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Price BD, Sojka A, Maity S, Chavez IM, Starck M, Wilson MZ, Han S, Sherwin MS. Field-domain rapid-scan EPR at 240GHz for studies of protein functional dynamics at room temperature. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2024; 366:107744. [PMID: 39096714 DOI: 10.1016/j.jmr.2024.107744] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/12/2024] [Revised: 07/22/2024] [Accepted: 07/24/2024] [Indexed: 08/05/2024]
Abstract
We present field-domain rapid-scan (RS) electron paramagnetic resonance (EPR) at 8.6T and 240GHz. To enable this technique, we upgraded a home-built EPR spectrometer with an FPGA-enabled digitizer and real-time processing software. The software leverages the Hilbert transform to recover the in-phase (I) and quadrature (Q) channels, and therefore the raw absorptive and dispersive signals, χ' and χ'', from their combined magnitude (I2+Q2). Averaging a magnitude is simpler than real-time coherent averaging and has the added benefit of permitting long-timescale signal averaging (up to at least 2.5×106 scans) because it eliminates the effects of source-receiver phase drift. Our rapid-scan (RS) EPR provides a signal-to-noise ratio that is approximately twice that of continuous wave (CW) EPR under the same experimental conditions, after scaling by the square root of acquisition time. We apply our RS EPR as an extension of the recently reported time-resolved Gd-Gd EPR (TiGGER) [Maity et al., 2023], which is able to monitor inter-residue distance changes during the photocycle of a photoresponsive protein through changes in the Gd-Gd dipolar couplings. RS, opposed to CW, returns field-swept spectra as a function of time with 10ms time resolution, and thus, adds a second dimension to the static field transients recorded by TiGGER. We were able to use RS TiGGER to track time-dependent and temperature-dependent kinetics of AsLOV2, a light-activated phototropin domain found in oats. The results presented here combine the benefits of RS EPR with the improved spectral resolution and sensitivity of Gd chelates at high magnetic fields. In the future, field-domain RS EPR at high magnetic fields may enable studies of other real-time kinetic processes with time resolutions that are otherwise difficult to access in the solution state.
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Affiliation(s)
- Brad D Price
- Department of Physics, University of California, Santa Barbara, 93106, CA, USA; Institute for Terahertz Science and Technology, University of California, Santa Barbara, 93106, CA, USA.
| | - Antonín Sojka
- Department of Physics, University of California, Santa Barbara, 93106, CA, USA; Institute for Terahertz Science and Technology, University of California, Santa Barbara, 93106, CA, USA
| | - Shiny Maity
- Department of Chemistry, University of California, Santa Barbara, 93106, CA, USA; Department of Chemistry, Northwestern University, 633 Clark Street, Evanston, 60208, IL, USA
| | - I Marcelo Chavez
- Department of Chemistry, University of California, Santa Barbara, 93106, CA, USA
| | - Matthieu Starck
- Department of Chemistry, Durham University, Durham, DH13LE, UK
| | - Maxwell Z Wilson
- Department Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara, 93106, CA, USA
| | - Songi Han
- Department of Chemistry, University of California, Santa Barbara, 93106, CA, USA; Department of Chemistry, Northwestern University, 633 Clark Street, Evanston, 60208, IL, USA
| | - Mark S Sherwin
- Department of Physics, University of California, Santa Barbara, 93106, CA, USA; Institute for Terahertz Science and Technology, University of California, Santa Barbara, 93106, CA, USA.
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2
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Jaiswal M, Tran TT, Guo J, Zhou M, Kundu S, Guo Z, Fanucci GE. Spin-labeling Insights into How Chemical Fixation Impacts Glycan Organization on Cells. APPLIED MAGNETIC RESONANCE 2024; 55:317-333. [PMID: 38469359 PMCID: PMC10927023 DOI: 10.1007/s00723-023-01624-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2023] [Revised: 09/21/2023] [Accepted: 09/22/2023] [Indexed: 03/13/2024]
Abstract
As new methods to interrogate glycan organization on cells develop, it is important to have a molecular level understanding of how chemical fixation can impact results and interpretations. Site-directed spin labeling technologies are well suited to study how the spin label mobility is impacted by local environmental conditions, such as those imposed by cross-linking effects of paraformaldehyde cell fixation methods. Here, we utilize three different azide-containing sugars for metabolic glycan engineering with HeLa cells to incorporate azido glycans that are modified with a DBCO-based nitroxide moiety via click reaction. Continuous wave X-band electron paramagnetic resonance spectroscopy is employed to characterize how the chronological sequence of chemical fixation and spin labeling impacts the local mobility and accessibility of the nitroxide-labeled glycans in the glycocalyx of HeLa cells. Results demonstrate that chemical fixation with paraformaldehyde can alter local glycan mobility and care should be taken in the analysis of data in any study where chemical fixation and cellular labeling occur.
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Affiliation(s)
- Mohit Jaiswal
- Department of Chemistry, University of Florida, 214 Leigh Hall, Gainesville, FL 32611, USA
| | - Trang T Tran
- Department of Chemistry, University of Florida, 214 Leigh Hall, Gainesville, FL 32611, USA
| | - Jiatong Guo
- Department of Chemistry, University of Florida, 214 Leigh Hall, Gainesville, FL 32611, USA
| | - Mingwei Zhou
- Department of Chemistry, University of Florida, 214 Leigh Hall, Gainesville, FL 32611, USA
| | - Sayan Kundu
- Department of Chemistry, University of Florida, 214 Leigh Hall, Gainesville, FL 32611, USA
| | - Zhongwu Guo
- Department of Chemistry, University of Florida, 214 Leigh Hall, Gainesville, FL 32611, USA
| | - Gail E Fanucci
- Department of Chemistry, University of Florida, 214 Leigh Hall, Gainesville, FL 32611, USA
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3
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Jaiswal M, Tran TT, Guo J, Zhou M, Kunda S, Guo Z, Fanucci G. Spin-labeling Insights into How Chemical Fixation Impacts Glycan Organization on Cells. RESEARCH SQUARE 2023:rs.3.rs-3039983. [PMID: 37398188 PMCID: PMC10312935 DOI: 10.21203/rs.3.rs-3039983/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/04/2023]
Abstract
As new methods to interrogate glycan organization on cells develop, it is important to have a molecular level understanding of how chemical fixation can impact results and interpretations. Site-directed spin labeling technologies are well suited to study how the spin label mobility is impacted by local environmental conditions, such as those imposed by cross-linking effects of paraformaldehyde cell fixation methods. Here, we utilize three different azide-containing sugars for metabolic glycan engineering with HeLa cells to incorporate azido glycans that are modified with a DBCO-based nitroxide moiety via click reaction. Continuous wave X-band electron paramagnetic resonance spectroscopy is employed to characterize how the chronological sequence of chemical fixation and spin labeling impacts the local mobility and accessibility of the nitroxide-labeled glycans in the glycocalyx of HeLa cells. Results demonstrate that chemical fixation with paraformaldehyde can alter local glycan mobility and care should be taken in the analysis of data in any study where chemical fixation and cellular labeling occur.
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4
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Ho PS, Kao TY, Li CC, Lan YJ, Lai YC, Chiang YW. Nanodisc Lipids Exhibit Singular Behaviors Implying Critical Phenomena. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2022; 38:15372-15383. [PMID: 36454955 DOI: 10.1021/acs.langmuir.2c02596] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
Abstract
Nanodiscs are broadly used for characterization of membrane proteins as they are generally assumed to provide a near-native environment. In fact, it is an open question whether the physical properties of lipids in nanodiscs and membrane vesicles of the same lipid composition are identical. Here, we investigate the properties of lipids (1,2-dipalmitoyl-sn-glycero-3-phosphocholine, 1,2-dilauroyl-sn-glycero-3-phosphocholine, and their mixtures) in two different sample types, nanodiscs and multilamellar vesicles, by means of spin-label electron spin resonance techniques. Our results provide a quantitative description of lipid dynamics and ordering, elucidating the molecular details of how lipids in the two sample types behave differently in response to temperature and lipid composition. We show that the properties of lipids are altered in nanodiscs such that the dissimilarity of the fluid and gel lipid phases is reduced, and the first-order phase transitions are largely abolished in nanodiscs. We unveil that the ensemble of lipids in the middle of a nanodisc bilayer, as probed by the end-chain spin-label 16-PC, is promoted to a state close to a miscibility critical point, thereby rendering the phase transitions continuous. Critical phenomena have recently been proposed to explain features of the heterogeneity in native cell membranes. Our results lay the groundwork for how to establish a near-native environment in nanodiscs with simple organization of lipid components.
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Affiliation(s)
- Pei-Shan Ho
- Department of Chemistry, National Tsing Hua University, Hsinchu 300-044, Taiwan
| | - Te-Yu Kao
- Department of Chemistry, National Tsing Hua University, Hsinchu 300-044, Taiwan
| | - Chieh-Chin Li
- Department of Chemistry, National Tsing Hua University, Hsinchu 300-044, Taiwan
| | - Yu-Jing Lan
- Department of Chemistry, National Tsing Hua University, Hsinchu 300-044, Taiwan
| | - Yei-Chen Lai
- Department of Chemistry, National Chung Hsing University, Taichung 402-002, Taiwan
| | - Yun-Wei Chiang
- Department of Chemistry, National Tsing Hua University, Hsinchu 300-044, Taiwan
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5
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Rabe P, Walla CC, Goodyear NK, Welsh J, Southwart R, Clifton I, Linyard JDS, Tumber A, Claridge TDW, Myers WK, Schofield CJ. Spectroscopic studies reveal details of substrate-induced conformational changes distant from the active site in isopenicillin N synthase. J Biol Chem 2022; 298:102249. [PMID: 35835215 PMCID: PMC9403350 DOI: 10.1016/j.jbc.2022.102249] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2022] [Revised: 07/06/2022] [Accepted: 07/07/2022] [Indexed: 11/06/2022] Open
Abstract
Isopenicillin N synthase (IPNS) catalyzes formation of the β-lactam and thiazolidine rings of isopenicillin N from its linear tripeptide l-δ-(α-aminoadipoyl)-l-cysteinyl-d-valine (ACV) substrate in an iron- and dioxygen (O2)-dependent four-electron oxidation without precedent in current synthetic chemistry. Recent X-ray free-electron laser studies including time-resolved serial femtosecond crystallography show that binding of O2 to the IPNS–Fe(II)–ACV complex induces unexpected conformational changes in α-helices on the surface of IPNS, in particular in α3 and α10. However, how substrate binding leads to conformational changes away from the active site is unknown. Here, using detailed 19F NMR and electron paramagnetic resonance experiments with labeled IPNS variants, we investigated motions in α3 and α10 induced by binding of ferrous iron, ACV, and the O2 analog nitric oxide, using the less mobile α6 for comparison. 19F NMR studies were carried out on singly and doubly labeled α3, α6, and α10 variants at different temperatures. In addition, double electron–electron resonance electron paramagnetic resonance analysis was carried out on doubly spin-labeled variants. The combined spectroscopic and crystallographic results reveal that substantial conformational changes in regions of IPNS including α3 and α10 are induced by binding of ACV and nitric oxide. Since IPNS is a member of the structural superfamily of 2-oxoglutarate-dependent oxygenases and related enzymes, related conformational changes may be of general importance in nonheme oxygenase catalysis.
