1
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Tripathy M, Srivastava A. Lipid packing in biological membranes governs protein localization and membrane permeability. Biophys J 2023; 122:2727-2743. [PMID: 37254482 PMCID: PMC10397809 DOI: 10.1016/j.bpj.2023.05.028] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2022] [Revised: 04/18/2023] [Accepted: 05/25/2023] [Indexed: 06/01/2023] Open
Abstract
Plasma membrane (PM) heterogeneity has long been implicated in various cellular functions. However, mechanistic principles governing functional regulations of lipid environment are not well understood due to the inherent complexities associated with the relevant length and timescales that limit both direct experimental measurements and their interpretation. In this context, computer simulations hold immense potential to investigate molecular-level interactions and mechanisms that lead to PM heterogeneity and its functions. Herein, we investigate spatial and dynamic heterogeneity in model membranes with coexisting liquid ordered and liquid disordered phases and characterize the membrane order in terms of the local topological changes in lipid environment using the nonaffine deformation framework. Furthermore, we probe the packing defects in these membranes, which can be considered as the conjugate of membrane order assessed in terms of the nonaffine parameter. In doing so, we formalize the connection between membrane packing and local membrane order and use that to explore the mechanistic principles behind their functions. Our observations suggest that heterogeneity in mixed phase membranes is a consequence of local lipid topology and its temporal evolution, which give rise to disparate lipid packing in ordered and disordered domains. This in turn governs the distinct nature of packing defects in these domains that can play a crucial role in preferential localization of proteins in mixed phase membranes. Furthermore, we observe that lipid packing also leads to contrasting distribution of free volume in the membrane core region in ordered and disordered membranes, which can lead to distinctive membrane permeability of small molecules. Our results, thus, indicate that heterogeneity in mixed phase membranes closely governs the membrane functions that may emerge from packing-related basic design principles.
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Affiliation(s)
- Madhusmita Tripathy
- Molecular Biophysics Unit, Indian Institute of Science Bangalore, Bangalore, Karnataka, India.
| | - Anand Srivastava
- Molecular Biophysics Unit, Indian Institute of Science Bangalore, Bangalore, Karnataka, India.
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2
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DiPasquale M, Deering TG, Desai D, Sharma AK, Amin S, Fox TE, Kester M, Katsaras J, Marquardt D, Heberle FA. Influence of ceramide on lipid domain stability studied with small-angle neutron scattering: The role of acyl chain length and unsaturation. Chem Phys Lipids 2022; 245:105205. [PMID: 35483419 PMCID: PMC9320172 DOI: 10.1016/j.chemphyslip.2022.105205] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2022] [Accepted: 04/11/2022] [Indexed: 12/13/2022]
Abstract
Ceramides and diacylglycerols are groups of lipids capable of nucleating and stabilizing ordered lipid domains, structures that have been implicated in a range of biological processes. Previous studies have used fluorescence reporter molecules to explore the influence of ceramide acyl chain structure on sphingolipid-rich ordered phases. Here, we use small-angle neutron scattering (SANS) to examine the ability of ceramides and diacylglycerols to promote lipid domain formation in the well-characterized domain-forming mixture DPPC/DOPC/cholesterol. SANS is a powerful, probe-free technique for interrogating membrane heterogeneity, as it is differentially sensitive to hydrogen's stable isotopes protium and deuterium. Specifically, neutron contrast is generated through selective deuteration of lipid species, thus enabling the detection of nanoscopic domains enriched in deuterated saturated lipids dispersed in a matrix of protiated unsaturated lipids. Using large unilamellar vesicles, we found that upon replacing 10 mol% DPPC with either C16:0 or C18:0 ceramide, or 16:0 diacylglycerol (dag), lipid domains persisted to higher temperatures. However, when DPPC was replaced with short chain (C6:0 or C12:0) or very long chain (C24:0) ceramides, or ceramides with unsaturated acyl chains of any length (C6:1(3), C6:1(5), C18:1, and C24:1), as well as C18:1-dag, lipid domains were destabilized, melting at lower temperatures than those in the DPPC/DOPC/cholesterol system. These results show how ceramide acyl chain length and unsaturation influence lipid domains and have implications for how cell membranes might modify their function through the generation of different ceramide species.
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Affiliation(s)
- Mitchell DiPasquale
- Department of Chemistry and Biochemistry, University of Windsor, Windsor N9B 3P4, ON, Canada
| | - Tye G Deering
- Department of Pharmacology, University of Virginia, Charlottesville 22908, VA, USA
| | - Dhimant Desai
- Department of Pharmacology, Penn State University, University Park 16801, PA, USA
| | - Arun K Sharma
- Department of Pharmacology, Penn State University, University Park 16801, PA, USA
| | - Shantu Amin
- Department of Pharmacology, Penn State University, University Park 16801, PA, USA
| | - Todd E Fox
- Department of Pharmacology, University of Virginia, Charlottesville 22908, VA, USA
| | - Mark Kester
- Department of Pharmacology, University of Virginia, Charlottesville 22908, VA, USA; Department of Molecular Physiology and Biophysics, University of Virginia, Charlottesville 22908, VA, USA
| | - John Katsaras
- Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge 37831, TN, USA; Joint Institute for Neutron Sciences, Oak Ridge National Laboratory, Oak Ridge 37831, TN, USA; Department of Physics and Astronomy, University of Tennessee, Knoxville 37996, TN, USA.
| | - Drew Marquardt
- Department of Chemistry and Biochemistry, University of Windsor, Windsor N9B 3P4, ON, Canada; Department of Physics, University of Windsor, Windsor N9B 3P4, ON, Canada.
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3
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Fanani ML, Nocelli NE, Zulueta Díaz YDLM. What can we learn about amphiphile-membrane interaction from model lipid membranes? BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2022; 1864:183781. [PMID: 34555419 DOI: 10.1016/j.bbamem.2021.183781] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/31/2021] [Revised: 08/30/2021] [Accepted: 09/14/2021] [Indexed: 10/20/2022]
Abstract
Surface-active amphiphiles find applications in a wide range of areas of industry such as agrochemicals, personal care, and pharmaceuticals. In many of these applications, interaction with cell membranes is a key factor for achieving their purpose. How do amphiphiles interact with lipid membranes? What are their bases for membrane specificity? Which biophysical properties of membranes are susceptible to modulation by amphiphilic membrane-effectors? What aspects of this interaction are important for performing their function? In our work on membrane biophysics over the years, questions like these have arisen and we now share some of our findings and discuss them in this review. This topic was approached focusing on the membrane properties and their alterations rather than on the amphiphile structure requirements for their interaction. Here, we do not aim to provide a comprehensive list of the modes of action of amphiphiles of biological interest but to help in understanding them.
