1
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Herzfeld J. Art, fact and artifact: reflections on the cross-talk between theory and experiment. Phys Chem Chem Phys 2024; 26:9848-9855. [PMID: 38502180 DOI: 10.1039/d4cp00005f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/20/2024]
Abstract
With the increasing sophistication of each, theory and experiment have become highly specialized endeavors conducted by separate research groups. A result has been a weakening of the coupling between them and occasional hostility. Examples are given and suggestions are offered for strengthening the traditional synergy between theory and experiment.
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2
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Herzfeld J. Adventures in interdisciplinary science: a half century at the nexus between chemistry, physics and biology. Phys Chem Chem Phys 2024; 26:6483-6489. [PMID: 38345336 DOI: 10.1039/d4cp90021a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/23/2024]
Abstract
A look back over five decades of research.
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Affiliation(s)
- Judith Herzfeld
- Department of Chemistry, Brandeis University, Waltham, Massachusetts, USA.
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3
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Quan Y, Ouyang Y, Mardini M, Palani RS, Banks D, Kempf J, Wenckebach WT, Griffin RG. Resonant Mixing Dynamic Nuclear Polarization. J Phys Chem Lett 2023; 14:7007-7013. [PMID: 37523253 DOI: 10.1021/acs.jpclett.3c01869] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/02/2023]
Abstract
We propose a mechanism for dynamic nuclear polarization that is different from the well-known Overhauser effect, solid effect, cross effect, and thermal mixing processes. We term it Resonant Mixing (RM), and we show that it arises from the evolution of the density matrix for a simple electron-nucleus coupled spin pair subject to weak microwave irradiation, the same interactions as the solid effect. However, the SE is optimal when the microwave field is off-resonance, whereas RM is optimal when the microwave field is on-resonance and involves the mixing of states by the microwave field together with the electron-nuclear coupling. Finally, we argue that this mechanism is responsible for the observed dispersive-shaped DNP field profile for trityl samples near the electron paramagnetic resonance center.
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Affiliation(s)
- Yifan Quan
- Francis Bitter Magnet Laboratory and Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Yifu Ouyang
- Francis Bitter Magnet Laboratory and Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Michael Mardini
- Francis Bitter Magnet Laboratory and Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Ravi Shankar Palani
- Francis Bitter Magnet Laboratory and Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Daniel Banks
- Bruker Biospin, 15 Fortune Drive, Billerica, Massachusetts 01821, United States
| | - James Kempf
- Bruker Biospin, 15 Fortune Drive, Billerica, Massachusetts 01821, United States
| | - W Tom Wenckebach
- Paul Scherrer Institute, 5232 Villigen PSI, Switzerland
- National High Magnetic Field Laboratory, University of Florida, Gainesville, Florida 32310, United States
| | - Robert G Griffin
- Francis Bitter Magnet Laboratory and Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
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4
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Amerein C, Banerjee U, Pang Z, Lu W, Pimenta V, Tan KO. In-house fabrication of 1.3 to 7 mm MAS drive caps using desktop 3D printers. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2023; 348:107391. [PMID: 36801500 DOI: 10.1016/j.jmr.2023.107391] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/22/2023] [Revised: 01/31/2023] [Accepted: 02/01/2023] [Indexed: 06/18/2023]
Abstract
The 3D-printing technology has emerged as a well-developed method to produce parts with considerably low cost and yet with high precision (<100 μm). Recent literature has shown that the 3D-printing technology can be exploited to fabricate a magic-angle spinning (MAS) system in solid-state nuclear magnetic resonance (NMR) spectroscopy. In particular, it was demonstrated that advanced industry-grade 3D printers could fabricate 3.2 mm MAS drive caps with intricate features, and the caps were shown to spin > 20 kHz. Here, we show that not only lab-affordable benchtop 3D printers can produce 3.2 mm drive caps with a similar quality as the commercialized version, but also smaller 2.5 mm and 1.3 mm MAS drive caps-despite a slight compromise in performance. All in-house fabricated drive caps (1.3 to 7 mm) can be consistently reproduced (>90 %) and achieve excellent spinning performances. In summary, the > 3.2 mm systems have similar performances as the commercial systems, while the 2.5- and 1.3-mm caps can spin up to 26 kHz ± 2 Hz, and 46 kHz ± 1 Hz, respectively. The low-cost and fast in-house fabrication of MAS drive caps allows easy prototyping of new MAS drive cap models and, possibly, new NMR applications. For instance, we have fabricated a 4 mm drive cap with a center hole that could allow better light penetration or sample insertion during MAS. Besides, an added groove design on the drive cap allows an airtight seal suitable for probing air- or moisture-sensitive materials. Moreover, the 3D-printed cap was shown to be robust for low-temperature MAS experiments at ∼ 100 K, making it suitable for DNP experiments.
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Affiliation(s)
- Cyriaque Amerein
- Laboratoire des Biomolécules, LBM, Département de Chimie, École Normale Supérieure, PSL University, Sorbonne Université, CNRS, 75005 Paris, France
| | - Utsab Banerjee
- Laboratoire des Biomolécules, LBM, Département de Chimie, École Normale Supérieure, PSL University, Sorbonne Université, CNRS, 75005 Paris, France
| | - Zhenfeng Pang
- Laboratoire des Biomolécules, LBM, Département de Chimie, École Normale Supérieure, PSL University, Sorbonne Université, CNRS, 75005 Paris, France
| | - Wenqing Lu
- Institut des Matériaux Poreux de Paris, Ecole Normale Supérieure, ESPCI Paris, CNRS, PSL University, 75005 Paris, France
| | - Vanessa Pimenta
- Institut des Matériaux Poreux de Paris, Ecole Normale Supérieure, ESPCI Paris, CNRS, PSL University, 75005 Paris, France
| | - Kong Ooi Tan
- Laboratoire des Biomolécules, LBM, Département de Chimie, École Normale Supérieure, PSL University, Sorbonne Université, CNRS, 75005 Paris, France.
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5
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Michaelis VK, Keeler EG, Bahri S, Ong TC, Daviso E, Colvin MT, Griffin RG. Biradical Polarizing Agents at High Fields. J Phys Chem B 2022; 126:7847-7856. [PMID: 36194539 PMCID: PMC9886493 DOI: 10.1021/acs.jpcb.2c03985] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The sensitivity enhancements available from dynamic nuclear polarization (DNP) are rapidly reshaping the research landscape and expanding the field of nuclear magnetic resonance (NMR) spectroscopy as a tool for solving complex chemical and structural problems. The past decade has seen considerable advances in this burgeoning method, while efforts to further improve its capabilities continue along many avenues. In this report, we examine the influence of static magnetic field strength and temperature on the reported 1H DNP enhancements from three conventional organic biradicals: TOTAPOL, AMUPol, and SPIROPOL. In contrast to the conventional wisdom, our findings show that at liquid nitrogen temperatures and 700 MHz/460.5 GHz, these three bisnitroxides all provide similar 1H DNP enhancements, ε ≈ 60. Furthermore, we investigate the influence of temperature, microwave power, magnetic field strength, and protein sample deuteration on the NMR experimental results.
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Affiliation(s)
- Vladimir K. Michaelis
- Department of Chemistry and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge 02139 Massachusetts, United States; Department of Chemistry, University of Alberta, Edmonton T6G 2G2 Alberta, Canada
| | - Eric G. Keeler
- Department of Chemistry and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge 02139 Massachusetts, United States; New York Structural Biology Center, New York 10027, New York, United States
| | - Salima Bahri
- Department of Chemistry and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge 02139 Massachusetts, United States; Bijvoet Center for Biomolecular Research, Utrecht University, Utrecht 3584CH, The Netherlands
| | - Ta-Chung Ong
- Department of Chemistry and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge 02139 Massachusetts, United States; Department of Chemistry and Biochemistry, University of California Los Angeles, Los Angeles 90095 California, United States
| | - Eugenio Daviso
- Department of Chemistry and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge 02139 Massachusetts, United States; Department of Scientific Support and Applications Development, Covaris LLC, Woburn 01801 Massachusetts, United States
| | - Michael T. Colvin
- Department of Chemistry and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge 02139 Massachusetts, United States; Ortho Clinical Diagnostics, Rochester 14626 New York, United States
| | - Robert G. Griffin
- Department of Chemistry and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge 02139 Massachusetts, United States
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6
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Chow WY, De Paëpe G, Hediger S. Biomolecular and Biological Applications of Solid-State NMR with Dynamic Nuclear Polarization Enhancement. Chem Rev 2022; 122:9795-9847. [PMID: 35446555 DOI: 10.1021/acs.chemrev.1c01043] [Citation(s) in RCA: 25] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Solid-state NMR spectroscopy (ssNMR) with magic-angle spinning (MAS) enables the investigation of biological systems within their native context, such as lipid membranes, viral capsid assemblies, and cells. However, such ambitious investigations often suffer from low sensitivity due to the presence of significant amounts of other molecular species, which reduces the effective concentration of the biomolecule or interaction of interest. Certain investigations requiring the detection of very low concentration species remain unfeasible even with increasing experimental time for signal averaging. By applying dynamic nuclear polarization (DNP) to overcome the sensitivity challenge, the experimental time required can be reduced by orders of magnitude, broadening the feasible scope of applications for biological solid-state NMR. In this review, we outline strategies commonly adopted for biological applications of DNP, indicate ongoing challenges, and present a comprehensive overview of biological investigations where MAS-DNP has led to unique insights.
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Affiliation(s)
- Wing Ying Chow
- Univ. Grenoble Alpes, CEA, CNRS, Interdisciplinary Research Institute of Grenoble (IRIG), Modeling and Exploration of Materials Laboratory (MEM), 38054 Grenoble, France.,Univ. Grenoble Alpes, CEA, CNRS, Inst. Biol. Struct. IBS, 38044 Grenoble, France
| | - Gaël De Paëpe
- Univ. Grenoble Alpes, CEA, CNRS, Interdisciplinary Research Institute of Grenoble (IRIG), Modeling and Exploration of Materials Laboratory (MEM), 38054 Grenoble, France
| | - Sabine Hediger
- Univ. Grenoble Alpes, CEA, CNRS, Interdisciplinary Research Institute of Grenoble (IRIG), Modeling and Exploration of Materials Laboratory (MEM), 38054 Grenoble, France
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7
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Tan KO, Griffin RG. Observation of a Four-Spin Solid Effect. J Chem Phys 2022; 156:174201. [PMID: 35525661 PMCID: PMC9068241 DOI: 10.1063/5.0091663] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
The two-spin solid effect (2SSE) is one of the established continuous wave dynamic nuclear polarization mechanisms that enables enhancement of nuclear magnetic resonance signals. It functions via a state-mixing mechanism that mediates the excitation of forbidden transitions in an electron–nuclear spin system. Specifically, microwave irradiation at frequencies ωμw ∼ ω0S ± ω0I, where ω0S and ω0I are electron and nuclear Larmor frequencies, respectively, yields enhanced nuclear spin polarization. Following the recent rediscovery of the three-spin solid effect (3SSE) [Tan et al., Sci. Adv. 5, eaax2743 (2019)], where the matching condition is given by ωμw = ω0S ± 2ω0I, we report here the first direct observation of the four-spin solid effect (4SSE) at ωμw = ω0S ± 3ω0I. The forbidden double- and quadruple-quantum transitions were observed in samples containing trityl radicals dispersed in a glycerol–water mixture at 0.35 T/15 MHz/9.8 GHz and 80 K. We present a derivation of the 4SSE effective Hamiltonian, matching conditions, and transition probabilities. Finally, we show that the experimental observations agree with the results from numerical simulations and analytical theory.