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Affiliation(s)
- Patrick Rabe
- Chemistry Research Laboratory, Department of Chemistry and the Ineos Oxford Institute for Antimicrobial Research, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA, United Kingdom.
| | - Carla C Walla
- Chemistry Research Laboratory, Department of Chemistry and the Ineos Oxford Institute for Antimicrobial Research, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA, United Kingdom
| | - Noelle K Goodyear
- Chemistry Research Laboratory, Department of Chemistry and the Ineos Oxford Institute for Antimicrobial Research, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA, United Kingdom
| | - Jordan Welsh
- Chemistry Research Laboratory, Department of Chemistry and the Ineos Oxford Institute for Antimicrobial Research, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA, United Kingdom; Inorganic Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QR, UK
| | - Rebecca Southwart
- Chemistry Research Laboratory, Department of Chemistry and the Ineos Oxford Institute for Antimicrobial Research, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA, United Kingdom
| | - Ian Clifton
- Chemistry Research Laboratory, Department of Chemistry and the Ineos Oxford Institute for Antimicrobial Research, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA, United Kingdom
| | - James D S Linyard
- Chemistry Research Laboratory, Department of Chemistry and the Ineos Oxford Institute for Antimicrobial Research, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA, United Kingdom
| | - Anthony Tumber
- Chemistry Research Laboratory, Department of Chemistry and the Ineos Oxford Institute for Antimicrobial Research, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA, United Kingdom
| | - Tim D W Claridge
- Chemistry Research Laboratory, Department of Chemistry and the Ineos Oxford Institute for Antimicrobial Research, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA, United Kingdom
| | - William K Myers
- Inorganic Chemistry Laboratory, Department of Chemistry, University of Oxford, South Parks Road, Oxford OX1 3QR, UK.
| | - Christopher J Schofield
- Chemistry Research Laboratory, Department of Chemistry and the Ineos Oxford Institute for Antimicrobial Research, University of Oxford, 12 Mansfield Road, Oxford OX1 3TA, United Kingdom.
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6
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Singewald K, Wilkinson JA, Hasanbasri Z, Saxena S. Beyond structure: Deciphering site-specific dynamics in proteins from double histidine-based EPR measurements. Protein Sci 2022; 31:e4359. [PMID: 35762707 DOI: 10.1002/pro.4359] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2022] [Revised: 05/16/2022] [Accepted: 05/20/2022] [Indexed: 12/27/2022]
Abstract
Site-specific dynamics in proteins are at the heart of protein function. While electron paramagnetic resonance (EPR) has potential to measure dynamics in large protein complexes, the reliance on flexible nitroxide labels is limitating especially for the accurate measurement of site-specific β-sheet dynamics. Here, we employed EPR spectroscopy to measure site-specific dynamics across the surface of a protein, GB1. Through the use of the double Histidine (dHis) motif, which enables labeling with a Cu(II) - nitrilotriacetic acid (NTA) complex, dynamics information was obtained for both α-helical and β-sheet sites. Spectral simulations of the resulting CW-EPR report unique site-specific fluctuations across the surface of GB1. Additionally, we performed molecular dynamics (MD) simulations to complement the EPR data. The dynamics observed from MD agree with the EPR results. Furthermore, we observe small changes in gǁ values for different sites, which may be due to small differences in coordination geometry and/or local electrostatics of the site. Taken together, this work expands the utility of Cu(II)NTA-based EPR measurements to probe information beyond distance constraints.
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Affiliation(s)
- Kevin Singewald
- Department of Chemistry, University of Pittsburgh, Pittsburgh, PA, USA
| | - James A Wilkinson
- Department of Chemistry, University of Pittsburgh, Pittsburgh, PA, USA
| | - Zikri Hasanbasri
- Department of Chemistry, University of Pittsburgh, Pittsburgh, PA, USA
| | - Sunil Saxena
- Department of Chemistry, University of Pittsburgh, Pittsburgh, PA, USA
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7
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Pan Y, Li H, Li Q, Lenertz M, Schuster I, Jordahl D, Zhu X, Chen B, Yang Z. Protocol for resolving enzyme orientation and dynamics in advanced porous materials via SDSL-EPR. STAR Protoc 2021; 2:100676. [PMID: 34308381 PMCID: PMC8287244 DOI: 10.1016/j.xpro.2021.100676] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
Enzyme encapsulation in metal-organic frameworks (MOFs)/covalent-organic frameworks (COFs) provides advancement in biocatalysis, yet the structural basis underlying the catalytic performance is challenging to probe. Here, we present an effective protocol to determine the orientation and dynamics of enzymes in MOFs/COFs using site-directed spin labeling and electron paramagnetic resonance spectroscopy. The protocol is demonstrated using lysozyme and can be generalized to other enzymes. For complete information on the generation and use of this protocol, please refer to Pan et al. (2021a). A protocol to resolve protein orientation/dynamics in porous materials is provided Site-directed spin labeling is combined with electron paramagnetic resonance Principles of protein labeling and key data acquisition steps are summarized Spectral simulation details with troubleshooting procedures are detailed
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Affiliation(s)
- Yanxiong Pan
- Department of Chemistry and Biochemistry, North Dakota State University, Fargo, ND 58102, USA
| | - Hui Li
- Department of Plant Sciences, North Dakota State University, Fargo, ND 58102, USA
| | - Qiaobin Li
- Department of Chemistry and Biochemistry, North Dakota State University, Fargo, ND 58102, USA
| | - Mary Lenertz
- Department of Chemistry and Biochemistry, North Dakota State University, Fargo, ND 58102, USA
| | - Isabelle Schuster
- Department of Chemistry and Biochemistry, North Dakota State University, Fargo, ND 58102, USA
| | - Drew Jordahl
- Department of Chemistry and Biochemistry, North Dakota State University, Fargo, ND 58102, USA
| | - Xiao Zhu
- Research Computing, Information Technology at Purdue (ITaP), Purdue University, West Lafayette, IN 47907, USA.,Department of Chemistry, Purdue University, West Lafayette, IN 47907, USA
| | - Bingcan Chen
- Department of Plant Sciences, North Dakota State University, Fargo, ND 58102, USA
| | - Zhongyu Yang
- Department of Chemistry and Biochemistry, North Dakota State University, Fargo, ND 58102, USA
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8
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Stochastic Modelling of 13C NMR Spin Relaxation Experiments in Oligosaccharides. Molecules 2021; 26:molecules26092418. [PMID: 33919330 PMCID: PMC8122627 DOI: 10.3390/molecules26092418] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2021] [Revised: 04/14/2021] [Accepted: 04/16/2021] [Indexed: 12/04/2022] Open
Abstract
A framework for the stochastic description of relaxation processes in flexible macromolecules including dissipative effects has been recently introduced, starting from an atomistic view, describing the joint relaxation of internal coordinates and global degrees of freedom, and depending on parameters recoverable from classic force fields (energetics) and medium modelling at the continuum level (friction tensors). The new approach provides a rational context for the interpretation of magnetic resonance relaxation experiments. In its simplest formulation, the semi-flexible Brownian (SFB) model has been until now shown to reproduce correctly correlation functions and spectral densities related to orientational properties obtained by direct molecular dynamics simulations of peptides. Here, for the first time, we applied directly the SFB approach to the practical evaluation of high-quality 13C nuclear magnetic resonance relaxation parameters, T1 and T2, and the heteronuclear NOE of several oligosaccharides, which were previously interpreted on the basis of refined ad hoc modelling. The calculated NMR relaxation parameters were in agreement with the experimental data, showing that this general approach can be applied to diverse classes of molecular systems, with the minimal usage of adjustable parameters.
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9
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Chandrasekaran S, Schneps CM, Dunleavy R, Lin C, DeOliveira CC, Ganguly A, Crane BR. Tuning flavin environment to detect and control light-induced conformational switching in Drosophila cryptochrome. Commun Biol 2021; 4:249. [PMID: 33637846 PMCID: PMC7910608 DOI: 10.1038/s42003-021-01766-2] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2020] [Accepted: 01/22/2021] [Indexed: 12/12/2022] Open
Abstract
Light-induction of an anionic semiquinone (SQ) flavin radical in Drosophila cryptochrome (dCRY) alters the dCRY conformation to promote binding and degradation of the circadian clock protein Timeless (TIM). Specific peptide ligation with sortase A attaches a nitroxide spin-probe to the dCRY C-terminal tail (CTT) while avoiding deleterious side reactions. Pulse dipolar electron-spin resonance spectroscopy from the CTT nitroxide to the SQ shows that flavin photoreduction shifts the CTT ~1 nm and increases its motion, without causing full displacement from the protein. dCRY engineered to form the neutral SQ serves as a dark-state proxy to reveal that the CTT remains docked when the flavin ring is reduced but uncharged. Substitutions of flavin-proximal His378 promote CTT undocking in the dark or diminish undocking in the light, consistent with molecular dynamics simulations and TIM degradation activity. The His378 variants inform on recognition motifs for dCRY cellular turnover and strategies for developing optogenetic tools. Chandrasekaran et al. engineered the Drosophila circadian clock protein Cryptochrome (dCRY) to form the neutral semiquinone, which serves as a dark-state proxy. They find that the C-terminal tail of dCRY remains docked when the flavin ring is reduced but uncharged. dCRY His378 variants provide insights into the recognition motifs for dCRY turnover and strategies for optogenetic tools.
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Affiliation(s)
| | - Connor M Schneps
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY, USA
| | - Robert Dunleavy
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY, USA
| | - Changfan Lin
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY, USA
| | | | - Abir Ganguly
- Institute for Quantitative Biomedicine, Rutgers University, Piscataway, NJ, USA
| | - Brian R Crane
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY, USA.
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10
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Dzikovski B, Khramtsov VV, Chandrasekaran S, Dunnam C, Shah M, Freed JH. Microsecond Exchange Processes Studied by Two-Dimensional ESR at 95 GHz. J Am Chem Soc 2020; 142:21368-21381. [PMID: 33305945 PMCID: PMC7810061 DOI: 10.1021/jacs.0c09469] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Exchange processes which include conformational change, protonation/deprotonation, and binding equilibria are routinely studied by 2D exchange NMR techniques, where information about the exchange of nuclei between environments with different NMR shifts is obtained from the development of cross-peaks. Whereas 2D NMR enables the real time study of millisecond and slower exchange processes, 2D ESR in the form of 2D-ELDOR (two-dimensional electron-electron double resonance) has the potential for such studies over the nanosecond to microsecond real time scales. Cross-peak development due to chemical exchange has been seen previously for semiquinones in ESR, but this is not possible for most common ESR probes, such as nitroxides, studied at typical ESR frequencies because, unlike NMR, the exchanging states yield ESR signals that are not resolved from each other within their respective line widths. But at 95 GHz, it becomes possible to resolve them in many cases because of the increased g-factor resolution. The 95 GHz instrumental developments occurring at ACERT now enable such studies. We demonstrate these new capabilities in two studies: (A) the protonation/deprotonation process for a pH-sensitive imidazoline spin label in aqueous solution where the exchange rate and the population ratio of the exchanging states are controlled by the concentration and pH of the buffer solution, respectively, and (B) a nitroxide radical partitioning between polar (aqueous) and nonpolar (phospholipid) environments in multilamellar lipid vesicles, where the cross-peak development arises from the exchange of the nitroxide between the two phases. This work represents the first example of the observation and analysis of cross-peaks arising from chemical exchange processes involving nitroxide spin labels.
