emitted light either from the donor, the acceptor, or both, or from a fragmentation channel that is specific to the acceptor when electronically excited. The challenge associated with the first approach is the collection and detection of photons emitted from a thin ion cloud that is not easily accessible while the second approach relies both on the photophysical and chemical behavior of the acceptor. In this review, we present the different instrumentation used for gas-phase FRET, including a discussion of advantages and disadvantages, and examples on how the technique has provided important structural information that is not easily obtainable otherwise. Furthermore, we describe how the spectroscopic properties of the dyes are affected by nearby electric fields, which is readily discernable from experiments on simple model systems with alkyl or π-conjugated bridges. Such spectral changes can have a significant effect on the FRET efficiency. Ideas for new directions are presented at the end with special focus on cold-ion spectroscopy.
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Affiliation(s)
- Jeppe Langeland
- Department of Physics and Astronomy, Aarhus University, Aarhus, Denmark
| | | | - Christina Kjær
- Department of Physics and Astronomy, Aarhus University, Aarhus, Denmark
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3
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Wu R, Svingou D, Metternich JB, Benzenberg LR, Zenobi R. Transition Metal Ion FRET-Based Probe to Study Cu(II)-Mediated Amyloid- β Ligand Binding. J Am Chem Soc 2024; 146:2102-2112. [PMID: 38225538 DOI: 10.1021/jacs.3c11533] [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: 01/17/2024]
Abstract
Recent therapeutic strategies suggest that small peptides can act as aggregation inhibitors of monomeric amyloid-β (Αβ) by inducing structural rearrangements upon complexation. However, characterizing the binding events in such dynamic and transient noncovalent complexes, especially in the presence of natively occurring metal ions, remains a challenge. Here, we deploy a combined transition metal ion Förster resonance energy transfer (tmFRET) and native ion mobility-mass spectrometry (IM-MS) approach to characterize the structure of mass- and charge-selected Aβ complexes with Cu(II) ions (a quencher) and a potential aggregation inhibitor, a small neuropeptide named leucine enkephalin (LE). We show conformational changes of monomeric Αβ species upon Cu(II)-binding, indicating an uncoiled N-terminus and a close interaction between the C-terminus and the central hydrophobic region. Furthermore, we introduce LE labeled at the N-terminus with a metal-chelating agent, nitrilotriacetic acid (NTA). This allows us to employ tmFRET to probe the binding even in low-abundance and transient Aβ-inhibitor-metal ion complexes. Complementary intramolecular distance and global shape information from tmFRET and native IM-MS, respectively, confirmed Cu(II) displacement toward the N-terminus of Αβ, which discloses the binding region and the inhibitor's orientation.
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Affiliation(s)
- Ri Wu
- Laboratory of Organic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zurich, 8093 Zurich, Switzerland
| | - Despoina Svingou
- Laboratory of Organic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zurich, 8093 Zurich, Switzerland
| | - Jonas B Metternich
- Laboratory of Organic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zurich, 8093 Zurich, Switzerland
| | - Lukas R Benzenberg
- Laboratory of Organic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zurich, 8093 Zurich, Switzerland
| | - Renato Zenobi
- Laboratory of Organic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zurich, 8093 Zurich, Switzerland
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4
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Lindkvist TT, Langeland J, Kjær C, Nielsen SB. Empirical Calibration of a Cylindrical Ion Trap for Mass-Selected Gas-Phase Fluorescence Spectroscopy. JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY 2024; 35:123-130. [PMID: 38079152 DOI: 10.1021/jasms.3c00349] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2024]
Abstract
The ion motion in a quadrupole ion trap of hyperbolic geometry is well described by the Mathieu equations. A simpler cylindrical ion trap has also gained significance and has been used by us for fluorescence-spectroscopy experiments. This design allows for the easy replacement of the end-cap with a mesh, enhancing the photon collection. It is crucial to obtain a firm understanding of the ion motion in cylindrical ion traps and their capability as mass spectrometers. We present here an empirical method of calibrating a cylindrical ion trap based on fluorescence detection. This can be done nearly background-free in a pulsed experiment. The ions are located at the center of the trap, where the field is primarily quadrupolar, and here an effective Mathieu description is found through an effective geometry parameter. In spectroscopy experiments, high buffer-gas pressures are needed to efficiently cool the ions, which complicates the ions' motion and hence their stability. Still, simulations show that the stability diagram closely aligns with the Mathieu diagram, albeit shifted due to collisions. We map the stability diagram for six molecular ions by fluorescence collection from four cations and two anions spanning m/z from 212 to 647. The stability diagram is parametrized through the Mathieu functions with an m/z-dependent effective geometry parameter and a q-dependent shrinkage of the diagram. Based on the calibration, we estimate the mass resolution to be +7/-3 Da for ions with masses in the hundreds of Da.
