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Collier CP, Bolmatov D, Elkins JG, Katsaras J. Nanoscopic lipid domains determined by microscopy and neutron scattering. Methods 2024; 223:127-135. [PMID: 38331125 DOI: 10.1016/j.ymeth.2024.01.020] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2023] [Revised: 01/22/2024] [Accepted: 01/26/2024] [Indexed: 02/10/2024] Open
Abstract
Biological membranes are highly complex supramolecular assemblies, which play central roles in biology. However, their complexity makes them challenging to study their nanoscale structures. To overcome this challenge, model membranes assembled using reduced sets of membrane-associated biomolecules have been found to be both excellent and tractable proxies for biological membranes. Due to their relative simplicity, they have been studied using a range of biophysical characterization techniques. In this review article, we will briefly detail the use of fluorescence and electron microscopies, and X-ray and neutron scattering techniques used over the past few decades to study the nanostructure of biological membranes.
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Affiliation(s)
- Charles P Collier
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN, USA
| | - Dima Bolmatov
- Department of Physics and Astronomy, University of Tennessee, Knoxville, TN, USA; Shull Wollan Center, Oak Ridge National Laboratory, Oak Ridge, TN, USA
| | - James G Elkins
- Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA
| | - John Katsaras
- Department of Physics and Astronomy, University of Tennessee, Knoxville, TN, USA; Shull Wollan Center, Oak Ridge National Laboratory, Oak Ridge, TN, USA; Neutron Scattering Division, Oak Ridge National Laboratorry, Oak Ridege, TN, USA
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2
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Porciello N, Cipria D, Masi G, Lanz AL, Milanetti E, Grottesi A, Howie D, Cobbold SP, Schermelleh L, He HT, D'Abramo M, Destainville N, Acuto O, Nika K. Role of the membrane anchor in the regulation of Lck activity. J Biol Chem 2022; 298:102663. [PMID: 36372231 PMCID: PMC9763865 DOI: 10.1016/j.jbc.2022.102663] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2022] [Revised: 10/10/2022] [Accepted: 10/12/2022] [Indexed: 11/13/2022] Open
Abstract
Theoretical work suggests that collective spatiotemporal behavior of integral membrane proteins should be modulated by boundary lipids sheathing their membrane anchors. Here, we show evidence for this prediction while investigating the mechanism for maintaining a steady amount of the active form of integral membrane protein Lck kinase (LckA) by Lck trans-autophosphorylation regulated by the phosphatase CD45. We used super-resolution microscopy, flow cytometry, and pharmacological and genetic perturbation to gain insight into the spatiotemporal context of this process. We found that LckA is generated exclusively at the plasma membrane, where CD45 maintains it in a ceaseless dynamic equilibrium with its unphosphorylated precursor. Steady LckA shows linear dependence, after an initial threshold, over a considerable range of Lck expression levels. This behavior fits a phenomenological model of trans-autophosphorylation that becomes more efficient with increasing LckA. We then challenged steady LckA formation by genetically swapping the Lck membrane anchor with structurally divergent ones, such as that of Src or the transmembrane domains of LAT, CD4, palmitoylation-defective CD4 and CD45 that were expected to drastically modify Lck boundary lipids. We observed small but significant changes in LckA generation, except for the CD45 transmembrane domain that drastically reduced LckA due to its excessive lateral proximity to CD45. Comprehensively, LckA formation and maintenance can be best explained by lipid bilayer critical density fluctuations rather than liquid-ordered phase-separated nanodomains, as previously thought, with "like/unlike" boundary lipids driving dynamical proximity and remoteness of Lck with itself and with CD45.
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Affiliation(s)
- Nicla Porciello
- T Cell Signalling Laboratory, Sir William Dunn School of Pathology, Oxford University, Oxford, United Kingdom
| | - Deborah Cipria
- T Cell Signalling Laboratory, Sir William Dunn School of Pathology, Oxford University, Oxford, United Kingdom
| | - Giulia Masi
- T Cell Signalling Laboratory, Sir William Dunn School of Pathology, Oxford University, Oxford, United Kingdom
| | - Anna-Lisa Lanz
- T Cell Signalling Laboratory, Sir William Dunn School of Pathology, Oxford University, Oxford, United Kingdom
| | - Edoardo Milanetti
- Department of Physics, University of Rome "La Sapienza", Rome, Italy
| | | | - Duncan Howie
- Sir William Dunn School of Pathology, Oxford University, Oxford, United Kingdom
| | - Steve P Cobbold
- Sir William Dunn School of Pathology, Oxford University, Oxford, United Kingdom
| | - Lothar Schermelleh
- Micron Advanced Bioimaging Unit, Department of Biochemistry, Oxford University, Oxford, United Kingdom
| | - Hai-Tao He
- Aix Marseille Université, CNRS, INSERM, CINL, Marseille, France
| | - Marco D'Abramo
- Department of Chemistry, University of Rome "La Sapienza", Rome, Italy
| | - Nicolas Destainville
- Laboratoire de Physique Théorique, Université Paul Sabatier, CNRS, UPS, Toulouse, France.
| | - Oreste Acuto
- T Cell Signalling Laboratory, Sir William Dunn School of Pathology, Oxford University, Oxford, United Kingdom.
| | - Konstantina Nika
- T Cell Signalling Laboratory, Sir William Dunn School of Pathology, Oxford University, Oxford, United Kingdom; Department of Biochemistry, School of Medicine, University of Patras, Patras, Greece.
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3
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Page EF, Blake MJ, Foley GA, Calhoun TR. Monitoring membranes: The exploration of biological bilayers with second harmonic generation. CHEMICAL PHYSICS REVIEWS 2022; 3:041307. [PMID: 36536669 PMCID: PMC9756348 DOI: 10.1063/5.0120888] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/15/2022] [Accepted: 11/03/2022] [Indexed: 12/23/2022]
Abstract
Nature's seemingly controlled chaos in heterogeneous two-dimensional cell membranes stands in stark contrast to the precise, often homogeneous, environment in an experimentalist's flask or carefully designed material system. Yet cell membranes can play a direct role, or serve as inspiration, in all fields of biology, chemistry, physics, and engineering. Our understanding of these ubiquitous structures continues to evolve despite over a century of study largely driven by the application of new technologies. Here, we review the insight afforded by second harmonic generation (SHG), a nonlinear optical technique. From potential measurements to adsorption and diffusion on both model and living systems, SHG complements existing techniques while presenting a large exploratory space for new discoveries.
