51
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Miscibility Transition Temperature Scales with Growth Temperature in a Zebrafish Cell Line. Biophys J 2017; 113:1212-1222. [PMID: 28552311 DOI: 10.1016/j.bpj.2017.04.052] [Citation(s) in RCA: 39] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2017] [Revised: 03/23/2017] [Accepted: 04/05/2017] [Indexed: 11/22/2022] Open
Abstract
Cells can alter the lipid content of their plasma membranes upon changes in their environment to maintain and adjust membrane function. Recent work suggests that some membrane functions arise because cellular plasma membranes are poised close to a miscibility transition under growth conditions. Here we report experiments utilizing giant plasma membrane vesicles (GPMVs) to explore how membrane transition temperature varies with growth temperature in a zebrafish cell line (ZF4) that can be adapted for growth between 20 and 32°C. We find that GPMV transition temperatures adjust to be 16.7 ± 1.2°C below growth temperature for four growth temperatures investigated and that adjustment occurs over roughly 2 days when temperature is abruptly lowered from 28 to 20°C. We also find that GPMVs have slightly different lipidomes when isolated from cells adapted for growth at 28 and 20°C. Similar to past work in vesicles derived from mammalian cells, fluctuating domains are observed in ZF4-derived GPMVs, consistent with their having critical membrane compositions. Taken together, these experimental results suggest that cells in culture biologically tune their membrane composition in a way that maintains specific proximity to a critical miscibility transition.
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Cocchi M, Minuto C, Tonello L, Gabrielli F, Bernroider G, Tuszynski JA, Cappello F, Rasenick M. Linoleic acid: Is this the key that unlocks the quantum brain? Insights linking broken symmetries in molecular biology, mood disorders and personalistic emergentism. BMC Neurosci 2017; 18:38. [PMID: 28420346 PMCID: PMC5395787 DOI: 10.1186/s12868-017-0356-1] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2017] [Accepted: 04/12/2017] [Indexed: 11/10/2022] Open
Abstract
In this paper we present a mechanistic model that integrates subneuronal structures, namely ion channels, membrane fatty acids, lipid rafts, G proteins and the cytoskeleton in a dynamic system that is finely tuned in a healthy brain. We also argue that subtle changes in the composition of the membrane's fatty acids may lead to down-stream effects causing dysregulation of the membrane, cytoskeleton and their interface. Such exquisite sensitivity to minor changes is known to occur in physical systems undergoing phase transitions, the simplest and most studied of them is the so-called Ising model, which exhibits a phase transition at a finite temperature between an ordered and disordered state in 2- or 3-dimensional space. We propose this model in the context of neuronal dynamics and further hypothesize that it may involve quantum degrees of freedom dependent upon variation in membrane domains associated with ion channels or microtubules. Finally, we provide a link between these physical characteristics of the dynamical mechanism to psychiatric disorders such as major depression and antidepressant action.
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Affiliation(s)
- Massimo Cocchi
- "Paolo Sotgiu" Institute for Research in Quantitative & Quantum Psychiatry & Cardiology, L.U.de.S. HEI, Malta, Switzerland. .,Department of Veterinary Medical Sciences, University of Bologna, Bologna, Italy.
| | | | - Lucio Tonello
- "Paolo Sotgiu" Institute for Research in Quantitative & Quantum Psychiatry & Cardiology, L.U.de.S. HEI, Malta, Switzerland
| | - Fabio Gabrielli
- "Paolo Sotgiu" Institute for Research in Quantitative & Quantum Psychiatry & Cardiology, L.U.de.S. HEI, Malta, Switzerland
| | - Gustav Bernroider
- Neurosignaling Unit, Department of Organismic Biology, University of Salzburg, Salzburg, Austria
| | - Jack A Tuszynski
- Department of Oncology, University of Alberta, Edmonton, Canada.,Department of Physics, University of Alberta, Edmonton, Canada
| | - Francesco Cappello
- Department of Biomedicine and Neuroscience, University of Palermo, Palermo, Italy.,Euro-Mediterranean Institute of Science and Technology, Palermo, Italy
| | - Mark Rasenick
- Department of Physiology & Biophysics and Psychiatry, University of Illinois College of Medicine, Chicago, IL, USA.,Jesse Brown VAMC, Chicago, IL, USA
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53
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Stone MB, Shelby SA, Núñez MF, Wisser K, Veatch SL. Protein sorting by lipid phase-like domains supports emergent signaling function in B lymphocyte plasma membranes. eLife 2017; 6. [PMID: 28145867 PMCID: PMC5373823 DOI: 10.7554/elife.19891] [Citation(s) in RCA: 138] [Impact Index Per Article: 19.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2016] [Accepted: 01/31/2017] [Indexed: 12/19/2022] Open
Abstract
Diverse cellular signaling events, including B cell receptor (BCR) activation, are hypothesized to be facilitated by domains enriched in specific plasma membrane lipids and proteins that resemble liquid-ordered phase-separated domains in model membranes. This concept remains controversial and lacks direct experimental support in intact cells. Here, we visualize ordered and disordered domains in mouse B lymphoma cell membranes using super-resolution fluorescence localization microscopy, demonstrate that clustered BCR resides within ordered phase-like domains capable of sorting key regulators of BCR activation, and present a minimal, predictive model where clustering receptors leads to their collective activation by stabilizing an extended ordered domain. These results provide evidence for the role of membrane domains in BCR signaling and a plausible mechanism of BCR activation via receptor clustering that could be generalized to other signaling pathways. Overall, these studies demonstrate that lipid mediated forces can bias biochemical networks in ways that broadly impact signal transduction. DOI:http://dx.doi.org/10.7554/eLife.19891.001 Membranes made of molecules called lipids surround every living cell to protect the cell's contents. Cells also communicate with the outside environment via their membranes. Proteins in the membrane receive information from the environment and trigger signaling pathways inside the cell to relay this information to the center of cell. The way in which proteins are organized on the membrane has a major influence on their signaling activity. Some areas of the membrane are more crowded with certain lipids and signaling proteins than others. Lipid and protein molecules of particular types can come together and form distinct areas called “ordered” and “disordered” domains. The lipids in ordered domains are more tightly packed than disordered domains and it is thought that this difference allows domains to selectively exclude or include certain proteins. Ordered domains are also known as "lipid rafts". Lipid rafts and disordered domains may help cells to control the activities of signaling pathways, however, technical limitations have made it difficult to study the roles of these domains. The membranes surrounding immune cells called B cells contain a protein called the B cell receptor, which engages with proteins from microbes and other foreign invaders. When the B cell receptor binds to a foreign protein it forms clusters with other B cell receptors and becomes active, triggering a signaling pathway that leads to immune responses. Stone, Shelby et al. examined lipid rafts and disordered domains in B cells from mice using a technique called super-resolution fluorescence microscopy. The results show that clusters of B cell receptors are present within lipid rafts. These clusters made the lipid rafts larger and more stable. A protein that is needed during the early stages of B cell receptor signaling was also found in the same lipid rafts. Another protein that terminates signaling was excluded because it prefers disordered domains. Together, this provides a local environment in certain areas of the membrane that favors receptor activity and supports the subsequent immune response. Future work is needed to understand how cells control the make-up of lipids and proteins within their membranes, and how defects in this regulation can alter signaling activity and lead to disease. DOI:http://dx.doi.org/10.7554/eLife.19891.002
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Affiliation(s)
- Matthew B Stone
- Department of Biophysics, University of Michigan, Ann Arbor, United States
| | - Sarah A Shelby
- Department of Biophysics, University of Michigan, Ann Arbor, United States
| | - Marcos F Núñez
- Department of Biophysics, University of Michigan, Ann Arbor, United States
| | - Kathleen Wisser
- Department of Biophysics, University of Michigan, Ann Arbor, United States
| | - Sarah L Veatch
- Department of Biophysics, University of Michigan, Ann Arbor, United States
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54
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Vega-Cabrera LA, Pardo-López L. Membrane remodeling and organization: Elements common to prokaryotes and eukaryotes. IUBMB Life 2017; 69:55-62. [DOI: 10.1002/iub.1604] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2016] [Accepted: 12/15/2016] [Indexed: 01/14/2023]
Affiliation(s)
- Luz A. Vega-Cabrera
- Instituto de Biotecnología, Universidad Nacional Autónoma de México; Apdo. Postal 510-3 Cuernavaca Morelos México
| | - Liliana Pardo-López
- Instituto de Biotecnología, Universidad Nacional Autónoma de México; Apdo. Postal 510-3 Cuernavaca Morelos México
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55
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Fujimoto T, Parmryd I. Interleaflet Coupling, Pinning, and Leaflet Asymmetry-Major Players in Plasma Membrane Nanodomain Formation. Front Cell Dev Biol 2017; 4:155. [PMID: 28119914 PMCID: PMC5222840 DOI: 10.3389/fcell.2016.00155] [Citation(s) in RCA: 82] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2016] [Accepted: 12/27/2016] [Indexed: 01/26/2023] Open
Abstract
The plasma membrane has a highly asymmetric distribution of lipids and contains dynamic nanodomains many of which are liquid entities surrounded by a second, slightly different, liquid environment. Contributing to the dynamics is a continuous repartitioning of components between the two types of liquids and transient links between lipids and proteins, both to extracellular matrix and cytoplasmic components, that temporarily pin membrane constituents. This make plasma membrane nanodomains exceptionally challenging to study and much of what is known about membrane domains has been deduced from studies on model membranes at equilibrium. However, living cells are by definition not at equilibrium and lipids are distributed asymmetrically with inositol phospholipids, phosphatidylethanolamines and phosphatidylserines confined mostly to the inner leaflet and glyco- and sphingolipids to the outer leaflet. Moreover, each phospholipid group encompasses a wealth of species with different acyl chain combinations whose lateral distribution is heterogeneous. It is becoming increasingly clear that asymmetry and pinning play important roles in plasma membrane nanodomain formation and coupling between the two lipid monolayers. How asymmetry, pinning, and interdigitation contribute to the plasma membrane organization is only beginning to be unraveled and here we discuss their roles and interdependence.