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Affiliation(s)
| | - Jeppe Langeland
- Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C, Denmark
| | - Christina Kjær
- Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C, Denmark
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5
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Talbot FO, Suarez CM, Nagy AM, Chen JC, Djavani-Tabrizi I, Clotea I, Jockusch RA. Robust Fluorescence Collection Module for Wide-Bore Ion Cyclotron Resonance Mass Spectrometers. Anal Chem 2023; 95:17193-17202. [PMID: 37963234 DOI: 10.1021/acs.analchem.3c01801] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2023]
Abstract
Mass spectrometers are at the heart of the most powerful toolboxes available to scientists when studying molecular structure, conformation, and dynamics in controlled molecular environments. Improved molecular characterization brought about by the implementation of new orthogonal methods into mass spectrometry-enabled analyses opens deeper insight into the complex interplay of forces that underlie chemistry. Here, we detail how one can add fluorescence detection to commercial ultrahigh-resolution Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometers without adverse effects to its preexisting analytical tools. This advance enables measurements based on fluorescence detection, such as Förster resonance energy transfer (FRET), to be used in conjunction with other MS/MS techniques to probe the conformation and dynamics of large biomolecules, such as proteins and their complexes, in the highly controlled environment of a Penning trap.
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Affiliation(s)
- Francis O Talbot
- Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, Canada
| | - Cynthia M Suarez
- Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, Canada
| | - Andrea M Nagy
- Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, Canada
| | - JoAnn C Chen
- Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, Canada
| | - Iden Djavani-Tabrizi
- Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, Canada
| | - Ioana Clotea
- Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, Canada
| | - Rebecca A Jockusch
- Department of Chemistry, University of Toronto, Toronto, Ontario M5S 3H6, Canada
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6
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Kjaer C, Vu-Phung A, Toft Lindkvist T, Langeland J, Brøndsted Nielsen S. Cryogenic Ion Fluorescence Spectroscopy: FRET in Rhodamine Homodimers and Heterodimers. Chemistry 2023; 29:e202302166. [PMID: 37565666 DOI: 10.1002/chem.202302166] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2023] [Revised: 08/02/2023] [Accepted: 08/07/2023] [Indexed: 08/12/2023]
Abstract
The internal electronic communication between two or more light-absorbers is fundamental for energy-transport processes, a field of large current interest. Here the intrinsic photophysics of homo- and heterodimers of rhodamine cations were studied where just two methylene units bridge the dyes. Gas-phase experiments were done on frozen molecular ions at cryogenic temperatures using the newly built LUNA2 mass spectroscopy setup in Aarhus. Both absorption (from fluorescence excitation) and dispersed-fluorescence spectra were measured. In the gas phase, there is no dielectric screening from solvent molecules, and the effect of charges on transition energies is maximum. Indeed, bands are redshifted compared to those of monomer dyes due to the electric field that each dye senses from the other in a dimer. Importantly, also, as two chemically identical dyes in a homodimer do not experience the same field along the long axis, each dye has separate absorption. At low temperatures, it is therefore possible to selectively excite one dye. Fluorescence is dominantly from the dye with the lowest transition energy no matter which dye is photoexcited. Hence this work unequivocally demonstrates Förster Resonance Energy Transfer even in homodimers where one dye acts as donor and the other as acceptor.