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Affiliation(s)
- Eleanor F. Page
- Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996, USA
| | - Marea J. Blake
- Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996, USA
| | - Grant A. Foley
- Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996, USA
| | - Tessa R. Calhoun
- Department of Chemistry, University of Tennessee, Knoxville, Tennessee 37996, USA
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4
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Chai YJ, Cheng CY, Liao YH, Lin CH, Hsieh CL. Heterogeneous nanoscopic lipid diffusion in the live cell membrane and its dependency on cholesterol. Biophys J 2022; 121:3146-3161. [PMID: 35841144 PMCID: PMC9463655 DOI: 10.1016/j.bpj.2022.07.008] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2021] [Revised: 03/08/2022] [Accepted: 07/06/2022] [Indexed: 11/02/2022] Open
Abstract
Cholesterol plays a unique role in the regulation of membrane organization and dynamics by modulating the membrane phase transition at the nanoscale. Unfortunately, due to their small sizes and dynamic nature, the effects of cholesterol-mediated membrane nanodomains on membrane dynamics remain elusive. Here, using ultrahigh-speed single-molecule tracking with advanced optical microscope techniques, we investigate the diffusive motion of single phospholipids in the live cell plasma membrane at the nanoscale and its dependency on the cholesterol concentration. We find that both saturated and unsaturated phospholipids undergo anomalous subdiffusion on the length scale of 10-100 nm. The diffusion characteristics exhibit considerable variations in space and in time, indicating that the nanoscopic lipid diffusion is highly heterogeneous. Importantly, through the statistical analysis, apparent dual-mobility subdiffusion is observed from the mixed diffusion behaviors. The measured subdiffusion agrees well with the hop diffusion model that represents a diffuser moving in a compartmentalized membrane created by the cytoskeleton meshwork. Cholesterol depletion diminishes the lipid mobility with an apparently smaller compartment size and a stronger confinement strength. Similar results are measured with temperature reduction, suggesting that the more heterogeneous and restricted diffusion is connected to the nanoscopic membrane phase transition. Our conclusion supports the model that cholesterol depletion induces the formation of gel-phase, solid-like membrane nanodomains. These nanodomains undergo restricted diffusion and act as diffusion obstacles to the membrane molecules that are excluded from the nanodomains. This work provides the experimental evidence that the nanoscopic lipid diffusion in the cell plasma membrane is heterogeneous and sensitive to the cholesterol concentration and temperature, shedding new light on the regulation mechanisms of nanoscopic membrane dynamics.
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Affiliation(s)
- Yu-Jo Chai
- Institute of Atomic and Molecular Sciences (IAMS), Academia Sinica, Taipei, Taiwan
| | - Ching-Ya Cheng
- Institute of Atomic and Molecular Sciences (IAMS), Academia Sinica, Taipei, Taiwan
| | - Yi-Hung Liao
- Institute of Atomic and Molecular Sciences (IAMS), Academia Sinica, Taipei, Taiwan
| | - Chih-Hsiang Lin
- Institute of Atomic and Molecular Sciences (IAMS), Academia Sinica, Taipei, Taiwan
| | - Chia-Lung Hsieh
- Institute of Atomic and Molecular Sciences (IAMS), Academia Sinica, Taipei, Taiwan.
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5
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Gupta R, Sharma VK, Gupta J, Ghosh SK. 1,3 Dialkylated Imidazolium Ionic Liquid Causes Interdigitated Domains in a Phospholipid Membrane. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2022; 38:3412-3421. [PMID: 35263113 DOI: 10.1021/acs.langmuir.1c03160] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Amphiphilic imidazolium-based ionic liquids (ILs) have proven their efficacy in altering the membrane integrity and dynamics. The present article investigates the phase-separated domains in a 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) membrane induced by 1,3 dialkylated imidazolium IL. Isotherm measurements on DPPC monolayers formed at the air-water interface have shown a decrease in the mean molecular area with the addition of this IL. The positive value of the excess Gibbs free energy of mixing indicates an unfavorable mixing of the IL into the lipid. This leads to IL-induced phase-separated domains in the multilayer of the lipid confirmed by the occurrence of two sets of equidistance peaks in the X-ray reflectivity data. The electron density profile along the surface normal obtained by the swelling method shows the bilayer thickness of the newly formed IL-rich phase to be substantially lower (∼34 Å) than the DPPC phase (∼45.8 Å). This IL-rich phase has been confirmed to be interdigitated, showing an enhanced electron density in the tail region due to the overlapping hydrocarbon chains. Differential scanning calorimetry measurements showed that the incorporation of IL enhances the fluidity of the lipid bilayer. Therefore, the study indicates the formation of an interdigitated phase with a lower order compared to the gel phase in the DPPC membrane supplemented with the IL.
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Affiliation(s)
- Ritika Gupta
- Department of Physics, School of Natural Sciences, Shiv Nadar University, NH 91, Tehsil Dadri, G. B. Nagar, Greater Noida, Uttar Pradesh 201314, India
| | - Veerendra K Sharma
- Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India
- Homi Bhabha National Institute, Anushaktinagar, Mumbai 400094, India
| | - Jyoti Gupta
- Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India
- Homi Bhabha National Institute, Anushaktinagar, Mumbai 400094, India
| | - Sajal K Ghosh
- Department of Physics, School of Natural Sciences, Shiv Nadar University, NH 91, Tehsil Dadri, G. B. Nagar, Greater Noida, Uttar Pradesh 201314, India
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6
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Nieto-Garai JA, Lorizate M, Contreras FX. Shedding light on membrane rafts structure and dynamics in living cells. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2022; 1864:183813. [PMID: 34748743 DOI: 10.1016/j.bbamem.2021.183813] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/30/2021] [Revised: 10/21/2021] [Accepted: 10/25/2021] [Indexed: 12/12/2022]
Abstract
Cellular membranes are fundamental building blocks regulating an extensive repertoire of biological functions. These structures contain lipids and membrane proteins that are known to laterally self-aggregate in the plane of the membrane, forming defined membrane nanoscale domains essential for protein activity. Membrane rafts are described as heterogeneous, dynamic, and short-lived cholesterol- and sphingolipid-enriched membrane nanodomains (10-200 nm) induced by lipid-protein and lipid-lipid interactions. Those membrane nanodomains have been extensively characterized using model membranes and in silico methods. However, despite the development of advanced fluorescence microscopy techniques, undoubted nanoscale visualization by imaging techniques of membrane rafts in the membrane of unperturbed living cells is still uncompleted, increasing the skepticism about their existence. Here, we broadly review recent biochemical and microscopy techniques used to investigate membrane rafts in living cells and we enumerate persistent open questions to answer before unlocking the mystery of membrane rafts in living cells.
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Affiliation(s)
- Jon Ander Nieto-Garai
- Department of Biochemistry and Molecular Biology, University of the Basque Country (UPV/EHU), Barrio Sarriena s/n, 48940 Bilbao, Spain.
| | - Maier Lorizate
- Department of Biochemistry and Molecular Biology, University of the Basque Country (UPV/EHU), Barrio Sarriena s/n, 48940 Bilbao, Spain; Instituto Biofisika (UPV/EHU, CSIC), Barrio Sarriena s/n, 48940 Bilbao, Spain
| | - F-Xabier Contreras
- Department of Biochemistry and Molecular Biology, University of the Basque Country (UPV/EHU), Barrio Sarriena s/n, 48940 Bilbao, Spain; Instituto Biofisika (UPV/EHU, CSIC), Barrio Sarriena s/n, 48940 Bilbao, Spain; IKERBASQUE, Basque Foundation for Science, 48011 Bilbao, Spain.
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7
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Wójtowicz K, Czogalla A, Trombik T, Łukaszewicz M. Surfactin cyclic lipopeptides change the plasma membrane composition and lateral organization in mammalian cells. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2021; 1863:183730. [PMID: 34419486 DOI: 10.1016/j.bbamem.2021.183730] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/15/2021] [Revised: 07/10/2021] [Accepted: 08/13/2021] [Indexed: 02/07/2023]
Abstract
The specific structure and composition of the cell plasma membrane (PM) is crucial for many cellular processes and can be targeted by various substances with potential medical applications. In this context, biosurfactants (BS) constitute a promising group of natural compounds that possess several biological functions, including anticancer activity. Despite the efficiency of BS, their mode of action had never been elucidated before. Here, we demonstrate the influence of cyclic lipopeptide surfactin (SU) on the PM of CHO-K1 cells. Both FLIM and svFCS experiments show that even a low concentration of SU causes significant changes in the membrane fluidity and dynamic molecular organization. Further, we demonstrate that SU causes a relevant dose-dependent reduction of cellular cholesterol by extracting it from the PM. Finally, we show that CHO-25RA cells characterized by increased cholesterol levels are more sensitive to SU treatment than CHO-K1 cells. We propose that sterols organizing the PM raft nanodomains, constitute a potential target for SU and other biosurfactants. In our opinion, the anticancer activity of biosurfactants is directly related with the higher cholesterol content found in many cancer cells.