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Affiliation(s)
- Toyoshi Fujimoto
- Department of Anatomy and Molecular Cell Biology, Nagoya University Graduate School of Medicine Nagoya, Japan
| | - Ingela Parmryd
- Science for Life Laboratory, Medical Cell Biology, Uppsala University Uppsala, Sweden
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56
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Compartmentalization of the Cell Membrane. J Mol Biol 2016; 428:4739-4748. [DOI: 10.1016/j.jmb.2016.09.022] [Citation(s) in RCA: 43] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2016] [Revised: 09/27/2016] [Accepted: 09/28/2016] [Indexed: 11/20/2022]
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57
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Schmid F. Physical mechanisms of micro- and nanodomain formation in multicomponent lipid membranes. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1859:509-528. [PMID: 27823927 DOI: 10.1016/j.bbamem.2016.10.021] [Citation(s) in RCA: 71] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/26/2016] [Revised: 10/19/2016] [Accepted: 10/27/2016] [Indexed: 12/17/2022]
Abstract
This article summarizes a variety of physical mechanisms proposed in the literature, which can generate micro- and nanodomains in multicomponent lipid bilayers and biomembranes. It mainly focusses on lipid-driven mechanisms that do not involve direct protein-protein interactions. Specifically, it considers (i) equilibrium mechanisms based on lipid-lipid phase separation such as critical cluster formation close to critical points, and multiple domain formation in curved geometries, (ii) equilibrium mechanisms that stabilize two-dimensional microemulsions, such as the effect of linactants and the effect of curvature-composition coupling in bilayers and monolayers, and (iii) non-equilibrium mechanisms induced by the interaction of a biomembrane with the cellular environment, such as membrane recycling and the pinning effects of the cytoplasm. Theoretical predictions are discussed together with simulations and experiments. The presentation is guided by the theory of phase transitions and critical phenomena, and the appendix summarizes the mathematical background in a concise way within the framework of the Ginzburg-Landau theory. This article is part of a Special Issue entitled: Lipid order/lipid defects and lipid-control of protein activity edited by Dirk Schneider.
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Affiliation(s)
- Friederike Schmid
- Institute of Physics, Johannes Gutenberg University, 55099 Mainz, Germany
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58
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Needham SR, Roberts SK, Arkhipov A, Mysore VP, Tynan CJ, Zanetti-Domingues LC, Kim ET, Losasso V, Korovesis D, Hirsch M, Rolfe DJ, Clarke DT, Winn MD, Lajevardipour A, Clayton AHA, Pike LJ, Perani M, Parker PJ, Shan Y, Shaw DE, Martin-Fernandez ML. EGFR oligomerization organizes kinase-active dimers into competent signalling platforms. Nat Commun 2016; 7:13307. [PMID: 27796308 PMCID: PMC5095584 DOI: 10.1038/ncomms13307] [Citation(s) in RCA: 123] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2015] [Accepted: 09/20/2016] [Indexed: 12/19/2022] Open
Abstract
Epidermal growth factor receptor (EGFR) signalling is activated by ligand-induced receptor dimerization. Notably, ligand binding also induces EGFR oligomerization, but the structures and functions of the oligomers are poorly understood. Here, we use fluorophore localization imaging with photobleaching to probe the structure of EGFR oligomers. We find that at physiological epidermal growth factor (EGF) concentrations, EGFR assembles into oligomers, as indicated by pairwise distances of receptor-bound fluorophore-conjugated EGF ligands. The pairwise ligand distances correspond well with the predictions of our structural model of the oligomers constructed from molecular dynamics simulations. The model suggests that oligomerization is mediated extracellularly by unoccupied ligand-binding sites and that oligomerization organizes kinase-active dimers in ways optimal for auto-phosphorylation in trans between neighbouring dimers. We argue that ligand-induced oligomerization is essential to the regulation of EGFR signalling. Epidermal growth factor receptors have been shown to oligomerise upon binding to their cognate ligands. Here, the authors use biochemical, biophysical and cell biology techniques to analyse the structures of these oligomers, and argue that these formations are required for signalling.
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Affiliation(s)
- Sarah R Needham
- Central Laser Facility, Research Complex at Harwell, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell Oxford, Didcot, Oxford OX11 0QX, UK
| | - Selene K Roberts
- Central Laser Facility, Research Complex at Harwell, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell Oxford, Didcot, Oxford OX11 0QX, UK
| | | | | | - Christopher J Tynan
- Central Laser Facility, Research Complex at Harwell, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell Oxford, Didcot, Oxford OX11 0QX, UK
| | - Laura C Zanetti-Domingues
- Central Laser Facility, Research Complex at Harwell, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell Oxford, Didcot, Oxford OX11 0QX, UK
| | - Eric T Kim
- D.E. Shaw Research, New York, New York 10036, USA
| | - Valeria Losasso
- Computational Science and Engineering Department, Science and Technology Facilities Council, Daresbury Laboratory, Warrington WA4 4AD, UK
| | - Dimitrios Korovesis
- Central Laser Facility, Research Complex at Harwell, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell Oxford, Didcot, Oxford OX11 0QX, UK
| | - Michael Hirsch
- Central Laser Facility, Research Complex at Harwell, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell Oxford, Didcot, Oxford OX11 0QX, UK
| | - Daniel J Rolfe
- Central Laser Facility, Research Complex at Harwell, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell Oxford, Didcot, Oxford OX11 0QX, UK
| | - David T Clarke
- Central Laser Facility, Research Complex at Harwell, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell Oxford, Didcot, Oxford OX11 0QX, UK
| | - Martyn D Winn
- Computational Science and Engineering Department, Science and Technology Facilities Council, Daresbury Laboratory, Warrington WA4 4AD, UK
| | - Alireza Lajevardipour
- Centre for Micro-Photonics, Faculty of Science, Engineering and Technology, Swinburne University of Technology, Hawthorn, Victoria 3122, Australia
| | - Andrew H A Clayton
- Centre for Micro-Photonics, Faculty of Science, Engineering and Technology, Swinburne University of Technology, Hawthorn, Victoria 3122, Australia
| | - Linda J Pike
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St Louis, Missouri 63110, USA
| | - Michela Perani
- Division of Cancer Studies, King's College London, Guy's Medical School Campus, London SE1 1UL, UK
| | - Peter J Parker
- Division of Cancer Studies, King's College London, Guy's Medical School Campus, London SE1 1UL, UK.,The Francis Crick Institute, Protein Phosphorylation Laboratory, 44 Lincoln's Inn Fields, London WC2A 3LY, UK
| | - Yibing Shan
- D.E. Shaw Research, New York, New York 10036, USA
| | - David E Shaw
- D.E. Shaw Research, New York, New York 10036, USA.,Department of Biochemistry and Molecular Biophysics, Columbia University, New York, New York 10032, USA
| | - Marisa L Martin-Fernandez
- Central Laser Facility, Research Complex at Harwell, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell Oxford, Didcot, Oxford OX11 0QX, UK
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59
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Eggeling C, Honigmann A. Closing the gap: The approach of optical and computational microscopy to uncover biomembrane organization. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1858:2558-2568. [DOI: 10.1016/j.bbamem.2016.03.025] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/08/2016] [Revised: 03/23/2016] [Accepted: 03/24/2016] [Indexed: 12/15/2022]
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60
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Bernardino de la Serna J, Schütz GJ, Eggeling C, Cebecauer M. There Is No Simple Model of the Plasma Membrane Organization. Front Cell Dev Biol 2016; 4:106. [PMID: 27747212 PMCID: PMC5040727 DOI: 10.3389/fcell.2016.00106] [Citation(s) in RCA: 97] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2016] [Accepted: 09/14/2016] [Indexed: 12/29/2022] Open
Abstract
Ever since technologies enabled the characterization of eukaryotic plasma membranes, heterogeneities in the distributions of its constituents were observed. Over the years this led to the proposal of various models describing the plasma membrane organization such as lipid shells, picket-and-fences, lipid rafts, or protein islands, as addressed in numerous publications and reviews. Instead of emphasizing on one model we in this review give a brief overview over current models and highlight how current experimental work in one or the other way do not support the existence of a single overarching model. Instead, we highlight the vast variety of membrane properties and components, their influences and impacts. We believe that highlighting such controversial discoveries will stimulate unbiased research on plasma membrane organization and functionality, leading to a better understanding of this essential cellular structure.
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Affiliation(s)
- Jorge Bernardino de la Serna
- Science and Technology Facilities Council, Rutherford Appleton Laboratory, Central Laser Facility, Research Complex at Harwell Harwell, UK
| | - Gerhard J Schütz
- Institute of Applied Physics, Technische Universität Wien Wien, Austria
| | - Christian Eggeling
- MRC Human Immunology Unit, Weatherall Institute of Molecular Medicine, University of Oxford Headley Way, UK
| | - Marek Cebecauer
- Department of Biophysical Chemistry, J.Heyrovsky Institute of Physical Chemistry, Czech Academy of Sciences Prague, Czech Republic
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61
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Shelby SA, Veatch SL, Holowka DA, Baird BA. Functional nanoscale coupling of Lyn kinase with IgE-FcεRI is restricted by the actin cytoskeleton in early antigen-stimulated signaling. Mol Biol Cell 2016; 27:3645-3658. [PMID: 27682583 PMCID: PMC5221596 DOI: 10.1091/mbc.e16-06-0425] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2016] [Accepted: 09/20/2016] [Indexed: 12/13/2022] Open
Abstract
Spatial targeting of signaling components to activated receptors on the plasma membrane is key for initiating signal transduction. The actin cytoskeleton restricts antigen-stimulated colocalization of IgE-FcεRI with membrane-anchored signaling partner Lyn kinase, and this regulation is mediated by organization of plasma membrane lipids. The allergic response is initiated on the plasma membrane of mast cells by phosphorylation of the receptor for immunoglobulin E (IgE), FcεRI, by Lyn kinase after IgE-FcεRI complexes are cross-linked by multivalent antigen. Signal transduction requires reorganization of receptors and membrane signaling proteins, but this spatial regulation is not well defined. We used fluorescence localization microscopy (FLM) and pair-correlation analysis to measure the codistribution of IgE-FcεRI and Lyn on the plasma membrane of fixed cells with 20- to 25-nm resolution. We directly visualized Lyn recruitment to IgE-FcεRI within 1 min of antigen stimulation. Parallel FLM experiments captured stimulation-induced FcεRI phosphorylation and colocalization of a saturated lipid-anchor probe derived from Lyn’s membrane anchorage. We used cytochalasin and latrunculin to investigate participation of the actin cytoskeleton in regulating functional interactions of FcεRI. Inhibition of actin polymerization by these agents enhanced colocalization of IgE-FcεRI with Lyn and its saturated lipid anchor at early stimulation times, accompanied by augmented phosphorylation within FcεRI clusters. Ising model simulations provide a simplified model consistent with our results. These findings extend previous evidence that IgE-FcεRI signaling is initiated by colocalization with Lyn in ordered lipid regions and that the actin cytoskeleton regulates this functional interaction by influencing the organization of membrane lipids.