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Affiliation(s)
- Christina Kjaer
- Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000, Aarhus C, Denmark
| | - André Vu-Phung
- Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000, Aarhus C, Denmark
| | - Thomas Toft Lindkvist
- Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000, Aarhus C, Denmark
| | - Jeppe Langeland
- Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000, Aarhus C, Denmark
| | - Steen Brøndsted Nielsen
- Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000, Aarhus C, Denmark
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7
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Wu R, Metternich JB, Kamenik AS, Tiwari P, Harrison JA, Kessen D, Akay H, Benzenberg LR, Chan TWD, Riniker S, Zenobi R. Determining the gas-phase structures of α-helical peptides from shape, microsolvation, and intramolecular distance data. Nat Commun 2023; 14:2913. [PMID: 37217470 PMCID: PMC10203302 DOI: 10.1038/s41467-023-38463-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2022] [Accepted: 04/19/2023] [Indexed: 05/24/2023] Open
Abstract
Mass spectrometry is a powerful technique for the structural and functional characterization of biomolecules. However, it remains challenging to accurately gauge the gas-phase structure of biomolecular ions and assess to what extent native-like structures are maintained. Here we propose a synergistic approach which utilizes Förster resonance energy transfer and two types of ion mobility spectrometry (i.e., traveling wave and differential) to provide multiple constraints (i.e., shape and intramolecular distance) for structure-refinement of gas-phase ions. We add microsolvation calculations to assess the interaction sites and energies between the biomolecular ions and gaseous additives. This combined strategy is employed to distinguish conformers and understand the gas-phase structures of two isomeric α-helical peptides that might differ in helicity. Our work allows more stringent structural characterization of biologically relevant molecules (e.g., peptide drugs) and large biomolecular ions than using only a single structural methodology in the gas phase.
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Affiliation(s)
- Ri Wu
- Laboratorium für Organische Chemie, D-CHAB, ETH Zürich, 8093, Zurich, Switzerland
| | - Jonas B Metternich
- Laboratorium für Organische Chemie, D-CHAB, ETH Zürich, 8093, Zurich, Switzerland
| | - Anna S Kamenik
- Laboratorium für Physikalische Chemie, D-CHAB, ETH Zürich, 8093, Zurich, Switzerland
| | - Prince Tiwari
- Laboratorium für Organische Chemie, D-CHAB, ETH Zürich, 8093, Zurich, Switzerland
- Laboratory of Atmospheric Chemistry, Paul Scherrer Institute, Forschungsstrasse 111, 5232, Villigen PSI, Switzerland
| | - Julian A Harrison
- Laboratorium für Organische Chemie, D-CHAB, ETH Zürich, 8093, Zurich, Switzerland
| | - Dennis Kessen
- Laboratorium für Organische Chemie, D-CHAB, ETH Zürich, 8093, Zurich, Switzerland
- University of Münster, MEET Battery Research Center, Corrensstrasse 46, 48149, Münster, Germany
| | - Hasan Akay
- Laboratorium für Organische Chemie, D-CHAB, ETH Zürich, 8093, Zurich, Switzerland
| | - Lukas R Benzenberg
- Laboratorium für Organische Chemie, D-CHAB, ETH Zürich, 8093, Zurich, Switzerland
| | - T-W Dominic Chan
- Department of Chemistry, The Chinese University of Hong Kong, Hong Kong SAR, People's Republic of China
| | - Sereina Riniker
- Laboratorium für Physikalische Chemie, D-CHAB, ETH Zürich, 8093, Zurich, Switzerland.
| | - Renato Zenobi
- Laboratorium für Organische Chemie, D-CHAB, ETH Zürich, 8093, Zurich, Switzerland.