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Affiliation(s)
- Boris Dzikovski
- Department of Chemistry and Chemical Biology, and ACERT, National Biomedical Center for Advanced Electron Spin Resonance Technology, Cornell University, Ithaca, New York 14853-1301, United States
| | - Valery V Khramtsov
- In Vivo Multifunctional Magnetic Resonance Center, Robert C. Byrd Health Sciences Center, West Virginia University, and Department of Biochemistry, West Virginia University School of Medicine, Morgantown, West Virginia 26506, United States
| | - Siddarth Chandrasekaran
- Department of Chemistry and Chemical Biology, and ACERT, National Biomedical Center for Advanced Electron Spin Resonance Technology, Cornell University, Ithaca, New York 14853-1301, United States
| | - Curt Dunnam
- Department of Chemistry and Chemical Biology, and ACERT, National Biomedical Center for Advanced Electron Spin Resonance Technology, Cornell University, Ithaca, New York 14853-1301, United States
| | - Meera Shah
- Department of Chemistry and Chemical Biology, and ACERT, National Biomedical Center for Advanced Electron Spin Resonance Technology, Cornell University, Ithaca, New York 14853-1301, United States
| | - Jack H Freed
- Department of Chemistry and Chemical Biology, and ACERT, National Biomedical Center for Advanced Electron Spin Resonance Technology, Cornell University, Ithaca, New York 14853-1301, United States
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11
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Georgieva ER. Protein Conformational Dynamics upon Association with the Surfaces of Lipid Membranes and Engineered Nanoparticles: Insights from Electron Paramagnetic Resonance Spectroscopy. Molecules 2020; 25:E5393. [PMID: 33218036 PMCID: PMC7698768 DOI: 10.3390/molecules25225393] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2020] [Revised: 11/15/2020] [Accepted: 11/16/2020] [Indexed: 11/16/2022] Open
Abstract
Detailed study of conformational rearrangements and dynamics of proteins is central to our understanding of their physiological functions and the loss of function. This review outlines the applications of the electron paramagnetic resonance (EPR) technique to study the structural aspects of proteins transitioning from a solution environment to the states in which they are associated with the surfaces of biological membranes or engineered nanoobjects. In the former case these structural transitions generally underlie functional protein states. The latter case is mostly relevant to the application of protein immobilization in biotechnological industries, developing methods for protein purification, etc. Therefore, evaluating the stability of the protein functional state is particularly important. EPR spectroscopy in the form of continuous-wave EPR or pulse EPR distance measurements in conjunction with protein spin labeling provides highly versatile and sensitive tools to characterize the changes in protein local dynamics as well as large conformational rearrangements. The technique can be widely utilized in studies of both protein-membrane and engineered nanoobject-protein complexes.
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Affiliation(s)
- Elka R Georgieva
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409, USA
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12
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Singewald K, Bogetti X, Sinha K, Rule GS, Saxena S. Double Histidine Based EPR Measurements at Physiological Temperatures Permit Site‐Specific Elucidation of Hidden Dynamics in Enzymes. Angew Chem Int Ed Engl 2020; 59:23040-23044. [DOI: 10.1002/anie.202009982] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2020] [Revised: 08/31/2020] [Indexed: 11/06/2022]
Affiliation(s)
- Kevin Singewald
- Department of Chemistry University of Pittsburgh Pittsburgh PA 15260 USA
| | - Xiaowei Bogetti
- Department of Chemistry University of Pittsburgh Pittsburgh PA 15260 USA
| | - Kaustubh Sinha
- Department of Biological Sciences Carnegie Mellon University Pittsburgh PA 15213 USA
| | - Gordon S Rule
- Department of Biological Sciences Carnegie Mellon University Pittsburgh PA 15213 USA
| | - Sunil Saxena
- Department of Chemistry University of Pittsburgh Pittsburgh PA 15260 USA
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13
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Singewald K, Bogetti X, Sinha K, Rule GS, Saxena S. Double Histidine Based EPR Measurements at Physiological Temperatures Permit Site‐Specific Elucidation of Hidden Dynamics in Enzymes. Angew Chem Int Ed Engl 2020. [DOI: 10.1002/ange.202009982] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Affiliation(s)
- Kevin Singewald
- Department of Chemistry University of Pittsburgh Pittsburgh PA 15260 USA
| | - Xiaowei Bogetti
- Department of Chemistry University of Pittsburgh Pittsburgh PA 15260 USA
| | - Kaustubh Sinha
- Department of Biological Sciences Carnegie Mellon University Pittsburgh PA 15213 USA
| | - Gordon S Rule
- Department of Biological Sciences Carnegie Mellon University Pittsburgh PA 15213 USA
| | - Sunil Saxena
- Department of Chemistry University of Pittsburgh Pittsburgh PA 15260 USA
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14
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Chow GK, Chavan AG, Heisler JC, Chang YG, LiWang A, Britt RD. Monitoring Protein-Protein Interactions in the Cyanobacterial Circadian Clock in Real Time via Electron Paramagnetic Resonance Spectroscopy. Biochemistry 2020; 59:2387-2400. [PMID: 32453554 PMCID: PMC7346098 DOI: 10.1021/acs.biochem.0c00279] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
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The cyanobacterial circadian clock
in Synechococcus elongatus consists of three proteins,
KaiA, KaiB, and KaiC. KaiA and KaiB
rhythmically interact with KaiC to generate stable oscillations of
KaiC phosphorylation with a period of 24 h. The observation of stable
circadian oscillations when the three clock proteins are reconstituted
and combined in vitro makes it an ideal system for understanding its
underlying molecular mechanisms and circadian clocks in general. These
oscillations were historically monitored in vitro by gel electrophoresis
of reaction mixtures based on the differing electrophoretic mobilities
between various phosphostates of KaiC. As the KaiC phospho-distribution
represents only one facet of the oscillations, orthogonal tools are
necessary to explore other interactions to generate a full description
of the system. However, previous biochemical assays are discontinuous
or qualitative. To circumvent these limitations, we developed a spin-labeled
KaiB mutant that can differentiate KaiC-bound KaiB from free KaiB
using continuous-wave electron paramagnetic resonance spectroscopy
that is minimally sensitive to KaiA. Similar to wild-type (WT-KaiB),
this labeled mutant, in combination with KaiA, sustains robust circadian
rhythms of KaiC phosphorylation. This labeled mutant is hence a functional
surrogate of WT-KaiB and thus participates in and reports on autonomous
macroscopic circadian rhythms generated by mixtures that include KaiA,
KaiC, and ATP. Quantitative kinetics could be extracted with improved
precision and time resolution. We describe design principles, data
analysis, and limitations of this quantitative binding assay and discuss
future research necessary to overcome these challenges.
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Affiliation(s)
- Gary K Chow
- Department of Chemistry, University of California, Davis, California 95616, United States
| | | | | | | | - Andy LiWang
- Center for Circadian Biology, University of California, San Diego, La Jolla, California 92093, United States
| | - R David Britt
- Department of Chemistry, University of California, Davis, California 95616, United States
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15
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Gupta P, Liang Z, Freed JH. Microsecond dynamics in proteins by two-dimensional ESR: Predictions. J Chem Phys 2020; 152:214112. [PMID: 32505151 PMCID: PMC7863697 DOI: 10.1063/5.0008094] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2020] [Accepted: 04/14/2020] [Indexed: 01/04/2023] Open
Abstract
Two-dimensional electron-electron double resonance (2D-ELDOR) provides extensive insight into molecular motions. Recent developments permitting experiments at higher frequencies (95 GHz) provide molecular orientational resolution, enabling a clearer description of the nature of the motions. In this work, simulations are provided for the example of domain motions within proteins that are themselves slowly tumbling in solution. These show the nature of the exchange cross-peaks that are predicted to develop in real time from such domain motions. However, we find that the existing theoretical methods for computing 2D-ELDOR experiments over a wide motional range begin to fail seriously when applied to very slow motions characteristic of proteins in solution. One reason is the failure to obtain accurate eigenvectors and eigenvalues of the complex symmetric stochastic Liouville matrices describing the experiment when computed by the efficient Lanczos algorithm in the range of very slow motion. Another, perhaps more serious, issue is that these matrices are "non-normal," such that for the very slow motional range even rigorous diagonalization algorithms do not yield the correct eigenvalues and eigenvectors. We have employed algorithms that overcome both these issues and lead to valid 2D-ELDOR predictions even for motions approaching the rigid limit. They are utilized to describe the development of cross-peaks in 2D-ELDOR at 95 GHz for a particular case of domain motion.
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Affiliation(s)
- Pranav Gupta
- Department of Chemistry and Chemical Biology, National Biomedical Center for Advanced ESR Technology, Cornell University, Ithaca, New York 14853, USA
| | - Zhichun Liang
- Department of Chemistry and Chemical Biology, National Biomedical Center for Advanced ESR Technology, Cornell University, Ithaca, New York 14853, USA
| | - Jack H. Freed
- Department of Chemistry and Chemical Biology, National Biomedical Center for Advanced ESR Technology, Cornell University, Ithaca, New York 14853, USA
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16
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Bogdanov AV, Tamura R, Vorobiev AK. Novel nitroxide biradical probe with spiro-fused rigid core for EPR determination of rotational mobility and orientational order of soft materials. Chem Phys Lett 2020. [DOI: 10.1016/j.cplett.2020.137432] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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17
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Martin PD, Svensson B, Thomas DD, Stoll S. Trajectory-Based Simulation of EPR Spectra: Models of Rotational Motion for Spin Labels on Proteins. J Phys Chem B 2019; 123:10131-10141. [PMID: 31693365 DOI: 10.1021/acs.jpcb.9b02693] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Direct time-domain simulation of continuous-wave (CW) electron paramagnetic resonance (EPR) spectra from molecular dynamics (MD) trajectories has become increasingly popular, especially for proteins labeled with nitroxide spin labels. Due to the time-consuming nature of simulating adequately long MD trajectories, two approximate methods have been developed to reduce the MD-trajectory length required for modeling EPR spectra: hindered Brownian diffusion (HBD) and hidden Markov models (HMMs). Here, we assess the accuracy of these two approximate methods relative to direct simulations from MD trajectories for three spin-labeled protein systems (a simple helical peptide, a soluble protein, and a membrane protein) and two nitroxide spin labels with differing mobilities (R1 and 2,2,6,6-tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic acid (TOAC)). We find that the HMMs generally outperform HBD. Although R1 dynamics partially resembles hindered Brownian diffusion, HMMs accommodate the multiple dynamic time scales for the transitions between rotameric states of R1 that cannot be captured accurately by a HBD model. The MD trajectories of the TOAC-labeled proteins show that its dynamics closely resembles slow multisite exchange between twist-boat and chair ring puckering states. This motion is modeled well by HMM but not by HBD. All MD-trajectory data processing, stochastic trajectory simulations, and CW EPR spectral simulations are implemented in EasySpin, a free software package for MATLAB.
