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Roubalova L, Vosahlikova M, Brejchova J, Sykora J, Rudajev V, Svoboda P. High Efficacy but Low Potency of δ-Opioid Receptor-G Protein Coupling in Brij-58-Treated, Low-Density Plasma Membrane Fragments. PLoS One 2015; 10:e0135664. [PMID: 26285205 PMCID: PMC4540457 DOI: 10.1371/journal.pone.0135664] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2014] [Accepted: 07/25/2015] [Indexed: 11/18/2022] Open
Abstract
Principal Findings HEK293 cells stably expressing PTX-insensitive δ-opioid receptor-Gi1α (C351I) fusion protein were homogenized, treated with low concentrations of non-ionic detergent Brij-58 at 0°C and fractionated by flotation in sucrose density gradient. In optimum range of detergent concentrations (0.025–0.05% w/v), Brij-58-treated, low-density membranes exhibited 2-3-fold higher efficacy of DADLE-stimulated, high-affinity [32P]GTPase and [35S]GTPγS binding than membranes of the same density prepared in the absence of detergent. The potency of agonist DADLE response was significantly decreased. At high detergent concentrations (>0.1%), the functional coupling between δ-opioid receptors and G proteins was completely diminished. The same detergent effects were measured in plasma membranes isolated from PTX-treated cells. Therefore, the effect of Brij-58 on δ-opioid receptor-G protein coupling was not restricted to the covalently bound Gi1α within δ-opioid receptor-Gi1α fusion protein, but it was also valid for PTX-sensitive G proteins of Gi/Go family endogenously expressed in HEK293 cells. Characterization of the direct effect of Brij-58 on the hydrophobic interior of isolated plasma membranes by steady-state anisotropy of diphenylhexatriene (DPH) fluorescence indicated a marked increase of membrane fluidity. The time-resolved analysis of decay of DPH fluorescence by the “wobble in cone” model of DPH motion in the membrane indicated that the exposure to the increasing concentrations of Brij-58 led to a decreased order and higher motional freedom of the dye. Summary Limited perturbation of plasma membrane integrity by low concentrations of non-ionic detergent Brij-58 results in alteration of δ-OR-G protein coupling. Maximum G protein-response to agonist stimulation (efficacy) is increased; affinity of response (potency) is decreased. The total degradation plasma membrane structure at high detergent concentrations results in diminution of functional coupling between δ-opioid receptors and G proteins.
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Affiliation(s)
- Lenka Roubalova
- Department of Biomathematics, Institute of Physiology of the Czech Academy of Sciences, Prague, Czech Republic
| | - Miroslava Vosahlikova
- Department of Biomathematics, Institute of Physiology of the Czech Academy of Sciences, Prague, Czech Republic
| | - Jana Brejchova
- Department of Biomathematics, Institute of Physiology of the Czech Academy of Sciences, Prague, Czech Republic
| | - Jan Sykora
- Department of Biophysical Chemistry, J. Heyrovsky Institute of Physical Chemistry of the Czech Academy of Sciences, Prague, Czech Republic
| | - Vladimir Rudajev
- Department of Neurochemistry, Institute of Physiology of the Czech Academy of Sciences, Prague, Czech Republic
| | - Petr Svoboda
- Department of Biomathematics, Institute of Physiology of the Czech Academy of Sciences, Prague, Czech Republic
- * E-mail:
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102
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Lindholm L, Ariöz C, Jawurek M, Liebau J, Mäler L, Wieslander Å, von Ballmoos C, Barth A. Effect of lipid bilayer properties on the photocycle of green proteorhodopsin. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2015; 1847:698-708. [DOI: 10.1016/j.bbabio.2015.04.011] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/04/2015] [Revised: 04/17/2015] [Accepted: 04/21/2015] [Indexed: 01/20/2023]
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103
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Choi HJ, Song JM, Bondy BJ, Compans RW, Kang SM, Prausnitz MR. Effect of Osmotic Pressure on the Stability of Whole Inactivated Influenza Vaccine for Coating on Microneedles. PLoS One 2015; 10:e0134431. [PMID: 26230936 PMCID: PMC4521748 DOI: 10.1371/journal.pone.0134431] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2015] [Accepted: 07/10/2015] [Indexed: 11/18/2022] Open
Abstract
Enveloped virus vaccines can be damaged by high osmotic strength solutions, such as those used to protect the vaccine antigen during drying, which contain high concentrations of sugars. We therefore studied shrinkage and activity loss of whole inactivated influenza virus in hyperosmotic solutions and used those findings to improve vaccine coating of microneedle patches for influenza vaccination. Using stopped-flow light scattering analysis, we found that the virus underwent an initial shrinkage on the order of 10% by volume within 5 s upon exposure to a hyperosmotic stress difference of 217 milliosmolarity. During this shrinkage, the virus envelope had very low osmotic water permeability (1 - 6×10-4 cm s-1) and high Arrhenius activation energy (Ea = 15.0 kcal mol-1), indicating that the water molecules diffused through the viral lipid membranes. After a quasi-stable state of approximately 20 s to 2 min, depending on the species and hypertonic osmotic strength difference of disaccharides, there was a second phase of viral shrinkage. At the highest osmotic strengths, this led to an undulating light scattering profile that appeared to be related to perturbation of the viral envelope resulting in loss of virus activity, as determined by in vitro hemagglutination measurements and in vivo immunogenicity studies in mice. Addition of carboxymethyl cellulose effectively prevented vaccine activity loss in vitro and in vivo, believed to be due to increasing the viscosity of concentrated sugar solution and thereby reducing osmotic stress during coating of microneedles. These results suggest that hyperosmotic solutions can cause biphasic shrinkage of whole inactivated influenza virus which can damage vaccine activity at high osmotic strength and that addition of a viscosity enhancer to the vaccine coating solution can prevent osmotically driven damage and thereby enable preparation of stable microneedle coating formulations for vaccination.
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Affiliation(s)
- Hyo-Jick Choi
- School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States of America
- Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta, Canada
| | - Jae-Min Song
- Department of Global Medical Science, Sungshin Women's University, Seoul, Korea
| | - Brian J. Bondy
- School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States of America
| | - Richard W. Compans
- Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, Georgia, United States of America
| | - Sang-Moo Kang
- Center for Inflammation, Immunity, & Infection and Department of Biology, Georgia State University, Atlanta, Georgia, United States of America
| | - Mark R. Prausnitz
- School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States of America
- * E-mail:
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104
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Sun Y, Sun TL, Huang HW. Physical properties of Escherichia coli spheroplast membranes. Biophys J 2015; 107:2082-90. [PMID: 25418093 DOI: 10.1016/j.bpj.2014.09.034] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2014] [Revised: 09/02/2014] [Accepted: 09/30/2014] [Indexed: 11/20/2022] Open
Abstract
We investigated the physical properties of bacterial cytoplasmic membranes by applying the method of micropipette aspiration to Escherichia coli spheroplasts. We found that the properties of spheroplast membranes are significantly different from that of laboratory-prepared lipid vesicles or that of previously investigated animal cells. The spheroplasts can adjust their internal osmolality by increasing their volumes more than three times upon osmotic downshift. Until the spheroplasts are swollen to their volume limit, their membranes are tensionless. At constant external osmolality, aspiration increases the surface area of the membrane and creates tension. What distinguishes spheroplast membranes from lipid bilayers is that the area change of a spheroplast membrane by tension is a relaxation process. No such time dependence is observed in lipid bilayers. The equilibrium tension-area relation is reversible. The apparent area stretching moduli are several times smaller than that of stretching a lipid bilayer. We conclude that spheroplasts maintain a minimum surface area without tension by a membrane reservoir that removes the excessive membranes from the minimum surface area. Volume expansion eventually exhausts the membrane reservoir; then the membrane behaves like a lipid bilayer with a comparable stretching modulus. Interestingly, the membranes cease to refold when spheroplasts lost viability, implying that the membrane reservoir is metabolically maintained.
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Affiliation(s)
- Yen Sun
- Department of Physics & Astronomy, Rice University, Houston, Texas
| | - Tzu-Lin Sun
- Department of Physics & Astronomy, Rice University, Houston, Texas
| | - Huey W Huang
- Department of Physics & Astronomy, Rice University, Houston, Texas.