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Affiliation(s)
| | - Robert G. Griffin
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, United States of America
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8
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Biedenbänder T, Aladin V, Saeidpour S, Corzilius B. Dynamic Nuclear Polarization for Sensitivity Enhancement in Biomolecular Solid-State NMR. Chem Rev 2022; 122:9738-9794. [PMID: 35099939 DOI: 10.1021/acs.chemrev.1c00776] [Citation(s) in RCA: 42] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Solid-state NMR with magic-angle spinning (MAS) is an important method in structural biology. While NMR can provide invaluable information about local geometry on an atomic scale even for large biomolecular assemblies lacking long-range order, it is often limited by low sensitivity due to small nuclear spin polarization in thermal equilibrium. Dynamic nuclear polarization (DNP) has evolved during the last decades to become a powerful method capable of increasing this sensitivity by two to three orders of magnitude, thereby reducing the valuable experimental time from weeks or months to just hours or days; in many cases, this allows experiments that would be otherwise completely unfeasible. In this review, we give an overview of the developments that have opened the field for DNP-enhanced biomolecular solid-state NMR including state-of-the-art applications at fast MAS and high magnetic field. We present DNP mechanisms, polarizing agents, and sample constitution methods suitable for biomolecules. A wide field of biomolecular NMR applications is covered including membrane proteins, amyloid fibrils, large biomolecular assemblies, and biomaterials. Finally, we present perspectives and recent developments that may shape the field of biomolecular DNP in the future.
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Affiliation(s)
- Thomas Biedenbänder
- Institute of Chemistry, University of Rostock, Albert-Einstein-Straße 3a, 18059 Rostock, Germany.,Department Life, Light & Matter, University of Rostock, Albert-Einstein-Straße 25, 18059 Rostock, Germany
| | - Victoria Aladin
- Institute of Chemistry, University of Rostock, Albert-Einstein-Straße 3a, 18059 Rostock, Germany.,Department Life, Light & Matter, University of Rostock, Albert-Einstein-Straße 25, 18059 Rostock, Germany
| | - Siavash Saeidpour
- Institute of Chemistry, University of Rostock, Albert-Einstein-Straße 3a, 18059 Rostock, Germany.,Department Life, Light & Matter, University of Rostock, Albert-Einstein-Straße 25, 18059 Rostock, Germany
| | - Björn Corzilius
- Institute of Chemistry, University of Rostock, Albert-Einstein-Straße 3a, 18059 Rostock, Germany.,Department Life, Light & Matter, University of Rostock, Albert-Einstein-Straße 25, 18059 Rostock, Germany
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9
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Bondar AN. Mechanisms of long-distance allosteric couplings in proton-binding membrane transporters. ADVANCES IN PROTEIN CHEMISTRY AND STRUCTURAL BIOLOGY 2022; 128:199-239. [PMID: 35034719 DOI: 10.1016/bs.apcsb.2021.09.002] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Abstract
Membrane transporters that use proton binding and proton transfer for function couple local protonation change with changes in protein conformation and water dynamics. Changes of protein conformation might be required to allow transient formation of hydrogen-bond networks that bridge proton donor and acceptor pairs separated by long distances. Inter-helical hydrogen-bond networks adjust rapidly to protonation change, and ensure rapid response of the protein structure and dynamics. Membrane transporters with known three-dimensional structures and proton-binding groups inform on general principles of protonation-coupled protein conformational dynamics. Inter-helical hydrogen bond motifs between proton-binding carboxylate groups and a polar sidechain are observed in unrelated membrane transporters, suggesting common principles of coupling protonation change with protein conformational dynamics.
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Affiliation(s)
- Ana-Nicoleta Bondar
- University of Bucharest, Faculty of Physics, Măgurele, Romania; Forschungszentrum Jülich, Institute of Computational Biomedicine, Jülich, Germany.
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10
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Liang L, Ji Y, Chen K, Gao P, Zhao Z, Hou G. Solid-State NMR Dipolar and Chemical Shift Anisotropy Recoupling Techniques for Structural and Dynamical Studies in Biological Systems. Chem Rev 2022; 122:9880-9942. [PMID: 35006680 DOI: 10.1021/acs.chemrev.1c00779] [Citation(s) in RCA: 16] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
With the development of NMR methodology and technology during the past decades, solid-state NMR (ssNMR) has become a particularly important tool for investigating structure and dynamics at atomic scale in biological systems, where the recoupling techniques play pivotal roles in modern high-resolution MAS NMR. In this review, following a brief introduction on the basic theory of recoupling in ssNMR, we highlight the recent advances in dipolar and chemical shift anisotropy recoupling methods, as well as their applications in structural determination and dynamical characterization at multiple time scales (i.e., fast-, intermediate-, and slow-motion). The performances of these prevalent recoupling techniques are compared and discussed in multiple aspects, together with the representative applications in biomolecules. Given the recent emerging advances in NMR technology, new challenges for recoupling methodology development and potential opportunities for biological systems are also discussed.
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Affiliation(s)
- Lixin Liang
- State Key Laboratory of Catalysis, National Laboratory for Clean Energy, 2011-Collaborative Innovation Center of Chemistry for Energy Materials, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Zhongshan Road 457, Dalian 116023, China.,University of Chinese Academy of Sciences, Beijing 100049, China
| | - Yi Ji
- State Key Laboratory of Catalysis, National Laboratory for Clean Energy, 2011-Collaborative Innovation Center of Chemistry for Energy Materials, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Zhongshan Road 457, Dalian 116023, China.,University of Chinese Academy of Sciences, Beijing 100049, China
| | - Kuizhi Chen
- State Key Laboratory of Catalysis, National Laboratory for Clean Energy, 2011-Collaborative Innovation Center of Chemistry for Energy Materials, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Zhongshan Road 457, Dalian 116023, China
| | - Pan Gao
- State Key Laboratory of Catalysis, National Laboratory for Clean Energy, 2011-Collaborative Innovation Center of Chemistry for Energy Materials, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Zhongshan Road 457, Dalian 116023, China
| | - Zhenchao Zhao
- State Key Laboratory of Catalysis, National Laboratory for Clean Energy, 2011-Collaborative Innovation Center of Chemistry for Energy Materials, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Zhongshan Road 457, Dalian 116023, China
| | - Guangjin Hou
- State Key Laboratory of Catalysis, National Laboratory for Clean Energy, 2011-Collaborative Innovation Center of Chemistry for Energy Materials, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Zhongshan Road 457, Dalian 116023, China
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11
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1H detection and dynamic nuclear polarization-enhanced NMR of Aβ 1-42 fibrils. Proc Natl Acad Sci U S A 2022; 119:2114413119. [PMID: 34969859 PMCID: PMC8740738 DOI: 10.1073/pnas.2114413119] [Citation(s) in RCA: 19] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/03/2021] [Indexed: 12/25/2022] Open
Abstract
Amyloid-β (Aβ) is the subject of intense scrutiny because of its close association with Alzheimer’s disease (AD), which currently afflicts about 50 million people worldwide. The results reported in this manuscript focus on the new possibilities provided by ultrafast magic-angle spinning (MAS) 1H detection and fast-MAS dynamic nuclear polarization (DNP), which have ushered in a new era for NMR-based structural biology, but whose potential has not yet been fully exploited for the structural investigation of complex amyloid assemblies. This work demonstrates the expeditious structural analysis of amyloid fibrils, without requiring preparation of large sample amounts, and sets the stage for future studies of unlabeled AD peptides derived from tissue samples available in limited quantities. Several publications describing high-resolution structures of amyloid-β (Aβ) and other fibrils have demonstrated that magic-angle spinning (MAS) NMR spectroscopy is an ideal tool for studying amyloids at atomic resolution. Nonetheless, MAS NMR suffers from low sensitivity, requiring relatively large amounts of samples and extensive signal acquisition periods, which in turn limits the questions that can be addressed by atomic-level spectroscopic studies. Here, we show that these drawbacks are removed by utilizing two relatively recent additions to the repertoire of MAS NMR experiments—namely, 1H detection and dynamic nuclear polarization (DNP). We show resolved and sensitive two-dimensional (2D) and three-dimensional (3D) correlations obtained on 13C,15N-enriched, and fully protonated samples of M0Aβ1-42 fibrils by high-field 1H-detected NMR at 23.4 T and 18.8 T, and 13C-detected DNP MAS NMR at 18.8 T. These spectra enable nearly complete resonance assignment of the core of M0Aβ1-42 (K16-A42) using submilligram sample quantities, as well as the detection of numerous unambiguous internuclear proximities defining both the structure of the core and the arrangement of the different monomers. An estimate of the sensitivity of the two approaches indicates that the DNP experiments are currently ∼6.5 times more sensitive than 1H detection. These results suggest that 1H detection and DNP may be the spectroscopic approaches of choice for future studies of Aβ and other amyloid systems.
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12
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Abstract
Microbial rhodopsins represent the most abundant phototrophic systems known today. A similar molecular architecture with seven transmembrane helices and a retinal cofactor linked to a lysine in helix 7 enables a wide range of functions including ion pumping, light-controlled ion channel gating, or sensing. Deciphering their molecular mechanisms therefore requires a combined consideration of structural, functional, and spectroscopic data in order to identify key factors determining their function. Important insight can be gained by solid-state NMR spectroscopy by which the large homo-oligomeric rhodopsin complexes can be studied directly within lipid bilayers. This chapter describes the methodological background and the necessary sample preparation requirements for the study of photointermediates, for the analysis of protonation states, H-bonding and chromophore conformations, for 3D structure determination, and for probing oligomer interfaces of microbial rhodopsins. The use of data extracted from these NMR experiments is discussed in the context of complementary biophysical methods.
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Affiliation(s)
- Clara Nassrin Kriebel
- Institute of Biophysical Chemistry, Goethe University Frankfurt, Frankfurt am Main, Germany
- Centre for Biomolecular Magnetic Resonance, Goethe University Frankfurt, Frankfurt am Main, Germany
| | - Johanna Becker-Baldus
- Institute of Biophysical Chemistry, Goethe University Frankfurt, Frankfurt am Main, Germany
- Centre for Biomolecular Magnetic Resonance, Goethe University Frankfurt, Frankfurt am Main, Germany
| | - Clemens Glaubitz
- Institute of Biophysical Chemistry, Goethe University Frankfurt, Frankfurt am Main, Germany.
- Centre for Biomolecular Magnetic Resonance, Goethe University Frankfurt, Frankfurt am Main, Germany.