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8
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Wu R, Benzenberg LR, Svingou D, Zenobi R. The Structure of Cyclic Neuropeptide Somatostatin and Octapeptide Octreotide in the Presence of Copper Ions: Insights from Transition Metal Ion FRET and Native Ion Mobility-Mass Spectrometry. J Am Chem Soc 2023; 145:10542-10547. [PMID: 37146120 DOI: 10.1021/jacs.2c13613] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
The conformation and function of somatostatin (SST), a cyclic neuropeptide, was recently found to be altered in the presence of Cu(II) ions, which leads to self-aggregation and loss of biological function as a neurotransmitter. However, the impact of Cu(II) ions on the structure and function of SST is not fully understood. In this work, transition metal ion Förster resonance energy transfer (tmFRET) and native ion mobility-mass spectrometry (IM-MS) were utilized to study the structures of well-defined gas-phase ions of SST and of a smaller analogue, octreotide (OCT). The tmFRET results suggest two binding sites of Cu(II) ions in both native-like SST and OCT ions, either in close proximity to the disulfide bond or complexed by two aromatic residues, consistent with results obtained from collision-induced dissociation (CID). The former binding site was reported to initiate aggregation of SST, while the latter binding site could directly affect the essential motif for receptor binding and therefore impair the biological function of SST and OCT when bound to SST receptors. Our results demonstrate that tmFRET is capable of locating transition metal ion binding sites in neuropeptides. Furthermore, multiple distance constraints (tmFRET) and global shape (IM-MS) provide additional structural insights of SST and OCT ions upon metal binding, which is related to the self-aggregation mechanisms and overall biological functions.
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Affiliation(s)
- Ri Wu
- Laboratorium für Organische Chemie, Department of Chemistry and Applied Biosciences, ETH Zürich, CH-8093 Zürich, Switzerland
| | - Lukas R Benzenberg
- Laboratorium für Organische Chemie, Department of Chemistry and Applied Biosciences, ETH Zürich, CH-8093 Zürich, Switzerland
| | - Despoina Svingou
- Laboratorium für Organische Chemie, Department of Chemistry and Applied Biosciences, ETH Zürich, CH-8093 Zürich, Switzerland
| | - Renato Zenobi
- Laboratorium für Organische Chemie, Department of Chemistry and Applied Biosciences, ETH Zürich, CH-8093 Zürich, Switzerland
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9
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Ashworth EK, Langeland J, Stockett MH, Lindkvist TT, Kjær C, Bull JN, Nielsen SB. Cryogenic Fluorescence Spectroscopy of Ionic Fluorones in Gaseous and Condensed Phases: New Light on Their Intrinsic Photophysics. J Phys Chem A 2022; 126:9553-9563. [PMID: 36529970 DOI: 10.1021/acs.jpca.2c07231] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Fluorescence spectroscopy of gas-phase ions generated through electrospray ionization is an emerging technique able to probe intrinsic molecular photophysics directly without perturbations from solvent interactions. While there is ample scope for the ongoing development of gas-phase fluorescence techniques, the recent expansion into low-temperature operating conditions accesses a wealth of data on intrinsic fluorophore photophysics, offering enhanced spectral resolution compared with room-temperature measurements, without matrix effects hindering the excited-state dynamics. This perspective reviews current progress on understanding the photophysics of anionic fluorone dyes, which exhibit an unusually large Stokes shift in the gas phase, and discusses how comparison of gas- and condensed-phase fluorescence spectra can fingerprint structural dynamics. The capacity for temperature-dependent measurements of both fluorescence emission and excitation spectra helps establish the foundation for the use of fluorone dyes as fluorescent tags in macromolecular structure determination. We suggest ideas for technique development.
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Affiliation(s)
- Eleanor K Ashworth
- School of Chemistry, University of East Anglia, NorwichNR4 7TJ, United Kingdom
| | - Jeppe Langeland
- Department of Physics and Astronomy, Aarhus University, Aarhus8000, Denmark
| | - Mark H Stockett
- Department of Physics, Stockholm University, SE-10691Stockholm, Sweden
| | | | - Christina Kjær
- Department of Physics and Astronomy, Aarhus University, Aarhus8000, Denmark
| | - James N Bull
- School of Chemistry, University of East Anglia, NorwichNR4 7TJ, United Kingdom
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10
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Dinesan H, Kumar SS. Laser-Induced Fluorescence (LIF) Spectroscopy of Trapped Molecular Ions in the Gas Phase. APPLIED SPECTROSCOPY 2022; 76:1393-1411. [PMID: 36263923 DOI: 10.1177/00037028221120830] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
This review focuses on the laser-induced fluorescence (LIF) spectroscopy of trapped gas-phase molecular ions, a developing field of research. Following a brief description of the theory and experimental approaches employed in general for fluorescence spectroscopy, the review summarizes the current state-of-the-art intrinsic fluorescence measurement techniques employed for gas-phase ions. Whereas the LIF spectroscopy of condensed matter systems is a well-developed area of research, the instrumentation used for such studies is not directly applicable to gas-phase ions. However, some measurement schemes employed in condensed-phase experiments could be highly beneficial for gas-phase investigations. We have included a brief discussion on some of these techniques as well. Quadrupole ion traps are commonly used for spatial confinement of ions in the ion-trap-based LIF. One of the main challenges involved in such experiments is the poor signal-to-noise ratio (SNR) arising due to weak gas-phase fluorescence emission, high background noise, and small solid angle for the fluorescence collection optics. The experimental approaches based on the integrated high-finesse optical cavities employed for the condensed-phase measurements provide a better (typically an order of magnitude more) SNR in the detected fluorescence than the single-pass detection schemes. Another key to improving the SNR is to exploit the maximum solid angle of light collection by choosing high numerical aperture (NA) collection optics. A combination of these two approaches integrated with ion traps could transmogrify this field, allowing one to study even weak fluorescence emission from gas-phase molecular ions. The review concludes by discussing the scope of the advances in the LIF instrumentation for detailed spectral characterization of fluorophores of weak gas-phase fluorescence emission, considering fluorescein as one example.