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Affiliation(s)
- Sarah A Shelby
- Department of Chemistry and Chemical Biology and Field of Biophysics, Cornell University, Ithaca, NY 14853
| | - Sarah L Veatch
- Department of Biophysics, University of Michigan, Ann Arbor, MI 48109
| | - David A Holowka
- Department of Chemistry and Chemical Biology and Field of Biophysics, Cornell University, Ithaca, NY 14853
| | - Barbara A Baird
- Department of Chemistry and Chemical Biology and Field of Biophysics, Cornell University, Ithaca, NY 14853
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62
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Levental I, Veatch S. The Continuing Mystery of Lipid Rafts. J Mol Biol 2016; 428:4749-4764. [PMID: 27575334 DOI: 10.1016/j.jmb.2016.08.022] [Citation(s) in RCA: 192] [Impact Index Per Article: 24.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2016] [Revised: 08/16/2016] [Accepted: 08/19/2016] [Indexed: 12/12/2022]
Abstract
Since its initial formalization nearly 20 years ago, the concept of lipid rafts has generated a tremendous amount of attention and interest and nearly as much controversy. The controversy is perhaps surprising because the notion itself is intuitive: compartmentalization in time and space is a ubiquitous theme at all scales of biology, and therefore, the partitioning of cellular membranes into lateral subdivision should be expected. Nevertheless, the physicochemical principles responsible for compartmentalization and the molecular mechanisms by which they are functionalized remain nearly as mysterious today as they were two decades ago. Herein, we review recent literature on this topic with a specific focus on the major open questions in the field including: (1) what are the best tools to assay raft behavior in living membranes? (2) what is the function of the complex lipidome of mammalian cells with respect to membrane organization? (3) what are the mechanisms that drive raft formation and determine their properties? (4) how can rafts be modulated? (5) how is membrane compartmentalization integrated into cellular signaling? Despite decades of intensive research, this compelling field remains full of fundamental questions.
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Affiliation(s)
- Ilya Levental
- McGovern Medical School at the University of Texas Houston, Department of Integrative Biology and Pharmacology
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63
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64
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Shivanandan A, Unnikrishnan J, Radenovic A. On characterizing protein spatial clusters with correlation approaches. Sci Rep 2016; 6:31164. [PMID: 27507257 PMCID: PMC4979030 DOI: 10.1038/srep31164] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2016] [Accepted: 07/15/2016] [Indexed: 12/31/2022] Open
Abstract
Spatial aggregation of proteins might have functional importance, e.g., in signaling, and nano-imaging can be used to study them. Such studies require accurate characterization of clusters based on noisy data. A set of spatial correlation approaches free of underlying cluster processes and input parameters have been widely used for this purpose. They include the radius of maximal aggregation ra obtained from Ripley’s L(r) − r function as an estimator of cluster size, and the estimation of various cluster parameters based on an exponential model of the Pair Correlation Function(PCF). While convenient, the accuracy of these methods is not clear: e.g., does it depend on how the molecules are distributed within the clusters, or on cluster parameters? We analyze these methods for a variety of cluster models. We find that ra relates to true cluster size by a factor that is nonlinearly dependent on parameters and that can be arbitrarily large. For the PCF method, for the models analyzed, we obtain linear relationships between the estimators and true parameters, and the estimators were found to be within ±100% of true parameters, depending on the model. Our results, based on an extendable general framework, point to the need for caution in applying these methods.
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Affiliation(s)
- Arun Shivanandan
- Laboratory of Nanoscale Biology, Institute of Bioengineering, Ecole Polytechnique Federale de Lausanne (EPFL), Lausanne 1015, Switzerland
| | - Jayakrishnan Unnikrishnan
- Audiovisual Communications Laboratory, School of Computer and Communication Sciences, Ecole Polytechnique Federale de Lausanne (EPFL), Lausanne 1015, Switzerland
| | - Aleksandra Radenovic
- Laboratory of Nanoscale Biology, Institute of Bioengineering, Ecole Polytechnique Federale de Lausanne (EPFL), Lausanne 1015, Switzerland
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65
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Machta BB, Gray E, Nouri M, McCarthy NLC, Gray EM, Miller AL, Brooks NJ, Veatch SL. Conditions that Stabilize Membrane Domains Also Antagonize n-Alcohol Anesthesia. Biophys J 2016; 111:537-545. [PMID: 27508437 PMCID: PMC4982967 DOI: 10.1016/j.bpj.2016.06.039] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2016] [Revised: 06/24/2016] [Accepted: 06/28/2016] [Indexed: 10/21/2022] Open
Abstract
Diverse molecules induce general anesthesia with potency strongly correlated with both their hydrophobicity and their effects on certain ion channels. We recently observed that several n-alcohol anesthetics inhibit heterogeneity in plasma-membrane-derived vesicles by lowering the critical temperature (Tc) for phase separation. Here, we exploit conditions that stabilize membrane heterogeneity to further test the correlation between the anesthetic potency of n-alcohols and effects on Tc. First, we show that hexadecanol acts oppositely to n-alcohol anesthetics on membrane mixing and antagonizes ethanol-induced anesthesia in a tadpole behavioral assay. Second, we show that two previously described "intoxication reversers" raise Tc and counter ethanol's effects in vesicles, mimicking the findings of previous electrophysiological and behavioral measurements. Third, we find that elevated hydrostatic pressure, long known to reverse anesthesia, also raises Tc in vesicles with a magnitude that counters the effect of butanol at relevant concentrations and pressures. Taken together, these results demonstrate that ΔTc predicts anesthetic potency for n-alcohols better than hydrophobicity in a range of contexts, supporting a mechanistic role for membrane heterogeneity in general anesthesia.
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Affiliation(s)
| | | | | | - Nicola L C McCarthy
- Department of Chemistry, Imperial College London, South Kensington Campus, London, United Kingdom
| | | | - Ann L Miller
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, Michigan
| | - Nicholas J Brooks
- Department of Chemistry, Imperial College London, South Kensington Campus, London, United Kingdom
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66
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Sierra-Valdez FJ, Ruiz-Suárez JC, Delint-Ramirez I. Pentobarbital modifies the lipid raft-protein interaction: A first clue about the anesthesia mechanism on NMDA and GABA A receptors. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1858:2603-2610. [PMID: 27457704 DOI: 10.1016/j.bbamem.2016.07.011] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/02/2016] [Revised: 07/19/2016] [Accepted: 07/21/2016] [Indexed: 12/13/2022]
Abstract
Recent studies have shown that anesthetic agents alter the physical properties of lipid rafts on model membranes. However, if this destabilization occurs in brain membranes, altering the lipid raft-protein interaction, remains unknown. We analyzed the effects produced by pentobarbital (PB) on brain plasma membranes and lipid rafts in vivo. We characterized for the first time the thermotropic behavior of plasma membranes, synaptosomes, and lipid rafts from rat brain. We found that the transition temperature from the ordered gel to disordered liquid phase of lipids is close to physiological temperature. We then studied the effect of PB on protein composition of lipid rafts. Our results show a reduction of the total protein associated to rafts, with a higher reduction of the NMDAR compared to the GABAA receptor. Both receptors are considered the main targets of PB. In general, our results suggest that lipid rafts could be plausible mediators in anesthetic action.
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Affiliation(s)
| | - J C Ruiz-Suárez
- Cinvestav-Monterrey, PIIT, Apodaca, Nuevo León, 66600, Mexico
| | - Ilse Delint-Ramirez
- Departamento de Farmacología y Toxicología, Facultad de Medicina, Universidad Autónoma de Nuevo León, Monterrey, Mexico; Centro de Investigación y Desarrollo en Ciencias de la Salud, Universidad Autónoma de Nuevo León, Monterrey, Mexico.
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67
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Burns MC, Nouri M, Veatch SL. Spot size variation FCS in simulations of the 2D Ising model. JOURNAL OF PHYSICS D: APPLIED PHYSICS 2016; 49:214001. [PMID: 27274570 PMCID: PMC4890970 DOI: 10.1088/0022-3727/49/21/214001] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Spot variation fluorescence correlation spectroscopy (svFCS) was developed to study the movement and organization of single molecules in plasma membranes. This experimental technique varies the size of an illumination area while measuring correlations in time using standard fluorescence correlation methods. Frequently, this data is interpreted using the assumption that correlation measurements reflect the dynamics of single molecule motions, and not motions of the average composition. Here, we explore how svFCS measurements report on the dynamics of components diffusing within simulations of a 2D Ising model with a conserved order parameter. Simulated correlation functions report on both the fast dynamics of single component mobility and the slower dynamics of the average composition. Over a range of simulation conditions, a conventional svFCS analysis suggests the presence of anomalous diffusion even though single molecule motions are nearly Brownian in these simulations. This misinterpretation is most significant when the surface density of the fluorescent label is elevated, therefore we suggest future measurements be made over a range of tracer densities. Some simulation conditions reproduce qualitative features of published svFCS experimental data. Overall, this work emphasizes the need to probe membranes using multiple complimentary experimental methodologies in order to draw conclusions regarding the nature of spatial and dynamical heterogeneity in these systems.