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13
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Yang C, Ooi Tan K, Griffin RG. DNPSOUP: A simulation software package for dynamic nuclear polarization. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2022; 334:107107. [PMID: 34894420 PMCID: PMC8819672 DOI: 10.1016/j.jmr.2021.107107] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/05/2021] [Revised: 11/04/2021] [Accepted: 11/05/2021] [Indexed: 06/01/2023]
Abstract
Dynamic Nuclear Polarization Simulation Optimized with a Unified Propagator (DNPSOUP) is an open-source numerical software program that models spin dynamics for dynamic nuclear polarization (DNP). The software package utilizes a direct numerical approach using the inhomogeneous master equation to treat the time evolution of the spin density operator under coherent Hamiltonians and stochastic relaxation effects. Here we present the details of the theory behind the software, starting from the master equation, and arriving at characteristic operators for any section of density operator time-evolution. We then provide an overview of the DNPSOUP software architecture. The efficacy of the program is demonstrated by simulating DNP field profiles on small spin systems exploiting both continuous wave and time-domain DNP mechanisms. Examples include Zeeman field profiles for the solid effect, Overhauser effect, and cross effect, and microwave field profiles for NOVEL, off-resonance NOVEL, the integrated solid effect, the stretched solid effect, and TOP-DNP. The software should facilitate a better understanding of the DNP process, aid in the design of optimized DNP polarizing agents, and allow us to examine new pulsed DNP methods at conditions that are not currently experimentally accessible, especially at high magnetic fields with high-power microwave pulses.
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Affiliation(s)
- Chen Yang
- Department of Chemistry and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, United States; Aspen Technology, Inc., 20 Crosby Drive, Bedford, MA 01730, United States
| | - Kong Ooi Tan
- Department of Chemistry and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, United States; Laboratoire des Biomolécules, LBM, Département de Chimie, École Normale Supérieure, PSL University, Sorbonne Université, CNRS, 75005 Paris, France
| | - Robert G Griffin
- Department of Chemistry and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, United States.
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14
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Delage-Laurin L, Palani RS, Golota N, Mardini M, Ouyang Y, Tan KO, Swager TM, Griffin RG. Overhauser Dynamic Nuclear Polarization with Selectively Deuterated BDPA Radicals. J Am Chem Soc 2021; 143:20281-20290. [PMID: 34813311 DOI: 10.1021/jacs.1c09406] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
The Overhauser effect (OE), commonly observed in NMR spectra of liquids and conducting solids, was recently discovered in insulating solids doped with the radical 1,3-bisdiphenylene-2-phenylallyl (BDPA). However, the mechanism of polarization transfer in OE-DNP in insulators is yet to be established, but hyperfine coupling of the radical to protons in BDPA has been proposed. In this paper we present a study that addresses the role of hyperfine couplings via the EPR and DNP measurements on some selectively deuterated BDPA radicals synthesized for this purpose. Newly developed synthetic routes enable selective deuteration at orthogonal positions or perdeuteration of the fluorene moieties with 2H incorporation of >93%. The fluorene moieties were subsequently used to synthesize two octadeuterated BDPA radicals, 1,3-[α,γ-d8]-BDPA and 1,3-[β,δ-d8]-BDPA, and a BDPA radical with perdeuterated fluorene moieties, 1,3-[α,β,γ,δ-d16]-BDPA. In contrast to the strong positive OE enhancement observed in degassed samples of fully protonated h21-BDPA (ε ∼ +70), perdeuteration of the fluorenes results in a negative enhancement (ε ∼ -13), while selective deuteration of α- and γ-positions (aiso ∼ 5.4 MHz) in BDPA results in a weak negative OE enhancement (ε ∼ -1). Furthermore, deuteration of β- and δ-positions (aiso ∼ 1.2 MHz) results in a positive OE enhancement (ε ∼ +36), albeit with a reduced magnitude relative to that observed in fully protonated BDPA. Our results clearly show the role of the hyperfine coupled α and γ 1H spins in the BDPA radical in determining the dominance of the zero and double-quantum cross-relaxation pathways and the polarization-transfer mechanism to the bulk matrix.
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Affiliation(s)
- Léo Delage-Laurin
- Institute for Soldier Nanotechnologies, Cambridge, Massachusetts 02139, United States
| | | | | | | | | | | | - Timothy M Swager
- Institute for Soldier Nanotechnologies, Cambridge, Massachusetts 02139, United States
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15
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Maag D, Mast T, Elstner M, Cui Q, Kubař T. O to bR transition in bacteriorhodopsin occurs through a proton hole mechanism. Proc Natl Acad Sci U S A 2021; 118:e2024803118. [PMID: 34561302 PMCID: PMC8488608 DOI: 10.1073/pnas.2024803118] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/04/2021] [Indexed: 12/27/2022] Open
Abstract
Extensive classical and quantum mechanical/molecular mechanical (QM/MM) molecular dynamics simulations are used to establish the structural features of the O state in bacteriorhodopsin (bR) and its conversion back to the bR ground state. The computed free energy surface is consistent with available experimental data for the kinetics and thermodynamics of the O to bR transition. The simulation results highlight the importance of the proton release group (PRG, consisting of Glu194/204) and the conserved arginine 82 in modulating the hydration level of the protein cavity. In particular, in the O state, deprotonation of the PRG and downward rotation of Arg82 lead to elevated hydration level and a continuous water network that connects the PRG to the protonated Asp85. Proton exchange through this water network is shown by ∼0.1-μs semiempirical QM/MM free energy simulations to occur through the generation and propagation of a proton hole, which is relayed by Asp212 and stabilized by Arg82. This mechanism provides an explanation for the observation that the D85S mutant of bacteriorhodopsin pumps chloride ions. The electrostatics-hydration coupling mechanism and the involvement of all titration states of water are likely applicable to many biomolecules involved in bioenergetic transduction.
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Affiliation(s)
- Denis Maag
- Institute of Physical Chemistry, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany
| | - Thilo Mast
- Institute of Physical Chemistry, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany
| | - Marcus Elstner
- Institute of Physical Chemistry, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany
- Institute for Biological Interfaces, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany
| | - Qiang Cui
- Department of Chemistry, Boston University, Boston, MA 02215
- Department of Physics, Boston University, Boston, MA 02215
- Department of Biomedical Engineering, Boston University, Boston, MA 02215
| | - Tomáš Kubař
- Institute of Physical Chemistry, Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany;
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16
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Can TV, Tan KO, Yang C, Weber RT, Griffin RG. Time domain DNP at 1.2 T. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2021; 329:107012. [PMID: 34186299 PMCID: PMC9148420 DOI: 10.1016/j.jmr.2021.107012] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/05/2021] [Revised: 05/26/2021] [Accepted: 05/27/2021] [Indexed: 05/28/2023]
Abstract
We present the results of an experimental pulsed DNP study at 1.2 T (33.5 GHz/51 MHz electron and 1H Larmor frequencies, respectively). The results include a comparison of constant-amplitude NOVEL (CA-NOVEL), ramped-amplitude NOVEL (RA-NOVEL) and the frequency-swept integrated solid effect (FS-ISE) experiments all of which were performed at the NOVEL matching condition, ω1S=ω0I, where ω1S is the electron Rabi frequency andω0I the proton Larmor frequency. To the best of our knowledge, this is the first pulsed DNP study carried out at field higher than X-band (0.35 T) using the NOVEL condition. A combination of high microwave power (∼150 W) and a microwave cavity with a high Q (∼500) allowed us to satisfy the NOVEL matching condition. We also observed stretched solid effect (S2E) contributions in the Zeeman field profiles when chirped pulses are applied. Furthermore, the high quality factor of the cavity limits the concentration of the radical to ∼5 mM and generates a hysteresis in the FS-ISE experiments. Nevertheless, we observe very high DNP enhancements that are comparable to the results at X-band. These promising outcomes suggest the importance of further studies at even higher fields that delineate the instrumentation and methods required for time domain DNP.
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Affiliation(s)
- T V Can
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, United States; Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, United States
| | - K O Tan
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, United States; Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, United States
| | - C Yang
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, United States; Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, United States
| | - R T Weber
- Bruker BioSpin Corporation, Billerica, MA 01821, United States
| | - R G Griffin
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, United States; Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA 02139, United States
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17
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Bondar AN. Proton-Binding Motifs of Membrane-Bound Proteins: From Bacteriorhodopsin to Spike Protein S. Front Chem 2021; 9:685761. [PMID: 34136464 PMCID: PMC8203321 DOI: 10.3389/fchem.2021.685761] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2021] [Accepted: 05/18/2021] [Indexed: 11/13/2022] Open
Abstract
Membrane-bound proteins that change protonation during function use specific protein groups to bind and transfer protons. Knowledge of the identity of the proton-binding groups is of paramount importance to decipher the reaction mechanism of the protein, and protonation states of prominent are studied extensively using experimental and computational approaches. Analyses of model transporters and receptors from different organisms, and with widely different biological functions, indicate common structure-sequence motifs at internal proton-binding sites. Proton-binding dynamic hydrogen-bond networks that are exposed to the bulk might provide alternative proton-binding sites and proton-binding pathways. In this perspective article I discuss protonation coupling and proton binding at internal and external carboxylate sites of proteins that use proton transfer for function. An inter-helical carboxylate-hydroxyl hydrogen-bond motif is present at functionally important sites of membrane proteins from archaea to the brain. External carboxylate-containing H-bond clusters are observed at putative proton-binding sites of protonation-coupled model proteins, raising the question of similar functionality in spike protein S.
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Affiliation(s)
- Ana-Nicoleta Bondar
- Freie Universität Berlin, Department of Physics, Theoretical Molecular Biophysics Group, Berlin, Germany
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18
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Pintér G, Hohmann K, Grün J, Wirmer-Bartoschek J, Glaubitz C, Fürtig B, Schwalbe H. Real-time nuclear magnetic resonance spectroscopy in the study of biomolecular kinetics and dynamics. MAGNETIC RESONANCE (GOTTINGEN, GERMANY) 2021; 2:291-320. [PMID: 37904763 PMCID: PMC10539803 DOI: 10.5194/mr-2-291-2021] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/03/2021] [Accepted: 04/07/2021] [Indexed: 11/01/2023]
Abstract
The review describes the application of nuclear magnetic resonance (NMR) spectroscopy to study kinetics of folding, refolding and aggregation of proteins, RNA and DNA. Time-resolved NMR experiments can be conducted in a reversible or an irreversible manner. In particular, irreversible folding experiments pose large requirements for (i) signal-to-noise due to the time limitations and (ii) synchronising of the refolding steps. Thus, this contribution discusses the application of methods for signal-to-noise increases, including dynamic nuclear polarisation, hyperpolarisation and photo-CIDNP for the study of time-resolved NMR studies. Further, methods are reviewed ranging from pressure and temperature jump, light induction to rapid mixing to induce rapidly non-equilibrium conditions required to initiate folding.
