1
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Heimburg T. The excitable fluid mosaic. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2023; 1865:184104. [PMID: 36642342 DOI: 10.1016/j.bbamem.2022.184104] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/21/2022] [Revised: 11/23/2022] [Accepted: 12/13/2022] [Indexed: 01/15/2023]
Abstract
The Fluid Mosaic Model by Singer & Nicolson proposes that biological membranes consist of a fluid lipid layer into which integral proteins are embedded. The lipid membrane acts as a two-dimensional liquid in which the proteins can diffuse and interact. Until today, this view seems very reasonable and is the predominant picture in the literature. However, there exist broad melting transitions in biomembranes some 10-20 degrees below physiological temperatures that reach up to body temperature. Since they are found below body temperature, Singer & Nicolson did not pay any further attention to the melting process. But this is a valid view only as long as nothing happens. The transition temperature can be influenced by membrane tension, pH, ionic strength and other variables. Therefore, it is not generally correct that the physiological temperature is above this transition. The control over the membrane state by changing the intensive variables renders the membrane as a whole excitable. One expects phase behavior and domain formation that leads to protein sorting and changes in membrane function. Thus, the lipids become an active ingredient of the biological membrane. The melting transition affects the elastic constants of the membrane. This allows for the generation of propagating pulses in nerves and the formation of ion-channel-like pores in the lipid membranes. Here we show that on top of the fluid mosaic concept there exists a wealth of excitable phenomena that go beyond the original picture of Singer & Nicolson.1.
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Affiliation(s)
- Thomas Heimburg
- Membrane Biophysics Group, Niels Bohr Institute, University of Copenhagen, Denmark.
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2
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Biophysical quantification of unitary solute and solvent permeabilities to enable translation to membrane science. J Memb Sci 2022. [DOI: 10.1016/j.memsci.2022.121308] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
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3
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Endoplasmic reticulum phospholipid scramblase activity revealed after protein reconstitution into giant unilamellar vesicles containing a photostable lipid reporter. Sci Rep 2021; 11:14364. [PMID: 34257324 PMCID: PMC8277826 DOI: 10.1038/s41598-021-93664-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2021] [Accepted: 06/28/2021] [Indexed: 02/04/2023] Open
Abstract
Transbilayer movement of phospholipids in biological membranes is mediated by a diverse set of lipid transporters. Among them are scramblases that facilitate a rapid bi-directional movement of lipids without metabolic energy input. Here, we established a new fluorescence microscopy-based assay for detecting phospholipid scramblase activity of membrane proteins upon their reconstitution into giant unilamellar vesicles formed from proteoliposomes by electroformation. The assay is based on chemical bleaching of fluorescence of a photostable ATTO-dye labeled phospholipid with the membrane-impermeant reductant sodium dithionite. We demonstrate that this new methodology is suitable for the study of the scramblase activity of the yeast endoplasmic reticulum at single vesicle level.
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4
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Bagatolli LA, Stock RP, Olsen LF. Coupled Response of Membrane Hydration with Oscillating Metabolism in Live Cells: An Alternative Way to Modulate Structural Aspects of Biological Membranes? Biomolecules 2019; 9:E687. [PMID: 31684090 PMCID: PMC6921054 DOI: 10.3390/biom9110687] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2019] [Revised: 10/29/2019] [Accepted: 10/30/2019] [Indexed: 12/12/2022] Open
Abstract
We propose that active metabolic processes may regulate structural changes in biological membranes via the physical state of cell water. This proposition is based on recent results obtained from our group in yeast cells displaying glycolytic oscillations, where we demonstrated that there is a tight coupling between the oscillatory behavior of glycolytic metabolites (ATP, NADH) and the extent of the dipolar relaxation of intracellular water, which oscillates synchronously. The mechanism we suggest involves the active participation of a polarized intracellular water network whose degree of polarization is dynamically modulated by temporal ATP fluctuations caused by metabolism with intervention of a functional cytoskeleton, as conceived in the long overlooked association-induction hypothesis (AIH) of Gilbert Ling. Our results show that the polarized state of intracellular water can be propagated from the cytosol to regions containing membranes. Since changes in the extent of the polarization of water impinge on its chemical activity, we hypothesize that metabolism dynamically controls the local structure of cellular membranes via lyotropic effects. This hypothesis offers an alternative way to interpret membrane related phenomena (e.g., changes in local curvature pertinent to endo/exocytosis or dynamical changes in membranous organelle structure, among others) by integrating relevant but mostly overlooked physicochemical characteristics of the cellular milieu.
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Affiliation(s)
- Luis A Bagatolli
- Instituto de Investigación Médica Mercedes y Martín Ferreyra-INIMEC (CONICET)-Universidad Nacional de Córdoba, Friuli 2434, Córdoba 5016, Argentina.
- Departamento de Química Biológica Ranwel Caputto, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Córdoba 5000, Argentina.
| | - Roberto P Stock
- MEMPHYS-International and Interdisciplinary Research Network, 5230 Odense, Denmark.
| | - Lars F Olsen
- University of Southern Denmark, Institute for Biochemistry and Molecular Biology, Campusvej 55, 5230 Odense, Denmark.
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5
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Raghuraman H, Chatterjee S, Das A. Site-Directed Fluorescence Approaches for Dynamic Structural Biology of Membrane Peptides and Proteins. Front Mol Biosci 2019; 6:96. [PMID: 31608290 PMCID: PMC6774292 DOI: 10.3389/fmolb.2019.00096] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2019] [Accepted: 09/11/2019] [Indexed: 12/31/2022] Open
Abstract
Membrane proteins mediate a number of cellular functions and are associated with several diseases and also play a crucial role in pathogenicity. Due to their importance in cellular structure and function, they are important drug targets for ~60% of drugs available in the market. Despite the technological advancement and recent successful outcomes in determining the high-resolution structural snapshot of membrane proteins, the mechanistic details underlining the complex functionalities of membrane proteins is least understood. This is largely due to lack of structural dynamics information pertaining to different functional states of membrane proteins in a membrane environment. Fluorescence spectroscopy is a widely used technique in the analysis of functionally-relevant structure and dynamics of membrane protein. This review is focused on various site-directed fluorescence (SDFL) approaches and their applications to explore structural information, conformational changes, hydration dynamics, and lipid-protein interactions of important classes of membrane proteins that include the pore-forming peptides/proteins, ion channels/transporters and G-protein coupled receptors.
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Affiliation(s)
- H. Raghuraman
- Crystallography and Molecular Biology Division, Saha Institute of Nuclear Physics, Homi Bhabha National Institute, Kolkata, India
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6
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Fusion assays for model membranes: a critical review. ADVANCES IN BIOMEMBRANES AND LIPID SELF-ASSEMBLY 2019. [DOI: 10.1016/bs.abl.2019.09.003] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/09/2022]
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7
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Betaneli V, Mücksch J, Schwille P. Fluorescence Correlation Spectroscopy to Examine Protein-Lipid Interactions in Membranes. Methods Mol Biol 2019; 2003:415-447. [PMID: 31218628 DOI: 10.1007/978-1-4939-9512-7_18] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Fluorescence correlation spectroscopy (FCS) is a versatile technique to study membrane dynamics and protein-lipid interactions. It can provide information about diffusion coefficients, concentrations, and molecular interactions of proteins and lipids in the membrane. These parameters allow for the determination of protein partitioning into different lipid environments, the identification of lipid domains, and the detection of lipid-protein complexes on the membrane. During the last decades, FCS studies were successfully performed on model membrane systems as also on living cells, to characterize protein-lipid interactions. Recent developments of the method described here improved quantitative measurements on membranes and decreased the number of potential artifacts. The aim of this chapter is to provide the reader with the necessary information and some practical guidelines to perform FCS studies on artificial and cellular membranes.