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Affiliation(s)
| | | | | | - Stefan Stoll
- Department of Chemistry , University of Washington , Seattle , Washington 98195 , United States
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18
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Meirovitch E, Freed JH. Local ordering and dynamics in anisotropic media by magnetic resonance: from liquid crystals to proteins. LIQUID CRYSTALS 2019; 47:1926-1954. [PMID: 32435078 PMCID: PMC7239324 DOI: 10.1080/02678292.2019.1622158] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/26/2019] [Indexed: 06/11/2023]
Abstract
Magnetic resonance methods have been used extensively for over 50 years to elucidate molecular structure and dynamics of liquid crystals (LCs), providing information quite unique in its rigour and extent. The ESR- or NMR-active probe is often a solute molecule reporting on characteristics associated with the surrounding (LC) medium, which exerts the spatial restrictions on the probe. The theoretical approaches developed for LCs are applicable to anisotropic media in general. Of particular interest is the interior space of a globular protein labelled, e.g. with a nitroxide moiety or a 15N-1H bond. The ESR or NMR label plays the role of the probe and the internal protein surroundings the role of the anisotropic medium. A general feature of the restricted motions is the local ordering, i.e. the nature, magnitude and symmetry of the spatial restraints exerted at the site of the moving probe. This property is the main theme of the present review article. We outline its treatment in our work from both the theoretical and the experimental points of view, highlighting the new physical insights gained. Our illustrations include studies on thermotropic (nematic and smectic) and lyotropic liquid crystals formed by phospholipids, in addition to studies of proteins.
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Affiliation(s)
- Eva Meirovitch
- The Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University, Ramat-Gan, Israel
| | - Jack H Freed
- Baker Laboratory of Chemistry and Chemical Biology, Cornell University, Ithaca, NY, USA
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19
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Polimeno A, Zerbetto M, Abergel D. Stochastic modeling of macromolecules in solution. I. Relaxation processes. J Chem Phys 2019; 150:184107. [PMID: 31091939 DOI: 10.1063/1.5077065] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
A framework for the stochastic description of relaxation processes in flexible macromolecules, including dissipative effects, is introduced from an atomistic point of view. Projection-operator techniques are employed to obtain multidimensional Fokker-Planck operators governing the relaxation of internal coordinates and global degrees of freedom and depending upon parameters fully recoverable from classic force fields (energetics) and continuum models (friction tensors). A hierarchy of approaches of different complexity is proposed in this unified context, aimed primarily at the interpretation of magnetic resonance relaxation experiments. In particular, a model based on a harmonic internal Hamiltonian is discussed as a test case.
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Affiliation(s)
- Antonino Polimeno
- Dipartimento di Scienze Chimiche, Università degli Studi di Padova, I-35131 Padova, Italy
| | - Mirco Zerbetto
- Dipartimento di Scienze Chimiche, Università degli Studi di Padova, I-35131 Padova, Italy
| | - Daniel Abergel
- Laboratoire des Biomolécules, LBM, Département de Chimie, Ecole Normale Supérieure, PSL University, Sorbonne Université, CNRS, 75005 Paris, France
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20
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Polimeno A, Zerbetto M, Abergel D. Stochastic modeling of macromolecules in solution. II. Spectral densities. J Chem Phys 2019; 150:184108. [PMID: 31091922 DOI: 10.1063/1.5077066] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
In Paper I [Polimeno et al., J. Chem. Phys. 150, 184107 (2019)], we proposed a general approach for interpreting relaxation properties of a macromolecule in solution, derived from an atomistic description. A simple scheme (the semiflexible Brownian, SFB, model) has been defined for the case of limited internal flexibility, but retaining full coupling with external degrees of freedom, inclusion of all of the momenta, and dissipation. Here we discuss the application of the SFB model to the practical evaluation of orientation spectral densities, based on two complementary computational treatments.
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Affiliation(s)
- Antonino Polimeno
- Dipartimento di Scienze Chimiche, Università degli Studi di Padova, I-35131 Padova, Italy
| | - Mirco Zerbetto
- Dipartimento di Scienze Chimiche, Università degli Studi di Padova, I-35131 Padova, Italy
| | - Daniel Abergel
- Laboratoire des Biomolécules, LBM, Département de Chimie, Ecole Normale Supérieure, PSL University, Sorbonne Université, CNRS, 75005 Paris, France
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21
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Wilson CB, Aronson S, Clayton JA, Glaser SJ, Han S, Sherwin MS. Multi-step phase-cycling in a free-electron laser-powered pulsed electron paramagnetic resonance spectrometer. Phys Chem Chem Phys 2018; 20:18097-18109. [PMID: 29938285 DOI: 10.1039/c8cp01876f] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Electron paramagnetic resonance (EPR) is a powerful tool for research in chemistry, biology, physics and materials science, which can benefit significantly from moving to frequencies above 100 GHz. In pulsed EPR spectrometers driven by powerful sub-THz oscillators, such as the free electron laser (FEL)-powered EPR spectrometer at UCSB, control of the duration, power and relative phases of the pulses in a sequence must be performed at the frequency and power level of the oscillator. Here we report on the implementation of an all-quasioptical four-step phase cycling procedure carried out directly at the kW power level of the 240 GHz pulses used in the FEL-powered EPR spectrometer. Phase shifts are introduced by modifying the optical path length of a 240 GHz pulse with precision-machined dielectric plates in a procedure we call phase cycling with optomechanical phase shifters (POPS), while numerical receiver phase cycling is implemented in post-processing. The POPS scheme was successfully used to reduce experimental dead times, enabling pulsed EPR of fast-relaxing spin systems such as gadolinium complexes at temperatures above 190 K. Coherence transfer pathway selection with POPS was used to perform spin echo relaxation experiments to measure the phase memory time of P1 centers in diamond in the presence of a strong unwanted FID signal in the background. The large excitation bandwidth of FEL-EPR, together with phase cycling, enabled the quantitative measurement of instantaneous electron spectral diffusion, from which the P1 center concentration was estimated to within 10%. Finally, phase cycling enabled saturation-recovery measurements of T1 in a trityl-water solution at room temperature - the first FEL-EPR measurement of electron T1.
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Affiliation(s)
- C Blake Wilson
- Department of Physics, University of California, Santa Barbara, Santa Barbara, California, USA.
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22
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Kuo YH, Chiang YW. Slow Dynamics around a Protein and Its Coupling to Solvent. ACS CENTRAL SCIENCE 2018; 4:645-655. [PMID: 29806012 PMCID: PMC5968437 DOI: 10.1021/acscentsci.8b00139] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/05/2018] [Indexed: 05/25/2023]
Abstract
Solvent is essential for protein dynamics and function, but its role in regulating the dynamics remains debated. Here, we employ saturation transfer electron spin resonance (ST-ESR) to explore the issue and characterize the dynamics on a longer (from μs to s) time scale than has been extensively studied. We first demonstrate the reliability of ST-ESR by showing that the dynamical changeovers revealed in the spectra agree to liquid-liquid transition (LLT) in the state diagram of the glycerol/water system. Then, we utilize ST-ESR with four different probes to systematically map out the variation in local (site-specific) dynamics around a protein surface at subfreezing temperatures (180-240 K) in 10 mol % glycerol/water mixtures. At highly exposed sites, protein and solvent dynamics are coupled, whereas they deviate from each other when temperature is greater than LLT temperature (∼190 K) of the solvent. At less exposed sites, protein however exhibits a dynamic, which is distinct from the bulk solvent, throughout the temperature range studied. Dominant dynamic components are thus revealed, showing that (from low to high temperatures) the overall structural fluctuation, rotamer dynamics, and internal side-chain dynamics, in turn, dominate the temperature dependence of spin-label motions. The structural fluctuation component is relatively slow, collective, and independent of protein structural segments, which is thus inferred to a fundamental dynamic component intrinsic to protein. This study corroborates that bulk solvent plasticizes protein and facilitates rather than slaves protein dynamics.
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23
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New limits of sensitivity of site-directed spin labeling electron paramagnetic resonance for membrane proteins. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2018; 1860:841-853. [DOI: 10.1016/j.bbamem.2017.12.009] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/12/2017] [Revised: 11/27/2017] [Accepted: 12/09/2017] [Indexed: 01/27/2023]
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24
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Hung CL, Lin YY, Chang HH, Chiang YW. Accessing local structural disruption of Bid protein during thermal denaturation by absorption-mode ESR spectroscopy. RSC Adv 2018; 8:34656-34669. [PMID: 35548640 PMCID: PMC9087001 DOI: 10.1039/c8ra06740f] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2018] [Accepted: 10/04/2018] [Indexed: 01/19/2023] Open
Abstract
The apoptotic function of Bid does not depend on its native structure.
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Affiliation(s)
- Chien-Lun Hung
- Department of Chemistry
- National Tsing Hua University
- Hsinchu 30013
- Taiwan
| | - Yu-Ying Lin
- Department of Chemistry
- National Tsing Hua University
- Hsinchu 30013
- Taiwan
| | - Hsin-Ho Chang
- Department of Chemistry
- National Tsing Hua University
- Hsinchu 30013
- Taiwan
| | - Yun-Wei Chiang
- Department of Chemistry
- National Tsing Hua University
- Hsinchu 30013
- Taiwan
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25
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Chang KJ, Kuo YH, Chiang YW. Study of Protein Dynamics under Nanoconfinement by Spin-Label ESR: A Case of T4 Lysozyme Protein. J Phys Chem B 2017; 121:4355-4363. [DOI: 10.1021/acs.jpcb.7b00014] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Affiliation(s)
- Kuo-Jung Chang
- Department of Chemistry, National Tsing Hua University, Hsinchu 30013, Taiwan
| | - Yun-Hsuan Kuo
- Department of Chemistry, National Tsing Hua University, Hsinchu 30013, Taiwan
| | - Yun-Wei Chiang
- Department of Chemistry, National Tsing Hua University, Hsinchu 30013, Taiwan
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26
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Spin Probe Multi-Frequency EPR Study of Unprocessed Cotton Fibers. Cell Biochem Biophys 2017; 75:211-226. [PMID: 28271339 DOI: 10.1007/s12013-017-0787-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2017] [Accepted: 02/21/2017] [Indexed: 10/20/2022]
Abstract
Known since the ancient times, cotton continues to be one of the essential materials for the human civilization. Cotton fibers are almost pure cellulose and contain both crystalline and amorphous nanodomains with different physicochemical properties. While understanding of interactions between the individual cellulose chains within the crystalline phase is important from a perspective of mechanical properties, studies of the amorphous phase lead to characterization of the essential transport parameters, such as solvent diffusion, dyeing, drug release, and toxin absorption, as well as more complex processes of enzymatic degradation. Here, we describe the use of spin probe electron paramagnetic resonance methods to study local polarity and heterogeneous viscosity of two types of unprocessed cotton fibers, G. hirsutum and G. barbadense, harvested in the State of North Carolina, USA. These fibers were loaded with two small molecule nitroxide probes that differ in polarity-Tempo and its more hydrophilic derivative Tempol-using a series of polar and non-polar solvents. The electron paramagnetic resonance spectra of the nitroxide-loaded cotton fibers were analyzed both semi-empirically and by least-squares simulations using a rigorous stochastic theory of electron paramagnetic resonance spectra developed by Freed and coworkers. A software package and least-squares fitting protocols were developed to carry out automatic simulations of multi-component electron paramagnetic resonance spectra in both first-derivative and the absorption forms at multiple resonance frequencies such as X-band (9.5 GHz) and W-band (94.3 GHz). The results are compared with the preceding electron paramagnetic resonance spin probe studies of a commercial bleached cotton sheeting carried out by Batchelor and coworkers. One of the results of this study is a demonstration of a co-existence of cellulose nanodomains with different physicochemical properties such as polarity and microviscosity that are affected by solvents and temperature. Spin labeling studies also revealed a macroscopic heterogeneity in the domain distribution along the cotton fibers and a critical role the cuticular layer is playing as a barrier for spin probe penetration. Finally but not lastly, the simultaneous multi-component least-squares simulation method of electron paramagnetic resonance spectra acquired at different resonant frequencies and the display forms (e.g., absorption and first-derivative displays) and the strategy of spectral parameter sharing could be potentially applicable to other heterogeneous biological systems in addition to the cotton fibers studies here.