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Affiliation(s)
- György Pintér
- Institute for Organic Chemistry and Chemical Biology, Center for
Biomolecular Magnetic Resonance (BMRZ), Johann Wolfgang
Goethe-Universität Frankfurt, Frankfurt 60438, Germany
| | - Katharina F. Hohmann
- Institute for Organic Chemistry and Chemical Biology, Center for
Biomolecular Magnetic Resonance (BMRZ), Johann Wolfgang
Goethe-Universität Frankfurt, Frankfurt 60438, Germany
| | - J. Tassilo Grün
- Institute for Organic Chemistry and Chemical Biology, Center for
Biomolecular Magnetic Resonance (BMRZ), Johann Wolfgang
Goethe-Universität Frankfurt, Frankfurt 60438, Germany
| | - Julia Wirmer-Bartoschek
- Institute for Organic Chemistry and Chemical Biology, Center for
Biomolecular Magnetic Resonance (BMRZ), Johann Wolfgang
Goethe-Universität Frankfurt, Frankfurt 60438, Germany
| | - Clemens Glaubitz
- Institute for Biophysical Chemistry, Center for Biomolecular Magnetic Resonance (BMRZ), Johann Wolfgang Goethe-Universität Frankfurt, Frankfurt 60438, Germany
| | - Boris Fürtig
- Institute for Organic Chemistry and Chemical Biology, Center for
Biomolecular Magnetic Resonance (BMRZ), Johann Wolfgang
Goethe-Universität Frankfurt, Frankfurt 60438, Germany
| | - Harald Schwalbe
- Institute for Organic Chemistry and Chemical Biology, Center for
Biomolecular Magnetic Resonance (BMRZ), Johann Wolfgang
Goethe-Universität Frankfurt, Frankfurt 60438, Germany
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19
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Jakdetchai O, Eberhardt P, Asido M, Kaur J, Kriebel CN, Mao J, Leeder AJ, Brown LJ, Brown RCD, Becker-Baldus J, Bamann C, Wachtveitl J, Glaubitz C. Probing the photointermediates of light-driven sodium ion pump KR2 by DNP-enhanced solid-state NMR. SCIENCE ADVANCES 2021; 7:7/11/eabf4213. [PMID: 33712469 PMCID: PMC7954446 DOI: 10.1126/sciadv.abf4213] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/27/2020] [Accepted: 01/29/2021] [Indexed: 06/10/2023]
Abstract
The functional mechanism of the light-driven sodium pump Krokinobacter eikastus rhodopsin 2 (KR2) raises fundamental questions since the transfer of cations must differ from the better-known principles of rhodopsin-based proton pumps. Addressing these questions must involve a better understanding of its photointermediates. Here, dynamic nuclear polarization-enhanced solid-state nuclear magnetic resonance spectroscopy on cryo-trapped photointermediates shows that the K-state with 13-cis retinal directly interconverts into the subsequent L-state with distinct retinal carbon chemical shift differences and an increased out-of-plane twist around the C14-C15 bond. The retinal converts back into an all-trans conformation in the O-intermediate, which is the key state for sodium transport. However, retinal carbon and Schiff base nitrogen chemical shifts differ from those observed in the KR2 dark state all-trans conformation, indicating a perturbation through the nearby bound sodium ion. Our findings are supplemented by optical and infrared spectroscopy and are discussed in the context of known three-dimensional structures.
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Affiliation(s)
- Orawan Jakdetchai
- Institute for Biophysical Chemistry and Center for Biomolecular Magnetic Resonance (BMRZ), Goethe University Frankfurt, Max von Laue Strasse 9, 60438 Frankfurt am Main, Germany
| | - Peter Eberhardt
- Institute of Physical and Theoretical Chemistry, Goethe University Frankfurt, Max von Laue Strasse 7, 60438 Frankfurt am Main, Germany
| | - Marvin Asido
- Institute of Physical and Theoretical Chemistry, Goethe University Frankfurt, Max von Laue Strasse 7, 60438 Frankfurt am Main, Germany
| | - Jagdeep Kaur
- Institute for Biophysical Chemistry and Center for Biomolecular Magnetic Resonance (BMRZ), Goethe University Frankfurt, Max von Laue Strasse 9, 60438 Frankfurt am Main, Germany
| | - Clara Nassrin Kriebel
- Institute for Biophysical Chemistry and Center for Biomolecular Magnetic Resonance (BMRZ), Goethe University Frankfurt, Max von Laue Strasse 9, 60438 Frankfurt am Main, Germany
| | - Jiafei Mao
- Institute for Biophysical Chemistry and Center for Biomolecular Magnetic Resonance (BMRZ), Goethe University Frankfurt, Max von Laue Strasse 9, 60438 Frankfurt am Main, Germany
| | - Alexander J Leeder
- Department of Chemistry, University of Southampton, Southampton SO17 1BJ, Great Britain
| | - Lynda J Brown
- Department of Chemistry, University of Southampton, Southampton SO17 1BJ, Great Britain
| | - Richard C D Brown
- Department of Chemistry, University of Southampton, Southampton SO17 1BJ, Great Britain
| | - Johanna Becker-Baldus
- Institute for Biophysical Chemistry and Center for Biomolecular Magnetic Resonance (BMRZ), Goethe University Frankfurt, Max von Laue Strasse 9, 60438 Frankfurt am Main, Germany
| | - Christian Bamann
- Max Planck Institute of Biophysics, Max von Laue Strasse 3, 60438 Frankfurt am Main, Germany
| | - Josef Wachtveitl
- Institute of Physical and Theoretical Chemistry, Goethe University Frankfurt, Max von Laue Strasse 7, 60438 Frankfurt am Main, Germany.
| | - Clemens Glaubitz
- Institute for Biophysical Chemistry and Center for Biomolecular Magnetic Resonance (BMRZ), Goethe University Frankfurt, Max von Laue Strasse 9, 60438 Frankfurt am Main, Germany.
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20
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Reif B, Ashbrook SE, Emsley L, Hong M. Solid-state NMR spectroscopy. NATURE REVIEWS. METHODS PRIMERS 2021; 1:2. [PMID: 34368784 PMCID: PMC8341432 DOI: 10.1038/s43586-020-00002-1] [Citation(s) in RCA: 155] [Impact Index Per Article: 51.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 10/29/2020] [Indexed: 12/18/2022]
Abstract
Solid-state nuclear magnetic resonance (NMR) spectroscopy is an atomic-level method used to determine the chemical structure, three-dimensional structure, and dynamics of solids and semi-solids. This Primer summarizes the basic principles of NMR as applied to the wide range of solid systems. The fundamental nuclear spin interactions and the effects of magnetic fields and radiofrequency pulses on nuclear spins are the same as in liquid-state NMR. However, because of the anisotropy of the interactions in the solid state, the majority of high-resolution solid-state NMR spectra is measured under magic-angle spinning (MAS), which has profound effects on the types of radiofrequency pulse sequences required to extract structural and dynamical information. We describe the most common MAS NMR experiments and data analysis approaches for investigating biological macromolecules, organic materials, and inorganic solids. Continuing development of sensitivity-enhancement approaches, including 1H-detected fast MAS experiments, dynamic nuclear polarization, and experiments tailored to ultrahigh magnetic fields, is described. We highlight recent applications of solid-state NMR to biological and materials chemistry. The Primer ends with a discussion of current limitations of NMR to study solids, and points to future avenues of development to further enhance the capabilities of this sophisticated spectroscopy for new applications.
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Affiliation(s)
- Bernd Reif
- Technische Universität München, Department Chemie, Lichtenbergstr. 4, D-85747 Garching, Germany
| | - Sharon E. Ashbrook
- School of Chemistry, University of St Andrews, North Haugh, St Andrews, KY16 9ST, UK
| | - Lyndon Emsley
- École Polytechnique Fédérale de Lausanne (EPFL), Institut des sciences et ingénierie chimiques, CH-1015 Lausanne, Switzerland
| | - Mei Hong
- Department of Chemistry and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, 170 Albany Street, Cambridge, MA 02139
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21
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Yeh V, Goode A, Bonev BB. Membrane Protein Structure Determination and Characterisation by Solution and Solid-State NMR. BIOLOGY 2020; 9:E396. [PMID: 33198410 PMCID: PMC7697852 DOI: 10.3390/biology9110396] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/21/2020] [Revised: 11/08/2020] [Accepted: 11/11/2020] [Indexed: 12/25/2022]
Abstract
Biological membranes define the interface of life and its basic unit, the cell. Membrane proteins play key roles in membrane functions, yet their structure and mechanisms remain poorly understood. Breakthroughs in crystallography and electron microscopy have invigorated structural analysis while failing to characterise key functional interactions with lipids, small molecules and membrane modulators, as well as their conformational polymorphism and dynamics. NMR is uniquely suited to resolving atomic environments within complex molecular assemblies and reporting on membrane organisation, protein structure, lipid and polysaccharide composition, conformational variations and molecular interactions. The main challenge in membrane protein studies at the atomic level remains the need for a membrane environment to support their fold. NMR studies in membrane mimetics and membranes of increasing complexity offer close to native environments for structural and molecular studies of membrane proteins. Solution NMR inherits high resolution from small molecule analysis, providing insights from detergent solubilised proteins and small molecular assemblies. Solid-state NMR achieves high resolution in membrane samples through fast sample spinning or sample alignment. Recent developments in dynamic nuclear polarisation NMR allow signal enhancement by orders of magnitude opening new opportunities for expanding the applications of NMR to studies of native membranes and whole cells.
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Affiliation(s)
| | | | - Boyan B. Bonev
- School of Life Sciences, University of Nottingham, Nottingham NG7 2UH, UK; (V.Y.); (A.G.)
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22
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Ono J, Imai M, Nishimura Y, Nakai H. Hydroxide Ion Carrier for Proton Pumps in Bacteriorhodopsin: Primary Proton Transfer. J Phys Chem B 2020; 124:8524-8539. [DOI: 10.1021/acs.jpcb.0c05507] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Junichi Ono
- Waseda Research Institute for Science and Engineering (WISE), Waseda University, 3-4-1 Okubo, Shinjuku, Tokyo 169-8555, Japan
- Elements Strategy Initiative for Catalysts & Batteries (ESICB), Kyoto University, 1-30 Goryo-Ohara, Nishikyo-ku, Kyoto 615-8245, Japan
| | - Minori Imai
- Department of Chemistry and Biochemistry, School of Advanced Science and Engineering, Waseda University, 3-4-1 Okubo, Shinjuku, Tokyo 169-8555, Japan
| | - Yoshifumi Nishimura
- Waseda Research Institute for Science and Engineering (WISE), Waseda University, 3-4-1 Okubo, Shinjuku, Tokyo 169-8555, Japan
| | - Hiromi Nakai
- Waseda Research Institute for Science and Engineering (WISE), Waseda University, 3-4-1 Okubo, Shinjuku, Tokyo 169-8555, Japan
- Elements Strategy Initiative for Catalysts & Batteries (ESICB), Kyoto University, 1-30 Goryo-Ohara, Nishikyo-ku, Kyoto 615-8245, Japan
- Department of Chemistry and Biochemistry, School of Advanced Science and Engineering, Waseda University, 3-4-1 Okubo, Shinjuku, Tokyo 169-8555, Japan
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23
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Abstract
The solid effect (SE) is a two spin dynamic nuclear polarization (DNP) mechanism that enhances the sensitivity in NMR experiments by irradiation of the electron-nuclear spin transitions with continuous wave (CW) microwaves at ω0S ± ω0I, where ω0S and ω0I are electron and nuclear Larmor frequencies, respectively. Using trityl (OX063), dispersed in a 60/40 glycerol/water mixture at 80 K, as a polarizing agent, we show here that application of a chirped microwave pulse, with a bandwidth comparable to the EPR line width applied at the SE matching condition, improves the enhancement by a factor of 2.4 over the CW method. Furthermore, the chirped pulse yields an enhancement that is ∼20% larger than obtained with the ramped-amplitude NOVEL (RA-NOVEL), which to date has achieved the largest enhancements in time domain DNP experiments. Numerical simulations suggest that the spins follow an adiabatic trajectory during the polarization transfer; hence, we denote this sequence as an adiabatic solid effect (ASE). We foresee that ASE will be a practical pulsed DNP experiment to be implemented at higher static magnetic fields due to the moderate power requirement. In particular, the ASE uses only 13% of the maximum microwave power required for RA-NOVEL.