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Affiliation(s)
- Maria Laura Fanani
- Departamento de Química Biológica Ranwel Caputto, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Córdoba, Argentina; Centro de Investigaciones en Química Biológica de Córdoba (CIQUIBIC), CONICET, Córdoba, Argentina.
| | - Natalia E Nocelli
- Departamento de Química Biológica Ranwel Caputto, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Córdoba, Argentina; Centro de Investigaciones en Química Biológica de Córdoba (CIQUIBIC), CONICET, Córdoba, Argentina
| | - Yenisleidy de Las Mercedes Zulueta Díaz
- Departamento de Química Biológica Ranwel Caputto, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Córdoba, Argentina; Centro de Investigaciones en Química Biológica de Córdoba (CIQUIBIC), CONICET, Córdoba, Argentina
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4
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Gohrbandt M, Lipski A, Grimshaw JW, Buttress JA, Baig Z, Herkenhoff B, Walter S, Kurre R, Deckers-Hebestreit G, Strahl H. Low membrane fluidity triggers lipid phase separation and protein segregation in living bacteria. EMBO J 2022; 41:e109800. [PMID: 35037270 PMCID: PMC8886542 DOI: 10.15252/embj.2021109800] [Citation(s) in RCA: 40] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2021] [Revised: 12/19/2021] [Accepted: 12/21/2021] [Indexed: 11/09/2022] Open
Abstract
All living organisms adapt their membrane lipid composition in response to changes in their environment or diet. These conserved membrane‐adaptive processes have been studied extensively. However, key concepts of membrane biology linked to regulation of lipid composition including homeoviscous adaptation maintaining stable levels of membrane fluidity, and gel‐fluid phase separation resulting in domain formation, heavily rely upon in vitro studies with model membranes or lipid extracts. Using the bacterial model organisms Escherichia coli and Bacillus subtilis, we now show that inadequate in vivo membrane fluidity interferes with essential complex cellular processes including cytokinesis, envelope expansion, chromosome replication/segregation and maintenance of membrane potential. Furthermore, we demonstrate that very low membrane fluidity is indeed capable of triggering large‐scale lipid phase separation and protein segregation in intact, protein‐crowded membranes of living cells; a process that coincides with the minimal level of fluidity capable of supporting growth. Importantly, the in vivo lipid phase separation is not associated with a breakdown of the membrane diffusion barrier function, thus explaining why the phase separation process induced by low fluidity is biologically reversible.
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Affiliation(s)
- Marvin Gohrbandt
- Mikrobiologie, Fachbereich Biologie/Chemie, Universität Osnabrück, Osnabrück, Germany
| | - André Lipski
- Lebensmittelmikrobiologie und -hygiene, Institut für Ernährungs- und Lebensmittelwissenschaften, Rheinische Friedrich-Wilhelms-Universität Bonn, Bonn, Germany
| | - James W Grimshaw
- Centre for Bacterial Cell Biology, Biosciences Institute, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne, UK
| | - Jessica A Buttress
- Centre for Bacterial Cell Biology, Biosciences Institute, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne, UK
| | - Zunera Baig
- Centre for Bacterial Cell Biology, Biosciences Institute, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne, UK
| | - Brigitte Herkenhoff
- Mikrobiologie, Fachbereich Biologie/Chemie, Universität Osnabrück, Osnabrück, Germany
| | - Stefan Walter
- Mikrobiologie, Fachbereich Biologie/Chemie, Universität Osnabrück, Osnabrück, Germany
| | - Rainer Kurre
- Center of Cellular Nanoanalytics, Integrated Bioimaging Facility, Universität Osnabrück, Osnabrück, Germany
| | | | - Henrik Strahl
- Centre for Bacterial Cell Biology, Biosciences Institute, Faculty of Medical Sciences, Newcastle University, Newcastle upon Tyne, UK
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5
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Obeid S, Guyomarc'h F. Atomic force microscopy of food assembly: Structural and mechanical insights at the nanoscale and potential opportunities from other fields. FOOD BIOSCI 2020. [DOI: 10.1016/j.fbio.2020.100654] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
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6
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Stottrup BL, TigreLazo J, Bagonza VB, Kunz JC, Zasadzinski JA. Comparison of Line Tension Measurement Methods for Lipid Monolayers at Liquid-Liquid Coexistence. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:16053-16061. [PMID: 31343892 PMCID: PMC6896218 DOI: 10.1021/acs.langmuir.9b01696] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
Several methods of measuring the line tension between phase-separated liquid-ordered-liquid -disordered domains in phospholipid-cholesterol systems have been proposed. These experimental techniques are typically internally self-consistent, but the measured line tension values vary widely among these techniques. To date, no measurement of line tension has utilized multiple experimental techniques to look at the same monolayer system. Here we compare two nonperturbative methods, Fourier analysis of boundary fluctuations (BA) and one proposed by Israelachvili involving the analysis of domain size distributions (SD), to extract the line tension in a 70 mol % DMPC/30 mol % dihydrocholesterol (DChol) mixture as a function of surface pressure. We show that BA predicts the expected variation in line tension measurements consistent with the theoretical critical exponent whereas SD does not. From this comparison, we conclude that the size distribution of monolayer domains is metastable and primarily determined by the kinetics of domain nucleation and subsequent aging.
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Affiliation(s)
- Benjamin L. Stottrup
- Department of Physics, Augsburg University, Minneapolis, Minnesota 55454, United States
| | - Juan TigreLazo
- Department of Physics, Augsburg University, Minneapolis, Minnesota 55454, United States
| | - Vision B. Bagonza
- Department of Physics, Augsburg University, Minneapolis, Minnesota 55454, United States
| | - Joan C. Kunz
- Department of Chemistry, Augsburg University, Minneapolis, Minnesota 55454, United States
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7
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Jaipuria G, Giller K, Leonov A, Becker S, Zweckstetter M. Insights into Cholesterol/Membrane Protein Interactions Using Paramagnetic Solid-State NMR. Chemistry 2018; 24:17606-17611. [PMID: 30255522 DOI: 10.1002/chem.201804550] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2018] [Indexed: 11/10/2022]
Abstract
Cholesterol is an essential component of animal cell membranes and impacts the structure and function of membrane proteins. But how cholesterol exerts its functions remains often enigmatic. Here, high-resolution solid-state NMR in combination with paramagnetic cholesterol analogues was shown to be a powerful approach to study the interaction of membrane proteins with cholesterol. Application of the method to the 169-residue translocator protein TSPO provides residue-specific information about its interaction with cholesterol. Comparison with NMR signal perturbations induced by diamagnetic cholesterol furthermore supports changes in the structure of mammalian TSPO caused by cholesterol binding.
