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Daniilidis M, Sperl LE, Müller BS, Babl A, Hagn F. Efficient Segmental Isotope Labeling of Integral Membrane Proteins for High-Resolution NMR Studies. J Am Chem Soc 2024; 146:15403-15410. [PMID: 38787792 PMCID: PMC11157531 DOI: 10.1021/jacs.4c03294] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2024] [Revised: 05/10/2024] [Accepted: 05/10/2024] [Indexed: 05/26/2024]
Abstract
High-resolution structural NMR analyses of membrane proteins are challenging due to their large size, resulting in broad resonances and strong signal overlap. Among the isotope labeling methods that can remedy this situation, segmental isotope labeling is a suitable strategy to simplify NMR spectra and retain high-resolution structural information. However, protein ligation within integral membrane proteins is complicated since the hydrophobic protein fragments are insoluble, and the removal of ligation side-products is elaborate. Here, we show that a stabilized split-intein system can be used for rapid and high-yield protein trans-splicing of integral membrane proteins under denaturing conditions. This setup enables segmental isotope labeling experiments within folded protein domains for NMR studies. We show that high-quality NMR spectra of markedly reduced complexity can be obtained in detergent micelles and lipid nanodiscs. Of note, the nanodisc insertion step specifically selects for the ligated and correctly folded membrane protein and simultaneously removes ligation byproducts. Using this tailored workflow, we show that high-resolution NMR structure determination is strongly facilitated with just two segmentally isotope-labeled membrane protein samples. The presented method will be broadly applicable to structural and dynamical investigations of (membrane-) proteins and their complexes by solution and solid-state NMR but also other structural methods where segmental labeling is beneficial.
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Affiliation(s)
- Melina Daniilidis
- Bavarian
NMR Center, Department of Bioscience, School of Natural Sciences, Technical University of Munich, Ernst-Otto-Fischer-Str. 2, 85748 Garching, Germany
| | - Laura E. Sperl
- Bavarian
NMR Center, Department of Bioscience, School of Natural Sciences, Technical University of Munich, Ernst-Otto-Fischer-Str. 2, 85748 Garching, Germany
| | - Benedikt S. Müller
- Bavarian
NMR Center, Department of Bioscience, School of Natural Sciences, Technical University of Munich, Ernst-Otto-Fischer-Str. 2, 85748 Garching, Germany
| | - Antonia Babl
- Bavarian
NMR Center, Department of Bioscience, School of Natural Sciences, Technical University of Munich, Ernst-Otto-Fischer-Str. 2, 85748 Garching, Germany
| | - Franz Hagn
- Bavarian
NMR Center, Department of Bioscience, School of Natural Sciences, Technical University of Munich, Ernst-Otto-Fischer-Str. 2, 85748 Garching, Germany
- Institute
of Structural Biology, Helmholtz Munich, Ingolstädter Landstr. 1, 85764 Neuherberg, Germany
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2
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Smith AA, Pacull EM, Stecher S, Hildebrand PW, Vogel A, Huster D. Analysis of the Dynamics of the Human Growth Hormone Secretagogue Receptor Reveals Insights into the Energy Landscape of the Molecule. Angew Chem Int Ed Engl 2023; 62:e202302003. [PMID: 37205715 DOI: 10.1002/anie.202302003] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2023] [Revised: 05/04/2023] [Accepted: 05/19/2023] [Indexed: 05/21/2023]
Abstract
G protein-coupled receptors initiate signal transduction in response to ligand binding. Growth hormone secretagogue receptor (GHSR), the focus of this study, binds the 28 residue peptide ghrelin. While structures of GHSR in different states of activation are available, dynamics within each state have not been investigated in depth. We analyze long molecular dynamics simulation trajectories using "detectors" to compare dynamics of the apo and ghrelin-bound states yielding timescale-specific amplitudes of motion. We identify differences in dynamics between apo and ghrelin-bound GHSR in the extracellular loop 2 and transmembrane helices 5-7. NMR of the GHSR histidine residues reveals chemical shift differences in these regions. We evaluate timescale specific correlation of motions between residues of ghrelin and GHSR, where binding yields a high degree of correlation for the first 8 ghrelin residues, but less correlation for the helical end. Finally, we investigate the traverse of GHSR over a rugged energy landscape via principal component analysis.
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Affiliation(s)
- Albert A Smith
- Institute of Medical Physics and Biophysics, University of Leipzig, Härtelstr. 16/18, 04107, Leipzig, Germany
| | - Emelyne M Pacull
- Institute of Medical Physics and Biophysics, University of Leipzig, Härtelstr. 16/18, 04107, Leipzig, Germany
| | - Sabrina Stecher
- Institute of Medical Physics and Biophysics, University of Leipzig, Härtelstr. 16/18, 04107, Leipzig, Germany
| | - Peter W Hildebrand
- Institute of Medical Physics and Biophysics, University of Leipzig, Härtelstr. 16/18, 04107, Leipzig, Germany
| | - Alexander Vogel
- Institute of Medical Physics and Biophysics, University of Leipzig, Härtelstr. 16/18, 04107, Leipzig, Germany
| | - Daniel Huster
- Institute of Medical Physics and Biophysics, University of Leipzig, Härtelstr. 16/18, 04107, Leipzig, Germany
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3
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Mohamadi M, Goricanec D, Wagner G, Hagn F. NMR sample optimization and backbone assignment of a stabilized neurotensin receptor. J Struct Biol 2023; 215:107970. [PMID: 37142193 PMCID: PMC10242673 DOI: 10.1016/j.jsb.2023.107970] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2023] [Revised: 04/25/2023] [Accepted: 04/29/2023] [Indexed: 05/06/2023]
Abstract
G protein-coupled receptors (GPCRs) are involved in a multitude of cellular signaling cascades and consequently are a prominent target for pharmaceutical drugs. In the past decades, a growing number of high-resolution structures of GPCRs has been solved, providing unprecedented insights into their mode of action. However, knowledge on the dynamical nature of GPCRs is equally important for a better functional understanding, which can be obtained by NMR spectroscopy. Here, we employed a combination of size exclusion chromatography, thermal stability measurements and 2D-NMR experiments for the NMR sample optimization of the stabilized neurotensin receptor type 1 (NTR1) variant HTGH4 bound to the agonist neurotensin. We identified the short-chain lipid di-heptanoyl-glycero-phosphocholine (DH7PC) as a promising membrane mimetic for high resolution NMR experiments and obtained a partial NMR backbone resonance assignment. However, internal membrane-incorporated parts of the protein were not visible due to lacking amide proton back-exchange. Nevertheless, NMR and hydrogen deuterium exchange (HDX) mass spectrometry experiments could be used to probe structural changes at the orthosteric ligand binding site in the agonist and antagonist bound states. To enhance amide proton exchange we partially unfolded HTGH4 and observed additional NMR signals in the transmembrane region. However, this procedure led to a higher sample heterogeneity, suggesting that other strategies need to be applied to obtain high-quality NMR spectra of the entire protein. In summary, the herein reported NMR characterization is an essential step toward a more complete resonance assignment of NTR1 and for probing its structural and dynamical features in different functional states.
