1
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Dhiman R, Perera RS, Poojari CS, Wiedemann HTA, Kappl R, Kay CWM, Hub JS, Schrul B. Hairpin protein partitioning from the ER to lipid droplets involves major structural rearrangements. Nat Commun 2024; 15:4504. [PMID: 38802378 PMCID: PMC11130287 DOI: 10.1038/s41467-024-48843-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2024] [Accepted: 05/15/2024] [Indexed: 05/29/2024] Open
Abstract
Lipid droplet (LD) function relies on proteins partitioning between the endoplasmic reticulum (ER) phospholipid bilayer and the LD monolayer membrane to control cellular adaptation to metabolic changes. It has been proposed that these hairpin proteins integrate into both membranes in a similar monotopic topology, enabling their passive lateral diffusion during LD emergence at the ER. Here, we combine biochemical solvent-accessibility assays, electron paramagnetic resonance spectroscopy and intra-molecular crosslinking experiments with molecular dynamics simulations, and determine distinct intramembrane positionings of the ER/LD protein UBXD8 in ER bilayer and LD monolayer membranes. UBXD8 is deeply inserted into the ER bilayer with a V-shaped topology and adopts an open-shallow conformation in the LD monolayer. Major structural rearrangements are required to enable ER-to-LD partitioning. Free energy calculations suggest that such structural transition is unlikely spontaneous, indicating that ER-to-LD protein partitioning relies on more complex mechanisms than anticipated and providing regulatory means for this trans-organelle protein trafficking.
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Affiliation(s)
- Ravi Dhiman
- Medical Biochemistry and Molecular Biology, Center for Molecular Signaling (PZMS), Faculty of Medicine, Saarland University, 66421, Homburg/Saar, Germany
| | - Rehani S Perera
- Medical Biochemistry and Molecular Biology, Center for Molecular Signaling (PZMS), Faculty of Medicine, Saarland University, 66421, Homburg/Saar, Germany
| | - Chetan S Poojari
- Theoretical Physics and Center for Biophysics, Saarland University, 66123, Saarbrücken, Germany
| | - Haakon T A Wiedemann
- Physical Chemistry and Chemistry Education, Saarland University, 66123, Saarbrücken, Germany
| | - Reinhard Kappl
- Department of Biophysics, Center for Integrative Physiology and Molecular Medicine (CIPMM), Faculty of Medicine, Saarland University, 66421, Homburg/Saar, Germany
| | - Christopher W M Kay
- Physical Chemistry and Chemistry Education, Saarland University, 66123, Saarbrücken, Germany
- London Centre for Nanotechnology, University College London, WC1H 0AH, London, UK
| | - Jochen S Hub
- Theoretical Physics and Center for Biophysics, Saarland University, 66123, Saarbrücken, Germany
| | - Bianca Schrul
- Medical Biochemistry and Molecular Biology, Center for Molecular Signaling (PZMS), Faculty of Medicine, Saarland University, 66421, Homburg/Saar, Germany.
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2
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Jaiswal M, Tran TT, Guo J, Zhou M, Kundu S, Guo Z, Fanucci GE. Spin-labeling Insights into How Chemical Fixation Impacts Glycan Organization on Cells. APPLIED MAGNETIC RESONANCE 2024; 55:317-333. [PMID: 38469359 PMCID: PMC10927023 DOI: 10.1007/s00723-023-01624-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2023] [Revised: 09/21/2023] [Accepted: 09/22/2023] [Indexed: 03/13/2024]
Abstract
As new methods to interrogate glycan organization on cells develop, it is important to have a molecular level understanding of how chemical fixation can impact results and interpretations. Site-directed spin labeling technologies are well suited to study how the spin label mobility is impacted by local environmental conditions, such as those imposed by cross-linking effects of paraformaldehyde cell fixation methods. Here, we utilize three different azide-containing sugars for metabolic glycan engineering with HeLa cells to incorporate azido glycans that are modified with a DBCO-based nitroxide moiety via click reaction. Continuous wave X-band electron paramagnetic resonance spectroscopy is employed to characterize how the chronological sequence of chemical fixation and spin labeling impacts the local mobility and accessibility of the nitroxide-labeled glycans in the glycocalyx of HeLa cells. Results demonstrate that chemical fixation with paraformaldehyde can alter local glycan mobility and care should be taken in the analysis of data in any study where chemical fixation and cellular labeling occur.
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Affiliation(s)
- Mohit Jaiswal
- Department of Chemistry, University of Florida, 214 Leigh Hall, Gainesville, FL 32611, USA
| | - Trang T Tran
- Department of Chemistry, University of Florida, 214 Leigh Hall, Gainesville, FL 32611, USA
| | - Jiatong Guo
- Department of Chemistry, University of Florida, 214 Leigh Hall, Gainesville, FL 32611, USA
| | - Mingwei Zhou
- Department of Chemistry, University of Florida, 214 Leigh Hall, Gainesville, FL 32611, USA
| | - Sayan Kundu
- Department of Chemistry, University of Florida, 214 Leigh Hall, Gainesville, FL 32611, USA
| | - Zhongwu Guo
- Department of Chemistry, University of Florida, 214 Leigh Hall, Gainesville, FL 32611, USA
| | - Gail E Fanucci
- Department of Chemistry, University of Florida, 214 Leigh Hall, Gainesville, FL 32611, USA
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3
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Cherniavskyi YK, Oliva R, Stellato M, Del Vecchio P, Galdiero S, Falanga A, Dames SA, Tieleman DP. Structural characterization of the antimicrobial peptides myxinidin and WMR in bacterial membrane mimetic micelles and bicelles. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2024; 1866:184272. [PMID: 38211645 DOI: 10.1016/j.bbamem.2024.184272] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/22/2023] [Revised: 01/03/2024] [Accepted: 01/04/2024] [Indexed: 01/13/2024]
Abstract
Antimicrobial peptides are a promising class of potential antibiotics that interact selectively with negatively charged lipid bilayers. This paper presents the structural characterization of the antimicrobial peptides myxinidin and WMR associated with bacterial membrane mimetic micelles and bicelles by NMR, CD spectroscopy, and molecular dynamics simulations. Both peptides adopt a different conformation in the lipidic environment than in aqueous solution. The location of the peptides in micelles and bicelles has been studied by paramagnetic relaxation enhancement experiments with paramagnetic tagged 5- and 16-doxyl stearic acid (5-/16-SASL). Molecular dynamics simulations of multiple copies of the peptides were used to obtain an atomic level of detail on membrane-peptide and peptide-peptide interactions. Our results highlight an essential role of the negatively charged membrane mimetic in the structural stability of both myxinidin and WMR. The peptides localize predominantly in the membrane's headgroup region and have a noticeable membrane thinning effect on the overall bilayer structure. Myxinidin and WMR show a different tendency to self-aggregate, which is also influenced by the membrane composition (DOPE/DOPG versus DOPE/DOPG/CL) and can be related to the previously observed difference in the ability of the peptides to disrupt different types of model membranes.
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Affiliation(s)
- Yevhen K Cherniavskyi
- Department of Biological Sciences and Centre for Molecular Simulation, University of Calgary, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada
| | - Rosario Oliva
- Department of Chemical Sciences, University of Naples "Federico II", via Cintia, 80126 Naples, Italy
| | - Marco Stellato
- Department of Chemical Sciences, University of Naples "Federico II", via Cintia, 80126 Naples, Italy
| | - Pompea Del Vecchio
- Department of Chemical Sciences, University of Naples "Federico II", via Cintia, 80126 Naples, Italy
| | - Stefania Galdiero
- Department of Pharmacy, University of Naples 'Federico II', Via Domenico Montesano 49, 80131 Naples, Italy
| | - Annarita Falanga
- Department of Agricultural Science, University of Naples 'Federico II', Via dell' Università 100, 80055 Portici, Naples, Italy
| | - Sonja A Dames
- Chair of Biomolecular NMR Spectroscopy, Department of Chemistry, Technische Universität München, Lichtenbergstr. 4, 85747 Garching, Germany; Hausdorff Center for Mathematics, University of Bonn, Endenicher Allee 62, 53115 Bonn, Germany; Institute of Structural Biology, Helmholtz Zentrum München, Ingolstädter Landstr. 1, 85764 Neuherberg, Germany.
| | - D Peter Tieleman
- Department of Biological Sciences and Centre for Molecular Simulation, University of Calgary, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada.
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4
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Khan RH, Rotich NC, Morris A, Ahammad T, Baral B, Sahu ID, Lorigan GA. Probing the Structural Topology and Dynamic Properties of gp28 Using Continuous Wave Electron Paramagnetic Resonance Spectroscopy. J Phys Chem B 2023; 127:9236-9247. [PMID: 37856870 DOI: 10.1021/acs.jpcb.3c03679] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2023]
Abstract
Lysis of Gram-negative bacteria by dsDNA phages is accomplished through either the canonical holin-endolysin pathway or the pinholin-SAR endolysin pathway. During lysis, the outer membrane (OM) is disrupted, typically by two-component spanins or unimolecular spanins. However, in the absence of spanins, phages use alternative proteins called Disruptin to disrupt the OM. The Disruptin family includes the cationic antimicrobial peptide gp28, which is found in the virulent podophage φKT. In this study, EPR spectroscopy was used to analyze the dynamics and topology of gp28 incorporated into a lipid bilayer, revealing differences in mobility, depth parameter, and membrane interaction among different segments and residues of the protein. Our results indicate that multiple points of helix 2 and helix 3 interact with the phospholipid membrane, while others are solvent-exposed, suggesting that gp28 is a surface-bound peptide. The CW-EPR power saturation data and helical wheel analysis confirmed the amphipathic-helical structure of gp28. Additionally, course-grain molecular dynamics simulations were further used to develop the structural model of the gp28 peptide associated with the lipid bilayers. Based on the data obtained in this study, we propose a structural topology model for gp28 with respect to the membrane. This work provides important insights into the structural and dynamic properties of gp28 incorporated into a lipid bilayer environment.
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Affiliation(s)
- Rasal H Khan
- Department of Chemistry and Biochemistry, Miami University, Oxford, Ohio 45056, United States
| | - Nancy C Rotich
- Department of Chemistry and Biochemistry, Miami University, Oxford, Ohio 45056, United States
| | - Andrew Morris
- Department of Chemistry and Biochemistry, Miami University, Oxford, Ohio 45056, United States
| | - Tanbir Ahammad
- Department of Chemistry and Biochemistry, Miami University, Oxford, Ohio 45056, United States
| | - Binaya Baral
- Department of Chemistry and Biochemistry, Miami University, Oxford, Ohio 45056, United States
| | - Indra D Sahu
- Natural Science Division, Campbellsville University, Campbellsville, Kentucky 42718, United States
| | - Gary A Lorigan
- Department of Chemistry and Biochemistry, Miami University, Oxford, Ohio 45056, United States
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5
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Subczynski WK, Pasenkiewicz-Gierula M, Widomska J. Protecting the Eye Lens from Oxidative Stress through Oxygen Regulation. Antioxidants (Basel) 2023; 12:1783. [PMID: 37760086 PMCID: PMC10525422 DOI: 10.3390/antiox12091783] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2023] [Revised: 09/08/2023] [Accepted: 09/18/2023] [Indexed: 09/29/2023] Open
Abstract
Molecular oxygen is a primary oxidant that is involved in the formation of active oxygen species and in the oxidation of lipids and proteins. Thus, controlling oxygen partial pressure (concentration) in the human organism, tissues, and organs can be the first step in protecting them against oxidative stress. However, it is not an easy task because oxygen is necessary for ATP synthesis by mitochondria and in many biochemical reactions taking place in all cells in the human body. Moreover, the blood circulatory system delivers oxygen to all parts of the body. The eye lens seems to be the only organ that is protected from the oxidative stress through the regulation of oxygen partial pressure. The basic mechanism that developed during evolution to protect the eye lens against oxidative damage is based on the maintenance of a very low concentration of oxygen within the lens. This antioxidant mechanism is supported by the resistance of both the lipid components of the lens membrane and cytosolic proteins to oxidation. Any disturbance, continuous or acute, in the working of this mechanism increases the oxygen concentration, in effect causing cataract development. Here, we describe the biophysical basis of the mechanism and its correlation with lens transparency.
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Affiliation(s)
| | - Marta Pasenkiewicz-Gierula
- Department of Computational Biophysics and Bioinformatics, Jagiellonian University, 30-387 Krakow, Poland;
| | - Justyna Widomska
- Department of Biophysics, Medical University of Lublin, 20-090 Lublin, Poland
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6
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Jaiswal M, Tran TT, Guo J, Zhou M, Kunda S, Guo Z, Fanucci G. Spin-labeling Insights into How Chemical Fixation Impacts Glycan Organization on Cells. RESEARCH SQUARE 2023:rs.3.rs-3039983. [PMID: 37398188 PMCID: PMC10312935 DOI: 10.21203/rs.3.rs-3039983/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/04/2023]
Abstract
As new methods to interrogate glycan organization on cells develop, it is important to have a molecular level understanding of how chemical fixation can impact results and interpretations. Site-directed spin labeling technologies are well suited to study how the spin label mobility is impacted by local environmental conditions, such as those imposed by cross-linking effects of paraformaldehyde cell fixation methods. Here, we utilize three different azide-containing sugars for metabolic glycan engineering with HeLa cells to incorporate azido glycans that are modified with a DBCO-based nitroxide moiety via click reaction. Continuous wave X-band electron paramagnetic resonance spectroscopy is employed to characterize how the chronological sequence of chemical fixation and spin labeling impacts the local mobility and accessibility of the nitroxide-labeled glycans in the glycocalyx of HeLa cells. Results demonstrate that chemical fixation with paraformaldehyde can alter local glycan mobility and care should be taken in the analysis of data in any study where chemical fixation and cellular labeling occur.