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Affiliation(s)
- Garima Jaipuria
- Deutsches Zentrum für Neurodegenerative Erkrankungen (DZNE), Von-Siebold-Str. 3a, 37075, Göttingen, Germany
| | - Karin Giller
- Department of NMR-based Structural Biology, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077, Göttingen, Germany
| | - Andrei Leonov
- Department of NMR-based Structural Biology, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077, Göttingen, Germany
| | - Stefan Becker
- Department of NMR-based Structural Biology, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077, Göttingen, Germany
| | - Markus Zweckstetter
- Deutsches Zentrum für Neurodegenerative Erkrankungen (DZNE), Von-Siebold-Str. 3a, 37075, Göttingen, Germany.,Department of NMR-based Structural Biology, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077, Göttingen, Germany
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8
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Rovere M, Sanderson JB, Fonseca‐Ornelas L, Patel DS, Bartels T. Refolding of helical soluble α‐synuclein through transient interaction with lipid interfaces. FEBS Lett 2018; 592:1464-1472. [DOI: 10.1002/1873-3468.13047] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2018] [Accepted: 03/28/2018] [Indexed: 11/10/2022]
Affiliation(s)
- Matteo Rovere
- Ann Romney Center for Neurologic Diseases Brigham and Women's Hospital and Harvard Medical School Boston MA USA
| | - John B. Sanderson
- Ann Romney Center for Neurologic Diseases Brigham and Women's Hospital and Harvard Medical School Boston MA USA
| | - Luis Fonseca‐Ornelas
- Ann Romney Center for Neurologic Diseases Brigham and Women's Hospital and Harvard Medical School Boston MA USA
| | - Dushyant S. Patel
- Ann Romney Center for Neurologic Diseases Brigham and Women's Hospital and Harvard Medical School Boston MA USA
| | - Tim Bartels
- Ann Romney Center for Neurologic Diseases Brigham and Women's Hospital and Harvard Medical School Boston MA USA
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9
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Fanani ML, Wilke N. Regulation of phase boundaries and phase-segregated patterns in model membranes. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2018; 1860:1972-1984. [PMID: 29505769 DOI: 10.1016/j.bbamem.2018.02.023] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/27/2017] [Revised: 02/20/2018] [Accepted: 02/20/2018] [Indexed: 12/13/2022]
Abstract
Demixing of components has long been described in model membranes. It is a consequence of non-ideal lateral interactions between membrane components, and it causes the presence of segregated phases, forming patches (domains) of different properties, thus introducing heterogeneity into the membrane. In the present review we first describe the processes through which domains are generated, how they grow, and why they are rounded, striped or fractal-like, as well as why they get distributed forming defined patterns. Next, we focus on the effect of an additive on a lipid mixture, which usually induces shifts in demixing points, thus stabilizing or destabilizing the phase-segregated state. Results found for different model membranes are summarized, detailing the ways in which phase segregation and the generated patterns may be modulated. We focus on which are, from our viewpoint, the most relevant regulating factors affecting the surface texture observed in model membranes. This article is part of a Special Issue entitled: Emergence of Complex Behavior in Biomembranes edited by Marjorie Longo.
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Affiliation(s)
- María Laura Fanani
- Universidad Nacional de Córdoba, Facultad de Ciencias Químicas, Departamento de Química Biológica "Ranwel Caputto", Córdoba, Argentina; CONICET, Universidad Nacional de Córdoba, Centro de Investigaciones en Química Biológica de Córdoba (CIQUIBIC), Córdoba, Argentina
| | - Natalia Wilke
- Universidad Nacional de Córdoba, Facultad de Ciencias Químicas, Departamento de Química Biológica "Ranwel Caputto", Córdoba, Argentina; CONICET, Universidad Nacional de Córdoba, Centro de Investigaciones en Química Biológica de Córdoba (CIQUIBIC), Córdoba, Argentina.
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10
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Nitsche JM, Kasting GB. A Universal Correlation Predicts Permeability Coefficients of Fluid- and Gel-Phase Phospholipid and Phospholipid-Cholesterol Bilayers for Arbitrary Solutes. J Pharm Sci 2017; 105:1762-1771. [PMID: 27112406 DOI: 10.1016/j.xphs.2016.02.012] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2015] [Revised: 01/26/2016] [Accepted: 02/02/2016] [Indexed: 11/24/2022]
Abstract
The permeability of gel-phase phospholipids is typically about an order of magnitude lower than that of the same compositions in the fluid phase, yet a quantitative description of the ordering factors leading to this difference has been elusive. The present analysis examines these factors with particular focus on the area per phospholipid chain, Ac, and its relationship to the minimum area per molecule in the crystalline state, A0. It is shown that fluid- and gel-phase phospholipid permeabilities can be reconciled by postulating a minimum area per chain Ac,0 = 17.1 Å(2), substantially less than one would estimate by dividing the accepted value A0 = 40.8 Å(2) by 2. An extended data set of phospholipid and phospholipid-cholesterol bilayer permeability data extending over 9 orders of magnitude is analyzed and correlated according to the developed relationship (N = 85, s = 0.3024, r(2) = 0.9332). Individual permeability values are consequently predicted to within an average deviation of 10(0.3024) or about a factor of 2. The analysis is broadly applicable in the fluid phase but is restricted to gel-phase phospholipid compositions that do not contain cholesterol. Guidance for the latter scenario is provided.
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Affiliation(s)
- Johannes M Nitsche
- Department of Chemical and Biological Engineering, University at Buffalo, The State University of New York, Buffalo, New York 14260-4200.
| | - Gerald B Kasting
- James L. Winkle College of Pharmacy, University of Cincinnati Academic Health Center, Cincinnati, Ohio 45267-0004
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11
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Gordon VD, O'Halloran TJ, Shindell O. Membrane adhesion and the formation of heterogeneities: biology, biophysics, and biotechnology. Phys Chem Chem Phys 2015; 17:15522-33. [PMID: 25866854 PMCID: PMC4465551 DOI: 10.1039/c4cp05876c] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Membrane adhesion is essential to many vital biological processes. Sites of membrane adhesion are often associated with heterogeneities in the lipid and protein composition of the membrane. These heterogeneities are thought to play functional roles by facilitating interactions between proteins. However, the causal links between membrane adhesion and membrane heterogeneities are not known. Here we survey the state of the field and indicate what we think are understudied areas ripe for development.
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Affiliation(s)
- V D Gordon
- The University of Texas at Austin, Department of Physics and Center for Nonlinear Dynamics, 2515 Speedway, Stop C1610, Austin, Texas 78712-1199, USA.