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Affiliation(s)
- Hemanth Dinesan
- Department of Physics and Center for Atomic, Molecular, and Optical Sciences and Technologies (CAMOST), 443874Indian Institute of Science Education and Research (IISER) Tirupati, Tirupati, India
| | - S Sunil Kumar
- Department of Physics and Center for Atomic, Molecular, and Optical Sciences and Technologies (CAMOST), 443874Indian Institute of Science Education and Research (IISER) Tirupati, Tirupati, India
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11
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Wu R, Metternich JB, Tiwari P, Benzenberg LR, Harrison JA, Liu Q, Zenobi R. Structural Studies of a Stapled Peptide with Native Ion Mobility-Mass Spectrometry and Transition Metal Ion Förster Resonance Energy Transfer in the Gas Phase. J Am Chem Soc 2022; 144:14441-14445. [PMID: 35943275 DOI: 10.1021/jacs.2c02776] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Native mass spectrometry has emerged as an important tool for gas-phase structural biology. However, the conformations that a biomolecular ion adopts in the gas phase can differ from those found in solution. Herein, we report a synergistic, native ion mobility-mass spectrometry (IM-MS) and transition metal ion Förster resonance energy transfer (tmFRET)-based approach to probe the gas-phase ion structures of a nonstapled peptide (nsp; Ac-CAARAAHAAAHARARA-NH2) and a stapled peptide (sp; Ac-CXARAXHAAAHARARA-NH2). The stapled peptide contains a single hydrocarbon chain connecting the peptide backbone in the i and i + 4 positions via a Grubbs ring-closure metathesis. Fluorescence lifetime measurements indicated that the Cu-bound complexes of carboxyrhodamine 6g (crh6g)-labeled stapled peptide (sp-crh6g) had a shorter donor-acceptor distance (rDA) than the labeled nonstapled peptide (nsp-crh6g). Experimental collision cross-section (CCS) values were then determined by native IM-MS, which could separate the conformations of Cu-bound complexes of nsp-crh6g and sp-crh6g. Finally, the experimental CCS (i.e., shape) and rDA (i.e., distance) values were used as constraints for computational studies, which unambiguously revealed how a staple reduces the elongation of the peptide ions in the gas phase. This study demonstrates the superiority of combining native IM-MS, tmFRET, and computational studies to investigate the structure of biomolecular ions.