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7
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Tessmer MH, Stoll S. A novel approach to modeling side chain ensembles of the bifunctional spin label RX. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.05.24.542139. [PMID: 37292623 PMCID: PMC10245940 DOI: 10.1101/2023.05.24.542139] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
We introduce a novel approach to modeling side chain ensembles of bifunctional spin labels. This approach utilizes rotamer libraries to generate side chain conformational ensembles. Because the bifunctional label is constrained by two attachment sites, the label is split into two monofunctional rotamers which are first attached to their respective sites, then rejoined by a local optimization in dihedral space. We validate this method against a set of previously published experimental data using the bifunctional spin label, RX. This method is relatively fast and can readily be used for both experimental analysis and protein modeling, providing significant advantages over modeling bifunctional labels with molecular dynamics simulations. Use of bifunctional labels for site directed spin labeling (SDSL) electron paramagnetic resonance (EPR) spectroscopy dramatically reduces label mobility, which can significantly improve resolution of small changes in protein backbone structure and dynamics. Coupling the use of bifunctional labels with side chain modeling methods allows for improved quantitative application of experimental SDSL EPR data to protein modeling.
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Affiliation(s)
- Maxx H. Tessmer
- Department of Chemistry, University of Washington, Seattle, WA 98103, United States
| | - Stefan Stoll
- Department of Chemistry, University of Washington, Seattle, WA 98103, United States
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8
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Role of membrane mimetics on biophysical EPR studies of membrane proteins. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2023; 1865:184138. [PMID: 36764474 DOI: 10.1016/j.bbamem.2023.184138] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/06/2022] [Revised: 02/01/2023] [Accepted: 02/03/2023] [Indexed: 02/11/2023]
Abstract
Biological membranes are essential in providing the stability of membrane proteins in a functional state. Functionally stable homogeneous sample is required for biophysical electron paramagnetic resonance (EPR) studies of membrane proteins for obtaining pertinent structural dynamics of the protein. Significant progresses have been made for the optimization of the suitable membrane environments required for biophysical EPR measurements. However, no universal membrane mimetic system is available that can solubilize all membrane proteins suitable for biophysical EPR studies while maintaining the functional integrity. Great efforts are needed to optimize the sample condition to obtain better EPR data quality of membrane proteins that can provide meaningful information on structural dynamics. In this mini-review, we will discuss important aspects of membrane mimetics for biophysical EPR measurements and current progress with some of the recent examples.
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9
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Tessmer MH, Stoll S. chiLife: An open-source Python package for in silico spin labeling and integrative protein modeling. PLoS Comput Biol 2023; 19:e1010834. [PMID: 37000838 PMCID: PMC10096462 DOI: 10.1371/journal.pcbi.1010834] [Citation(s) in RCA: 14] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2022] [Revised: 04/12/2023] [Accepted: 03/16/2023] [Indexed: 04/03/2023] Open
Abstract
Here we introduce chiLife, a Python package for site-directed spin label (SDSL) modeling for electron paramagnetic resonance (EPR) spectroscopy, in particular double electron-electron resonance (DEER). It is based on in silico attachment of rotamer ensemble representations of spin labels to protein structures. chiLife enables the development of custom protein analysis and modeling pipelines using SDSL EPR experimental data. It allows the user to add custom spin labels, scoring functions and spin label modeling methods. chiLife is designed with integration into third-party software in mind, to take advantage of the diverse and rapidly expanding set of molecular modeling tools available with a Python interface. This article describes the main design principles of chiLife and presents a series of examples.
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Affiliation(s)
- Maxx H. Tessmer
- Department of Chemistry, University of Washington, Seattle, Washington United States of America
| | - Stefan Stoll
- Department of Chemistry, University of Washington, Seattle, Washington United States of America
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10
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Morris AK, Perera RS, Sahu ID, Lorigan GA. Topological examination of the bacteriophage lambda S holin by EPR spectroscopy. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2023; 1865:184083. [PMID: 36370910 PMCID: PMC9771973 DOI: 10.1016/j.bbamem.2022.184083] [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: 04/01/2022] [Revised: 10/26/2022] [Accepted: 10/31/2022] [Indexed: 11/11/2022]
Abstract
The S protein from bacteriophage lambda is a three-helix transmembrane protein produced by the prophage which accumulates in the host membrane during late gene expression. It is responsible for the first step in lysing the host cell at the end of the viral life cycle by multimerizing together to form large pores which permeabilize the host membrane to allow the escape of virions. Several previous studies have established a model for the assembly of holin into functional holes and the manner in which they pack together, but it is still not fully understood how the very rapid transition from monomer or dimer to multimeric pore occurs with such precise timing once the requisite threshold is reached. Here, site-directed spin labeling with a nitroxide label at introduced cysteine residues is used to corroborate existing topological data from a crosslinking study of the multimerized holin by EPR spectroscopy. CW-EPR spectral lineshape analysis and power saturation data are consistent with a three-helix topology with an unstructured C-terminal domain, as well as at least one interface on transmembrane domain 1 which is exposed to the lumen of the hole, and a highly constrained steric environment suggestive of a tight helical packing interface at transmembrane domain 2.
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Affiliation(s)
- Andrew K Morris
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA.
| | - Rehani S Perera
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA.
| | - Indra D Sahu
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA; Natural Science Division, Campbellsville University, Campbellsville, KY 42718, USA.
| | - Gary A Lorigan
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA.
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11
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Hecker F, Fries L, Hiller M, Chiesa M, Bennati M. 17 O Hyperfine Spectroscopy Reveals Hydration Structure of Nitroxide Radicals in Aqueous Solutions. Angew Chem Int Ed Engl 2023; 62:e202213700. [PMID: 36399425 PMCID: PMC10107301 DOI: 10.1002/anie.202213700] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2022] [Revised: 11/14/2022] [Accepted: 11/17/2022] [Indexed: 11/19/2022]
Abstract
The hydration structure of nitroxide radicals in aqueous solutions is elucidated by advanced 17 O hyperfine (hf) spectroscopy with support of quantum chemical calculations and MD simulations. A piperidine and a pyrrolidine-based nitroxide radical are compared and show clear differences in the preferred directionality of H-bond formation. We demonstrate that these scenarios are best represented in 17 O hf spectra, where in-plane coordination over σ ${\sigma }$ -type H-bonding leads to little spin density transfer on the water oxygen and small hf couplings, whereas π ${{\rm \pi }}$ -type perpendicular coordination generates much larger hf couplings. Quantitative analysis of the spectra based on MD simulations and DFT predicted hf parameters is consistent with a distribution of close solvating water molecules, in which directionality is influenced by subtle steric effects of the ring and the methyl group substituents.
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Affiliation(s)
- Fabian Hecker
- Research Group EPR spectroscopy, Max Planck Institute for Multidisciplinary Sciences, Am Fassberg 11, 37077, Göttingen, Germany
| | - Lisa Fries
- Research Group EPR spectroscopy, Max Planck Institute for Multidisciplinary Sciences, Am Fassberg 11, 37077, Göttingen, Germany.,Current address: Center for Biostructural Imaging of Neurodegeneration, Medical Center Göttingen, Von-Siebold-Straße 3a, 37075, Göttingen, Germany.,NMR Signal Enhancement Group, Max Planck Institute for Multidisciplinary Sciences, Am Fassberg 11, 37077, Göttingen, Germany
| | - Markus Hiller
- Research Group EPR spectroscopy, Max Planck Institute for Multidisciplinary Sciences, Am Fassberg 11, 37077, Göttingen, Germany.,Current address: Isotope Technologies Dresden, Rossendorfer Ring 42, 01328, Dresden, Germany
| | - Mario Chiesa
- Department of Chemistry, University of Torino, Via Giuria 9, 10125, Torino, Italy
| | - Marina Bennati
- Research Group EPR spectroscopy, Max Planck Institute for Multidisciplinary Sciences, Am Fassberg 11, 37077, Göttingen, Germany.,Department of Chemistry, Georg August University Göttingen, Tammanstrasse 2, 37077, Göttingen, Germany
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12
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Krajewski M, Piotrowski P, Mech W, Korona KP, Wojtkiewicz J, Pilch M, Kaim A, Drabińska A, Kamińska M. Optical Properties and Light-Induced Charge Transfer in Selected Aromatic C60 Fullerene Derivatives and in Their Bulk Heterojunctions with Poly(3-Hexylthiophene). MATERIALS (BASEL, SWITZERLAND) 2022; 15:6908. [PMID: 36234249 PMCID: PMC9571621 DOI: 10.3390/ma15196908] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/31/2022] [Revised: 09/26/2022] [Accepted: 09/28/2022] [Indexed: 06/16/2023]
Abstract
Fullerene derivatives offer great scope for modification of the basic molecule, often called a buckyball. In recent years, they have been the subject of numerous studies, in particular in terms of their applications, including in solar cells. Here, the properties of four recently synthesized fullerene C60 derivatives were examined regarding their optical properties and the efficiency of the charge transfer process, both in fullerene derivatives themselves and in their heterojunctions with poly (3-hexylthiophene). Optical absorption, electron spin resonance (ESR), and time-resolved photoluminescence (TRPL) techniques were applied to study the synthesized molecules. It was shown that the absorption processes in fullerene derivatives are dominated by absorption of the fullerene cage and do not significantly depend on the type of the derivative. It was also found by ESR and TRPL studies that asymmetrical, dipole-like derivatives exhibit stronger light-induced charge transfer properties than their symmetrical counterparts. The observed inhomogeneous broadening of the ESR lines indicated a large disorder of all polymer-fullerene derivative blends. The density functional theory was applied to explain the results of the optical absorption experiments.
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Affiliation(s)
- Maciej Krajewski
- Faculty of Physics, University of Warsaw, Pasteura 5, 02-093 Warsaw, Poland
| | - Piotr Piotrowski
- Faculty of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland
| | - Wojciech Mech
- Faculty of Physics, University of Warsaw, Pasteura 5, 02-093 Warsaw, Poland
| | | | - Jacek Wojtkiewicz
- Faculty of Physics, University of Warsaw, Pasteura 5, 02-093 Warsaw, Poland
| | - Marek Pilch
- Faculty of Physics, University of Warsaw, Pasteura 5, 02-093 Warsaw, Poland
| | - Andrzej Kaim
- Faculty of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland
| | - Aneta Drabińska
- Faculty of Physics, University of Warsaw, Pasteura 5, 02-093 Warsaw, Poland
| | - Maria Kamińska
- Faculty of Physics, University of Warsaw, Pasteura 5, 02-093 Warsaw, Poland
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13
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Campbell C, Faleel FDM, Scheyer MW, Haralu S, Williams PL, Carbo WD, Wilson-Taylor AS, Patel NH, Sanders CR, Lorigan GA, Sahu ID. Comparing the structural dynamics of the human KCNE3 in reconstituted micelle and lipid bilayered vesicle environments. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2022; 1864:183974. [PMID: 35716725 DOI: 10.1016/j.bbamem.2022.183974] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/20/2021] [Revised: 05/12/2022] [Accepted: 05/25/2022] [Indexed: 06/15/2023]
Abstract
KCNE3 is a single transmembrane protein of the KCNE family that modulates the function and trafficking of several voltage-gated potassium channels, including KCNQ1. Structural studies of KCNE3 have been previously conducted in a wide range of model membrane mimics. However, it is important to assess the impact of the membrane mimics used on the observed conformation and dynamics. In this study, we have optimized a method for the reconstitution of the KCNE3 into POPC/POPG lipid bilayer vesicles for electron paramagnetic resonance (EPR) spectroscopy. Our CD spectroscopic data suggested that the degree of regular secondary structure for KCNE3 protein reconstituted into lipid bilayered vesicle is significantly higher than in DPC detergent micelles. Electron paramagnetic resonance (EPR) spectroscopy in combination with site-directed spin labeling (SDSL) was used to probe the structural dynamics of S49C, M59C, L67C, V85C, and S101C mutations of KCNE3 in both DPC micelles and in POPC/POPG lipid bilayered vesicles. Our CW-EPR power saturation data suggested that the site S74C is buried inside the lipid bilayered membrane while the site V85C is located outside the membrane, in contrast to DPC micelle results. These results suggest that the KCNE3 micelle structures need to be refined using data obtained in the lipid bilayered vesicles in order to ascertain the native structure of KCNE3. This work will provide guidelines for detailed structural studies of KCNE3 in a more native membrane environment and comparing the lipid bilayer results to the isotropic bicelle structure and to the KCNQ1-bound cryo-EM structure.
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Affiliation(s)
- Conner Campbell
- Natural Science Division, Campbellsville University, Campbellsville, KY, United States of America
| | | | - Matthew W Scheyer
- Natural Science Division, Campbellsville University, Campbellsville, KY, United States of America
| | - Samuel Haralu
- Natural Science Division, Campbellsville University, Campbellsville, KY, United States of America
| | - Patrick L Williams
- Natural Science Division, Campbellsville University, Campbellsville, KY, United States of America
| | - William David Carbo
- Natural Science Division, Campbellsville University, Campbellsville, KY, United States of America
| | | | - Nima H Patel
- Natural Science Division, Campbellsville University, Campbellsville, KY, United States of America
| | - Charles R Sanders
- Department of Biochemistry and Center for Structural Biology, Vanderbilt University, Nashville, TN, United States of America
| | - Gary A Lorigan
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH, United States of America
| | - Indra D Sahu
- Natural Science Division, Campbellsville University, Campbellsville, KY, United States of America; Department of Chemistry and Biochemistry, Miami University, Oxford, OH, United States of America.