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Affiliation(s)
- Mariam Mohamadi
- Bavarian NMR Center (BNMRZ) and Structural Membrane Biochemistry, Dept. of Bioscience, TUM School of Natural Sciences, Technical University of Munich, 85748 Garching, Germany
| | - David Goricanec
- Bavarian NMR Center (BNMRZ) and Structural Membrane Biochemistry, Dept. of Bioscience, TUM School of Natural Sciences, Technical University of Munich, 85748 Garching, Germany
| | - Gerhard Wagner
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA
| | - Franz Hagn
- Bavarian NMR Center (BNMRZ) and Structural Membrane Biochemistry, Dept. of Bioscience, TUM School of Natural Sciences, Technical University of Munich, 85748 Garching, Germany; Institute of Structural Biology, Molecular Targets and Therapeutics Center, Helmholtz Munich 85764 Neuherberg, Germany.
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4
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Schmidt P, Vogel A, Schwarze B, Seufert F, Licha K, Wycisk V, Kilian W, Hildebrand PW, Mitschang L. Towards Probing Conformational States of Y2 Receptor Using Hyperpolarized 129Xe NMR. Molecules 2023; 28:molecules28031424. [PMID: 36771089 PMCID: PMC9919357 DOI: 10.3390/molecules28031424] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2022] [Revised: 01/20/2023] [Accepted: 01/30/2023] [Indexed: 02/05/2023] Open
Abstract
G protein-coupled receptors can adopt many different conformational states, each of them exhibiting different restraints towards downstream signaling pathways. One promising strategy to identify and quantify this conformational landscape is to introduce a cysteine at a receptor site sensitive to different states and label this cysteine with a probe for detection. Here, the application of NMR of hyperpolarized 129Xe for the detection of the conformational states of human neuropeptide Y2 receptor is introduced. The xenon trapping cage molecule cryptophane-A attached to a cysteine in extracellular loop 2 of the receptor facilitates chemical exchange saturation transfer experiments without and in the presence of native ligand neuropeptide Y. High-quality spectra indicative of structural states of the receptor-cage conjugate were obtained. Specifically, five signals could be assigned to the conjugate in the apo form. After the addition of NPY, one additional signal and subtle modifications in the persisting signals could be detected. The correlation of the spectroscopic signals and structural states was achieved with molecular dynamics simulations, suggesting frequent contact between the xenon trapping cage and the receptor surface but a preferred interaction with the bound ligand.
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Affiliation(s)
- Peter Schmidt
- Institute of Medical Physics and Biophysics, Medical Faculty, University of Leipzig, Haertelstrasse 16-18, 04107 Leipzig, Germany
| | - Alexander Vogel
- Institute of Medical Physics and Biophysics, Medical Faculty, University of Leipzig, Haertelstrasse 16-18, 04107 Leipzig, Germany
| | - Benedikt Schwarze
- Institute of Medical Physics and Biophysics, Medical Faculty, University of Leipzig, Haertelstrasse 16-18, 04107 Leipzig, Germany
| | - Florian Seufert
- Institute of Medical Physics and Biophysics, Medical Faculty, University of Leipzig, Haertelstrasse 16-18, 04107 Leipzig, Germany
| | - Kai Licha
- Institute of Chemistry and Biochemistry, Freie Universitaet Berlin, Takustrasse 3, 14195 Berlin, Germany
| | - Virginia Wycisk
- Institute of Chemistry and Biochemistry, Freie Universitaet Berlin, Takustrasse 3, 14195 Berlin, Germany
| | - Wolfgang Kilian
- Physikalisch-Technische Bundesanstalt Braunschweig und Berlin (PTB), Abbestrasse 2-12, 10587 Berlin, Germany
| | - Peter W. Hildebrand
- Institute of Medical Physics and Biophysics, Medical Faculty, University of Leipzig, Haertelstrasse 16-18, 04107 Leipzig, Germany
| | - Lorenz Mitschang
- Physikalisch-Technische Bundesanstalt Braunschweig und Berlin (PTB), Abbestrasse 2-12, 10587 Berlin, Germany
- Correspondence:
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5
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Ahlawat S, Mote KR, Lakomek NA, Agarwal V. Solid-State NMR: Methods for Biological Solids. Chem Rev 2022; 122:9643-9737. [PMID: 35238547 DOI: 10.1021/acs.chemrev.1c00852] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
In the last two decades, solid-state nuclear magnetic resonance (ssNMR) spectroscopy has transformed from a spectroscopic technique investigating small molecules and industrial polymers to a potent tool decrypting structure and underlying dynamics of complex biological systems, such as membrane proteins, fibrils, and assemblies, in near-physiological environments and temperatures. This transformation can be ascribed to improvements in hardware design, sample preparation, pulsed methods, isotope labeling strategies, resolution, and sensitivity. The fundamental engagement between nuclear spins and radio-frequency pulses in the presence of a strong static magnetic field is identical between solution and ssNMR, but the experimental procedures vastly differ because of the absence of molecular tumbling in solids. This review discusses routinely employed state-of-the-art static and MAS pulsed NMR methods relevant for biological samples with rotational correlation times exceeding 100's of nanoseconds. Recent developments in signal filtering approaches, proton methodologies, and multiple acquisition techniques to boost sensitivity and speed up data acquisition at fast MAS are also discussed. Several examples of protein structures (globular, membrane, fibrils, and assemblies) solved with ssNMR spectroscopy have been considered. We also discuss integrated approaches to structurally characterize challenging biological systems and some newly emanating subdisciplines in ssNMR spectroscopy.