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Affiliation(s)
- Kong Ooi Tan
- Francis Bitter Magnet Laboratory and Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Ralph T Weber
- Bruker BioSpin Corporation, Billerica, Massachusetts 01821, United States
| | - Thach V Can
- Francis Bitter Magnet Laboratory and Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Robert G Griffin
- Francis Bitter Magnet Laboratory and Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
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24
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Mentink-Vigier F. Optimizing nitroxide biradicals for cross-effect MAS-DNP: the role of g-tensors' distance. Phys Chem Chem Phys 2020; 22:3643-3652. [PMID: 31998899 DOI: 10.1039/c9cp06201g] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Nitroxide biradicals are common polarizing agents used to enhance the sensitivity of solid-state NMR experiments via Magic Angle Spinning Dynamic Nuclear Polarization (MAS-DNP). These biradicals are used to increase the polarization of protons through the cross-effect mechanism, which requires two unpaired electrons with a Larmor frequency difference greater than that of the protons. From their early conception, the relative orientation of the nitroxide rings has been identified as a critical factor determining their MAS-DNP performance. However, the MAS leads to a complex DNP mechanism with time dependent energy level anti-crossings making it difficult to pinpoint the role of relative g-tensor orientation. In this article, a single parameter called "g-tensors' distance" is introduced to characterize the relative orientation's impact on the MAS-DNP field profiles. It is demonstrated for the first time how the g-tensors' distance determines the nuclear hyperpolarization and depolarization properties of a given biradical. This provides a new critical parameter that paves the way for more efficient bis-nitroxides for MAS-DNP.
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Affiliation(s)
- Frédéric Mentink-Vigier
- National High Magnetic Field Laboratory, Florida State University, 1800 E. Paul Dirac Dr, Tallahassee, FL 32310, USA.
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25
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Friedrich D, Brünig FN, Nieuwkoop AJ, Netz RR, Hegemann P, Oschkinat H. Collective exchange processes reveal an active site proton cage in bacteriorhodopsin. Commun Biol 2020; 3:4. [PMID: 31925324 PMCID: PMC6941954 DOI: 10.1038/s42003-019-0733-7] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2019] [Accepted: 12/02/2019] [Indexed: 01/01/2023] Open
Abstract
Proton translocation across membranes is vital to all kingdoms of life. Mechanistically, it relies on characteristic proton flows and modifications of hydrogen bonding patterns, termed protonation dynamics, which can be directly observed by fast magic angle spinning (MAS) NMR. Here, we demonstrate that reversible proton displacement in the active site of bacteriorhodopsin already takes place in its equilibrated dark-state, providing new information on the underlying hydrogen exchange processes. In particular, MAS NMR reveals proton exchange at D85 and the retinal Schiff base, suggesting a tautomeric equilibrium and thus partial ionization of D85. We provide evidence for a proton cage and detect a preformed proton path between D85 and the proton shuttle R82. The protons at D96 and D85 exchange with water, in line with ab initio molecular dynamics simulations. We propose that retinal isomerization makes the observed proton exchange processes irreversible and delivers a proton towards the extracellular release site. Daniel Friedrich et al. show that reversible proton translocation occurs in the dark–state of bacteriorhodopsin, involving the retinal Schiff base and D85 exchanging protons with H2O. They find evidence of an active site proton cage and possible proton transfer via R82.
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Affiliation(s)
- Daniel Friedrich
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie, Robert-Rössle-Str. 10, 13125, Berlin, Germany.,Freie Universität Berlin, Institut für Chemie und Biochemie, 14195, Berlin, Germany.,Department of Molecular and Cellular Biology, Harvard University, 52 Oxford Street, Cambridge, MA, 02138, USA.,Department of Cancer Biology, Dana-Farber Cancer Institute, 360 Longwood Avenue, Boston, MA, 02215, USA
| | - Florian N Brünig
- Freie Universität Berlin, Fachbereich Physik, 14195, Berlin, Germany
| | - Andrew J Nieuwkoop
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie, Robert-Rössle-Str. 10, 13125, Berlin, Germany.,Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, 123 Bevier Road, Piscataway, NJ, 08854, USA
| | - Roland R Netz
- Freie Universität Berlin, Fachbereich Physik, 14195, Berlin, Germany
| | - Peter Hegemann
- Humboldt-Universität zu Berlin, Institut für Biologie, Invalidenstr. 42, 10115, Berlin, Germany
| | - Hartmut Oschkinat
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie, Robert-Rössle-Str. 10, 13125, Berlin, Germany. .,Freie Universität Berlin, Institut für Chemie und Biochemie, 14195, Berlin, Germany.
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26
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Exploring Protein Structures by DNP-Enhanced Methyl Solid-State NMR Spectroscopy. J Am Chem Soc 2019; 141:19888-19901. [DOI: 10.1021/jacs.9b11195] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
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27
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Chen PH, Gao C, Barnes AB. Perspectives on microwave coupling into cylindrical and spherical rotors with dielectric lenses for magic angle spinning dynamic nuclear polarization. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2019; 308:106518. [PMID: 31345770 DOI: 10.1016/j.jmr.2019.07.005] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2018] [Revised: 07/03/2019] [Accepted: 07/05/2019] [Indexed: 06/10/2023]
Abstract
Continuous wave dynamic nuclear polarization (DNP) increases the sensitivity of NMR, yet intense microwave fields are required to transition magic angle spinning (MAS) DNP to the time domain. Here we describe and analyze Teflon lenses for cylindrical and spherical MAS rotors that focus microwave power and increase the electron Rabi frequency, ν1s. Using a commercial simulation package, we solve the Maxwell equations and determine the propagation and focusing of millimeter waves (198 GHz). We then calculate the microwave intensity in a time-independent fashion to compute the ν1s. With a nominal microwave power input of 5 W, the average ν1s is 0.38 MHz within a 22 μL sample volume in a 3.2 mm outer diameter (OD) cylindrical rotor without a Teflon lens. Decreasing the sample volume to 3 μL and focusing the microwave beam with a Teflon lens increases the ν1s to 1.5 MHz. Microwave polarization and intensity perturbations associated with diffraction through the radiofrequency coil, losses from penetration through the rotor wall, and mechanical limitations of the separation between the lens and sample are significant challenges to improving microwave coupling in MAS DNP instrumentation. To overcome these issues, we introduce a novel focusing strategy using dielectric microwave lenses installed within spinning rotors. One such 9.5 mm OD cylindrical rotor assembly implements a Teflon focusing lens to increase the ν1s to 2.7 MHz within a 2 μL sample. Further, to access high spinning frequencies while also increasing ν1s, we analyze microwave coupling into MAS spheres. For 9.5 mm OD spherical rotors, we compute a ν1s of 0.36 MHz within a sample volume of 161 μL, and 2.5 MHz within a 3 μL sample placed at the focal point of a novel double lens insert. We conclude with an analysis and discussion of sub-millimeter diamond spherical rotors for time domain DNP at spinning frequencies >100 kHz. Sub-millimeter spherical rotors better overlap a tightly focused microwave beam, resulting in a ν1s of 2.2 MHz. Lastly, we propose that sub-millimeter dielectric spherical microwave resonators will provide a means to substantially improve electron spin control in the future.
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Affiliation(s)
- Pin-Hui Chen
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA; Department of Physics, Washington University in St. Louis, St. Louis, MO 63130, USA
| | - Chukun Gao
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA
| | - Alexander B Barnes
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA.
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28
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Reese M, George C, Yang C, Jawla S, Grün JT, Schwalbe H, Redfield C, Temkin RJ, Griffin RG. Modular, triple-resonance, transmission line DNP MAS probe for 500 MHz/330 GHz. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2019; 307:106573. [PMID: 31505305 PMCID: PMC6766420 DOI: 10.1016/j.jmr.2019.106573] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2019] [Revised: 08/12/2019] [Accepted: 08/13/2019] [Indexed: 06/10/2023]
Abstract
We describe the design and construction of a modular, triple-resonance, fully balanced, DNP-MAS probe based on transmission line technology and its integration into a 500 MHz/330 GHz DNP-NMR spectrometer. A novel quantitative probe design and characterization strategy is developed and employed to achieve optimal sensitivity, RF homogeneity and excellent isolation between channels. The resulting three channel HCN probe has a modular design with each individual, swappable module being equipped with connectorized, transmission line ports. This strategy permits attachment of a mating connector that facilitates accurate impedance measurements at these ports and allows characterization and adjustment (e.g. for balancing or tuning/matching) of each component individually. The RF performance of the probe is excellent; for example, the 13C channel attains a Rabi frequency of 280 kHz for a 3.2 mm rotor. In addition, a frequency tunable 330 GHz gyrotron operating at the second harmonic of the electron cyclotron frequency was developed for DNP applications. Careful alignment of the corrugated waveguide led to minimal loss of the microwave power, and an enhancement factor ε = 180 was achieved for U-13C urea in the glassy matrix at 80 K. We demonstrated the operation of the system with acquisition of multidimensional spectra of cross-linked lysozyme crystals which are insoluble in glycerol-water mixtures used for DNP and samples of RNA.
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Affiliation(s)
- Marcel Reese
- Department of Chemistry and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, United States
| | - Christy George
- Department of Chemistry and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, United States
| | - Chen Yang
- Department of Chemistry and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, United States
| | - Sudheer Jawla
- Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA 02139, United States
| | - J Tassilo Grün
- Institute for Organic Chemistry and Chemical Biology, Center for Biomolecular Magnetic Resonance, Johann Wolfgang Goethe-Universität Frankfurt, 60438 Frankfurt, Germany
| | - Harald Schwalbe
- Institute for Organic Chemistry and Chemical Biology, Center for Biomolecular Magnetic Resonance, Johann Wolfgang Goethe-Universität Frankfurt, 60438 Frankfurt, Germany
| | - Christina Redfield
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, United Kingdom
| | - Richard J Temkin
- Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA 02139, United States; Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, United States
| | - Robert G Griffin
- Department of Chemistry and Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, United States.