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14
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Subczynski WK, Widomska J, Raguz M, Pasenkiewicz-Gierula M. Molecular oxygen as a probe molecule in EPR spin-labeling studies of membrane structure and dynamics. OXYGEN (BASEL, SWITZERLAND) 2022; 2:295-316. [PMID: 36852103 PMCID: PMC9965258 DOI: 10.3390/oxygen2030021] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Molecular oxygen (O2) is the perfect probe molecule for membrane studies carried out using the saturation recovery EPR technique. O2 is a small, paramagnetic, hydrophobic enough molecule that easily partitions into a membrane's different phases and domains. In membrane studies, the saturation recovery EPR method requires two paramagnetic probes: a lipid-analog nitroxide spin label and an oxygen molecule. The experimentally derived parameters of this method are the spin-lattice relaxation times (T 1s) of spin labels and rates of bimolecular collisions between O2 and the nitroxide fragment. Thanks to the long T 1 of lipid spin labels (from 1 to 10 μs), the approach is very sensitive to changes of the local (around the nitroxide fragment) O2 diffusion-concentration product. Small variations in the lipid packing affect O2 solubility and O2 diffusion, which can be detected by the shortening of T 1 of spin labels. Using O2 as a probe molecule and a different lipid spin label inserted into specific phases of the membrane and membrane domains allows data about the lateral arrangement of lipid membranes to be obtained. Moreover, using a lipid spin label with the nitroxide fragment attached to its head group or a hydrocarbon chain at different positions also enables data about molecular dynamics and structure at different membrane depths to be obtained. Thus, the method can be used to investigate not only the lateral organization of the membrane (i.e., the presence of membrane domains and phases), but also the depth-dependent membrane structure and dynamics, and, hence, the membrane properties in three dimensions.
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Affiliation(s)
- Witold K. Subczynski
- Department of Biophysics, Medical College on Wisconsin, Milwaukee, United States
| | - Justyna Widomska
- Department of Biophysics, Medical University of Lublin, Lublin, Poland
| | - Marija Raguz
- Department of Medical Physics and Biophysics, University of Split School of Medicine, Split, Croatia
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15
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Aryal CM, Bui NN, Song L, Pan J. The N-terminal helices of amphiphysin and endophilin have different capabilities of membrane remodeling. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2022; 1864:183907. [PMID: 35247332 DOI: 10.1016/j.bbamem.2022.183907] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/13/2021] [Revised: 02/17/2022] [Accepted: 02/24/2022] [Indexed: 06/14/2023]
Abstract
Amphiphysin and endophilin are two members of the N-BAR protein family. We have reported membrane interactions of the helix 0 of endophilin (H0-Endo). Here we investigate membrane modulations caused by the helix 0 of amphiphysin (H0-Amph). Electron paramagnetic resonance (EPR) spectroscopy was used to explore membrane properties. H0-Amph was found to reduce lipid mobility, make the membrane interior more polar, and decrease lipid chain orientational order. The EPR data also showed that for anionic membranes, H0-Endo acted as a more potent modulator. For instance, at peptide-to-lipid (P/L) ratio of 1/20, the peak-to-peak splitting was increased by 0.27 G and 1.89 G by H0-Amph and H0-Endo, respectively. Similarly, H0-Endo caused a larger change in the bilayer polarity than H0-Amph (30% versus 12% at P/L = 1/20). At P/L = 1/50, the chain orientational order was decreased by 26% and 66% by H0-Amph and H0-Endo, respectively. The different capabilities were explained by considering hydrophobicity score distributions. We employed atomic force microscopy to investigate membrane structural changes. Both peptides caused the formation of micron-sized holes. Interestingly, only H0-Amph induced membrane fusion as evidenced by the formation of high-rise regions. Lastly, experiments of giant unilamellar vesicles showed that H0-Amph and H0-Endo generated thin tubules and miniscule vesicles, respectively. Together, our studies showed that both helices are effective in altering membrane properties; the observed changes might be important for membrane curvature induction. Importantly, comparisons between the two peptides revealed that the degree of membrane remodeling is dependent on the sequence of the N-terminal helix of the N-BAR protein family.
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Affiliation(s)
- Chinta M Aryal
- Department of Physics, University of South Florida, Tampa, FL 33620, United States of America; MED-Cancer & Cell Biology, University of Cincinnati, Cincinnati, OH 45267
| | - Nhat Nguyen Bui
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, United States of America
| | - Likai Song
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, United States of America.
| | - Jianjun Pan
- Department of Physics, University of South Florida, Tampa, FL 33620, United States of America.
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16
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Ahammad T, Khan RH, Sahu ID, Drew DL, Faul E, Li T, McCarrick RM, Lorigan GA. Pinholin S 21 mutations induce structural topology and conformational changes. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2021; 1863:183771. [PMID: 34499883 DOI: 10.1016/j.bbamem.2021.183771] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2021] [Revised: 08/30/2021] [Accepted: 09/01/2021] [Indexed: 12/23/2022]
Abstract
The bacteriophage infection cycle is terminated at a predefined time to release the progeny virions via a robust lytic system composed of holin, endolysin, and spanin proteins. Holin is the timekeeper of this process. Pinholin S21 is a prototype holin of phage Φ21, which determines the timing of host cell lysis through the coordinated efforts of pinholin and antipinholin. However, mutations in pinholin and antipinholin play a significant role in modulating the timing of lysis depending on adverse or favorable growth conditions. Earlier studies have shown that single point mutations of pinholin S21 alter the cell lysis timing, a proxy for pinholin function as lysis is also dependent on other lytic proteins. In this study, continuous wave electron paramagnetic resonance (CW-EPR) power saturation and double electron-electron resonance (DEER) spectroscopic techniques were used to directly probe the effects of mutations on the structure and conformational changes of pinholin S21 that correlate with pinholin function. DEER and CW-EPR power saturation data clearly demonstrate that increased hydrophilicity induced by residue mutations accelerate the externalization of antipinholin transmembrane domain 1 (TMD1), while increased hydrophobicity prevents the externalization of TMD1. This altered hydrophobicity is potentially accelerating or delaying the activation of pinholin S21. It was also found that mutations can influence intra- or intermolecular interactions in this system, which contribute to the activation of pinholin and modulate the cell lysis timing. This could be a novel approach to analyze the mutational effects on other holin systems, as well as any other membrane protein in which mutation directly leads to structural and conformational changes.
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Affiliation(s)
- Tanbir Ahammad
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA
| | - Rasal H Khan
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA
| | - Indra D Sahu
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA; Natural Science Division, Campbellsville University, Campbellsville, KY 42718, USA
| | - Daniel L Drew
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA
| | - Emily Faul
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA
| | - Tianyan Li
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA
| | - Robert M McCarrick
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA
| | - Gary A Lorigan
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA.
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17
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Subczynski WK, Widomska J, Stein N, Swartz HM. Factors determining barrier properties to oxygen transport across model and cell plasma membranes based on EPR spin-label oximetry. APPLIED MAGNETIC RESONANCE 2021; 52:1237-1260. [PMID: 36267674 PMCID: PMC9581439 DOI: 10.1007/s00723-021-01412-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/21/2021] [Revised: 07/23/2021] [Accepted: 08/04/2021] [Indexed: 06/01/2023]
Abstract
This review is motivated by the exciting new area of radiation therapy using a phenomenon termed FLASH in which oxygen is thought to have a central role. Well-established principles of radiation biology and physics suggest that if oxygen has a strong role, it should be the level at the DNA. The key aspect discussed is the rate of oxygen diffusion. If oxygen freely diffuses into cells and rapidly equilibrates, then measurements in the extracellular compartment would enable FLASH to be investigated using existing methodologies that can readily measure oxygen in the extracellular compartment. EPR spin-label oximetry allows evaluation of the oxygen permeability coefficient across lipid bilayer membranes. It is established that simple fluid phase lipid bilayers are not barriers to oxygen transport. However, further investigations indicate that many physical and chemical (compositional) factor can significantly decrease this permeation. In biological cell plasma membranes, the lipid bilayer forms the matrix in which integral membrane proteins are immersed, changing organization and properties of the lipid matrix. To evaluate oxygen permeability coefficients across these complex membranes, oxygen permeation across all membrane domains and components must be considered. In this review, we consider many of the factors that affect (decrease) oxygen permeation across cell plasma membranes. Finally, we address the question, can the plasma membrane of the cell form a barrier to the free diffusion of oxygen into the cell interior? If there is a barrier then this must be considered in the investigations of the role of oxygen in FLASH.
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Affiliation(s)
- Witold K. Subczynski
- Department of Biophysics, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA
| | - Justyna Widomska
- Department of Biophysics, Medical University of Lublin, Jaczewskiego 4, Lublin, Poland
| | - Natalia Stein
- Department of Biophysics, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA
| | - Harold M. Swartz
- Department of Radiology, The Geisel School of Medicine at Dartmouth, Lebanon, NH 03766, USA
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18
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Majeed S, Ahmad AB, Sehar U, Georgieva ER. Lipid Membrane Mimetics in Functional and Structural Studies of Integral Membrane Proteins. MEMBRANES 2021; 11:685. [PMID: 34564502 PMCID: PMC8470526 DOI: 10.3390/membranes11090685] [Citation(s) in RCA: 29] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/27/2021] [Revised: 08/18/2021] [Accepted: 08/30/2021] [Indexed: 12/12/2022]
Abstract
Integral membrane proteins (IMPs) fulfill important physiological functions by providing cell-environment, cell-cell and virus-host communication; nutrients intake; export of toxic compounds out of cells; and more. However, some IMPs have obliterated functions due to polypeptide mutations, modifications in membrane properties and/or other environmental factors-resulting in damaged binding to ligands and the adoption of non-physiological conformations that prevent the protein from returning to its physiological state. Thus, elucidating IMPs' mechanisms of function and malfunction at the molecular level is important for enhancing our understanding of cell and organism physiology. This understanding also helps pharmaceutical developments for restoring or inhibiting protein activity. To this end, in vitro studies provide invaluable information about IMPs' structure and the relation between structural dynamics and function. Typically, these studies are conducted on transferred from native membranes to membrane-mimicking nano-platforms (membrane mimetics) purified IMPs. Here, we review the most widely used membrane mimetics in structural and functional studies of IMPs. These membrane mimetics are detergents, liposomes, bicelles, nanodiscs/Lipodisqs, amphipols, and lipidic cubic phases. We also discuss the protocols for IMPs reconstitution in membrane mimetics as well as the applicability of these membrane mimetic-IMP complexes in studies via a variety of biochemical, biophysical, and structural biology techniques.
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Affiliation(s)
- Saman Majeed
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409, USA
| | - Akram Bani Ahmad
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409, USA
| | - Ujala Sehar
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409, USA
| | - Elka R Georgieva
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409, USA
- Department of Cell Physiology and Molecular Biophysics, Texas Tech University Health Science Center, Lubbock, TX 79409, USA
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19
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Thorsen MK, Lai A, Lee MW, Hoogerheide DP, Wong GCL, Freed JH, Heldwein EE. Highly Basic Clusters in the Herpes Simplex Virus 1 Nuclear Egress Complex Drive Membrane Budding by Inducing Lipid Ordering. mBio 2021; 12:e0154821. [PMID: 34425706 PMCID: PMC8406295 DOI: 10.1128/mbio.01548-21] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2021] [Accepted: 07/28/2021] [Indexed: 02/01/2023] Open
Abstract
During replication of herpesviruses, capsids escape from the nucleus into the cytoplasm by budding at the inner nuclear membrane. This unusual process is mediated by the viral nuclear egress complex (NEC) that deforms the membrane around the capsid by oligomerizing into a hexagonal, membrane-bound scaffold. Here, we found that highly basic membrane-proximal regions (MPRs) of the NEC alter lipid order by inserting into the lipid headgroups and promote negative Gaussian curvature. We also find that the electrostatic interactions between the MPRs and the membranes are essential for membrane deformation. One of the MPRs is phosphorylated by a viral kinase during infection, and the corresponding phosphomimicking mutations block capsid nuclear egress. We show that the same phosphomimicking mutations disrupt the NEC-membrane interactions and inhibit NEC-mediated budding in vitro, providing a biophysical explanation for the in vivo phenomenon. Our data suggest that the NEC generates negative membrane curvature by both lipid ordering and protein scaffolding and that phosphorylation acts as an off switch that inhibits the membrane-budding activity of the NEC to prevent capsid-less budding. IMPORTANCE Herpesviruses are large viruses that infect nearly all vertebrates and some invertebrates and cause lifelong infections in most of the world's population. During replication, herpesviruses export their capsids from the nucleus into the cytoplasm by an unusual mechanism in which the viral nuclear egress complex (NEC) deforms the nuclear membrane around the capsid. However, how membrane deformation is achieved is unclear. Here, we show that the NEC from herpes simplex virus 1, a prototypical herpesvirus, uses clusters of positive charges to bind membranes and order membrane lipids. Reducing the positive charge or introducing negative charges weakens the membrane deforming ability of the NEC. We propose that the virus employs electrostatics to deform nuclear membrane around the capsid and can control this process by changing the NEC charge through phosphorylation. Blocking NEC-membrane interactions could be exploited as a therapeutic strategy.