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12
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Curthoys NM, Parent M, Mlodzianoski M, Nelson AJ, Lilieholm J, Butler MB, Valles M, Hess ST. Dances with Membranes: Breakthroughs from Super-resolution Imaging. CURRENT TOPICS IN MEMBRANES 2015; 75:59-123. [PMID: 26015281 PMCID: PMC5584789 DOI: 10.1016/bs.ctm.2015.03.008] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Biological membrane organization mediates numerous cellular functions and has also been connected with an immense number of human diseases. However, until recently, experimental methodologies have been unable to directly visualize the nanoscale details of biological membranes, particularly in intact living cells. Numerous models explaining membrane organization have been proposed, but testing those models has required indirect methods; the desire to directly image proteins and lipids in living cell membranes is a strong motivation for the advancement of technology. The development of super-resolution microscopy has provided powerful tools for quantification of membrane organization at the level of individual proteins and lipids, and many of these tools are compatible with living cells. Previously inaccessible questions are now being addressed, and the field of membrane biology is developing rapidly. This chapter discusses how the development of super-resolution microscopy has led to fundamental advances in the field of biological membrane organization. We summarize the history and some models explaining how proteins are organized in cell membranes, and give an overview of various super-resolution techniques and methods of quantifying super-resolution data. We discuss the application of super-resolution techniques to membrane biology in general, and also with specific reference to the fields of actin and actin-binding proteins, virus infection, mitochondria, immune cell biology, and phosphoinositide signaling. Finally, we present our hopes and expectations for the future of super-resolution microscopy in the field of membrane biology.
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Affiliation(s)
- Nikki M. Curthoys
- Department of Physics and Astronomy, University of Maine, Orono, ME, USA
| | - Matthew Parent
- Department of Physics and Astronomy, University of Maine, Orono, ME, USA
| | | | - Andrew J. Nelson
- Department of Physics and Astronomy, University of Maine, Orono, ME, USA
| | - Jennifer Lilieholm
- Department of Physics and Astronomy, University of Maine, Orono, ME, USA
| | - Michael B. Butler
- Department of Physics and Astronomy, University of Maine, Orono, ME, USA
| | - Matthew Valles
- Department of Physics and Astronomy, University of Maine, Orono, ME, USA
| | - Samuel T. Hess
- Department of Physics and Astronomy, University of Maine, Orono, ME, USA
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13
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Visualizing monolayers with a water-soluble fluorophore to quantify adsorption, desorption, and the double layer. Proc Natl Acad Sci U S A 2015; 112:E826-35. [PMID: 25675499 DOI: 10.1073/pnas.1419033112] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Contrast in confocal microscopy of phase-separated monolayers at the air-water interface can be generated by the selective adsorption of water-soluble fluorescent dyes to disordered monolayer phases. Optical sectioning minimizes the fluorescence signal from the subphase, whereas convolution of the measured point spread function with a simple box model of the interface provides quantitative assessment of the excess dye concentration associated with the monolayer. Coexisting liquid-expanded, liquid-condensed, and gas phases could be visualized due to differential dye adsorption in the liquid-expanded and gas phases. Dye preferentially adsorbed to the liquid-disordered phase during immiscible liquid-liquid phase coexistence, and the contrast persisted through the critical point as shown by characteristic circle-to-stripe shape transitions. The measured dye concentration in the disordered phase depended on the phase composition and surface pressure, and the dye was expelled from the film at the end of coexistence. The excess concentration of a cationic dye within the double layer adjacent to an anionic phospholipid monolayer was quantified as a function of subphase ionic strength, and the changes in measured excess agreed with those predicted by the mean-field Gouy-Chapman equations. This provided a rapid and noninvasive optical method of measuring the fractional dissociation of lipid headgroups and the monolayer surface potential.
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14
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Gray E, Karslake J, Machta BB, Veatch SL. Liquid general anesthetics lower critical temperatures in plasma membrane vesicles. Biophys J 2014; 105:2751-9. [PMID: 24359747 DOI: 10.1016/j.bpj.2013.11.005] [Citation(s) in RCA: 79] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2013] [Revised: 10/31/2013] [Accepted: 11/04/2013] [Indexed: 12/21/2022] Open
Abstract
A large and diverse array of small hydrophobic molecules induce general anesthesia. Their efficacy as anesthetics has been shown to correlate both with their affinity for a hydrophobic environment and with their potency in inhibiting certain ligand-gated ion channels. In this study we explore the effects that n-alcohols and other liquid anesthetics have on the two-dimensional miscibility critical point observed in cell-derived giant plasma membrane vesicles (GPMVs). We show that anesthetics depress the critical temperature (Tc) of these GPMVs without strongly altering the ratio of the two liquid phases found below Tc. The magnitude of this affect is consistent across n-alcohols when their concentration is rescaled by the median anesthetic concentration (AC50) for tadpole anesthesia, but not when plotted against the overall concentration in solution. At AC50 we see a 4°C downward shift in Tc, much larger than is typically seen in the main chain transition at these anesthetic concentrations. GPMV miscibility critical temperatures are also lowered to a similar extent by propofol, phenylethanol, and isopropanol when added at anesthetic concentrations, but not by tetradecanol or 2,6 diterbutylphenol, two structural analogs of general anesthetics that are hydrophobic but have no anesthetic potency. We propose that liquid general anesthetics provide an experimental tool for lowering critical temperatures in plasma membranes of intact cells, which we predict will reduce lipid-mediated heterogeneity in a way that is complimentary to increasing or decreasing cholesterol. Also, several possible implications of our results are discussed in the context of current models of anesthetic action on ligand-gated ion channels.
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Affiliation(s)
- Ellyn Gray
- Department of Biophysics, University of Michigan, Ann Arbor MI 48109
| | - Joshua Karslake
- Department of Biophysics, University of Michigan, Ann Arbor MI 48109
| | - Benjamin B Machta
- Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton NJ 08544.
| | - Sarah L Veatch
- Department of Biophysics, University of Michigan, Ann Arbor MI 48109.
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15
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Choi S, Kim K, Fellows CM, Cao KD, Lin B, Lee KYC, Squires TM, Zasadzinski JA. Influence of molecular coherence on surface viscosity. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2014; 30:8829-38. [PMID: 24991992 PMCID: PMC4334248 DOI: 10.1021/la501615g] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
Adding small fractions of cholesterol decreases the interfacial viscosity of dipalmitoylphosphatidylcholine (DPPC) monolayers by an order of magnitude per wt %. Grazing incidence X-ray diffraction shows that cholesterol at these small fractions does not mix ideally with DPPC but rather induces nanophase separated structures of an ordered, primarily DPPC phase bordered by a line-active, disordered, mixed DPPC-cholesterol phase. We propose that the free area in the classic Cohen and Turnbull model of viscosity is inversely proportional to the number of molecules in the coherence area, or product of the two coherence lengths. Cholesterol significantly reduces the coherence area of the crystals as well as the interfacial viscosity. Using this free area collapses the surface viscosity data for all surface pressures and cholesterol fractions to a universal logarithmic relation. The extent of molecular coherence appears to be a fundamental factor in determining surface viscosity in ordered monolayers.