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Affiliation(s)
- Viktoria Betaneli
- Medical Faculty "Carl Gustav Carus", Institute of Physiological Chemistry, Technische Universität Dresden, Dresden, Germany
| | - Jonas Mücksch
- Max Planck Institute of Biochemistry, Martinsried, Germany
| | - Petra Schwille
- Max Planck Institute of Biochemistry, Martinsried, Germany.
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8
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Methods of reconstitution to investigate membrane protein function. Methods 2018; 147:126-141. [DOI: 10.1016/j.ymeth.2018.02.012] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2018] [Accepted: 02/13/2018] [Indexed: 02/06/2023] Open
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9
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Kirchhoff H. Structure-function relationships in photosynthetic membranes: Challenges and emerging fields. PLANT SCIENCE : AN INTERNATIONAL JOURNAL OF EXPERIMENTAL PLANT BIOLOGY 2018; 266:76-82. [PMID: 29241569 DOI: 10.1016/j.plantsci.2017.09.021] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/07/2017] [Revised: 09/26/2017] [Accepted: 09/29/2017] [Indexed: 05/17/2023]
Abstract
Oxygenic photosynthesis is a fundamental biological process that shaped the earth's biosphere. The process of energy transformation is hosted in highly specialized thylakoid membranes that adjust their architecture in response to environmental cues at different structural levels leading to the adjustment of photosynthetic functions. This review presents structure-function dynamics ranging from the whole membrane system over the mesoscopic level (protein ensembles) down to interactions between lipids and protein complexes. On the whole membrane level, thylakoid membranes constantly change their overall shape (e.g. membranes swell and shrink or destack and stack) that controls vital functions of energy transformation. Furthermore, the physical connection and transition between stacked grana thylakoid and unstacked membrane regions that determines mass transport between these sub-compartments is a crucial open question. On the mesoscopic level, it turns out that reorganizations between disordered and ordered protein arrangements is central for light harvesting and lateral diffusion processes. It has to be unraveled how changes in mesoscopic protein organization are controlled. Finally, dynamic physicochemical properties of the lipid bilayer can determine the structure and organization of photosynthetic membrane proteins, a field that is highly neglected so far. This review focusses on open questions and challenging problems in photosynthesis research.
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Affiliation(s)
- Helmut Kirchhoff
- Institute of Biological Chemistry, Washington State University, P.O. Box 646340, Pullman, 99164, WA, USA.
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10
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Hermann E, Ries J, García-Sáez AJ. Scanning fluorescence correlation spectroscopy on biomembranes. Methods Mol Biol 2015; 1232:181-197. [PMID: 25331137 DOI: 10.1007/978-1-4939-1752-5_15] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Fluorescence correlation spectroscopy (FCS) is a powerful quantitative method to study dynamical properties of biophysical systems. It exploits the temporal autocorrelation of fluorescence intensity fluctuations originating from a tiny volume (~fL). A theoretical model function can be then fitted to the measured auto-correlation curve to obtain physical parameters such as local concentration and diffusion time. However, the application of FCS on membranes is coupled to several difficulties like accurate positioning and stability of the set-up. In this book chapter, we explain the theoretical framework of point FCS and Scanning FCS (SFCS), which is a variation especially suitable for membrane studies. We present a list of materials necessary for SFCS studies on Giant Unilamellar Vesicles (GUVs). Finally, we provide simple protocols for the preparation of GUVs, calibration of the microscope setup, and acquisition and analysis of SFCS data to determine diffusion coefficients and concentrations of fluorescent particles embedded in lipid membranes.
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Affiliation(s)
- Eduard Hermann
- Max Planck Institute for Intelligent Systems, Heisenbergstr 3, 70569, Stuttgart, Germany,
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11
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Unsay JD, García-Sáez AJ. Scanning fluorescence correlation spectroscopy in model membrane systems. Methods Mol Biol 2013; 1033:185-205. [PMID: 23996179 DOI: 10.1007/978-1-62703-487-6_13] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Fluorescence correlation spectroscopy (FCS) is an emerging technique employed in biophysical studies that exploits the temporal autocorrelation of fluorescence intensity fluctuations measured in a tiny volume (in the order of fL). The autocorrelation curve derived from the fluctuations can then be fitted with diffusion models to obtain parameters such as diffusion time and number of particles in the diffusion volume/area. Application of FCS to membranes allows studying membrane component dynamics, which includes mobility and interactions between the components. However, FCS encounters several difficulties like accurate positioning and stability of the setup when applied to membranes. Here, we describe the theoretical basis of point FCS as well as the scanning FCS (SFCS) approach, which is a practical way to address the challenges of FCS with membranes. We also list materials necessary for FCS experiments on two model membrane systems: (1) supported lipid bilayers and (2) giant unilamellar vesicles. Finally, we present simple protocols for the preparation of these model membrane systems, calibration of the microscope setup for FCS, and acquisition and analysis of point FCS and SFCS data so that diffusion coefficients and concentrations of fluorescent probes within lipid membranes can be calculated.
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12
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Betaneli V, Schwille P. Fluorescence correlation spectroscopy to examine protein-lipid interactions in membranes. Methods Mol Biol 2013; 974:253-278. [PMID: 23404280 DOI: 10.1007/978-1-62703-275-9_12] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Fluorescence correlation spectroscopy (FCS) is a versatile technique to study membrane dynamics and protein-lipid interactions. It can provide information about diffusion coefficients, concentrations, and molecular interactions of proteins and lipids in the membrane. These parameters allow the determination of protein partitioning into different lipid environments, the identification of lipid domains, and the detection of lipid-protein complexes on the membrane. During the last decade, FCS studies were successfully performed on model membrane systems as also on living cells, to characterize protein-lipid interactions. Recent developments of the method described here improved quantitative measurements on membranes and decreased the number of potential artifacts. The aim of this chapter is to provide the reader with the necessary information and some practical guidelines to perform FCS studies on artificial and cellular membranes.