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68
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Ackerman DG, Feigenson GW. Effects of Transmembrane α-Helix Length and Concentration on Phase Behavior in Four-Component Lipid Mixtures: A Molecular Dynamics Study. J Phys Chem B 2016; 120:4064-77. [PMID: 27081858 DOI: 10.1021/acs.jpcb.6b00611] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
We used coarse-grained molecular dynamics simulations to examine the effects of transmembrane α-helical WALP peptides on the behavior of four-component lipid mixtures. These mixtures contain a high-melting temperature (high-Tm) lipid, a nanodomain-inducing low-Tm lipid, a macrodomain-inducing low-Tm lipid and cholesterol to model the outer leaflet of cell plasma membranes. In a series of simulations, we incrementally replace the nanodomain-inducing low-Tm lipid by the macrodomain-inducing low-Tm lipid and measure how lipid and phase properties are altered by the addition of WALPs of different length. Regardless of the ratio of the two low-Tm lipids, shorter WALPs increase domain size and all WALPs increase domain alignment between the two leaflets. These effects are smallest for the longest WALP tested, and increase with increasing WALP concentration. Thus, our simulations explain the experimental observation that WALPs induce macroscopic domains in otherwise nanodomain-forming lipid-only mixtures (unpublished). Since the cell plasma membrane contains a large fraction of transmembrane proteins, these findings link the behavior of lipid-only model membranes in vitro to phase behavior in vivo.
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Affiliation(s)
- David G Ackerman
- Department of Molecular Biology and Genetics, Cornell University , Ithaca, New York 14853, United States
| | - Gerald W Feigenson
- Department of Molecular Biology and Genetics, Cornell University , Ithaca, New York 14853, United States
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69
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Roles for lipid heterogeneity in immunoreceptor signaling. Biochim Biophys Acta Mol Cell Biol Lipids 2016; 1861:830-836. [PMID: 26995463 DOI: 10.1016/j.bbalip.2016.03.019] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2015] [Revised: 03/12/2016] [Accepted: 03/14/2016] [Indexed: 11/22/2022]
Abstract
Immune receptors that specifically recognize foreign antigens to activate leukocytes in adaptive immune responses belong to a family of multichain cell surface proteins. All of these contain immunoreceptor tyrosine-based activation motifs in one or more subunits that initiate signaling cascades following stimulated tyrosine phosphorylation by Src-family kinases. As highlighted in this review, lipids participate in this initial activation step, as well as in more downstream signaling steps. We summarize evidence for cholesterol-dependent ordered lipids serving to regulate the store-operated Ca(2+) channel, Orai1, and we describe the sensitivity of Orai1 coupling to the ER Ca(2+) sensor, STIM1, to inhibition by polyunsaturated fatty acids. Phosphoinositides play key roles in regulating STIM1-Orai1 coupling, as well as in the stimulated Ca(2+) oscillations that are a consequence of IgE receptor signaling in mast cells. They also participate in the coupling between the plasma membrane and the actin cytoskeleton, which regulates immune receptor responses in T cells, B cells, and mast cells, both positively and negatively, depending on the cellular context. Recent studies show that other phospholipids with mostly saturated acylation also participate in coupling between receptors and the actin cytoskeleton. Lipid heterogeneity is a central feature of the intimate relationship between the plasma membrane and the actin cytoskeleton. The detailed nature of these interactions and how they are dynamically regulated to initiate and propagate receptor-mediated cell signaling are challenging questions for further investigation. This article is part of a Special Issue entitled: The cellular lipid landscape edited by Tim P. Levine and Anant K. Menon.
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70
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Daniels BC, Ellison CJ, Krakauer DC, Flack JC. Quantifying collectivity. Curr Opin Neurobiol 2016; 37:106-113. [PMID: 26874472 DOI: 10.1016/j.conb.2016.01.012] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2016] [Accepted: 01/23/2016] [Indexed: 12/11/2022]
Abstract
In biological function emerges from the interactions of components with only partially aligned interests. An example is the brain-a large aggregation of neurons capable of producing unitary, coherent output. A theory for how such aggregations produce coherent output remains elusive. A first question we might ask is how collective is the behavior of the components? Here we introduce two properties of collectivity and illustrate how these properties can be quantified using approaches from information theory and statistical physics. First, amplification quantifies the sensitivity of the large scale to information at the small scale and is related to the notion of criticality in statistical physics. Second, decomposability reveals the extent to which aggregate behavior is reducible to individual contributions or is the result of synergistic interactions among components forming larger subgroups. These measures facilitate identification of causally important components and subgroups that might be experimentally manipulated to study the evolution and controllability of biological circuits and their outputs.
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Affiliation(s)
- Bryan C Daniels
- ASU-SFI Center for Biosocial Complex Systems, Arizona State University, United States.
| | - Christopher J Ellison
- Center for Complexity and Collective Computation, Wisconsin Institute for Discovery, University of Wisconsin-Madison, United States
| | - David C Krakauer
- Santa Fe Institute, Santa Fe, NM 87501, United States; ASU-SFI Center for Biosocial Complex Systems, Arizona State University, United States; Center for Complexity and Collective Computation, Wisconsin Institute for Discovery, University of Wisconsin-Madison, United States
| | - Jessica C Flack
- Santa Fe Institute, Santa Fe, NM 87501, United States; ASU-SFI Center for Biosocial Complex Systems, Arizona State University, United States; Center for Complexity and Collective Computation, Wisconsin Institute for Discovery, University of Wisconsin-Madison, United States.
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71
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Lange Y, Steck TL. Active membrane cholesterol as a physiological effector. Chem Phys Lipids 2016; 199:74-93. [PMID: 26874289 DOI: 10.1016/j.chemphyslip.2016.02.003] [Citation(s) in RCA: 58] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2015] [Revised: 02/04/2016] [Accepted: 02/08/2016] [Indexed: 02/05/2023]
Abstract
Sterols associate preferentially with plasma membrane sphingolipids and saturated phospholipids to form stoichiometric complexes. Cholesterol in molar excess of the capacity of these polar bilayer lipids has a high accessibility and fugacity; we call this fraction active cholesterol. This review first considers how active cholesterol serves as an upstream regulator of cellular sterol homeostasis. The mechanism appears to utilize the redistribution of active cholesterol down its diffusional gradient to the endoplasmic reticulum and mitochondria, where it binds multiple effectors and directs their feedback activity. We have also reviewed a broad literature in search of a role for active cholesterol (as opposed to bulk cholesterol or lipid domains such as rafts) in the activity of diverse membrane proteins. Several systems provide such evidence, implicating, in particular, caveolin-1, various kinds of ABC-type cholesterol transporters, solute transporters, receptors and ion channels. We suggest that this larger role for active cholesterol warrants close attention and can be tested easily.
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Affiliation(s)
- Yvonne Lange
- Department of Pathology, Rush University Medical Center, 1653 W. Congress Parkway, Chicago, IL 60612, USA.
| | - Theodore L Steck
- Department of Biochemistry and Molecular Biology, University of Chicago, 929 East 57th Street, Chicago, IL 60637, USA.
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72
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Smith AW, Huang HH, Endres NF, Rhodes C, Groves JT. Dynamic Organization of Myristoylated Src in the Live Cell Plasma Membrane. J Phys Chem B 2016; 120:867-76. [DOI: 10.1021/acs.jpcb.5b08887] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Adam W. Smith
- Department
of Chemistry, University of California, Berkeley, California 94720, United States
- Department
of Chemistry, University of Akron, Akron, Ohio 44303, United States
| | - Hector H. Huang
- Department
of Chemistry, University of California, Berkeley, California 94720, United States
- Howard
Hughes Medical Institute, Department of Molecular and Cell Biology, University of California, Berkeley, California 94720, United States
| | - Nicholas F. Endres
- Howard
Hughes Medical Institute, Department of Molecular and Cell Biology, University of California, Berkeley, California 94720, United States
| | - Christopher Rhodes
- Department
of Chemistry, University of California, Berkeley, California 94720, United States
| | - Jay T. Groves
- Department
of Chemistry, University of California, Berkeley, California 94720, United States
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73
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Simons K. Cell membranes: A subjective perspective. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2016; 1858:2569-2572. [PMID: 26827711 DOI: 10.1016/j.bbamem.2016.01.023] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/26/2015] [Revised: 01/19/2016] [Accepted: 01/21/2016] [Indexed: 11/29/2022]
Abstract
Cell membranes have developed a tremendous complexity of lipids and proteins geared to perform the functions cells require. The lipids have for long remained in the background and are now regaining their role as important building blocks of cells. Their main function is to form the matrix of our cell membranes where they support a variety of functions essential for life. This 2-dimensional fluid matrix has evolved unexpected material properties that involve both lipid-lipid and lipid-protein interactions. This perspective is a short summary of the challenges that this field faces and discusses potential ways and means for coming to grips with the properties of this incredible fluid. This article is part of a Special Issue entitled: Biosimulations edited by Ilpo Vattulainen and Tomasz Róg.
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Affiliation(s)
- Kai Simons
- Max-Planck-Institute of Molecular Cell Biology and Genetics, Pfotenhauerstr. 108, 01307 Dresden, Germany.
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74
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Reigada R, Mikhailov AS. Equilibrium microphase separation in the two-leaflet model of lipid membranes. Phys Rev E 2016; 93:010401. [PMID: 26871009 DOI: 10.1103/physreve.93.010401] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2015] [Indexed: 06/05/2023]
Abstract
Because of the coupling between local lipid composition and the thickness of the membrane, microphase separation in two-component lipid membranes can take place; such effects may underlie the formation of equilibrium nanoscale rafts. Using a kinetic description, this phenomenon is analytically and numerically investigated. The phase diagram is constructed through the stability analysis for linearized kinetic equations, and conditions for microphase separation are discussed. Simulations of the full kinetic model reveal the development of equilibrium membrane nanostructures with various morphologies from the initial uniform state.