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Affiliation(s)
- Siyoung
Q. Choi
- Chemical
Engineering and Materials Science, University
of Minnesota, Minneapolis, Minnesota 55455, United States
| | - Kyuhan Kim
- Department
of Chemical Engineering, University of California, Santa Barbara, California 93106, United States
| | - Colin M. Fellows
- Department
of Chemical Engineering, University of California, Santa Barbara, California 93106, United States
| | - Kathleen D. Cao
- Department
of Chemistry and James Franck Institute, University of Chicago, Chicago, Illinois 60637, United States
| | - Binhua Lin
- Center
for Advanced Radiation Sources and James Franck Institute, University of Chicago, Chicago, Illinois 60637, United States
| | - Ka Yee C. Lee
- Department
of Chemistry and James Franck Institute, University of Chicago, Chicago, Illinois 60637, United States
| | - Todd M. Squires
- Department
of Chemical Engineering, University of California, Santa Barbara, California 93106, United States
| | - Joseph A. Zasadzinski
- Chemical
Engineering and Materials Science, University
of Minnesota, Minneapolis, Minnesota 55455, United States
- E-mail: . Phone: 612-626-2957
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16
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Xia Y, Sun J, Liang D. Aggregation, fusion, and leakage of liposomes induced by peptides. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2014; 30:7334-7342. [PMID: 24911839 DOI: 10.1021/la501618f] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Biological membranes are heterogeneous systems. Their functions are closely related to the lipid lateral segregation in the presence of membrane proteins. In this work, we designed two peptides, amphiphilic cationic peptides K3L8K3 and nonamphiphilic peptides K20, and studied their interactions with binary liposomes in different phases (Lα, Lβ', and Lα/Lβ'). As mimics of membrane proteins, both K3L8K3 and K20 can cause the liposomes to aggregate, fuse, or leak. These processes were closely related to the phases of liposomes. For the liposomes in Lα phase, heavy aggregation, fusion, and leakage were observed in the presence of either K20 or K3L8K3. For the liposomes in Lβ' phase, neither K3L8K3 nor K20 can induce fusion or leakage. For the liposomes in Lα/Lβ' phase, K3L8K3 caused the liposomes to aggregate, fuse, and leak, while K20 only led to aggregation. The kinetics of aggregation, fusion, and leakage in each phase were recorded, and they were related to the lipid demixing in the presence of the peptide. Our work not only gained insight into the effect of the lipid demixing on the interactions between peptide and membrane, but also helped in developing drug delivery vehicles with liposomes as the platform.
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Affiliation(s)
- Yuqiong Xia
- Beijing National Laboratory for Molecular Sciences and the Key Laboratory of Polymer Chemistry and Physics of Ministry of Education, College of Chemistry and Molecular Engineering, Peking University , Beijing, 100871, China
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17
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Molecular origins of bending rigidity in lipids with isolated and conjugated double bonds: The effect of cholesterol. Chem Phys Lipids 2014; 178:18-26. [DOI: 10.1016/j.chemphyslip.2013.12.012] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2013] [Revised: 12/23/2013] [Accepted: 12/24/2013] [Indexed: 01/19/2023]
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18
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Ontong P, Hatada Y, Taniguchi S, Kakizaki I, Itano N. Effect of a cholesterol-rich lipid environment on the enzymatic activity of reconstituted hyaluronan synthase. Biochem Biophys Res Commun 2013; 443:666-71. [PMID: 24333423 DOI: 10.1016/j.bbrc.2013.12.028] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2013] [Accepted: 12/04/2013] [Indexed: 11/25/2022]
Abstract
Hyaluronan synthase (HAS) is a unique membrane-associated glycosyltransferase and its activity is lipid dependent. The dependence however is not well understood, especially in vertebrate systems. Here we investigated the functional association of hyaluronan synthesis in a cholesterol-rich membrane-environment. The culture of human dermal fibroblasts in lipoprotein-depleted medium attenuated the synthesis of hyaluronan. The sequestration of cellular cholesterol by methyl-ß-cyclodextrin also decreased the hyaluronan production of fibroblasts, as well as the HAS activity. To directly evaluate the effects of cholesterol on HAS activity, a recombinant human HAS2 protein with a histidine-tag was expressed as a membrane protein by using a baculovirus system, then successfully solubilized, and isolated by affinity chromatography. When the recombinant HAS2 proteins were reconstituted into liposomes composed of both saturated phosphatidylcholine and cholesterol, this provided a higher enzyme activity as compared with the liposomes formed by phosphatidylcholine alone. Cholesterol regulates HAS2 activity in a biphasic manner, depending on the molar ratio of phosphatidylcholine to cholesterol. Furthermore, the activation profiles of different lipid compositions were determined in the presence or absence of cholesterol. Cholesterol had the opposite effect on the HAS2 activity in liposomes composed of phosphatidylethanolamine or phosphatidylserine. Taken together, the present data suggests a clear functional association between HAS activity and cholesterol-dependent alterations in the physical and chemical properties of cell membranes.
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Affiliation(s)
- Pawared Ontong
- Division of Engineering (Biotechnology), Graduate School of Engineering, Kyoto Sangyo University, Kita-ku, Kyoto 603-8555, Japan
| | - Yasuyo Hatada
- Department of Molecular Oncology, Division of Molecular and Cellular Biology, Institute of Pathogenesis and Disease Prevention, Shinshu University Graduate School of Medicine, Matsumoto, Nagano 390-8621, Japan
| | - Shun'ichiro Taniguchi
- Department of Molecular Oncology, Division of Molecular and Cellular Biology, Institute of Pathogenesis and Disease Prevention, Shinshu University Graduate School of Medicine, Matsumoto, Nagano 390-8621, Japan
| | - Ikuko Kakizaki
- Department of Glycotechnology, Center for Advanced Medical Research, Hirosaki University Graduate School of Medicine, 5 Zaifu-cho, Hirosaki 036-8562, Japan
| | - Naoki Itano
- Division of Engineering (Biotechnology), Graduate School of Engineering, Kyoto Sangyo University, Kita-ku, Kyoto 603-8555, Japan; Department of Molecular Biosciences, Faculty of Life Sciences, Kyoto Sangyo University, Kita-ku, Kyoto 603-8555, Japan.