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29
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Eddy MT, Yu TY, Wagner G, Griffin RG. Structural characterization of the human membrane protein VDAC2 in lipid bilayers by MAS NMR. JOURNAL OF BIOMOLECULAR NMR 2019; 73:451-460. [PMID: 31407201 PMCID: PMC6819253 DOI: 10.1007/s10858-019-00242-8] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/03/2019] [Accepted: 03/19/2019] [Indexed: 05/25/2023]
Abstract
The second isoform of the human voltage dependent anion channel (VDAC2) is a mitochondrial porin that translocates calcium and other metabolites across the outer mitochondrial membrane. VDAC2 has been implicated in cardioprotection and plays a critical role in a unique apoptotic pathway in tumor cells. Despite its medical importance, there have been few biophysical studies of VDAC2 in large part due to the difficulty of obtaining homogeneous preparations of the protein for spectroscopic characterization. Here we present high resolution magic angle spinning nuclear magnetic resonance (NMR) data obtained from homogeneous preparation of human VDAC2 in 2D crystalline lipid bilayers. The excellent resolution in the spectra permit several sequence-specific assignments of the signals for a large portion of the VDAC2 N-terminus and several other residues in two- and three-dimensional heteronuclear correlation experiments. The first 12 residues appear to be dynamic, are not visible in cross polarization experiments, and they are not sufficiently mobile on very fast timescales to be visible in 13C INEPT experiments. A comparison of the NMR spectra of VDAC2 and VDAC1 obtained from highly similar preparations demonstrates that the spectral quality, line shapes and peak dispersion exhibited by the two proteins are nearly identical. This suggests an overall similar dynamic behavior and conformational homogeneity, which is in contrast to two earlier reports that suggested an inherent conformational heterogeneity of VDAC2 in membranes. The current data suggest that the sample preparation and spectroscopic methods are likely applicable to studying other human membrane porins, including human VDAC3, which has not yet been structurally characterized.
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Affiliation(s)
- Matthew T Eddy
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
- Departments of Chemistry, University of Florida, Gainesville, FL, 32611, USA
| | - Tsyr-Yan Yu
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, 02115, USA
- Institute of Atomic and Molecular Sciences, Academia Sinica, Taipei, 10617, Taiwan, Republic of China
| | - Gerhard Wagner
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA, 02115, USA
| | - Robert G Griffin
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.
- Francis Bitter Magnet Laboratory, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA.
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30
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Application of millisecond time-resolved solid state NMR to the kinetics and mechanism of melittin self-assembly. Proc Natl Acad Sci U S A 2019; 116:16717-16722. [PMID: 31387974 DOI: 10.1073/pnas.1908006116] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Common experimental approaches for characterizing structural conversion processes such as protein folding and self-assembly do not report on all aspects of the evolution from an initial state to the final state. Here, we demonstrate an approach that is based on rapid mixing, freeze-trapping, and low-temperature solid-state NMR (ssNMR) with signal enhancements from dynamic nuclear polarization (DNP). Experiments on the folding and tetramerization of the 26-residue peptide melittin following a rapid pH jump show that multiple aspects of molecular structure can be followed with millisecond time resolution, including secondary structure at specific isotopically labeled sites, intramolecular and intermolecular contacts between specific pairs of labeled residues, and overall structural order. DNP-enhanced ssNMR data reveal that conversion of conformationally disordered melittin monomers at low pH to α-helical conformations at neutral pH occurs on nearly the same timescale as formation of antiparallel melittin dimers, about 6 to 9 ms for 0.3 mM melittin at 24 °C in aqueous solution containing 20% (vol/vol) glycerol and 75 mM sodium phosphate. Although stopped-flow fluorescence data suggest that melittin tetramers form quickly after dimerization, ssNMR spectra show that full structural order within melittin tetramers develops more slowly, in ∼60 ms. Time-resolved ssNMR is likely to find many applications to biomolecular structural conversion processes, including early stages of amyloid formation, viral capsid formation, and protein-protein recognition.
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31
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Salnikov ES, Aussenac F, Abel S, Purea A, Tordo P, Ouari O, Bechinger B. Dynamic Nuclear Polarization / solid-state NMR of membranes. Thermal effects and sample geometry. SOLID STATE NUCLEAR MAGNETIC RESONANCE 2019; 100:70-76. [PMID: 30995597 DOI: 10.1016/j.ssnmr.2019.03.004] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/27/2018] [Revised: 03/18/2019] [Accepted: 03/18/2019] [Indexed: 06/09/2023]
Abstract
Whereas specially designed dinitroxide biradicals, reconstitution protocols, oriented sample geometries and NMR probes have helped to much increase the DNP enhancement factors of membrane samples they still lag considerably behind those obtained from glasses made of protein solutions. Here we show that not only the MAS rotor material but also the distribution of the membrane samples within the NMR rotor have a pronounced effect on the DNP enhancement. These observations are rationalized with the cooling efficiency and the internal properties of the sample, monitored by their T1 relaxation, microwave ON versus OFF signal intensities and DNP effect. The data are suggestive that for membranes the speed of cooling has a pronounced effect on the membrane properties and concomitantly the distribution of biradicals within the sample.
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Affiliation(s)
| | | | - Sebastian Abel
- Aix-Marseille University, CNRS, UMR 7273, Institut de Chimie Radicalaire, 13013, Marseille, France
| | | | - Paul Tordo
- Aix-Marseille University, CNRS, UMR 7273, Institut de Chimie Radicalaire, 13013, Marseille, France
| | - Olivier Ouari
- Aix-Marseille University, CNRS, UMR 7273, Institut de Chimie Radicalaire, 13013, Marseille, France
| | - Burkhard Bechinger
- Institute of Chemistry, University of Strasbourg / CNRS, UMR7177, 67070, Strasbourg, France.
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32
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Wang X, Caulkins BG, Riviere G, Mueller LJ, Mentink-Vigier F, Long JR. Direct dynamic nuclear polarization of 15N and 13C spins at 14.1 T using a trityl radical and magic angle spinning. SOLID STATE NUCLEAR MAGNETIC RESONANCE 2019; 100:85-91. [PMID: 31026722 PMCID: PMC6604067 DOI: 10.1016/j.ssnmr.2019.03.009] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/07/2019] [Revised: 03/27/2019] [Accepted: 03/28/2019] [Indexed: 05/05/2023]
Abstract
We investigate solid-state dynamic nuclear polarization of 13C and 15N nuclei using monoradical trityl OX063 as a polarizing agent in a magnetic field of 14.1 T with magic angle spinning at ∼100 K. We monitored the field dependence of direct 13C and 15N polarization for frozen [13C, 15N] urea and achieved maximum absolute enhancement factors of 240 and 470, respectively. The field profiles are consistent with polarization of 15N spins via either the solid effect or the cross effect, and polarization of 13C spins via a combination of cross effect and solid effect. For microcrystalline, 15N-enriched tryptophan synthase sample containing trityl radical, a 1500-fold increase in 15N signal was observed under microwave irradiation. These results show the promise of trityl radicals and their derivatives for direct polarization of low gamma, spin-½ nuclei at high magnetic fields and suggest a novel approach for selectively polarizing specific moieties or for polarizing systems which have low levels of protonation.
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Affiliation(s)
- Xiaoling Wang
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL, 32310, USA
| | - Bethany G Caulkins
- Department of Chemistry, University of California Riverside, Riverside, CA, 92521, USA
| | - Gwladys Riviere
- Department of Biochemistry and Molecular Biology, McKnight Brain Institute and National High Magnetic Field Laboratory, University of Florida, Gainesville, FL, 32610-0245, USA
| | - Leonard J Mueller
- Department of Chemistry, University of California Riverside, Riverside, CA, 92521, USA
| | - Frederic Mentink-Vigier
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL, 32310, USA
| | - Joanna R Long
- Department of Biochemistry and Molecular Biology, McKnight Brain Institute and National High Magnetic Field Laboratory, University of Florida, Gainesville, FL, 32610-0245, USA.
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33
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Gao C, Judge PT, Sesti EL, Price LE, Alaniva N, Saliba EP, Albert BJ, Soper NJ, Chen PH, Barnes AB. Four millimeter spherical rotors spinning at 28 kHz with double-saddle coils for cross polarization NMR. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2019; 303:1-6. [PMID: 30978570 DOI: 10.1016/j.jmr.2019.03.006] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2019] [Revised: 03/07/2019] [Accepted: 03/20/2019] [Indexed: 06/09/2023]
Abstract
Spherical rotors in magic angle spinning (MAS) experiments have significant advantages over traditional cylindrical rotors including simplified spinning implementation, easy sample exchange, more efficient microwave coupling for dynamic nuclear polarization (DNP), and feasibility of downscaling to access higher spinning frequencies. Here, we implement spherical rotors with 4 mm outside diameter (o.d.) and demonstrate spinning >28 kHz using a single aperture for spinning gas. We show a modified stator geometry to improve fiber optic detection, increase NMR filling factor, and improve alignment for sample exchange and microwave irradiation. Higher NMR Rabi frequencies were obtained using smaller radiofrequency (RF) coils on small-diameter spherical rotors, compared to our previous implementation of MAS spheres with an o.d. of 9.5 mm. We report nutation fields of 110 kHz on 13C with 820 W of input power and 100 kHz on 1H with 800 W of input power. Proton decoupling fields of 78 kHz were applied over 20 ms of signal acquisition without any sign of arcing. Compared to our initial demonstration of a split coil for 9.5 mm spheres, this current implementation of a double-saddle coil inductor for 4 mm spheres not only intensifies the RF fields, but also improves RF homogeneity. We achieve an 810°/90° nutation intensity ratio of 0.84 at 300.197 MHz (1H). We also show electromagnetic simulations predicting a nearly 3-fold improvement in electron Rabi frequency of 0.99 MHz (with 4 mm spheres) compared to 0.38 MHz (with 3.2 mm cylinders), with 5 W of incident microwave power. Further improvements in magnetic resonance spin control are expected as RF inductors and microwave coupling are optimized for spherical rotors and scaled down to the micron scale.
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Affiliation(s)
- Chukun Gao
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA
| | - Patrick T Judge
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA; Department of Biochemistry, Biophysics & Structural Biology, Washington University in St. Louis, St. Louis, MO 63110, USA
| | - Erika L Sesti
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA
| | - Lauren E Price
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA
| | - Nicholas Alaniva
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA
| | - Edward P Saliba
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA
| | - Brice J Albert
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA
| | - Nathan J Soper
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA
| | - Pin-Hui Chen
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA; Department of Physics, Washington University in St. Louis, St. Louis, MO 63130, USA
| | - Alexander B Barnes
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA.