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Affiliation(s)
- Sahil Ahlawat
- Tata Institute of Fundamental Research Hyderabad, Survey No. 36/P Gopanpally, Serilingampally, Ranga Reddy District, Hyderabad 500046, Telangana, India
| | - Kaustubh R Mote
- Tata Institute of Fundamental Research Hyderabad, Survey No. 36/P Gopanpally, Serilingampally, Ranga Reddy District, Hyderabad 500046, Telangana, India
| | - Nils-Alexander Lakomek
- University of Düsseldorf, Institute for Physical Biology, Universitätsstraße 1, 40225 Düsseldorf, Germany
| | - Vipin Agarwal
- Tata Institute of Fundamental Research Hyderabad, Survey No. 36/P Gopanpally, Serilingampally, Ranga Reddy District, Hyderabad 500046, Telangana, India
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6
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Abiko LA, Rogowski M, Gautier A, Schertler G, Grzesiek S. Efficient production of a functional G protein-coupled receptor in E. coli for structural studies. JOURNAL OF BIOMOLECULAR NMR 2021; 75:25-38. [PMID: 33501610 PMCID: PMC7897205 DOI: 10.1007/s10858-020-00354-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/18/2020] [Accepted: 12/08/2020] [Indexed: 05/22/2023]
Abstract
G protein-coupled receptors (GPCRs) are transmembrane signal transducers which regulate many key physiological process. Since their discovery, their analysis has been limited by difficulties in obtaining sufficient amounts of the receptors in high-quality, functional form from heterologous expression hosts. Albeit highly attractive because of its simplicity and the ease of isotope labeling for NMR studies, heterologous expression of functional GPCRs in E. coli has proven particularly challenging due to the absence of the more evolved protein expression and folding machinery of higher eukaryotic hosts. Here we first give an overview on the previous strategies for GPCR E. coli expression and then describe the development of an optimized robust protocol for the E. coli expression and purification of two mutants of the turkey β1-adrenergic receptor (β1AR) uniformly or selectively labeled in 15N or 2H,15N. These mutants had been previously optimized for thermal stability using insect cell expression and used successfully in crystallographic and NMR studies. The same sequences were then used for E. coli expression. Optimization of E. coli expression was achieved by a quantitative analysis of losses of receptor material at each step of the solubilization and purification procedure. Final yields are 0.2-0.3 mg receptor per liter culture. Whereas both expressed mutants are well folded and competent for orthosteric ligand binding, the less stable YY-β1AR mutant also comprises the two native tyrosines Y5.58 and Y7.53, which enable G protein binding. High-quality 1H-15N TROSY spectra were obtained for E. coli-expressed YY-β1AR in three different functional states (antagonist, agonist, and agonist + G protein-mimicking nanobody-bound), which are identical to spectra obtained of the same forms of the receptor expressed in insect cells. NdeI and AgeI restriction sites introduced into the expression plasmid allow for the easy replacement of the receptor gene by other GPCR genes of interest, and the provided quantitative workflow analysis may guide the respective adaptation of the purification protocol.
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Affiliation(s)
- Layara Akemi Abiko
- Focal Area Structural Biology and Biophysics, Biozentrum, University of Basel, 4056, Basel, Switzerland.
| | - Marco Rogowski
- Focal Area Structural Biology and Biophysics, Biozentrum, University of Basel, 4056, Basel, Switzerland
| | - Antoine Gautier
- Focal Area Structural Biology and Biophysics, Biozentrum, University of Basel, 4056, Basel, Switzerland
- Paul Scherrer Institute, 5232, Villigen, Switzerland
| | | | - Stephan Grzesiek
- Focal Area Structural Biology and Biophysics, Biozentrum, University of Basel, 4056, Basel, Switzerland.
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7
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Luo Q, Hu J, Yang G, Yuan X, Chen Z, Wang D, Lu Y, Zhu L, Wang G. Fasting Increases Iron Export by Modulating Ferroportin 1 Expression Through the Ghrelin/GHSR1α/MAPK Pathway in the Liver. Biol Trace Elem Res 2021; 199:267-277. [PMID: 32215811 DOI: 10.1007/s12011-020-02114-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/19/2020] [Accepted: 03/08/2020] [Indexed: 11/29/2022]
Abstract
The liver is contributed to maintaining body iron homeostasis and controlling of body adaptation to fasting. Although previous studies implied a negative relationship between iron and ghrelin in both mice and humans, it remains to be explored whether fasting or ghrelin has a functional effect on iron homeostasis in the liver. In this study, we examined the roles of fasting and ghrelin in modulating the protein expression of Fpn1, transferrin receptor 1 (TfR1), and ferritin light chain (Ft-L), as well as the mRNA expression of ghrelin, hepcidin, ghrelin O-acyltransferase (GOAT), and growth hormone secretagogue receptor 1 alpha (GHSR1α) in mouse liver and cultured hepatocytes. Our in vivo results suggested that fasting significantly upregulated the mRNA expression of ghrelin, GOAT, and GHSR1α, as well as the protein levels of ghrelin, Fpn1, and Ft-L, but not TfR1, in mouse liver. Interestingly, mRNA expression of hepcidin did not change significantly after fasting. Meanwhile, in cultured hepatocytes, ghrelin significantly increased the protein expression of Fpn1 but not Ft-L and TfR1 and significantly enhanced ERK phosphorylation. Furthermore, the pretreatment of cultured hepatocytes with either a pERK inhibitor or a GHSR1α antagonist abolished the effects of ghrelin on Fpn1 expression and ERK phosphorylation. Our findings confirmed that fasting increases iron export in the liver by upregulating Fpn1 expression through the ghrelin/GHSR1α/MAPK signaling pathway.