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19
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Kim K, Choi SQ, Zell ZA, Squires TM, Zasadzinski JA. Effect of cholesterol nanodomains on monolayer morphology and dynamics. Proc Natl Acad Sci U S A 2013; 110:E3054-60. [PMID: 23901107 PMCID: PMC3746890 DOI: 10.1073/pnas.1303304110] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
At low mole fractions, cholesterol segregates into 10- to 100-nm-diameter nanodomains dispersed throughout primarily dipalmitoylphosphatidylcholine (DPPC) domains in mixed DPPC:cholesterol monolayers. The nanodomains consist of 6:1 DPPC:cholesterol "complexes" that decorate and lengthen DPPC domain boundaries, consistent with a reduced line tension, λ. The surface viscosity of the monolayer, ηs, decreases exponentially with the area fraction of the nanodomains at fixed surface pressure over the 0.1- to 10-Hz range of frequencies common to respiration. At fixed cholesterol fraction, the surface viscosity increases exponentially with surface pressure in similar ways for all cholesterol fractions. This increase can be explained with a free-area model that relates ηs to the pure DPPC monolayer compressibility and collapse pressure. The elastic modulus, G', initially decreases with cholesterol fraction, consistent with the decrease in λ expected from the line-active nanodomains, in analogy to 3D emulsions. However, increasing cholesterol further causes a sharp increase in G' between 4 and 5 mol% cholesterol owing to an evolution in the domain morphology, so that the monolayer is elastic rather than viscous over 0.1-10 Hz. Understanding the effects of small mole fractions of cholesterol should help resolve the controversial role cholesterol plays in human lung surfactants and may give clues as to how cholesterol influences raft formation in cell membranes.
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Affiliation(s)
- KyuHan Kim
- Department of Chemical Engineering, University of California, Santa Barbara, CA 93106; and
| | - Siyoung Q. Choi
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455
| | - Zachary A. Zell
- Department of Chemical Engineering, University of California, Santa Barbara, CA 93106; and
| | - Todd M. Squires
- Department of Chemical Engineering, University of California, Santa Barbara, CA 93106; and
| | - Joseph A. Zasadzinski
- Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455
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20
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Davis JH, Ziani L, Schmidt ML. Critical fluctuations in DOPC/DPPC-d62/cholesterol mixtures: 2H magnetic resonance and relaxation. J Chem Phys 2013; 139:045104. [DOI: 10.1063/1.4816366] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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21
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Khelashvili G, Harries D. How Cholesterol Tilt Modulates the Mechanical Properties of Saturated and Unsaturated Lipid Membranes. J Phys Chem B 2013; 117:2411-21. [DOI: 10.1021/jp3122006] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Affiliation(s)
- George Khelashvili
- Department of Physiology and Biophysics, Weill Cornell Medical College, New York,
New York 10065, United States
| | - Daniel Harries
- Institute of Chemistry and the Fritz Haber Research Center, The Hebrew University of Jerusalem,
Jerusalem 91904, Israel
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22
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Khelashvili G, Harries D. How sterol tilt regulates properties and organization of lipid membranes and membrane insertions. Chem Phys Lipids 2013; 169:113-23. [PMID: 23291283 DOI: 10.1016/j.chemphyslip.2012.12.006] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2012] [Revised: 12/17/2012] [Accepted: 12/21/2012] [Indexed: 01/08/2023]
Abstract
Serving as a crucial component of mammalian cells, cholesterol critically regulates the functions of biomembranes. This review focuses on a specific property of cholesterol and other sterols: the tilt modulus χ that quantifies the energetic cost of tilting sterol molecules inside the lipid membrane. We show how χ is involved in determining properties of cholesterol-containing membranes, and detail a novel approach to quantify its value from atomistic molecular dynamics (MD) simulations. Specifically, we link χ with other structural, thermodynamic, and mechanical properties of cholesterol-containing lipid membranes, and delineate how this useful parameter can be obtained from the sterol tilt probability distributions derived from relatively small-scale unbiased MD simulations. We demonstrate how the tilt modulus quantitatively describes the aligning field that sterol molecules create inside the phospholipid bilayers, and we relate χ to the bending rigidity of the lipid bilayer through effective tilt and splay energy contributions to the elastic deformations. Moreover, we show how χ can conveniently characterize the "condensing effect" of cholesterol on phospholipids. Finally, we demonstrate the importance of this cholesterol aligning field to the proper folding and interactions of membrane peptides. Given the relative ease of obtaining the tilt modulus from atomistic simulations, we propose that χ can be routinely used to characterize the mechanical properties of sterol/lipid bilayers, and can also serve as a required fitting parameter in multi-scaled simulations of lipid membrane models to relate the different levels of coarse-grained details.
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Affiliation(s)
- George Khelashvili
- Department of Physiology and Biophysics, Weill Medical College of Cornell University, 1300 York Avenue, Room LC-501B, New York, NY, USA.
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23
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Machta BB, Veatch SL, Sethna JP. Critical Casimir forces in cellular membranes. PHYSICAL REVIEW LETTERS 2012; 109:138101. [PMID: 23030121 PMCID: PMC3711834 DOI: 10.1103/physrevlett.109.138101] [Citation(s) in RCA: 62] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/14/2012] [Indexed: 05/23/2023]
Abstract
Recent experiments suggest that membranes of living cells are tuned close to a miscibility critical point in the two-dimensional Ising universality class. We propose that one role for this proximity to criticality in live cells is to provide a conduit for relatively long-range critical Casimir forces. Using techniques from conformal field theory we calculate potentials of mean force between membrane bound inclusions mediated by their local interactions with the composition order parameter. We verify these calculations using Monte Carlo simulations where we also compare critical and off-critical results. Our findings suggest that membrane bound proteins experience weak yet long-range forces mediated by critical composition fluctuations in the plasma membranes of living cells.
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Affiliation(s)
- Benjamin B Machta
- Department of Physics, Cornell University, Ithaca, New York 14850, USA
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24
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Fischer T, Risselada HJ, Vink RLC. Membrane lateral structure: the influence of immobilized particles on domain size. Phys Chem Chem Phys 2012; 14:14500-8. [PMID: 22782576 DOI: 10.1039/c2cp41417a] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
In experiments on model membranes, formation of large domains of different lipid composition is readily observed. However, no such phase separation is observed in the membranes of intact cells. Instead, small transient inhomogeneities called lipid rafts are expected in these systems. One of the numerous attempts to explain small domains refers to the coupling of the membrane to its surroundings, which leads to the immobilization of some of the membrane molecules. These immobilized molecules then act as static obstacles for the remaining mobile ones. We present detailed Molecular Dynamics simulations demonstrating that this can indeed account for small domains. This confirms previous Monte Carlo studies based on simplified models. Furthermore, by directly comparing domain structures obtained using Molecular Dynamics to Monte Carlo simulations of the Ising model, we demonstrate that domain formation in the presence of obstacles is remarkably insensitive to the details of the molecular interactions.