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Affiliation(s)
- Ramon Reigada
- Departament de Química Física i Institut de Química Teòrica i Computacional (IQTCUB), Universitat de Barcelona, Avinguda Diagonal 647, 08028 Barcelona, Spain
| | - Alexander S Mikhailov
- Abteilung Physikalische Chemie, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany
- Department of Mathematics and Life Sciences, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, 739-8530, Japan
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75
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Fujimoto T, Parmryd I. Interleaflet Coupling, Pinning, and Leaflet Asymmetry-Major Players in Plasma Membrane Nanodomain Formation. Front Cell Dev Biol 2016. [PMID: 28119914 DOI: 10.3389/fcell.2016.0015] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/11/2023] Open
Abstract
The plasma membrane has a highly asymmetric distribution of lipids and contains dynamic nanodomains many of which are liquid entities surrounded by a second, slightly different, liquid environment. Contributing to the dynamics is a continuous repartitioning of components between the two types of liquids and transient links between lipids and proteins, both to extracellular matrix and cytoplasmic components, that temporarily pin membrane constituents. This make plasma membrane nanodomains exceptionally challenging to study and much of what is known about membrane domains has been deduced from studies on model membranes at equilibrium. However, living cells are by definition not at equilibrium and lipids are distributed asymmetrically with inositol phospholipids, phosphatidylethanolamines and phosphatidylserines confined mostly to the inner leaflet and glyco- and sphingolipids to the outer leaflet. Moreover, each phospholipid group encompasses a wealth of species with different acyl chain combinations whose lateral distribution is heterogeneous. It is becoming increasingly clear that asymmetry and pinning play important roles in plasma membrane nanodomain formation and coupling between the two lipid monolayers. How asymmetry, pinning, and interdigitation contribute to the plasma membrane organization is only beginning to be unraveled and here we discuss their roles and interdependence.
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Affiliation(s)
- Toyoshi Fujimoto
- Department of Anatomy and Molecular Cell Biology, Nagoya University Graduate School of Medicine Nagoya, Japan
| | - Ingela Parmryd
- Science for Life Laboratory, Medical Cell Biology, Uppsala University Uppsala, Sweden
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76
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Khadka NK, Ho CS, Pan J. Macroscopic and Nanoscopic Heterogeneous Structures in a Three-Component Lipid Bilayer Mixtures Determined by Atomic Force Microscopy. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2015; 31:12417-12425. [PMID: 26506226 DOI: 10.1021/acs.langmuir.5b02863] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Much of lipid raft properties can be inferred from phase behavior of multicomponent lipid membranes. We use liquid compatible atomic force microscopy (AFM) to study a three-component system composed of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), egg sphingomyelin (eSM), and cholesterol. Specifically, we obtain macroscopic and nanoscopic heterogeneous structures in a broad compositional space of DOPC/eSM/cholesterol (23 °C). In the macroscopic liquid coexisting region, we quantify area fraction of the coexisting phases and determine a set of thermodynamic tie-lines. When lipid compositions are near the critical point, we obtain fluctuation-like nanoscopic structures. We also use AFM height images to explore the hypothetical three-phase coexisting region. Finally, we use fluorescence microscopy to compare the phase behavior from our AFM measurements to that in free-floating giant unilamellar vesicles (GUVs). Our results highlight the role of lipid composition in mediating lipid domain formation and stability.
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Affiliation(s)
- Nawal K Khadka
- Department of Physics, University of South Florida , Tampa, Florida 33620, United States
| | - Chian Sing Ho
- Department of Physics, University of South Florida , Tampa, Florida 33620, United States
| | - Jianjun Pan
- Department of Physics, University of South Florida , Tampa, Florida 33620, United States
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77
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Wehrens M, ten Wolde PR, Mugler A. Positive feedback can lead to dynamic nanometer-scale clustering on cell membranes. J Chem Phys 2015; 141:205102. [PMID: 25429963 DOI: 10.1063/1.4901888] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Clustering of molecules on biological membranes is a widely observed phenomenon. A key example is the clustering of the oncoprotein Ras, which is known to be important for signal transduction in mammalian cells. Yet, the mechanism by which Ras clusters form and are maintained remains unclear. Recently, it has been discovered that activated Ras promotes further Ras activation. Here we show using particle-based simulation that this positive feedback is sufficient to produce persistent clusters of active Ras molecules at the nanometer scale via a dynamic nucleation mechanism. Furthermore, we find that our cluster statistics are consistent with experimental observations of the Ras system. Interestingly, we show that our model does not support a Turing regime of macroscopic reaction-diffusion patterning, and therefore that the clustering we observe is a purely stochastic effect, arising from the coupling of positive feedback with the discrete nature of individual molecules. These results underscore the importance of stochastic and dynamic properties of reaction diffusion systems for biological behavior.
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Affiliation(s)
- Martijn Wehrens
- FOM Institute AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands
| | | | - Andrew Mugler
- FOM Institute AMOLF, Science Park 104, 1098 XG Amsterdam, The Netherlands
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78
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Camley BA, Brown FLH. Fluctuating hydrodynamics of multicomponent membranes with embedded proteins. J Chem Phys 2015; 141:075103. [PMID: 25149817 DOI: 10.1063/1.4892802] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
A simulation method for the dynamics of inhomogeneous lipid bilayer membranes is presented. The membrane is treated using stochastic Saffman-Delbrück hydrodynamics, coupled to a phase-field description of lipid composition and discrete membrane proteins. Multiple applications are considered to validate and parameterize the model. The dynamics of membrane composition fluctuations above the critical point and phase separation dynamics below the critical point are studied in some detail, including the effects of adding proteins to the mixture.
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Affiliation(s)
- Brian A Camley
- Department of Physics and Center for Theoretical Biological Physics, University of California, San Diego, La Jolla, California 92093, USA
| | - Frank L H Brown
- Department of Physics, University of California, Santa Barbara, Santa Barbara, California 93106, USA
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79
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Raghunathan K, Ahsan A, Ray D, Nyati MK, Veatch SL. Membrane Transition Temperature Determines Cisplatin Response. PLoS One 2015; 10:e0140925. [PMID: 26484687 PMCID: PMC4618528 DOI: 10.1371/journal.pone.0140925] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2015] [Accepted: 10/01/2015] [Indexed: 11/19/2022] Open
Abstract
Cisplatin is a classical chemotherapeutic agent used in treating several forms of cancer including head and neck. However, cells develop resistance to the drug in some patients through a range of mechanisms, some of which are poorly understood. Using isolated plasma membrane vesicles as a model system, we present evidence suggesting that cisplatin induced resistance may be due to certain changes in the bio-physical properties of plasma membranes. Giant plasma membrane vesicles (GPMVs) isolated from cortical cytoskeleton exhibit a miscibility transition between a single liquid phase at high temperature and two distinct coexisting liquid phases at low temperature. The temperature at which this transition occurs is hypothesized to reflect the magnitude of membrane heterogeneity at physiological temperature. We find that addition of cisplatin to vesicles isolated from cisplatin-sensitive cells result in a lowering of this miscibility transition temperature, whereas in cisplatin-resistant cells such treatment does not affect the transition temperature. To explore if this is a cause or consequence of cisplatin resistance, we tested if addition of cisplatin in combination with agents that modulate GPMV transition temperatures can affect cisplatin sensitivity. We found that cells become more sensitive to cisplatin when isopropanol, an agent that lowers GPMV transition temperature, was combined with cisplatin. Conversely, cells became resistant to cisplatin when added in combination with menthol that raises GPMV transition temperatures. These data suggest that changes in plasma membrane heterogeneity augments or suppresses signaling events initiated in the plasma membranes that can determine response to cisplatin. We postulate that desired perturbations of membrane heterogeneity could provide an effective therapeutic strategy to overcome cisplatin resistance for certain patients.
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Affiliation(s)
- Krishnan Raghunathan
- Department of Biophysics, University of Michigan, Ann Arbor, Michigan, United States of America
| | - Aarif Ahsan
- Department of Radiation Oncology, University of Michigan, Ann Arbor, Michigan, United States of America
| | - Dipankar Ray
- Department of Radiation Oncology, University of Michigan, Ann Arbor, Michigan, United States of America
| | - Mukesh K. Nyati
- Department of Radiation Oncology, University of Michigan, Ann Arbor, Michigan, United States of America
| | - Sarah L. Veatch
- Department of Biophysics, University of Michigan, Ann Arbor, Michigan, United States of America
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80
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Growth Conditions and Cell Cycle Phase Modulate Phase Transition Temperatures in RBL-2H3 Derived Plasma Membrane Vesicles. PLoS One 2015; 10:e0137741. [PMID: 26368288 PMCID: PMC4569273 DOI: 10.1371/journal.pone.0137741] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2015] [Accepted: 08/21/2015] [Indexed: 01/06/2023] Open
Abstract
Giant plasma membrane vesicle (GPMV) isolated from a flask of RBL-2H3 cells appear uniform at physiological temperatures and contain coexisting liquid-ordered and liquid-disordered phases at low temperatures. While a single GPMV transitions between these two states at a well-defined temperature, there is significant vesicle-to-vesicle heterogeneity in a single preparation of cells, and average transition temperatures can vary significantly between preparations. In this study, we explore how GPMV transition temperatures depend on growth conditions, and find that average transition temperatures are negatively correlated with average cell density over 15°C in transition temperature and nearly three orders of magnitude in average surface density. In addition, average transition temperatures are reduced by close to 10°C when GPMVs are isolated from cells starved of serum overnight, and elevated transition temperatures are restored when serum-starved cells are incubated in serum-containing media for 12 h. We also investigated variation in transition temperature of GPMVs isolated from cells synchronized at the G1/S border through a double Thymidine block and find that average transition temperatures are systematically higher in GPMVs produced from G1 or M phase cells than in GPMVs prepared from S or G1 phase cells. Reduced miscibility transition temperatures are also observed in GPMVs prepared from cells treated with TRAIL to induce apoptosis or sphingomyelinase, and in some cases a gel phase is observed at temperatures above the miscibility transition in these vesicles. We conclude that at least some variability in GPMV transition temperature arises from variation in the local density of cells and asynchrony of the cell cycle. It is hypothesized that GPMV transition temperatures are a proxy for the magnitude of lipid-mediated membrane heterogeneity in intact cell plasma membranes at growth temperatures. If so, these results suggest that cells tune their plasma membrane composition in order to control the magnitude of membrane heterogeneity in response to different growth conditions.
