1
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Weakly HMJ, Keller SL. Coupling liquid phases in 3D condensates and 2D membranes: Successes, challenges, and tools. Biophys J 2024; 123:1329-1341. [PMID: 38160256 PMCID: PMC11163299 DOI: 10.1016/j.bpj.2023.12.023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2023] [Revised: 12/05/2023] [Accepted: 12/26/2023] [Indexed: 01/03/2024] Open
Abstract
This review describes the major experimental challenges researchers meet when attempting to couple phase separation between membranes and condensates. Although it is well known that phase separation in a 2D membrane could affect molecules capable of forming a 3D condensate (and vice versa), few researchers have quantified the effects to date. The scarcity of these measurements is not due to a lack of intense interest or effort in the field. Rather, it reflects significant experimental challenges in manipulating coupled membranes and condensates to yield quantitative values. These challenges transcend many molecular details, which means they impact a wide range of systems. This review highlights recent exciting successes in the field, and it lays out a comprehensive list of tools that address potential pitfalls for researchers who are considering coupling membranes with condensates.
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Affiliation(s)
- Heidi M J Weakly
- Department of Chemistry, University of Washington - Seattle, Seattle, Washington
| | - Sarah L Keller
- Department of Chemistry, University of Washington - Seattle, Seattle, Washington.
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2
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Su WC, Ho JCS, Gettel DL, Rowland AT, Keating CD, Parikh AN. Kinetic control of shape deformations and membrane phase separation inside giant vesicles. Nat Chem 2024; 16:54-62. [PMID: 37414881 DOI: 10.1038/s41557-023-01267-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2021] [Accepted: 06/06/2023] [Indexed: 07/08/2023]
Abstract
A variety of cellular processes use liquid-liquid phase separation (LLPS) to create functional levels of organization, but the kinetic pathways by which it proceeds remain incompletely understood. Here in real time, we monitor the dynamics of LLPS of mixtures of segregatively phase-separating polymers inside all-synthetic, giant unilamellar vesicles. After dynamically triggering phase separation, we find that the ensuing relaxation-en route to the new equilibrium-is non-trivially modulated by a dynamic interplay between the coarsening of the evolving droplet phase and the interactive membrane boundary. The membrane boundary is preferentially wetted by one of the incipient phases, dynamically arresting the progression of coarsening and deforming the membrane. When the vesicles are composed of phase-separating mixtures of common lipids, LLPS within the vesicular interior becomes coupled to the membrane's compositional degrees of freedom, producing microphase-separated membrane textures. This coupling of bulk and surface phase-separation processes suggests a physical principle by which LLPS inside living cells might be dynamically regulated and communicated to the cellular boundaries.
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Affiliation(s)
- Wan-Chih Su
- Chemistry Graduate Program, University of California, Davis, CA, USA
| | - James C S Ho
- Singapore Centre for Environmental Life Sciences Engineering and Institute for Digital Molecular Analytics and Science, Nanyang Technological University, Nanyang Technological University, Singapore, Singapore
| | - Douglas L Gettel
- Chemical Engineering Graduate Program, University of California, Davis, CA, USA
| | - Andrew T Rowland
- Department of Chemistry, The Pennsylvania State University, University Park, PA, USA
| | - Christine D Keating
- Department of Chemistry, The Pennsylvania State University, University Park, PA, USA.
| | - Atul N Parikh
- Chemistry Graduate Program, University of California, Davis, CA, USA.
- Singapore Centre for Environmental Life Sciences Engineering and Institute for Digital Molecular Analytics and Science, Nanyang Technological University, Nanyang Technological University, Singapore, Singapore.
- Chemical Engineering Graduate Program, University of California, Davis, CA, USA.
- Biomedical Engineering Graduate Programs, University of California, Davis, CA, USA.
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3
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Shelby SA, Veatch SL. The Membrane Phase Transition Gives Rise to Responsive Plasma Membrane Structure and Function. Cold Spring Harb Perspect Biol 2023; 15:a041395. [PMID: 37553204 PMCID: PMC10626261 DOI: 10.1101/cshperspect.a041395] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/10/2023]
Abstract
Several groups have recently reported evidence for the emergence of domains in cell plasma membranes when membrane proteins are organized by ligand binding or assembly of membrane proximal scaffolds. These domains recruit and retain components that favor the liquid-ordered phase, adding to a decades-old literature interrogating the contribution of membrane phase separation in plasma membrane organization and function. Here we propose that both past and present observations are consistent with a model in which membranes have a high compositional susceptibility, arising from their thermodynamic state in a single phase that is close to a miscibility phase transition. This rigorous framework naturally allows for both transient structure in the form of composition fluctuations and long-lived structure in the form of induced domains. In this way, the biological tuning of plasma membrane composition enables a responsive compositional landscape that facilitates and augments cellular biochemistry vital to plasma membrane functions.
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Affiliation(s)
- Sarah A Shelby
- Biochemistry & Cellular and Molecular Biology, University of Tennessee Knoxville, Knoxville, Tennessee 37996, USA
| | - Sarah L Veatch
- Program in Biophysics, University of Michigan, Ann Arbor, Michigan 48109, USA
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4
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Wang Y, Palzhanov Y, Dang DT, Quaini A, Olshanskii M, Majd S. On Fusogenicity of Positively Charged Phased-Separated Lipid Vesicles: Experiments and Computational Simulations. Biomolecules 2023; 13:1473. [PMID: 37892155 PMCID: PMC10605210 DOI: 10.3390/biom13101473] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2023] [Revised: 09/19/2023] [Accepted: 09/27/2023] [Indexed: 10/29/2023] Open
Abstract
This paper studies the fusogenicity of cationic liposomes in relation to their surface distribution of cationic lipids and utilizes membrane phase separation to control this surface distribution. It is found that concentrating the cationic lipids into small surface patches on liposomes, through phase-separation, can enhance liposome's fusogenicity. Further concentrating these lipids into smaller patches on the surface of liposomes led to an increased level of fusogenicity. These experimental findings are supported by numerical simulations using a mathematical model for phase-separated charged liposomes. Findings of this study may be used for design and development of highly fusogenic liposomes with minimal level of toxicity.
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Affiliation(s)
- Yifei Wang
- Department of Biomedical Engineering, University of Houston, 3551 Cullen Blvd, Houston, TX 77204, USA; (Y.W.)
| | - Yerbol Palzhanov
- Department of Mathematics, University of Houston, 3551 Cullen Blvd, Houston, TX 77204, USA; (Y.P.); (M.O.)
| | - Dang T. Dang
- Department of Biomedical Engineering, University of Houston, 3551 Cullen Blvd, Houston, TX 77204, USA; (Y.W.)
| | - Annalisa Quaini
- Department of Mathematics, University of Houston, 3551 Cullen Blvd, Houston, TX 77204, USA; (Y.P.); (M.O.)
| | - Maxim Olshanskii
- Department of Mathematics, University of Houston, 3551 Cullen Blvd, Houston, TX 77204, USA; (Y.P.); (M.O.)
| | - Sheereen Majd
- Department of Biomedical Engineering, University of Houston, 3551 Cullen Blvd, Houston, TX 77204, USA; (Y.W.)
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5
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Shelby SA, Castello-Serrano I, Wisser KC, Levental I, Veatch SL. Membrane phase separation drives responsive assembly of receptor signaling domains. Nat Chem Biol 2023; 19:750-758. [PMID: 36997644 PMCID: PMC10771812 DOI: 10.1038/s41589-023-01268-8] [Citation(s) in RCA: 50] [Impact Index Per Article: 50.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2022] [Accepted: 01/17/2023] [Indexed: 04/01/2023]
Abstract
Plasma membrane heterogeneity has been tied to a litany of cellular functions and is often explained by analogy to membrane phase separation; however, models based on phase separation alone fall short of describing the rich organization available within cell membranes. Here we present comprehensive experimental evidence motivating an updated model of plasma membrane heterogeneity in which membrane domains assemble in response to protein scaffolds. Quantitative super-resolution nanoscopy measurements in live B lymphocytes detect membrane domains that emerge upon clustering B cell receptors (BCRs). These domains enrich and retain membrane proteins based on their preference for the liquid-ordered phase. Unlike phase-separated membranes that consist of binary phases with defined compositions, membrane composition at BCR clusters is modulated through the protein constituents in clusters and the composition of the membrane overall. This tunable domain structure is detected through the variable sorting of membrane probes and impacts the magnitude of BCR activation.