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27
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Petrlova J, Hilt S, Budamagunta M, Domingo-Espín J, Voss JC, Lagerstedt JO. Molecular crowding impacts the structure of apolipoprotein A-I with potential implications on in vivo metabolism and function. Biopolymers 2016; 105:683-92. [PMID: 27122373 DOI: 10.1002/bip.22865] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2015] [Revised: 03/14/2016] [Accepted: 04/25/2016] [Indexed: 11/08/2022]
Abstract
The effect molecular crowding, defined as the volume exclusion exerted by one soluble inert molecule upon another soluble molecule, has on the structure and self-interaction of lipid-free apoA-I were explored. The influence of molecular crowding on lipid-free apoA-I oligomerization and internal dynamics has been analyzed using electron paramagnetic resonance (EPR) spectroscopy measurements of nitroxide spin label at selected positions throughout the protein sequence and at varying concentrations of the crowding agent Ficoll-70. The targeted positions include sites previously shown to be sensitive for detecting intermolecular interaction via spin-spin coupling. Circular dichroism was used to study secondary structural changes in lipid-free apoA-I imposed by increasing concentrations of the crowding agent. Crosslinking and SDS-PAGE gel analysis was employed to further characterize the role molecular crowding plays in inducing apoA-I oligomerization. It was concluded that the dynamic apoA-I structure and oligomeric state was altered in the presence of the crowding agent. It was also found that the C-terminal was slightly more sensitive to molecular crowding. Finally, the data described the region around residue 217 in the C-terminal domain of apoA-I as the most sensitive reporter of the crowding-induced self-association of apoA-I. The implications of this behavior to in vivo functionality are discussed. © 2016 Wiley Periodicals, Inc. Biopolymers 105: 683-692, 2016.
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Affiliation(s)
- Jitka Petrlova
- Department of Experimental Medical Science, Lund University, Lund, S-221 84, Sweden
| | - Silvia Hilt
- Department of Biochemistry and Molecular Medicine, University of California, Davis, CA, 95616
| | - Madhu Budamagunta
- Department of Biochemistry and Molecular Medicine, University of California, Davis, CA, 95616
| | - Joan Domingo-Espín
- Department of Experimental Medical Science, Lund University, Lund, S-221 84, Sweden
| | - John C Voss
- Department of Experimental Medical Science, Lund University, Lund, S-221 84, Sweden.,Department of Biochemistry and Molecular Medicine, University of California, Davis, CA, 95616
| | - Jens O Lagerstedt
- Department of Experimental Medical Science, Lund University, Lund, S-221 84, Sweden
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28
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Song L, Liu Z, Kaur P, Esquiaqui JM, Hunter RI, Hill S, Smith GM, Fanucci GE. Toward increased concentration sensitivity for continuous wave EPR investigations of spin-labeled biological macromolecules at high fields. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2016; 265:188-196. [PMID: 26923151 DOI: 10.1016/j.jmr.2016.02.007] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/30/2015] [Revised: 02/09/2016] [Accepted: 02/10/2016] [Indexed: 06/05/2023]
Abstract
High-field, high-frequency electron paramagnetic resonance (EPR) spectroscopy at W-(∼94 GHz) and D-band (∼140 GHz) is important for investigating the conformational dynamics of flexible biological macromolecules because this frequency range has increased spectral sensitivity to nitroxide motion over the 100 ps to 2 ns regime. However, low concentration sensitivity remains a roadblock for studying aqueous samples at high magnetic fields. Here, we examine the sensitivity of a non-resonant thin-layer cylindrical sample holder, coupled to a quasi-optical induction-mode W-band EPR spectrometer (HiPER), for continuous wave (CW) EPR analyses of: (i) the aqueous nitroxide standard, TEMPO; (ii) the unstructured to α-helical transition of a model IDP protein; and (iii) the base-stacking transition in a kink-turn motif of a large 232 nt RNA. For sample volumes of ∼50 μL, concentration sensitivities of 2-20 μM were achieved, representing a ∼10-fold enhancement compared to a cylindrical TE011 resonator on a commercial Bruker W-band spectrometer. These results therefore highlight the sensitivity of the thin-layer sample holders employed in HiPER for spin-labeling studies of biological macromolecules at high fields, where applications can extend to other systems that are facilitated by the modest sample volumes and ease of sample loading and geometry.
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Affiliation(s)
- Likai Song
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, USA
| | - Zhanglong Liu
- Department of Chemistry, University of Florida, PO Box 117200, Gainesville, FL 32611, USA
| | - Pavanjeet Kaur
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, USA; Department of Physics, Florida State University, Tallahassee, FL 32306, USA
| | - Jackie M Esquiaqui
- Department of Chemistry, University of Florida, PO Box 117200, Gainesville, FL 32611, USA
| | - Robert I Hunter
- School of Physics and Astronomy, University of St. Andrews, North Haugh, St. Andrews KY16 9SS, United Kingdom
| | - Stephen Hill
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, USA; Department of Physics, Florida State University, Tallahassee, FL 32306, USA
| | - Graham M Smith
- School of Physics and Astronomy, University of St. Andrews, North Haugh, St. Andrews KY16 9SS, United Kingdom
| | - Gail E Fanucci
- Department of Chemistry, University of Florida, PO Box 117200, Gainesville, FL 32611, USA.
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29
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Tchaicheeyan O, Freed JH, Meirovitch E. Local Ordering at Mobile Sites in Proteins from Nuclear Magnetic Resonance Relaxation: The Role of Site Symmetry. J Phys Chem B 2016; 120:2886-98. [PMID: 26938937 DOI: 10.1021/acs.jpcb.6b00524] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Restricted motions in proteins (e.g., N-H bond dynamics) are studied effectively with NMR. By analogy with restricted motions in liquid crystals (LC), the local ordering has in the past been primarily represented by potentials comprising the L = 2, |K| = 0, 2 spherical harmonics. However, probes dissolved in LCs experience nonpolar ordering, often referred to as alignment, while protein-anchored probes experience polar ordering, often referred to as orientation. In this study we investigate the role of local (site) symmetry in the context of the polarity of the local ordering. We find that potentials comprising the L = 1, |K| = 0, 1 spherical harmonics represent adequately polar ordering. It is useful to characterize potential symmetry in terms of the irreducible representations of D2h point group, which is already implicit in the definition of the rotational diffusion tensor. Thus, the relevant rhombic L = 1 potentials have B1u and B3u symmetry whereas the relevant rhombic L = 2 potentials have Ag symmetry. A comprehensive scheme where local potentials and corresponding probability density functions (PDFs) are represented in Cartesian and spherical coordinates clarifies how they are affected by polar and nonpolar ordering. The Cartesian coordinates are chosen so that the principal axis of polar axial PDF is pointing along the z-axis, whereas the principal axis of the nonpolar axial PDF is pointing along ±z. Two-term axial potentials with 1 ≤ L ≤ 3 exhibit substantial diversity; they are expected to be useful in NMR-relaxation-data-fitting. It is shown how potential coefficients are reflected in the experimental order parameters. The comprehensive scheme representing local potentials and PDFs is exemplified for the L = 2 case using experimental data from (15)N-labeled plexin-B1 and thioredoxin, (2)H-, and (13)C-labeled benzenehexa-n-alkanoates, and nitroxide-labeled T4 lysozyme. Future prospects for improved ordering analysis based on combined atomistic and mesoscopic approaches are delineated.
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Affiliation(s)
- Oren Tchaicheeyan
- The Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University , Ramat-Gan 52900, Israel
| | - Jack H Freed
- Baker Laboratory of Chemistry and Chemical Biology, Cornell University , Ithaca, New York 14853-1301, United States
| | - Eva Meirovitch
- The Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University , Ramat-Gan 52900, Israel
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30
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Franck JM, Chandrasekaran S, Dzikovski B, Dunnam CR, Freed JH. Focus: Two-dimensional electron-electron double resonance and molecular motions: The challenge of higher frequencies. J Chem Phys 2016; 142:212302. [PMID: 26049420 DOI: 10.1063/1.4917322] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The development, applications, and current challenges of the pulsed ESR technique of two-dimensional Electron-Electron Double Resonance (2D ELDOR) are described. This is a three-pulse technique akin to 2D Exchange Nuclear Magnetic Resonance, but involving electron spins, usually in the form of spin-probes or spin-labels. As a result, it required the extension to much higher frequencies, i.e., microwaves, and much faster time scales, with π/2 pulses in the 2-3 ns range. It has proven very useful for studying molecular dynamics in complex fluids, and spectral results can be explained by fitting theoretical models (also described) that provide a detailed analysis of the molecular dynamics and structure. We discuss concepts that also appear in other forms of 2D spectroscopy but emphasize the unique advantages and difficulties that are intrinsic to ESR. Advantages include the ability to tune the resonance frequency, in order to probe different motional ranges, while challenges include the high ratio of the detection dead time vs. the relaxation times. We review several important 2D ELDOR studies of molecular dynamics. (1) The results from a spin probe dissolved in a liquid crystal are followed throughout the isotropic → nematic → liquid-like smectic → solid-like smectic → crystalline phases as the temperature is reduced and are interpreted in terms of the slowly relaxing local structure model. Here, the labeled molecule is undergoing overall motion in the macroscopically aligned sample, as well as responding to local site fluctuations. (2) Several examples involving model phospholipid membranes are provided, including the dynamic structural characterization of the boundary lipid that coats a transmembrane peptide dimer. Additionally, subtle differences can be elicited for the phospholipid membrane phases: liquid disordered, liquid ordered, and gel, and the subtle effects upon the membrane, of antigen cross-linking of receptors on the surface of plasma membrane, vesicles can be observed. These 2D ELDOR experiments are performed as a function of mixing time, Tm, i.e., the time between the second and third π/2 pulses, which provides a third dimension. In fact, a fourth dimension may be added by varying the ESR frequency/magnetic field combination. Therefore, (3) it is shown how continuous-wave multifrequency ESR studies enable the decomposition of complex dynamics of, e.g., proteins by virtue of their respective time scales. These studies motivate our current efforts that are directed to extend 2D ELDOR to higher frequencies, 95 GHz in particular (from 9 and 17 GHz), in order to enable multi-frequency 2D ELDOR. This required the development of quasi-optical methods for performing the mm-wave experiments, which are summarized. We demonstrate state-of-the-art 95 GHz 2D ELDOR spectroscopy through its ability to resolve the two signals from a spin probe dissolved in both the lipid phase and the coexisting aqueous phase. As current 95 GHz experiments are restricted by limited spectral coverage of the π/2 pulse, as well as the very short T2 relaxation times of the electron spins, we discuss how these limitations are being addressed.