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81
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Oxygen depletion speeds and simplifies diffusion in HeLa cells. Biophys J 2015; 107:1873-1884. [PMID: 25418168 DOI: 10.1016/j.bpj.2014.08.023] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2014] [Revised: 08/25/2014] [Accepted: 08/26/2014] [Indexed: 12/28/2022] Open
Abstract
Many cell types undergo a hypoxic response in the presence of low oxygen, which can lead to transcriptional, metabolic, and structural changes within the cell. Many biophysical studies to probe the localization and dynamics of single fluorescently labeled molecules in live cells either require or benefit from low-oxygen conditions. In this study, we examine how low-oxygen conditions alter the mobility of a series of plasma membrane proteins with a range of anchoring motifs in HeLa cells at 37°C. Under high-oxygen conditions, diffusion of all proteins is heterogeneous and confined. When oxygen is reduced with an enzymatic oxygen-scavenging system for ≥ 15 min, diffusion rates increase by > 2-fold, motion becomes unconfined on the timescales and distance scales investigated, and distributions of diffusion coefficients are remarkably consistent with those expected from Brownian motion. More subtle changes in protein mobility are observed in several other laboratory cell lines examined under both high- and low-oxygen conditions. Morphological changes and actin remodeling are observed in HeLa cells placed in a low-oxygen environment for 30 min, but changes are less apparent in the other cell types investigated. This suggests that changes in actin structure are responsible for increased diffusion in hypoxic HeLa cells, although superresolution localization measurements in chemically fixed cells indicate that membrane proteins do not colocalize with F-actin under either experimental condition. These studies emphasize the importance of controls in single-molecule imaging measurements, and indicate that acute response to low oxygen in HeLa cells leads to dramatic changes in plasma membrane structure. It is possible that these changes are either a cause or consequence of phenotypic changes in solid tumor cells associated with increased drug resistance and malignancy.
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82
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Yang ST, Kiessling V, Simmons JA, White JM, Tamm LK. HIV gp41-mediated membrane fusion occurs at edges of cholesterol-rich lipid domains. Nat Chem Biol 2015; 11:424-31. [PMID: 25915200 PMCID: PMC4433777 DOI: 10.1038/nchembio.1800] [Citation(s) in RCA: 143] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2014] [Accepted: 03/25/2015] [Indexed: 12/31/2022]
Abstract
Lipid rafts in plasma membranes have emerged as possible platforms for the entry of HIV and other viruses into cells. However, little is known about how lipid phase heterogeneity contributes to viral entry because of the fine-grained and still poorly understood complexity of biological membranes. We used model systems mimicking HIV envelopes and T cell membranes and found that raft-like liquid-ordered (Lo-phase) lipid domains were necessary and sufficient for efficient membrane targeting and fusion. Interestingly, membrane binding and fusion were low in homogeneous liquid-disordered (Ld-phase) and Lo-phase membranes, indicating that lipid phase heterogeneity is essential. The HIV fusion peptide preferentially targeted to Lo-Ld boundary regions and promoted full fusion at the interface between ordered and disordered lipids. Ld-phase vesicles proceeded only to hemifusion. Thus, we propose that edges but not areas of raft-like ordered lipid domains are vital for HIV entry and membrane fusion.
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Affiliation(s)
- Sung-Tae Yang
- Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, Virginia 22908, U.S.A
- Center for Membrane Biology, University of Virginia, Charlottesville, Virginia 22908, USA
| | - Volker Kiessling
- Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, Virginia 22908, U.S.A
- Center for Membrane Biology, University of Virginia, Charlottesville, Virginia 22908, USA
| | - James A. Simmons
- Department of Cell Biology, University of Virginia, Charlottesville, Virginia 22908, USA
- Center for Membrane Biology, University of Virginia, Charlottesville, Virginia 22908, USA
| | - Judith M. White
- Department of Cell Biology, University of Virginia, Charlottesville, Virginia 22908, USA
- Center for Membrane Biology, University of Virginia, Charlottesville, Virginia 22908, USA
| | - Lukas K. Tamm
- Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, Virginia 22908, U.S.A
- Center for Membrane Biology, University of Virginia, Charlottesville, Virginia 22908, USA
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83
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LeVine MV, Weinstein H. AIM for Allostery: Using the Ising Model to Understand Information Processing and Transmission in Allosteric Biomolecular Systems. ENTROPY 2015; 17:2895-2918. [PMID: 26594108 PMCID: PMC4652859 DOI: 10.3390/e17052895] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
In performing their biological functions, molecular machines must process and transmit information with high fidelity. Information transmission requires dynamic coupling between the conformations of discrete structural components within the protein positioned far from one another on the molecular scale. This type of biomolecular “action at a distance” is termed allostery. Although allostery is ubiquitous in biological regulation and signal transduction, its treatment in theoretical models has mostly eschewed quantitative descriptions involving the system's underlying structural components and their interactions. Here, we show how Ising models can be used to formulate an approach to allostery in a structural context of interactions between the constitutive components by building simple allosteric constructs we termed Allosteric Ising Models (AIMs). We introduce the use of AIMs in analytical and numerical calculations that relate thermodynamic descriptions of allostery to the structural context, and then show that many fundamental properties of allostery, such as the multiplicative property of parallel allosteric channels, are revealed from the analysis of such models. The power of exploring mechanistic structural models of allosteric function in more complex systems by using AIMs is demonstrated by building a model of allosteric signaling for an experimentally well-characterized asymmetric homodimer of the dopamine D2 receptor.
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Affiliation(s)
- Michael V. LeVine
- Department of Physiology and Biophysics, Weill Cornell Medical College, Cornell University, New York, NY 10065, USA
| | - Harel Weinstein
- Department of Physiology and Biophysics, Weill Cornell Medical College, Cornell University, New York, NY 10065, USA
- HRH Prince Alwaleed Bin Talal Bin Abdulaziz Alsaud Institute of Computational Biomedicine, Weill Cornell Medical College, Cornell University, New York, NY 10065, USA
- Author to whom correspondence should be addressed;
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84
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Sevcsik E, Brameshuber M, Fölser M, Weghuber J, Honigmann A, Schütz GJ. GPI-anchored proteins do not reside in ordered domains in the live cell plasma membrane. Nat Commun 2015; 6:6969. [PMID: 25897971 PMCID: PMC4430820 DOI: 10.1038/ncomms7969] [Citation(s) in RCA: 91] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2014] [Accepted: 03/18/2015] [Indexed: 02/07/2023] Open
Abstract
The organization of proteins and lipids in the plasma membrane has been the subject of a long-lasting debate. Membrane rafts of higher lipid chain order were proposed to mediate protein interactions, but have thus far not been directly observed. Here we use protein micropatterning combined with single-molecule tracking to put current models to the test: we rearranged lipid-anchored raft proteins (glycosylphosphatidylinositol(GPI)-anchored-mGFP) directly in the live cell plasma membrane and measured the effect on the local membrane environment. Intriguingly, this treatment does neither nucleate the formation of an ordered membrane phase nor result in any enrichment of nanoscopic-ordered domains within the micropatterned regions. In contrast, we find that immobilized mGFP-GPIs behave as inert obstacles to the diffusion of other membrane constituents without influencing their membrane environment over distances beyond their physical size. Our results indicate that phase partitioning is not a fundamental element of protein organization in the plasma membrane.
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Affiliation(s)
- Eva Sevcsik
- Institute of Applied Physics, Vienna University of Technology, Wiedner Hauptstrasse 8-10, Vienna 1040, Austria
| | - Mario Brameshuber
- Institute of Applied Physics, Vienna University of Technology, Wiedner Hauptstrasse 8-10, Vienna 1040, Austria
| | - Martin Fölser
- Institute of Applied Physics, Vienna University of Technology, Wiedner Hauptstrasse 8-10, Vienna 1040, Austria
| | - Julian Weghuber
- School of Engineering and Environmental Sciences, University of Applied Sciences Upper Austria, Stelzhamerstrasse 23, Wels 4600, Austria
| | - Alf Honigmann
- Department of NanoBiophotonics, Max-Planck-Institute for Biophysical Chemistry, Am Fassberg 11, Göttingen 37077, Germany
| | - Gerhard J Schütz
- Institute of Applied Physics, Vienna University of Technology, Wiedner Hauptstrasse 8-10, Vienna 1040, Austria
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85
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Levental KR, Levental I. Giant plasma membrane vesicles: models for understanding membrane organization. CURRENT TOPICS IN MEMBRANES 2015; 75:25-57. [PMID: 26015280 DOI: 10.1016/bs.ctm.2015.03.009] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The organization of eukaryotic membranes into functional domains continues to fascinate and puzzle cell biologists and biophysicists. The lipid raft hypothesis proposes that collective lipid interactions compartmentalize the membrane into coexisting liquid domains that are central to membrane physiology. This hypothesis has proven controversial because such structures cannot be directly visualized in live cells by light microscopy. The recent observations of liquid-liquid phase separation in biological membranes are an important validation of the raft hypothesis and enable application of the experimental toolbox of membrane physics to a biologically complex phase-separated membrane. This review addresses the role of giant plasma membrane vesicles (GPMVs) in refining the raft hypothesis and expands on the application of GPMVs as an experimental model to answer some of key outstanding problems in membrane biology.
