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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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Ji X, Wang N, Wang J, Wang T, Huang X, Hao H. Non-destructive real-time monitoring and investigation of the self-assembly process using fluorescent probes. Chem Sci 2024; 15:3800-3830. [PMID: 38487216 PMCID: PMC10935763 DOI: 10.1039/d3sc06527h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2023] [Accepted: 01/22/2024] [Indexed: 03/17/2024] Open
Abstract
Self-assembly has been considered as a strategy to construct superstructures with specific functions, which has been widely used in many different fields, such as bionics, catalysis, and pharmacology. A detailed and in-depth analysis of the self-assembly mechanism is beneficial for directionally and accurately regulating the self-assembly process of substances. Fluorescent probes exhibit unique advantages of sensitivity, non-destructiveness, and real-time self-assembly tracking, compared with traditional methods. In this work, the design principle of fluorescent probes with different functions and their applications for the detection of thermodynamic and kinetic parameters during the self-assembly process were systematically reviewed. Their efficiency, limitations and advantages are also discussed. Furthermore, the promising perspectives of fluorescent probes for investigating the self-assembly process are also discussed and suggested.
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Affiliation(s)
- Xiongtao Ji
- National Engineering Research Center of Industrial Crystallization Technology, School of Chemical Engineering and Technology, Tianjin University Tianjin 300072 China
| | - Na Wang
- National Engineering Research Center of Industrial Crystallization Technology, School of Chemical Engineering and Technology, Tianjin University Tianjin 300072 China
- Collaborative Innovation Center of Chemical Science and Engineering (Tianjin) Tianjin 300072 China
- State Key Laboratory of Chemical Engineering, School of Chemical Engineering and Technology, Tianjin University Tianjin 300072 China +86-22-27374971 +86-22-27405754
| | - Jingkang Wang
- National Engineering Research Center of Industrial Crystallization Technology, School of Chemical Engineering and Technology, Tianjin University Tianjin 300072 China
- Collaborative Innovation Center of Chemical Science and Engineering (Tianjin) Tianjin 300072 China
- State Key Laboratory of Chemical Engineering, School of Chemical Engineering and Technology, Tianjin University Tianjin 300072 China +86-22-27374971 +86-22-27405754
| | - Ting Wang
- National Engineering Research Center of Industrial Crystallization Technology, School of Chemical Engineering and Technology, Tianjin University Tianjin 300072 China
- Collaborative Innovation Center of Chemical Science and Engineering (Tianjin) Tianjin 300072 China
- State Key Laboratory of Chemical Engineering, School of Chemical Engineering and Technology, Tianjin University Tianjin 300072 China +86-22-27374971 +86-22-27405754
| | - Xin Huang
- National Engineering Research Center of Industrial Crystallization Technology, School of Chemical Engineering and Technology, Tianjin University Tianjin 300072 China
- Collaborative Innovation Center of Chemical Science and Engineering (Tianjin) Tianjin 300072 China
- State Key Laboratory of Chemical Engineering, School of Chemical Engineering and Technology, Tianjin University Tianjin 300072 China +86-22-27374971 +86-22-27405754
| | - Hongxun Hao
- National Engineering Research Center of Industrial Crystallization Technology, School of Chemical Engineering and Technology, Tianjin University Tianjin 300072 China
- Collaborative Innovation Center of Chemical Science and Engineering (Tianjin) Tianjin 300072 China
- State Key Laboratory of Chemical Engineering, School of Chemical Engineering and Technology, Tianjin University Tianjin 300072 China +86-22-27374971 +86-22-27405754
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4
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Kyrychenko A, Ladokhin AS. Fluorescent Probes and Quenchers in Studies of Protein Folding and Protein-Lipid Interactions. CHEM REC 2024; 24:e202300232. [PMID: 37695081 PMCID: PMC11113672 DOI: 10.1002/tcr.202300232] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2023] [Revised: 08/20/2023] [Indexed: 09/12/2023]
Abstract
Fluorescence spectroscopy provides numerous methodological tools for structural and functional studies of biological macromolecules and their complexes. All fluorescence-based approaches require either existence of an intrinsic probe or an introduction of an extrinsic one. Moreover, studies of complex systems often require an additional introduction of a specific quencher molecule acting in combination with a fluorophore to provide structural or thermodynamic information. Here, we review the fundamentals and summarize the latest progress in applications of different classes of fluorescent probes and their specific quenchers, aimed at studies of protein folding and protein-membrane interactions. Specifically, we discuss various environment-sensitive dyes, FRET probes, probes for short-distance measurements, and several probe-quencher pairs for studies of membrane penetration of proteins and peptides. The goals of this review are: (a) to familiarize the readership with the general concept that complex biological systems often require both a probe and a quencher to decipher mechanistic details of functioning and (b) to provide example of the immediate applications of the described methods.