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Affiliation(s)
- Qianqian Luo
- Department of Physiology and Hypoxic Biomedicine, Institute of Special Environmental Medicine and Co-innovation Center of Neuroregeneration, Nantong University, 9 Seyuan Road, Chongchuan District, Nantong, 226019, Jiangsu, China
| | - Jianan Hu
- Department of Physiology and Hypoxic Biomedicine, Institute of Special Environmental Medicine and Co-innovation Center of Neuroregeneration, Nantong University, 9 Seyuan Road, Chongchuan District, Nantong, 226019, Jiangsu, China
| | - Guang Yang
- Department of Geriatrics, Hubei Provincial Hospital of Traditional Chinese Medicine, Wuhan, Hubei, China
- Hubei Provincial Academy of Traditional Chinese Medicine, Wuhan, Hubei, China
| | - Xiaoyu Yuan
- Department of Physiology and Hypoxic Biomedicine, Institute of Special Environmental Medicine and Co-innovation Center of Neuroregeneration, Nantong University, 9 Seyuan Road, Chongchuan District, Nantong, 226019, Jiangsu, China
| | - Zhongping Chen
- Department of Physiology and Hypoxic Biomedicine, Institute of Special Environmental Medicine and Co-innovation Center of Neuroregeneration, Nantong University, 9 Seyuan Road, Chongchuan District, Nantong, 226019, Jiangsu, China
| | - Dan Wang
- Department of Physiology and Hypoxic Biomedicine, Institute of Special Environmental Medicine and Co-innovation Center of Neuroregeneration, Nantong University, 9 Seyuan Road, Chongchuan District, Nantong, 226019, Jiangsu, China
| | - Yapeng Lu
- Department of Physiology and Hypoxic Biomedicine, Institute of Special Environmental Medicine and Co-innovation Center of Neuroregeneration, Nantong University, 9 Seyuan Road, Chongchuan District, Nantong, 226019, Jiangsu, China
| | - Li Zhu
- Department of Physiology and Hypoxic Biomedicine, Institute of Special Environmental Medicine and Co-innovation Center of Neuroregeneration, Nantong University, 9 Seyuan Road, Chongchuan District, Nantong, 226019, Jiangsu, China.
| | - Guohua Wang
- Department of Physiology and Hypoxic Biomedicine, Institute of Special Environmental Medicine and Co-innovation Center of Neuroregeneration, Nantong University, 9 Seyuan Road, Chongchuan District, Nantong, 226019, Jiangsu, China.
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8
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Krug U, Gloge A, Schmidt P, Becker‐Baldus J, Bernhard F, Kaiser A, Montag C, Gauglitz M, Vishnivetskiy SA, Gurevich VV, Beck‐Sickinger AG, Glaubitz C, Huster D. The Conformational Equilibrium of the Neuropeptide Y2 Receptor in Bilayer Membranes. Angew Chem Int Ed Engl 2020; 59:23854-23861. [PMID: 32790043 PMCID: PMC7736470 DOI: 10.1002/anie.202006075] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2020] [Revised: 07/13/2020] [Indexed: 12/23/2022]
Abstract
Dynamic structural transitions within the seven-transmembrane bundle represent the mechanism by which G-protein-coupled receptors convert an extracellular chemical signal into an intracellular biological function. Here, the conformational dynamics of the neuropeptide Y receptor type 2 (Y2R) during activation was investigated. The apo, full agonist-, and arrestin-bound states of Y2R were prepared by cell-free expression, functional refolding, and reconstitution into lipid membranes. To study conformational transitions between these states, all six tryptophans of Y2R were 13 C-labeled. NMR-signal assignment was achieved by dynamic-nuclear-polarization enhancement and the individual functional states of the receptor were characterized by monitoring 13 C NMR chemical shifts. Activation of Y2R is mediated by molecular switches involving the toggle switch residue Trp2816.48 of the highly conserved SWLP motif and Trp3277.55 adjacent to the NPxxY motif. Furthermore, a conformationally preserved "cysteine lock"-Trp11623.50 was identified.