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Affiliation(s)
- Viktoria Betaneli
- Biophysics, BIOTEC, Technische Universitat Dresden, Dresden, Germany
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13
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Smith AW. Lipid–protein interactions in biological membranes: A dynamic perspective. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2012; 1818:172-7. [DOI: 10.1016/j.bbamem.2011.06.015] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/31/2011] [Revised: 06/21/2011] [Accepted: 06/23/2011] [Indexed: 01/31/2023]
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14
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Aimon S, Manzi J, Schmidt D, Poveda Larrosa JA, Bassereau P, Toombes GES. Functional reconstitution of a voltage-gated potassium channel in giant unilamellar vesicles. PLoS One 2011; 6:e25529. [PMID: 21998666 PMCID: PMC3188570 DOI: 10.1371/journal.pone.0025529] [Citation(s) in RCA: 88] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2011] [Accepted: 09/05/2011] [Indexed: 11/19/2022] Open
Abstract
Voltage-gated ion channels are key players in cellular excitability. Recent studies suggest that their behavior can depend strongly on the membrane lipid composition and physical state. In vivo studies of membrane/channel and channel/channel interactions are challenging as membrane properties are actively regulated in living cells, and are difficult to control in experimental settings. We developed a method to reconstitute functional voltage-gated ion channels into cell-sized Giant Unilamellar Vesicles (GUVs) in which membrane composition, tension and geometry can be controlled. First, a voltage-gated potassium channel, KvAP, was purified, fluorescently labeled and reconstituted into small proteoliposomes. Small proteoliposomes were then converted into GUVs via electroformation. GUVs could be formed using different lipid compositions and buffers containing low (5 mM) or near-physiological (100 mM) salt concentrations. Protein incorporation into GUVs was characterized with quantitative confocal microscopy, and the protein density of GUVs was comparable to the small proteoliposomes from which they were formed. Furthermore, patch-clamp measurements confirmed that the reconstituted channels retained potassium selectivity and voltage-gated activation. GUVs containing functional voltage-gated ion channels will allow the study of channel activity, distribution and diffusion while controlling membrane state, and should prove a powerful tool for understanding how the membrane modulates cellular excitability.
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Affiliation(s)
- Sophie Aimon
- Unité Mixte de Recherche (UMR) 168, Physico-Chimie Curie, Centre National de la Recherche Scientifique (CNRS), Institut Curie, Centre de Recherche, Université Pierre et Marie Curie, Paris, France
| | - John Manzi
- Unité Mixte de Recherche (UMR) 168, Physico-Chimie Curie, Centre National de la Recherche Scientifique (CNRS), Institut Curie, Centre de Recherche, Université Pierre et Marie Curie, Paris, France
| | - Daniel Schmidt
- Howard Hughes Medical Institute, Laboratory of Molecular Neurobiology and Biophysics, Rockefeller University, New York, New York, United States of America
| | | | - Patricia Bassereau
- Unité Mixte de Recherche (UMR) 168, Physico-Chimie Curie, Centre National de la Recherche Scientifique (CNRS), Institut Curie, Centre de Recherche, Université Pierre et Marie Curie, Paris, France
- * E-mail:
| | - Gilman E. S. Toombes
- Unité Mixte de Recherche (UMR) 168, Physico-Chimie Curie, Centre National de la Recherche Scientifique (CNRS), Institut Curie, Centre de Recherche, Université Pierre et Marie Curie, Paris, France
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15
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Meilhac N, Destainville N. Clusters of proteins in biomembranes: insights into the roles of interaction potential shapes and of protein diversity. J Phys Chem B 2011; 115:7190-9. [PMID: 21528886 DOI: 10.1021/jp1099865] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
It has recently been proposed that proteins embedded in lipidic biomembranes can spontaneously self-organize into stable small clusters, or membrane nanodomains, due to the competition between short-range attractive and longer-range repulsive forces between proteins, specific to these systems. In this paper, we carry on our investigation, by Monte Carlo simulations, of different aspects of cluster phases of proteins in biomembranes. First, we compare different long-range potentials (including notably three-body terms) to demonstrate that the existence of cluster phases should be quite generic. Furthermore, a real membrane contains hundreds of different protein species that are far from being randomly distributed in these nanodomains. We take this protein diversity into account by modulating protein-protein interaction potentials both at short and longer range. We confirm theoretical predictions in terms of biological cluster specialization by deciphering how clusters recruit only a few protein species. In this respect, we highlight that cluster phases can turn out to be an advantage at the biological level, for example by enhancing the cell response to external stimuli.
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Affiliation(s)
- Nicolas Meilhac
- Université de Toulouse, UPS, Laboratoire de Physique Théorique (IRSAMC), Toulouse, France
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16
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A Multiparametric Fluorescence Approach for Biomembrane Studies. ACTA ACUST UNITED AC 2011. [DOI: 10.1016/b978-0-12-387721-5.00005-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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17
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Effect of energy metabolism on protein motility in the bacterial outer membrane. Biophys J 2009; 97:1305-12. [PMID: 19720018 DOI: 10.1016/j.bpj.2009.06.027] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2009] [Revised: 06/12/2009] [Accepted: 06/15/2009] [Indexed: 11/21/2022] Open
Abstract
We demonstrate the energy dependence of the motion of a porin, the lambda-receptor, in the outer membrane of living Escherichia coli by single molecule investigations. By poisoning the bacteria with arsenate and azide, the bacterial energy metabolism was stopped. The motility of individual lambda-receptors significantly and rapidly decreased upon energy depletion. We suggest two different causes for the ceased motility upon comprised energy metabolism: One possible cause is that the cell uses energy to actively wiggle its proteins, this energy being one order-of-magnitude larger than thermal energy. Another possible cause is an induced change in the connection between the lambda-receptor and the membrane structure, for instance by a stiffening of part of the membrane structure. Treatment of the cells with ampicillin, which directly targets the bacterial cell wall by inhibiting cross-linking of the peptidoglycan layer, had an effect similar to energy depletion and the motility of the lambda-receptor significantly decreased. Since the lambda-receptor is closely linked to the peptidoglycan layer, we propose that lambda-receptor motility is directly coupled to the constant and dynamic energy-consuming reconstruction of the peptidoglycan layer. The result of this motion could be to facilitate transport of maltose-dextrins through the porin.
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18
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Kriegsmann J, Gregor I, von der Hocht I, Klare J, Engelhard M, Enderlein J, Fitter J. Translational diffusion and interaction of a photoreceptor and its cognate transducer observed in giant unilamellar vesicles by using dual-focus FCS. Chembiochem 2009; 10:1823-9. [PMID: 19551796 DOI: 10.1002/cbic.200900251] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
In order to monitor membrane-protein binding in lipid bilayers at physiological protein concentrations, we employed the recently developed dual-focus fluorescence correlation spectroscopy (2fFCS) technique. In a case study on a photoreceptor consisting of seven transmembrane helices and its cognate transducer (two transmembrane helices), the lateral diffusion for these integral membrane proteins was analyzed in giant unilamellar vesicles (GUVs). The two-dimensional diffusion coefficients of both separately diffusing proteins differ significantly, with D = 2.2 x 10(-8) cm2 s(-1) for the photoreceptor and with D = 4.1 x 10(-8) cm2 s(-1) for the transducer. In GUVs with both membrane proteins present together, we observed significantly smaller diffusion coefficients for labelled transducer molecules; this indicates the presence of larger diffusing units and therefore intermolecular protein binding. Based on the phenomenological dependence of diffusion coefficients on the molecule's cylindrical radius, we are able to estimate the degree of membrane protein binding on a quantitative level.