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Affiliation(s)
- John M Franck
- Department of Chemistry and Chemical Biology and National Biomedical Center for Advanced ESR Technology, Cornell University, Ithaca, New York 14853, USA
| | - Siddarth Chandrasekaran
- Department of Chemistry and Chemical Biology and National Biomedical Center for Advanced ESR Technology, Cornell University, Ithaca, New York 14853, USA
| | - Boris Dzikovski
- Department of Chemistry and Chemical Biology and National Biomedical Center for Advanced ESR Technology, Cornell University, Ithaca, New York 14853, USA
| | - Curt R Dunnam
- Department of Chemistry and Chemical Biology and National Biomedical Center for Advanced ESR Technology, Cornell University, Ithaca, New York 14853, USA
| | - Jack H Freed
- Department of Chemistry and Chemical Biology and National Biomedical Center for Advanced ESR Technology, Cornell University, Ithaca, New York 14853, USA
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Fraind AM, Ryzhkov LR, Tovar JD. Chain Dynamics, Relaxation Times, and Conductivities of Bithiophene–Acene Copolymers Measured Using High Frequency Saturation Transfer EPR. J Phys Chem B 2016; 120:1033-9. [DOI: 10.1021/acs.jpcb.5b11212] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
| | - Lev R. Ryzhkov
- Department
of Chemistry Towson University, Towson, Maryland 21252 United States
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32
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Bogdanov AV, Vorobiev AK. Orientation order and rotation mobility of nitroxide biradicals determined by quantitative simulation of EPR spectra. Phys Chem Chem Phys 2016; 18:31144-31153. [DOI: 10.1039/c6cp05815a] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The biradical spin probe technique was used to obtain information on the molecular dynamics and structure of isotropic and anisotropic liquids.
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33
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Chen JL, Yang Y, Zhang LL, Liang H, Huber T, Su XC, Otting G. Analysis of the solution conformations of T4 lysozyme by paramagnetic NMR spectroscopy. Phys Chem Chem Phys 2016; 18:5850-9. [DOI: 10.1039/c5cp07196h] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Paramagnetic data show that the average structure of T4-lysozyme in solution is more open than its crystal structure.
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Affiliation(s)
- Jia-Liang Chen
- State Key Laboratory of Elemento-organic Chemistry
- The Collaborative Innovation Center of Chemical Science and Engineering (Tianjin)
- Nankai University
- Tianjin 300071
- China
| | - Yin Yang
- State Key Laboratory of Elemento-organic Chemistry
- The Collaborative Innovation Center of Chemical Science and Engineering (Tianjin)
- Nankai University
- Tianjin 300071
- China
| | - Lin-Lin Zhang
- State Key Laboratory of Elemento-organic Chemistry
- The Collaborative Innovation Center of Chemical Science and Engineering (Tianjin)
- Nankai University
- Tianjin 300071
- China
| | - Haobo Liang
- Research School of Chemistry
- Australian National University
- Canberra
- Australia
| | - Thomas Huber
- Research School of Chemistry
- Australian National University
- Canberra
- Australia
| | - Xun-Cheng Su
- State Key Laboratory of Elemento-organic Chemistry
- The Collaborative Innovation Center of Chemical Science and Engineering (Tianjin)
- Nankai University
- Tianjin 300071
- China
| | - Gottfried Otting
- Research School of Chemistry
- Australian National University
- Canberra
- Australia
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Srivastava M, Anderson CL, Freed JH. A New Wavelet Denoising Method for Selecting Decomposition Levels and Noise Thresholds. IEEE ACCESS : PRACTICAL INNOVATIONS, OPEN SOLUTIONS 2016; 4:3862-3877. [PMID: 27795877 PMCID: PMC5079185 DOI: 10.1109/access.2016.2587581] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
A new method is presented to denoise 1-D experimental signals using wavelet transforms. Although the state-of- the-art wavelet denoising methods perform better than other denoising methods, they are not very effective for experimental signals. Unlike images and other signals, experimental signals in chemical and biophysical applications for example, are less tolerant to signal distortion and under-denoising caused by the standard wavelet denoising methods. The new method 1) provides a method to select the number of decomposition levels to denoise, 2) uses a new formula to calculate noise thresholds that does not require noise estimation, 3) uses separate noise thresholds for positive and negative wavelet coefficients, 4) applies denoising to the Approximation component, and 5) allows the flexibility to adjust the noise thresholds. The new method is applied to continuous wave electron spin resonance (cw-ESR) spectra and it is found that it increases the signal-to-noise ratio (SNR) by more than 32 dB without distorting the signal, whereas standard denoising methods improve the SNR by less than 10 dB and with some distortion. Also, its computation time is more than 6 times faster.
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Affiliation(s)
- Madhur Srivastava
- National Biomedical Center for Advanced ESR Technology (ACERT) and the Nancy E. and Peter C. Meinig School of Biomedical Engineering, Cornell University, Ithaca, NY, 14853 USA
| | - C. Lindsay Anderson
- Department of Biological and Environmental Engineering, Cornell University, Ithaca, NY, 14853 USA
| | - Jack H. Freed
- National Biomedical Center for Advanced ESR Technology (ACERT) and the Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY, 14853 USA
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35
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Meirovitch E, Liang Z, Freed JH. Protein Dynamics in the Solid State from (2)H NMR Line Shape Analysis. II. MOMD Applied to C-D and C-CD3 Probes. J Phys Chem B 2015; 119:14022-32. [PMID: 26402431 PMCID: PMC4676681 DOI: 10.1021/acs.jpcb.5b07434] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
![]()
Deuterium
line shape analysis from mobile C–D and C–CD3 groups has emerged as a particularly useful tool for studying
dynamics in the solid state. The theoretical models devised so far
consist typically of sets of independent dynamic modes. Each such
mode is simple and usually case-specific. In this scenario, model
improvement entails adding yet another mode (thereby changing the
overall model), comparison of different cases is difficult, and ambiguity
is unavoidable. We recently developed the microscopic order macroscopic
disorder (MOMD) approach as a single-mode alternative. In MOMD, the
local spatial restrictions are expressed by an anisotropic potential,
the local motion by a diffusion tensor, and the local molecular geometry
by relative (magnetic and model-related) tensor orientations, all
of adjustable symmetry. This approach provides a consistent method
of analysis, thus resolving the issues above. In this study, we apply
MOMD to PS-adsorbed LKα14 peptide and dimethylammonium tetraphenylborate
(C–CD3 and N–CD3 dynamics, respectively),
as well as HhaI methyltransferase target DNA and
phase III of benzene-6-hexanoate (C–D dynamics). The success
with fitting these four disparate cases, as well as the two cases
in the previous report, demonstrates the generality of this MOMD-based
approach. In this study, C–D and C–CD3 are
both found to execute axial diffusion (rates R⊥ and R∥) in the
presence of a rhombic potential given by the L =
2 spherical harmonics (coefficients c02 and c22). R⊥ (R∥) is in the 102–103 (104–105) s–1 range, and c02 and c22 are on the
order of 2–3 kBT. Specific parameter values are determined for each mobile site.
The diffusion and quadrupolar tensors are tilted at either 120°
(consistent with trans–gauche isomerization) or nearly 110.5° (consistent with methyl exchange).
Future prospects include extension of the MOMD formalism to include
MAS, and application to 15N and 13C nuclei.
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Affiliation(s)
- Eva Meirovitch
- The Mina and Everard Goodman Faculty of Life Sciences, Bar-Ilan University , Ramat-Gan 52900, Israel
| | - Zhichun Liang
- Baker Laboratory of Chemistry and Chemical Biology, Cornell University , Ithaca, New York 14853-1301, United States
| | - Jack H Freed
- Baker Laboratory of Chemistry and Chemical Biology, Cornell University , Ithaca, New York 14853-1301, United States
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36
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Casey TM, Fanucci GE. Spin labeling and Double Electron-Electron Resonance (DEER) to Deconstruct Conformational Ensembles of HIV Protease. Methods Enzymol 2015; 564:153-87. [PMID: 26477251 DOI: 10.1016/bs.mie.2015.07.019] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
An understanding of macromolecular conformational equilibrium in biological systems is oftentimes essential to understand function, dysfunction, and disease. For the past few years, our lab has been utilizing site-directed spin labeling (SDSL), coupled with electron paramagnetic resonance (EPR) spectroscopy, to characterize the conformational ensemble and ligand-induced conformational shifts of HIV-1 protease (HIV-1PR). The biomedical importance of characterizing the fractional occupancy of states within the conformational ensemble critically impacts our hypothesis of a conformational selection mechanism of drug-resistance evolution in HIV-1PR. The purpose of the following chapter is to give a timeline perspective of our SDSL EPR approach to characterizing conformational sampling of HIV-1PR. We provide detailed instructions for the procedure utilized in analyzing distance profiles for HIV-1PR obtained from pulsed electron-electron double resonance (PELDOR). Specifically, we employ a version of PELDOR known as double electron-electron resonance (DEER). Data are processed with the software package "DeerAnalysis" (http://www.epr.ethz.ch/software), which implements Tikhonov regularization (TKR), to generate a distance profile from electron spin-echo amplitude modulations. We assign meaning to resultant distance profiles based upon a conformational sampling model, which is described herein. The TKR distance profiles are reconstructed with a linear combination of Gaussian functions, which is then statistically analyzed. In general, DEER has proven powerful for observing structural ensembles in proteins and, more recently, nucleic acids. Our goal is to present our advances in order to aid readers in similar applications.
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Affiliation(s)
- Thomas M Casey
- Department of Chemistry, University of Florida, Gainesville, Florida, USA
| | - Gail E Fanucci
- Department of Chemistry, University of Florida, Gainesville, Florida, USA.