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Affiliation(s)
- Ulrike Krug
- Institute of Medical Physics and BiophysicsUniversity of LeipzigHärtelstr. 16–1804107LeipzigGermany
| | - Anika Gloge
- Institute of Medical Physics and BiophysicsUniversity of LeipzigHärtelstr. 16–1804107LeipzigGermany
| | - Peter Schmidt
- Institute of Medical Physics and BiophysicsUniversity of LeipzigHärtelstr. 16–1804107LeipzigGermany
| | - Johanna Becker‐Baldus
- Institute of Biophysical ChemistryGoethe University FrankfurtGermany
- Center for Biomolecular Magnetic ResonanceGoethe University FrankfurtGermany
| | - Frank Bernhard
- Institute of Biophysical ChemistryGoethe University FrankfurtGermany
- Center for Biomolecular Magnetic ResonanceGoethe University FrankfurtGermany
| | - Anette Kaiser
- Institute of BiochemistryUniversity of LeipzigLeipzigGermany
| | - Cindy Montag
- Institute of Medical Physics and BiophysicsUniversity of LeipzigHärtelstr. 16–1804107LeipzigGermany
| | - Marcel Gauglitz
- Institute of Medical Physics and BiophysicsUniversity of LeipzigHärtelstr. 16–1804107LeipzigGermany
- Berlin Joint Electron Paramagnetic Resonance LaboratoryFree University BerlinGermany
| | | | | | | | - Clemens Glaubitz
- Institute of Biophysical ChemistryGoethe University FrankfurtGermany
- Center for Biomolecular Magnetic ResonanceGoethe University FrankfurtGermany
| | - Daniel Huster
- Institute of Medical Physics and BiophysicsUniversity of LeipzigHärtelstr. 16–1804107LeipzigGermany
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9
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Krug U, Gloge A, Schmidt P, Becker‐Baldus J, Bernhard F, Kaiser A, Montag C, Gauglitz M, Vishnivetskiy SA, Gurevich VV, Beck‐Sickinger AG, Glaubitz C, Huster D. Das Konformationsgleichgewicht des Neuropeptid‐Y2‐Rezeptors in Lipidmembranen. Angew Chem Int Ed Engl 2020. [DOI: 10.1002/ange.202006075] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Ulrike Krug
- Institut für Medizinische Physik und Biophysik Universität Leipzig Härtelstr. 16–18 04107 Leipzig Deutschland
| | - Anika Gloge
- Institut für Medizinische Physik und Biophysik Universität Leipzig Härtelstr. 16–18 04107 Leipzig Deutschland
| | - Peter Schmidt
- Institut für Medizinische Physik und Biophysik Universität Leipzig Härtelstr. 16–18 04107 Leipzig Deutschland
| | - Johanna Becker‐Baldus
- Institut für Biophysikalische Chemie Goethe-Universität Frankfurt am Main Deutschland
- Zentrum für Biomolekulare Magnetresonanz Goethe-Universität Frankfurt am Main Deutschland
| | - Frank Bernhard
- Institut für Biophysikalische Chemie Goethe-Universität Frankfurt am Main Deutschland
- Zentrum für Biomolekulare Magnetresonanz Goethe-Universität Frankfurt am Main Deutschland
| | - Anette Kaiser
- Institut für Biochemie Universität Leipzig Deutschland
| | - Cindy Montag
- Institut für Medizinische Physik und Biophysik Universität Leipzig Härtelstr. 16–18 04107 Leipzig Deutschland
| | - Marcel Gauglitz
- Institut für Medizinische Physik und Biophysik Universität Leipzig Härtelstr. 16–18 04107 Leipzig Deutschland
- Berlin Joint Electron Paramagnetic Resonance Laboratory Freie Universität Berlin Deutschland
| | | | | | | | - Clemens Glaubitz
- Institut für Biophysikalische Chemie Goethe-Universität Frankfurt am Main Deutschland
- Zentrum für Biomolekulare Magnetresonanz Goethe-Universität Frankfurt am Main Deutschland
| | - Daniel Huster
- Institut für Medizinische Physik und Biophysik Universität Leipzig Härtelstr. 16–18 04107 Leipzig Deutschland
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10
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Vogel A, Bosse M, Gauglitz M, Wistuba S, Schmidt P, Kaiser A, Gurevich VV, Beck-Sickinger AG, Hildebrand PW, Huster D. The Dynamics of the Neuropeptide Y Receptor Type 1 Investigated by Solid-State NMR and Molecular Dynamics Simulation. Molecules 2020; 25:E5489. [PMID: 33255213 PMCID: PMC7727705 DOI: 10.3390/molecules25235489] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2020] [Revised: 11/09/2020] [Accepted: 11/12/2020] [Indexed: 01/08/2023] Open
Abstract
We report data on the structural dynamics of the neuropeptide Y (NPY) G-protein-coupled receptor (GPCR) type 1 (Y1R), a typical representative of class A peptide ligand GPCRs, using a combination of solid-state NMR and molecular dynamics (MD) simulation. First, the equilibrium dynamics of Y1R were studied using 15N-NMR and quantitative determination of 1H-13C order parameters through the measurement of dipolar couplings in separated-local-field NMR experiments. Order parameters reporting the amplitudes of the molecular motions of the C-H bond vectors of Y1R in DMPC membranes are 0.57 for the Cα sites and lower in the side chains (0.37 for the CH2 and 0.18 for the CH3 groups). Different NMR excitation schemes identify relatively rigid and also dynamic segments of the molecule. In monounsaturated membranes composed of longer lipid chains, Y1R is more rigid, attributed to a higher hydrophobic thickness of the lipid membrane. The presence of an antagonist or NPY has little influence on the amplitude of motions, whereas the addition of agonist and arrestin led to a pronounced rigidization. To investigate Y1R dynamics with site resolution, we conducted extensive all-atom MD simulations of the apo and antagonist-bound state. In each state, three replicas with a length of 20 μs (with one exception, where the trajectory length was 10 μs) were conducted. In these simulations, order parameters of each residue were determined and showed high values in the transmembrane helices, whereas the loops and termini exhibit much lower order. The extracellular helix segments undergo larger amplitude motions than their intracellular counterparts, whereas the opposite is observed for the loops, Helix 8, and termini. Only minor differences in order were observed between the apo and antagonist-bound state, whereas the time scale of the motions is shorter for the apo state. Although these relatively fast motions occurring with correlation times of ns up to a few µs have no direct relevance for receptor activation, it is believed that they represent the prerequisite for larger conformational transitions in proteins.