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34
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Viger‐Gravel J, Avalos CE, Kubicki DJ, Gajan D, Lelli M, Ouari O, Lesage A, Emsley L. 19
F Magic Angle Spinning Dynamic Nuclear Polarization Enhanced NMR Spectroscopy. Angew Chem Int Ed Engl 2019. [DOI: 10.1002/ange.201814416] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Jasmine Viger‐Gravel
- Institut des Sciences et Ingénierie ChimiquesEcole Polytechnique Fédérale de Lausanne (EPFL) 1015 Lausanne Switzerland
| | - Claudia E. Avalos
- Institut des Sciences et Ingénierie ChimiquesEcole Polytechnique Fédérale de Lausanne (EPFL) 1015 Lausanne Switzerland
| | - Dominik J. Kubicki
- Institut des Sciences et Ingénierie ChimiquesEcole Polytechnique Fédérale de Lausanne (EPFL) 1015 Lausanne Switzerland
| | - David Gajan
- Université de LyonInstitut des Sciences Analytiques (UMR 5280 CNRS/UCBL/ENS Lyon)Centre de RMN à Très Hauts Champs 69100 Villeurbanne France
| | - Moreno Lelli
- Center of Magnetic Resonance (CERM)University of Florence Via Luigi Sacconi 6 50019 Sesto Fiorentino Italy
- Department of Chemistry “Ugo Schiff”University of Florence Via della Lastruccia 3 50019 Sesto Fiorentino Italy
| | - Olivier Ouari
- Aix Marseille UnivCNRSICR UMR 7273, 13397 13013 Marseille France
| | - Anne Lesage
- Université de LyonInstitut des Sciences Analytiques (UMR 5280 CNRS/UCBL/ENS Lyon)Centre de RMN à Très Hauts Champs 69100 Villeurbanne France
| | - Lyndon Emsley
- Institut des Sciences et Ingénierie ChimiquesEcole Polytechnique Fédérale de Lausanne (EPFL) 1015 Lausanne Switzerland
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35
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Viger‐Gravel J, Avalos CE, Kubicki DJ, Gajan D, Lelli M, Ouari O, Lesage A, Emsley L. 19
F Magic Angle Spinning Dynamic Nuclear Polarization Enhanced NMR Spectroscopy. Angew Chem Int Ed Engl 2019; 58:7249-7253. [DOI: 10.1002/anie.201814416] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2018] [Revised: 04/02/2019] [Indexed: 11/10/2022]
Affiliation(s)
- Jasmine Viger‐Gravel
- Institut des Sciences et Ingénierie ChimiquesEcole Polytechnique Fédérale de Lausanne (EPFL) 1015 Lausanne Switzerland
| | - Claudia E. Avalos
- Institut des Sciences et Ingénierie ChimiquesEcole Polytechnique Fédérale de Lausanne (EPFL) 1015 Lausanne Switzerland
| | - Dominik J. Kubicki
- Institut des Sciences et Ingénierie ChimiquesEcole Polytechnique Fédérale de Lausanne (EPFL) 1015 Lausanne Switzerland
| | - David Gajan
- Université de LyonInstitut des Sciences Analytiques (UMR 5280 CNRS/UCBL/ENS Lyon)Centre de RMN à Très Hauts Champs 69100 Villeurbanne France
| | - Moreno Lelli
- Center of Magnetic Resonance (CERM)University of Florence Via Luigi Sacconi 6 50019 Sesto Fiorentino Italy
- Department of Chemistry “Ugo Schiff”University of Florence Via della Lastruccia 3 50019 Sesto Fiorentino Italy
| | - Olivier Ouari
- Aix Marseille UnivCNRSICR UMR 7273, 13397 13013 Marseille France
| | - Anne Lesage
- Université de LyonInstitut des Sciences Analytiques (UMR 5280 CNRS/UCBL/ENS Lyon)Centre de RMN à Très Hauts Champs 69100 Villeurbanne France
| | - Lyndon Emsley
- Institut des Sciences et Ingénierie ChimiquesEcole Polytechnique Fédérale de Lausanne (EPFL) 1015 Lausanne Switzerland
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36
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Abstract
Membranes surrounding the biological cell and its internal compartments host proteins that catalyze chemical reactions essential for the functioning of the cell. Rather than being a passive structural matrix that holds membrane-embedded proteins in place, the membrane can largely shape the conformational energy landscape of membrane proteins and impact the energetics of their chemical reaction. Here, we highlight the challenges in understanding how lipids impact the conformational energy landscape of macromolecular membrane complexes whose functioning involves chemical reactions including proton transfer. We review here advances in our understanding of how chemical reactions occur at membrane interfaces gleaned with both theoretical and experimental advances using simple protein systems as guides. Our perspective is that of bridging experiments with theory to understand general physicochemical principles of membrane reactions, with a long term goal of furthering our understanding of the role of the lipids on the functioning of complex macromolecular assemblies at the membrane interface.
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Affiliation(s)
- Ana-Nicoleta Bondar
- Freie Universität Berlin , Department of Physics, Theoretical Molecular Biophysics Group , Arnimallee 14 , D-14195 Berlin , Germany
| | - M Joanne Lemieux
- University of Alberta , Department of Biochemistry, Membrane Protein Disease Research Group , Edmonton , Alberta T6G 2H7 , Canada
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37
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Mandala VS, Hong M. High-sensitivity protein solid-state NMR spectroscopy. Curr Opin Struct Biol 2019; 58:183-190. [PMID: 31031067 DOI: 10.1016/j.sbi.2019.03.027] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2018] [Revised: 03/17/2019] [Accepted: 03/21/2019] [Indexed: 10/27/2022]
Abstract
The sensitivity of solid-state nuclear magnetic resonance (SSNMR) spectroscopy for structural biology is significantly increased by 1H detection under fast magic-angle spinning (MAS) and by dynamic nuclear polarization (DNP) from electron spins to nuclear spins. The former allows studies of the structure and dynamics of small quantities of proteins under physiological conditions, while the latter permits studies of large biomolecular complexes in lipid membranes and cells, protein intermediates, and protein conformational distributions. We highlight recent applications of these two emerging SSNMR technologies and point out areas for future development.
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Affiliation(s)
- Venkata S Mandala
- Department of Chemistry, Massachusetts Institute of Technology, 170 Albany Street, Cambridge, MA 02139, United States
| | - Mei Hong
- Department of Chemistry, Massachusetts Institute of Technology, 170 Albany Street, Cambridge, MA 02139, United States.
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38
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Alaniva N, Saliba EP, Sesti EL, Judge PT, Barnes AB. Electron Decoupling with Chirped Microwave Pulses for Rapid Signal Acquisition and Electron Saturation Recovery. Angew Chem Int Ed Engl 2019; 58:7259-7262. [DOI: 10.1002/anie.201900139] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2019] [Revised: 03/01/2019] [Indexed: 11/07/2022]
Affiliation(s)
- Nicholas Alaniva
- Department of Chemistry Washington University in St. Louis One Brookings Drive St. Louis MO 63130 USA
| | - Edward P. Saliba
- Department of Chemistry Washington University in St. Louis One Brookings Drive St. Louis MO 63130 USA
| | - Erika L. Sesti
- Department of Chemistry Washington University in St. Louis One Brookings Drive St. Louis MO 63130 USA
| | - Patrick T. Judge
- Department of Chemistry Washington University in St. Louis One Brookings Drive St. Louis MO 63130 USA
- Department of Biochemistry, Biophysics, and Biology Washington University in St. Louis School of Medicine 660 S. Euclid Ave St Louis MO 63110 USA
| | - Alexander B. Barnes
- Department of Chemistry Washington University in St. Louis One Brookings Drive St. Louis MO 63130 USA
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39
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Alaniva N, Saliba EP, Sesti EL, Judge PT, Barnes AB. Electron Decoupling with Chirped Microwave Pulses for Rapid Signal Acquisition and Electron Saturation Recovery. Angew Chem Int Ed Engl 2019. [DOI: 10.1002/ange.201900139] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Affiliation(s)
- Nicholas Alaniva
- Department of Chemistry Washington University in St. Louis One Brookings Drive St. Louis MO 63130 USA
| | - Edward P. Saliba
- Department of Chemistry Washington University in St. Louis One Brookings Drive St. Louis MO 63130 USA
| | - Erika L. Sesti
- Department of Chemistry Washington University in St. Louis One Brookings Drive St. Louis MO 63130 USA
| | - Patrick T. Judge
- Department of Chemistry Washington University in St. Louis One Brookings Drive St. Louis MO 63130 USA
- Department of Biochemistry, Biophysics, and Biology Washington University in St. Louis School of Medicine 660 S. Euclid Ave St Louis MO 63110 USA
| | - Alexander B. Barnes
- Department of Chemistry Washington University in St. Louis One Brookings Drive St. Louis MO 63130 USA
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40
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Photocycle-dependent conformational changes in the proteorhodopsin cross-protomer Asp-His-Trp triad revealed by DNP-enhanced MAS-NMR. Proc Natl Acad Sci U S A 2019; 116:8342-8349. [PMID: 30948633 DOI: 10.1073/pnas.1817665116] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Proteorhodopsin (PR) is a highly abundant, pentameric, light-driven proton pump. Proton transfer is linked to a canonical photocycle typical for microbial ion pumps. Although the PR monomer is able to undergo a full photocycle, the question arises whether the pentameric complex formed in the membrane via specific cross-protomer interactions plays a role in its functional mechanism. Here, we use dynamic nuclear polarization (DNP)-enhanced solid-state magic-angle spinning (MAS) NMR in combination with light-induced cryotrapping of photointermediates to address this topic. The highly conserved residue H75 is located at the protomer interface. We show that it switches from the (τ)- to the (π)-tautomer and changes its ring orientation in the M state. It couples to W34 across the oligomerization interface based on specific His/Trp ring orientations while stabilizing the pKa of the primary proton acceptor D97 within the same protomer. We further show that specific W34 mutations have a drastic effect on D97 and proton transfer mediated through H75. The residue H75 defines a cross-protomer Asp-His-Trp triad, which potentially serves as a pH-dependent regulator for proton transfer. Our data represent light-dependent, functionally relevant cross talk between protomers of a microbial rhodopsin homo-oligomer.
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41
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Lacabanne D, Fogeron ML, Wiegand T, Cadalbert R, Meier BH, Böckmann A. Protein sample preparation for solid-state NMR investigations. PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY 2019; 110:20-33. [PMID: 30803692 DOI: 10.1016/j.pnmrs.2019.01.001] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/07/2018] [Revised: 01/11/2019] [Accepted: 01/12/2019] [Indexed: 06/09/2023]
Abstract
Preparation of a protein sample for solid-state NMR is in many aspects similar to solution-state NMR approaches, mainly with respect to the need for stable isotope labeling. But the possibility of using solid-state NMR to investigate membrane proteins in (native) lipids adds the important requirement of adapted membrane-reconstitution schemes. Also, dynamic nuclear polarization and paramagnetic NMR in solids need specific schemes using metal ions and radicals. Sample sedimentation has enabled structural investigations of objects inaccessible to other structural techniques, but rotor filling using sedimentation has become increasingly complex with smaller and smaller rotors, as needed for higher and higher magic-angle spinning (MAS) frequencies. Furthermore, solid-state NMR can investigate very large proteins and their complexes without the concomitant increase in line widths, motivating the use of selective labeling and unlabeling strategies, as well as segmental labeling, to decongest spectra. The possibility of investigating sub-milligram amounts of protein today using advanced fast MAS techniques enables alternative protein synthesis schemes such as cell-free expression. Here we review these specific aspects of solid-state NMR sample preparation.