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Affiliation(s)
- Ri Wu
- Laboratorium für Organische Chemie, Department of Chemistry and Applied Biosciences, ETH Zürich, CH-8093 Zürich, Switzerland
| | - Jonas B Metternich
- Laboratorium für Organische Chemie, Department of Chemistry and Applied Biosciences, ETH Zürich, CH-8093 Zürich, Switzerland
| | - Prince Tiwari
- Laboratorium für Organische Chemie, Department of Chemistry and Applied Biosciences, ETH Zürich, CH-8093 Zürich, Switzerland
| | - Lukas R Benzenberg
- Laboratorium für Organische Chemie, Department of Chemistry and Applied Biosciences, ETH Zürich, CH-8093 Zürich, Switzerland
| | - Julian A Harrison
- Laboratorium für Organische Chemie, Department of Chemistry and Applied Biosciences, ETH Zürich, CH-8093 Zürich, Switzerland
| | - Qinlei Liu
- Laboratorium für Organische Chemie, Department of Chemistry and Applied Biosciences, ETH Zürich, CH-8093 Zürich, Switzerland
| | - Renato Zenobi
- Laboratorium für Organische Chemie, Department of Chemistry and Applied Biosciences, ETH Zürich, CH-8093 Zürich, Switzerland
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12
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Wu R, Metternich JB, Tiwari P, Zenobi R. Adapting a Fourier Transform Ion Cyclotron Resonance Mass Spectrometer for Gas-Phase Fluorescence Spectroscopy Measurement of Trapped Biomolecular Ions. Anal Chem 2021; 93:15626-15632. [PMID: 34784193 DOI: 10.1021/acs.analchem.1c02858] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Gas-phase fluorescence spectroscopy is still in its infancy, which demands further instrumental developments. In this study, a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS), equipped with a lab-developed data acquisition system, was coupled to a tunable femtosecond laser and a state-of-the-art optical system for fluorescence studies of mass-selected ions. For excitation, a laser beam was focused (beam size < 1.0 mm) into the cylindrical ICR cell. A wire mesh replaced the back trapping plate, allowing ∼10% of the fluorescence emitted from trapped ions to be collected by a lens installed beside the wire mesh. The collected fluorescence light was then transmitted outside of the mass spectrometer via fiber optics. A novel accumulation during detection (ADD) scheme was developed to increase the duty cycle of gas-phase fluorescence spectroscopy experiments. With ADD, >90% duty cycle for mass spectrometry and fluorescence experiments could be achieved. This instrument was able to perform fluorescence experiments on various ions, from simple rhodamine dyes to large biomolecules (i.e., peptides and proteins) labeled with dyes of various optical properties. A fluorescence lifetime measurement of trapped rhodamine 6G cations was also performed, yielding a value of 5.97 ± 0.23 ns. This setup has a broad mass range and decent fluorescence spectroscopy performance (i.e., the emission spectrum of rhodamine 6G can be acquired with good S/N in a minute). Finally, this setup also allows more challenging gas-phase fluorescence spectroscopy experiments, for example, of low quantum yield fluorophores and large biomolecules in their native state that appear at high m/z, which may not be doable with quadrupole ion traps (QIT).
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Affiliation(s)
- Ri Wu
- Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir-Prelog-Weg 3, 8093 Zürich, Switzerland
| | - Jonas B Metternich
- Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir-Prelog-Weg 3, 8093 Zürich, Switzerland
| | - Prince Tiwari
- Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir-Prelog-Weg 3, 8093 Zürich, Switzerland
| | - Renato Zenobi
- Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir-Prelog-Weg 3, 8093 Zürich, Switzerland
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13
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Vogt E, Langeland J, Kjær C, Lindkvist TT, Kjaergaard HG, Nielsen SB. Effect of Freezing out Vibrational Modes on Gas-Phase Fluorescence Spectra of Small Ionic Dyes. J Phys Chem Lett 2021; 12:11346-11352. [PMID: 34780698 DOI: 10.1021/acs.jpclett.1c03259] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
While action spectroscopy of cold molecular ions is a well-established technique to provide vibrationally resolved absorption features, fluorescence experiments are still challenging. Here we report the fluorescence spectra of pyronin-Y and resorufin ions at 100 K using a newly constructed setup. Spectra narrow upon cooling, and the emission maxima blueshift. Temperature effects are attributed to the population of vibrational excited levels in S1, and that frequencies are lower in S1 than in S0. This picture is supported by calculated spectra based on a Franck-Condon model that not only predicts the observed change in maximum, but also assigns Franck-Condon active vibrations. In-plane vibrational modes that preserve the mirror plane present in both S0 and S1 of resorufin and pyronin Y account for most of the observed vibrational bands. Finally, at low temperatures, it is important to pick an excitation wavelength as far to the red as possible to not reheat the ions.