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105
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Vladkova R. Chlorophyllais the crucial redox sensor and transmembrane signal transmitter in the cytochromeb6fcomplex. Components and mechanisms of state transitions from the hydrophobic mismatch viewpoint. J Biomol Struct Dyn 2015; 34:824-54. [DOI: 10.1080/07391102.2015.1056551] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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106
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Ashkar R, Nagao M, Butler PD, Woodka AC, Sen MK, Koga T. Tuning membrane thickness fluctuations in model lipid bilayers. Biophys J 2015; 109:106-12. [PMID: 26153707 PMCID: PMC4571027 DOI: 10.1016/j.bpj.2015.05.033] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2015] [Revised: 05/22/2015] [Accepted: 05/28/2015] [Indexed: 11/21/2022] Open
Abstract
Membrane thickness fluctuations have been associated with a variety of critical membrane phenomena, such as cellular exchange, pore formation, and protein binding, which are intimately related to cell functionality and effective pharmaceuticals. Therefore, understanding how these fluctuations are controlled can remarkably impact medical applications involving selective macromolecule binding and efficient cellular drug intake. Interestingly, previous reports on single-component bilayers show almost identical thickness fluctuation patterns for all investigated lipid tail-lengths, with similar temperature-independent membrane thickness fluctuation amplitude in the fluid phase and a rapid suppression of fluctuations upon transition to the gel phase. Presumably, in vivo functions require a tunability of these parameters, suggesting that more complex model systems are necessary. In this study, we explore lipid tail-length mismatch as a regulator for membrane fluctuations. Unilamellar vesicles of an equimolar mixture of dimyristoylphosphatidylcholine and distearoylphosphatidylcholine molecules, with different tail-lengths and melting transition temperatures, are used as a model system for this next level of complexity. Indeed, this binary system exhibits a significant response of membrane dynamics to thermal variations. The system also suggests a decoupling of the amplitude and the relaxation time of the membrane thickness fluctuations, implying a potential for independent control of these two key parameters.
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Affiliation(s)
- Rana Ashkar
- National Institute of Standards and Technology (NIST) Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland; Department of Material Science and Engineering, University of Maryland, College Park, Maryland
| | - Michihiro Nagao
- National Institute of Standards and Technology (NIST) Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland; Center for Exploration of Energy and Matter, Indiana University, Bloomington, Indiana.
| | - Paul D Butler
- National Institute of Standards and Technology (NIST) Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland; Department of Chemical & Biomolecular Engineering, University of Delaware, Newark, Delaware
| | - Andrea C Woodka
- Department of Chemistry & Life Science, United States Military Academy, West Point, New York
| | - Mani K Sen
- Department of Materials Science and Engineering, Stony Brook University, Stony Brook, New York
| | - Tadanori Koga
- Department of Materials Science and Engineering, Stony Brook University, Stony Brook, New York; Chemical and Molecular Engineering Program, Stony Brook University, Stony Brook, New York
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107
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Orchestration of membrane receptor signaling by membrane lipids. Biochimie 2015; 113:111-24. [DOI: 10.1016/j.biochi.2015.04.005] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2014] [Accepted: 04/05/2015] [Indexed: 12/20/2022]
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108
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De Marothy MT, Elofsson A. Marginally hydrophobic transmembrane α-helices shaping membrane protein folding. Protein Sci 2015; 24:1057-74. [PMID: 25970811 DOI: 10.1002/pro.2698] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2015] [Accepted: 04/24/2015] [Indexed: 01/12/2023]
Abstract
Cells have developed an incredible machinery to facilitate the insertion of membrane proteins into the membrane. While we have a fairly good understanding of the mechanism and determinants of membrane integration, more data is needed to understand the insertion of membrane proteins with more complex insertion and folding pathways. This review will focus on marginally hydrophobic transmembrane helices and their influence on membrane protein folding. These weakly hydrophobic transmembrane segments are by themselves not recognized by the translocon and therefore rely on local sequence context for membrane integration. How can such segments reside within the membrane? We will discuss this in the light of features found in the protein itself as well as the environment it resides in. Several characteristics in proteins have been described to influence the insertion of marginally hydrophobic helices. Additionally, the influence of biological membranes is significant. To begin with, the actual cost for having polar groups within the membrane may not be as high as expected; the presence of proteins in the membrane as well as characteristics of some amino acids may enable a transmembrane helix to harbor a charged residue. The lipid environment has also been shown to directly influence the topology as well as membrane boundaries of transmembrane helices-implying a dynamic relationship between membrane proteins and their environment.
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Affiliation(s)
- Minttu T De Marothy
- Department of Biochemistry and Biophysics Science for Life Laboratory, Stockholm University, Solna, SE-171 21, Sweden
| | - Arne Elofsson
- Department of Biochemistry and Biophysics Science for Life Laboratory, Stockholm University, Solna, SE-171 21, Sweden
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109
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Cordeiro RM. Molecular dynamics simulations of the transport of reactive oxygen species by mammalian and plant aquaporins. Biochim Biophys Acta Gen Subj 2015; 1850:1786-94. [PMID: 25982446 DOI: 10.1016/j.bbagen.2015.05.007] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2015] [Revised: 05/06/2015] [Accepted: 05/07/2015] [Indexed: 11/25/2022]
Abstract
BACKGROUND Aquaporins are responsible for water transport across lipid membranes. They are also able to transport reactive oxygen species, playing an important role in redox signaling. Certain plant aquaporins have even the ability to be regulated by oxidative stress. However, the underlying mechanisms are still not fully understood. METHODS Here, molecular dynamics simulations were employed to determine the activation free energies related to the transport of reactive oxygen species through both mammalian and plant aquaporin models. RESULTS AND CONCLUSIONS Both aquaporins may transport hydrogen peroxide (H2O2) and the protonated form of superoxide radicals (HO2). The solution-to-pore transfer free energies were low for small oxy-radicals, suggesting that even highly reactive hydroxyl radicals (HO) might have access to the pore interior and oxidize amino acids responsible for channel selectivity. In the plant aquaporin, no significant change in water permeability was observed upon oxidation of the solvent-exposed disulfide bonds at the extracellular region. During the simulated time scale, the existence of a direct oxidative gating mechanism involving these disulfide bonds could not be demonstrated. GENERAL SIGNIFICANCE Simulation results may improve the understanding of redox signaling mechanisms and help in the interpretation of protein oxidative labeling experiments.
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Affiliation(s)
- Rodrigo M Cordeiro
- Centro de Ciências Naturais e Humanas, Universidade Federal do ABC, Avenida dos Estados 5001, CEP 09210-580, Santo André, SP, Brazil.
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110
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Arnold W, Giroud S, Valencak TG, Ruf T. Ecophysiology of Omega Fatty Acids: A Lid for Every Jar. Physiology (Bethesda) 2015; 30:232-40. [DOI: 10.1152/physiol.00047.2014] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Omega fatty acids affect various physiological functions, such as locomotion, cardiac function, and thermogenesis. We highlight evidence from animal models that points to pathways by which specific omega fatty acids exert differential effects. We suggest that optimizing the omega fatty acid composition of tissues involves trade-offs between costs and benefits of specific fatty acids.
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Affiliation(s)
- Walter Arnold
- Department of Integrative Biology and Evolution, Research Institute of Wildlife Ecology, University of Veterinary Medicine Vienna, Austria
| | - Sylvain Giroud
- Department of Integrative Biology and Evolution, Research Institute of Wildlife Ecology, University of Veterinary Medicine Vienna, Austria
| | - Teresa G. Valencak
- Department of Integrative Biology and Evolution, Research Institute of Wildlife Ecology, University of Veterinary Medicine Vienna, Austria
| | - Thomas Ruf
- Department of Integrative Biology and Evolution, Research Institute of Wildlife Ecology, University of Veterinary Medicine Vienna, Austria
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111
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Yi X, Gao H. Cell interaction with graphene microsheets: near-orthogonal cutting versus parallel attachment. NANOSCALE 2015; 7:5457-5467. [PMID: 25732111 DOI: 10.1039/c4nr06170e] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Recent experiments indicate that graphene microsheets can either undergo a near-orthogonal cutting or a parallel attachment mode of interaction with cell membranes. Here we perform a theoretical analysis to characterize the deformed membrane microstructure and investigate how these two interaction modes are influenced by the splay, tilt, compression, tension, bending and adhesion energies of the membrane. Our analysis indicates that, driven by the membrane splay and tension energies, a two-dimensional microsheet such as graphene would adopt a near-perpendicular configuration with respect to the membrane in the transmembrane penetration mode, whereas the membrane bending and tension energies would lead to parallel attachment in the absence of cross membrane penetration. These interaction modes may have broad implications in applications involving drug delivery, cell encapsulation and protection, and the measurement of the dynamic cell response.