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Affiliation(s)
- Karolina Wójtowicz
- Department of Biotransformation, Faculty of Biotechnology, University of Wrocław, Wrocław, Poland
| | - Aleksander Czogalla
- Department of Cytobiochemistry, Faculty of Biotechnology, University of Wrocław, Wrocław, Poland
| | - Tomasz Trombik
- Department of Biophysics, Faculty of Biotechnology, University of Wrocław, Wrocław, Poland.
| | - Marcin Łukaszewicz
- Department of Biotransformation, Faculty of Biotechnology, University of Wrocław, Wrocław, Poland.
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8
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Winkler PM, García-Parajo MF. Correlative nanophotonic approaches to enlighten the nanoscale dynamics of living cell membranes. Biochem Soc Trans 2021; 49:2357-2369. [PMID: 34495333 PMCID: PMC8589428 DOI: 10.1042/bst20210457] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2021] [Revised: 08/03/2021] [Accepted: 08/10/2021] [Indexed: 01/31/2023]
Abstract
Dynamic compartmentalization is a prevailing principle regulating the spatiotemporal organization of the living cell membrane from the nano- up to the mesoscale. This non-arbitrary organization is intricately linked to cell function. On living cell membranes, dynamic domains or 'membrane rafts' enriched with cholesterol, sphingolipids and other certain proteins exist at the nanoscale serving as signaling and sorting platforms. Moreover, it has been postulated that other local organizers of the cell membrane such as intrinsic protein interactions, the extracellular matrix and/or the actin cytoskeleton synergize with rafts to provide spatiotemporal hierarchy to the membrane. Elucidating the intricate coupling of multiple spatial and temporal scales requires the application of correlative techniques, with a particular need for simultaneous nanometer spatial precision and microsecond temporal resolution. Here, we review novel fluorescence-based techniques that readily allow to decode nanoscale membrane dynamics with unprecedented spatiotemporal resolution and single-molecule sensitivity. We particularly focus on correlative approaches from the field of nanophotonics. Notably, we introduce a versatile planar nanoantenna platform combined with fluorescence correlation spectroscopy to study spatiotemporal heterogeneities on living cell membranes at the nano- up to the mesoscale. Finally, we outline remaining future technological challenges and comment on potential directions to advance our understanding of cell membrane dynamics under the influence of the actin cytoskeleton and extracellular matrix in uttermost detail.
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Affiliation(s)
- Pamina M. Winkler
- ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860 Barcelona, Spain
| | - María F. García-Parajo
- ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860 Barcelona, Spain
- ICREA, Pg. Lluis Companys 23, 08010 Barcelona, Spain
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9
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Molecular Diffusion of ABCA1 at the Cell Surface of Living Cells Assessed by svFCS. MEMBRANES 2021; 11:membranes11070498. [PMID: 34209140 PMCID: PMC8306713 DOI: 10.3390/membranes11070498] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/10/2021] [Revised: 06/23/2021] [Accepted: 06/29/2021] [Indexed: 11/17/2022]
Abstract
Extensive studies showed the crucial role of ATP binding cassette (ABC) transporter ABCA1 in organizing the lipid microenvironment at the plasma membrane (PM) of living cells. However, the exact role of this protein in terms of lipid redistribution and lateral reorganization of the PM is still being discussed. Here, we took advantage of the spot variation fluorescence correlation spectroscopy (svFCS) to investigate the molecular dynamics of the ABCA1 expressed at the PM of Chinese hamster ovary cells (CHO-K1). We confirmed that this protein is strongly confined into the raft nanodomains. Next, in agreement with our previous observations, we showed that amphotericin B does not affect the diffusion properties of an active ABCA1 in contrary to inactive mutant ABCA1MM. We also evidenced that ApoA1 influences the molecular diffusion properties of ABCA1. Finally, we showed that the molecular confinement of ABCA1 depends on the cholesterol content in the PM, but presumably, this is not the only factor responsible for that. We concluded that the molecular dynamics of ABCA1 strongly depends on its activity and the PM composition. We hypothesize that other factors than lipids (i.e., proteins) are responsible for the strong confinement of ABCA1 in PM nanodomains which possibility has to be elucidated.
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10
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Kell DB. A protet-based, protonic charge transfer model of energy coupling in oxidative and photosynthetic phosphorylation. Adv Microb Physiol 2021; 78:1-177. [PMID: 34147184 DOI: 10.1016/bs.ampbs.2021.01.001] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Textbooks of biochemistry will explain that the otherwise endergonic reactions of ATP synthesis can be driven by the exergonic reactions of respiratory electron transport, and that these two half-reactions are catalyzed by protein complexes embedded in the same, closed membrane. These views are correct. The textbooks also state that, according to the chemiosmotic coupling hypothesis, a (or the) kinetically and thermodynamically competent intermediate linking the two half-reactions is the electrochemical difference of protons that is in equilibrium with that between the two bulk phases that the coupling membrane serves to separate. This gradient consists of a membrane potential term Δψ and a pH gradient term ΔpH, and is known colloquially as the protonmotive force or pmf. Artificial imposition of a pmf can drive phosphorylation, but only if the pmf exceeds some 150-170mV; to achieve in vivo rates the imposed pmf must reach 200mV. The key question then is 'does the pmf generated by electron transport exceed 200mV, or even 170mV?' The possibly surprising answer, from a great many kinds of experiment and sources of evidence, including direct measurements with microelectrodes, indicates it that it does not. Observable pH changes driven by electron transport are real, and they control various processes; however, compensating ion movements restrict the Δψ component to low values. A protet-based model, that I outline here, can account for all the necessary observations, including all of those inconsistent with chemiosmotic coupling, and provides for a variety of testable hypotheses by which it might be refined.
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Affiliation(s)
- Douglas B Kell
- Department of Biochemistry and Systems Biology, Institute of Systems, Molecular and Integrative, Biology, University of Liverpool, Liverpool, United Kingdom; The Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, Lyngby, Denmark.