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Affiliation(s)
- Sarah A Shelby
- Program in Biophysics, University of Michigan, Ann Arbor, MI, USA
- Department of Biochemistry & Cellular and Molecular Biology, University of Tennessee Knoxville, Knoxville, TN, USA
| | - Ivan Castello-Serrano
- Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA, USA
| | | | - Ilya Levental
- Department of Molecular Physiology and Biological Physics, University of Virginia, Charlottesville, VA, USA
| | - Sarah L Veatch
- Program in Biophysics, University of Michigan, Ann Arbor, MI, USA.
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6
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Wang HY, Chan SH, Dey S, Castello-Serrano I, Rosen MK, Ditlev JA, Levental KR, Levental I. Coupling of protein condensates to ordered lipid domains determines functional membrane organization. SCIENCE ADVANCES 2023; 9:eadf6205. [PMID: 37126554 PMCID: PMC10132753 DOI: 10.1126/sciadv.adf6205] [Citation(s) in RCA: 26] [Impact Index Per Article: 26.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
During T cell activation, the transmembrane adaptor protein LAT (linker for activation of T cells) forms biomolecular condensates with Grb2 and Sos1, facilitating signaling. LAT has also been associated with cholesterol-rich condensed lipid domains; However, the potential coupling between protein condensation and lipid phase separation and its role in organizing T cell signaling were unknown. Here, we report that LAT/Grb2/Sos1 condensates reconstituted on model membranes can induce and template lipid domains, indicating strong coupling between lipid- and protein-based phase separation. Correspondingly, activation of T cells induces cytoplasmic protein condensates that associate with and stabilize raft-like membrane domains. Inversely, lipid domains nucleate and stabilize LAT protein condensates in both reconstituted and living systems. This coupling of lipid and protein assembly is functionally important, as uncoupling of lipid domains from cytoplasmic protein condensates abrogates T cell activation. Thus, thermodynamic coupling between protein condensates and ordered lipid domains regulates the functional organization of living membranes.
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Affiliation(s)
- Hong-Yin Wang
- Department of Molecular Physiology and Biological Physics, Center for Membrane and Cell Physiology, University of Virginia, Charlottesville, VA 22903, USA
| | - Sze Ham Chan
- Department of Molecular Physiology and Biological Physics, Center for Membrane and Cell Physiology, University of Virginia, Charlottesville, VA 22903, USA
| | - Simli Dey
- Department of Molecular Physiology and Biological Physics, Center for Membrane and Cell Physiology, University of Virginia, Charlottesville, VA 22903, USA
| | - Ivan Castello-Serrano
- Department of Molecular Physiology and Biological Physics, Center for Membrane and Cell Physiology, University of Virginia, Charlottesville, VA 22903, USA
| | - Michael K Rosen
- Department of Biophysics and Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
| | - Jonathon A Ditlev
- Department of Biophysics and Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
- Program in Molecular Medicine, Program in Cell Biology, Hospital for Sick Children, Toronto, ON M5G 0A4, Canada
- Department of Biochemistry, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Kandice R Levental
- Department of Molecular Physiology and Biological Physics, Center for Membrane and Cell Physiology, University of Virginia, Charlottesville, VA 22903, USA
| | - Ilya Levental
- Department of Molecular Physiology and Biological Physics, Center for Membrane and Cell Physiology, University of Virginia, Charlottesville, VA 22903, USA
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7
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Reinhard J, Leveille CL, Cornell CE, Merz AJ, Klose C, Ernst R, Keller SL. Remodeling of yeast vacuole membrane lipidomes from the log (one phase) to stationary stage (two phases). Biophys J 2023; 122:1043-1057. [PMID: 36635960 PMCID: PMC10111276 DOI: 10.1016/j.bpj.2023.01.009] [Citation(s) in RCA: 9] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2022] [Revised: 01/03/2023] [Accepted: 01/09/2023] [Indexed: 01/13/2023] Open
Abstract
Upon nutrient limitation, budding yeast of Saccharomyces cerevisiae shift from fast growth (the log stage) to quiescence (the stationary stage). This shift is accompanied by liquid-liquid phase separation in the membrane of the vacuole, an endosomal organelle. Recent work indicates that the resulting micrometer-scale domains in vacuole membranes enable yeast to survive periods of stress. An outstanding question is which molecular changes might cause this membrane phase separation. Here, we conduct lipidomics of vacuole membranes in both the log and stationary stages. Isolation of pure vacuole membranes is challenging in the stationary stage, when lipid droplets are in close contact with vacuoles. Immuno-isolation has previously been shown to successfully purify log-stage vacuole membranes with high organelle specificity, but it was not previously possible to immuno-isolate stationary-stage vacuole membranes. Here, we develop Mam3 as a bait protein for vacuole immuno-isolation, and demonstrate low contamination by non-vacuolar membranes. We find that stationary-stage vacuole membranes contain surprisingly high fractions of phosphatidylcholine lipids (∼40%), roughly twice as much as log-stage membranes. Moreover, in the stationary stage, these lipids have higher melting temperatures, due to longer and more saturated acyl chains. Another surprise is that no significant change in sterol content is observed. These lipidomic changes, which are largely reflected on the whole-cell level, fit within the predominant view that phase separation in membranes requires at least three types of molecules to be present: lipids with high melting temperatures, lipids with low melting temperatures, and sterols.
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Affiliation(s)
- John Reinhard
- Medical Biochemistry and Molecular Biology, Medical Faculty, Saarland University, Homburg, Germany; PZMS, Center for Molecular Signaling, Medical Faculty, Saarland University, Homburg, Germany
| | | | | | - Alexey J Merz
- Department of Biochemistry, University of Washington, Seattle, WA
| | | | - Robert Ernst
- Medical Biochemistry and Molecular Biology, Medical Faculty, Saarland University, Homburg, Germany; PZMS, Center for Molecular Signaling, Medical Faculty, Saarland University, Homburg, Germany.
| | - Sarah L Keller
- Department of Chemistry, University of Washington, Seattle, WA.
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8
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Veatch SL, Rogers N, Decker A, Shelby SA. The plasma membrane as an adaptable fluid mosaic. BIOCHIMICA ET BIOPHYSICA ACTA. BIOMEMBRANES 2023; 1865:184114. [PMID: 36581017 PMCID: PMC9922517 DOI: 10.1016/j.bbamem.2022.184114] [Citation(s) in RCA: 13] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/07/2022] [Revised: 12/18/2022] [Accepted: 12/20/2022] [Indexed: 12/27/2022]
Abstract
The fluid mosaic model proposed by Singer and Nicolson established a powerful framework to interrogate biological membranes that has stood the test of time. They proposed that the membrane is a simple fluid, meaning that proteins and lipids are randomly distributed over distances larger than those dictated by direct interactions. Here we present an update to this model that describes a spatially adaptable fluid membrane capable of tuning local composition in response to forces originating outside the membrane plane. This revision is rooted in the thermodynamics of lipid mixtures, draws from recent experimental results, and suggests new modes of membrane function.
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Affiliation(s)
- Sarah L Veatch
- Program in Biophysics, University of Michigan, Ann Arbor, MI, USA.
| | - Nat Rogers
- Program in Biophysics, University of Michigan, Ann Arbor, MI, USA
| | - Adam Decker
- Program in Biophysics, University of Michigan, Ann Arbor, MI, USA
| | - Sarah A Shelby
- Program in Biophysics, University of Michigan, Ann Arbor, MI, USA.
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9
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Li L, Ji J, Song F, Hu J. Intercellular Receptor-ligand Binding: Effect of Protein-membrane Interaction. J Mol Biol 2023; 435:167787. [PMID: 35952805 DOI: 10.1016/j.jmb.2022.167787] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2022] [Revised: 08/03/2022] [Accepted: 08/04/2022] [Indexed: 02/04/2023]
Abstract
Gaining insights into the intercellular receptor-ligand binding is of great importance for understanding numerous physiological and pathological processes, and stimulating new strategies in drug design and discovery. In contrast to the in vitro protein interaction in solution, the anchored receptor and ligand molecules interact with membrane in situ, which affects the intercellular receptor-ligand binding. Here, we review theoretical, simulation and experimental works regarding the regulatory effects of protein-membrane interactions on intercellular receptor-ligand binding mainly from the following aspects: membrane fluctuations, membrane curvature, glycocalyx, and lipid raft. In addition, we discuss biomedical significances and possible research directions to advance the field and highlight the importance of understanding of coupling effects of these factors in pharmaceutical development.