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Affiliation(s)
- Xin Yi
- School of Engineering, Brown University, Providence, Rhode Island 02912, USA.
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112
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Brejchová J, Sýkora J, Ostašov P, Merta L, Roubalová L, Janáček J, Hof M, Svoboda P. TRH-receptor mobility and function in intact and cholesterol-depleted plasma membrane of HEK293 cells stably expressing TRH-R-eGFP. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2015; 1848:781-96. [DOI: 10.1016/j.bbamem.2014.11.029] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/01/2014] [Revised: 11/24/2014] [Accepted: 11/26/2014] [Indexed: 01/03/2023]
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113
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Kulig W, Jurkiewicz P, Olżyńska A, Tynkkynen J, Javanainen M, Manna M, Rog T, Hof M, Vattulainen I, Jungwirth P. Experimental determination and computational interpretation of biophysical properties of lipid bilayers enriched by cholesteryl hemisuccinate. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2015; 1848:422-32. [DOI: 10.1016/j.bbamem.2014.10.032] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/30/2014] [Revised: 10/06/2014] [Accepted: 10/20/2014] [Indexed: 10/24/2022]
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114
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115
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Yoshida K, Takashima A, Nishio I. Effect of dibucaine hydrochloride on raft-like lipid domains in model membrane systems. MEDCHEMCOMM 2015. [DOI: 10.1039/c5md00108k] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
To clarify the biophysical and/or physicochemical mechanism of anaesthesia, we investigated the influence of dibucaine hydrochloride (DC·HCl), a local anaesthetic, on raft-like domains in ternary liposomes composed of dioleoylphosphatidylcholine (DOPC), dipalmitoylphosphatidylcholine (DPPC) and cholesterol (Chol).
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Affiliation(s)
- Kazunari Yoshida
- New Industry Creation Hatchery Center
- Tohoku University
- 6-6-10 Aoba
- Aoba-ku
- Japan
| | - Akito Takashima
- Department of Physics and Mathematics
- College of Science and Engineering
- Aoyama Gakuin University
- 5-10-1 Fuchinobe
- Sagamihara
| | - Izumi Nishio
- Department of Physics and Mathematics
- College of Science and Engineering
- Aoyama Gakuin University
- 5-10-1 Fuchinobe
- Sagamihara
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116
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Haselwandter CA, Wingreen NS. The role of membrane-mediated interactions in the assembly and architecture of chemoreceptor lattices. PLoS Comput Biol 2014; 10:e1003932. [PMID: 25503274 PMCID: PMC4263354 DOI: 10.1371/journal.pcbi.1003932] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2014] [Accepted: 09/22/2014] [Indexed: 01/04/2023] Open
Abstract
In vivo fluorescence microscopy and electron cryo-tomography have revealed that chemoreceptors self-assemble into extended honeycomb lattices of chemoreceptor trimers with a well-defined relative orientation of trimers. The signaling response of the observed chemoreceptor lattices is remarkable for its extreme sensitivity, which relies crucially on cooperative interactions among chemoreceptor trimers. In common with other membrane proteins, chemoreceptor trimers are expected to deform the surrounding lipid bilayer, inducing membrane-mediated anisotropic interactions between neighboring trimers. Here we introduce a biophysical model of bilayer-chemoreceptor interactions, which allows us to quantify the role of membrane-mediated interactions in the assembly and architecture of chemoreceptor lattices. We find that, even in the absence of direct protein-protein interactions, membrane-mediated interactions can yield assembly of chemoreceptor lattices at very dilute trimer concentrations. The model correctly predicts the observed honeycomb architecture of chemoreceptor lattices as well as the observed relative orientation of chemoreceptor trimers, suggests a series of “gateway” states for chemoreceptor lattice assembly, and provides a simple mechanism for the localization of large chemoreceptor lattices to the cell poles. Our model of bilayer-chemoreceptor interactions also helps to explain the observed dependence of chemotactic signaling on lipid bilayer properties. Finally, we consider the possibility that membrane-mediated interactions might contribute to cooperativity among neighboring chemoreceptor trimers. The chemotaxis system allows bacteria to respond to minute changes in chemical concentration, and serves as a paradigm for biological signal processing and the self-assembly of large protein lattices in living cells. The sensitivity of the chemotaxis system relies crucially on cooperative interactions among chemoreceptor trimers, which are organized into intricate honeycomb lattices. Chemoreceptors are membrane proteins and, hence, are expected to deform the surrounding lipid bilayer, leading to membrane-mediated interactions between chemoreceptor trimers. Using a biophysical model of bilayer-chemoreceptor interactions we show that the membrane-mediated interactions induced by chemoreceptor trimers provide a mechanism for the observed self-assembly of chemoreceptor lattices. We find that the directionality of membrane-mediated interactions between trimers complements protein-protein interactions in the stabilization of the observed honeycomb architecture of chemoreceptor lattices. Our results suggest that the symmetry of membrane protein complexes such as chemoreceptor trimers is reflected in the anisotropy of membrane-mediated interactions, yielding a general mechanism for the self-assembly of ordered protein lattices in cell membranes.
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Affiliation(s)
- Christoph A. Haselwandter
- Departments of Physics & Astronomy and Biological Sciences, University of Southern California, Los Angeles, California, United States of America
- * E-mail: (CAH); (NSW)
| | - Ned S. Wingreen
- Department of Molecular Biology, Princeton University, Princeton, New Jersey, United States of America
- * E-mail: (CAH); (NSW)
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117
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118
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Pieffet G, Botero A, Peters GH, Forero-Shelton M, Leidy C. Exploring the local elastic properties of bilayer membranes using molecular dynamics simulations. J Phys Chem B 2014; 118:12883-91. [PMID: 25325715 DOI: 10.1021/jp504427a] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Membrane mechanical elastic properties regulate a variety of cellular processes involving local membrane deformation, such as ion channel function and vesicle fusion. In this work, we used molecular dynamics simulations to estimate the local elastic properties of a membrane. For this, we calculated the energy needed to extract a DOPE lipid molecule, modified with a linker chain, from a POPC bilayer membrane using the umbrella sampling technique. Although the extraction energy entails several contributions related not only to elastic deformation but also to solvation, careful analysis of the potential of mean force (PMF) allowed us to dissect the elastic contribution. With this information, we calculated an effective linear spring constant of 44 ± 4 kJ·nm(-2)·mol(-1) for the DOPC membrane, in agreement with experimental estimates. The membrane deformation profile was determined independently during the stretching process in molecular detail, allowing us to fit this profile to a previously proposed continuum elastic model. Through this approach, we calculated an effective membrane spring constant of 42 kJ·nm(-2)·mol(-1), which is in good agreement with the PMF calculation. Furthermore, the solvation energy we derived from the data is shown to match the solvation energy estimated from critical micelle formation constants. This methodology can be used to determine how changes in lipid composition or the presence of membrane modifiers can affect the elastic properties of a membrane at a local level.
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Affiliation(s)
- Gilles Pieffet
- Department of Physics, Universidad de los Andes , Carrera 1 No 18A 10, Bogotá, Colombia
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119
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The mechanosensitive channel of small conductance (MscS) functions as a Jack-in-the box. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2014; 1848:159-66. [PMID: 25450806 DOI: 10.1016/j.bbamem.2014.10.022] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/14/2014] [Revised: 10/04/2014] [Accepted: 10/15/2014] [Indexed: 11/23/2022]
Abstract
Phenotypical analysis of the lipid interacting residues in the closed state of the mechanosensitive channel of small conductance (MscS) from Escherichia coli (E. coli) has previously shown that these residues are critical for channel function. In the closed state, mutation of individual hydrophobic lipid lining residues to alanine, thus reducing the hydrophobicity, resulted in phenotypic changes that were observable using in vivo assays. Here, in an analogous set of experiments, we identify eleven residues in the first transmembrane domain of the open state of MscS that interact with the lipid bilayer. Each of these residues was mutated to alanine and leucine to modulate their hydrophobic interaction with the lipid tail-groups in the open state. The effects of these changes on channel function were analyzed using in vivo bacterial assays and patch clamp electrophysiology. Mutant channels were found to be functionally indistinguishable from wildtype MscS. Thus, mutation of open-state lipid interacting residues does not differentially stabilize or destabilize the open, closed, intermediate, or transition states of MscS. Based on these results and other data from the literature, we propose a new gating paradigm for MscS where MscS acts as a "Jack-In-The-Box" with the intrinsic bilayer lateral pressure holding the channel in the closed state. In this model, upon application of extrinsic tension the channel springs into the open state due to relief of the intrinsic lipid bilayer pressure.