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11
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Gunther G, Malacrida L, Jameson DM, Gratton E, Sánchez SA. LAURDAN since Weber: The Quest for Visualizing Membrane Heterogeneity. Acc Chem Res 2021; 54:976-987. [PMID: 33513300 PMCID: PMC8552415 DOI: 10.1021/acs.accounts.0c00687] [Citation(s) in RCA: 42] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Any chemist studying the interaction of molecules with lipid assemblies will eventually be confronted by the topic of membrane bilayer heterogeneity and may ultimately encounter the heterogeneity of natural membranes. In artificial bilayers, heterogeneity is defined by phase segregation that can be in the nano- and micrometer range. In biological bilayers, heterogeneity is considered in the context of small (10-200 nm) sterol and sphingolipid-enriched heterogeneous and highly dynamic domains. Several techniques can be used to assess membrane heterogeneity in living systems. Our approach is to use a fluorescent reporter molecule immersed in the bilayer, which, by changes in its spectroscopic properties, senses physical-chemistry aspects of the membrane. This dye in combination with microscopy and fluctuation techniques can give information about membrane heterogeneity at different temporal and spatial levels: going from average fluidity to number and diffusion coefficient of nanodomains. LAURDAN (6-dodecanoyl-2-(dimethylamino) naphthalene), is a fluorescent probe designed and synthesized in 1979 by Gregorio Weber with the purpose to study the phenomenon of dipolar relaxation. The spectral displacement observed when LAURDAN is either in fluid or gel phase permitted the use of the technique in the field of membrane dynamics. The quantitation of the spectral displacement was first addressed by the generalized polarization (GP) function in the cuvette, a ratio of the difference in intensity at two wavelengths divided by their sum. In 1997, GP measurements were done for the first time in the microscope, adding to the technique the spatial resolution and allowing the visualization of lipid segregation both in liposomes and cells. A new prospective to the membrane heterogeneity was obtained when LAURDAN fluorescent lifetime measurements were done in the microscope. Two channel lifetime imaging provides information on membrane polarity and dipole relaxation (the two parameters responsible for the spectral shift of LAURDAN), and the application of phasor analysis allows pixel by pixel understanding of these two parameters in the membrane. To increase temporal resolution, LAURDAN GP was combined with fluctuation correlation spectroscopy (FCS) and the motility of nanometric highly packed structures in biological membranes was registered. Lately the application of phasor analysis to spectral images from membranes labeled with LAURDAN allows us to study the full spectra pixel by pixel in an image. All these methodologies, using LAURDAN, offer the possibility to address different properties of membranes depending on the question being asked. In this Account, we will focus on the principles, advantages, and limitations of different approaches to orient the reader to select the most appropriate technique for their research.
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Affiliation(s)
- German Gunther
- Facultad de Ciencias Químicas y Farmacéuticas, Universidad de Chile, Sergio Livingstone P. 1007, Santiago 8380492, Chile
| | - Leonel Malacrida
- Advanced Microscopy and Biophotonics Unit, Hospital de Clínicas, Universidad de la República, Montevideo-Uruguay. Advanced Bioimaging Unit, Institut Pasteur Montevideo, Av. Italia s/n, 90600 Montevideo, Uruguay
| | - David M Jameson
- Department of Cell and Molecular Biology, John A. Burns School of Medicine, University of Hawaii, 651 Ilalo Street, Biosciences 222, Honolulu, Hawaii 96813, United States
| | - Enrico Gratton
- Laboratory for Fluorescence Dynamics, 3210 Natural Sciences II, University of California, Irvine, Irvine, California 92697-2725, United States
| | - Susana A Sánchez
- Departamento de Polímeros, Facultad de Ciencias Químicas, Universidad de Concepción, Edmundo Larenas 129, Concepción 4070371, Chile
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12
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Revealing Plasma Membrane Nano-Domains with Diffusion Analysis Methods. MEMBRANES 2020; 10:membranes10110314. [PMID: 33138102 PMCID: PMC7693849 DOI: 10.3390/membranes10110314] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/01/2020] [Revised: 10/26/2020] [Accepted: 10/26/2020] [Indexed: 12/18/2022]
Abstract
Nano-domains are sub-light-diffraction-sized heterogeneous areas in the plasma membrane of cells, which are involved in cell signalling and membrane trafficking. Throughout the last thirty years, these nano-domains have been researched extensively and have been the subject of multiple theories and models: the lipid raft theory, the fence model, and the protein oligomerization theory. Strong evidence exists for all of these, and consequently they were combined into a hierarchal model. Measurements of protein and lipid diffusion coefficients and patterns have been instrumental in plasma membrane research and by extension in nano-domain research. This has led to the development of multiple methodologies that can measure diffusion and confinement parameters including single particle tracking, fluorescence correlation spectroscopy, image correlation spectroscopy and fluorescence recovery after photobleaching. Here we review the performance and strengths of these methods in the context of their use in identification and characterization of plasma membrane nano-domains.
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13
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Tsai YT, Moore W, Kim H, Budin I. Bringing rafts to life: Lessons learned from lipid organization across diverse biological membranes. Chem Phys Lipids 2020; 233:104984. [PMID: 33203526 DOI: 10.1016/j.chemphyslip.2020.104984] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2020] [Revised: 09/13/2020] [Accepted: 09/28/2020] [Indexed: 10/23/2022]
Abstract
The ability of lipids to drive lateral organization is a remarkable feature of membranes and has been hypothesized to underlie the architecture of cells. Models for lipid rafts and related domains were originally based on the mammalian plasma membrane, but the nature of heterogeneity in this system is still not fully resolved. However, the concept of lipid-driven organization has been highly influential across biology, and has led to discoveries in organisms that feature a diversity of lipid chemistries and physiological needs. Here we review several emerging and instructive cases of membrane organization in non-mammalian systems. In bacteria, several types of membrane domains that act in metabolism and signaling have been elucidated. These widen our view of what constitutes a raft, but also introduce new questions about the relationship between organization and function. In yeast, observable membrane organization is found in both the plasma membrane and the vacuole. The latter serves as the best example of classic membrane phase partitioning in a living system to date, suggesting that internal organelles are important membranes to investigate across eukaryotes. Finally, we highlight plants as powerful model systems for complex membrane interactions in multicellular organisms. Plant membranes are organized by unique glycosphingolipids, supporting the importance of carbohydrate interactions in organizing lateral domains. These examples demonstrate that membrane organization is a potentially universal phenonenon in biology and argue for the continued broadening of lipid physical chemistry research into a wide range of systems.
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Affiliation(s)
- Yi-Ting Tsai
- Department of Chemistry & Biochemistry, University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093, United States
| | - William Moore
- Department of Chemistry & Biochemistry, University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093, United States
| | - Hyesoo Kim
- Department of Chemistry & Biochemistry, University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093, United States
| | - Itay Budin
- Department of Chemistry & Biochemistry, University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093, United States.
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14
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Wu A, Wojtowicz K, Savary S, Hamon Y, Trombik T. Do ABC transporters regulate plasma membrane organization? Cell Mol Biol Lett 2020; 25:37. [PMID: 32647530 PMCID: PMC7336681 DOI: 10.1186/s11658-020-00224-x] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2020] [Accepted: 05/05/2020] [Indexed: 12/29/2022] Open
Abstract
The plasma membrane (PM) spatiotemporal organization is one of the major factors controlling cell signaling and whole-cell homeostasis. The PM lipids, including cholesterol, determine the physicochemical properties of the membrane bilayer and thus play a crucial role in all membrane-dependent cellular processes. It is known that lipid content and distribution in the PM are not random, and their transversal and lateral organization is highly controlled. Mainly sphingolipid- and cholesterol-rich lipid nanodomains, historically referred to as rafts, are extremely dynamic “hot spots” of the PM controlling the function of many cell surface proteins and receptors. In the first part of this review, we will focus on the recent advances of PM investigation and the current PM concept. In the second part, we will discuss the importance of several classes of ABC transporters whose substrates are lipids for the PM organization and dynamics. Finally, we will briefly present the significance of lipid ABC transporters for immune responses.