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Affiliation(s)
- Long Li
- Kuang Yaming Honors School and Institute for Brain Sciences, Nanjing University, 210023 Nanjing, China; State Key Laboratory of Nonlinear Mechanics and Beijing Key Laboratory of Engineered Construction and Mechanobiology, Institute of Mechanics, Chinese Academy of Sciences, 100190 Beijing, China
| | - Jing Ji
- Key Laboratory of Biomechanics and Mechanobiology (Beihang University), Ministry of Education Beijing Advanced Innovation Center for Biomedical Engineering School of Biological Science and Medical Engineering, Beihang University, Beijing 100083, China.
| | - Fan Song
- State Key Laboratory of Nonlinear Mechanics and Beijing Key Laboratory of Engineered Construction and Mechanobiology, Institute of Mechanics, Chinese Academy of Sciences, 100190 Beijing, China; School of Engineering Science, University of Chinese Academy of Sciences, 100049 Beijing, China
| | - Jinglei Hu
- Kuang Yaming Honors School and Institute for Brain Sciences, Nanjing University, 210023 Nanjing, China.
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10
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Li L, Hu J, Różycki B, Ji J, Song F. Interplay of receptor-ligand binding and lipid domain formation during cell adhesion. Front Mol Biosci 2022; 9:1019477. [PMID: 36203878 PMCID: PMC9531914 DOI: 10.3389/fmolb.2022.1019477] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2022] [Accepted: 09/05/2022] [Indexed: 11/20/2022] Open
Abstract
Cell adhesion involved in biological processes such as cell migration, immune responses, and cancer metastasis, is mediated by the specific binding of receptor and ligand proteins. Some of these proteins exhibit affinity for nanoscale lipid clusters in cell membranes. A key question is how these nanoscale lipid clusters influence and react to the receptor-ligand binding during cell adhesion. In this article, we review recent computational studies that shed new light on the interplay of the receptor-ligand binding and the formation of lipid domains in adhering membranes. These studies indicate that the receptor-ligand binding promotes coalescence of lipid clusters into mesoscale domains, which, in turn, enhances both the affinity and cooperativity of the receptor-ligand binding in cell-cell adhesion with mobile ligands. In contrast, in the case of cell-extracellular matrix adhesion with immobile ligands, the receptor-ligand binding and the lipid cluster coalescence can be correlated or anti-correlated, depending strongly on the ligand distribution. These findings deepen our understanding of correlations between cell adhesion and membrane heterogeneities.
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Affiliation(s)
- Long Li
- Kuang Yaming Honors School and Institute for Brain Sciences, Nanjing University, Nanjing, China
- State Key Laboratory of Nonlinear Mechanics and Beijing Key Laboratory of Engineered Construction and Mechanobiology, Institute of Mechanics, Chinese Academy of Sciences, Beijing, China
| | - Jinglei Hu
- Kuang Yaming Honors School and Institute for Brain Sciences, Nanjing University, Nanjing, China
- *Correspondence: Jinglei Hu, ; Bartosz Różycki, ; Jing Ji,
| | - Bartosz Różycki
- Institute of Physics, Polish Academy of Sciences, Warsaw, Poland
- *Correspondence: Jinglei Hu, ; Bartosz Różycki, ; Jing Ji,
| | - Jing Ji
- Key Laboratory of Biomechanics and Mechanobiology (Beihang University), Ministry of Education Beijing Advanced Innovation Center for Biomedical Engineering School of Biological Science and Medical Engineering, Beihang University, Beijing, China
- *Correspondence: Jinglei Hu, ; Bartosz Różycki, ; Jing Ji,
| | - Fan Song
- State Key Laboratory of Nonlinear Mechanics and Beijing Key Laboratory of Engineered Construction and Mechanobiology, Institute of Mechanics, Chinese Academy of Sciences, Beijing, China
- School of Engineering Science, University of Chinese Academy of Sciences, Beijing, China
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11
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Yeast cells actively tune their membranes to phase separate at temperatures that scale with growth temperatures. Proc Natl Acad Sci U S A 2022; 119:2116007119. [PMID: 35046036 PMCID: PMC8795566 DOI: 10.1073/pnas.2116007119] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/06/2021] [Indexed: 02/06/2023] Open
Abstract
Phase separation in membranes creates domains enriched in specific components. To date, the best example of micrometer-scale phase separation in the membrane of an unperturbed, living cell occurs in a yeast (Saccharomyces cerevisiae) organelle called the vacuole. Recent studies indicate that the phases are functionally important, enabling yeast survival during periods of stress. We discovered that yeast regulate this phase transition; the temperature at which membrane components mix into a single phase is ∼15 °C above the growth temperature. To maintain this offset, yeast may tune the level of ergosterol (a molecule that is structurally similar to cholesterol) in their membranes. Surprisingly, depleting sterols in vacuole membranes causes them to phase separate, in contrast to previous assumptions. Membranes of vacuoles, the lysosomal organelles of Saccharomyces cerevisiae (budding yeast), undergo extraordinary changes during the cell’s normal growth cycle. The cycle begins with a stage of rapid cell growth. Then, as glucose becomes scarce, growth slows, and vacuole membranes phase separate into micrometer-scale domains of two liquid phases. Recent studies suggest that these domains promote yeast survival by organizing membrane proteins that play key roles in a central signaling pathway conserved among eukaryotes (TORC1). An outstanding question in the field has been whether cells regulate phase transitions in response to new physical conditions and how this occurs. Here, we measure transition temperatures and find that after an increase of roughly 15 °C, vacuole membranes appear uniform, independent of growth temperature. Moreover, populations of cells grown at a single temperature regulate this transition to occur over a surprisingly narrow temperature range. Remarkably, the transition temperature scales linearly with the growth temperature, demonstrating that the cells physiologically adapt to maintain proximity to the transition. Next, we ask how yeast adjust their membranes to achieve phase separation. We isolate vacuoles from yeast during the rapid stage of growth, when their membranes do not natively exhibit domains. Ergosterol is the major sterol in yeast. We find that domains appear when ergosterol is depleted, contradicting the prevalent assumption that increases in sterol concentration generally cause membrane phase separation in vivo, but in agreement with previous studies using artificial and cell-derived membranes.
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12
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Surface densities prewet a near-critical membrane. Proc Natl Acad Sci U S A 2021; 118:2103401118. [PMID: 34599097 DOI: 10.1073/pnas.2103401118] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/03/2021] [Indexed: 11/18/2022] Open
Abstract
Recent work has highlighted roles for thermodynamic phase behavior in diverse cellular processes. Proteins and nucleic acids can phase separate into three-dimensional liquid droplets in the cytoplasm and nucleus and the plasma membrane of animal cells appears tuned close to a two-dimensional liquid-liquid critical point. In some examples, cytoplasmic proteins aggregate at plasma membrane domains, forming structures such as the postsynaptic density and diverse signaling clusters. Here we examine the physics of these surface densities, employing minimal simulations of polymers prone to phase separation coupled to an Ising membrane surface in conjunction with a complementary Landau theory. We argue that these surface densities are a phase reminiscent of prewetting, in which a molecularly thin three-dimensional liquid forms on a usually solid surface. However, in surface densities the solid surface is replaced by a membrane with an independent propensity to phase separate. We show that proximity to criticality in the membrane dramatically increases the parameter regime in which a prewetting-like transition occurs, leading to a broad region where coexisting surface phases can form even when a bulk phase is unstable. Our simulations naturally exhibit three-surface phase coexistence even though both the membrane and the polymer bulk only display two-phase coexistence on their own. We argue that the physics of these surface densities may be shared with diverse functional structures seen in eukaryotic cells.
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13
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Abstract
Lateral organization in the plane of the plasma membrane is an important driver of biological processes. The past dozen years have seen increasing experimental support for the notion that lipid organization plays an important role in modulating this heterogeneity. Various biophysical mechanisms rooted in the concept of liquid-liquid phase separation have been proposed to explain diverse experimental observations of heterogeneity in model and cell membranes with distinct but overlapping applicability. In this review, we focus on the evidence for and the consequences of the hypothesis that the plasma membrane is poised near an equilibrium miscibility critical point. Critical phenomena explain certain features of the heterogeneity observed in cells and model systems but also go beyond heterogeneity to predict other interesting phenomena, including responses to perturbations in membrane composition.