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Affiliation(s)
- Emil Vogt
- Department of Chemistry, University of Copenhagen, 2100 Copenhagen Ø, Denmark
| | - Jeppe Langeland
- Department of Physics and Astronomy, Aarhus University, 8000 Aarhus, Denmark
| | - Christina Kjær
- Department of Physics and Astronomy, Aarhus University, 8000 Aarhus, Denmark
| | | | - Henrik G Kjaergaard
- Department of Chemistry, University of Copenhagen, 2100 Copenhagen Ø, Denmark
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14
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Tiwari P, Wu R, Metternich JB, Zenobi R. Transition Metal Ion FRET in the Gas Phase: A 10-40 Å Range Molecular Ruler for Mass-Selected Biomolecular Ions. J Am Chem Soc 2021; 143:11291-11295. [PMID: 34291949 DOI: 10.1021/jacs.1c01915] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Structural studies of mass-selected biomolecules in the gas phase can reveal their intrinsic properties and provide useful benchmarks for biomolecular modeling. Here, we report the first evidence of transition metal ion FRET (tmFRET) in the gas phase and its application to measure short (10-40 Å) biomolecular backbone distances. The measured FRET efficiencies in rhodamine dye (donor) labeled helical peptides complexed with Cu2+ ions (acceptor) decreased with increasing donor - acceptor distances, confirming the occurrence of tmFRET. The distances estimated for similar peptide sequences from the FRET efficiencies were consistently longer in the gas phase compared to those reported in solution, indicating an expanded structure and a possible loss of helicity.
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Affiliation(s)
- Prince Tiwari
- Department of Chemistry and Applied Biosciences, ETH Zürich Vladimir-Prelog-Weg 3, 8093 Zürich, Switzerland
| | - Ri Wu
- Department of Chemistry and Applied Biosciences, ETH Zürich Vladimir-Prelog-Weg 3, 8093 Zürich, Switzerland
| | - Jonas B Metternich
- Department of Chemistry and Applied Biosciences, ETH Zürich Vladimir-Prelog-Weg 3, 8093 Zürich, Switzerland
| | - Renato Zenobi
- Department of Chemistry and Applied Biosciences, ETH Zürich Vladimir-Prelog-Weg 3, 8093 Zürich, Switzerland
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15
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Tiwari P, Czar MF, Zenobi R. Fluorescence-Based Detection of the Desolvation Process of Protein Ions Generated in an Aqueous Electrospray Plume. Anal Chem 2021; 93:3635-3642. [PMID: 33557519 DOI: 10.1021/acs.analchem.0c05396] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A new experimental setup to study laser-induced fluorescence from analytes at different locations in an electrospray plume has been developed. The high fluorescence collection efficiency (∼2%) of the setup, along with a sensitive charge coupled device (CCD) detector, enabled the study of low ion concentrations (down to ∼fM) in the plume. The use of small electrospray tip inner diameters (<1 μm) facilitated the fast desolvation of gaseous protein ions in an aqueous electrospray plume. Fluorescence spectra were acquired from specific locations along the plume axis in different aqueous electrospray plumes with three different analytes: a rhodamine dye and two proteins (ubiquitin and apomyoglobin) labeled with rhodamine dyes. To confirm the presence of gaseous ions, pure gas-phase fluorescence spectra were acquired in the vacuum of a modified ion trap mass spectrometer. These spectra were used to fit to confirm the presence of gaseous species in the corresponding spectra obtained from the electrospray plume. This study shows that with small inner diameter spray capillaries, gaseous protein ions generated at atmospheric pressure in an electrospray plume can be detected with fluorescence-based techniques. Fluorescence measurements can be used to study their structure in the electrospray plume, and the dynamics as they transition from solution to the gas phase and in the early stages after desolvation from charged droplets. Other techniques can also be applied to further study gaseous biomolecular structures under ambient conditions immediately after desolvation.
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Affiliation(s)
- Prince Tiwari
- Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir-Prelog-Weg 3, 8093Zürich, Switzerland
| | - Martin F Czar
- Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir-Prelog-Weg 3, 8093Zürich, Switzerland
| | - Renato Zenobi
- Department of Chemistry and Applied Biosciences, ETH Zürich, Vladimir-Prelog-Weg 3, 8093Zürich, Switzerland
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