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Affiliation(s)
- Timo Fischer
- Institute of Theoretical Physics, Georg-August-Universität Göttingen, Göttingen, Germany
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25
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Velikova V, Várkonyi Z, Szabó M, Maslenkova L, Nogues I, Kovács L, Peeva V, Busheva M, Garab G, Sharkey TD, Loreto F. Increased thermostability of thylakoid membranes in isoprene-emitting leaves probed with three biophysical techniques. PLANT PHYSIOLOGY 2011; 157:905-16. [PMID: 21807886 PMCID: PMC3192565 DOI: 10.1104/pp.111.182519] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2011] [Accepted: 07/28/2011] [Indexed: 05/19/2023]
Abstract
Three biophysical approaches were used to get insight into increased thermostability of thylakoid membranes in isoprene-emittingplants.Arabidopsis (Arabidopsis thaliana) plants genetically modified to make isoprene and Platanus orientalis leaves, in which isoprene emission was chemically inhibited, were used. First, in the circular dichroism spectrum the transition temperature of the main band at 694 nm was higher in the presence of isoprene, indicating that the heat stability of chiral macrodomains of chloroplast membranes, and specifically the stability of ordered arrays of light-harvesting complex II-photosystem II in the stacked region of the thylakoid grana, was improved in the presence of isoprene. Second, the decay of electrochromic absorbance changes resulting from the electric field component of the proton motive force (ΔA₅₁₅) was evaluated following single-turnover saturating flashes. The decay of ΔA₅₁₅ was faster in the absence of isoprene when leaves of Arabidopsis and Platanus were exposed to high temperature, indicating that isoprene protects the thylakoid membranes against leakiness at elevated temperature. Finally, thermoluminescence measurements revealed that S₂Q(B)⁻ charge recombination was shifted to higher temperature in Arabidopsis and Platanus plants in the presence of isoprene, indicating higher activation energy for S₂Q(B)⁻ redox pair, which enables isoprene-emitting plants to perform efficient primary photochemistry of photosystem II even at higher temperatures. The data provide biophysical evidence that isoprene improves the integrity and functionality of the thylakoid membranes at high temperature. These results contribute to our understanding of isoprene mechanism of action in plant protection against environmental stresses.
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Affiliation(s)
| | | | | | | | | | | | | | | | | | | | - Francesco Loreto
- Institute of Plant Physiology and Genetics (V.V., L.M., V.P.) and Institute of Biophysics and Biomedical Engineering (M.B.), Bulgarian Academy of Sciences, 1113 Sofia, Bulgaria; Institute of Plant Biology, Biological Research Center, Hungarian Academy of Sciences, 6726 Szeged, Hungary (Z.V., M.S., L.K., G.G.); Institute of Agroenvironmental and Forest Biology, National Research Council, 00015 Monterotondo, Rome, Italy (I.N.); Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824 (T.D.S.); Institute for Plant Protection, National Research Council, 50019 Sesto Fiorentino, Florence, Italy (F.L.)
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26
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Gallier S, Gragson D, Jiménez-Flores R, Everett DW. Surface characterization of bovine milk phospholipid monolayers by Langmuir isotherms and microscopic techniques. JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY 2010; 58:12275-12285. [PMID: 21067228 PMCID: PMC4392927 DOI: 10.1021/jf102185a] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Monolayers were prepared from phospholipids extracted from bovine milk and used as a model system to mimic the native milk fat globule membrane (MFGM) surface structure in various microscopic experiments. The natural complex mixtures of phospholipids were isolated from bovine raw milk, raw cream, processed whole milk, and buttermilk powder by total lipid extraction and solid-phase extraction. A Langmuir film balance mounted on an epifluorescence microscope was used to analyze the physical behavior of the monolayer films and the phase coexistence resulting from the formation of phospholipid microdomains within these films. Atomic force microscopy was used for nanometer-scale topographic resolution of the microdomains. This study allowed comparison of the behavior of phospholipid monolayers from dairy products at different stages of processing, analysis of the formation of microdomains, and the study of the effect of milk processing on lipid-lipid interactions and phase coexistence. It was observed that milk processing changes the physical behavior of phospholipid monolayers by altering the phospholipid profile and the fatty acid distribution.
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Affiliation(s)
- Sophie Gallier
- Department of Food Science, University of Otago, Dunedin, New Zealand
- Dairy Products Technology Center, California Polytechnic State University, San Luis Obispo, California, USA
| | - Derek Gragson
- Department of Chemistry and Biochemistry, California Polytechnic State University, San Luis Obispo, California, USA
| | - Rafael Jiménez-Flores
- Dairy Products Technology Center, California Polytechnic State University, San Luis Obispo, California, USA
| | - David W. Everett
- Department of Food Science, University of Otago, Dunedin, New Zealand
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27
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Celli A, Gratton E. Dynamics of lipid domain formation: fluctuation analysis. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2009; 1798:1368-76. [PMID: 20025848 DOI: 10.1016/j.bbamem.2009.12.002] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/29/2009] [Revised: 11/14/2009] [Accepted: 12/02/2009] [Indexed: 01/02/2023]
Abstract
Scanning-fluctuation correlation spectroscopy was used to detect subresolution organizational fluctuations in the lipid liquid-crystalline phase for single lipid model systems. We used the fluorescent probe Laurdan which is sensitive to the amount of water in the membrane to show that there is a spatial heterogeneity on the scale of few pixels (the size of the pixel is 50 nm). We calculated the pixel variance of the GP function and we found that the variance has a peak at the phase transition for 3 different samples made of pure lipids. The pixel variance has an abrupt change at the phase transition of the membrane and then it slowly decreases at higher temperature. The relatively large variance of the GP indicates that the liquid phase of the membrane is quite heterogeneous even several degrees higher than the phase transition temperature. We interpreted this result as evidence of an underlying microscale structure of the membrane in which water is not uniformly distributed at the micron scale. Imaging of these microstructures shows that the pixels with different GP tend to concentrate in specific domains in the membrane. In the case of single lipid membrane, the statistical and fluctuation analysis of the GP data shows that even such simple lipid systems are capable of generating and maintaining stable structural and organizational heterogeneities.
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Affiliation(s)
- Anna Celli
- Dermatology Department, University of California San Francisco, San Francisco, CA 94121, USA
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28
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Oreopoulos J, Yip CM. Combinatorial microscopy for the study of protein–membrane interactions in supported lipid bilayers: Order parameter measurements by combined polarized TIRFM/AFM. J Struct Biol 2009; 168:21-36. [DOI: 10.1016/j.jsb.2009.02.011] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2008] [Revised: 02/23/2009] [Accepted: 02/24/2009] [Indexed: 02/06/2023]
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29
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Oreopoulos J, Yip CM. Probing membrane order and topography in supported lipid bilayers by combined polarized total internal reflection fluorescence-atomic force microscopy. Biophys J 2009; 96:1970-84. [PMID: 19254557 DOI: 10.1016/j.bpj.2008.11.041] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2008] [Accepted: 11/17/2008] [Indexed: 11/19/2022] Open
Abstract
Determining the local structure, dynamics, and conformational requirements for protein-protein and protein-lipid interactions in membranes is critical to understanding biological processes ranging from signaling to the translocating and membranolytic action of antimicrobial peptides. We report here the application of a combined polarized total internal reflection fluorescence microscopy-in situ atomic force microscopy platform. This platform's ability to image membrane orientational order was demonstrated on DOPC/DSPC/cholesterol model membranes containing the fluorescent membrane probe, DiI-C(20) or BODIPY-PC. Spatially resolved order parameters and fluorophore tilt angles extracted from the polarized total internal reflection fluorescence microscopy images were in good agreement with the topographical details resolved by in situ atomic force microscopy, portending use of this technique for high-resolution characterization of membrane domain structures and peptide-membrane interactions.