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Affiliation(s)
- Thomas R Shaw
- Program in Applied Physics, University of Michigan, Ann Arbor, Michigan 48109, USA;
| | - Subhadip Ghosh
- Program in Biophysics, University of Michigan, Ann Arbor, Michigan 48109, USA
| | - Sarah L Veatch
- Program in Applied Physics, University of Michigan, Ann Arbor, Michigan 48109, USA; .,Program in Biophysics, University of Michigan, Ann Arbor, Michigan 48109, USA.,Department of Physics, University of Michigan, Ann Arbor, Michigan 48109, USA
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14
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Li L, Wang X, Wu H, Shao Y, Wu H, Song F. Interplay Between Receptor-Ligand Binding and Lipid Domain Formation Depends on the Mobility of Ligands in Cell-Substrate Adhesion. Front Mol Biosci 2021; 8:655662. [PMID: 33987204 PMCID: PMC8112205 DOI: 10.3389/fmolb.2021.655662] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2021] [Accepted: 02/17/2021] [Indexed: 12/20/2022] Open
Abstract
Cell-cell adhesion and the adhesion of cells to extracellular matrix are mediated by the specific binding of receptors on the cell membrane to their cognate ligands on the opposing surface. The adhesion receptors can exhibit affinity for nanoscale lipid clusters that form in the cell membrane. Experimental studies of such adhesion systems often involve a cell adhering either to a solid surface with immobile ligands or a supported lipid bilayer with mobile ligands. A central question in these cell-substrate adhesions is how the mobility of the ligands physically affects their binding to the adhesion receptors and thereby the behavior of the nanoscale lipid clusters associated with the receptors. Using a statistical mechanical model and Monte Carlo simulations for the adhesion of cells to substrates with ligands, we find that, for mobile ligands, binding to adhesion receptors can promote the formation of mesoscale lipid domains, which in turn enhances the receptor-ligand binding. However, in the case of immobile ligands, the receptor-ligand binding and the tendency for the nanoscale lipid clusters to further coalesce depend on the distribution of the ligands on the substrate. Our findings help to explain why different adhesion experiments for identifying the interplay between receptor-ligand binding and heterogeneities in cell membranes led to contradictory results.
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Affiliation(s)
- Long Li
- State Key Laboratory of Nonlinear Mechanics (LNM) and Beijing Key Laboratory of Engineered Construction and Mechanobiology, Institute of Mechanics, Chinese Academy of Sciences, Beijing, China
| | - Xiaohuan Wang
- State Key Laboratory of Nonlinear Mechanics (LNM) and Beijing Key Laboratory of Engineered Construction and Mechanobiology, Institute of Mechanics, Chinese Academy of Sciences, Beijing, China
- School of Engineering Science, University of Chinese Academy of Sciences, Beijing, China
| | - Helong Wu
- College of Mechanical Engineering, Zhejiang University of Technology, Hangzhou, China
| | - Yingfeng Shao
- State Key Laboratory of Nonlinear Mechanics (LNM) and Beijing Key Laboratory of Engineered Construction and Mechanobiology, Institute of Mechanics, Chinese Academy of Sciences, Beijing, China
| | - Huaping Wu
- College of Mechanical Engineering, Zhejiang University of Technology, Hangzhou, China
| | - Fan Song
- State Key Laboratory of Nonlinear Mechanics (LNM) and Beijing Key Laboratory of Engineered Construction and Mechanobiology, Institute of Mechanics, Chinese Academy of Sciences, Beijing, China
- School of Engineering Science, University of Chinese Academy of Sciences, Beijing, China
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15
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Ngassam VN, Su WC, Gettel DL, Deng Y, Yang Z, Wang-Tomic N, Sharma VP, Purushothaman S, Parikh AN. Recurrent dynamics of rupture transitions of giant lipid vesicles at solid surfaces. Biophys J 2021; 120:586-597. [PMID: 33460597 DOI: 10.1016/j.bpj.2021.01.006] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2020] [Revised: 11/20/2020] [Accepted: 01/07/2021] [Indexed: 10/22/2022] Open
Abstract
Single giant unilamellar vesicles (GUVs) rupture spontaneously from their salt-laden suspension onto solid surfaces. At hydrophobic surfaces, the GUVs rupture via a recurrent, bouncing ball rhythm. During each contact, the GUVs, rendered tense by the substrate interactions, porate, and spread a molecularly transformed motif of a monomolecular layer on the hydrophobic surface from the point of contact in a symmetric manner. The competition from pore closure, however, limits the spreading and produces a daughter vesicle, which re-engages with the substrate. At solid hydrophilic surfaces, by contrast, GUVs rupture via a distinctly different recurrent burst-heal dynamics; during burst, single pores nucleate at the contact boundary of the adhering vesicles, facilitating asymmetric spreading and producing a "heart"-shaped membrane patch. During the healing phase, the competing pore closure produces a daughter vesicle. In both cases, the pattern of burst-reseal events repeats multiple times, splashing and spreading the vesicular fragments as bilayer patches at the solid surface in a pulsatory manner. These remarkable recurrent dynamics arise, not because of the elastic properties of the solid surface, but because the competition between membrane spreading and pore healing, prompted by the surface-energy-dependent adhesion, determine the course of the topological transition.
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Affiliation(s)
- Viviane N Ngassam
- Department of Biomedical Engineering, University of California, Davis, California
| | - Wan-Chih Su
- Department of Chemistry, University of California, Davis, California
| | - Douglas L Gettel
- Department of Chemical Engineering, University of California, Davis, California
| | - Yawen Deng
- Department of Biomedical Engineering, University of California, Davis, California
| | - Zexu Yang
- Department of Biomedical Engineering, University of California, Davis, California
| | - Neven Wang-Tomic
- Department of Biomedical Engineering, University of California, Davis, California
| | - Varun P Sharma
- Department of Biomedical Engineering, University of California, Davis, California
| | - Sowmya Purushothaman
- Department of Biomedical Engineering, University of California, Davis, California
| | - Atul N Parikh
- Department of Biomedical Engineering, University of California, Davis, California; Department of Chemistry, University of California, Davis, California; Department of Chemical Engineering, University of California, Davis, California; Department of Materials Science and Engineering, University of California, Davis, California.
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16
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Schäfer AB, Wenzel M. A How-To Guide for Mode of Action Analysis of Antimicrobial Peptides. Front Cell Infect Microbiol 2020; 10:540898. [PMID: 33194788 PMCID: PMC7604286 DOI: 10.3389/fcimb.2020.540898] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2020] [Accepted: 09/18/2020] [Indexed: 12/11/2022] Open
Abstract
Antimicrobial peptides (AMPs) are a promising alternative to classical antibiotics in the fight against multi-resistant bacteria. They are produced by organisms from all domains of life and constitute a nearly universal defense mechanism against infectious agents. No drug can be approved without information about its mechanism of action. In order to use them in a clinical setting, it is pivotal to understand how AMPs work. While many pore-forming AMPs are well-characterized in model membrane systems, non-pore-forming peptides are often poorly understood. Moreover, there is evidence that pore formation may not happen or not play a role in vivo. It is therefore imperative to study how AMPs interact with their targets in vivo and consequently kill microorganisms. This has been difficult in the past, since established methods did not provide much mechanistic detail. Especially, methods to study membrane-active compounds have been scarce. Recent advances, in particular in microscopy technology and cell biological labeling techniques, now allow studying mechanisms of AMPs in unprecedented detail. This review gives an overview of available in vivo methods to investigate the antibacterial mechanisms of AMPs. In addition to classical mode of action classification assays, we discuss global profiling techniques, such as genomic and proteomic approaches, as well as bacterial cytological profiling and other cell biological assays. We cover approaches to determine the effects of AMPs on cell morphology, outer membrane, cell wall, and inner membrane properties, cellular macromolecules, and protein targets. We particularly expand on methods to examine cytoplasmic membrane parameters, such as composition, thickness, organization, fluidity, potential, and the functionality of membrane-associated processes. This review aims to provide a guide for researchers, who seek a broad overview of the available methodology to study the mechanisms of AMPs in living bacteria.
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Affiliation(s)
| | - Michaela Wenzel
- Division of Chemical Biology, Department of Biology and Biological Engineering, Chalmers University of Technology, Gothenburg, Sweden
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17
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Sengupta P, Lippincott-Schwartz J. Revisiting Membrane Microdomains and Phase Separation: A Viral Perspective. Viruses 2020; 12:v12070745. [PMID: 32664429 PMCID: PMC7412473 DOI: 10.3390/v12070745] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2020] [Revised: 06/29/2020] [Accepted: 07/07/2020] [Indexed: 12/11/2022] Open
Abstract
Retroviruses selectively incorporate a specific subset of host cell proteins and lipids into their outer membrane when they bud out from the host plasma membrane. This specialized viral membrane composition is critical for both viral survivability and infectivity. Here, we review recent findings from live cell imaging of single virus assembly demonstrating that proteins and lipids sort into the HIV retroviral membrane by a mechanism of lipid-based phase partitioning. The findings showed that multimerizing HIV Gag at the assembly site creates a liquid-ordered lipid phase enriched in cholesterol and sphingolipids. Proteins with affinity for this specialized lipid environment partition into it, resulting in the selective incorporation of proteins into the nascent viral membrane. Building on this and other work in the field, we propose a model describing how HIV Gag induces phase separation of the viral assembly site through a mechanism involving transbilayer coupling of lipid acyl chains and membrane curvature changes. Similar phase-partitioning pathways in response to multimerizing structural proteins likely help sort proteins into the membranes of other budding structures within cells.