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Affiliation(s)
- Michael K. Thorsen
- Department of Molecular Biology and Microbiology, Graduate Program in Cellular, Molecular and Developmental Biology, Tufts University School of Medicine, Boston, Massachusetts, USA
| | - Alex Lai
- Department of Chemistry and Chemical Biology and National Biomedical Center for Advanced Electron Spin Resonance Technology, Cornell University, Ithaca, New York, USA
| | - Michelle W. Lee
- Department of Bioengineering, Department of Chemistry and Biochemistry, California NanoSystems Institute, University of California, Los Angeles, Los Angeles, California, USA
| | - David P. Hoogerheide
- Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland, USA
| | - Gerard C. L. Wong
- Department of Bioengineering, Department of Chemistry and Biochemistry, California NanoSystems Institute, University of California, Los Angeles, Los Angeles, California, USA
| | - Jack H. Freed
- Department of Chemistry and Chemical Biology and National Biomedical Center for Advanced Electron Spin Resonance Technology, Cornell University, Ithaca, New York, USA
| | - Ekaterina E. Heldwein
- Department of Molecular Biology and Microbiology, Graduate Program in Cellular, Molecular and Developmental Biology, Tufts University School of Medicine, Boston, Massachusetts, USA
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20
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Probing Structural Dynamics of Membrane Proteins Using Electron Paramagnetic Resonance Spectroscopic Techniques. BIOPHYSICA 2021. [DOI: 10.3390/biophysica1020009] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Membrane proteins are essential for the survival of living organisms. They are involved in important biological functions including transportation of ions and molecules across the cell membrane and triggering the signaling pathways. They are targets of more than half of the modern medical drugs. Despite their biological significance, information about the structural dynamics of membrane proteins is lagging when compared to that of globular proteins. The major challenges with these systems are low expression yields and lack of appropriate solubilizing medium required for biophysical techniques. Electron paramagnetic resonance (EPR) spectroscopy coupled with site directed spin labeling (SDSL) is a rapidly growing powerful biophysical technique that can be used to obtain pertinent structural and dynamic information on membrane proteins. In this brief review, we will focus on the overview of the widely used EPR approaches and their emerging applications to answer structural and conformational dynamics related questions on important membrane protein systems.
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21
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Stein N, Subczynski WK. Oxygen Transport Parameter in Plasma Membrane of Eye Lens Fiber Cells by Saturation Recovery EPR. APPLIED MAGNETIC RESONANCE 2021; 52:61-80. [PMID: 33776217 PMCID: PMC7992188 DOI: 10.1007/s00723-020-01237-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2020] [Revised: 07/24/2020] [Indexed: 06/02/2023]
Abstract
A probability distribution of rate constants contained within an exponential-like saturation recovery (SR) electron paramagnetic resonance signal can be constructed using stretched exponential function fitting parameters. Previously (Stein et al. Appl. Magn. Reson. 2019.), application of this method was limited to the case where only one relaxation process, namely spin-lattice relaxations due to the rotational diffusion of the spin labels in the intact eye-lens membranes, contributed to an exponential-like SR signal. These conditions were achieved for thoroughly deoxygenated samples. Here, the case is described where the second relaxation process, namely Heisenberg exchange between the spin label and molecular oxygen that occurs during bimolecular collisions, contributes to the decay of SR signals. We have further developed the theory for application of stretched exponential function to analyze SR signals involving these two processes. This new approach allows separation of stretched exponential parameters, namely characteristic stretched rates and heterogeneity parameters for both processes. Knowing these parameters allowed us to separately construct the probability distributions of spin-lattice relaxation rates determined by the rotational diffusion of spin labels and the distribution of relaxations induced strictly by collisions with molecular oxygen. The later distribution is determined by the distribution of oxygen diffusion concentration products within the membrane, which forms a sensitive new way to describe membrane fluidity and heterogeneity. This method was validated in silico and by fitting SR signals from spin-labeled intact nuclear fiber cell plasma membranes extracted from porcine eye lenses equilibrated with different fractions of air.
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Affiliation(s)
- N. Stein
- Corresponding Authors: Natalia Stein, Department of Biophysics, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA, Tel: (414) 955-4038; Fax: (414) 955-6512; , Witold K. Subczynski, Department of Biophysics, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA, Tel: (414) 955-4044; Fax: (414) 955-6512;
| | - W. K. Subczynski
- Corresponding Authors: Natalia Stein, Department of Biophysics, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA, Tel: (414) 955-4038; Fax: (414) 955-6512; , Witold K. Subczynski, Department of Biophysics, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA, Tel: (414) 955-4044; Fax: (414) 955-6512;
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22
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Ahammad T, Drew DL, Sahu ID, Khan RH, Butcher BJ, Serafin RA, Galende AP, McCarrick RM, Lorigan GA. Conformational Differences Are Observed for the Active and Inactive Forms of Pinholin S 21 Using DEER Spectroscopy. J Phys Chem B 2020; 124:11396-11405. [PMID: 33289567 DOI: 10.1021/acs.jpcb.0c09081] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Bacteriophages have evolved with an efficient host cell lysis mechanism to terminate the infection cycle and release the new progeny virions at the optimum time, allowing adaptation with the changing host and environment. Among the lytic proteins, holin controls the first and rate-limiting step of host cell lysis by permeabilizing the inner membrane at an allele-specific time known as "holin triggering". Pinholin S21 is a prototype holin of phage Φ21 which makes many nanoscale holes and destroys the proton motive force, which in turn activates the signal anchor release (SAR) endolysin system to degrade the peptidoglycan layer of the host cell and destruction of the outer membrane by the spanin complex. Like many others, phage Φ21 has two holin proteins: active pinholin and antipinholin. The antipinholin form differs only by three extra amino acids at the N-terminus; however, it has a different structural topology and conformation with respect to the membrane. Predefined combinations of active pinholin and antipinholin fine-tune the lysis timing through structural dynamics and conformational changes. Previously, the dynamics and topology of active pinholin and antipinholin were investigated (Ahammad et al. JPCB 2019, 2020) using continuous wave electron paramagnetic resonance (CW-EPR) spectroscopy. However, detailed structural studies and direct comparison of these two forms of pinholin S21 are absent in the literature. In this study, the structural topology and conformations of active pinholin (S2168) and inactive antipinholin (S2168IRS) in DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine) proteoliposomes were investigated using the four-pulse double electron-electron resonance (DEER) EPR spectroscopic technique to measure distances between transmembrane domains 1 and 2 (TMD1 and TMD2). Five sets of interlabel distances were measured via DEER spectroscopy for both the active and inactive forms of pinholin S21. Structural models of the active pinholin and inactive antipinholin forms in DMPC proteoliposomes were obtained using the experimental DEER distances coupled with the simulated annealing software package Xplor-NIH. TMD2 of S2168 remains in the lipid bilayer, and TMD1 is partially externalized from the bilayer with some residues located on the surface. However, both TMDs remain incorporated in the lipid bilayer for the inactive S2168IRS form. This study demonstrates, for the first time, clear structural topology and conformational differences between the two forms of pinholin S21. This work will pave the way for further studies of other holin systems using the DEER spectroscopic technique and will give structural insight into these biological clocks in molecular detail.
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Affiliation(s)
- Tanbir Ahammad
- Department of Chemistry and Biochemistry, Miami University, Oxford, Ohio 45056, United States
| | - Daniel L Drew
- Department of Chemistry and Biochemistry, Miami University, Oxford, Ohio 45056, United States
| | - Indra D Sahu
- Department of Chemistry and Biochemistry, Miami University, Oxford, Ohio 45056, United States.,Natural Science Division, Campbellsville University, Campbellsville, Kentucky 42718, United States
| | - Rasal H Khan
- Department of Chemistry and Biochemistry, Miami University, Oxford, Ohio 45056, United States
| | - Brandon J Butcher
- Department of Chemistry and Biochemistry, Miami University, Oxford, Ohio 45056, United States
| | - Rachel A Serafin
- Department of Chemistry and Biochemistry, Miami University, Oxford, Ohio 45056, United States
| | - Alberto P Galende
- Natural Science Division, Campbellsville University, Campbellsville, Kentucky 42718, United States
| | - Robert M McCarrick
- Department of Chemistry and Biochemistry, Miami University, Oxford, Ohio 45056, United States
| | - Gary A Lorigan
- Department of Chemistry and Biochemistry, Miami University, Oxford, Ohio 45056, United States
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23
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Yu L, Fang W, He Y, Cai W, Wei W, Tian C. Secondary structure and transmembrane topology analysis of the N-terminal domain of the inner membrane protein EccE 1 from M. smegmatis using site-directed spin labeling EPR. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2020; 1863:183515. [PMID: 33245893 DOI: 10.1016/j.bbamem.2020.183515] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 08/07/2020] [Revised: 10/29/2020] [Accepted: 11/20/2020] [Indexed: 10/22/2022]
Abstract
Protein EccE1 is an essential component of the mycobacterial ESX-1 secretion system, which plays a crucial part in the process of virulence factors secretion, especially for pathogenic mycobacteria such as Mycobacterium tuberculosis. While EccE1 was previously postulated to be the inner membrane pore-forming unit of a membrane complex through which substrates are transported, the structural properties of EccE1 remains to be explored. In the present study, systematic Site-Directed Spin Labeling (SDSL) and Electron Paramagnetic Resonance (EPR) spectroscopic studies was carried out to reveal the secondary structure and transmembrane topology of the N-terminal Domain of EccE1 protein (EccE1-NTD) from M. smegmatis in detergent micelles. EPR-based mobility and accessibility analysis of the R1 side chain for 64 residue positions of EccE1-NTD indicates that the transmembrane domain adopts two α-helices spanning Phe7-Cys30 and Leu36-Ile54. A tentative structural topology model of EccE1-NTD embedded in membrane is also suggested based on EPR spectroscopic data in this study, which will provide further insights into this protein and the ESX secretion systems of mycobacteria.
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Affiliation(s)
- Lu Yu
- High Magnetic Field Laboratory, Chinese Academy of Science, Hefei, Anhui 230031, China.
| | - Wei Fang
- Hefei National Laboratory for Physical Sciences at Microscale and School of Life Sciences, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Yao He
- Hefei National Laboratory for Physical Sciences at Microscale and School of Life Sciences, University of Science and Technology of China, Hefei, Anhui 230026, China
| | - Wenguang Cai
- School of Life Sciences, Anhui University, 111 Jiulong Road, Hefei, Anhui 230601, China
| | - Wei Wei
- Department of Chemistry, University of Science and Technology of China, Hefei 230026, China
| | - Changlin Tian
- High Magnetic Field Laboratory, Chinese Academy of Science, Hefei, Anhui 230031, China; Hefei National Laboratory for Physical Sciences at Microscale and School of Life Sciences, University of Science and Technology of China, Hefei, Anhui 230026, China.
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24
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Georgieva ER. Protein Conformational Dynamics upon Association with the Surfaces of Lipid Membranes and Engineered Nanoparticles: Insights from Electron Paramagnetic Resonance Spectroscopy. Molecules 2020; 25:E5393. [PMID: 33218036 PMCID: PMC7698768 DOI: 10.3390/molecules25225393] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2020] [Revised: 11/15/2020] [Accepted: 11/16/2020] [Indexed: 11/16/2022] Open
Abstract
Detailed study of conformational rearrangements and dynamics of proteins is central to our understanding of their physiological functions and the loss of function. This review outlines the applications of the electron paramagnetic resonance (EPR) technique to study the structural aspects of proteins transitioning from a solution environment to the states in which they are associated with the surfaces of biological membranes or engineered nanoobjects. In the former case these structural transitions generally underlie functional protein states. The latter case is mostly relevant to the application of protein immobilization in biotechnological industries, developing methods for protein purification, etc. Therefore, evaluating the stability of the protein functional state is particularly important. EPR spectroscopy in the form of continuous-wave EPR or pulse EPR distance measurements in conjunction with protein spin labeling provides highly versatile and sensitive tools to characterize the changes in protein local dynamics as well as large conformational rearrangements. The technique can be widely utilized in studies of both protein-membrane and engineered nanoobject-protein complexes.
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Affiliation(s)
- Elka R Georgieva
- Department of Chemistry and Biochemistry, Texas Tech University, Lubbock, TX 79409, USA
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25
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Tessmer MH, DeCero SA, Del Alamo D, Riegert MO, Meiler J, Frank DW, Feix JB. Characterization of the ExoU activation mechanism using EPR and integrative modeling. Sci Rep 2020; 10:19700. [PMID: 33184362 PMCID: PMC7665212 DOI: 10.1038/s41598-020-76023-3] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2020] [Accepted: 10/19/2020] [Indexed: 12/17/2022] Open
Abstract
ExoU, a type III secreted phospholipase effector of Pseudomonas aeruginosa, serves as a prototype to model large, dynamic, membrane-associated proteins. ExoU is synergistically activated by interactions with membrane lipids and ubiquitin. To dissect the activation mechanism, structural homology was used to identify an unstructured loop of approximately 20 residues in the ExoU amino acid sequence. Mutational analyses indicate the importance of specific loop amino acid residues in mediating catalytic activity. Engineered disulfide cross-links show that loop movement is required for activation. Site directed spin labeling EPR and DEER (double electron-electron resonance) studies of apo and holo states demonstrate local conformational changes at specific sites within the loop and a conformational shift of the loop during activation. These data are consistent with the formation of a substrate-binding pocket providing access to the catalytic site. DEER distance distributions were used as constraints in RosettaDEER to construct ensemble models of the loop in both apo and holo states, significantly extending the range for modeling a conformationally dynamic loop.