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Affiliation(s)
- Jana Kriegsmann
- Research Centre Jülich, ISB 2: Molecular Biophysics, 52425 Jülich, Germany
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19
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Yamashita H, Voïtchovsky K, Uchihashi T, Contera SA, Ryan JF, Ando T. Dynamics of bacteriorhodopsin 2D crystal observed by high-speed atomic force microscopy. J Struct Biol 2009; 167:153-8. [DOI: 10.1016/j.jsb.2009.04.011] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2009] [Accepted: 04/28/2009] [Indexed: 10/20/2022]
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20
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Ries J, Chiantia S, Schwille P. Accurate determination of membrane dynamics with line-scan FCS. Biophys J 2009; 96:1999-2008. [PMID: 19254560 DOI: 10.1016/j.bpj.2008.12.3888] [Citation(s) in RCA: 126] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2008] [Accepted: 12/03/2008] [Indexed: 11/28/2022] Open
Abstract
Here we present an efficient implementation of line-scan fluorescence correlation spectroscopy (i.e., one-dimensional spatio-temporal image correlation spectroscopy) using a commercial laser scanning microscope, which allows the accurate measurement of diffusion coefficients and concentrations in biological lipid membranes within seconds. Line-scan fluorescence correlation spectroscopy is a calibration-free technique. Therefore, it is insensitive to optical artifacts, saturation, or incorrect positioning of the laser focus. In addition, it is virtually unaffected by photobleaching. Correction schemes for residual inhomogeneities and depletion of fluorophores due to photobleaching extend the applicability of line-scan fluorescence correlation spectroscopy to more demanding systems. This technique enabled us to measure accurate diffusion coefficients and partition coefficients of fluorescent lipids in phase-separating supported bilayers of three commonly used raft-mimicking compositions. Furthermore, we probed the temperature dependence of the diffusion coefficient in several model membranes, and in human embryonic kidney cell membranes not affected by temperature-induced optical aberrations.
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Affiliation(s)
- Jonas Ries
- Technical University of Dresden, Biotechnologisches Zentrum, Dresden, Germany
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21
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Fluorescence correlation spectroscopy for the study of membrane dynamics and protein/lipid interactions. Methods 2008; 46:116-22. [PMID: 18634881 DOI: 10.1016/j.ymeth.2008.06.011] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2008] [Revised: 05/27/2008] [Accepted: 06/05/2008] [Indexed: 11/22/2022] Open
Abstract
Fluorescence correlation spectroscopy (FCS) is a powerful technique to study dynamic biomolecular processes. It allows the estimation of concentrations, diffusion coefficients, molecular interactions, and other processes causing fluctuations in the fluorescence intensity, thus yielding information about aggregation processes, enzymatic reactions, or partition coefficients. During the last years, FCS has been successfully applied to model and cellular membranes, proving to be a promising tool for the study of membrane dynamics and protein/lipid interactions. Here we describe the theoretical basis of FCS and some practical implications for its application in membrane studies. We discuss sources of potential artifacts, such as membrane undulations, positioning of the detection volume, and photobleaching. Special attention is paid to aspects related to instrumentation and sample preparation as well as data acquisition and analysis. Finally, we comment on some strategies recently developed for the specific improvement of FCS measurements on membranes.
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22
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Monte Carlo study of single molecule diffusion can elucidate the mechanism of B cell synapse formation. Biophys J 2008; 95:1118-25. [PMID: 18456833 DOI: 10.1529/biophysj.107.122564] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
B cell receptors have been shown to cluster at the intercellular junction between a B cell and an antigen-presenting cell in the form of a segregated pattern of B cell receptor/antigen complexes known as an immunological synapse. We use random walk-based theoretical arguments and Monte Carlo simulations to study the effect of diffusion of surface-bound molecules on B cell synapse formation. Our results show that B cell synapse formation is optimal for a limited range of receptor-ligand complex diffusion coefficient values, typically one-to-two orders of magnitude lower than the diffusion coefficient of free receptors. Such lower mobility of receptor-ligand complexes can significantly affect the diffusion of a tagged receptor or ligand in an affinity dependent manner, as the binding/unbinding of such receptor or ligand molecules crucially depends on affinity. Our work shows how single molecule tracking experiments can be used to estimate the order of magnitude of the diffusion coefficient of receptor-ligand complexes, which is difficult to measure directly in experiments due to the finite lifetime of receptor-ligand bonds. We also show how such antigen movement data at the single molecule level can provide insight into the B cell synapse formation mechanism. Thus, our results can guide further single molecule tracking experiments to elucidate the synapse formation mechanism in B cells, and potentially in other immune cells.
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23
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Ries J, Schwille P. New concepts for fluorescence correlation spectroscopy on membranes. Phys Chem Chem Phys 2008; 10:3487-97. [PMID: 18548154 DOI: 10.1039/b718132a] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Fluorescence correlation spectroscopy (FCS) is a powerful tool to measure useful physical quantities such as concentrations, diffusion coefficients, diffusion modes or binding parameters, both in model and cell membranes. However, it can suffer from severe artifacts, especially in non-ideal systems. Here we assess the potential and limitations of standard confocal FCS on lipid membranes and present recent developments which facilitate accurate and quantitative measurements on such systems. In particular, we discuss calibration-free diffusion and concentration measurements using z-scan FCS and two focus FCS and present several approaches using scanning FCS to accurately measure slow dynamics. We also show how surface confined FCS enables the study of membrane dynamics even in presence of a strong cytosolic background and how FCS with a variable detection area can reveal submicroscopic heterogeneities in cell membranes.
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Affiliation(s)
- Jonas Ries
- Biotechnologisches Zentrum, TU Dresden, Tatzberg 47-51, Dresden, D-01307, Germany
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24
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Leitenberger SM, Reister-Gottfried E, Seifert U. Curvature coupling dependence of membrane protein diffusion coefficients. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2008; 24:1254-1261. [PMID: 18072795 DOI: 10.1021/la702319q] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
We consider the lateral diffusion of a protein interacting with the curvature of the membrane. The interaction energy is minimized if the particle is at a membrane position with a certain curvature that agrees with the spontaneous curvature of the particle. We employ stochastic simulations that take into account both the thermal fluctuations of the membrane and the diffusive behavior of the particle. In this study, we neglect the influence of the particle on the membrane dynamics, thus the membrane dynamics agrees with that of a freely fluctuating membrane. Overall, we find that this curvature coupling substantially enhances the diffusion coefficient. We compare the ratio of the projected or measured diffusion coefficient and the free intramembrane diffusion coefficient, which is a parameter of the simulations, with analytical results that rely on several approximations. We find that the simulations always lead to a somewhat smaller diffusion coefficient than that from our analytical approach. A detailed study of the correlations of the forces acting on the particle indicates that the diffusing inclusion tries to follow favorable positions on the membrane such that forces along the trajectory are on average smaller than they would be for random particle positions.
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25
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Destainville N. Cluster phases of membrane proteins. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2008; 77:011905. [PMID: 18351874 DOI: 10.1103/physreve.77.011905] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/07/2007] [Revised: 12/03/2007] [Indexed: 05/26/2023]
Abstract
A physical scenario accounting for the existence of size-limited submicrometric domains in cell membranes is proposed. It is based on the numerical investigation of the counterpart, in lipidic membranes where proteins are diffusing, of the recently discovered cluster phases in colloidal suspensions. I demonstrate that the interactions between proteins, namely, short-range attraction and longer-range repulsion, make possible the existence of stable small clusters. The consequences are explored in terms of membrane organization and diffusion properties. The connection with lipid rafts is discussed, and the apparent protein diffusion coefficient as a function of their concentration is analyzed.