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120
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Yue T, Feng D, Zhang X. The interplay between the clustering of transmembrane proteins and coupling of anchored membrane proteins. MOLECULAR SIMULATION 2014. [DOI: 10.1080/08927022.2013.824575] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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121
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Tonnesen A, Christensen SM, Tkach V, Stamou D. Geometrical membrane curvature as an allosteric regulator of membrane protein structure and function. Biophys J 2014; 106:201-9. [PMID: 24411252 DOI: 10.1016/j.bpj.2013.11.023] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2013] [Revised: 11/07/2013] [Accepted: 11/12/2013] [Indexed: 10/25/2022] Open
Abstract
Transmembrane proteins are embedded in cellular membranes of varied lipid composition and geometrical curvature. Here, we studied for the first time the allosteric effect of geometrical membrane curvature on transmembrane protein structure and function. We used single-channel optical analysis of the prototypic transmembrane β-barrel α-hemolysin (α-HL) reconstituted on immobilized single small unilamellar liposomes of different diameter and therefore curvature. Our data demonstrate that physiologically abundant geometrical membrane curvatures can enforce a dramatic allosteric regulation (1000-fold inhibition) of α-HL permeability. High membrane curvatures (1/diameter ~1/40 nm(-1)) compressed the effective pore diameter of α-HL from 14.2 ± 0.8 Å to 11.4 ± 0.6 Å. This reduction in effective pore area (~40%) when combined with the area compressibility of α-HL revealed an effective membrane tension of ~50 mN/m and a curvature-imposed protein deformation energy of ~7 kBT. Such substantial energies have been shown to conformationally activate, or unfold, β-barrel and α-helical transmembrane proteins, suggesting that membrane curvature could likely regulate allosterically the structure and function of transmembrane proteins in general.
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Affiliation(s)
- Asger Tonnesen
- Bionanotechnology and Nanomedicine Laboratory, Department of Chemistry, University of Copenhagen, Copenhagen, Denmark; Nano-Science Center, University of Copenhagen, Copenhagen, Denmark; Lundbeck Foundation Center for Biomembranes in Nanomedicine, University of Copenhagen, Copenhagen, Denmark
| | - Sune M Christensen
- Bionanotechnology and Nanomedicine Laboratory, Department of Chemistry, University of Copenhagen, Copenhagen, Denmark; Nano-Science Center, University of Copenhagen, Copenhagen, Denmark; Lundbeck Foundation Center for Biomembranes in Nanomedicine, University of Copenhagen, Copenhagen, Denmark
| | - Vadym Tkach
- Bionanotechnology and Nanomedicine Laboratory, Department of Chemistry, University of Copenhagen, Copenhagen, Denmark; Nano-Science Center, University of Copenhagen, Copenhagen, Denmark; Lundbeck Foundation Center for Biomembranes in Nanomedicine, University of Copenhagen, Copenhagen, Denmark
| | - Dimitrios Stamou
- Bionanotechnology and Nanomedicine Laboratory, Department of Chemistry, University of Copenhagen, Copenhagen, Denmark; Nano-Science Center, University of Copenhagen, Copenhagen, Denmark; Lundbeck Foundation Center for Biomembranes in Nanomedicine, University of Copenhagen, Copenhagen, Denmark.
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122
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Evidence of conformational changes in oil molecules with protein aggregation and conformational changes at oil–‘protein solution’ interface. Colloids Surf B Biointerfaces 2014; 120:132-41. [DOI: 10.1016/j.colsurfb.2014.03.045] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2013] [Revised: 03/04/2014] [Accepted: 03/25/2014] [Indexed: 11/20/2022]
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123
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Assembly and stability of Salmonella enterica ser. Typhi TolC protein in POPE and DMPE. J Biol Phys 2014; 40:387-400. [PMID: 25011632 DOI: 10.1007/s10867-014-9357-9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2014] [Accepted: 05/23/2014] [Indexed: 10/25/2022] Open
Abstract
In this work we assessed the suitability of two different lipid membranes for the simulation of a TolC protein from Salmonella enterica serovar Typhi. The TolC protein family is found in many pathogenic Gram-negative bacteria including Vibrio cholera and Pseudomonas aeruginosa and acts as an outer membrane channel for expulsion of drug and toxin from the cell. In S. typhi, the causative agent for typhoid fever, the TolC outer membrane protein is an antigen for the pathogen. The lipid environment is an important modulator of membrane protein structure and function. We evaluated the conformation of the TolC protein in the presence of DMPE and POPE bilayers using molecular dynamics simulation. The S. typhi TolC protein exhibited similar conformational dynamics to TolC and its homologues. Conformational flexibility of the protein is seen in the C-terminal, extracellular loops, and α-helical region. Despite differences in the two lipids, significant similarities in the motion of the protein in POPE and DMPE were observed, including the rotational motion of the C-terminal residues and the partially open extracellular loops. However, analysis of the trajectories demonstrated effects of hydrophobic matching of the TolC protein in the membrane, particularly in the lengthening of the lipids and subtle movements of the protein's β-barrel towards the lower leaflet in DMPE. The study exhibited the use of molecular dynamics simulation in revealing the differential effect of membrane proteins and lipids on each other. In this study, POPE is potentially a more suitable model for future simulation of the S. typhi TolC protein.
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124
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Kel O, Tamimi A, Fayer MD. The Influence of Cholesterol on Fast Dynamics Inside of Vesicle and Planar Phospholipid Bilayers Measured with 2D IR Spectroscopy. J Phys Chem B 2014; 119:8852-62. [DOI: 10.1021/jp503940k] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Affiliation(s)
- Oksana Kel
- Department
of Chemistry, Stanford University, Stanford, California 94305-5080, United States
| | - Amr Tamimi
- Department
of Chemistry, Stanford University, Stanford, California 94305-5080, United States
| | - Michael D. Fayer
- Department
of Chemistry, Stanford University, Stanford, California 94305-5080, United States
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125
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Solanko LM, Honigmann A, Midtiby HS, Lund FW, Brewer JR, Dekaris V, Bittman R, Eggeling C, Wüstner D. Membrane orientation and lateral diffusion of BODIPY-cholesterol as a function of probe structure. Biophys J 2014; 105:2082-92. [PMID: 24209853 DOI: 10.1016/j.bpj.2013.09.031] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2013] [Revised: 08/26/2013] [Accepted: 09/16/2013] [Indexed: 11/29/2022] Open
Abstract
Cholesterol tagged with the BODIPY fluorophore via the central difluoroboron moiety of the dye (B-Chol) is a promising probe for studying intracellular cholesterol dynamics. We synthesized a new BODIPY-cholesterol probe (B-P-Chol) with the fluorophore attached via one of its pyrrole rings to carbon-24 of cholesterol (B-P-Chol). Using two-photon fluorescence polarimetry in giant unilamellar vesicles and in the plasma membrane (PM) of living intact and actin-disrupted cells, we show that the BODIPY-groups in B-Chol and B-P-Chol are oriented perpendicular and almost parallel to the bilayer normal, respectively. B-Chol is in all three membrane systems much stronger oriented than B-P-Chol. Interestingly, we found that the lateral diffusion in the PM was two times slower for B-Chol than for B-P-Chol, although we found no difference in lateral diffusion in model membranes. Stimulated emission depletion microscopy, performed for the first time, to our knowledge, with fluorescent sterols, revealed that the difference in lateral diffusion of the BODIPY-cholesterol probes was not caused by anomalous subdiffusion, because diffusion of both analogs in the PM was free but not hindered. Our combined measurements show that the position and orientation of the BODIPY moiety in cholesterol analogs have a severe influence on lateral diffusion specifically in the PM of living cells.