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18
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Affiliation(s)
- Ilya Levental
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Houston, TX. mailto:
| | - Hong-Yin Wang
- Department of Integrative Biology and Pharmacology, University of Texas Health Science Center at Houston, Houston, TX
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19
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Levental I, Levental KR, Heberle FA. Lipid Rafts: Controversies Resolved, Mysteries Remain. Trends Cell Biol 2020; 30:341-353. [PMID: 32302547 DOI: 10.1016/j.tcb.2020.01.009] [Citation(s) in RCA: 322] [Impact Index Per Article: 80.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2019] [Revised: 01/23/2020] [Accepted: 01/24/2020] [Indexed: 01/08/2023]
Abstract
The lipid raft hypothesis postulates that lipid-lipid interactions can laterally organize biological membranes into domains of distinct structures, compositions, and functions. This proposal has in equal measure exhilarated and frustrated membrane research for decades. While the physicochemical principles underlying lipid-driven domains has been explored and is well understood, the existence and relevance of such domains in cells remains elusive, despite decades of research. Here, we review the conceptual underpinnings of the raft hypothesis and critically discuss the supporting and contradicting evidence in cells, focusing on why controversies about the composition, properties, and even the very existence of lipid rafts remain unresolved. Finally, we highlight several recent breakthroughs that may resolve existing controversies and suggest general approaches for moving beyond questions of the existence of rafts and towards understanding their physiological significance.
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Affiliation(s)
- Ilya Levental
- Department of Integrative Biology and Pharmacology, McGovern Medical School, University of Texas Health Science Center, Houston, TX 70030, USA.
| | - Kandice R Levental
- Department of Integrative Biology and Pharmacology, McGovern Medical School, University of Texas Health Science Center, Houston, TX 70030, USA
| | - Frederick A Heberle
- Department of Chemistry, University of Tennessee, Knoxville, TN 37996, USA; Shull Wollan Center, Oak Ridge National Laboratory, Oak Ridge, TN 33830, USA
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20
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Li G, Wang Q, Kakuda S, London E. Nanodomains can persist at physiologic temperature in plasma membrane vesicles and be modulated by altering cell lipids. J Lipid Res 2020; 61:758-766. [PMID: 31964764 DOI: 10.1194/jlr.ra119000565] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2019] [Revised: 01/06/2020] [Indexed: 01/04/2023] Open
Abstract
The formation and properties of liquid-ordered (Lo) lipid domains (rafts) in the plasma membrane are still poorly understood. This limits our ability to manipulate ordered lipid domain-dependent biological functions. Giant plasma membrane vesicles (GPMVs) undergo large-scale phase separations into coexisting Lo and liquid-disordered lipid domains. However, large-scale phase separation in GPMVs detected by light microscopy is observed only at low temperatures. Comparing Förster resonance energy transfer-detected versus light microscopy-detected domain formation, we found that nanodomains, domains of nanometer size, persist at temperatures up to 20°C higher than large-scale phases, up to physiologic temperature. The persistence of nanodomains at higher temperatures is consistent with previously reported theoretical calculations. To investigate the sensitivity of nanodomains to lipid composition, GPMVs were prepared from mammalian cells in which sterol, phospholipid, or sphingolipid composition in the plasma membrane outer leaflet had been altered by cyclodextrin-catalyzed lipid exchange. Lipid substitutions that stabilize or destabilize ordered domain formation in artificial lipid vesicles had a similar effect on the thermal stability of nanodomains and large-scale phase separation in GPMVs, with nanodomains persisting at higher temperatures than large-scale phases for a wide range of lipid compositions. This indicates that it is likely that plasma membrane nanodomains can form under physiologic conditions more readily than large-scale phase separation. We also conclude that membrane lipid substitutions carried out in intact cells are able to modulate the propensity of plasma membranes to form ordered domains. This implies lipid substitutions can be used to alter biological processes dependent upon ordered domains.
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Affiliation(s)
- Guangtao Li
- Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, NY 11794-5215
| | - Qing Wang
- Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, NY 11794-5215
| | - Shinako Kakuda
- Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, NY 11794-5215
| | - Erwin London
- Department of Biochemistry and Cell Biology, Stony Brook University, Stony Brook, NY 11794-5215. mailto:
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21
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Núñez MF, Wisser K, Veatch SL. Synergistic factors control kinase-phosphatase organization in B-cells engaged with supported bilayers. Mol Biol Cell 2019; 31:667-682. [PMID: 31877064 PMCID: PMC7202075 DOI: 10.1091/mbc.e19-09-0507] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
B-cells become activated by ligands with varying valency and mode of presentation to the B-cell receptor (BCR). We previously demonstrated that clustering the immunoglobulin M (IgM) isotype of BCR with an artificial soluble cross-linker stabilized an ordered phase-like domain that enriched kinases and depleted phosphatases to promote receptor tyrosine phosphorylation. BCR is also activated by ligands presented at surfaces, and here we activate B-cells via supported bilayers of phosphatidylcholine lipids, a natural ligand for the IgM BCR expressed in the CH27 cells used. Using superresolution fluorescence localization microscopy, along with a quantitative cross-correlation analysis, we find that BRCs engaged with bilayers sort minimal peptide markers of liquid-ordered and liquid-disordered phases, indicating that ordered-domain stabilization is a general feature of BCR clustering. The phosphatase CD45 is more strongly excluded from bilayer-engaged BRCs than a transmembrane peptide, indicating that mechanisms other than domain partitioning contribute to its organization. Experimental observations are assembled into a minimal model of receptor activation that incorporates both ordered domains and direct phosphatase exclusion mechanisms to produce a more sensitive response.
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Affiliation(s)
| | - Kathleen Wisser
- Department of Biophysics, University of Michigan, Ann Arbor, MI 48105
| | - Sarah L Veatch
- Department of Biophysics, University of Michigan, Ann Arbor, MI 48105
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22
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Trementozzi AN, Imam ZI, Mendicino M, Hayden CC, Stachowiak JC. Liposome-Mediated Chemotherapeutic Delivery Is Synergistically Enhanced by Ternary Lipid Compositions and Cationic Lipids. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:12532-12542. [PMID: 31476123 PMCID: PMC6918482 DOI: 10.1021/acs.langmuir.9b01965] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Most small molecule chemotherapeutics must cross one or more cellular membrane barriers to reach their biochemical targets. Owing to the relatively low solubility of chemotherapeutics in the lipid membrane environment, high doses are often required to achieve a therapeutic effect. The resulting systemic toxicity has motivated efforts to improve the efficiency of chemotherapeutic delivery to the cellular interior. Toward this end, liposomes containing lipids with cationic head groups have been shown to permeabilize cellular membranes, resulting in the more efficient release of encapsulated drugs into the cytoplasm. However, the high concentrations of cationic lipids required to achieve efficient delivery remain a key limitation, frequently resulting in toxicity. Toward overcoming this limitation, here, we investigate the ability of ternary lipid mixtures to enhance liposomal delivery. Specifically, we investigate the delivery of the chemotherapeutic, doxorubicin, using ternary liposomes that are homogeneous at physiological temperature but have the potential to undergo membrane phase separation upon contact with the cell surface. This approach, which relies upon the ability of membrane phase boundaries to promote drug release, provides a novel method for reducing the overall concentration of cationic lipids required for efficient delivery. Our results show that this approach improves the performance of doxorubicin by up to 5-fold in comparison to the delivery of the same drug by conventional liposomes. These data demonstrate that ternary lipid compositions and cationic lipids can be combined synergistically to substantially improve the efficiency of chemotherapeutic delivery in vitro.