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Affiliation(s)
- Nicolas Destainville
- Laboratoire de Physique Théorique-IRSAMC, UMR CNRS-UPS 5152, Université de Toulouse, 31062 Toulouse Cedex 9, France
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26
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Campillo C, Pépin-Donat B, Viallat A. Responsive viscoelastic giant lipid vesicles filled with a poly(N-isopropylacrylamide) artificial cytoskeleton. SOFT MATTER 2007; 3:1421-1427. [PMID: 32900123 DOI: 10.1039/b710474j] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Responsive giant lipid vesicles filled with aqueous PolyNipam sol (SFV) or gel (GFV) were prepared by ultra-violet polymerisation performed in situ. Upon crossing the lower critical transition temperature of PolyNipam, SFVs and GFVs undergo a significant change of their structural and mechanical properties or a drastic volume transition, respectively. Rheometric and micropipette experiments show that both internal viscosity of SFVs and internal shear modulus of GFVs are tunable over several orders of magnitude and lie in the range observed for living cells. Moreover, the vesicle membrane is strongly bound to the internal polymer medium, making these systems interesting for mimicking the basic mechanical behaviour of passive living cells.
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Affiliation(s)
- Clément Campillo
- Adhésion et Inflammation, Inserm U600, CNRS UMR 62 12 Université Méditerranée, case 937, 163 av de Luminy, 13288 Marseille Cedex, France.
| | - Brigitte Pépin-Donat
- Laboratoire d'Electronique Moléculaire et Hybride, UMR 5819 SPrAM (CEA-CNRS-UJF)/DRFMC/CEA-Grenoble, 38054 Grenoble Cedex 9, France.
| | - Annie Viallat
- Adhésion et Inflammation, Inserm U600, CNRS UMR 62 12 Université Méditerranée, case 937, 163 av de Luminy, 13288 Marseille Cedex, France.
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27
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Giahi A, El Alaoui Faris M, Bassereau P, Salditt T. Active membranes studied by X-ray scattering. THE EUROPEAN PHYSICAL JOURNAL. E, SOFT MATTER 2007; 23:431-7. [PMID: 17712523 DOI: 10.1140/epje/i2007-10203-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/26/2007] [Accepted: 07/05/2007] [Indexed: 05/16/2023]
Abstract
In view of recent theories of "active" membranes, we have studied multilamellar phospholipid membrane stacks with reconstituted transmembrane protein bacteriorhodopsin (BR) under different illumination conditions by X-ray scattering. The light-active protein is considered as an active constituent which drives the system out of equilibrium and is predicted to change the collective fluctuation properties of the membranes. Using X-ray reflectivity, X-ray non-specular (diffuse) scattering, and grazing incidence scattering, we find no detectable change in the scattering curves when changing the illumination condition. In particular the intermembrane spacing d remains constant, after eliminating hydration-related artifacts by design of a suitable sample environment. The absence of any observable non-equilibrium effects in the experimental window is discussed in view of the relevant parameters and recent theories.
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Affiliation(s)
- A Giahi
- Institut für Röntgenphysik, Friedrich-Hund-Platz 1, 37073, Göttingen, Germany.
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28
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García-Sáez AJ, Schwille P. Single molecule techniques for the study of membrane proteins. Appl Microbiol Biotechnol 2007; 76:257-66. [PMID: 17497147 DOI: 10.1007/s00253-007-1007-8] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2007] [Revised: 04/17/2007] [Accepted: 04/17/2007] [Indexed: 11/26/2022]
Abstract
Single molecule techniques promise novel information about the properties and behavior of individual particles, thus enabling access to molecular heterogeneities in biological systems. Their recent developments to accommodate membrane studies have significantly deepened the understanding of membrane proteins. In this short review, we will describe the basics of the three most common single-molecule techniques used on membrane proteins: fluorescence correlation spectroscopy, single particle tracking, and atomic force microscopy. We will discuss the most relevant findings made during the recent years and their contribution to the membrane protein field.
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Affiliation(s)
- Ana J García-Sáez
- Biophysics Group, Biotechnologisches Zentrum (BIOTEC) der TU Dresden, Tatzberg 47-51, 01307 Dresden, Germany
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29
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Davis RW, Flores A, Barrick TA, Cox JM, Brozik SM, Lopez GP, Brozik JA. Nanoporous microbead supported bilayers: stability, physical characterization, and incorporation of functional transmembrane proteins. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2007; 23:3864-72. [PMID: 17315891 DOI: 10.1021/la062576t] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
The introduction of functional transmembrane proteins into supported bilayer-based biomimetic systems presents a significant challenge for biophysics. Among the various methods for producing supported bilayers, liposomal fusion offers a versatile method for the introduction of membrane proteins into supported bilayers on a variety of substrates. In this study, the properties of protein containing unilamellar phosphocholine lipid bilayers on nanoporous silica microspheres are investigated. The effects of the silica substrate, pore structure, and the substrate curvature on the stability of the membrane and the functionality of the membrane protein are determined. Supported bilayers on porous silica microspheres show a significant increase in surface area on surfaces with structures in excess of 10 nm as well as an overall decrease in stability resulting from increasing pore size and curvature. Comparison of the liposomal and detergent-mediated introduction of purified bacteriorhodopsin (bR) and the human type 3 serotonin receptor (5HT3R) are investigated focusing on the resulting protein function, diffusion, orientation, and incorporation efficiency. In both cases, functional proteins are observed; however, the reconstitution efficiency and orientation selectivity are significantly enhanced through detergent-mediated protein reconstitution. The results of these experiments provide a basis for bulk ionic and fluorescent dye-based compartmentalization assays as well as single-molecule optical and single-channel electrochemical interrogation of transmembrane proteins in a biomimetic platform.
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Affiliation(s)
- Ryan W Davis
- Department of Chemistry, The University of New Mexico, Albuquerque, New Mexico 87131, USA
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30
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Tsourkas PK, Baumgarth N, Simon SI, Raychaudhuri S. Mechanisms of B-cell synapse formation predicted by Monte Carlo simulation. Biophys J 2007; 92:4196-208. [PMID: 17384077 PMCID: PMC1877775 DOI: 10.1529/biophysj.106.094995] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The clustering of B-cell receptor (BCR) molecules and the formation of the protein segregation structure known as the "immunological synapse" at the contact region between B cells and antigen presenting cells appears to precede antigen (Ag) uptake by B cells. The mature B-cell synapse is characterized by a central cluster of BCR/Ag molecular complexes surrounded by a ring of LFA-1/ICAM-1 complexes. In this study, we investigate the biophysical mechanisms that drive immunological synapse formation in B cells by means of Monte Carlo simulation. Our approach simulates individual reaction and diffusion events on cell surfaces in a probabilistic manner with a clearly defined mapping between our model's probabilistic parameters and their physical equivalents. Our model incorporates the bivalent nature of the BCR as well as changes in membrane shape due to receptor-ligand binding. We find that differences in affinity and bond stiffness between BCR/Ag and LFA-1/ICAM-1 are sufficient to drive synapse formation in the absence of membrane deformation. When significant membrane deformation occurs as a result of receptor-ligand binding, our model predicts the affinity-dependent mechanism needs to be complemented by a BCR signaling-driven shift in LFA-1 affinity from low to high in order for synapses to form.