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Affiliation(s)
- Maxx H Tessmer
- Department of Chemistry, University of Washington, Seattle, WA, USA
| | - Samuel A DeCero
- Department of Microbiology and Immunology, Medical College of Wisconsin, Milwaukee, WI, USA
| | - Diego Del Alamo
- Department of Chemistry and Center for Structural Biology, Vanderbilt University, Nashville, TN, USA
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN, USA
| | - Molly O Riegert
- Department of Microbiology and Immunology, Medical College of Wisconsin, Milwaukee, WI, USA
| | - Jens Meiler
- Department of Chemistry and Center for Structural Biology, Vanderbilt University, Nashville, TN, USA
- Institute for Drug Discovery, Leipzig University Medical School, Leipzig SAC, Germany
| | - Dara W Frank
- Department of Microbiology and Immunology, Medical College of Wisconsin, Milwaukee, WI, USA.
| | - Jimmy B Feix
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI, USA
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26
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Schmallegger M, Barbon A, Bortolus M, Chemelli A, Bilkis I, Gescheidt G, Weiner L. Systematic Quantification of Electron Transfer in a Bare Phospholipid Membrane Using Nitroxide-Labeled Stearic Acids: Distance Dependence, Kinetics, and Activation Parameters. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2020; 36:10429-10437. [PMID: 32787070 PMCID: PMC7586382 DOI: 10.1021/acs.langmuir.0c01585] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/28/2020] [Revised: 07/24/2020] [Indexed: 06/11/2023]
Abstract
In this report, we present a method to characterize the kinetics of electron transfer across the bilayer of a unilamellar liposome composed of 1,2-dimyristoyl-sn-glycero-3-phosphocholine. The method utilizes synthetic phospholipids containing noninvasive nitroxide spin labels having the >N-O• moiety at well-defined distances from the outer surface of the liposome to serve as reporters for their local environment and, at the same time, permit measurement of the kinetics of electron transfer. We used 5-doxyl and 16-doxyl stearic acids. The paramagnetic >N-O• moiety is photo-oxidized to the corresponding diamagnetic oxoammonium cation by a ruthenium electron acceptor formed in the solution. Electron transfer is monitored by three independent spectroscopic methods: by both steady-state and time-resolved electron paramagnetic resonance and by optical spectroscopy. These techniques allowed us to differentiate between the electron transfer rates of nitroxides located in the outer leaflet of the phospholipid bilayer and of those located in the inner leaflet. Measurement of electron transfer rates as a function of temperature revealed a low-activation barrier (ΔG‡ ∼ 40 kJ/mol) that supports a tunneling mechanism.
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Affiliation(s)
- Max Schmallegger
- Institute
of Physical and Theoretical Chemistry, Graz
University of Technology, Stremayrgasse 9, Graz 8010, Austria
| | - Antonio Barbon
- Dipartimento
di Scienze Chimiche, Università degli
Studi di Padova, Via Marzolo 1, Padova 35131, Italy
| | - Marco Bortolus
- Dipartimento
di Scienze Chimiche, Università degli
Studi di Padova, Via Marzolo 1, Padova 35131, Italy
| | - Angela Chemelli
- Institute
of Inorganic Chemistry, Graz University
of Technology, Stremayrgasse 9, Graz 8010, Austria
| | - Itzhak Bilkis
- Faculty
of Agricultural, Food and Environmental Sciences, Hebrew University, Rehovot 76100, Israel
| | - Georg Gescheidt
- Institute
of Physical and Theoretical Chemistry, Graz
University of Technology, Stremayrgasse 9, Graz 8010, Austria
| | - Lev Weiner
- Department
of Chemical Research Support, Weizmann Institute
of Science, Rehovot 76100, Israel
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27
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Ahammad T, Drew DL, Khan RH, Sahu ID, Faul E, Li T, Lorigan GA. Structural Dynamics and Topology of the Inactive Form of S 21 Holin in a Lipid Bilayer Using Continuous-Wave Electron Paramagnetic Resonance Spectroscopy. J Phys Chem B 2020; 124:5370-5379. [PMID: 32501696 DOI: 10.1021/acs.jpcb.0c03575] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The bacteriophage infection cycle plays a crucial role in recycling the world's biomass. Bacteriophages devise various cell lysis systems to strictly control the length of the infection cycle for an efficient phage life cycle. Phages evolved with lysis protein systems, which can control and fine-tune the length of this infection cycle depending on the host and growing environment. Among these lysis proteins, holin controls the first and rate-limiting step of host cell lysis by permeabilizing the inner membrane at an allele-specific time and concentration hence known as the simplest molecular clock. Pinholin S21 is the holin from phage Φ21, which defines the cell lysis time through a predefined ratio of active pinholin and antipinholin (inactive form of pinholin). Active pinholin and antipinholin fine-tune the lysis timing through structural dynamics and conformational changes. Previously we reported the structural dynamics and topology of active pinholin S2168. Currently, there is no detailed structural study of the antipinholin using biophysical techniques. In this study, the structural dynamics and topology of antipinholin S2168IRS in DMPC proteoliposomes is investigated using electron paramagnetic resonance (EPR) spectroscopic techniques. Continuous-wave (CW) EPR line shape analysis experiments of 35 different R1 side chains of S2168IRS indicated restricted mobility of the transmembrane domains (TMDs), which were predicted to be inside the lipid bilayer when compared to the N- and C-termini R1 side chains. In addition, the R1 accessibility test performed on 24 residues using the CW-EPR power saturation experiment indicated that TMD1 and TMD2 of S2168IRS were incorporated into the lipid bilayer where N- and C-termini were located outside of the lipid bilayer. Based on this study, a tentative model of S2168IRS is proposed where both TMDs remain incorporated into the lipid bilayer and N- and C-termini are located outside of the lipid bilayer. This work will pave the way for the further studies of other holins using biophysical techniques and will give structural insights into these biological clocks in molecular detail.
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Affiliation(s)
- Tanbir Ahammad
- Department of Chemistry and Biochemistry, Miami University, Oxford, Ohio 45056, United States
| | - Daniel L Drew
- Department of Chemistry and Biochemistry, Miami University, Oxford, Ohio 45056, United States
| | - Rasal H Khan
- Department of Chemistry and Biochemistry, Miami University, Oxford, Ohio 45056, United States
| | - Indra D Sahu
- Department of Chemistry and Biochemistry, Miami University, Oxford, Ohio 45056, United States.,Natural Science Division, Campbellsville University, Campbellsville, Kentucky 42718, United States
| | - Emily Faul
- Department of Chemistry and Biochemistry, Miami University, Oxford, Ohio 45056, United States
| | - Tianyan Li
- Department of Chemistry and Biochemistry, Miami University, Oxford, Ohio 45056, United States
| | - Gary A Lorigan
- Department of Chemistry and Biochemistry, Miami University, Oxford, Ohio 45056, United States
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28
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Aryal CM, Bui NN, Khadka NK, Song L, Pan J. The helix 0 of endophilin modifies membrane material properties and induces local curvature. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2020; 1862:183397. [PMID: 32533976 DOI: 10.1016/j.bbamem.2020.183397] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/10/2020] [Revised: 06/04/2020] [Accepted: 06/09/2020] [Indexed: 11/26/2022]
Abstract
The amphipathic helix 0 of endophilin (i.e., H0-Endo) is important to membrane binding, but its function of curvature generation remains controversial. We used electron paramagnetic resonance (EPR) spectroscopy to study effects of H0-Endo on membrane material properties. We found that H0-Endo reduced lipid chain mobility and increased bilayer polarity, i.e., making the bilayer interior more polar. Lipid-dependent examination revealed that anionic lipids augmented the effect of H0-Endo, while cholesterol had a minimal impact. Our EPR spectroscopy of magnetically aligned bicelles showed that as the peptide-to-lipid ratio increased, the lipid chain orientational order decreased gradually, followed by a sudden loss. We discuss an interfacial-bound model of the amphipathic H0-Endo to account for all EPR data. We used atomic force microscopy and fluorescence microscopy to explore membrane morphological changes. We found that H0-Endo caused the formation of micron-sized holes in mica-supported planar bilayers. Hole formation is likely caused by two competing forces - the adhesion force exerted by the substrate represses bilayer budging, whereas the line tension originating from peptide clustering has a tendency of destabilizing bilayer organization. In the absence of substrate influences, membrane curvature induction was manifested by generating small vesicles surrounding giant unilamellar vesicles. Our results of membrane perforation and vesiculation suggest that the functionality of H0-Endo is more than just coordinating membrane binding of endophilin.
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Affiliation(s)
- Chinta M Aryal
- Department of Physics, University of South Florida, Tampa, FL 33620, United States of America
| | - Nhat Nguyen Bui
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, United States of America
| | - Nawal K Khadka
- Department of Physics, University of South Florida, Tampa, FL 33620, United States of America
| | - Likai Song
- National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, United States of America.
| | - Jianjun Pan
- Department of Physics, University of South Florida, Tampa, FL 33620, United States of America.
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29
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Zadlo A, Mokrzyński K, Ito S, Wakamatsu K, Sarna T. The influence of iron on selected properties of synthetic pheomelanin. Cell Biochem Biophys 2020; 78:181-189. [PMID: 32451722 PMCID: PMC7266848 DOI: 10.1007/s12013-020-00918-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2020] [Accepted: 05/08/2020] [Indexed: 11/29/2022]
Abstract
It is believed that while eumelanin plays photoprotective and antioxidant role in pigmented tissues, pheomelanin being more photoreactive could behave as a phototoxic agent. Although the metal ion-sequestering ability of melanin might be protective, transition metal ions present in natural melanins could affect their physicochemical properties. The aim of this research was to study iron binding by pheomelanin and analyze how such a binding affects selected properties of the melanin. Synthetic pheomelanin (CDM), prepared by enzymatic oxidation of DOPA in the presence of cysteine was analyzed by electron paramagnetic resonance (EPR) spectroscopy, spectrophotometry, chemical analysis, and time-resolved measurements of singlet oxygen phosphorescence. Iron broadened EPR signal of melanin and increased its optical absorption. Iron bound to melanin exhibited EPR signal at g = 4.3, typical for high-spin iron (III). Iron bound to melanin significantly altered the kinetics of melanin photodegradation, which in turn modified the accessibility and stability of the melanin–iron complexes as indicated by the release of iron from melanin induced by diethylenetriaminepentaacetic acid and KCN. Although bound to melanin iron little affects initial stages of photodegradation of CDM, the effect of iron becomes more pronounced at later stages of melanin photolysis.
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Affiliation(s)
- Andrzej Zadlo
- Department of Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Krakow, Poland.
| | - Krystian Mokrzyński
- Department of Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Krakow, Poland
| | - Shosuke Ito
- Department of Chemistry, Fujita Health University School of Medical Sciences, Toyoake, Japan
| | - Kazumasa Wakamatsu
- Department of Chemistry, Fujita Health University School of Medical Sciences, Toyoake, Japan
| | - Tadeusz Sarna
- Department of Biophysics, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Krakow, Poland
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30
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Sahu ID, Lorigan GA. Electron Paramagnetic Resonance as a Tool for Studying Membrane Proteins. Biomolecules 2020; 10:E763. [PMID: 32414134 PMCID: PMC7278021 DOI: 10.3390/biom10050763] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2020] [Revised: 04/24/2020] [Accepted: 04/24/2020] [Indexed: 12/13/2022] Open
Abstract
Membrane proteins possess a variety of functions essential to the survival of organisms. However, due to their inherent hydrophobic nature, it is extremely difficult to probe the structure and dynamic properties of membrane proteins using traditional biophysical techniques, particularly in their native environments. Electron paramagnetic resonance (EPR) spectroscopy in combination with site-directed spin labeling (SDSL) is a very powerful and rapidly growing biophysical technique to study pertinent structural and dynamic properties of membrane proteins with no size restrictions. In this review, we will briefly discuss the most commonly used EPR techniques and their recent applications for answering structure and conformational dynamics related questions of important membrane protein systems.
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Affiliation(s)
- Indra D. Sahu
- Natural Science Division, Campbellsville University, Campbellsville, KY 42718, USA
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA
| | - Gary A. Lorigan
- Department of Chemistry and Biochemistry, Miami University, Oxford, OH 45056, USA
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31
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EPR of site-directed spin-labeled proteins: A powerful tool to study structural flexibility. Arch Biochem Biophys 2020; 684:108323. [DOI: 10.1016/j.abb.2020.108323] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2019] [Revised: 02/17/2020] [Accepted: 02/24/2020] [Indexed: 12/20/2022]
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32
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Ghysels A, Krämer A, Venable RM, Teague WE, Lyman E, Gawrisch K, Pastor RW. Permeability of membranes in the liquid ordered and liquid disordered phases. Nat Commun 2019; 10:5616. [PMID: 31819053 PMCID: PMC6901538 DOI: 10.1038/s41467-019-13432-7] [Citation(s) in RCA: 63] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2019] [Accepted: 11/06/2019] [Indexed: 11/09/2022] Open
Abstract
The functional significance of ordered nanodomains (or rafts) in cholesterol rich eukaryotic cell membranes has only begun to be explored. This study exploits the correspondence of cellular rafts and liquid ordered (Lo) phases of three-component lipid bilayers to examine permeability. Molecular dynamics simulations of Lo phase dipalmitoylphosphatidylcholine (DPPC), dioleoylphosphatidylcholine (DOPC), and cholesterol show that oxygen and water transit a leaflet through the DOPC and cholesterol rich boundaries of hexagonally packed DPPC microdomains, freely diffuse along the bilayer midplane, and escape the membrane along the boundary regions. Electron paramagnetic resonance experiments provide critical validation: the measured ratio of oxygen concentrations near the midplanes of liquid disordered (Ld) and Lo bilayers of DPPC/DOPC/cholesterol is 1.75 ± 0.35, in very good agreement with 1.3 ± 0.3 obtained from simulation. The results show how cellular rafts can be structurally rigid signaling platforms while remaining nearly as permeable to small molecules as the Ld phase.