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Affiliation(s)
- Kandice R Levental
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston - Medical School, Houston, TX, USA
| | - Ilya Levental
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston - Medical School, Houston, TX, USA
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86
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Meerschaert RL, Kelly CV. Trace membrane additives affect lipid phases with distinct mechanisms: a modified Ising model. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2015; 44:227-33. [PMID: 25820530 PMCID: PMC4412547 DOI: 10.1007/s00249-015-1017-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/19/2014] [Revised: 02/25/2015] [Accepted: 03/05/2015] [Indexed: 12/13/2022]
Abstract
The addition of trace molecules into membranes can significantly alter the morphology of the co-existing liquid phases and lipid phase transition temperature. Membrane additives may affect lipid phase dynamics through preferentially partitioning to the boundary between lipid phases or preferentially mixing into one lipid phase. The characteristic differences between these mechanisms are demonstrated here in a minimalistic nearest neighbor model to provide a framework for how slight changes to membrane composition may affect lipid-phase-dependent processes, such as lipid-raft formation, immunological signaling, and molecular sorting preceding endocytosis with coexisting liquid phases. Within the low mole fractions explored here (≤3 mol%), increasing the additive concentration linearly changed the phase miscibility temperature. Rotationally asymmetric Janus particles reduced the miscibility transition temperature for all fractions and degree of phase polarization. Rotationally symmetric additives, however, either increased or decreased the phase miscibility temperature depending on the phase preference of the additive. While most experimental molecules may contain aspects of both of these idealized additives, this model provides a broad framework to quantify the effects of membrane additives in regard to lipid phase preference, lipid-raft association, and contribution to lipid phase-dependent molecular sorting.
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87
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Huang H, Simsek MF, Jin W, Pralle A. Effect of receptor dimerization on membrane lipid raft structure continuously quantified on single cells by camera based fluorescence correlation spectroscopy. PLoS One 2015; 10:e0121777. [PMID: 25811483 PMCID: PMC4374828 DOI: 10.1371/journal.pone.0121777] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2014] [Accepted: 02/10/2015] [Indexed: 02/07/2023] Open
Abstract
Membrane bound cell signaling is modulated by the membrane ultra-structure, which itself may be affected by signaling. However, measuring the interaction of membrane proteins with membrane structures in intact cells in real-time poses considerable challenges. In this paper we present a non-destructive fluorescence method that quantifies these interactions in single cells, and is able to monitor the same cell continuously to observe small changes. This approach combines total internal fluorescence microscopy with fluorescence correlation spectroscopy to measure the protein's diffusion and molecular concentration in different sized areas simultaneously. It correctly differentiates proteins interacting with membrane fences from proteins interacting with cholesterol-stabilized domains, or lipid rafts. This method detects small perturbations of the membrane ultra-structure or of a protein's tendency to dimerize. Through continuous monitoring of single cells, we demonstrate how dimerization of GPI-anchored proteins increases their association with the structural domains. Using a dual-color approach we study the effect of dimerization of one GPI-anchored protein on another type of GPI-anchored protein expressed in the same cell. Scans over the cell surface reveal a correlation between cholesterol stabilized domains and membrane cytoskeleton.
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Affiliation(s)
- Heng Huang
- Department of Physics, University at Buffalo the State University of New York, Buffalo, New York, United States of America
| | - M. Fethullah Simsek
- Department of Physics, University at Buffalo the State University of New York, Buffalo, New York, United States of America
| | - Weixiang Jin
- Department of Physics, University at Buffalo the State University of New York, Buffalo, New York, United States of America
| | - Arnd Pralle
- Department of Physics, University at Buffalo the State University of New York, Buffalo, New York, United States of America
- Department of Biophysics and Physiology, University at Buffalo the State University of New York, Buffalo, New York, United States of America
- * E-mail:
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88
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Lee IH, Saha S, Polley A, Huang H, Mayor S, Rao M, Groves JT. Live cell plasma membranes do not exhibit a miscibility phase transition over a wide range of temperatures. J Phys Chem B 2015; 119:4450-9. [PMID: 25747462 DOI: 10.1021/jp512839q] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Lipid/cholesterol mixtures derived from cell membranes as well as their synthetic reconstitutions exhibit well-defined miscibility phase transitions and critical phenomena near physiological temperatures. This suggests that lipid/cholesterol-mediated phase separation plays a role in the organization of live cell membranes. However, macroscopic lipid-phase separation is not generally observed in cell membranes, and the degree to which properties of isolated lipid mixtures are preserved in the cell membrane remain unknown. A fundamental property of phase transitions is that the variation of tagged particle diffusion with temperature exhibits an abrupt change as the system passes through the transition, even when the two phases are distributed in a nanometer-scale emulsion. We support this using a variety of Monte Carlo and atomistic simulations on model lipid membrane systems. However, temperature-dependent fluorescence correlation spectroscopy of labeled lipids and membrane-anchored proteins in live cell membranes shows a consistently smooth increase in the diffusion coefficient as a function of temperature. We find no evidence of a discrete miscibility phase transition throughout a wide range of temperatures: 14-37 °C. This contrasts the behavior of giant plasma membrane vesicles (GPMVs) blebbed from the same cells, which do exhibit phase transitions and macroscopic phase separation. Fluorescence lifetime analysis of a DiI probe in both cases reveals a significant environmental difference between the live cell and the GPMV. Taken together, these data suggest the live cell membrane may avoid the miscibility phase transition inherent to its lipid constituents by actively regulating physical parameters, such as tension, in the membrane.
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Affiliation(s)
- Il-Hyung Lee
- †Department of Chemistry, California Institute for Quantitative Biosciences (QB3), Howard Hughes Medical Institute, University of California, Berkeley, California 94720, United States
| | - Suvrajit Saha
- §National Centre for Biological Sciences (TIFR), Bellary Road, Bangalore 560065, India
| | - Anirban Polley
- ∥Raman Research Institute, C.V. Raman Avenue, Bangalore 560080, India
| | - Hector Huang
- †Department of Chemistry, California Institute for Quantitative Biosciences (QB3), Howard Hughes Medical Institute, University of California, Berkeley, California 94720, United States
| | - Satyajit Mayor
- §National Centre for Biological Sciences (TIFR), Bellary Road, Bangalore 560065, India
| | - Madan Rao
- §National Centre for Biological Sciences (TIFR), Bellary Road, Bangalore 560065, India.,∥Raman Research Institute, C.V. Raman Avenue, Bangalore 560080, India
| | - Jay T Groves
- †Department of Chemistry, California Institute for Quantitative Biosciences (QB3), Howard Hughes Medical Institute, University of California, Berkeley, California 94720, United States.,‡Materials Sciences Division, Physical Biosciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720, United States
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89
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Arumugam S, Petrov EP, Schwille P. Cytoskeletal pinning controls phase separation in multicomponent lipid membranes. Biophys J 2015; 108:1104-13. [PMID: 25762322 PMCID: PMC4375424 DOI: 10.1016/j.bpj.2014.12.050] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2014] [Revised: 12/22/2014] [Accepted: 12/23/2014] [Indexed: 11/22/2022] Open
Abstract
We study the effect of a minimal cytoskeletal network formed on the surface of giant unilamellar vesicles by the prokaryotic tubulin homolog, FtsZ, on phase separation in freestanding lipid membranes. FtsZ has been modified to interact with the membrane through a membrane targeting sequence from the prokaryotic protein MinD. FtsZ with the attached membrane targeting sequence efficiently forms a highly interconnected network on membranes with a concentration-dependent mesh size, much similar to the eukaryotic cytoskeletal network underlying the plasma membrane. Using giant unilamellar vesicles formed from a quaternary lipid mixture, we demonstrate that the artificial membrane-associated cytoskeleton, on the one hand, suppresses large-scale phase separation below the phase transition temperature, and, on the other hand, preserves phase separation above the transition temperature. Our experimental observations support the ideas put forward in our previous simulation study: In particular, the picket fence effect on phase separation may explain why micrometer-scale membrane domains are observed in isolated, cytoskeleton-free giant plasma membrane vesicles, but not in intact cell membranes. The experimentally observed suppression of large-scale phase separation much below the transition temperatures also serves as an argument in favor of the cryoprotective role of the cytoskeleton.
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Affiliation(s)
- Senthil Arumugam
- Institut Curie, Centre de Recherche, Paris, France; CNRS, UMR 168, Physico-chimie Curie, Paris, France; CNRS, UMR 3666, Endocytic Trafficking and Therapeutic Delivery Group, Paris, France
| | - Eugene P Petrov
- Max Planck Institute of Biochemistry, Department of Cellular and Molecular Biophysics, Am Klopferspitz 18, Martinsried, Germany.
| | - Petra Schwille
- Max Planck Institute of Biochemistry, Department of Cellular and Molecular Biophysics, Am Klopferspitz 18, Martinsried, Germany.
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90
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Magenau A, Owen DM, Yamamoto Y, Tran J, Kwiatek JM, Parton RG, Gaus K. Discreet and distinct clustering of five model membrane proteins revealed by single molecule localization microscopy. Mol Membr Biol 2015; 32:11-8. [PMID: 25586872 DOI: 10.3109/09687688.2014.990997] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Compartmentalization is a functionally important property of the plasma membrane, yet the underlying principles that organize membrane proteins into distinct domains are not well understood. Using single molecule localization microscopy, we assessed the clustering of five model membrane proteins in the plasma membrane of HeLa cells. All five proteins formed discrete and distinct nano-scaled clusters. The extent of clustering of the five proteins, independent of their membrane anchors, increased significantly when the fluorescent protein mEOS2 was employed, suggesting that protein-protein interactions are a key driver for clustering. Further, actin depolymerization or reduction of membrane order had a greater, and in some instances opposing effects on the clustering of membrane proteins fused to mEOS2 compared to PS-CFP2-fusion proteins. The data propose that protein interactions can override the lateral organization imposed by membrane anchors to provide an exquisite regulation of the mosaic-like compartmentalization of the plasma membrane.
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Affiliation(s)
- Astrid Magenau
- Centre for Vascular Research and Australian Centre for NanoMedicine, University of New South Wales , Sydney, Australia
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91
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92
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Schuberth C, Wedlich-Söldner R. Building a patchwork - The yeast plasma membrane as model to study lateral domain formation. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2014; 1853:767-74. [PMID: 25541280 DOI: 10.1016/j.bbamcr.2014.12.019] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/06/2014] [Revised: 12/01/2014] [Accepted: 12/14/2014] [Indexed: 01/03/2023]
Abstract
The plasma membrane (PM) has to fulfill a wide range of biological functions including selective uptake of substances, signal transduction and modulation of cell polarity and cell shape. To allow efficient regulation of these processes many resident proteins and lipids of the PM are laterally segregated into different functional domains. A particularly striking example of lateral segregation has been described for the budding yeast PM, where integral membrane proteins as well as lipids exhibit very slow translational mobility and form a patchwork of many overlapping micron-sized domains. Here we discuss the molecular and physical mechanisms contributing to the formation of a multi-domain membrane and review our current understanding of yeast PM organization. Many of the fundamental principles underlying membrane self-assembly and organization identified in yeast are expected to equally hold true in other organisms, even for the more transient and elusive organization of the PM in mammalian cells. This article is part of a Special Issue entitled: Nanoscale membrane organisation and signalling.