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Affiliation(s)
| | - Zachary I. Imam
- Department of Biomedical Engineering, The University of Texas at Austin, TX
| | - Morgan Mendicino
- Department of Biomedical Engineering, The University of Texas at Austin, TX
| | - Carl C. Hayden
- Department of Biomedical Engineering, The University of Texas at Austin, TX
| | - Jeanne C. Stachowiak
- Department of Biomedical Engineering, The University of Texas at Austin, TX
- Institute for Cellular and Molecular Biology, The University of Texas at Austin, TX
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23
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Raggi C, Diociaiuti M, Caracciolo G, Fratini F, Fantozzi L, Piccaro G, Fecchi K, Pizzi E, Marano G, Ciaffoni F, Bravo E, Fiani ML, Sargiacomo M. Caveolin-1 Endows Order in Cholesterol-Rich Detergent Resistant Membranes. Biomolecules 2019; 9:biom9070287. [PMID: 31319608 PMCID: PMC6680987 DOI: 10.3390/biom9070287] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2019] [Revised: 06/27/2019] [Accepted: 07/14/2019] [Indexed: 01/14/2023] Open
Abstract
Cholesterol-enriched functional portions of plasma membranes, such as caveolae and rafts, were isolated from lungs of wild-type (WT) and caveolin-1 knockout (Cav-1 KO) mice within detergent resistant membranes (DRMs). To gain insight into their molecular composition we performed proteomic and lipid analysis on WT and Cav-1 KO-DRMs that showed predicted variations of proteomic profiles and negligible differences in lipid composition, while Langmuir monolayer technique and small and wide-angle X-ray scattering (SAXS-WAXS) were here originally introduced to study DRMs biophysical association state. Langmuir analysis of Cav-1 containing DRMs displayed an isotherm with a clear-cut feature, suggesting the coexistence of the liquid-ordered (Lo) phase typical of the raft structure, namely “cholesterol-rich Lo phase”, with a phase fully missing in Cav-1 KO that we named “caveolin-induced Lo phase”. Furthermore, while the sole lipid component of both WT and KO-DRMs showed qualitatively similar isotherm configuration, the reinsertion of recombinant Cav-1 into WT-DRMs lipids restored the WT-DRM pattern. X-ray diffraction results confirmed that Cav-1 causes the formation of a “caveolin-induced Lo phase”, as suggested by Langmuir experiments, allowing us to speculate about a possible structural model. These results show that the unique molecular link between Cav-1 and cholesterol can spur functional order in a lipid bilayer strictly derived from biological sources.
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Affiliation(s)
- Carla Raggi
- National Center for Control and Evaluation of Medicines, Istituto Superiore di Sanità, 00161 Rome, Italy
| | - Marco Diociaiuti
- National Center for Rare Diseases, Istituto Superiore di Sanità, 00161 Rome, Italy
| | - Giulio Caracciolo
- Department of Molecular Medicine, "La Sapienza" University, 00161 Rome, Italy
| | - Federica Fratini
- Scientific Service for Core Facilities, Istituto Superiore di Sanità, 00161 Rome, Italy
| | - Luca Fantozzi
- Present address : ARPALAZIO, Via Salaria per L'Aquila 6/8, 02100 Rieti, Italy
| | | | - Katia Fecchi
- Reference Centre for Gender Medicine, Istituto Superiore di Sanità, 00161 Rome, Italy
| | - Elisabetta Pizzi
- Scientific Service for Core Facilities, Istituto Superiore di Sanità, 00161 Rome, Italy
| | - Giuseppe Marano
- Reference Centre for Gender Medicine, Istituto Superiore di Sanità, 00161 Rome, Italy
| | - Fiorella Ciaffoni
- Scientific Service for Core Facilities, Istituto Superiore di Sanità, 00161 Rome, Italy
| | - Elena Bravo
- Scientific Service for Research Coordination and Support, Istituto Superiore di Sanità, 00161 Rome, Italy
| | - Maria L Fiani
- National Center for Global Health, Istituto Superiore di Sanità, 00161 Rome, Italy.
| | - Massimo Sargiacomo
- National Center for Global Health, Istituto Superiore di Sanità, 00161 Rome, Italy.
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24
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Dimova R. Giant Vesicles and Their Use in Assays for Assessing Membrane Phase State, Curvature, Mechanics, and Electrical Properties. Annu Rev Biophys 2019; 48:93-119. [DOI: 10.1146/annurev-biophys-052118-115342] [Citation(s) in RCA: 67] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Giant unilamellar vesicles represent a promising and extremely useful model biomembrane system for systematic measurements of mechanical, thermodynamic, electrical, and rheological properties of lipid bilayers as a function of membrane composition, surrounding media, and temperature. The most important advantage of giant vesicles over other model membrane systems is that the membrane responses to external factors such as ions, (macro)molecules, hydrodynamic flows, or electromagnetic fields can be directly observed under the microscope. Here, we briefly review approaches for giant vesicle preparation and describe several assays used for deducing the membrane phase state and measuring a number of material properties, with further emphasis on membrane reshaping and curvature.
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Affiliation(s)
- Rumiana Dimova
- Max Planck Institute of Colloids and Interfaces, Science Park Golm, 14424 Potsdam, Germany
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25
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Kimchi O, Veatch SL, Machta BB. Ion channels can be allosterically regulated by membrane domains near a de-mixing critical point. J Gen Physiol 2018; 150:1769-1777. [PMID: 30455180 PMCID: PMC6279359 DOI: 10.1085/jgp.201711900] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2017] [Revised: 08/24/2018] [Accepted: 10/25/2018] [Indexed: 12/17/2022] Open
Abstract
Ion channels are embedded in the plasma membrane, a compositionally diverse two-dimensional liquid that has the potential to exert profound influence on their function. Recent experiments suggest that this membrane is poised close to an Ising critical point, below which cell-derived plasma membrane vesicles phase separate into coexisting liquid phases. Related critical points have long been the focus of study in simplified physical systems, but their potential roles in biological function have been underexplored. Here we apply both exact and stochastic techniques to the lattice Ising model to study several ramifications of proximity to criticality for idealized lattice channels, whose function is coupled through boundary interactions to critical fluctuations of membrane composition. Because of diverging susceptibilities of system properties to thermodynamic parameters near a critical point, such a lattice channel's activity becomes strongly influenced by perturbations that affect the critical temperature of the underlying Ising model. In addition, its kinetics acquire a range of time scales from its surrounding membrane, naturally leading to non-Markovian dynamics. Our model may help to unify existing experimental results relating the effects of small-molecule perturbations on membrane properties and ion channel function. We also suggest ways in which the role of this mechanism in regulating real ion channels and other membrane-bound proteins could be tested in the future.
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Affiliation(s)
- Ofer Kimchi
- Department of Physics, Princeton University, Princeton, NJ.,Harvard Graduate Program in Biophysics, Harvard University, Cambridge, MA
| | - Sarah L Veatch
- Department of Biophysics, University of Michigan, Ann Arbor, MI
| | - Benjamin B Machta
- Department of Physics, Princeton University, Princeton, NJ .,Lewis-Sigler Institute, Princeton University, Princeton, NJ.,Department of Physics, Yale University, New Haven, CT.,Systems Biology Institute, Yale University, West Haven, CT
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26
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Omardien S, Drijfhout JW, Vaz FM, Wenzel M, Hamoen LW, Zaat SA, Brul S. Bactericidal activity of amphipathic cationic antimicrobial peptides involves altering the membrane fluidity when interacting with the phospholipid bilayer. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2018; 1860:2404-2415. [DOI: 10.1016/j.bbamem.2018.06.004] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/08/2017] [Revised: 06/05/2018] [Accepted: 06/06/2018] [Indexed: 12/22/2022]
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27
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Wenzel M, Vischer NOE, Strahl H, Hamoen LW. Assessing Membrane Fluidity and Visualizing Fluid Membrane Domains in Bacteria Using Fluorescent Membrane Dyes. Bio Protoc 2018; 8:e3063. [PMID: 34532528 DOI: 10.21769/bioprotoc.3063] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2018] [Revised: 10/06/2018] [Accepted: 10/29/2018] [Indexed: 11/02/2022] Open
Abstract
Membrane fluidity is a key parameter of bacterial membranes that undergoes quick adaptation in response to environmental challenges and has recently emerged as an important factor in the antibacterial mechanism of membrane-targeting antibiotics. The specific level of membrane fluidity is not uniform across the bacterial cell membrane. Rather, specialized microdomains associated with different cellular functions can exhibit fluidity values that significantly deviate from the average. Assessing changes in the overall membrane fluidity and formation of membrane microdomains is therefore pivotal to understand both the functional organization of the bacterial cell membrane as well as antibiotic mechanisms. Here we describe how two fluorescent membrane dyes, laurdan and DiIC12, can be employed to assess membrane fluidity in living bacteria. We focus on Bacillus subtilis, since this organism has been relatively well-studied with respect to membrane domains. However, we also describe how these assays can be adapted for other bacteria such as Staphylococcus aureus and Streptococcus pneumoniae.