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Affiliation(s)
- An Ghysels
- Center for Molecular Modeling, Ghent University, Technologiepark 46, 9052, Gent, Belgium.
| | - Andreas Krämer
- Laboratory of Computational Biology, National Heart Lung Blood Institute, National Institutes of Health, Bethesda, MD, 20892, USA
| | - Richard M Venable
- Laboratory of Computational Biology, National Heart Lung Blood Institute, National Institutes of Health, Bethesda, MD, 20892, USA
| | - Walter E Teague
- Laboratory of Membrane Biochemistry and Biophysics, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD, 20892, USA
| | - Edward Lyman
- Department of Physics and Astronomy and Department of Chemistry and Biochemistry, University of Delaware, Newark, 19716, DE, USA
| | - Klaus Gawrisch
- Laboratory of Membrane Biochemistry and Biophysics, National Institute on Alcohol Abuse and Alcoholism, National Institutes of Health, Bethesda, MD, 20892, USA
| | - Richard W Pastor
- Laboratory of Computational Biology, National Heart Lung Blood Institute, National Institutes of Health, Bethesda, MD, 20892, USA.
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33
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Ahammad T, Drew DL, Sahu ID, Serafin RA, Clowes KR, Lorigan GA. Continuous Wave Electron Paramagnetic Resonance Spectroscopy Reveals the Structural Topology and Dynamic Properties of Active Pinholin S 2168 in a Lipid Bilayer. J Phys Chem B 2019; 123:8048-8056. [PMID: 31478671 DOI: 10.1021/acs.jpcb.9b06480] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Pinholin S2168 is an essential part of the phage Φ21 lytic protein system to release the virus progeny at the end of the infection cycle. It is known as the simplest natural timing system for its precise control of hole formation in the inner cytoplasmic membrane. Pinholin S2168 is a 68 amino acid integral membrane protein consisting of two transmembrane domains (TMDs) called TMD1 and TMD2. Despite its biological importance, structural and dynamic information of the S2168 protein in a membrane environment is not well understood. Systematic site-directed spin labeling and continuous wave electron paramagnetic resonance (CW-EPR) spectroscopic studies of pinholin S2168 in 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) proteoliposomes are used to reveal the structural topology and dynamic properties in a native-like environment. CW-EPR spectral line-shape analysis of the R1 side chain for 39 residue positions of S2168 indicates that the TMDs have more restricted mobility when compared to the N- and C-termini. CW-EPR power saturation data indicate that TMD1 partially externalizes from the lipid bilayer and interacts with the membrane surface, whereas TMD2 remains buried in the lipid bilayer in the active conformation of pinholin S2168. A tentative structural topology model of pinholin S2168 is also suggested based on EPR spectroscopic data reported in this study.
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Affiliation(s)
- Tanbir Ahammad
- Department of Chemistry and Biochemistry , Miami University , Oxford , Ohio 45056 , United States
| | - Daniel L Drew
- Department of Chemistry and Biochemistry , Miami University , Oxford , Ohio 45056 , United States
| | - Indra D Sahu
- Department of Chemistry and Biochemistry , Miami University , Oxford , Ohio 45056 , United States
| | - Rachel A Serafin
- Department of Chemistry and Biochemistry , Miami University , Oxford , Ohio 45056 , United States
| | - Katherine R Clowes
- Department of Chemistry and Biochemistry , Miami University , Oxford , Ohio 45056 , United States
| | - Gary A Lorigan
- Department of Chemistry and Biochemistry , Miami University , Oxford , Ohio 45056 , United States
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34
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Tao M, Pandey NK, Barnes R, Han S, Langen R. Structure of Membrane-Bound Huntingtin Exon 1 Reveals Membrane Interaction and Aggregation Mechanisms. Structure 2019; 27:1570-1580.e4. [PMID: 31466833 DOI: 10.1016/j.str.2019.08.003] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2019] [Revised: 07/23/2019] [Accepted: 08/09/2019] [Indexed: 02/08/2023]
Abstract
Huntington's disease is caused by a polyQ expansion in the first exon of huntingtin (Httex1). Membrane interaction of huntingtin is of physiological and pathological relevance. Using electron paramagnetic resonance and Overhauser dynamic nuclear polarization, we find that the N-terminal residues 3-13 of wild-type Httex1(Q25) form a membrane-bound, amphipathic α helix. This helix is positioned in the interfacial region, where it is sensitive to membrane curvature and electrostatic interactions with head-group charges. Residues 14-22, which contain the first five residues of the polyQ region, are in a transition region that remains in the interfacial region without taking up a stable, α-helical structure. The remaining C-terminal portion is solvent exposed. The phosphomimetic S13D/S16D mutations, which are known to protect from toxicity, inhibit membrane binding and attenuate membrane-mediated aggregation of mutant Httex1(Q46) due to electrostatic repulsion. Targeting the N-terminal membrane anchor using post-translational modifications or specific binders could be a potential means to reduce aggregation and toxicity in vivo.
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Affiliation(s)
- Meixin Tao
- Department of Neuroscience and Physiology, Department of Biochemistry and Molecular Medicine, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, CA 90033, USA
| | - Nitin K Pandey
- Department of Neuroscience and Physiology, Department of Biochemistry and Molecular Medicine, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, CA 90033, USA
| | - Ryan Barnes
- Department of Chemistry and Biochemistry, Department of Chemical Engineering, University of California Santa Barbara, Santa Barbara, CA 93106, USA
| | - Songi Han
- Department of Chemistry and Biochemistry, Department of Chemical Engineering, University of California Santa Barbara, Santa Barbara, CA 93106, USA
| | - Ralf Langen
- Department of Neuroscience and Physiology, Department of Biochemistry and Molecular Medicine, Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, CA 90033, USA.
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35
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Lai Y, Kuo Y, Chiang Y. Identifying Protein Conformational Dynamics Using Spin‐label ESR. Chem Asian J 2019; 14:3981-3991. [DOI: 10.1002/asia.201900855] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2019] [Revised: 08/02/2019] [Indexed: 12/24/2022]
Affiliation(s)
- Yei‐Chen Lai
- Department of Chemistry National Tsing Hua University Hsinchu 30013 Taiwan
- Department of Chemistry&Biochemistry University of California Santa Barbara CA 93106-9510 USA
| | - Yun‐Hsuan Kuo
- Department of Chemistry National Tsing Hua University Hsinchu 30013 Taiwan
| | - Yun‐Wei Chiang
- Department of Chemistry National Tsing Hua University Hsinchu 30013 Taiwan
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36
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Kreutzberger AJB, Ji M, Aaron J, Mihaljević L, Urban S. Rhomboid distorts lipids to break the viscosity-imposed speed limit of membrane diffusion. Science 2019; 363:363/6426/eaao0076. [PMID: 30705155 DOI: 10.1126/science.aao0076] [Citation(s) in RCA: 56] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2017] [Revised: 10/30/2018] [Accepted: 12/07/2018] [Indexed: 12/25/2022]
Abstract
Enzymes that cut proteins inside membranes regulate diverse cellular events, including cell signaling, homeostasis, and host-pathogen interactions. Adaptations that enable catalysis in this exceptional environment are poorly understood. We visualized single molecules of multiple rhomboid intramembrane proteases and unrelated proteins in living cells (human and Drosophila) and planar lipid bilayers. Notably, only rhomboid proteins were able to diffuse above the Saffman-Delbrück viscosity limit of the membrane. Hydrophobic mismatch with the irregularly shaped rhomboid fold distorted surrounding lipids and propelled rhomboid diffusion. The rate of substrate processing in living cells scaled with rhomboid diffusivity. Thus, intramembrane proteolysis is naturally diffusion-limited, but cells mitigate this constraint by using the rhomboid fold to overcome the "speed limit" of membrane diffusion.
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Affiliation(s)
- Alex J B Kreutzberger
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Room 507 PCTB, 725 North Wolfe Street, Baltimore, MD 21205, USA
| | - Ming Ji
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Room 507 PCTB, 725 North Wolfe Street, Baltimore, MD 21205, USA
| | - Jesse Aaron
- Howard Hughes Medical Institute, Advanced Imaging Center, Janelia Research Campus, 19700 Helix Drive, Ashburn, VA 20147, USA
| | - Ljubica Mihaljević
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Room 507 PCTB, 725 North Wolfe Street, Baltimore, MD 21205, USA
| | - Siniša Urban
- Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Room 507 PCTB, 725 North Wolfe Street, Baltimore, MD 21205, USA. .,Howard Hughes Medical Institute, Advanced Imaging Center, Janelia Research Campus, 19700 Helix Drive, Ashburn, VA 20147, USA
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37
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Kim G, Raymond HE, Herneisen AL, Wong-Rolle A, Howard KP. The distal cytoplasmic tail of the influenza A M2 protein dynamically extends from the membrane. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2019; 1861:1421-1427. [PMID: 31153909 DOI: 10.1016/j.bbamem.2019.05.021] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/05/2019] [Revised: 05/24/2019] [Accepted: 05/28/2019] [Indexed: 12/19/2022]
Abstract
The influenza A M2 protein is a multifunctional membrane-associated homotetramer that orchestrates several essential events in the viral infection cycle. The monomeric subunits of the M2 homotetramer consist of an N-terminal ectodomain, a transmembrane domain, and a C-terminal cytoplasmic domain. The transmembrane domain forms a four-helix proton channel that promotes uncoating of virions upon host cell entry. The membrane-proximal region of the C-terminal domain forms a surface-associated amphipathic helix necessary for viral budding. The structure of the remaining ~34 residues of the distal cytoplasmic tail has yet to be fully characterized despite the functional significance of this region for influenza infectivity. Here, we extend structural and dynamic studies of the poorly characterized M2 cytoplasmic tail. We used SDSL-EPR to collect site-specific information on the mobility, solvent accessibility, and conformational properties of residues 61-70 of the full-length, cell-expressed M2 protein reconstituted into liposomes. Our analysis is consistent with the predominant population of the C-terminal tail dynamically extending away from the membranes surface into the aqueous medium. These findings provide insight into the hypothesis that the C-terminal domain serves as a sensor that regulates how M2 protein participates in critical events in the viral infection cycle.
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Affiliation(s)
- Grace Kim
- Department of Chemistry and Biochemistry, Swarthmore College, Swarthmore, PA 19081, United States of America
| | - Hayley E Raymond
- Department of Chemistry and Biochemistry, Swarthmore College, Swarthmore, PA 19081, United States of America
| | - Alice L Herneisen
- Department of Chemistry and Biochemistry, Swarthmore College, Swarthmore, PA 19081, United States of America
| | - Abigail Wong-Rolle
- Department of Chemistry and Biochemistry, Swarthmore College, Swarthmore, PA 19081, United States of America
| | - Kathleen P Howard
- Department of Chemistry and Biochemistry, Swarthmore College, Swarthmore, PA 19081, United States of America.
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38
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Hervis YP, Valle A, Dunkel S, Klare JP, Canet L, Lanio ME, Alvarez C, Pazos IF, Steinhoff HJ. Architecture of the pore forming toxin sticholysin I in membranes. J Struct Biol 2019; 208:30-42. [PMID: 31330179 DOI: 10.1016/j.jsb.2019.07.008] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2019] [Revised: 07/02/2019] [Accepted: 07/17/2019] [Indexed: 12/28/2022]
Abstract
Sticholysin I (StI) is a toxin produced by the sea anemone Stichodactyla helianthus and belonging to the actinoporins family. Upon binding to sphingomyelin-containing membranes StI forms oligomeric pores, thereby leading to cell death. According to recent controversial experimental evidences, the pore architecture of actinoporins is a debated topic. Here, we investigated the StI topology in membranes by site-directed spin labeling and electron paramagnetic resonance spectroscopy. The results reveal that StI in membrane exhibits an oligomeric architecture with heterogeneous stoichiometry of predominantly eight or nine protomers, according to the available structural models. The StI topology resembles the conic pore structure reported for the actinoporin fragaceatoxin C. Our data show that StI coexists in two membrane-associated conformations, with the N-terminal segment either attached to the protein core or inserted in the membrane forming the pore. This finding suggests a 'pre-pore' to 'pore' transition determined by a conformational change that detaches the N-terminal segment.
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Affiliation(s)
- Yadira P Hervis
- Center for Protein Studies/Department of Biochemistry, University of Havana, Calle 25 #455 e/I y J, Vedado, Plaza de la Revolución, ZIP 10400, Havana, Cuba.
| | - Aisel Valle
- Center for Protein Studies/Department of Biochemistry, University of Havana, Calle 25 #455 e/I y J, Vedado, Plaza de la Revolución, ZIP 10400, Havana, Cuba.
| | - Sabrina Dunkel
- Department of Physics, University of Osnabrueck, Barbarastr. 7, 49076 Osnabrueck, Germany.
| | - Johann P Klare
- Department of Physics, University of Osnabrueck, Barbarastr. 7, 49076 Osnabrueck, Germany.
| | - Liem Canet
- Center for Protein Studies/Department of Biochemistry, University of Havana, Calle 25 #455 e/I y J, Vedado, Plaza de la Revolución, ZIP 10400, Havana, Cuba.
| | - Maria E Lanio
- Center for Protein Studies/Department of Biochemistry, University of Havana, Calle 25 #455 e/I y J, Vedado, Plaza de la Revolución, ZIP 10400, Havana, Cuba.
| | - Carlos Alvarez
- Center for Protein Studies/Department of Biochemistry, University of Havana, Calle 25 #455 e/I y J, Vedado, Plaza de la Revolución, ZIP 10400, Havana, Cuba.
| | - Isabel F Pazos
- Center for Protein Studies/Department of Biochemistry, University of Havana, Calle 25 #455 e/I y J, Vedado, Plaza de la Revolución, ZIP 10400, Havana, Cuba.
| | - Heinz-J Steinhoff
- Department of Physics, University of Osnabrueck, Barbarastr. 7, 49076 Osnabrueck, Germany.