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Affiliation(s)
- Alexander Vogel
- Institute for Medical Physics and Biophysics, University of Leipzig, Härtelstr. 16-18, D-04107 Leipzig, Germany; (A.V.); (M.B.); (M.G.); (S.W.); (P.S.)
| | - Mathias Bosse
- Institute for Medical Physics and Biophysics, University of Leipzig, Härtelstr. 16-18, D-04107 Leipzig, Germany; (A.V.); (M.B.); (M.G.); (S.W.); (P.S.)
| | - Marcel Gauglitz
- Institute for Medical Physics and Biophysics, University of Leipzig, Härtelstr. 16-18, D-04107 Leipzig, Germany; (A.V.); (M.B.); (M.G.); (S.W.); (P.S.)
| | - Sarah Wistuba
- Institute for Medical Physics and Biophysics, University of Leipzig, Härtelstr. 16-18, D-04107 Leipzig, Germany; (A.V.); (M.B.); (M.G.); (S.W.); (P.S.)
| | - Peter Schmidt
- Institute for Medical Physics and Biophysics, University of Leipzig, Härtelstr. 16-18, D-04107 Leipzig, Germany; (A.V.); (M.B.); (M.G.); (S.W.); (P.S.)
| | - Anette Kaiser
- Faculty of Life Sciences, Institute of Biochemistry, University of Leipzig, Brüderstr. 34, D-04103 Leipzig, Germany; (A.K.); (A.G.B.-S.)
| | - Vsevolod V. Gurevich
- Vanderbilt University Medical Center, 2200 Pierce Avenue, Nashville, TN 37232, USA;
| | - Annette G. Beck-Sickinger
- Faculty of Life Sciences, Institute of Biochemistry, University of Leipzig, Brüderstr. 34, D-04103 Leipzig, Germany; (A.K.); (A.G.B.-S.)
| | - Peter W. Hildebrand
- Institute for Medical Physics and Biophysics, University of Leipzig, Härtelstr. 16-18, D-04107 Leipzig, Germany; (A.V.); (M.B.); (M.G.); (S.W.); (P.S.)
| | - Daniel Huster
- Institute for Medical Physics and Biophysics, University of Leipzig, Härtelstr. 16-18, D-04107 Leipzig, Germany; (A.V.); (M.B.); (M.G.); (S.W.); (P.S.)
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11
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Pacull EM, Sendker F, Bernhard F, Scheidt HA, Schmidt P, Huster D, Krug U. Integration of Cell-Free Expression and Solid-State NMR to Investigate the Dynamic Properties of Different Sites of the Growth Hormone Secretagogue Receptor. Front Pharmacol 2020; 11:562113. [PMID: 33324203 PMCID: PMC7723455 DOI: 10.3389/fphar.2020.562113] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2020] [Accepted: 09/21/2020] [Indexed: 01/09/2023] Open
Abstract
Cell-free expression represents an attractive method to produce large quantities of selectively labeled protein for NMR applications. Here, cell-free expression was used to label specific regions of the growth hormone secretagogue receptor (GHSR) with NMR-active isotopes. The GHSR is a member of the class A family of G protein-coupled receptors. A cell-free expression system was established to produce the GHSR in the precipitated form. The solubilized receptor was refolded in vitro and reconstituted into DMPC lipid membranes. Methionines, arginines, and histidines were chosen for 13C-labeling as they are representative for the transmembrane domains, the loops and flanking regions of the transmembrane α-helices, and the C-terminus of the receptor, respectively. The dynamics of the isotopically labeled residues was characterized by solid-state NMR measuring motionally averaged 1H-13C dipolar couplings, which were converted into molecular order parameters. Separated local field DIPSHIFT experiments under magic-angle spinning conditions using either varying cross polarization contact times or direct excitation provided order parameters for these residues showing that the C-terminus was the segment with the highest motional amplitude. The loop regions and helix ends as well as the transmembrane regions of the GHSR represent relatively rigid segments in the overall very flexible receptor molecule. Although no site resolution could be achieved in the experiments, the previously reported highly dynamic character of the receptor concluded from uniformly 13C labeled receptor samples could be further specified by this segmental labeling approach, leading to a more diversified understanding of the receptor dynamics under equilibrium conditions.
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Affiliation(s)
- Emelyne M Pacull
- Institute for Medical Physics and Biophysics, University of Leipzig, Leipzig, Germany
| | - Franziska Sendker
- Institute for Medical Physics and Biophysics, University of Leipzig, Leipzig, Germany
| | - Frank Bernhard
- Institute of Biophysical Chemistry, Goethe University Frankfurt, Frankfurt am Main, Germany.,Center for Biomolecular Magnetic Resonance, Goethe University Frankfurt, Frankfurt am Main, Germany
| | - Holger A Scheidt
- Institute for Medical Physics and Biophysics, University of Leipzig, Leipzig, Germany
| | - Peter Schmidt
- Institute for Medical Physics and Biophysics, University of Leipzig, Leipzig, Germany
| | - Daniel Huster
- Institute for Medical Physics and Biophysics, University of Leipzig, Leipzig, Germany
| | - Ulrike Krug
- Institute for Medical Physics and Biophysics, University of Leipzig, Leipzig, Germany
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12
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Jones AJY, Gabriel F, Tandale A, Nietlispach D. Structure and Dynamics of GPCRs in Lipid Membranes: Physical Principles and Experimental Approaches. Molecules 2020; 25:E4729. [PMID: 33076366 PMCID: PMC7587580 DOI: 10.3390/molecules25204729] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2020] [Revised: 10/11/2020] [Accepted: 10/12/2020] [Indexed: 02/06/2023] Open
Abstract
Over the past decade, the vast amount of information generated through structural and biophysical studies of GPCRs has provided unprecedented mechanistic insight into the complex signalling behaviour of these receptors. With this recent information surge, it has also become increasingly apparent that in order to reproduce the various effects that lipids and membranes exert on the biological function for these allosteric receptors, in vitro studies of GPCRs need to be conducted under conditions that adequately approximate the native lipid bilayer environment. In the first part of this review, we assess some of the more general effects that a membrane environment exerts on lipid bilayer-embedded proteins such as GPCRs. This is then followed by the consideration of more specific effects, including stoichiometric interactions with specific lipid subtypes. In the final section, we survey a range of different membrane mimetics that are currently used for in vitro studies, with a focus on NMR applications.