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Affiliation(s)
- Lukasz M Solanko
- Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense M, Denmark
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126
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Van Lehn RC, Alexander-Katz A. Fusion of Ligand-Coated Nanoparticles with Lipid Bilayers: Effect of Ligand Flexibility. J Phys Chem A 2014; 118:5848-56. [DOI: 10.1021/jp411662c] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Affiliation(s)
- Reid C. Van Lehn
- Department of Materials Science
and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
| | - Alfredo Alexander-Katz
- Department of Materials Science
and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
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127
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Rice AM, Mahling R, Fealey ME, Rannikko A, Dunleavy K, Hendrickson T, Lohese KJ, Kruggel S, Heiling H, Harren D, Sutton RB, Pastor J, Hinderliter A. Randomly organized lipids and marginally stable proteins: a coupling of weak interactions to optimize membrane signaling. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2014; 1838:2331-40. [PMID: 24657395 DOI: 10.1016/j.bbamem.2014.03.005] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/06/2013] [Revised: 02/28/2014] [Accepted: 03/14/2014] [Indexed: 02/08/2023]
Abstract
Eukaryotic lipids in a bilayer are dominated by weak cooperative interactions. These interactions impart highly dynamic and pliable properties to the membrane. C2 domain-containing proteins in the membrane also interact weakly and cooperatively giving rise to a high degree of conformational plasticity. We propose that this feature of weak energetics and plasticity shared by lipids and C2 domain-containing proteins enhance a cell's ability to transduce information across the membrane. We explored this hypothesis using information theory to assess the information storage capacity of model and mast cell membranes, as well as differential scanning calorimetry, carboxyfluorescein release assays, and tryptophan fluorescence to assess protein and membrane stability. The distribution of lipids in mast cell membranes encoded 5.6-5.8bits of information. More information resided in the acyl chains than the head groups and in the inner leaflet of the plasma membrane than the outer leaflet. When the lipid composition and information content of model membranes were varied, the associated C2 domains underwent large changes in stability and denaturation profile. The C2 domain-containing proteins are therefore acutely sensitive to the composition and information content of their associated lipids. Together, these findings suggest that the maximum flow of signaling information through the membrane and into the cell is optimized by the cooperation of near-random distributions of membrane lipids and proteins. This article is part of a Special Issue entitled: Interfacially Active Peptides and Proteins. Guest Editors: William C. Wimley and Kalina Hristova.
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Affiliation(s)
- Anne M Rice
- Department of Chemistry and Biochemistry, University of Minnesota Duluth, Duluth, MN, USA; Department of Cell Physiology and Molecular Biophysics, Texas Tech University Health Sciences Center, Lubbock, TX, USA
| | - Ryan Mahling
- Department of Chemistry and Biochemistry, University of Minnesota Duluth, Duluth, MN, USA
| | - Michael E Fealey
- Department of Chemistry and Biochemistry, University of Minnesota Duluth, Duluth, MN, USA
| | - Anika Rannikko
- Department of Chemistry and Biochemistry, University of Minnesota Duluth, Duluth, MN, USA
| | - Katie Dunleavy
- Department of Chemistry and Biochemistry, University of Minnesota Duluth, Duluth, MN, USA
| | - Troy Hendrickson
- Department of Chemistry and Biochemistry, University of Minnesota Duluth, Duluth, MN, USA
| | - K Jean Lohese
- Department of Chemistry and Biochemistry, University of Minnesota Duluth, Duluth, MN, USA
| | - Spencer Kruggel
- Department of Chemistry and Biochemistry, University of Minnesota Duluth, Duluth, MN, USA
| | - Hillary Heiling
- Department of Chemistry and Biochemistry, University of Minnesota Duluth, Duluth, MN, USA
| | - Daniel Harren
- Department of Chemistry and Biochemistry, University of Minnesota Duluth, Duluth, MN, USA
| | - R Bryan Sutton
- Department of Cell Physiology and Molecular Biophysics, Texas Tech University Health Sciences Center, Lubbock, TX, USA
| | - John Pastor
- Department of Biology, University of Minnesota Duluth, Duluth, MN, USA
| | - Anne Hinderliter
- Department of Chemistry and Biochemistry, University of Minnesota Duluth, Duluth, MN, USA.
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128
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Vošahlíková M, Jurkiewicz P, Roubalová L, Hof M, Svoboda P. High- and low-affinity sites for sodium in δ-OR-Gi1α (Cys (351)-Ile (351)) fusion protein stably expressed in HEK293 cells; functional significance and correlation with biophysical state of plasma membrane. Naunyn Schmiedebergs Arch Pharmacol 2014; 387:487-502. [PMID: 24577425 DOI: 10.1007/s00210-014-0962-8] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2013] [Accepted: 02/10/2014] [Indexed: 12/31/2022]
Abstract
The effect of sodium, potassium, and lithium on δ-opioid receptor ligand binding parameters and coupling with the cognate G proteins was compared in model HEK293 cell line stably expressing PTX-insensitive δ-OR-Gi1α (Cys(351)-Ile(351)) fusion protein. Agonist [(3)H]DADLE binding was decreased in the order Na(+) ≫ Li(+) > K(+) > (+)NMDG. When plotted as a function of increasing NaCl concentrations, the binding was best-fitted with a two-phase exponential decay considering two Na(+)-responsive sites (r (2) = 0.99). High-affinity Na(+)-sites were characterized by Kd = 7.9 mM and represented 25 % of the basal level determined in the absence of ions. The remaining 75 % represented the low-affinity sites (Kd = 463 mM). Inhibition of [(3)H]DADLE binding by lithium, potassium, and (+)-NMDG proceeded in low-affinity manner only. Surprisingly, the affinity/potency of DADLE-stimulated [(35)S]GTPγS binding was increased in a reverse order: Na(+) < K(+) < Li(+). This result was demonstrated in PTX-treated as well as PTX-untreated cells. Therefore, it is not restricted to Gi1α(Cys(351)-Ile(351)) within the δ-OR-Gi1α fusion protein, but is also valid for stimulation of endogenous G proteins of Gi/Go family in HEK293 cells. Biophysical studies of interaction of ions with polar head-group region of lipids using Laurdan generalized polarization indicated the low-affinity type of interaction only proceeding in the order: Cs(+) < K(+) < Na(+) < Li(+). The results are discussed in terms of interaction of Na(+), K(+) and Li(+) with the high- and low-affinity sites located in water-accessible part of δ-OR binding pocket. We also consider the role of negatively charged Cl(-), Br(-), and I(-) counter anions in inhibition of both [(3)H]DADLE and [(35)S]GTPγS binding.
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Affiliation(s)
- Miroslava Vošahlíková
- Institute of Physiology, Academy of Sciences of the Czech Republic v.v.i., Vídeňská 1083, 14220, Prague 4, Czech Republic
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129
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Kopec W, Khandelia H. Reinforcing the membrane-mediated mechanism of action of the anti-tuberculosis candidate drug thioridazine with molecular simulations. J Comput Aided Mol Des 2014; 28:123-34. [DOI: 10.1007/s10822-014-9737-z] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2013] [Accepted: 02/19/2014] [Indexed: 10/25/2022]
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130
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Pomorski TG, Nylander T, Cárdenas M. Model cell membranes: discerning lipid and protein contributions in shaping the cell. Adv Colloid Interface Sci 2014; 205:207-20. [PMID: 24268587 DOI: 10.1016/j.cis.2013.10.028] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2013] [Revised: 10/24/2013] [Accepted: 10/24/2013] [Indexed: 01/01/2023]
Abstract
The high complexity of biological membranes has motivated the development and application of a wide range of model membrane systems to study biochemical and biophysical aspects of membranes in situ under well defined conditions. The aim is to provide fundamental understanding of processes controlled by membrane structure, permeability and curvature as well as membrane proteins by using a wide range of biochemical, biophysical and microscopic techniques. This review gives an overview of some currently used model biomembrane systems. We will also discuss some key membrane protein properties that are relevant for protein-membrane interactions in terms of protein structure and how it is affected by membrane composition, phase behavior and curvature.
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Affiliation(s)
- Thomas Günther Pomorski
- Centre for Membrane Pumps in Cells and Disease-PUMPKIN, Department of Plant and Environmental Sciences, University of Copenhagen, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Denmark
| | - Tommy Nylander
- Department of Chemistry, Division of Physical Chemistry, Lund University, Gettingevägen 60, SE-22100 Lund, Sweden
| | - Marité Cárdenas
- Department of Chemistry/Nano-Science Center, University of Copenhagen, DK-2100 Copenhagen, Denmark.