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Affiliation(s)
- John Oreopoulos
- Institute of Biomaterials and Biomedical Engineering, Terrence Donnelly Centre for Cellular and Biomolecular Research, University of Toronto, Toronto, Canada
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30
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Davis JH, Clair JJ, Juhasz J. Phase equilibria in DOPC/DPPC-d62/cholesterol mixtures. Biophys J 2009; 96:521-39. [PMID: 19167302 DOI: 10.1016/j.bpj.2008.09.042] [Citation(s) in RCA: 134] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2008] [Accepted: 09/30/2008] [Indexed: 01/18/2023] Open
Abstract
There is broad interest in the question of fluid-fluid phase coexistence in membranes, in particular, whether evidence for liquid-disordered (l(d))-liquid-ordered (l(o)) two-phase regions or membrane "rafts" can be found in natural membranes. In model membrane systems, such phase behavior is observed, and we have used deuterium nuclear magnetic resonance spectroscopy to map the phase boundaries of ternary mixtures containing 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), chain-perdeuterated 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC-d(62)), and cholesterol. For both this ternary model system and the binary DPPC-d(62)/cholesterol system, we present clear evidence for l(d)-l(o) two-phase coexistence. We have selected sample compositions to focus on this region of fluid-fluid phase coexistence and to determine its temperature and composition ranges. The deuterium nuclear magnetic resonance spectra for compositions near the l(d)-l(o) phase boundary at high cholesterol concentrations show evidence of exchange broadening or critical fluctuations in composition, similar to that reported by Vist and Davis. There appears to be a line of critical compositions ranging from 48 degrees C for a DOPC/DPPC-d(62)/cholesterol composition of 0:75:25, to approximately -8 degrees C for the composition 57:14:29. At temperatures below this two-phase region, there is a region of three-phase coexistence (l(d)-l(o)-gel). These results are collected and presented in terms of a partial ternary phase diagram that is consistent with previously reported results of Vist and Davis.
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Affiliation(s)
- James H Davis
- Department of Physics, University of Guelph, Guelph, Ontario, Canada.
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31
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An introduction to critical points for biophysicists; observations of compositional heterogeneity in lipid membranes. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2008; 1788:53-63. [PMID: 18930706 DOI: 10.1016/j.bbamem.2008.09.010] [Citation(s) in RCA: 199] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2008] [Revised: 09/12/2008] [Accepted: 09/15/2008] [Indexed: 01/12/2023]
Abstract
Scaling laws associated with critical points have the power to greatly simplify our description of complex biophysical systems. We first review basic concepts and equations associated with critical phenomena for the general reader. We then apply these concepts to the specific biophysical system of lipid membranes. We recently reported that lipid membranes can contain composition fluctuations that behave in a manner consistent with the two-dimensional Ising universality class. Near the membrane's critical point, these fluctuations are micron-sized, clearly observable by fluorescence microscopy. At higher temperatures, above the critical point, we expect to find submicron fluctuations. In separate work, we have reported that plasma membranes isolated directly from cells exhibit the same Ising behavior as model membranes do. We review other models describing submicron lateral inhomogeneity in membranes, including microemulsions, nanodomains, and mean field critical fluctuations, and we describe experimental tests that may distinguish these models.
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32
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Veatch SL, Cicuta P, Sengupta P, Honerkamp-Smith A, Holowka D, Baird B. Critical fluctuations in plasma membrane vesicles. ACS Chem Biol 2008; 3:287-93. [PMID: 18484709 DOI: 10.1021/cb800012x] [Citation(s) in RCA: 332] [Impact Index Per Article: 20.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
We demonstrate critical behavior in giant plasma membrane vesicles (GPMVs) that are isolated directly from living cells. GPMVs contain two liquid phases at low temperatures and one liquid phase at high temperatures and exhibit transition temperatures in the range of 15 to 25 degrees C. In the two-phase region, line tensions linearly approach zero as temperature is increased to the transition. In the one-phase region, micrometer-scale composition fluctuations occur and become increasingly large and long-lived as temperature is decreased to the transition. These results indicate proximity to a critical point and are quantitatively consistent with established theory. Our observations of robust critical fluctuations suggest that the compositions of mammalian plasma membranes are tuned to reside near a miscibility critical point and that heterogeneity corresponding to < 50 nm-sized compositional fluctuations are present in GPMV membranes at physiological temperatures. Our results provide new insights for plasma membrane heterogeneity that may be related to functional lipid raft domains in live cells.
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Affiliation(s)
- Sarah L. Veatch
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853
| | - Pietro Cicuta
- Cavendish Laboratory University of Cambridge, Cambridge, UK CB30HE
| | - Prabuddha Sengupta
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853
| | | | - David Holowka
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853
| | - Barbara Baird
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853
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Line tensions, correlation lengths, and critical exponents in lipid membranes near critical points. Biophys J 2008; 95:236-46. [PMID: 18424504 DOI: 10.1529/biophysj.107.128421] [Citation(s) in RCA: 233] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Membranes containing a wide variety of ternary mixtures of high chain-melting temperature lipids, low chain-melting temperature lipids, and cholesterol undergo lateral phase separation into coexisting liquid phases at a miscibility transition. When membranes are prepared from a ternary lipid mixture at a critical composition, they pass through a miscibility critical point at the transition temperature. Since the critical temperature is typically on the order of room temperature, membranes provide an unusual opportunity in which to perform a quantitative study of biophysical systems that exhibit critical phenomena in the two-dimensional Ising universality class. As a critical point is approached from either high or low temperature, the scale of fluctuations in lipid composition, set by the correlation length, diverges. In addition, as a critical point is approached from low temperature, the line tension between coexisting phases decreases to zero. Here we quantitatively evaluate the temperature dependence of line tension between liquid domains and of fluctuation correlation lengths in lipid membranes to extract a critical exponent, nu. We obtain nu = 1.2 +/- 0.2, consistent with the Ising model prediction nu = 1. We also evaluate the probability distributions of pixel intensities in fluorescence images of membranes. From the temperature dependence of these distributions above the critical temperature, we extract an independent critical exponent of beta = 0.124 +/- 0.03, which is consistent with the Ising prediction of beta = 1/8.
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