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Affiliation(s)
- Michaela Wenzel
- Bacterial Cell Biology, Swammerdam Institute for Life Sciences, University of Amsterdam, Amsterdam, The Netherlands.,Department of Medical Microbiology and Infection Control, Amsterdam University Medical Centers, Location VUMC, Amsterdam, The Netherlands
| | - Norbert O E Vischer
- Bacterial Cell Biology, Swammerdam Institute for Life Sciences, University of Amsterdam, Amsterdam, The Netherlands
| | - Henrik Strahl
- Centre for Bacterial Cell Biology, Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle upon Tyne, United Kingdom
| | - Leendert W Hamoen
- Bacterial Cell Biology, Swammerdam Institute for Life Sciences, University of Amsterdam, Amsterdam, The Netherlands
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28
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The Multifaceted Antibacterial Mechanisms of the Pioneering Peptide Antibiotics Tyrocidine and Gramicidin S. mBio 2018; 9:mBio.00802-18. [PMID: 30301848 PMCID: PMC6178620 DOI: 10.1128/mbio.00802-18] [Citation(s) in RCA: 68] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
Cyclic β-sheet decapeptides, such as tyrocidines and gramicidin S, were among the first antibiotics in clinical application. Although they have been used for such a long time, there is virtually no resistance to them, which has led to a renewed interest in this peptide class. Both tyrocidines and gramicidin S are thought to disrupt the bacterial membrane. However, this knowledge is mainly derived from in vitro studies, and there is surprisingly little knowledge about how these long-established antibiotics kill bacteria. Our results shed new light on the antibacterial mechanism of β-sheet peptide antibiotics and explain why they are still so effective and why there is so little resistance to them. Cyclic β-sheet decapeptides from the tyrocidine group and the homologous gramicidin S were the first commercially used antibiotics, yet it remains unclear exactly how they kill bacteria. We investigated their mode of action using a bacterial cytological profiling approach. Tyrocidines form defined ion-conducting pores, induce lipid phase separation, and strongly reduce membrane fluidity, resulting in delocalization of a broad range of peripheral and integral membrane proteins. Interestingly, they also cause DNA damage and interfere with DNA-binding proteins. Despite sharing 50% sequence identity with tyrocidines, gramicidin S causes only mild lipid demixing with minor effects on membrane fluidity and permeability. Gramicidin S delocalizes peripheral membrane proteins involved in cell division and cell envelope synthesis but does not affect integral membrane proteins or DNA. Our results shed a new light on the multifaceted antibacterial mechanisms of these antibiotics and explain why resistance to them is virtually nonexistent.
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29
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Gerstle Z, Desai R, Veatch SL. Giant Plasma Membrane Vesicles: An Experimental Tool for Probing the Effects of Drugs and Other Conditions on Membrane Domain Stability. Methods Enzymol 2018; 603:129-150. [PMID: 29673522 DOI: 10.1016/bs.mie.2018.02.007] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Giant plasma membrane vesicles (GPMVs) are isolated directly from living cells and provide an alternative to vesicles constructed of synthetic or purified lipids as an experimental model system for use in a wide range of assays. GPMVs capture much of the compositional protein and lipid complexity of intact cell plasma membranes, are filled with cytoplasm, and are free from contamination with membranes from internal organelles. GPMVs often exhibit a miscibility transition below the growth temperature of their parent cells. GPMVs labeled with a fluorescent protein or lipid analog appear uniform on the micron-scale when imaged above the miscibility transition temperature, and separate into coexisting liquid domains with differing membrane compositions and physical properties below this temperature. The presence of this miscibility transition in isolated GPMVs suggests that a similar phase-like heterogeneity occurs in intact plasma membranes under growth conditions, albeit on smaller length scales. In this context, GPMVs provide a simple and controlled experimental system to explore how drugs and other environmental conditions alter the composition and stability of phase-like domains in intact cell membranes. This chapter describes methods to generate and isolate GPMVs from adherent mammalian cells and to interrogate their miscibility transition temperatures using fluorescence microscopy.
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Affiliation(s)
- Zoe Gerstle
- University of Michigan, Ann Arbor, MI, United States
| | - Rohan Desai
- University of Michigan, Ann Arbor, MI, United States
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30
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Jin W, Simsek MF, Pralle A. Quantifying spatial and temporal variations of the cell membrane ultra-structure by bimFCS. Methods 2018. [PMID: 29530504 DOI: 10.1016/j.ymeth.2018.02.019] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
It has been long recognized that the cell membrane is heterogeneous on scales ranging from a couple of molecules to micrometers in size and hence diffusion of receptors is length scale dependent. This heterogeneity modulates many cell-membrane-associated processes requiring transient spatiotemporal separation of components. The transient increase in local concentration of interacting signal components enables robust signaling in an otherwise thermally noisy system. Understanding how lipids and proteins self-organize and interact with the cell cortex requires quantifying the motion of the components. Multi-length scale diffusion measurements by single particle tracking, fluorescence correlation spectroscopy (FCS) or related techniques are able to identify components being transiently trapped in nanodomains, from freely moving one and from ones with reduced long-scale diffusion due to interaction with the cell cortex. One particular implementation of multi-length scale diffusion measurements is the combination of FCS with a spatially resolved detector, such as a camera and two-dimensional extended excitation profile. The main advantages of this approach are that all length scales are interrogated simultaneously, uniquely permits quantifying changes to the membrane structure caused by extrenal or internal perturbations. Here, we review how combining total internal reflection microscopy (TIRF) with FC resolves the membrane organization in living cells. We show how to implement the method, which requires only a few seconds of data acquisition to quantify membrane nanodomains, or the spacing of membrane fences caused by the actin cortex. The choice of diffusing fluorescent probe determines which membrane heterogeneity is detected. We review the instrument, sample preparation, experimental and computational requirements to perform such measurements, and discuss the potential and limitations. The discussion includes examples of spatial and temporal comparisons of the membrane structure in response to perturbations demonstrating the complex cell physiology.
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Affiliation(s)
- Weixiang Jin
- Dept. of Physics, 239 Fronczak Hall, University at Buffalo, SUNY, Buffalo, NY 14260-1500, United States
| | - M Fethullah Simsek
- Dept. of Physics, 239 Fronczak Hall, University at Buffalo, SUNY, Buffalo, NY 14260-1500, United States
| | - Arnd Pralle
- Dept. of Physics, 239 Fronczak Hall, University at Buffalo, SUNY, Buffalo, NY 14260-1500, United States.
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Imam ZI, Kenyon LE, Ashby G, Nagib F, Mendicino M, Zhao C, Gadok AK, Stachowiak JC. Phase-Separated Liposomes Enhance the Efficiency of Macromolecular Delivery to the Cellular Cytoplasm. Cell Mol Bioeng 2017; 10:387-403. [PMID: 29104698 PMCID: PMC5665383 DOI: 10.1007/s12195-017-0489-4] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2017] [Accepted: 05/11/2017] [Indexed: 11/28/2022] Open
Abstract
INTRODUCTION From viruses to organelles, fusion of biological membranes is used by diverse biological systems to deliver macromolecules across membrane barriers. Membrane fusion is also a potentially efficient mechanism for the delivery of macromolecular therapeutics to the cellular cytoplasm. However, a key shortcoming of existing fusogenic liposomal systems is that they are inefficient, requiring a high concentration of fusion-promoting lipids in order to cross cellular membrane barriers. OBJECTIVES Toward addressing this limitation, our experiments explore the extent to which membrane fusion can be amplified by using the process of lipid membrane phase separation to concentrate fusion-promoting lipids within distinct regions of the membrane surface. METHODS We used confocal fluorescence microscopy to investigate the integration of fusion-promoting lipids into a ternary lipid membrane system that separated into liquid-ordered and liquid-disordered membrane phases. Additionally, we quantified the impact of membrane phase separation on the efficiency with which liposomes transferred lipids and encapsulated macromolecules to cells, using a combination of confocal fluorescence imaging and flow cytometry. RESULTS Here we report that concentrating fusion-promoting lipids within phase-separated lipid domains on the surfaces of liposomes significantly increases the efficiency of liposome fusion with model membranes and cells. In particular, membrane phase separation enhanced the delivery of lipids and model macromolecules to the cytoplasm of tumor cells by at least 4-fold in comparison to homogenous liposomes. CONCLUSIONS Our findings demonstrate that phase separation can enhance membrane fusion by locally concentrating fusion-promoting lipids on the surface of liposomes. This work represents the first application of lipid membrane phase separation in the design of biomaterials-based delivery systems. Additionally, these results lay the ground work for developing fusogenic liposomes that are triggered by physical and molecular cues associated with target cells.