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131
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Ubiquinone accumulation improves osmotic-stress tolerance in Escherichia coli. Nat Chem Biol 2014; 10:266-72. [DOI: 10.1038/nchembio.1437] [Citation(s) in RCA: 107] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2013] [Accepted: 11/25/2013] [Indexed: 11/08/2022]
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132
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Sample preparation: A critical step in the analysis of cholesterol oxidation products. Food Chem 2014; 145:918-26. [DOI: 10.1016/j.foodchem.2013.08.123] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2013] [Revised: 06/28/2013] [Accepted: 08/28/2013] [Indexed: 11/15/2022]
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133
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Van Lehn RC, Alexander-Katz A. Free energy change for insertion of charged, monolayer-protected nanoparticles into lipid bilayers. SOFT MATTER 2014; 10:648-58. [PMID: 24795979 DOI: 10.1039/c3sm52329b] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
Charged, monolayer-protected gold nanoparticles (AuNPs) with core diameters smaller than 10 nm have recently emerged as a prominent class of nanomaterial for use in targeted drug delivery and biosensing. In particular, recent experimental studies showed that AuNPs protected by a binary mixture of purely hydrophobic and anionic, end-functionalized alkanethiol ligands were able to spontaneously penetrate through cell membranes via a non-endocytic, non-disruptive mechanism. The critical step in the penetration process is a fusion step during which the AuNPs insert into the hydrophobic core of the bilayer. This fusion step is driven by hydrophobic forces as inserted AuNPs minimize their exposed hydrophobic surface area and thereby lower their free energy compared to particles in the bulk. Here, we explore the effect of the large parameter space of composition, size, ligand length, morphology, and hydrophobicity strength on the change in the free energy upon insertion. Using a newly developed implicit bilayer, implicit solvent simulation model, our work shows that there is a size cutoff for insertion that has a strong dependence on surface composition and ligand chemistry. Our results agree well with previous experimental findings for a particular value of the hydrophobicity strength. This work provides physical insight that may be used to both understand the insertion of AuNPs into bilayers and guide the design of monolayers to either encourage or inhibit insertion.
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134
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Size-dependent ultrafast structural dynamics inside phospholipid vesicle bilayers measured with 2D IR vibrational echoes. Proc Natl Acad Sci U S A 2014; 111:918-23. [PMID: 24395796 DOI: 10.1073/pnas.1323110111] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The ultrafast structural dynamics inside the bilayers of dilauroylphosphatidylcholine (DLPC) and dipalmitoylphosphatidylcholine vesicles with 70, 90, and 125 nm diameters were directly measured with 2D IR vibrational echo spectroscopy. The antisymmetric CO stretch of tungsten hexacarbonyl was used as a vibrational probe and provided information on spectral diffusion (structural dynamics) in the alkyl region of the bilayers. Although the CO stretch absorption spectra remain the same, the interior structural dynamics become faster as the size of the vesicles decrease, with the size dependence greater for dipalmitoylphosphatidylcholine than for DLPC. As DLPC vesicles become larger, the interior dynamics approach those of the planar bilayer.
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135
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Fioroni M, Dworeck T, Rodríguez-Ropero F. Theoretical Considerations and Computational Tools. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2014; 794:69-93. [DOI: 10.1007/978-94-007-7429-2_4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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136
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Kong X, Qin S, Lu D, Liu Z. Surface tension effects on the phase transition of a DPPC bilayer with and without protein: a molecular dynamics simulation. Phys Chem Chem Phys 2014; 16:8434-40. [DOI: 10.1039/c3cp55524k] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A coarse-grained molecular dynamics simulation was applied to illustrate the phase transition behavior of the pure DPPC bilayer and aquaporin-embedded DPPC bilayer under different surface tensions.
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Affiliation(s)
- Xian Kong
- Department of Chemical Engineering
- Tsinghua University
- Beijing, China
| | - Shanshan Qin
- Key Laboratory of Bioorganic Phosphorous Chemistry and Chemical Biology (Ministry of Education)
- Department of Chemistry
- Tsinghua University
- Beijing 100084, P. R. China
| | - Diannan Lu
- Department of Chemical Engineering
- Tsinghua University
- Beijing, China
| | - Zheng Liu
- Department of Chemical Engineering
- Tsinghua University
- Beijing, China
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137
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Ion channel stability of Gramicidin A in lipid bilayers: Effect of hydrophobic mismatch. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2014; 1838:328-38. [DOI: 10.1016/j.bbamem.2013.10.005] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2013] [Revised: 09/20/2013] [Accepted: 10/03/2013] [Indexed: 11/18/2022]
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138
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Choi HJ, Montemagno CD. Recent Progress in Advanced Nanobiological Materials for Energy and Environmental Applications. MATERIALS 2013; 6:5821-5856. [PMID: 28788424 PMCID: PMC5452742 DOI: 10.3390/ma6125821] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/25/2013] [Revised: 11/26/2013] [Accepted: 11/28/2013] [Indexed: 11/25/2022]
Abstract
In this review, we briefly introduce our efforts to reconstruct cellular life processes by mimicking natural systems and the applications of these systems to energy and environmental problems. Functional units of in vitro cellular life processes are based on the fabrication of artificial organelles using protein-incorporated polymersomes and the creation of bioreactors. This concept of an artificial organelle originates from the first synthesis of poly(siloxane)-poly(alkyloxazoline) block copolymers three decades ago and the first demonstration of protein activity in the polymer membrane a decade ago. The increased value of biomimetic polymers results from many research efforts to find new applications such as functionally active membranes and a biochemical-producing polymersome. At the same time, foam research has advanced to the point that biomolecules can be efficiently produced in the aqueous channels of foam. Ongoing research includes replication of complex biological processes, such as an artificial Calvin cycle for application in biofuel and specialty chemical production, and carbon dioxide sequestration. We believe that the development of optimally designed biomimetic polymers and stable/biocompatible bioreactors would contribute to the realization of the benefits of biomimetic systems. Thus, this paper seeks to review previous research efforts, examine current knowledge/key technical parameters, and identify technical challenges ahead.
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Affiliation(s)
- Hyo-Jick Choi
- National Institute for Nanotechnology and Department of Chemical and Materials Engineering, University of Alberta, Edmonton, AB T6G 2M9, Canada.
| | - Carlo D Montemagno
- National Institute for Nanotechnology and Department of Chemical and Materials Engineering, University of Alberta, Edmonton, AB T6G 2M9, Canada.
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139
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Barnes KR, Cozzi RRF, Robertson G, Marshall WS. Cold acclimation of NaCl secretion in a eurythermic teleost: mitochondrial function and gill remodeling. Comp Biochem Physiol A Mol Integr Physiol 2013; 168:50-62. [PMID: 24239670 DOI: 10.1016/j.cbpa.2013.11.004] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2013] [Revised: 10/30/2013] [Accepted: 11/06/2013] [Indexed: 10/26/2022]
Abstract
Active chloride secretion, measured as short-circuit current (Isc) in ionocytes of opercular epithelia (OE) in the eurythermic, euryoxic, and euryhaline killifish or mummichog (Fundulus heteroclitus) was studied in cold (5°C) and warm (20°C) acclimated fish to determine if homeoviscous adaptation aided chloride secretion in the cold. Isolated opercular epithelia were cooled from 30°C to 0.2°C for warm and cold acclimated fish; from 30 to 8°C, Isc decreased with Q10=1.68 for warm and Q10=1.56 for cold acclimated tissues. By Arrhenius plots, there is a critical temperature, 8°C, below which aerobic Isc decreased sharply (Q10=6.90 for warm and 4.23 for cold acclimated tissues), suggesting a shift in mitochondrial efficiency of oxidative phosphorylation. In anaerobic conditions (0.5mM NaCN; N2 saturation), chloride transport continued at a lower rate, and Isc decrease with cooling below 8°C was less pronounced (Q10=2.95 for warm and 3.08 for cold), suggesting a shift in transporter function in plasma membrane. Under anaerobic conditions, NaCl secretion at 20°C was reversibly inhibited by hypotonic shock, indicating normal regulation of transport. Chloride secretion in warm-acclimated fish was supported mostly (75% at 20°C) by aerobic metabolism, whereas that for cold-acclimated fish was lower (55% at 20°C), suggesting a greater reliance on anaerobic metabolism in the cold. Once acclimated to cold, ionocytes may be temporarily incapable of increasing their aerobic ATP supply, even when warmed to 30°C. In cold acclimated fish there was increased polyunsaturated fatty acid composition of gill epithelium (consistent with homeoviscous adaptation) and gill remodeling, wherein epithelial cells filled the interlamellar space (interlamellar cell mass, ILCM) by as much as 70%, thus increasing diffusion distance against passive ion gain. Most ionocytes in these thickened epithelial masses became taller, still connecting basal lamina with the environment, consistent with the continuing transport rates at low temperatures. Whereas the low aerobic scope of cold-acclimated fish and thickened gill epithelium is appropriate to winter inactivity, metabolic depression and anaerobiosis, the large aerobic scope of warm-acclimated fish favors active foraging at high temperatures.