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Affiliation(s)
- Ambroise Wu
- Faculty of Biotechnology, University of Wroclaw, Wroclaw, Poland
| | | | - Stephane Savary
- Lab. Bio-PeroxIL EA7270, University of Bourgogne Franche-Comté, Dijon, France
| | - Yannick Hamon
- Aix Marseille University, CNRS, INSERM, CIML, Centre d'Immunologie de Marseille-Luminy, Marseille, France
| | - Tomasz Trombik
- Faculty of Biotechnology, University of Wroclaw, Wroclaw, Poland
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15
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Sankaran J, Wohland T. Fluorescence strategies for mapping cell membrane dynamics and structures. APL Bioeng 2020; 4:020901. [PMID: 32478279 PMCID: PMC7228782 DOI: 10.1063/1.5143945] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2020] [Accepted: 04/17/2020] [Indexed: 12/20/2022] Open
Abstract
Fluorescence spectroscopy has been a cornerstone of research in membrane dynamics and organization. Technological advances in fluorescence spectroscopy went hand in hand with discovery of various physicochemical properties of membranes at nanometric spatial and microsecond timescales. In this perspective, we discuss the various challenges associated with quantification of physicochemical properties of membranes and how various modes of fluorescence spectroscopy have overcome these challenges to shed light on the structure and organization of membranes. Finally, we discuss newer measurement strategies and data analysis tools to investigate the structure, dynamics, and organization of membranes.
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16
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Abstract
The interactions between lipids and proteins are one of the most fundamental processes in living organisms, responsible for critical cellular events ranging from replication, cell division, signaling, and movement. Enabling the central coupling responsible for maintaining the functionality of the breadth of proteins, receptors, and enzymes that find their natural home in biological membranes, the fundamental mechanisms of recognition of protein for lipid, and vice versa, have been a focal point of biochemical and biophysical investigations for many decades. Complexes of lipids and proteins, such as the various lipoprotein factions, play central roles in the trafficking of important proteins, small molecules and metabolites and are often implicated in disease states. Recently an engineered lipoprotein particle, termed the nanodisc, a modified form of the human high density lipoprotein fraction, has served as a membrane mimetic for the investigation of membrane proteins and studies of lipid-protein interactions. In this review, we summarize the current knowledge regarding this self-assembling lipid-protein complex and provide examples for its utility in the investigation of a large number of biological systems.
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17
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Bag N, Holowka DA, Baird BA. Imaging FCS delineates subtle heterogeneity in plasma membranes of resting mast cells. Mol Biol Cell 2020; 31:709-723. [PMID: 31895009 PMCID: PMC7202073 DOI: 10.1091/mbc.e19-10-0559] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
A myriad of transient, nanoscopic lipid- and protein-based interactions confer a steady-state organization of the plasma membrane in resting cells that is poised to orchestrate assembly of key signaling components upon reception of an extracellular stimulus. Although difficult to observe directly in live cells, these subtle interactions can be discerned by their impact on the diffusion of membrane constituents. Here, we quantified the diffusion properties of a panel of structurally distinct lipid, lipid-anchored, and transmembrane (TM) probes in RBL mast cells by imaging fluorescence correlation spectroscopy (ImFCS). We developed a statistical analysis of data combined from many pixels over multiple cells to characterize differences in diffusion coefficients as small as 10%, which reflect differences in underlying interactions. We found that the distinctive diffusion properties of lipid probes can be explained by their dynamic partitioning into Lo-like proteolipid nanodomains, which encompass a major fraction of the membrane and whose physical properties are influenced by actin polymerization. Effects on diffusion of functional protein modules in both lipid-anchored and TM probes reflect additional complexity in steady state membrane organization. The contrast we observe between different probes diffusing through the same membrane milieu represents the dynamic resting steady state, which serves as a baseline for monitoring plasma membrane remodeling that occurs upon stimulation.
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Affiliation(s)
- Nirmalya Bag
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853
| | - David A Holowka
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853
| | - Barbara A Baird
- Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853
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18
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Wu A, Grela E, Wójtowicz K, Filipczak N, Hamon Y, Luchowski R, Grudziński W, Raducka-Jaszul O, Gagoś M, Szczepaniak A, Chimini G, Gruszecki WI, Trombik T. ABCA1 transporter reduces amphotericin B cytotoxicity in mammalian cells. Cell Mol Life Sci 2019; 76:4979-4994. [PMID: 31134303 PMCID: PMC6881254 DOI: 10.1007/s00018-019-03154-w] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2019] [Revised: 05/07/2019] [Accepted: 05/16/2019] [Indexed: 01/20/2023]
Abstract
Amphotericin B (AmB) belongs to a group of polyene antibiotics commonly used in the treatment of systemic mycotic infections. A widely accepted mechanism of action of AmB is based on the formation of an oligomeric pore structure within the plasma membrane (PM) by interaction with membrane sterols. Although AmB binds preferentially to ergosterol, it can also bind to cholesterol in the mammalian PM and cause severe cellular toxicity. The lipid content and its lateral organization at the cell PM appear to be significant for AmB binding. Several ATP-binding cassette (ABC) transporters, including ABCA1, play a crucial role in lipid translocation, cholesterol redistribution and efflux. Here, we demonstrate that cells expressing ABCA1 are more resistant to AmB treatment, while cells lacking ABCA1 expression or expressing non-active ABCA1MM mutant display increased sensitivity. Further, a FLIM analysis of AmB-treated cells reveals a fraction of the antibiotic molecules, characterized by relatively high fluorescence lifetimes (> 6 ns), involved in formation of bulk cholesterol-AmB structures at the surface of ABCA1-expressing cells. Finally, lowering the cellular cholesterol content abolishes resistance of ABCA1-expressing cells to AmB. Therefore, we propose that ABCA1-mediated cholesterol efflux from cells induces formation of bulk cholesterol-AmB structures at the cell surface, preventing AmB cytotoxicity.
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Affiliation(s)
- A Wu
- Faculty of Biotechnology, University of Wroclaw, 50-383, Wrocław, Poland
| | - E Grela
- Department of Biophysics, Institute of Physics, Maria Curie-Sklodowska University, 20-031, Lublin, Poland
| | - K Wójtowicz
- Faculty of Biotechnology, University of Wroclaw, 50-383, Wrocław, Poland
| | - N Filipczak
- Faculty of Biotechnology, University of Wroclaw, 50-383, Wrocław, Poland
| | - Y Hamon
- Aix Marseille University, CNRS, INSERM, CIML, Marseille, France
| | - R Luchowski
- Department of Biophysics, Institute of Physics, Maria Curie-Sklodowska University, 20-031, Lublin, Poland
| | - W Grudziński
- Department of Biophysics, Institute of Physics, Maria Curie-Sklodowska University, 20-031, Lublin, Poland
| | - O Raducka-Jaszul
- Faculty of Biotechnology, University of Wroclaw, 50-383, Wrocław, Poland
| | - M Gagoś
- Department of Cell Biology, Maria Curie-Skłodowska University, 20-033, Lublin, Poland
| | - A Szczepaniak
- Faculty of Biotechnology, University of Wroclaw, 50-383, Wrocław, Poland
| | - G Chimini
- Aix Marseille University, CNRS, INSERM, CIML, Marseille, France
| | - W I Gruszecki
- Department of Biophysics, Institute of Physics, Maria Curie-Sklodowska University, 20-031, Lublin, Poland
| | - T Trombik
- Faculty of Biotechnology, University of Wroclaw, 50-383, Wrocław, Poland.