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Affiliation(s)
- Denis Lacabanne
- Molecular Microbiology and Structural Biochemistry, Labex Ecofect, UMR 5086 CNRS/Université de Lyon, 69367 Lyon, France; Physical Chemistry, ETH Zurich, 8093 Zurich, Switzerland
| | - Marie-Laure Fogeron
- Molecular Microbiology and Structural Biochemistry, Labex Ecofect, UMR 5086 CNRS/Université de Lyon, 69367 Lyon, France
| | - Thomas Wiegand
- Physical Chemistry, ETH Zurich, 8093 Zurich, Switzerland
| | | | - Beat H Meier
- Physical Chemistry, ETH Zurich, 8093 Zurich, Switzerland.
| | - Anja Böckmann
- Molecular Microbiology and Structural Biochemistry, Labex Ecofect, UMR 5086 CNRS/Université de Lyon, 69367 Lyon, France.
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42
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Mei G, Mamaeva N, Ganapathy S, Wang P, DeGrip WJ, Rothschild KJ. Raman spectroscopy of a near infrared absorbing proteorhodopsin: Similarities to the bacteriorhodopsin O photointermediate. PLoS One 2018; 13:e0209506. [PMID: 30586409 PMCID: PMC6306260 DOI: 10.1371/journal.pone.0209506] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2018] [Accepted: 12/06/2018] [Indexed: 02/07/2023] Open
Abstract
Microbial rhodopsins have become an important tool in the field of optogenetics. However, effective in vivo optogenetics is in many cases severely limited due to the strong absorption and scattering of visible light by biological tissues. Recently, a combination of opsin site-directed mutagenesis and analog retinal substitution has produced variants of proteorhodopsin which absorb maximally in the near-infrared (NIR). In this study, UV-Visible-NIR absorption and resonance Raman spectroscopy were used to study the double mutant, D212N/F234S, of green absorbing proteorhodopsin (GPR) regenerated with MMAR, a retinal analog containing a methylamino modified β-ionone ring. Four distinct subcomponent absorption bands with peak maxima near 560, 620, 710 and 780 nm are detected with the NIR bands dominant at pH <7.3, and the visible bands dominant at pH 9.5. FT-Raman using 1064-nm excitation reveal two strong ethylenic bands at 1482 and 1498 cm-1 corresponding to the NIR subcomponent absorption bands based on an extended linear correlation between λmax and γC = C. This spectrum exhibits two intense bands in the fingerprint and HOOP mode regions that are highly characteristic of the O640 photointermediate from the light-adapted bacteriorhodopsin photocycle. In contrast, 532-nm excitation enhances the 560-nm component, which exhibits bands very similar to light-adapted bacteriorhodopsin and/or the acid-purple form of bacteriorhodopsin. Native GPR and its mutant D97N when regenerated with MMAR also exhibit similar absorption and Raman bands but with weaker contributions from the NIR absorbing components. Based on these results it is proposed that the NIR absorption in GPR-D212N/F234S with MMAR arises from an O-like chromophore, where the Schiff base counterion D97 is protonated and the MMAR adopts an all-trans configuration with a non-planar geometry due to twists in the conjugated polyene segment. This configuration is characterized by extensive charge delocalization, most likely involving nitrogens atoms in the MMAR chromophore.
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Affiliation(s)
- Gaoxiang Mei
- Molecular Biophysics Laboratory, Photonics Center and Department of Physics, Boston University, Boston, Massachusetts, United States of America
| | - Natalia Mamaeva
- Molecular Biophysics Laboratory, Photonics Center and Department of Physics, Boston University, Boston, Massachusetts, United States of America
| | - Srividya Ganapathy
- Department of Biophysical Organic Chemistry, Leiden Institute of Chemistry, Leiden UniversityAR Leiden, The Netherlands
| | - Peng Wang
- Bruker Corporation, Billerica, MA, United States of America
| | - Willem J. DeGrip
- Department of Biophysical Organic Chemistry, Leiden Institute of Chemistry, Leiden UniversityAR Leiden, The Netherlands
| | - Kenneth J. Rothschild
- Molecular Biophysics Laboratory, Photonics Center and Department of Physics, Boston University, Boston, Massachusetts, United States of America
- * E-mail:
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GPCR drug discovery: integrating solution NMR data with crystal and cryo-EM structures. Nat Rev Drug Discov 2018; 18:59-82. [PMID: 30410121 DOI: 10.1038/nrd.2018.180] [Citation(s) in RCA: 154] [Impact Index Per Article: 25.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The 826 G protein-coupled receptors (GPCRs) in the human proteome regulate key physiological processes and thus have long been attractive drug targets. With the crystal structures of more than 50 different human GPCRs determined over the past decade, an initial platform for structure-based rational design has been established for drugs that target GPCRs, which is currently being augmented with cryo-electron microscopy (cryo-EM) structures of higher-order GPCR complexes. Nuclear magnetic resonance (NMR) spectroscopy in solution is one of the key approaches for expanding this platform with dynamic features, which can be accessed at physiological temperature and with minimal modification of the wild-type GPCR covalent structures. Here, we review strategies for the use of advanced biochemistry and NMR techniques with GPCRs, survey projects in which crystal or cryo-EM structures have been complemented with NMR investigations and discuss the impact of this integrative approach on GPCR biology and drug discovery.
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Kaur H, Abreu B, Akhmetzyanov D, Lakatos-Karoly A, Soares CM, Prisner T, Glaubitz C. Unexplored Nucleotide Binding Modes for the ABC Exporter MsbA. J Am Chem Soc 2018; 140:14112-14125. [PMID: 30289253 DOI: 10.1021/jacs.8b06739] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The ATP-binding cassette (ABC) transporter MsbA is an ATP-driven lipid-A flippase. It belongs to the ABC protein superfamily whose members are characterized by conserved motifs in their nucleotide binding domains (NBDs), which are responsible for ATP hydrolysis. Recently, it was found that MsbA could catalyze a reverse adenylate kinase (rAK)-like reaction in addition to ATP hydrolysis. Both reactions are connected and mediated by the same conserved NBD domains. Here, the structural foundations underlying the nucleotide binding to MsbA were therefore explored using a concerted approach based on conventional- and DNP-enhanced solid-state NMR, pulsed-EPR, and MD simulations. MsbA reconstituted into lipid bilayers was trapped in various catalytic states corresponding to intermediates of the coupled ATPase-rAK mechanism. The analysis of nucleotide-binding dependent chemical shift changes, and the detection of through-space contacts between bound nucleotides and MsbA within these states provides evidence for an additional nucleotide-binding site in close proximity to the Q-loop and the His-Switch. By replacing Mg2+ with Mn2+ and employing pulsed EPR spectroscopy, evidence is provided that this newly found nucleotide binding site does not interfere with the coordination of the required metal ion. Molecular dynamic (MD) simulations of nucleotide and metal binding required for the coupled ATPase-rAK mechanism have been used to corroborate these experimental findings and provide additional insight into nucleotide location, orientation, and possible binding modes.
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Affiliation(s)
- Hundeep Kaur
- Institute for Biophysical Chemistry & Centre for Biomolecular Magnetic Resonance , Goethe-University Frankfurt , 60438 Frankfurt , Germany
| | - Bárbara Abreu
- ITQB NOVA, Instituto de Tecnologia Química e Biológica António Xavier , Universidade Nova de Lisboa , 2780-157 Oeiras , Portugal
| | - Dmitry Akhmetzyanov
- Institute for Physical and Theoretical Chemistry & Centre for Biomolecular Magnetic Resonance , Goethe-University Frankfurt , 60438 Frankfurt , Germany
| | - Andrea Lakatos-Karoly
- Institute for Biophysical Chemistry & Centre for Biomolecular Magnetic Resonance , Goethe-University Frankfurt , 60438 Frankfurt , Germany
| | - Cláudio M Soares
- ITQB NOVA, Instituto de Tecnologia Química e Biológica António Xavier , Universidade Nova de Lisboa , 2780-157 Oeiras , Portugal
| | - Thomas Prisner
- Institute for Physical and Theoretical Chemistry & Centre for Biomolecular Magnetic Resonance , Goethe-University Frankfurt , 60438 Frankfurt , Germany
| | - Clemens Glaubitz
- Institute for Biophysical Chemistry & Centre for Biomolecular Magnetic Resonance , Goethe-University Frankfurt , 60438 Frankfurt , Germany
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45
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Chen P, Albert BJ, Gao C, Alaniva N, Price LE, Scott FJ, Saliba EP, Sesti EL, Judge PT, Fisher EW, Barnes AB. Magic angle spinning spheres. SCIENCE ADVANCES 2018; 4:eaau1540. [PMID: 30255153 PMCID: PMC6155130 DOI: 10.1126/sciadv.aau1540] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/14/2018] [Accepted: 08/10/2018] [Indexed: 05/18/2023]
Abstract
Magic angle spinning (MAS) is commonly used in nuclear magnetic resonance of solids to improve spectral resolution. Rather than using cylindrical rotors for MAS, we demonstrate that spherical rotors can be spun stably at the magic angle. Spherical rotors conserve valuable space in the probe head and simplify sample exchange and microwave coupling for dynamic nuclear polarization. In this current implementation of spherical rotors, a single gas stream provides bearing gas to reduce friction, drive propulsion to generate and maintain angular momentum, and variable temperature control for thermostating. Grooves are machined directly into zirconia spheres, thereby converting the rotor body into a robust turbine with high torque. We demonstrate that 9.5-mm-outside diameter spherical rotors can be spun at frequencies up to 4.6 kHz with N2(g) and 10.6 kHz with He(g). Angular stability of the spinning axis is demonstrated by observation of 79Br rotational echoes out to 10 ms from KBr packed within spherical rotors. Spinning frequency stability of ±1 Hz is achieved with resistive heating feedback control. A sample size of 36 μl can be accommodated in 9.5-mm-diameter spheres with a cylindrical hole machined along the spinning axis. We further show that spheres can be more extensively hollowed out to accommodate 161 μl of the sample, which provides superior signal-to-noise ratio compared to traditional 3.2-mm-diameter cylindrical rotors.
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Affiliation(s)
- Pinhui Chen
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA
- Department of Physics, Washington University in St. Louis, St. Louis, MO 63130, USA
| | - Brice J. Albert
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA
| | - Chukun Gao
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA
| | - Nicholas Alaniva
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA
| | - Lauren E. Price
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA
| | - Faith J. Scott
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA
| | - Edward P. Saliba
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA
| | - Erika L. Sesti
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA
| | - Patrick T. Judge
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA
- Department of Biochemistry, Biophysics and Structural Biology, Washington University in St. Louis, St. Louis, MO 63110, USA
| | - Edward W. Fisher
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA
- Department of Biochemistry, Biophysics and Structural Biology, Washington University in St. Louis, St. Louis, MO 63110, USA
| | - Alexander B. Barnes
- Department of Chemistry, Washington University in St. Louis, St. Louis, MO 63130, USA
- Corresponding author.
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