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Affiliation(s)
- Katelyn R Barnes
- Department of Biology, St. Francis Xavier University, Antigonish, Nova Scotia B2G 2W5, Canada
| | - Regina R F Cozzi
- Department of Biology, St. Francis Xavier University, Antigonish, Nova Scotia B2G 2W5, Canada
| | - George Robertson
- Department of Biology, St. Francis Xavier University, Antigonish, Nova Scotia B2G 2W5, Canada
| | - William S Marshall
- Department of Biology, St. Francis Xavier University, Antigonish, Nova Scotia B2G 2W5, Canada.
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140
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Gapsys V, de Groot BL, Briones R. Computational analysis of local membrane properties. J Comput Aided Mol Des 2013; 27:845-58. [PMID: 24150904 PMCID: PMC3882000 DOI: 10.1007/s10822-013-9684-0] [Citation(s) in RCA: 127] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2013] [Accepted: 10/07/2013] [Indexed: 11/29/2022]
Abstract
In the field of biomolecular simulations, dynamics of phospholipid membranes is of special interest. A number of proteins, including channels, transporters, receptors and short peptides are embedded in lipid bilayers and tightly interact with phospholipids. While the experimental measurements report on the spatial and/or temporal average membrane properties, simulation results are not restricted to the average properties. In the current study, we present a collection of methods for an efficient local membrane property calculation, comprising bilayer thickness, area per lipid, deuterium order parameters, Gaussian and mean curvature. The local membrane property calculation allows for a direct mapping of the membrane features, which subsequently can be used for further analysis and visualization of the processes of interest. The main features of the described methods are highlighted in a number of membrane systems, namely: a pure dimyristoyl-phosphatidyl-choline (DMPC) bilayer, a fusion peptide interacting with a membrane, voltage-dependent anion channel protein embedded in a DMPC bilayer, cholesterol enriched bilayer and a coarse grained simulation of a curved palmitoyl-oleoyl-phosphatidyl-choline lipid membrane. The local membrane property analysis proves to provide an intuitive and detailed view on the observables that are otherwise interpreted as averaged bilayer properties.
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Affiliation(s)
- Vytautas Gapsys
- Computational Biomolecular Dynamics Group, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077, Göttingen, Germany,
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141
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Khmelenina VN, Suzina NE, Trotsenko YA. Surface layers of methanotrophic bacteria. Microbiology (Reading) 2013. [DOI: 10.1134/s0026261713050068] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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142
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A distinct mechanism for activating uncoupled nicotinic acetylcholine receptors. Nat Chem Biol 2013; 9:701-7. [DOI: 10.1038/nchembio.1338] [Citation(s) in RCA: 82] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2012] [Accepted: 08/06/2013] [Indexed: 01/08/2023]
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143
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Kel O, Tamimi A, Thielges MC, Fayer MD. Ultrafast Structural Dynamics Inside Planar Phospholipid Multibilayer Model Cell Membranes Measured with 2D IR Spectroscopy. J Am Chem Soc 2013; 135:11063-74. [DOI: 10.1021/ja403675x] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Oksana Kel
- Department of Chemistry, Stanford University, Stanford, California 94305, United
States
| | - Amr Tamimi
- Department of Chemistry, Stanford University, Stanford, California 94305, United
States
| | - Megan C. Thielges
- Department of Chemistry, Stanford University, Stanford, California 94305, United
States
| | - Michael D. Fayer
- Department of Chemistry, Stanford University, Stanford, California 94305, United
States
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144
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Haselwandter CA, Phillips R. Connection between oligomeric state and gating characteristics of mechanosensitive ion channels. PLoS Comput Biol 2013; 9:e1003055. [PMID: 23696720 PMCID: PMC3656111 DOI: 10.1371/journal.pcbi.1003055] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2012] [Accepted: 03/08/2013] [Indexed: 01/06/2023] Open
Abstract
The mechanosensitive channel of large conductance (MscL) is capable of transducing mechanical stimuli such as membrane tension into an electrochemical response. MscL provides a widely-studied model system for mechanotransduction and, more generally, for how bilayer mechanical properties regulate protein conformational changes. Much effort has been expended on the detailed experimental characterization of the molecular structure and biological function of MscL. However, despite its central significance, even basic issues such as the physiologically relevant oligomeric states and molecular structures of MscL remain a matter of debate. In particular, tetrameric, pentameric, and hexameric oligomeric states of MscL have been proposed, together with a range of detailed molecular structures of MscL in the closed and open channel states. Previous theoretical work has shown that the basic phenomenology of MscL gating can be understood using an elastic model describing the energetic cost of the thickness deformations induced by MscL in the surrounding lipid bilayer. Here, we generalize this elastic model to account for the proposed oligomeric states and hydrophobic shapes of MscL. We find that the oligomeric state and hydrophobic shape of MscL are reflected in the energetic cost of lipid bilayer deformations. We make quantitative predictions pertaining to the gating characteristics associated with various structural models of MscL and, in particular, show that different oligomeric states and hydrophobic shapes of MscL yield distinct membrane contributions to the gating energy and gating tension. Thus, the functional properties of MscL provide a signature of the oligomeric state and hydrophobic shape of MscL. Our results suggest that, in addition to the hydrophobic mismatch between membrane proteins and the surrounding lipid bilayer, the symmetry and shape of the hydrophobic surfaces of membrane proteins play an important role in the regulation of protein function by bilayer membranes.
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Affiliation(s)
- Christoph A. Haselwandter
- Department of Physics and Astronomy, University of Southern California, Los Angeles, California, United States of America
- Department of Applied Physics, California Institute of Technology, Pasadena, California, United States of America
- * E-mail: (CAH); (RP)
| | - Rob Phillips
- Department of Applied Physics, California Institute of Technology, Pasadena, California, United States of America
- * E-mail: (CAH); (RP)
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145
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Kapoor S, Werkmüller A, Goody RS, Waldmann H, Winter R. Pressure modulation of Ras-membrane interactions and intervesicle transfer. J Am Chem Soc 2013; 135:6149-56. [PMID: 23560466 DOI: 10.1021/ja312671j] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Proteins attached to the plasma membrane frequently encounter mechanical stresses, including high hydrostatic pressure (HHP) stress. Signaling pathways involving membrane-associated small GTPases (e.g., Ras) have been identified as critical loci for pressure perturbation. However, the impact of mechanical stimuli on biological outputs is still largely terra incognita. The present study explores the effect of HHP on the membrane association, dissociation, and intervesicle transfer process of N-Ras by using a FRET-based assay to obtain the kinetic parameters and volumetric properties along the reaction path of these processes. Notably, membrane association is fostered upon pressurization. Conversely, depending on the nature and lateral organization of the lipid membrane, acceleration or retardation is observed for the dissociation step. In addition, HHP can be inferred as a positive regulator of N-Ras clustering, in particular in heterogeneous membranes. The susceptibility of membrane interaction to pressure raises the idea of a role of lipidated signaling molecules as mechanosensors, transducing mechanical stimuli to chemical signals by regulating their membrane binding and dissociation. Finally, our results provide first insights into the influence of pressure on membrane-associated Ras-controlled signaling events in organisms living under extreme environmental conditions such as those that are encountered in the deep sea and sub-seafloor environments, where pressures reach the kilobar (100 MPa) range.