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Affiliation(s)
- Alexander Kyrychenko
- Institute of Chemistry and School of Chemistry, V. N. Karazin Kharkiv National University, 4 Svobody sq., Kharkiv, 61022, Ukraine
| | - Alexey S Ladokhin
- Department of Biochemistry and Molecular Biology, The University of Kansas Medical Center, 3901 Rainbow Boulevard, Kansas City, KS, 66160, United States
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5
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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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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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Mubeen M, Ain NU, Khalid MA, Mukhtar M, Naz B, Siddique Z, Ul-Hamid A, Iqbal A. Enhancing the FRET by tuning the bandgap of acceptor ternary ZnCdS quantum dots. RSC Adv 2023; 13:19096-19105. [PMID: 37362335 PMCID: PMC10288831 DOI: 10.1039/d3ra03233g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2023] [Accepted: 06/16/2023] [Indexed: 06/28/2023] Open
Abstract
In this article, we report the band gap tuning of ternary ZnCdS quantum dots (QDs) by varying the concentration of the capping ligand, mercaptoacetic acid (MAA). The functionalization of QDs leads to the control of their size and band gap due to the quantum confinement effect, causing blue shift in the absorption and photoluminescence (PL) spectra with a gradual change in the concentration of the capping ligand from 0.5 to 2.5 M. Ensulizole (2-phenylbenzimidazole-5-sulfonic acid) is an important organic ultraviolet (UV) filter that is frequently used in sunscreen cosmetics. An effective overlapping of the PL spectrum of ensulizole and the absorption spectrum of QDs with 2.5 M MAA is achieved. A formidable decrease in the PL intensity and the PL lifetime of ensulizole promotes an efficient Förster resonance energy transfer (FRET) from sunscreen ensulizole to the QDs. The magnitude of the FRET efficiency (E) is ∼70%. This very high value of E is the signature of the existence of a very fast energy transfer process from ensulizole to the MAA functionalized ZnCdS QDs. The dyad system consisting of ZnCdS QDs and ensulizole sunscreen can serve as a prototype model to develop a better understanding of the photochemistry of ensulizole and consequently the formulation of more efficient sunscreen cosmetics.
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Affiliation(s)
- Muhammad Mubeen
- Department of Chemistry, Quaid-I-Azam University Islamabad-45320 Pakistan
| | - Noor Ul Ain
- Department of Chemistry, Quaid-I-Azam University Islamabad-45320 Pakistan
| | | | - Maria Mukhtar
- Department of Chemistry, Quaid-I-Azam University Islamabad-45320 Pakistan
| | - Bushra Naz
- Department of Chemistry, Quaid-I-Azam University Islamabad-45320 Pakistan
| | - Zumaira Siddique
- Department of Chemistry, Quaid-I-Azam University Islamabad-45320 Pakistan
| | - Anwar Ul-Hamid
- Core Research Facilities, King Fahd University of Petroleum & Minerals Dhahran 31261 Saudi Arabia
| | - Azhar Iqbal
- Department of Chemistry, Quaid-I-Azam University Islamabad-45320 Pakistan
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8
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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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9
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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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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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