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Nyenhuis SB, Thapa A, Cafiso DS. Phosphatidylinositol 4,5 Bisphosphate Controls the cis and trans Interactions of Synaptotagmin 1. Biophys J 2019; 117:247-257. [PMID: 31301806 DOI: 10.1016/j.bpj.2019.06.016] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2019] [Revised: 05/20/2019] [Accepted: 06/18/2019] [Indexed: 11/28/2022] Open
Abstract
Synaptotagmin 1 acts as the Ca2+ sensor for synchronous neurotransmitter release; however, the mechanism by which it functions is not understood and is presently a topic of considerable interest. Here, we describe measurements on full-length membrane-reconstituted synaptotagmin 1 using site-directed spin labeling in which we characterize the linker region as well as the cis (vesicle membrane) and trans (cytoplasmic membrane) binding of its two C2 domains. In the full-length protein, the C2A domain does not undergo membrane insertion in the absence of Ca2+; however, the C2B domain will bind to and penetrate in trans to a membrane containing phosphatidylinositol 4,5 bisphosphate, even if phosphatidylserine (PS) is present in the cis membrane. In the presence of Ca2+, the Ca2+ binding loops of C2A and C2B both insert into the membrane interface; moreover, C2A preferentially inserts into PS-containing bilayers and will bind in a cis configuration to membranes containing PS even if a phosphatidylinositol 4,5 bisphosphate membrane is presented in trans. The data are consistent with a bridging activity for synaptotagmin 1 in which the two domains bind to opposing vesicle and plasma membranes. The failure of C2A to bind membranes in the absence of Ca2+ and the long unstructured segment linking C2A to the vesicle membrane indicates that synaptotagmin 1 could act to significantly shorten the vesicle-plasma membrane distance with increasing levels of Ca2+.
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Affiliation(s)
- Sarah B Nyenhuis
- Department of Chemistry and Center for Membrane Biology, University of Virginia, Charlottesville, Virginia
| | - Anusa Thapa
- Department of Chemistry and Center for Membrane Biology, University of Virginia, Charlottesville, Virginia
| | - David S Cafiso
- Department of Chemistry and Center for Membrane Biology, University of Virginia, Charlottesville, Virginia.
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40
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Martin PD, James ZM, Thomas DD. Effect of Phosphorylation on Interactions between Transmembrane Domains of SERCA and Phospholamban. Biophys J 2019; 114:2573-2583. [PMID: 29874608 DOI: 10.1016/j.bpj.2018.04.035] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2018] [Revised: 03/29/2018] [Accepted: 04/18/2018] [Indexed: 01/27/2023] Open
Abstract
We have used site-directed spin labeling and electron paramagnetic resonance (EPR) to map interactions between the transmembrane (TM) domains of the sarcoplasmic reticulum Ca2+-ATPase (SERCA) and phospholamban (PLB) as affected by PLB phosphorylation. In the cardiac sarcoplasmic reticulum, PLB binding to SERCA results in Ca-dependent enzyme inhibition, which is reversed by PLB phosphorylation at Ser16. Previous spectroscopic studies on SERCA-PLB have largely focused on the cytoplasmic domain of PLB, showing that phosphorylation induces a structural shift in this domain relative to SERCA. However, SERCA inhibition is due entirely to TM domain interactions. Therefore, we focus here on PLB's TM domain, attaching Cys-reactive spin labels at five different positions. In each case, continuous-wave EPR indicated moderate spin-label mobility, with the addition of SERCA revealing two populations, one indistinguishable from PLB alone and another with more restricted rotational mobility, presumably due to SERCA-binding. Phosphorylation had no effect on the rotational mobility of either component but significantly decreased the mole fraction of the restricted component. Solvent-accessibility experiments using power-saturation EPR and saturation-recovery EPR confirmed that these two spectral components were SERCA-bound and unbound PLB and showed that phosphorylation increased the overall lipid accessibility of the TM domain by increasing the fraction of unbound PLB. However-based on these results-at physiological levels of SERCA and PLB, most SERCA would have bound PLB even after phosphorylation. Additionally, no structural shift in the TM domain of SERCA-bound PLB was detected, as there were no significant changes in membrane insertion depth or its accessibility. Therefore, we conclude that under physiological conditions, the phosphorylation of PLB induces little or no change in the interaction of the TM domain with SERCA, so relief of inhibition is predominantly due to the previously observed structural shift in the cytoplasmic domain.
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Affiliation(s)
- Peter D Martin
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota; School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota
| | - Zachary M James
- Department of Physiology and Biophysics, University of Washington, Seattle, Washington
| | - David D Thomas
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota; School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota.
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41
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Xia C, Shen AL, Duangkaew P, Kotewong R, Rongnoparut P, Feix J, Kim JJP. Structural and Functional Studies of the Membrane-Binding Domain of NADPH-Cytochrome P450 Oxidoreductase. Biochemistry 2019; 58:2408-2418. [PMID: 31009206 PMCID: PMC6873807 DOI: 10.1021/acs.biochem.9b00130] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
NADPH-cytochrome P450 oxidoreductase (CYPOR), the essential flavoprotein of the microsomal cytochrome P450 monooxygenase system, is anchored in the phospholipid bilayer by its amino-terminal membrane-binding domain (MBD), which is necessary for efficient electron transfer to cytochrome P450. Although crystallographic and kinetic studies have established the structure of the soluble catalytic domain and the role of conformational motions in the control of electron transfer, the role of the MBD is largely unknown. We examined the role of the MBD in P450 catalysis through studies of amino-terminal deletion mutants and site-directed spin labeling. We show that the MBD spans the membrane and present a model for the orientation of CYPOR on the membrane capable of forming a complex with cytochrome P450. EPR power saturation measurements of CYPOR mutants in liposomes containing a lipid/Ni(II) chelate identified a region of the soluble domain interacting with the membrane. The deletion of more than 29 residues from the N-terminus of CYPOR decreases cytochrome P450 activity concomitant with alterations in electrophoretic mobility and an increased resistance to protease digestion. The altered kinetic properties of these mutants are consistent with electron transfer through random collisions rather than via formation of a stable CYPOR-P450 complex. Purified MBD binds weakly to cytochrome P450, suggesting that other interactions are also required for CYPOR-P450 complex formation. We propose that the MBD and flexible tether region of CYPOR, residues 51-63, play an important role in facilitating the movement of the soluble domain relative to the membrane and in promoting multiple orientations that permit specific interactions of CYPOR with its varied partners.
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Affiliation(s)
- Chuanwu Xia
- Department of Biochemistry , Medical College of Wisconsin , Milwaukee , Wisconsin 53226 , United States
| | - Anna L Shen
- McArdle Laboratory for Cancer Research , University of Wisconsin-Madison , Madison , Wisconsin 53706 , United States
| | - Panida Duangkaew
- Department of Biochemistry , Medical College of Wisconsin , Milwaukee , Wisconsin 53226 , United States
- Department of Biochemistry, Faculty of Science , Mahidol University , Bangkok 10400 , Thailand
| | - Rattanawadee Kotewong
- Department of Biochemistry , Medical College of Wisconsin , Milwaukee , Wisconsin 53226 , United States
- Department of Biochemistry, Faculty of Science , Mahidol University , Bangkok 10400 , Thailand
| | - Pornpimol Rongnoparut
- Department of Biochemistry, Faculty of Science , Mahidol University , Bangkok 10400 , Thailand
| | - Jimmy Feix
- Department of Biophysics , Medical College of Wisconsin , Milwaukee , Wisconsin 53226 , United States
| | - Jung-Ja P Kim
- Department of Biochemistry , Medical College of Wisconsin , Milwaukee , Wisconsin 53226 , United States
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42
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Kieber M, Ono T, Oliver RC, Nyenhuis SB, Tieleman DP, Columbus L. The Fluidity of Phosphocholine and Maltoside Micelles and the Effect of CHAPS. Biophys J 2019; 116:1682-1691. [PMID: 31023535 DOI: 10.1016/j.bpj.2019.03.019] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2018] [Revised: 03/13/2019] [Accepted: 03/20/2019] [Indexed: 11/17/2022] Open
Abstract
The dynamics of phosphocholine and maltoside micelles, detergents frequently used for membrane protein structure determination, were investigated using electron paramagnetic resonance of spin probes doped into the micelles. Specifically, phosphocholines are frequently used detergents in NMR studies, and maltosides are frequently used in x-ray crystallography structure determination. Beyond the structural and electrostatic differences, this study aimed to determine whether there are differences in the local chain dynamics (i.e., fluidity). The nitroxide probe rotational dynamics in longer chain detergents is more restricted than in shorter chain detergents, and maltoside micelles are more restricted than phosphocholine micelles. Furthermore, the micelle microviscosity can be modulated with mixtures, as demonstrated with mixtures of 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate with n-dodecylphosphocholine, n-tetradecylphosphocholine, n-decyl-β-D-maltoside, or n-dodecyl-β-D-maltoside. These results indicate that observed differences in membrane protein stability in these detergents could be due to fluidity in addition to the already determined structural differences.
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Affiliation(s)
- Marissa Kieber
- Department of Chemistry, University of Virginia, Charlottesville, Virginia
| | - Tomihiro Ono
- Department of Chemistry, University of Virginia, Charlottesville, Virginia
| | - Ryan C Oliver
- Department of Chemistry, University of Virginia, Charlottesville, Virginia
| | - Sarah B Nyenhuis
- Department of Chemistry, University of Virginia, Charlottesville, Virginia
| | - D Peter Tieleman
- Department of Biological Sciences and Centre for Molecular Simulation, University of Calgary, Calgary, Alberta, Canada
| | - Linda Columbus
- Department of Chemistry, University of Virginia, Charlottesville, Virginia.
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43
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Vasquez-Montes V, Vargas-Uribe M, Pandey NK, Rodnin MV, Langen R, Ladokhin AS. Lipid-modulation of membrane insertion and refolding of the apoptotic inhibitor Bcl-xL. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2019; 1867:691-700. [PMID: 31004798 DOI: 10.1016/j.bbapap.2019.04.006] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/08/2019] [Accepted: 04/16/2019] [Indexed: 02/07/2023]
Abstract
Bcl-xL is a member of the Bcl-2 family of apoptotic regulators, responsible for inhibiting the permeabilization of the mitochondrial outer membrane, and a promising anti-cancer target. Bcl-xL exists in the following conformations, each believed to play a role in the inhibition of apoptosis: (a) a soluble folded conformation, (b) a membrane-anchored (by its C-terminal α8 helix) form, which retains the same fold as in solution and (c) refolded membrane-inserted conformations, for which no structural data are available. Previous studies established that in the cell Bcl-xL exists in a dynamic equilibrium between soluble and membranous states, however, no direct evidence exists in support of either anchored or inserted conformation of the membranous state in vivo. In this in vitro study, we employed a combination of fluorescence and EPR spectroscopy to characterize structural features of the bilayer-inserted conformation of Bcl-xL and the lipid modulation of its membrane insertion transition. Our results indicate that the core hydrophobic helix α6 inserts into the bilayer without adopting a transmembrane orientation. This insertion disrupts the packing of Bcl-xL and releases the regulatory N-terminal BH4 domain (α1) from the rest of the protein structure. Our data demonstrate that both insertion and refolding of Bcl-xL are modulated by lipid composition, which brings the apparent pKa of insertion to the threshold of physiological pH. We hypothesize that conformational rearrangements associated with the bilayer insertion of Bcl-xL result in its switching to a so-called non-canonical mode of apoptotic inhibition. Presented results suggest that the alteration in lipid composition before and during apoptosis can serve as an additional factor regulating the permeabilization of the mitochondrial outer membrane.
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Affiliation(s)
- Victor Vasquez-Montes
- Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, KS 66160, USA
| | - Mauricio Vargas-Uribe
- Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, KS 66160, USA
| | - Nitin K Pandey
- Zilkha Neurogenetic Institute, University of Southern California, Los Angeles, CA 90033, USA
| | - Mykola V Rodnin
- Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, KS 66160, USA
| | - Ralf Langen
- Zilkha Neurogenetic Institute, University of Southern California, Los Angeles, CA 90033, USA
| | - Alexey S Ladokhin
- Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, KS 66160, USA.