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Affiliation(s)
| | | | | | - Daniel Nietlispach
- Department of Biochemistry, University of Cambridge, 80 Tennis Court Road, Cambridge CB2 1GA, UK; (A.J.Y.J.); (F.G.); (A.T.)
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13
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Capturing Peptide-GPCR Interactions and Their Dynamics. Molecules 2020; 25:molecules25204724. [PMID: 33076289 PMCID: PMC7587574 DOI: 10.3390/molecules25204724] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2020] [Revised: 10/08/2020] [Accepted: 10/09/2020] [Indexed: 12/16/2022] Open
Abstract
Many biological functions of peptides are mediated through G protein-coupled receptors (GPCRs). Upon ligand binding, GPCRs undergo conformational changes that facilitate the binding and activation of multiple effectors. GPCRs regulate nearly all physiological processes and are a favorite pharmacological target. In particular, drugs are sought after that elicit the recruitment of selected effectors only (biased ligands). Understanding how ligands bind to GPCRs and which conformational changes they induce is a fundamental step toward the development of more efficient and specific drugs. Moreover, it is emerging that the dynamic of the ligand–receptor interaction contributes to the specificity of both ligand recognition and effector recruitment, an aspect that is missing in structural snapshots from crystallography. We describe here biochemical and biophysical techniques to address ligand–receptor interactions in their structural and dynamic aspects, which include mutagenesis, crosslinking, spectroscopic techniques, and mass-spectrometry profiling. With a main focus on peptide receptors, we present methods to unveil the ligand–receptor contact interface and methods that address conformational changes both in the ligand and the GPCR. The presented studies highlight a wide structural heterogeneity among peptide receptors, reveal distinct structural changes occurring during ligand binding and a surprisingly high dynamics of the ligand–GPCR complexes.
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14
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Probing the Y 2 Receptor on Transmembrane, Intra- and Extra-Cellular Sites for EPR Measurements. Molecules 2020; 25:molecules25184143. [PMID: 32927734 PMCID: PMC7571237 DOI: 10.3390/molecules25184143] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2020] [Revised: 09/04/2020] [Accepted: 09/09/2020] [Indexed: 02/07/2023] Open
Abstract
The function of G protein-coupled receptors is intrinsically linked to their conformational dynamics. In conjugation with site-directed spin labeling, electron paramagnetic resonance (EPR) spectroscopy provides powerful tools to study the highly dynamic conformational states of these proteins. Here, we explored positions for nitroxide spin labeling coupled to single cysteines, introduced at transmembrane, intra- and extra-cellular sites of the human neuropeptide Y2 receptor. Receptor mutants were functionally analyzed in cell culture system, expressed in Escherichia coli fermentation with yields of up to 10 mg of purified protein per liter expression medium and functionally reconstituted into a lipid bicelle environment. Successful spin labeling was confirmed by a fluorescence assay and continuous wave EPR measurements. EPR spectra revealed mobile and immobile populations, indicating multiple dynamic conformational states of the receptor. We found that the singly mutated positions by MTSL ((1-oxyl-2,2,5,5-tetramethyl-2,5-dihydro-1H-pyrrol-3-yl) methyl methanesulfonothioate) have a water exposed immobilized conformation as their main conformation, while in case of the IDSL (bis(1-oxyl-2,2,5,5-tetramethyl-3-imidazolin-4-yl) disulfide) labeled positions, the main conformation are mainly of hydrophobic nature. Further, double cysteine mutants were generated and examined for potential applications of distance measurements by double electron–electron resonance (DEER) pulsed EPR technique on the receptor.
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15
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Bender BJ, Vortmeier G, Ernicke S, Bosse M, Kaiser A, Els-Heindl S, Krug U, Beck-Sickinger A, Meiler J, Huster D. Structural Model of Ghrelin Bound to its G Protein-Coupled Receptor. Structure 2019; 27:537-544.e4. [PMID: 30686667 DOI: 10.1016/j.str.2018.12.004] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2018] [Revised: 09/14/2018] [Accepted: 12/05/2018] [Indexed: 12/27/2022]
Abstract
The peptide ghrelin targets the growth hormone secretagogue receptor 1a (GHSR) to signal changes in cell metabolism and is a sought-after therapeutic target, although no structure is known to date. To investigate the structural basis of ghrelin binding to GHSR, we used solid-state nuclear magnetic resonance (NMR) spectroscopy, site-directed mutagenesis, and Rosetta modeling. The use of saturation transfer difference NMR identified key residues in the peptide for receptor binding beyond the known motif. This information combined with assignment of the secondary structure of ghrelin in its receptor-bound state was incorporated into Rosetta using an approach that accounts for flexible binding partners. The NMR data and models revealed an extended binding surface that was confirmed via mutagenesis. Our results agree with a growing evidence of peptides interacting via two sites at G protein-coupled receptors.