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Affiliation(s)
- Christian Schuberth
- Institute of Cell Dynamics and Imaging, University of Münster, Von-Esmarch-Str. 56, 48149 Münster, Germany; Cells-in-Motion Cluster of Excellence (EXC 1003 - CiM), University of Münster, Münster, Germany
| | - Roland Wedlich-Söldner
- Institute of Cell Dynamics and Imaging, University of Münster, Von-Esmarch-Str. 56, 48149 Münster, Germany; Cells-in-Motion Cluster of Excellence (EXC 1003 - CiM), University of Münster, Münster, Germany.
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93
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Sadeghi S, Vink RLC. Membrane sorting via the extracellular matrix. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2014; 1848:527-31. [PMID: 25450353 DOI: 10.1016/j.bbamem.2014.10.035] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2014] [Revised: 10/06/2014] [Accepted: 10/21/2014] [Indexed: 12/16/2022]
Abstract
We consider the coupling between a membrane and the extracellular matrix. Computer simulations demonstrate that the latter coupling is able to sort lipids. It is assumed that membranes are elastic manifolds, and that this manifold is disrupted by the extracellular matrix. For a solid-supported membrane with an actin network on top, regions of positive curvature are induced below the actin fibers. A similar mechanism is conceivable by assuming that the proteins which connect the cytoskeleton to the membrane induce local membrane curvature. The regions of non-zero curvature exist irrespective of any phase transition the lipids themselves may undergo. For lipids that prefer certain curvature, the extracellular matrix thus provides a spatial template for the resulting lateral domain structure of the membrane.
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Affiliation(s)
- Sina Sadeghi
- Institute of Theoretical Physics, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, D-37077 Göttingen, Germany.
| | - Richard L C Vink
- Institute of Theoretical Physics, Georg-August-Universität Göttingen, Friedrich-Hund-Platz 1, D-37077 Göttingen, Germany
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94
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Alessandrini A, Facci P. Phase transitions in supported lipid bilayers studied by AFM. SOFT MATTER 2014; 10:7145-7164. [PMID: 25090108 DOI: 10.1039/c4sm01104j] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We review the capabilities of Atomic Force Microscopy (AFM) in the study of phase transitions in Supported Lipid Bilayers (SLBs). AFM represents a powerful technique to cover the resolution range not available to fluorescence imaging techniques and where spectroscopic data suggest what the relevant lateral scale for domain formation might be. Phase transitions of lipid bilayers involve the formation of domains characterized by different heights with respect to the surrounding phase and are therefore easily identified by AFM in liquid solution once the bilayer is confined to a flat surface. Even if not endowed with high time resolution, AFM allows light to be shed on some aspects related to lipid phase transitions in the case of both a single lipid component and lipid mixtures containing sterols also. We discuss here the obtained results in light of the peculiarities of supported lipid bilayer model systems.
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Affiliation(s)
- Andrea Alessandrini
- Dipartimento di Scienze Fisiche, Informatiche e Matematiche, Via Campi 213/A, 41125, Modena, Italy.
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95
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Sadeghi S, Müller M, Vink RLC. Raft formation in lipid bilayers coupled to curvature. Biophys J 2014; 107:1591-600. [PMID: 25296311 PMCID: PMC4190607 DOI: 10.1016/j.bpj.2014.07.072] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2014] [Revised: 07/09/2014] [Accepted: 07/15/2014] [Indexed: 11/05/2022] Open
Abstract
We present computer simulations of a membrane in which the local composition is coupled to the local membrane curvature. At high temperatures (i.e., above the temperature of macroscopic phase separation), finite-sized transient domains are observed, reminiscent of lipid rafts. The domain size is in the range of hundred nanometers, and set by the membrane elastic properties. These findings are in line with the notion of the membrane as a curvature-induced microemulsion. At low temperature, the membrane phase separates. The transition to the phase-separated regime is continuous and belongs to the two-dimensional Ising universality class when the coupling to curvature is weak, but becomes first-order for strong curvature-composition coupling.
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Affiliation(s)
- Sina Sadeghi
- Institute of Theoretical Physics, Georg-August-Universität Göttingen, Göttingen, Germany.
| | - Marcus Müller
- Institute of Theoretical Physics, Georg-August-Universität Göttingen, Göttingen, Germany
| | - Richard L C Vink
- Institute of Theoretical Physics, Georg-August-Universität Göttingen, Göttingen, Germany
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96
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Liang Q, Wu QY, Wang ZY. Effect of hydrophobic mismatch on domain formation and peptide sorting in the multicomponent lipid bilayers in the presence of immobilized peptides. J Chem Phys 2014; 141:074702. [DOI: 10.1063/1.4891931] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Affiliation(s)
- Qing Liang
- Center for Statistical and Theoretical Condensed Matter Physics and Department of Physics, Zhejiang Normal University, Jinhua 321004, People's Republic of China
- Department of Physics, Ningbo University, Ningbo 315211, People's Republic of China
| | - Qing-Yan Wu
- Center for Statistical and Theoretical Condensed Matter Physics and Department of Physics, Zhejiang Normal University, Jinhua 321004, People's Republic of China
| | - Zhi-Yong Wang
- School of Optoelectronic Information, Chongqing University of Technology, Chongqing 400054, People's Republic of China
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97
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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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98
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Sikder MKU, Stone KA, Kumar PBS, Laradji M. Combined effect of cortical cytoskeleton and transmembrane proteins on domain formation in biomembranes. J Chem Phys 2014; 141:054902. [PMID: 25106608 PMCID: PMC4119197 DOI: 10.1063/1.4890655] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2014] [Accepted: 06/25/2014] [Indexed: 11/14/2022] Open
Abstract
We investigate the combined effects of transmembrane proteins and the subjacent cytoskeleton on the dynamics of phase separation in multicomponent lipid bilayers using computer simulations of a particle-based implicit solvent model for lipid membranes with soft-core interactions. We find that microphase separation can be achieved by the protein confinement by the cytoskeleton. Our results have relevance to the finite size of lipid rafts in the plasma membrane of mammalian cells.
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Affiliation(s)
| | - Kyle A Stone
- Department of Physics, The University of Memphis, Memphis, Tennessee 38152, USA
| | - P B Sunil Kumar
- Department of Physics, Indian Institute of Technology Madras, Chennai 600 036, India and MEMPHYS - Center for Biomembrane Physics, University of Southern Denmark, DK-5230 Odense, Denmark
| | - Mohamed Laradji
- Department of Physics, The University of Memphis, Memphis, Tennessee 38152, USA and MEMPHYS - Center for Biomembrane Physics, University of Southern Denmark, DK-5230 Odense, Denmark
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99
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Shelby SA, Holowka D, Baird B, Veatch SL. Distinct stages of stimulated FcεRI receptor clustering and immobilization are identified through superresolution imaging. Biophys J 2014; 105:2343-54. [PMID: 24268146 DOI: 10.1016/j.bpj.2013.09.049] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2013] [Revised: 09/05/2013] [Accepted: 09/09/2013] [Indexed: 12/25/2022] Open
Abstract
Recent advances in fluorescence localization microscopy have made it possible to image chemically fixed and living cells at 20 nm lateral resolution. We apply this methodology to simultaneously record receptor organization and dynamics on the ventral surface of live RBL-2H3 mast cells undergoing antigen-mediated signaling. Cross-linking of IgE bound to FcεRI by multivalent antigen initiates mast cell activation, which leads to inflammatory responses physiologically. We quantify receptor organization and dynamics as cells are stimulated at room temperature (22°C). Within 2 min of antigen addition, receptor diffusion coefficients decrease by an order of magnitude, and single-particle trajectories are confined. Within 5 min of antigen addition, receptors organize into clusters containing ∼100 receptors with average radii of ∼70 nm. By comparing simultaneous measurements of clustering and mobility, we determine that there are two distinct stages of receptor clustering. In the first stage, which precedes stimulated Ca(2+) mobilization, receptors slow dramatically but are not tightly clustered. In the second stage, receptors are tightly packed and confined. We find that stimulation-dependent changes in both receptor clustering and mobility can be reversed by displacing multivalent antigen with monovalent ligands, and that these changes can be modulated through enrichment or reduction in cellular cholesterol levels.
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Affiliation(s)
- Sarah A Shelby
- Department of Chemistry and Chemical Biology, and Field of Biophysics, Cornell University, Ithaca, NY
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Active organization of membrane constituents in living cells. Curr Opin Cell Biol 2014; 29:126-32. [PMID: 24975942 DOI: 10.1016/j.ceb.2014.05.007] [Citation(s) in RCA: 81] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2014] [Revised: 04/09/2014] [Accepted: 05/10/2014] [Indexed: 11/24/2022]
Abstract
A search for organizing principles underlying molecular patterning at the cell surface and its regulation over different scales is necessary. This is important for understanding how the cell builds membrane bound organelles that emanate from it and for how the cell interacts with its physical and chemical milieu. This requires a broad framework to rationalize the mass of accumulated data about the spatial localization and dynamics of its constituents, and their physical and chemical environment. Lateral heterogeneities in the organization of membrane components of a living cell appear to be a hallmark of how a cell addresses sorting and signaling functions. Here we explore two classes of mechanisms of segregation of membrane components in the plasma membrane. We suggest that viewing the membrane as a passive, thermally equilibrated system is unlikely to provide an adequate framework to understand the mechanisms of membrane component segregation in vivo. Instead the surface of living cells behaves as an active membrane composite.
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