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19
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Verardo D, Agnarsson B, Zhdanov VP, Höök F, Linke H. Single-Molecule Detection with Lightguiding Nanowires: Determination of Protein Concentration and Diffusivity in Supported Lipid Bilayers. NANO LETTERS 2019; 19:6182-6191. [PMID: 31369284 DOI: 10.1021/acs.nanolett.9b02226] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Determining the surface concentration and diffusivity of cell-membrane-bound molecules is central to the understanding of numerous important biochemical processes taking place at cell membranes. Here we use the high aspect ratio and lightguiding properties of semiconductor nanowires (NWs) to detect the presence of single freely diffusing proteins bound to a lipid bilayer covering the NW surface. Simultaneous observation of light-emission dynamics of hundreds of individual NWs occurring on the time scale of only a few seconds is interpreted using analytical models and employed to determine both surface concentration and diffusivity of cholera toxin subunit B (CTxB) bound to GM1 gangliosides in supported lipid bilayer (SLB) at surface concentrations down to below one CTxB per μm2. In particular, a decrease in diffusivity was observed with increasing GM1 content in the SLB, suggesting increasing multivalent binding of CTxB to GM1. The lightguiding capability of the NWs makes the method compatible with conventional epifluorescence microscopy, and it is shown to work well for both photostable and photosensitive dyes. These features make the concept an interesting complement to existing techniques for studying the diffusivity of low-abundance cell-membrane-bound molecules, expanding the rapidly growing use of semiconductor NWs in various bioanalytical sensor applications and live cell studies.
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Affiliation(s)
- Damiano Verardo
- NanoLund and Solid State Physics , Lund University , 22100 Lund , Sweden
| | - Björn Agnarsson
- Department of Physics , Chalmers University of Technology , 41296 Göteborg , Sweden
| | - Vladimir P Zhdanov
- Department of Physics , Chalmers University of Technology , 41296 Göteborg , Sweden
- Boreskov Institute of Catalysis , Russian Academy of Sciences , Novosibirsk 630090 , Russia
| | - Fredrik Höök
- Department of Physics , Chalmers University of Technology , 41296 Göteborg , Sweden
| | - Heiner Linke
- NanoLund and Solid State Physics , Lund University , 22100 Lund , Sweden
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20
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Sarkar P, Chattopadhyay A. Exploring membrane organization at varying spatiotemporal resolutions utilizing fluorescence-based approaches: implications in membrane biology. Phys Chem Chem Phys 2019; 21:11554-11563. [DOI: 10.1039/c9cp02087j] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Representative experimental approaches based on dynamic fluorescence microscopy to analyze organization and dynamics of membrane lipids and proteins.
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Affiliation(s)
- Parijat Sarkar
- CSIR-Centre for Cellular and Molecular Biology
- Hyderabad 500 007
- India
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21
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Santos AL, Preta G. Lipids in the cell: organisation regulates function. Cell Mol Life Sci 2018; 75:1909-1927. [PMID: 29427074 PMCID: PMC11105414 DOI: 10.1007/s00018-018-2765-4] [Citation(s) in RCA: 56] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2017] [Revised: 01/04/2018] [Accepted: 01/29/2018] [Indexed: 12/19/2022]
Abstract
Lipids are fundamental building blocks of all cells and play important roles in the pathogenesis of different diseases, including inflammation, autoimmune disease, cancer, and neurodegeneration. The lipid composition of different organelles can vary substantially from cell to cell, but increasing evidence demonstrates that lipids become organised specifically in each compartment, and this organisation is essential for regulating cell function. For example, lipid microdomains in the plasma membrane, known as lipid rafts, are platforms for concentrating protein receptors and can influence intra-cellular signalling. Lipid organisation is tightly regulated and can be observed across different model organisms, including bacteria, yeast, Drosophila, and Caenorhabditis elegans, suggesting that lipid organisation is evolutionarily conserved. In this review, we summarise the importance and function of specific lipid domains in main cellular organelles and discuss recent advances that investigate how these specific and highly regulated structures contribute to diverse biological processes.
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Affiliation(s)
- Ana L Santos
- Institut National de la Santé et de la Recherche Médicale, U1001 and Faculté de Médecine, Université Paris Descartes, Sorbonne Paris Cité, Paris, France
| | - Giulio Preta
- Institute of Biochemistry, Vilnius University, Sauletekio 7, LT-10257, Vilnius, Lithuania.
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22
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Wang R, Brustlein S, Mailfert S, Fabre R, Fallet M, Sivankutty S, Rigneault H, Marguet D. A straightforward STED-background corrected fitting model for unbiased STED-FCS analyses. Methods 2018; 140-141:212-222. [DOI: 10.1016/j.ymeth.2018.02.010] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2017] [Revised: 12/22/2017] [Accepted: 02/09/2018] [Indexed: 11/16/2022] Open
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23
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Sarangi NK, Roobala C, Basu JK. Unraveling complex nanoscale lipid dynamics in simple model biomembranes: Insights from fluorescence correlation spectroscopy in super-resolution stimulated emission depletion mode. Methods 2018; 140-141:198-211. [DOI: 10.1016/j.ymeth.2017.11.011] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2017] [Revised: 11/18/2017] [Accepted: 11/19/2017] [Indexed: 12/24/2022] Open
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24
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Wang L, Xue Y, Xing J, Song K, Lin J. Exploring the Spatiotemporal Organization of Membrane Proteins in Living Plant Cells. ANNUAL REVIEW OF PLANT BIOLOGY 2018; 69:525-551. [PMID: 29489393 DOI: 10.1146/annurev-arplant-042817-040233] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
Plasma membrane proteins have important roles in transport and signal transduction. Deciphering the spatiotemporal organization of these proteins provides crucial information for elucidating the links between the behaviors of different molecules. However, monitoring membrane proteins without disrupting their membrane environment remains difficult. Over the past decade, many studies have developed single-molecule techniques, opening avenues for probing the stoichiometry and interactions of membrane proteins in their native environment by providing nanometer-scale spatial information and nanosecond-scale temporal information. In this review, we assess recent progress in the development of labeling and imaging technology for membrane protein analysis. We focus in particular on several single-molecule techniques for quantifying the dynamics and assembly of membrane proteins. Finally, we provide examples of how these new techniques are advancing our understanding of the complex biological functions of membrane proteins.
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Affiliation(s)
- Li Wang
- Beijing Advanced Innovation Center for Tree Breeding by Molecular Design, Beijing Forestry University, Beijing 100083, China;
- Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China
- College of Horticulture and Plant Protection, Yangzhou University, Yangzhou 225009, China
| | - Yiqun Xue
- Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China
| | - Jingjing Xing
- Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China
| | - Kai Song
- Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China
| | - Jinxing Lin
- Beijing Advanced Innovation Center for Tree Breeding by Molecular Design, Beijing Forestry University, Beijing 100083, China;
- Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China
- College of Biological Sciences and Biotechnology, Beijing Forestry University, Beijing 100083, China
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25
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Compartmentalization of the plasma membrane. Curr Opin Cell Biol 2018; 53:15-21. [PMID: 29656224 DOI: 10.1016/j.ceb.2018.04.002] [Citation(s) in RCA: 46] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2018] [Revised: 04/03/2018] [Accepted: 04/04/2018] [Indexed: 11/23/2022]
Abstract
The compartmentalization of the plasma membrane is essential for cells to perform specialized biochemical functions, in particular those responsible for intracellular and intercellular signaling pathways. Study of membrane compartmentalization requires state-of-the-art imaging tools that can reveal dynamics of individual molecules with high spatial and temporal resolution. In addition, quantitative analyses are employed to identify transient changes in molecule dynamics. In this review, membrane compartments are classified as stable domains, transient compartments, or nanodomains where proteins aggregate. Interestingly, in most cases, the cortical cytoskeleton plays important roles. Recent studies of the membrane-cytoskeleton interface are providing new insights about membrane organization involving a scale-free self-similar fractal structure and cytoskeleton active processes coupled to membrane dynamics.