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Affiliation(s)
- Brian Joseph Bender
- Department of Pharmacology and Center for Structural Biology, Vanderbilt University, Nashville, TN 37232, USA
| | - Gerrit Vortmeier
- Institute for Medical Physics and Biophysics, Medical Department, Leipzig University, Härtelstrasse 16-18, 04107 Leipzig, Germany
| | - Stefan Ernicke
- Institute of Biochemistry, Faculty of Life Sciences, Leipzig University, Brüderstrasse 34, 04103 Leipzig, Germany
| | - Mathias Bosse
- Institute for Medical Physics and Biophysics, Medical Department, Leipzig University, Härtelstrasse 16-18, 04107 Leipzig, Germany
| | - Anette Kaiser
- Institute of Biochemistry, Faculty of Life Sciences, Leipzig University, Brüderstrasse 34, 04103 Leipzig, Germany
| | - Sylvia Els-Heindl
- Institute of Biochemistry, Faculty of Life Sciences, Leipzig University, Brüderstrasse 34, 04103 Leipzig, Germany
| | - Ulrike Krug
- Institute for Medical Physics and Biophysics, Medical Department, Leipzig University, Härtelstrasse 16-18, 04107 Leipzig, Germany
| | - Annette Beck-Sickinger
- Institute of Biochemistry, Faculty of Life Sciences, Leipzig University, Brüderstrasse 34, 04103 Leipzig, Germany
| | - Jens Meiler
- Department of Pharmacology and Center for Structural Biology, Vanderbilt University, Nashville, TN 37232, USA.
| | - Daniel Huster
- Institute for Medical Physics and Biophysics, Medical Department, Leipzig University, Härtelstrasse 16-18, 04107 Leipzig, Germany.
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16
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Casiraghi M, Damian M, Lescop E, Banères JL, Catoire LJ. Illuminating the Energy Landscape of GPCRs: The Key Contribution of Solution-State NMR Associated with Escherichia coli as an Expression Host. Biochemistry 2018; 57:2297-2307. [PMID: 29607648 DOI: 10.1021/acs.biochem.8b00035] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Conformational dynamics of GPCRs are central to their function but are difficult to explore at the atomic scale. Solution-state NMR has provided the major contribution in that area of study during the past decade, despite nonoptimized labeling schemes due to the use of insect cells and, to a lesser extent, yeast as the main expression hosts. Indeed, the most efficient isotope-labeling scheme ever to address energy landscape issues for large proteins or protein complexes relies on the use of 13CH3 probes immersed in a perdeuterated dipolar environment, which is essentially out of reach of eukaryotic expression systems. In contrast, although its contribution has been underestimated because of technical issues, Escherichia coli is by far the best-adapted host for such labeling. As it is now tightly controlled, we show in this review that bacterial expression can provide an NMR spectral resolution never achieved in the GPCR field.
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Affiliation(s)
- Marina Casiraghi
- Laboratoire de Biologie Physico-Chimique des Protéines Membranaires , UMR 7099, CNRS/Université Paris Diderot, Sorbonne Paris Cité, Institut de Biologie Physico-Chimique (FRC 550) , 13 rue Pierre et Marie Curie , 75005 Paris , France
| | - Marjorie Damian
- Institut des Biomolécules Max Mousseron (IBMM), UMR5247 CNRS, Université Montpellier, ENSCM , 15 av. Charles Flahault , 34093 Montpellier , France
| | - Ewen Lescop
- Institut de Chimie des Substances Naturelles, CNRS UPR 2301, Université Paris-Sud, Université Paris-Saclay , 1 av. de la Terrasse , 91198 Gif-sur-Yvette , France
| | - Jean-Louis Banères
- Institut des Biomolécules Max Mousseron (IBMM), UMR5247 CNRS, Université Montpellier, ENSCM , 15 av. Charles Flahault , 34093 Montpellier , France
| | - Laurent J Catoire
- Laboratoire de Biologie Physico-Chimique des Protéines Membranaires , UMR 7099, CNRS/Université Paris Diderot, Sorbonne Paris Cité, Institut de Biologie Physico-Chimique (FRC 550) , 13 rue Pierre et Marie Curie , 75005 Paris , France
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17
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Schmidt P, Bender BJ, Kaiser A, Gulati K, Scheidt HA, Hamm HE, Meiler J, Beck-Sickinger AG, Huster D. Improved in Vitro Folding of the Y 2 G Protein-Coupled Receptor into Bicelles. Front Mol Biosci 2018; 4:100. [PMID: 29387686 PMCID: PMC5776092 DOI: 10.3389/fmolb.2017.00100] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2017] [Accepted: 12/28/2017] [Indexed: 12/26/2022] Open
Abstract
Prerequisite for structural studies on G protein-coupled receptors is the preparation of highly concentrated, stable, and biologically active receptor samples in milligram amounts of protein. Here, we present an improved protocol for Escherichia coli expression, functional refolding, and reconstitution into bicelles of the human neuropeptide Y receptor type 2 (Y2R) for solution and solid-state NMR experiments. The isotopically labeled receptor is expressed in inclusion bodies and purified using SDS. We studied the details of an improved preparation protocol including the in vitro folding of the receptor, e.g., the native disulfide bridge formation, the exchange of the denaturating detergent SDS, and the functional reconstitution into bicelle environments of varying size. Full pharmacological functionality of the Y2R preparation was shown by a ligand affinity of 4 nM and G-protein activation. Further, simple NMR experiments are used to test sample quality in high micromolar concentration.
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Affiliation(s)
- Peter Schmidt
- Faculty of Medicine, Institute for Medical Physics and Biophysics, Leipzig University, Leipzig, Germany
| | - Brian J Bender
- Center for Structural Biology, Vanderbilt University, Nashville, TN, United States.,Department of Pharmacology, Vanderbilt University Medical Center, Nashville, TN, United States
| | - Anette Kaiser
- Faculty of Life Sciences, Institute of Biochemistry, University of Leipzig, Leipzig, Germany
| | - Khushboo Gulati
- Department of Biotechnology, Indian Institute of Technology Roorkee, Uttarakhand, India
| | - Holger A Scheidt
- Faculty of Medicine, Institute for Medical Physics and Biophysics, Leipzig University, Leipzig, Germany
| | - Heidi E Hamm
- Department of Pharmacology, Vanderbilt University Medical Center, Nashville, TN, United States
| | - Jens Meiler
- Center for Structural Biology, Vanderbilt University, Nashville, TN, United States.,Department of Pharmacology, Vanderbilt University Medical Center, Nashville, TN, United States
| | | | - Daniel Huster
- Faculty of Medicine, Institute for Medical Physics and Biophysics, Leipzig University, Leipzig, Germany
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