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Affiliation(s)
- Shobhna Kapoor
- Physical Chemistry I-Biophysical Chemistry, Faculty of Chemistry, TU Dortmund University, Otto-Hahn-Strasse 6, D-44227 Dortmund, Germany
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146
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Kumar SKK, Tamimi A, Fayer MD. Dynamics in the interior of AOT lamellae investigated with two-dimensional infrared spectroscopy. J Am Chem Soc 2013; 135:5118-26. [PMID: 23465101 DOI: 10.1021/ja312676e] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The dynamics inside the organic regions of aerosol-OT (AOT)/water mixtures in the lamellar mesophase, bicontinuous cubic (BC) phase, and in an analogous molecule without the charged sulfonate headgroup are investigated by observing spectral diffusion, orientational relaxation and population relaxation using ultrafast two-dimensional infrared (2D IR) vibrational echo spectroscopy and IR pump-probe experiments on the asymmetric CO stretch of a vibrational probe, tungsten hexacarbonyl (W(CO)6). The water layer thickness between the bilayer planes in the lamellar phase was varied. For comparison, the dynamics of W(CO)6 in the normal liquid bis(2-ethylhexyl) succinate (EHS), which is analogous to AOT but has no charged sulfonate headgroup, were also studied. The 2D IR experiments measure spectral diffusion, which results from the structural evolution of the system. Spectral diffusion is quantified by the frequency-frequency correlation function (FFCF). In addition to a homogeneous component, the FFCFs are biexponential decays with fast and slow time components of ∼12.5 and ∼150 ps in the lamellar phase. Both components of the FFCF are independent of the number of water molecules per headgroup for the lamellae, but they slow somewhat in the BC phase. The dynamics in the ordered phases are in sharp contrast to the dynamics in EHS, which displays fast and slow components of the FFCF of 5 and 80 ps, respectively. As the hydration level of AOT increases, vibrational lifetime decreases, suggesting some change in the local environment of W(CO)6 with water content.
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Affiliation(s)
- S K Karthick Kumar
- Department of Chemistry, Stanford University , Stanford, California 94305, United States
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147
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Pan J, Heberle FA, Petruzielo RS, Katsaras J. Using small-angle neutron scattering to detect nanoscopic lipid domains. Chem Phys Lipids 2013; 170-171:19-32. [PMID: 23518250 DOI: 10.1016/j.chemphyslip.2013.02.012] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2013] [Revised: 02/27/2013] [Accepted: 02/28/2013] [Indexed: 11/25/2022]
Abstract
The cell plasma membrane is a complex system, which is thought to be capable of exhibiting non-random lateral organization. Studies of live cells and model membranes have yielded mechanisms responsible for the formation, growth, and maintenance of nanoscopic heterogeneities, although the existence and mechanisms that give rise to these heterogeneities remain controversial. Small-angle neutron scattering (SANS) is a tool ideally suited to interrogate lateral heterogeneity in model membranes, primarily due to its unique spatial resolution (i.e., ~5-100nm) and its ability to resolve structure with minimal perturbation to the membrane. In this review we examine several methods used to analyze the SANS signal arising from freely suspended unilamellar vesicles containing lateral heterogeneity. Specifically, we discuss an analytical model for a single, round domain on a spherical vesicle. We then discuss a numerical method that uses Monte Carlo simulation to describe systems with multiple domains and/or more complicated morphologies. Also discussed are several model-independent approaches that are sensitive to membrane heterogeneity. The review concludes with several recent applications of SANS to the study of membrane raft mixtures.
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Affiliation(s)
- Jianjun Pan
- Biology and Soft Matter Division, Neutron Sciences Directorate, Oak Ridge National Laboratory, Oak Ridge, TN 37831, United States.
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148
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Burke KA, Yates EA, Legleiter J. Biophysical insights into how surfaces, including lipid membranes, modulate protein aggregation related to neurodegeneration. Front Neurol 2013; 4:17. [PMID: 23459674 PMCID: PMC3585431 DOI: 10.3389/fneur.2013.00017] [Citation(s) in RCA: 81] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2012] [Accepted: 02/09/2013] [Indexed: 11/13/2022] Open
Abstract
There are a vast number of neurodegenerative diseases, including Alzheimer’s disease (AD), Parkinson’s disease (PD), and Huntington’s disease (HD), associated with the rearrangement of specific proteins to non-native conformations that promotes aggregation and deposition within tissues and/or cellular compartments. These diseases are commonly classified as protein-misfolding or amyloid diseases. The interaction of these proteins with liquid/surface interfaces is a fundamental phenomenon with potential implications for protein-misfolding diseases. Kinetic and thermodynamic studies indicate that significant conformational changes can be induced in proteins encountering surfaces, which can play a critical role in nucleating aggregate formation or stabilizing specific aggregation states. Surfaces of particular interest in neurodegenerative diseases are cellular and subcellular membranes that are predominately comprised of lipid components. The two-dimensional liquid environments provided by lipid bilayers can profoundly alter protein structure and dynamics by both specific and non-specific interactions. Importantly for misfolding diseases, these bilayer properties can not only modulate protein conformation, but also exert influence on aggregation state. A detailed understanding of the influence of (sub)cellular surfaces in driving protein aggregation and/or stabilizing specific aggregate forms could provide new insights into toxic mechanisms associated with these diseases. Here, we review the influence of surfaces in driving and stabilizing protein aggregation with a specific emphasis on lipid membranes.
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Affiliation(s)
- Kathleen A Burke
- C. Eugene Bennett Department of Chemistry, West Virginia University Morgantown, WV, USA
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149
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Haselwandter CA, Phillips R. Directional interactions and cooperativity between mechanosensitive membrane proteins. EUROPHYSICS LETTERS 2013; 101:68002p1-68002p6. [PMID: 25309021 PMCID: PMC4193682 DOI: 10.1209/0295-5075/101/68002] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
While modern structural biology has provided us with a rich and diverse picture of membrane proteins, the biological function of membrane proteins is often influenced by the mechanical properties of the surrounding lipid bilayer. Here we explore the relation between the shape of membrane proteins and the cooperative function of membrane proteins induced by membrane-mediated elastic interactions. For the experimental model system of mechanosensitive ion channels we find that the sign and strength of elastic interactions depend on the protein shape, yielding distinct cooperative gating curves for distinct protein orientations. Our approach predicts how directional elastic interactions affect the molecular structure, organization, and biological function of proteins in crowded membranes.
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Affiliation(s)
- Christoph A Haselwandter
- Department of Physics and Astronomy, University of Southern California - Los Angeles, CA 90089, USA ; Department of Applied Physics, California Institute of Technology - Pasadena, CA 91125, USA
| | - Rob Phillips
- Department of Applied Physics, California Institute of Technology - Pasadena, CA 91125, USA
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150
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Doux JPF, Hall BA, Killian JA. How lipid headgroups sense the membrane environment: an application of ¹⁴N NMR. Biophys J 2013; 103:1245-53. [PMID: 22995497 DOI: 10.1016/j.bpj.2012.08.031] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2012] [Revised: 08/03/2012] [Accepted: 08/10/2012] [Indexed: 11/16/2022] Open
Abstract
The orientation of lipid headgroups may serve as a powerful sensor of electrostatic interactions in membranes. As shown previously by (2)H NMR measurements, the headgroup of phosphatidylcholine (PC) behaves like an electrometer and varies its orientation according to the membrane surface charge. Here, we explored the use of solid-state (14)N NMR as a relatively simple and label-free method to study the orientation of the PC headgroup in model membrane systems of varying composition. We found that (14)N NMR is sufficiently sensitive to detect small changes in headgroup orientation upon introduction of positively and negatively charged lipids and we developed an approach to directly convert the (14)N quadrupolar splittings into an average orientation of the PC polar headgroup. Our results show that inclusion of cholesterol or mixing of lipids with different length acyl chains does not significantly affect the orientation of the PC headgroup. In contrast, measurements with cationic (KALP), neutral (Ac-KALP), and pH-sensitive (HALP) transmembrane peptides show very systematic changes in headgroup orientation, depending on the amount of charge in the peptide side chains and on their precise localization at the interface, as modulated by varying the extent of hydrophobic peptide/lipid mismatch. Finally, our measurements suggest an unexpectedly strong preferential enrichment of the anionic lipid phosphatidylglycerol around the cationic KALP peptide in ternary mixtures with PC. We believe that these results are important for understanding protein/lipid interactions and that they may help parametrization of membrane properties in computational studies.
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Affiliation(s)
- Jacques P F Doux
- Membrane Biochemistry and Biophysics, Bijvoet Center for Biomolecular Research, Utrecht University, Utrecht, The Netherlands
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