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26
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Ras hyperactivation versus overexpression: Lessons from Ras dynamics in Candida albicans. Sci Rep 2018; 8:5248. [PMID: 29588468 PMCID: PMC5869725 DOI: 10.1038/s41598-018-23187-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2016] [Accepted: 03/06/2018] [Indexed: 12/25/2022] Open
Abstract
Ras signaling in response to environmental cues is critical for cellular morphogenesis in eukaryotes. This signaling is tightly regulated and its activation involves multiple players. Sometimes Ras signaling may be hyperactivated. In C. albicans, a human pathogenic fungus, we demonstrate that dynamics of hyperactivated Ras1 (Ras1G13V or Ras1 in Hsp90 deficient strains) can be reliably differentiated from that of normal Ras1 at (near) single molecule level using fluorescence correlation spectroscopy (FCS). Ras1 hyperactivation results in significantly slower dynamics due to actin polymerization. Activating actin polymerization by jasplakinolide can produce hyperactivated Ras1 dynamics. In a sterol-deficient hyperfilamentous GPI mutant of C. albicans too, Ras1 hyperactivation results from Hsp90 downregulation and causes actin polymerization. Hyperactivated Ras1 co-localizes with G-actin at the plasma membrane rather than with F-actin. Depolymerizing actin with cytochalasin D results in faster Ras1 dynamics in these and other strains that show Ras1 hyperactivation. Further, ergosterol does not influence Ras1 dynamics.
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27
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Montis C, Busatto S, Valle F, Zendrini A, Salvatore A, Gerelli Y, Berti D, Bergese P. Biogenic Supported Lipid Bilayers from Nanosized Extracellular Vesicles. ACTA ACUST UNITED AC 2018. [DOI: 10.1002/adbi.201700200] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Affiliation(s)
- Costanza Montis
- Department of Chemistry; University of Florence and CSGI; via della Lastruccia 3 50019 Florence Italy
| | - Sara Busatto
- Department of Molecular and Translational Medicine; University of Brescia; CSGI and INSTM, viale Europa 11 25123 Brescia Italy
| | | | - Andrea Zendrini
- Department of Molecular and Translational Medicine; University of Brescia; CSGI and INSTM, viale Europa 11 25123 Brescia Italy
| | - Annalisa Salvatore
- Department of Chemistry; University of Florence and CSGI; via della Lastruccia 3 50019 Florence Italy
| | - Yuri Gerelli
- Institut Laue-Langevin; 71 Avenue des Martyrs BP 156 F-38000 Grenoble France
| | - Debora Berti
- Department of Chemistry; University of Florence and CSGI; via della Lastruccia 3 50019 Florence Italy
| | - Paolo Bergese
- Department of Molecular and Translational Medicine; University of Brescia; CSGI and INSTM, viale Europa 11 25123 Brescia Italy
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28
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Mann D, Güldenhaupt J, Schartner J, Gerwert K, Kötting C. The protonation states of GTP and GppNHp in Ras proteins. J Biol Chem 2018; 293:3871-3879. [PMID: 29382720 DOI: 10.1074/jbc.ra117.001110] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2017] [Revised: 01/29/2018] [Indexed: 01/09/2023] Open
Abstract
The small GTPase Ras transmits signals in a variety of cellular signaling pathways, most prominently in cell proliferation. GTP hydrolysis in the active center of Ras acts as a prototype for many GTPases and is the key to the understanding of several diseases, including cancer. Therefore, Ras has been the focus of intense research over the last decades. A recent neutron diffraction crystal structure of Ras indicated a protonated γ-guanylyl imidodiphosphate (γ-GppNHp) group, which has put the protonation state of GTP in question. A possible protonation of GTP was not considered in previously published mechanistic studies. To determine the detailed prehydrolysis state of Ras, we calculated infrared and NMR spectra from quantum mechanics/molecular mechanics (QM/MM) simulations and compared them with those from previous studies. Furthermore, we measured infrared spectra of GTP and several GTP analogs bound to lipidated Ras on a membrane system under near-native conditions. Our findings unify results from previous studies and indicate a structural model confirming the hypothesis that γ-GTP is fully deprotonated in the prehydrolysis state of Ras.
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Affiliation(s)
- Daniel Mann
- From the Department of Biophysics, Ruhr University Bochum, 44780 Bochum, Germany and
| | - Jörn Güldenhaupt
- From the Department of Biophysics, Ruhr University Bochum, 44780 Bochum, Germany and
| | - Jonas Schartner
- From the Department of Biophysics, Ruhr University Bochum, 44780 Bochum, Germany and
| | - Klaus Gerwert
- From the Department of Biophysics, Ruhr University Bochum, 44780 Bochum, Germany and .,Max-Planck-Gesellschaft-Chinese Academy of Sciences (MPG-CAS) Partner Institute for Computational Biology (PICB), Shanghai 200031, China
| | - Carsten Kötting
- From the Department of Biophysics, Ruhr University Bochum, 44780 Bochum, Germany and
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29
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Winkler PM, Regmi R, Flauraud V, Brugger J, Rigneault H, Wenger J, García-Parajo MF. Optical Antenna-Based Fluorescence Correlation Spectroscopy to Probe the Nanoscale Dynamics of Biological Membranes. J Phys Chem Lett 2018; 9:110-119. [PMID: 29240442 DOI: 10.1021/acs.jpclett.7b02818] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
The plasma membrane of living cells is compartmentalized at multiple spatial scales ranging from the nano- to the mesoscale. This nonrandom organization is crucial for a large number of cellular functions. At the nanoscale, cell membranes organize into dynamic nanoassemblies enriched by cholesterol, sphingolipids, and certain types of proteins. Investigating these nanoassemblies known as lipid rafts is of paramount interest in fundamental cell biology. However, this goal requires simultaneous nanometer spatial precision and microsecond temporal resolution, which is beyond the reach of common microscopes. Optical antennas based on metallic nanostructures efficiently enhance and confine light into nanometer dimensions, breaching the diffraction limit of light. In this Perspective, we discuss recent progress combining optical antennas with fluorescence correlation spectroscopy (FCS) to monitor microsecond dynamics at nanoscale spatial dimensions. These new developments offer numerous opportunities to investigate lipid and protein dynamics in both mimetic and native biological membranes.