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44
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Dixit G, Sahu ID, Reynolds WD, Wadsworth TM, Harding BD, Jaycox CK, Dabney-Smith C, Sanders CR, Lorigan GA. Probing the Dynamics and Structural Topology of the Reconstituted Human KCNQ1 Voltage Sensor Domain (Q1-VSD) in Lipid Bilayers Using Electron Paramagnetic Resonance Spectroscopy. Biochemistry 2019; 58:965-973. [PMID: 30620191 DOI: 10.1021/acs.biochem.8b01042] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
KCNQ1 (Kv7.1 or KvLQT1) is a potassium ion channel protein found in the heart, ear, and other tissues. In complex with the KCNE1 accessory protein, it plays a role during the repolarization phase of the cardiac action potential. Mutations in the channel have been associated with several diseases, including congenital deafness and long QT syndrome. Nuclear magnetic resonance (NMR) structural studies in detergent micelles and a cryo-electron microscopy structure of KCNQ1 from Xenopus laevis have shown that the voltage sensor domain (Q1-VSD) of the channel has four transmembrane helices, S1-S4, being overall structurally similar with other VSDs. In this study, we describe a reliable method for the reconstitution of Q1-VSD into (POPC/POPG) lipid bilayer vesicles. Site-directed spin labeling electron paramagnetic resonance spectroscopy was used to probe the structural dynamics and topology of several residues of Q1-VSD in POPC/POPG lipid bilayer vesicles. Several mutants were probed to determine their location and corresponding immersion depth (in angstroms) with respect to the membrane. The dynamics of the bilayer vesicles upon incorporation of Q1-VSD were studied using 31P solid-state NMR spectroscopy by varying the protein:lipid molar ratios confirming the interaction of the protein with the bilayer vesicles. Circular dichroism spectroscopic data showed that the α-helical content of Q1-VSD is higher for the protein reconstituted in vesicles than in previous studies using DPC detergent micelles. This study provides insight into the structural topology and dynamics of Q1-VSD reconstituted in a lipid bilayer environment, forming the basis for more advanced structural and functional studies.
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Affiliation(s)
- Gunjan Dixit
- Department of Chemistry and Biochemistry , Miami University , 651 East High Street , Oxford , Ohio 45056 , United States
| | - Indra D Sahu
- Department of Chemistry and Biochemistry , Miami University , 651 East High Street , Oxford , Ohio 45056 , United States
| | - Warren D Reynolds
- Department of Chemistry and Biochemistry , Miami University , 651 East High Street , Oxford , Ohio 45056 , United States
| | - Tessa M Wadsworth
- Department of Chemistry and Biochemistry , Miami University , 651 East High Street , Oxford , Ohio 45056 , United States
| | - Benjamin D Harding
- Department of Chemistry and Biochemistry , Miami University , 651 East High Street , Oxford , Ohio 45056 , United States
| | - Colleen K Jaycox
- Department of Chemistry and Biochemistry , Miami University , 651 East High Street , Oxford , Ohio 45056 , United States
| | - Carole Dabney-Smith
- Department of Chemistry and Biochemistry , Miami University , 651 East High Street , Oxford , Ohio 45056 , United States
| | - Charles R Sanders
- Department of Biochemistry and Center for Structural Biology , Vanderbilt University , Nashville , Tennessee 37240 , United States
| | - Gary A Lorigan
- Department of Chemistry and Biochemistry , Miami University , 651 East High Street , Oxford , Ohio 45056 , United States
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45
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Caputo GA, London E. Analyzing Transmembrane Protein and Hydrophobic Helix Topography by Dual Fluorescence Quenching. Methods Mol Biol 2019; 2003:351-368. [PMID: 31218625 DOI: 10.1007/978-1-4939-9512-7_15] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The location of fluorescent groups relative to the lipid bilayer can be evaluated using fluorescence quenchers embedded in the membrane and/or dissolved in aqueous solution. Quenching can be used to define the membrane topography of membrane proteins and individual membrane-embedded hydrophobic helices by combining it with the placement of fluorescent groups, including Trp, at defined sequence positions. This chapter briefly discusses various quenching methods for studies of membrane protein topography, and provides detailed protocols for dual quencher analysis (DQA), a rapid, highly sensitive, and experimentally flexible approach in which the information gained from both a membrane-embedded and aqueous quencher is combined. The advantages of the DQA method include flexibility with regard to the bilayer compositions to which it can be applied, including membranes composed of lipids of varying head group and acyl chain compositions, as well as the ability to identify mixed populations of fluorophores residing at different depths within the bilayer.
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Affiliation(s)
- Gregory A Caputo
- Department of Chemistry and Biochemistry, Rowan University, Glassboro, NJ, USA
| | - Erwin London
- Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, NY, USA.
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46
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Bordignon E, Kucher S, Polyhach Y. EPR Techniques to Probe Insertion and Conformation of Spin-Labeled Proteins in Lipid Bilayers. Methods Mol Biol 2019; 2003:493-528. [PMID: 31218631 DOI: 10.1007/978-1-4939-9512-7_21] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Electron paramagnetic resonance (EPR) spectroscopy of spin-labeled membrane proteins is a valuable biophysical technique to study structural details and conformational transitions of proteins close to their physiological environment, for example, in liposomes, membrane bilayers, and nanodiscs. Unlike in nuclear magnetic resonance (NMR) spectroscopy, having only one or few specific side chains labeled at a time with paramagnetic probes makes the size of the object under investigation irrelevant in terms of technique sensitivity. As a drawback, extensive site-directed mutagenesis is required in order to analyze the properties of the protein under investigation. EPR can provide detailed information on side chain dynamics of large membrane proteins or protein complexes embedded in membranes with an exquisite sensitivity for flexible regions and on water accessibility profiles across the membrane bilayer. Moreover, distances between the two spin-labeled side chains in membrane proteins can be detected with high precision at cryogenic temperatures. The application of EPR to membrane proteins still presents some challenges in terms of sample preparation, sensitivity and data interpretation, thus it is difficult to give ready-to-go methodological recipes. However, new technological developments (arbitrary waveform generators) and new spin labels spectroscopically orthogonal to nitroxides increased the range of applicability from in vitro toward in-cell EPR experiments. This chapter is an updated version of the one published in the first edition of the book and describes the state of the art in the application of nitroxide-based site-directed spin labeling EPR to membrane proteins, addressing new tools such as arbitrary waveform generators and spectroscopically orthogonal labels, such as Gd(III)-based labels. We will present challenges in sample preparation and data analysis for functional and structural membrane protein studies using site-directed spin labeling techniques and give experimental details on EPR techniques providing information on side chain dynamics and water accessibility using nitroxide probes. An updated optimal Q-band DEER setup for nitroxide probes will be described, and its extension to gadolinium-containing samples will be addressed.
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Affiliation(s)
- Enrica Bordignon
- Faculty of Chemistry and Biochemistry, Ruhr University Bochum, Bochum, Germany.
| | - Svetlana Kucher
- Faculty of Chemistry and Biochemistry, Ruhr University Bochum, Bochum, Germany
| | - Yevhen Polyhach
- Laboratory of Physical Chemistry, ETH Zurich, Zurich, Switzerland
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47
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Khounlo R, Hawk BJ, Shin YK. EPR Lineshape Analysis to Investigate the SNARE Folding Intermediates. Methods Mol Biol 2019; 1860:33-51. [PMID: 30317497 PMCID: PMC6429964 DOI: 10.1007/978-1-4939-8760-3_3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
SNARE complex formation, which is believed to drive intracellular membrane fusion, transits through multiple conformational states along the membrane fusion pathway. The SNARE intermediates are biologically important because they serve as targets for fusion regulators and clostridial neurotoxins. Spin-labeling EPR has contributed significantly to the understanding of the structures and the dynamics of SNARE intermediates. In particular, the EPR lineshape analysis, which is highly sensitive to protein conformational changes such as the local coil-to-helix transition, has revealed the sequential compacting steps leading to formation of the highly stable four-helix bundle.
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Affiliation(s)
- Ryan Khounlo
- Iowa State University, Roy J. Carver Department of Biochemistry, Biophysics & Molecular Biology, 4138 Molecular Biology Building, 2437 Pammel Dr, Ames, IA 50011,
| | - Brenden J.D. Hawk
- Iowa State University, Roy J. Carver Department of Biochemistry, Biophysics & Molecular Biology, 4138 Molecular Biology Building, 2437 Pammel Dr, Ames, IA 50011,
| | - Yeon-Kyun Shin
- Iowa State University, Roy J. Carver Department of Biochemistry, Biophysics & Molecular Biology, 4152 Molecular Biology Building, 2437 Pammel Dr, Ames, IA 50011,
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48
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CW EPR and DEER Methods to Determine BCL-2 Family Protein Structure and Interactions: Application of Site-Directed Spin Labeling to BAK Apoptotic Pores. Methods Mol Biol 2018. [PMID: 30536012 DOI: 10.1007/978-1-4939-8861-7_18] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
Abstract
The continuous wave (CW) and pulse electron paramagnetic resonance (EPR) methods enable the measurement of distances between spin-labeled residues in biopolymers including proteins, providing structural information. Here we describe the CW EPR deconvolution/convolution method and the four-pulse double electron-electron resonance (DEER) approach for distance determination, which were applied to elucidate the organization of the BAK apoptotic pores formed in the lipid bilayers.
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49
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Pan J, Dalzini A, Khadka NK, Aryal CM, Song L. Lipid Extraction by α-Synuclein Generates Semi-Transmembrane Defects and Lipoprotein Nanoparticles. ACS OMEGA 2018; 3:9586-9597. [PMID: 30198000 PMCID: PMC6120733 DOI: 10.1021/acsomega.8b01462] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/26/2018] [Accepted: 08/07/2018] [Indexed: 05/17/2023]
Abstract
Modulations of synaptic membranes play an essential role in the physiological and pathological functions of the presynaptic protein α-synuclein (αSyn). Here we used solution atomic force microscopy (AFM) and electron paramagnetic resonance (EPR) spectroscopy to investigate membrane modulations caused by αSyn. We used several lipid bilayers to explore how different lipid species may regulate αSyn-membrane interactions. We found that at a protein-to-lipid ratio of ∼1/9, αSyn perturbed lipid bilayers by generating semi-transmembrane defects that only span one leaflet. In addition, αSyn coaggregates with lipid molecules to produce ∼10 nm-sized lipoprotein nanoparticles. The obtained AFM data are consistent with the apolipoprotein characteristic of αSyn. The role of anionic lipids was elucidated by comparing results from zwitterionic and anionic lipid bilayers. Specifically, our AFM measurements showed that anionic bilayers had a larger tendency of forming bilayer defects; similarly, our EPR measurements revealed that anionic bilayers exhibited more substantial changes in lipid chain mobility and bilayer polarity. We also studied the effect of cholesterol. We found that cholesterol increased the capability of αSyn in inducing bilayer defects and altering lipid chain mobility and bilayer polarity. These data can be explained by an increase in the lipid headgroup-headgroup spacing and/or specific cholesterol-αSyn interactions. Interestingly, we found an inhibitory effect of the cone-shaped phosphatidylethanolamine lipids on αSyn-induced bilayer remodeling. We explained our data by considering interlipid hydrogen-bonding that can stabilize bilayer organization and suppress lipid extraction. Our results of lipid-dependent membrane modulations are likely relevant to αSyn functioning.
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Affiliation(s)
- Jianjun Pan
- Department
of Physics, University of South Florida, Tampa, Florida 33620, United States
- E-mail: (J.P.)
| | - Annalisa Dalzini
- National
High Magnetic Field Laboratory, Florida
State University, Tallahassee, Florida 32310, United States
| | - Nawal K. Khadka
- Department
of Physics, University of South Florida, Tampa, Florida 33620, United States
| | - Chinta M. Aryal
- Department
of Physics, University of South Florida, Tampa, Florida 33620, United States
| | - Likai Song
- National
High Magnetic Field Laboratory, Florida
State University, Tallahassee, Florida 32310, United States
- E-mail: (L.S.)
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50
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Feix JB, Kohn S, Tessmer MH, Anderson DM, Frank DW. Conformational Changes and Membrane Interaction of the Bacterial Phospholipase, ExoU: Characterization by Site-Directed Spin Labeling. Cell Biochem Biophys 2018; 77:79-87. [PMID: 30047043 DOI: 10.1007/s12013-018-0851-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2018] [Accepted: 07/12/2018] [Indexed: 12/20/2022]
Abstract
Numerous pathogenic bacteria produce proteins evolved to facilitate their survival and dissemination by modifying the host environment. These proteins, termed effectors, often play a significant role in determining the virulence of the infection. Consequently, bacterial effectors constitute an important class of targets for the development of novel antibiotics. ExoU is a potent phospholipase effector produced by the opportunistic pathogen Pseudomonas aeruginosa. Previous studies have established that the phospholipase activity of ExoU requires non-covalent interaction with ubiquitin, however the molecular details of the mechanism of activation and the manner in which ExoU associates with a target lipid bilayer are not understood. In this review we describe our recent studies using site-directed spin labeling (SDSL) and EPR spectroscopy to elucidate the conformational changes and membrane interactions that accompany activation of ExoU. We find that ubiquitin binding and membrane interaction act synergistically to produce structural transitions that occur upon ExoU activation, and that the C-terminal four-helix bundle of ExoU functions as a phospholipid-binding domain, facilitating the association of ExoU with the membrane surface.
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Affiliation(s)
- Jimmy B Feix
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI, 53226, USA.
| | - Samantha Kohn
- Department of Biophysics, Medical College of Wisconsin, Milwaukee, WI, 53226, USA
| | - Maxx H Tessmer
- Department of Microbiology and Immunology, Medical College of Wisconsin, Milwaukee, WI, 53226, USA
| | - David M Anderson
- Department of Pathology, Microbiology and Immunology, Vanderbilt University, Nashville, TN, 37232, USA
| | - Dara W Frank
- Department of Microbiology and Immunology, Medical College of Wisconsin, Milwaukee, WI, 53226, USA
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