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Affiliation(s)
- Philippos K Tsourkas
- Department of Biomedical Engineering, University of California-Davis, Davis, California, USA
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31
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Chen CH, Chen HY. Finite-size domains in membranes with active two-state inclusions. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2006; 74:051917. [PMID: 17279949 DOI: 10.1103/physreve.74.051917] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/17/2005] [Revised: 10/29/2006] [Indexed: 05/13/2023]
Abstract
The distribution of inclusion-rich domains in membranes with active two-state inclusions is studied by simulations. Our study shows that typical size of inclusion-rich domains (L) can be controlled by inclusion activities in several ways. When there is effective attraction between state-1 inclusions, we find: (i) Small domains with only several inclusions are observed for inclusions with time scales (approximately 10(-3)s) and interaction energy [approximately Omicron(kBT)] comparable to motor proteins. (ii) L scales as 13 power of the lifetime of state-1 for a wide range of parameters. (iii) L shows a switch-like dependence on state-2 lifetime k12(-1). That is, L depends weakly on k12 when k12<k12* but increases rapidly with k12 when k12>k12*, the crossover k12* occurs when the diffusion length of a typical state-2 inclusion within its lifetime is comparable to L. (iv) Inclusion-curvature coupling provides another length scale that competes with the effects of transition rates.
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Affiliation(s)
- Chien-Hsun Chen
- Department of Physics, Center for Complex Systems, National Central University, Jhongli, 32054 Taiwan
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32
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Wasungu L, Hoekstra D. Cationic lipids, lipoplexes and intracellular delivery of genes. J Control Release 2006; 116:255-64. [PMID: 16914222 DOI: 10.1016/j.jconrel.2006.06.024] [Citation(s) in RCA: 406] [Impact Index Per Article: 22.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2006] [Accepted: 06/21/2006] [Indexed: 11/30/2022]
Abstract
As a consequence of several setbacks encountered by viral technology in achieving efficient and safe gene therapy in clinical trials, non-viral gene delivery vectors are considered to date as a valuable alternative and to hold promise for future therapeutic applications. Nevertheless, the transfection efficiency mediated by these non-viral gene delivery vectors has to be improved, especially in vivo, to benefit fully from their advantages. Cationic lipid/nucleic acid complexes or lipoplexes have been the subject of intensive investigations in recent years to understand the parameters governing the efficiency of transfection. Specifically, the comprehension of such mechanisms, from the formation of the complexes to their intracellular delivery, will lead to the design of better adapted non-viral vectors for gene therapy applications. Here, we will discuss some recent developments in the field on the structure/function relationship of cationic lipids in the mechanism of transfection, and where appropriate, we will make a comparison with mechanisms of viral and polyplex-mediated gene delivery. Cationic lipids are often used in combination with helper lipids such as DOPE or cholesterol. The effect of DOPE on lipoplex assembly and the relevance of the structural properties of the lipoplexes in destabilizing endosomal membranes and mediating endosomal escape of DNA will be discussed.
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Affiliation(s)
- Luc Wasungu
- Department of Cell Biology, Section Membrane Cell Biology, University of Groningen, University Medical Center Groningen, Antonius Deusinglaan 1, 9713 AV Groningen, The Netherlands
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33
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Lomholt MA. Mechanics of nonplanar membranes with force-dipole activity. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2006; 73:061913. [PMID: 16906870 DOI: 10.1103/physreve.73.061913] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/27/2005] [Revised: 03/15/2006] [Indexed: 05/11/2023]
Abstract
A study is made of how active membrane proteins can modify the long wavelength mechanics of fluid membranes. The activity of the proteins is modelled as disturbing the protein surroundings through nonlocal force distributions of which a force-dipole distribution is the simplest example. An analytic expression describing how the activity modifies the force-balance equation for the membrane surface is obtained in the form of a moment expansion of the force distribution. This expression allows for further studies of the consequences of the activity for nonplanar membranes. In particular the active contributions to mechanical properties such as tension and bending moments become apparent. It is also explained how the activity can induce a hydrodynamic attraction between the active proteins in the membrane.
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Affiliation(s)
- Michael A Lomholt
- NORDITA--Nordic Institute for Theoretical Physics, Blegdamsvej 17, 2100 Copenhagen Ø, Denmark.
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34
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Ming M, Lu M, Balashov SP, Ebrey TG, Li Q, Ding J. pH dependence of light-driven proton pumping by an archaerhodopsin from Tibet: comparison with bacteriorhodopsin. Biophys J 2006; 90:3322-32. [PMID: 16473896 PMCID: PMC1432102 DOI: 10.1529/biophysj.105.076547] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2005] [Accepted: 01/19/2006] [Indexed: 11/18/2022] Open
Abstract
The pH-dependence of photocycle of archaerhodopsin 4 (AR4) was examined, and the underlying proton pumping mechanism investigated. AR4 is a retinal-containing membrane protein isolated from a strain of halobacteria from a Tibetan salt lake. It acts as a light-driven proton pump like bacteriorhodopsin (BR). However, AR4 exhibits an "abnormal" feature--the time sequence of proton release and uptake is reversed at neutral pH. We show here that the temporal sequence of AR4 reversed to "normal"--proton release preceding proton uptake--when the pH is increased above 8.6. We estimated the pK(a) of the proton release complex (PRC) in the M-intermediate to be approximately 8.4, much higher than 5.7 of wide-type BR. The pH-dependence of the rate constant of M-formation shows that the pK(a) of PRC in the initial state of AR4 is approximately 10.4, whereas it is 9.7 in BR. Thus in AR4, the chromophore photoisomerization and subsequent proton transport from the Schiff base to Asp-85 is coupled to a decrease in the pK(a) of PRC from 10.4 to 8.4, which is 2 pK units less than in BR (4 units). This weakened coupling accounts for the lack of early proton release at neutral pH and the reversed time sequence of proton release and uptake in AR4. Nevertheless the PRC in AR4 effectively facilitates deprotonation of primary proton acceptor and recovery of initial state at neutral pH. We found also that all pK(a)s of the key amino acid residues in AR4 were elevated compared to those of BR.
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Affiliation(s)
- Ming Ming
- Key Laboratory of Molecular Engineering of Polymers, Department of Macromolecular Science, Fudan University, Shanghai, China
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35
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Gov NS. Diffusion in curved fluid membranes. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2006; 73:041918. [PMID: 16711847 DOI: 10.1103/physreve.73.041918] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/22/2005] [Revised: 02/01/2006] [Indexed: 05/09/2023]
Abstract
We analyze theoretically the effects of curvature on the diffusion in a fluid membrane, within the Saffman-Delbrück hydrodynamic model. We calculate the effect of curvature on the intrinsic fluidity of a membrane through changes in its thickness, for both static or fluctuating curvature. We treat both thermal curvature fluctuations, and fluctuations due to active processes. Such curvature fluctuations increase the average membrane thickness and diminish the projected area, thereby decreasing the diffusion coefficient. This calculation allows us to predict the effect of shear flow on the membrane diffusion, and to compare to observations on living cells.
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Affiliation(s)
- Nir S Gov
- Department of Chemical Physics, The Weizmann Institute of Science, P.O. Box 26, Rehovot, Israel 76100
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36
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Lin LCL, Gov N, Brown FLH. Nonequilibrium membrane fluctuations driven by active proteins. J Chem Phys 2006; 124:74903. [PMID: 16497078 DOI: 10.1063/1.2166383] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We extend a model for nonthermal membrane undulations driven by active (adenosine triphosphate-dependent or light-harvesting) membrane proteins [N. Gov, Phys. Rev. Lett. 93, 268104 (2004)]. The present model accounts for the fact that proteins can diffuse laterally across the membrane surface and that individual proteins are expected to exert forces preferentially in one normal direction over the other (due to their orientation within the bilayer). The addition of these effects alters the scaling of fluctuation amplitudes with system size. Additionally, theoretical arguments and dynamic simulations both suggest that, in certain regimes, the probability distribution of fluctuation amplitudes is expected to be non-Gaussian (in contrast to thermal systems).