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Affiliation(s)
- Zachary I. Imam
- Department of Biomedical Engineering, The University of Texas at Austin, Austin, TX USA
| | - Laura E. Kenyon
- Department of Biomedical Engineering, The University of Texas at Austin, Austin, TX USA
| | - Grant Ashby
- Department of Biomedical Engineering, The University of Texas at Austin, Austin, TX USA
| | - Fatema Nagib
- Department of Biomedical Engineering, The University of Texas at Austin, Austin, TX USA
| | - Morgan Mendicino
- Department of Biomedical Engineering, The University of Texas at Austin, Austin, TX USA
| | - Chi Zhao
- Department of Biomedical Engineering, The University of Texas at Austin, Austin, TX USA
| | - Avinash K. Gadok
- Department of Biomedical Engineering, The University of Texas at Austin, Austin, TX USA
| | - Jeanne C. Stachowiak
- Department of Biomedical Engineering, The University of Texas at Austin, Austin, TX USA
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32
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Honerkamp-Smith AR. Zebrafish Keep Their Cool. Biophys J 2017; 113:1175-1176. [PMID: 28554481 DOI: 10.1016/j.bpj.2017.05.003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2017] [Revised: 04/28/2017] [Accepted: 05/04/2017] [Indexed: 12/27/2022] Open
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Abstract
The bacterial cytoplasmic membrane is composed of roughly equal proportions of lipids and proteins. The main lipid components are phospholipids, which vary in acyl chain length, saturation, and branching and carry head groups that vary in size and charge. Phospholipid variants determine membrane properties such as fluidity and charge that in turn modulate interactions with membrane-associated proteins. We summarize recent advances in understanding bacterial membrane structure and function, focusing particularly on the possible existence and significance of specialized membrane domains. We review the role of membrane curvature as a spatial cue for recruitment and regulation of proteins involved in morphogenic functions, especially elongation and division. Finally, we examine the role of the membrane, especially regulation of synthesis and fluid properties, in the life cycle of cell wall-deficient L-form bacteria.
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Affiliation(s)
- Henrik Strahl
- Centre for Bacterial Cell Biology, Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle Upon Tyne, NE2 4AX United Kingdom; ,
| | - Jeff Errington
- Centre for Bacterial Cell Biology, Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle Upon Tyne, NE2 4AX United Kingdom; ,
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34
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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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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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36
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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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37
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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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38
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Blosser MC, Honerkamp-Smith AR, Han T, Haataja M, Keller SL. Transbilayer Colocalization of Lipid Domains Explained via Measurement of Strong Coupling Parameters. Biophys J 2016; 109:2317-27. [PMID: 26636943 DOI: 10.1016/j.bpj.2015.10.031] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2015] [Revised: 10/16/2015] [Accepted: 10/26/2015] [Indexed: 01/03/2023] Open
Abstract
When micron-scale compositional heterogeneity develops in membranes, the distribution of lipids on one face of the membrane strongly affects the distribution on the other. Specifically, when lipid membranes phase separate into coexisting liquid phases, domains in each monolayer leaflet of the membrane are colocalized with domains in the opposite leaflet. Colocalized domains have never been observed to spontaneously move out of registry. This result indicates that the lipid compositions in one leaflet are strongly coupled to compositions in the opposing leaflet. Predictions of the interleaflet coupling parameter, Λ, vary by a factor of 50. We measure the value of Λ by applying high shear forces to supported lipid bilayers. This causes the upper leaflet to slide over the lower leaflet, moving domains out of registry. We find that the threshold shear stress required to deregister domains in the upper and lower leaflets increases with the inverse length of domains. We derive a simple, closed-form expression relating the threshold shear to Λ, and find Λ = 0.016 ± 0.004 kBT/nm2.
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Affiliation(s)
- Matthew C Blosser
- Departments of Chemistry and Physics, University of Washington, Seattle, Washington
| | - Aurelia R Honerkamp-Smith
- Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge, United Kingdom
| | - Tao Han
- Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey
| | - Mikko Haataja
- Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey
| | - Sarah L Keller
- Departments of Chemistry and Physics, University of Washington, Seattle, Washington.
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39
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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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40
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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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41
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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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42
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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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43
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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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44
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Bleecker JV, Cox PA, Foster RN, Litz JP, Blosser MC, Castner DG, Keller SL. Thickness Mismatch of Coexisting Liquid Phases in Noncanonical Lipid Bilayers. J Phys Chem B 2016; 120:2761-70. [PMID: 26890258 DOI: 10.1021/acs.jpcb.5b10165] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Lipid composition dictates membrane thickness, which in turn can influence membrane protein activity. Lipid composition also determines whether a membrane demixes into coexisting liquid-crystalline phases. Previous direct measurements of demixed lipid membranes have always found a liquid-ordered phase that is thicker than the liquid-disordered phase. Here we investigated noncanonical ternary lipid mixtures designed to produce bilayers with thicker disordered phases than ordered phases. The membranes were composed of short, saturated (ordered) lipids; long, unsaturated (disordered) lipids; and cholesterol. We found that few of these systems yield coexisting liquid phases above 10 °C. For membranes that do demix into two liquid phases, we measured the thickness mismatch between the phases by atomic force microscopy and found that not one of the systems yields thicker disordered than ordered phases under standard experimental conditions. We found no monotonic relationship between demixing temperatures of these ternary systems and either estimated thickness mismatches between the liquid phases or the physical parameters of single-component membranes composed of the individual lipids. These results highlight the robustness of a membrane's liquid-ordered phase to be thicker than the liquid-disordered phase, regardless of the membrane's lipid composition.
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Affiliation(s)
- Joan V Bleecker
- Departments of Chemistry, ‡Chemical Engineering, and §Bioengineering, University of Washington , Seattle, Washington 98195, United States
| | - Phillip A Cox
- Departments of Chemistry, ‡Chemical Engineering, and §Bioengineering, University of Washington , Seattle, Washington 98195, United States
| | - Rami N Foster
- Departments of Chemistry, ‡Chemical Engineering, and §Bioengineering, University of Washington , Seattle, Washington 98195, United States
| | - Jonathan P Litz
- Departments of Chemistry, ‡Chemical Engineering, and §Bioengineering, University of Washington , Seattle, Washington 98195, United States
| | - Matthew C Blosser
- Departments of Chemistry, ‡Chemical Engineering, and §Bioengineering, University of Washington , Seattle, Washington 98195, United States
| | - David G Castner
- Departments of Chemistry, ‡Chemical Engineering, and §Bioengineering, University of Washington , Seattle, Washington 98195, United States
| | - Sarah L Keller
- Departments of Chemistry, ‡Chemical Engineering, and §Bioengineering, University of Washington , Seattle, Washington 98195, United States
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45
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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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46
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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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47
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Membrane nanodomains: contribution of curvature and interaction with proteins and cytoskeleton. Essays Biochem 2015; 57:109-19. [PMID: 25658348 DOI: 10.1042/bse0570109] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
The understanding of lipid membranes and their organization has undergone significant development with better techniques and therefore more resolved experiments. Many new factors and organizing principles have been discovered, and interplay between these factors is expected to result in rich functional behaviours. The major factors regulating the lateral membrane heterogeneity, apart from the well-studied phase separation, are cytoskeleton pinning, clustering of lipids and curvature. These factors are effective means to create membrane domains that provide rich biological functionality. We review the recent advances and concepts of membrane heterogeneity organization by curvature, cytoskeleton and clustering proteins.
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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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Gordon VD, O'Halloran TJ, Shindell O. Membrane adhesion and the formation of heterogeneities: biology, biophysics, and biotechnology. Phys Chem Chem Phys 2015; 17:15522-33. [PMID: 25866854 PMCID: PMC4465551 DOI: 10.1039/c4cp05876c] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Membrane adhesion is essential to many vital biological processes. Sites of membrane adhesion are often associated with heterogeneities in the lipid and protein composition of the membrane. These heterogeneities are thought to play functional roles by facilitating interactions between proteins. However, the causal links between membrane adhesion and membrane heterogeneities are not known. Here we survey the state of the field and indicate what we think are understudied areas ripe for development.
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Affiliation(s)
- V D Gordon
- The University of Texas at Austin, Department of Physics and Center for Nonlinear Dynamics, 2515 Speedway, Stop C1610, Austin, Texas 78712-1199, USA.
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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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