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37
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Bifunctional Spin Labeling of Muscle Proteins: Accurate Rotational Dynamics, Orientation, and Distance by EPR. Methods Enzymol 2015; 564:101-23. [PMID: 26477249 DOI: 10.1016/bs.mie.2015.06.029] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/21/2023]
Abstract
While EPR allows for the characterization of protein structure and function due to its exquisite sensitivity to spin label dynamics, orientation, and distance, these measurements are often limited in sensitivity due to the use of labels that are attached via flexible monofunctional bonds, incurring additional disorder and nanosecond dynamics. In this chapter, we present methods for using a bifunctional spin label (BSL) to measure muscle protein structure and dynamics. We demonstrate that bifunctional attachment eliminates nanosecond internal rotation of the spin label, thereby allowing the accurate measurement of protein backbone rotational dynamics, including microsecond-to-millisecond motions by saturation transfer EPR. BSL also allows for accurate determination of helix orientation and disorder in mechanically and magnetically aligned systems, due to the label's stereospecific attachment. Similarly, labeling with a pair of BSL greatly enhances the resolution and accuracy of distance measurements measured by double electron-electron resonance (DEER). Finally, when BSL is applied to a protein with high helical content in an assembly with high orientational order (e.g., muscle fiber or membrane), two-probe DEER experiments can be combined with single-probe EPR experiments on an oriented sample in a process we call BEER, which has the potential for ab initio high-resolution structure determination.
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38
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Guzzi R, Bartucci R. Electron spin resonance of spin-labeled lipid assemblies and proteins. Arch Biochem Biophys 2015; 580:102-11. [PMID: 26116378 DOI: 10.1016/j.abb.2015.06.015] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2015] [Revised: 06/18/2015] [Accepted: 06/22/2015] [Indexed: 01/29/2023]
Abstract
Spin-label electron spin resonance (ESR) spectroscopy is a valuable means to study molecular mobility and interactions in biological systems. This paper deals with conventional, continuous wave ESR of nitroxide spin-labels at 9-GHz providing an introduction to the basic principles of the technique and applications to self-assembled lipid aggregates and proteins. Emphasis is given to segmental lipid chain order and rotational dynamics of lipid structures, environmental polarity of membranes and proteins, structure and conformational dynamics of proteins.
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Affiliation(s)
- Rita Guzzi
- Department of Physics, University of Calabria, 87036 Rende (CS), Italy
| | - Rosa Bartucci
- Department of Physics, University of Calabria, 87036 Rende (CS), Italy.
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39
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Structure-relaxation mechanism for the response of T4 lysozyme cavity mutants to hydrostatic pressure. Proc Natl Acad Sci U S A 2015; 112:E2437-46. [PMID: 25918400 DOI: 10.1073/pnas.1506505112] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Application of hydrostatic pressure shifts protein conformational equilibria in a direction to reduce the volume of the system. A current view is that the volume reduction is dominated by elimination of voids or cavities in the protein interior via cavity hydration, although an alternative mechanism wherein cavities are filled with protein side chains resulting from a structure relaxation has been suggested [López CJ, Yang Z, Altenbach C, Hubbell WL (2013) Proc Natl Acad Sci USA 110(46):E4306-E4315]. In the present study, mechanisms for elimination of cavities under high pressure are investigated in the L99A cavity mutant of T4 lysozyme and derivatives thereof using site-directed spin labeling, pressure-resolved double electron-electron resonance, and high-pressure circular dichroism spectroscopy. In the L99A mutant, the ground state is in equilibrium with an excited state of only ∼ 3% of the population in which the cavity is filled by a protein side chain [Bouvignies et al. (2011) Nature 477(7362):111-114]. The results of the present study show that in L99A the native ground state is the dominant conformation to pressures of 3 kbar, with cavity hydration apparently taking place in the range of 2-3 kbar. However, in the presence of additional mutations that lower the free energy of the excited state, pressure strongly populates the excited state, thereby eliminating the cavity with a native side chain rather than solvent. Thus, both cavity hydration and structure relaxation are mechanisms for cavity elimination under pressure, and which is dominant is determined by details of the energy landscape.
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40
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Abstract
Ion channels open and close in response to diverse stimuli, and the molecular events underlying these processes are extensively modulated by ligands of both endogenous and exogenous origin. In the past decade, high-resolution structures of several channel types have been solved, providing unprecedented details of the molecular architecture of these membrane proteins. Intrinsic conformational flexibility of ion channels critically governs their functions. However, the dynamics underlying gating mechanisms and modulations are obscured in the information from crystal structures. While nuclear magnetic resonance spectroscopic methods allow direct measurements of protein dynamics, they are limited by the large size of these membrane protein assemblies in detergent micelles or lipid membranes. Electron paramagnetic resonance (EPR) spectroscopy has emerged as a key biophysical tool to characterize structural dynamics of ion channels and to determine stimulus-driven conformational transition between functional states in a physiological environment. This review will provide an overview of the recent advances in the field of voltage- and ligand-gated channels and highlight some of the challenges and controversies surrounding the structural information available. It will discuss general methods used in site-directed spin labeling and EPR spectroscopy and illustrate how findings from these studies have narrowed the gap between high-resolution structures and gating mechanisms in membranes, and have thereby helped reconcile seemingly disparate models of ion channel function.
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41
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Georgieva ER, Xiao S, Borbat PP, Freed JH, Eliezer D. Tau binds to lipid membrane surfaces via short amphipathic helices located in its microtubule-binding repeats. Biophys J 2015; 107:1441-52. [PMID: 25229151 DOI: 10.1016/j.bpj.2014.07.046] [Citation(s) in RCA: 81] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2014] [Revised: 07/18/2014] [Accepted: 07/24/2014] [Indexed: 11/16/2022] Open
Abstract
Tau is a microtubule-associated protein that is genetically linked to dementia and linked to Alzheimer's disease via its presence in intraneuronal neurofibrillary tangle deposits, where it takes the form of aggregated paired helical and straight filaments. Although the precise mechanisms by which tau contributes to neurodegeneration remain unclear, tau aggregation is commonly considered to be a critical component of tau-mediated pathogenicity. Nevertheless, the context in which tau aggregation begins in vivo is unknown. Tau is enriched in membrane-rich neuronal structures such as axons and growth cones, and can interact with membranes both via intermediary proteins and directly via its microtubule-binding domain (MBD). Membranes efficiently facilitate tau aggregation in vitro, and may therefore provide a physiologically relevant context for nucleating tau aggregation in vivo. Furthermore, tau-membrane interactions may potentially play a role in tau's poorly understood normal physiological functions. Despite the potential importance of direct tau-membrane interactions for tau pathology and physiology, the structural mechanisms that underlie such interactions remain to be elucidated. Here, we employ electron spin resonance spectroscopy to investigate the secondary and long-range structural properties of the MBD of three-repeat tau isoforms when bound to lipid vesicles and membrane mimetics. We show that the membrane interactions of the tau MBD are mediated by short amphipathic helices formed within each of the MBD repeats in the membrane-bound state. To our knowledge, this is the first detailed elucidation of helical tau structure in the context of intact lipid bilayers. We further show, for the first time (to our knowledge), that these individual helical regions behave as independent membrane-binding sites linked by flexible connecting regions. These results represent the first (to our knowledge) detailed structural view of membrane-bound tau and provide insights into potential mechanisms for membrane-mediated tau aggregation. Furthermore, the results may have implications for the structural basis of tau-microtubule interactions and microtubule-mediated tau aggregation.
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Affiliation(s)
- Elka R Georgieva
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York; National Biomedical Center for Advanced ESR Technology, Cornell University, Ithaca, New York
| | - Shifeng Xiao
- Department of Biochemistry, Weill Cornell Medical College, New York, New York; Program in Structural Biology, Weill Cornell Medical College, New York, New York
| | - Peter P Borbat
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York; National Biomedical Center for Advanced ESR Technology, Cornell University, Ithaca, New York
| | - Jack H Freed
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York; National Biomedical Center for Advanced ESR Technology, Cornell University, Ithaca, New York.
| | - David Eliezer
- Department of Biochemistry, Weill Cornell Medical College, New York, New York; Program in Structural Biology, Weill Cornell Medical College, New York, New York.
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42
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Abergel D, Volpato A, Coutant EP, Polimeno A. On the reliability of NMR relaxation data analyses: a Markov Chain Monte Carlo approach. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2014; 246:94-103. [PMID: 25117152 DOI: 10.1016/j.jmr.2014.07.007] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/25/2014] [Revised: 07/01/2014] [Accepted: 07/02/2014] [Indexed: 06/03/2023]
Abstract
The analysis of NMR relaxation data is revisited along the lines of a Bayesian approach. Using a Markov Chain Monte Carlo strategy of data fitting, we investigate conditions under which relaxation data can be effectively interpreted in terms of internal dynamics. The limitations to the extraction of kinetic parameters that characterize internal dynamics are analyzed, and we show that extracting characteristic time scales shorter than a few tens of ps is very unlikely. However, using MCMC methods, reliable estimates of the marginal probability distributions and estimators (average, standard deviations, etc.) can still be obtained for subsets of the model parameters. Thus, unlike more conventional strategies of data analysis, the method avoids a model selection process. In addition, it indicates what information may be extracted from the data, but also what cannot.
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Affiliation(s)
- Daniel Abergel
- Ecole Normale Supérieure, Departement de Chimie, UMR 7203 CNRS-UPMC-ENS, 24, rue Lhomond, 75005 Paris, France.
| | - Andrea Volpato
- Padua University - Department of Chemical Sciences, Via Marzolo 1, 35131 Padua, Italy
| | - Eloi P Coutant
- Ecole Normale Supérieure, Departement de Chimie, UMR 7203 CNRS-UPMC-ENS, 24, rue Lhomond, 75005 Paris, France
| | - Antonino Polimeno
- Padua University - Department of Chemical Sciences, Via Marzolo 1, 35131 Padua, Italy.
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43
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Casey TM, Liu Z, Esquiaqui JM, Pirman NL, Milshteyn E, Fanucci GE. Continuous wave W- and D-band EPR spectroscopy offer "sweet-spots" for characterizing conformational changes and dynamics in intrinsically disordered proteins. Biochem Biophys Res Commun 2014; 450:723-8. [PMID: 24950408 DOI: 10.1016/j.bbrc.2014.06.045] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2014] [Accepted: 06/10/2014] [Indexed: 11/28/2022]
Abstract
Site-directed spin labeling (SDSL) electron paramagnetic resonance (EPR) spectroscopy is a powerful tool for characterizing conformational sampling and dynamics in biological macromolecules. Here we demonstrate that nitroxide spectra collected at frequencies higher than X-band (∼9.5 GHz) have sensitivity to the timescale of motion sampled by highly dynamic intrinsically disordered proteins (IDPs). The 68 amino acid protein IA3, was spin-labeled at two distinct sites and a comparison of X-band, Q-band (35 GHz) and W-band (95 GHz) spectra are shown for this protein as it undergoes the helical transition chemically induced by tri-fluoroethanol. Experimental spectra at W-band showed pronounced line shape dispersion corresponding to a change in correlation time from ∼0.3 ns (unstructured) to ∼0.6 ns (α-helical) as indicated by comparison with simulations. Experimental and simulated spectra at X- and Q-bands showed minimal dispersion over this range, illustrating the utility of SDSL EPR at higher frequencies for characterizing structural transitions and dynamics in IDPs.