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Affiliation(s)
- Lawrence C-L Lin
- Department of Physics, University of California, Santa Barbara, 93106-9530, USA
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37
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Gambin Y, Lopez-Esparza R, Reffay M, Sierecki E, Gov NS, Genest M, Hodges RS, Urbach W. Lateral mobility of proteins in liquid membranes revisited. Proc Natl Acad Sci U S A 2006; 103:2098-102. [PMID: 16461891 PMCID: PMC1413751 DOI: 10.1073/pnas.0511026103] [Citation(s) in RCA: 270] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The biological function of transmembrane proteins is closely related to their insertion, which has most often been studied through their lateral mobility. For >30 years, it has been thought that hardly any information on the size of the diffusing object can be extracted from such experiments. Indeed, the hydrodynamic model developed by Saffman and Delbrück predicts a weak, logarithmic dependence of the diffusion coefficient D with the radius R of the protein. Despite widespread use, its validity has never been thoroughly investigated. To check this model, we measured the diffusion coefficients of various peptides and transmembrane proteins, incorporated into giant unilamellar vesicles of 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine (SOPC) or in model bilayers of tunable thickness. We show in this work that, for several integral proteins spanning a large range of sizes, the diffusion coefficient is strongly linked to the protein dimensions. A heuristic model results in a Stokes-like expression for D, (D proportional, variant 1/R), which fits literature data as well as ours. Diffusion measurement is then a fast and fruitful method; it allows determining the oligomerization degree of proteins or studying lipid-protein and protein-protein interactions within bilayers.
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Affiliation(s)
- Y Gambin
- Laboratoire de Physique Statistique de l'Ecole Normale Supérieure, Unité Mixte de Recherche 8550, Centre National de la Recherche Scientifique-Université Paris 6, 24 Rue Lhomond, 75005 Paris, France.
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38
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Kahya N, Brown DA, Schwille P. Raft Partitioning and Dynamic Behavior of Human Placental Alkaline Phosphatase in Giant Unilamellar Vesicles. Biochemistry 2005; 44:7479-89. [PMID: 15895991 DOI: 10.1021/bi047429d] [Citation(s) in RCA: 144] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Much attention has recently been drawn to the hypothesis that cellular membranes organize in functionalized platforms called rafts, enriched in sphingolipids and cholesterol. The notion that glycosylphosphatidylinositol (GPI)-anchored proteins are strongly associated with rafts is based on their insolubility in nonionic detergents. However, detergent-based methodologies for identifying raft association are indirect and potentially prone to artifacts. On the other hand, rafts have proven to be difficult to visualize and investigate in living cells. A number of studies have demonstrated that model membranes provide a valuable tool for elucidating some of the raft properties. Here, we present a model membrane system based on domain-forming giant unilamellar vesicles (GUVs), in which the GPI-anchored protein, human placental alkaline phosphatase (PLAP), has been functionally reconstituted. Raft morphology, protein raft partitioning, and dynamic behavior have been characterized by fluorescence confocal microscopy and fluorescence correlation spectroscopy (FCS). Approximately 20-30% of PLAP associate with sphingomyelin-enriched domains. The affinity of PLAP for the liquid-ordered (l(o)) phase is compared to that of a nonraft protein, bacteriorhodopsin. Next, detergent extraction was carried out on PLAP-containing GUVs as a function of temperature, to relate the lipid and protein organization in distinct phases of the GUVs to the composition of detergent resistant membranes (DRMs). Finally, antibody-mediated cross-linking of PLAP induces a shift of its partition coefficient in favor of the l(o) phase.
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Affiliation(s)
- Nicoletta Kahya
- Max Planck Institute of Molecular Cell Biology and Genetics, Dresden University of Technology, Pfotenhauerstrasse 108, 01307 Dresden, Germany
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39
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Korlach J, Reichle C, Müller T, Schnelle T, Webb WW. Trapping, deformation, and rotation of giant unilamellar vesicles in octode dielectrophoretic field cages. Biophys J 2005; 89:554-62. [PMID: 15863477 PMCID: PMC1366554 DOI: 10.1529/biophysj.104.050401] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The behavior of freestanding lipid bilayer membranes under the influence of dielectric force potentials was studied by trapping, holding, and rotating individual giant unilamellar vesicles (GUVs) inside dielectrophoretic microfield cages. Using laser scanning confocal microscopy and three-dimensional image reconstructions of GUVs labeled with fluorescent membrane probes, field strength and frequency-dependent vesicle deformations were observed which are explained by calculations of the dielectric force potentials inside the cage. Dynamical membrane properties under the influence of the field cage were studied by fluorescence correlation spectroscopy, circumventing potential artifacts associated with measurements involving GUV immobilization on support surfaces. Lipid transport could be accelerated markedly by the applied fields, aided by hydrodynamic fluid streaming which was also studied by fluorescence correlation spectroscopy.
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Affiliation(s)
- J Korlach
- School of Applied & Engineering Physics, Clark Hall, Cornell University, Ithaca, New York, USA
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40
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Girard P, Prost J, Bassereau P. Passive or active fluctuations in membranes containing proteins. PHYSICAL REVIEW LETTERS 2005; 94:088102. [PMID: 15783939 DOI: 10.1103/physrevlett.94.088102] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/27/2004] [Indexed: 05/16/2023]
Abstract
We have experimentally investigated the effect of a transmembrane protein, the Ca2+-ATPase, on shape fluctuations of giant vesicles. By using the micropipette method, we have measured a substantial renormalization of the bending modulus due to the presence of proteins in the membrane. Moreover, we have produced the first quantitative measurement of the active force dipole associated with the amplification of the fluctuations when the proteins are activated by adenosine 5'-triphosphate (ATP).
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Affiliation(s)
- P Girard
- PhysicoChimie Curie, UMR CNRS-Institut Curie 168, 11 rue Pierre et Marie Curie, 75231 Paris CEDEX 05, France
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41
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Poolman B, Doeven MK, Geertsma ER, Biemans-Oldehinkel E, Konings WN, Rees DC. Functional analysis of detergent-solubilized and membrane-reconstituted ATP-binding cassette transporters. Methods Enzymol 2005; 400:429-59. [PMID: 16399364 DOI: 10.1016/s0076-6879(05)00025-x] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/04/2022]
Abstract
ATP-binding cassette (ABC) transporters are vital to any living system and are involved in the translocation of a wide variety of substances, from ions and nutrients to high molecular weight proteins. This chapter describes methods used to purify and membrane reconstitute ABC transporters in a fully functional state. The procedures are largely based on our experience with substrate-binding protein-dependent ABC uptake systems from bacteria, but the approaches should be applicable to multisubunit membrane complexes in general. Also, we present simple methods, based on substrate binding or translocation, to follow the activity of the protein complexes in detergent-solubilized and/or membrane-reconstituted state(s).
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Affiliation(s)
- Bert Poolman
- Department of Biochemistry, Groningen Biomolecular Sciences and Biotechnology Institute and Materials Science Centre(plus), University of Groningen, The Netherlands
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Doeven MK, Folgering JHA, Krasnikov V, Geertsma ER, van den Bogaart G, Poolman B. Distribution, lateral mobility and function of membrane proteins incorporated into giant unilamellar vesicles. Biophys J 2004; 88:1134-42. [PMID: 15574707 PMCID: PMC1305118 DOI: 10.1529/biophysj.104.053413] [Citation(s) in RCA: 108] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
GUVs have been widely used for studies on lipid mobility, membrane dynamics and lipid domain (raft) formation, using single molecule techniques like fluorescence correlation spectroscopy. Reports on membrane protein dynamics in these types of model membranes are by far less advanced due to the difficulty of incorporating proteins into GUVs in a functional state. We have used sucrose to prevent four distinct membrane protein(s) (complexes) from inactivating during the dehydration step of the GUV-formation process. The amount of sucrose was optimized such that the proteins retained 100% biological activity, and many proteo-GUVs were obtained. Although GUVs could be formed by hydration of lipid mixtures composed of neutral and anionic lipids, an alternate current electric field was required for GUV formation from neutral lipids. Distribution, lateral mobility, and function of an ATP-binding cassette transport system, an ion-linked transporter, and a mechanosensitive channel in GUVs were determined by confocal imaging, fluorescence correlation spectroscopy, patch-clamp measurements, and biochemical techniques. In addition, we show that sucrose slows down the lateral mobility of fluorescent lipid analogs, possibly due to hydrogen-bonding with the lipid headgroups, leading to larger complexes with reduced mobility.
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Affiliation(s)
- Mark K Doeven
- Department of Biochemistry, Groningen Biomolecular Sciences and Biotechnology Institute and Materials Science Centre, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
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Inoue M, Digman MA, Cheng M, Breusegem SY, Halaihel N, Sorribas V, Mantulin WW, Gratton E, Barry NP, Levi M. Partitioning of NaPi cotransporter in cholesterol-, sphingomyelin-, and glycosphingolipid-enriched membrane domains modulates NaPi protein diffusion, clustering, and activity. J Biol Chem 2004; 279:49160-71. [PMID: 15355967 DOI: 10.1074/jbc.m408942200] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In dietary potassium deficiency there is a decrease in the transport activity of the type IIa sodium/phosphate cotransporter protein (NaPi) despite an increase in its apical membrane abundance. This novel posttranslational regulation of NaPi activity is mediated by the increased glycosphingolipid content of the potassium-deficient apical membrane. However, the mechanisms by which these lipids modulate NaPi activity have not been determined. We determined if in potassium deficiency NaPi is increasingly partitioned in cholesterol-, sphingomyelin-, and glycosphingolipid-enriched microdomains of the apical membrane and if the increased presence of NaPi in these microdomains modulates its activity. By using a detergent-free density gradient flotation technique, we found that 80% of the apical membrane NaPi partitions into the low density cholesterol-, sphingomyelin-, and GM1-enriched fractions characterized as "lipid raft" fractions. In potassium deficiency, a higher proportion of NaPi was localized in the lipid raft fractions. By combining fluorescence correlation spectroscopy and photon counting histogram methods for control and potassium-deficient apical membranes reconstituted into giant unilamellar vesicles, we showed a 2-fold decrease in lateral diffusion of NaPi protein and a greater than 2-fold increase in size of protein aggregates/clusters in potassium deficiency. Our results indicate that NaPi protein is localized in membrane microdomains, that in potassium deficiency a larger proportion of NaPi protein is present in these microdomains, and that NaPi lateral diffusion is slowed down and NaPi aggregation/clustering is increased in potassium deficiency, both of which could be associated with the decreased Na/Pi cotransport activity in potassium deficiency.
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Affiliation(s)
- Makoto Inoue
- Department of Medicine, University of Colorado Health Sciences Center and Denver Veterans Affairs Medical Center, Denver, Colorado 80262, USA
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Kahya N, Scherfeld D, Bacia K, Schwille P. Lipid domain formation and dynamics in giant unilamellar vesicles explored by fluorescence correlation spectroscopy. J Struct Biol 2004; 147:77-89. [PMID: 15109608 DOI: 10.1016/j.jsb.2003.09.021] [Citation(s) in RCA: 128] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2003] [Revised: 09/04/2003] [Indexed: 10/26/2022]
Abstract
Lipids in eukaryotic cell membranes have been shown to cluster in "rafts" with different lipid/protein compositions and molecular packing. Model membranes such as giant unilamellar vesicles (GUVs) provide a key system to elucidate the physical mechanisms of raft assembly. Despite the large amount of work devoted to the detection and characterization of rafts, one of the most important pieces of information still missing in the picture of the cell membrane is dynamics: how lipids organize and move in rafts and how they modulate membrane fluidity. This missing element is of crucial importance for the trafficking at and from the periphery of the cell regulated by endo- and exocytosis and, in general, for the constant turnover which redistributes membrane components. Here, we review studies of combined confocal fluorescence microscopy and fluorescence correlation spectroscopy on lipid dynamics and organization in rafts assembled in GUVs prepared from various lipid mixtures which are relevant to the problem of raft formation.
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Affiliation(s)
- Nicoletta Kahya
- Experimental Biophysics Group, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Goettingen, Germany
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Mostafa HIA. Light adaptation of bacteriorhodopsin correlates with dielectric spectral kinetics in purple membrane. Biochem Biophys Res Commun 2004; 315:857-65. [PMID: 14985091 DOI: 10.1016/j.bbrc.2004.01.135] [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: 01/16/2004] [Indexed: 11/28/2022]
Abstract
The retinal protein, bacteriorhodopsin (bR), has several potential bioelectronic applications and it is considered as a model for G-protein coupled receptors. Its electrical parameters, therefore, deserve particular attention. Such parameters could be determined by virtue of studying its dielectric spectrum in the low frequency range (20 Hz-1 MHz). The kinetics of dark-light adaptation of bR is reported in terms of electrical parameters of the purple membrane (PM) containing bR. The data have exhibited sudden pronounced increase in the ac-conductivity, upon illuminating the dark-adapted bR (DA-bR), which may be considered in further implications of bR for biotechnological applications. These changes turned out to be composed of, at least, two growing exponential components: one relatively fast followed by slower one. Their lifetime ratio exhibited decreases with increasing the frequency; meanwhile, their amplitude ratio displayed very exciting behavior at significant frequencies. This may correlate the kinetics of light adaptation to relaxations in PM. Moreover, the light adaptation has been observed to cause initial fast and large decreases in dc-conductivity with subsequent slower and smaller decreases. Changing the conductivity during the time of light adaptation reflects changes in the surface charge of the PM. The lifetimes of these events, therefore, help follow the kinetics of the pathway of conformational changes that might be occurring during light adaptation. The dipole moment (permanent and induced) of PM, in addition to, its size showed one exponential growth of comparable lifetime (approximately 7 min) during the light adaptation. The variation in PM size from dark to light state should be in keeping with that diffusion may influence the three-dimensional data storage in data processing based on bR.
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Affiliation(s)
- Hamdy I A Mostafa
- Department of Biophysics, Faculty of Science, Cairo University, 12613 Giza, Egypt.
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