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Affiliation(s)
- Thomas M Casey
- Department of Chemistry, University of Florida, PO Box 117200, Gainesville, FL 32611, USA
| | - Zhanglong Liu
- Department of Chemistry, University of Florida, PO Box 117200, Gainesville, FL 32611, USA
| | - Jackie M Esquiaqui
- Department of Chemistry, University of Florida, PO Box 117200, Gainesville, FL 32611, USA
| | - Natasha L Pirman
- Department of Chemistry, University of Florida, PO Box 117200, Gainesville, FL 32611, USA
| | - Eugene Milshteyn
- Department of Chemistry, University of Florida, PO Box 117200, Gainesville, FL 32611, USA
| | - Gail E Fanucci
- Department of Chemistry, University of Florida, PO Box 117200, Gainesville, FL 32611, USA.
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44
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Sezer D, Roux B. Markov State and Diffusive Stochastic Models in Electron Spin Resonance. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2014; 797:115-38. [DOI: 10.1007/978-94-007-7606-7_10] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/14/2023]
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45
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Shapiro YE, Meirovitch E. The eigenmode perspective of NMR spin relaxation in proteins. J Chem Phys 2013; 139:225104. [DOI: 10.1063/1.4838436] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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46
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Circular dichroism and site-directed spin labeling reveal structural and dynamical features of high-pressure states of myoglobin. Proc Natl Acad Sci U S A 2013; 110:E4714-22. [PMID: 24248390 DOI: 10.1073/pnas.1320124110] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Excited states of proteins may play important roles in function, yet are difficult to study spectroscopically because of their sparse population. High hydrostatic pressure increases the equilibrium population of excited states, enabling their characterization [Akasaka K (2003) Biochemistry 42:10875-85]. High-pressure site-directed spin-labeling EPR (SDSL-EPR) was developed recently to map the site-specific structure and dynamics of excited states populated by pressure. To monitor global secondary structure content by circular dichroism (CD) at high pressure, a modified optical cell using a custom MgF2 window with a reduced aperture is introduced. Here, a combination of SDSL-EPR and CD is used to map reversible structural transitions in holomyoglobin and apomyoglobin (apoMb) as a function of applied pressure up to 2 kbar. CD shows that the high-pressure excited state of apoMb at pH 6 has helical content identical to that of native apoMb, but reversible changes reflecting the appearance of a conformational ensemble are observed by SDSL-EPR, suggesting a helical topology that fluctuates slowly on the EPR time scale. Although the high-pressure state of apoMb at pH 6 has been referred to as a molten globule, the data presented here reveal significant differences from the well-characterized pH 4.1 molten globule of apoMb. Pressure-populated states of both holomyoglobin and apoMb at pH 4.1 have significantly less helical structure, and for the latter, that may correspond to a transient folding intermediate.
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Lagerstedt JO, Petrlova J, Hilt S, Marek A, Chung Y, Sriram R, Budamagunta MS, Desreux JF, Thonon D, Jue T, Smirnov AI, Voss JC. EPR assessment of protein sites for incorporation of Gd(III) MRI contrast labels. CONTRAST MEDIA & MOLECULAR IMAGING 2013; 8:252-64. [PMID: 23606429 DOI: 10.1002/cmmi.1518] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/01/2012] [Revised: 10/30/2012] [Accepted: 11/03/2012] [Indexed: 11/06/2022]
Abstract
We have engineered apolipoprotein A-I (apoA-I), a major protein constituent of high-density lipoprotein (HDL), to contain DOTA-chelated Gd(III) as an MRI contrast agent for the purpose of imaging reconstituted HDL (rHDL) biodistribution, metabolism and regulation in vivo. This protein contrast agent was obtained by attaching the thiol-reactive Gd[MTS-ADO3A] label at Cys residues replaced at four distinct positions (52, 55, 76 and 80) in apoA-I. MRI of infused mice previously showed that the Gd-labeled apoA-I migrates to both the liver and the kidney, the organs responsible for HDL catabolism; however, the contrast properties of apoA-I are superior when the ADO3A moiety is located at position 55, compared with the protein labeled at positions 52, 76 or 80. It is shown here that continuous wave X-band (9 GHz) electron paramagnetic resonance (EPR) spectroscopy is capable of detecting differences in the Gd(III) signal when comparing the labeled protein in the lipid-free with the rHDL state. Furthermore, the values of NMR relaxivity obtained for labeled variants in both the lipid-free and rHDL states correlate to the product of the X-band Gd(III) spectral width and the collision frequency between a nitroxide spin label and a polar relaxation agent. Consistent with its superior relaxivity measured by NMR, the rHDL-associated apoA-I containing the Gd[MTS-ADO3A] probe attached to position 55 displays favorable dynamic and water accessibility properties as determined by X-band EPR. While room temperature EPR requires >1 m m Gd(III)-labeled and only >10 µ m nitroxide-labeled protein to resolve the spectrum, the volume requirement is exceptionally low (~5 µl). Thus, X-band EPR provides a practical assessment for the suitability of imaging candidates containing the site-directed ADO3A contrast probe.
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Affiliation(s)
- Jens O Lagerstedt
- Department of Experimental Medical Science, Lund University, Lund, Sweden
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Möbius K, Lubitz W, Savitsky A. High-field EPR on membrane proteins - crossing the gap to NMR. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2013; 75:1-49. [PMID: 24160760 DOI: 10.1016/j.pnmrs.2013.07.002] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/17/2013] [Revised: 07/15/2013] [Accepted: 07/15/2013] [Indexed: 06/02/2023]
Abstract
In this review on advanced EPR spectroscopy, which addresses both the EPR and NMR communities, considerable emphasis is put on delineating the complementarity of NMR and EPR concerning the measurement of molecular interactions in large biomolecules. From these interactions, detailed information can be revealed on structure and dynamics of macromolecules embedded in solution- or solid-state environments. New developments in pulsed microwave and sweepable cryomagnet technology as well as ultrafast electronics for signal data handling and processing have pushed to new horizons the limits of EPR spectroscopy and its multifrequency extensions concerning the sensitivity of detection, the selectivity with respect to interactions, and the resolution in frequency and time domains. One of the most important advances has been the extension of EPR to high magnetic fields and microwave frequencies, very much in analogy to what happens in NMR. This is exemplified by referring to ongoing efforts for signal enhancement in both NMR and EPR double-resonance techniques by exploiting dynamic nuclear or electron spin polarization via unpaired electron spins and their electron-nuclear or electron-electron interactions. Signal and resolution enhancements are particularly spectacular for double-resonance techniques such as ENDOR and PELDOR at high magnetic fields. They provide greatly improved orientational selection for disordered samples that approaches single-crystal resolution at canonical g-tensor orientations - even for molecules with small g-anisotropies. Exchange of experience between the EPR and NMR communities allows for handling polarization and resolution improvement strategies in an optimal manner. Consequently, a dramatic improvement of EPR detection sensitivity could be achieved, even for short-lived paramagnetic reaction intermediates. Unique structural and dynamic information is thus revealed that can hardly be obtained by any other analytical techniques. Micromolar quantities of sample molecules have become sufficient to characterize stable and transient reaction intermediates of complex molecular systems - offering highly interesting applications for chemists, biochemists and molecular biologists. In three case studies, representative examples of advanced EPR spectroscopy are reviewed: (I) High-field PELDOR and ENDOR structure determination of cation-anion radical pairs in reaction centers from photosynthetic purple bacteria and cyanobacteria (Photosystem I); (II) High-field ENDOR and ELDOR-detected NMR spectroscopy on the oxygen-evolving complex of Photosystem II; and (III) High-field electron dipolar spectroscopy on nitroxide spin-labelled bacteriorhodopsin for structure-function studies. An extended conclusion with an outlook to further developments and applications is also presented.
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Affiliation(s)
- Klaus Möbius
- Max Planck Institute for Chemical Energy Conversion, Stiftstrasse 34-36, D-45470 Mülheim an der Ruhr, Germany; Department of Physics, Free University Berlin, Arnimallee 14, D-14195 Berlin, Germany.
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Edwards DT, Zhang Y, Glaser SJ, Han S, Sherwin MS. Phase cycling with a 240 GHz, free electron laser-powered electron paramagnetic resonance spectrometer. Phys Chem Chem Phys 2013; 15:5707-19. [PMID: 23474874 DOI: 10.1039/c3cp44492a] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Electron paramagnetic resonance (EPR) powered by a free electron laser (FEL) has been shown to dramatically expand the capabilities of EPR at frequencies above ~100 GHz, where other high-power sources are unavailable. High-power pulses are necessary to achieve fast (<10 ns) spin rotations in order to alleviate the limited excitation bandwidth and time resolution that typically hamper pulsed EPR at these high frequencies. While at these frequencies, an FEL is the only source that provides ~1 kW of power and can be tuned continuously up to frequencies above 1 THz, it has only recently been implemented for one- and two-pulse EPR, and the capabilities of the FEL as an EPR source are still being expanded. This manuscript presents phase cycling of two pulses in an FEL-EPR spectrometer operating at 240 GHz. Given that the FEL, unlike amplifiers, cannot be easily phase-locked to a reference source, we instead apply retrospective data processing to measure the relative phase of each FEL pulse in order to correct the signal phase accordingly. This allows the measured signal to be averaged coherently, and the randomly changing phase of the FEL pulse results in a stochastic phase cycle, which, in the limit of many pulses, efficiently cancels artifacts and improves sensitivity. Further, the relative phase between the first and second pulse, which originates from the difference in path length traversed by each pulse, can be experimentally measured without phase-sensitive detection. We show that the relative phase of the two pulses can be precisely tuned, as well as distinctly switched by a fixed amount, with the insertion of a dielectric material into the quasi-optical path of one of the pulses. Taken together, these techniques offer many of the advantages of arbitrary phase control, and allow application of phase cycling to dramatically enhance signal quality in pulsed EPR experiments utilizing high-power sources that cannot be phase-locked.
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Affiliation(s)
- Devin T Edwards
- Department of Physics, University of California, Santa Barbara, Santa Barbara, California 93106, USA.
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Sahu ID, McCarrick RM, Lorigan GA. Use of electron paramagnetic resonance to solve biochemical problems. Biochemistry 2013; 52:5967-84. [PMID: 23961941 PMCID: PMC3839053 DOI: 10.1021/bi400834a] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Electron paramagnetic resonance (EPR) spectroscopy is a very powerful biophysical tool that can provide valuable structural and dynamic information about a wide variety of biological systems. The intent of this review is to provide a general overview for biochemists and biological researchers of the most commonly used EPR methods and how these techniques can be used to answer important biological questions. The topics discussed could easily fill one or more textbooks; thus, we present a brief background on several important biological EPR techniques and an overview of several interesting studies that have successfully used EPR to solve pertinent biological problems. The review consists of the following sections: an introduction to EPR techniques, spin-labeling methods, and studies of naturally occurring organic radicals and EPR active transition metal systems that are presented as a series of case studies in which EPR spectroscopy has been used to greatly further our understanding of several important biological systems.
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Affiliation(s)
- Indra D. Sahu
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH
| | | | - Gary A. Lorigan
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH
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