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Affiliation(s)
- Pamina M Winkler
- ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology , 08860 Barcelona, Spain
| | - Raju Regmi
- ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology , 08860 Barcelona, Spain
- Aix Marseille Univ, CNRS, Centrale Marseille, Institut Fresnel , Marseille, France
| | - Valentin Flauraud
- Microsystems Laboratory, Institute of Microengineering, Ecole Polytechnique Fédérale de Lausanne , 1015 Lausanne, Switzerland
| | - Jürgen Brugger
- Microsystems Laboratory, Institute of Microengineering, Ecole Polytechnique Fédérale de Lausanne , 1015 Lausanne, Switzerland
| | - Hervé Rigneault
- Aix Marseille Univ, CNRS, Centrale Marseille, Institut Fresnel , Marseille, France
| | - Jérôme Wenger
- Aix Marseille Univ, CNRS, Centrale Marseille, Institut Fresnel , Marseille, France
| | - María F García-Parajo
- ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology , 08860 Barcelona, Spain
- ICREA , Pg. Lluís Companys 23, 08010 Barcelona, Spain
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30
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Sarangi NK, Basu JK. Pathways for creation and annihilation of nanoscale biomembrane domains reveal alpha and beta-toxin nanopore formation processes. Phys Chem Chem Phys 2018; 20:29116-29130. [DOI: 10.1039/c8cp05729j] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Raft-like functional domains with putative sizes of 20–200 nm and which are evolving dynamically are believed to be the most crucial regions in cellular membranes which determine cell signaling and various functions of cells.
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Affiliation(s)
| | - Jaydeep Kumar Basu
- Department of Physics
- Indian Institute of Science
- Bangalore – 560 012
- India
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31
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Elson EL. Introduction to fluorescence correlation Spectroscopy-Brief and simple. Methods 2017; 140-141:3-9. [PMID: 29155128 DOI: 10.1016/j.ymeth.2017.11.005] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2017] [Accepted: 11/13/2017] [Indexed: 02/04/2023] Open
Affiliation(s)
- Elliot L Elson
- Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, 660 South Euclid Avenue, St. Louis, MO 63110, USA.
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32
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3D nerve cell cultures and complex physiological relevance. Drug Discov Today 2017; 23:22-25. [PMID: 29074438 DOI: 10.1016/j.drudis.2017.10.014] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2017] [Revised: 10/01/2017] [Accepted: 10/16/2017] [Indexed: 11/20/2022]
Abstract
The field of tissue engineering has not yet provided knowledge on which a consensus for the complex physiological relevance (CPR) of neuronal cultures could be established. The CPR of 3D neuronal cultures can have a profound impact on the drug discovery process through the validation of in vitro models for the study of neuropsychiatric and degenerative diseases, as well as screening for neurotoxicity during drug development. Herein, we assemble evidence in support of the potential of [Ca2+]i oscillation frequency as a CPR outcome that can demonstrate the in vivo-like behavior of 3D cultures and differentiate them from 2D monolayers. We demonstrate that [Ca2+]i oscillation frequencies in 2D cultures are significantly higher than those found in 3D cultures, and provide a possible molecular explanation.
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Sarangi NK, Ayappa KG, Basu JK. Complex dynamics at the nanoscale in simple biomembranes. Sci Rep 2017; 7:11173. [PMID: 28894156 PMCID: PMC5593986 DOI: 10.1038/s41598-017-11068-5] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2017] [Accepted: 07/28/2017] [Indexed: 11/25/2022] Open
Abstract
Nature is known to engineer complex compositional and dynamical platforms in biological membranes. Understanding this complex landscape requires techniques to simultaneously detect membrane re-organization and dynamics at the nanoscale. Using super-resolution stimulated emission depletion (STED) microscopy coupled with fluorescence correlation spectroscopy (FCS), we reveal direct experimental evidence of dynamic heterogeneity at the nanoscale in binary phospholipid-cholesterol bilayers. Domain formation on the length scale of ~200–600 nm due to local cholesterol compositional heterogeneity is found to be more prominent at high cholesterol content giving rise to distinct intra-domain lipid dynamics. STED-FCS reveals unique dynamical crossover phenomena at length scales of ~100–150 nm within each of these macroscopic regions. The extent of dynamic heterogeneity due to intra-domain hindered lipid diffusion as reflected from the crossover length scale, is driven by cholesterol packing and organization, uniquely influenced by phospholipid type. These results on simple binary model bilayer systems provide novel insights into pathways leading to the emergence of complex nanodomain substructures with implications for a wide variety of membrane mediated cellular events.
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Affiliation(s)
- Nirod Kumar Sarangi
- Department of Physics, Indian Institute of Science, Bangalore, 560 012, India
| | - K G Ayappa
- Department of Chemical Engineering, Indian Institute of Science, Bangalore, 560 012, India. .,Center for Biosystems Science and Engineering, Indian Institute of Science, Bangalore, 560 012, India.
| | - Jaydeep Kumar Basu
- Department of Physics, Indian Institute of Science, Bangalore, 560 012, India.
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Khadem SMJ, Hille C, Löhmannsröben HG, Sokolov IM. Spot variation fluorescence correlation spectroscopy by data post-processing. Sci Rep 2017; 7:5614. [PMID: 28717215 PMCID: PMC5514068 DOI: 10.1038/s41598-017-05672-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2016] [Accepted: 05/26/2017] [Indexed: 11/09/2022] Open
Abstract
Spot variation fluorescence correlation spectroscopy (SV-FCS) is a variant of the FCS techniques which may give useful information about the structural organisation of the medium in which the diffusion takes place. We show that the same results can be obtained by post-processing the photon count data from ordinary FCS measurements. By using this method, one obtains the fluorescence autocorrelation functions for sizes of confocal volume, which are effectively smaller than that of the initial FCS measurement. The photon counts of the initial experiment are first transformed into smooth intensity trace using kernel smoothing method or to a piecewise-continuous intensity trace using binning and then a non-linear transformation is applied to this trace. The result of this transformation mimics the photon count rate in an experiment performed with a smaller confocal volume. The applicability of the method is established in extensive numerical simulations and directly supported in in-vitro experiments. The procedure is then applied to the diffusion of AlexaFluor647-labeled streptavidin in living cells.
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Affiliation(s)
- S M J Khadem
- Humboldt University Berlin, Institute of Physics, Berlin, D-12489, Germany. .,Humboldt University Berlin, School of Analytical Sciences Adlershof (SALSA), Berlin, D-12489, Germany.
| | - C Hille
- University of Potsdam, Institute of Chemistry, Karl-Liebknecht-Str. 24-25, D-14476, Potsdam-Golm, Germany
| | - H-G Löhmannsröben
- Humboldt University Berlin, School of Analytical Sciences Adlershof (SALSA), Berlin, D-12489, Germany.,University of Potsdam, Institute of Chemistry, Karl-Liebknecht-Str. 24-25, D-14476, Potsdam-Golm, Germany
| | - I M Sokolov
- Humboldt University Berlin, Institute of Physics, Berlin, D-12489, Germany.,Humboldt University Berlin, School of Analytical Sciences Adlershof (SALSA), Berlin, D-12489, Germany
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35
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Reorganization of Lipid Diffusion by Myelin Basic Protein as Revealed by STED Nanoscopy. Biophys J 2017; 110:2441-2450. [PMID: 27276262 PMCID: PMC4906378 DOI: 10.1016/j.bpj.2016.04.047] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2015] [Revised: 03/30/2016] [Accepted: 04/25/2016] [Indexed: 12/13/2022] Open
Abstract
Myelin is a multilayered membrane that ensheathes axonal fibers in the vertebrate nervous system, allowing fast propagation of nerve action potentials. It contains densely packed lipids, lacks an actin-based cytocortex, and requires myelin basic protein (MBP) as its major structural component. This protein is the basic constituent of the proteinaceous meshwork that is localized between adjacent cytoplasmic membranes of the myelin sheath. Yet, it is not clear how MBP influences the organization and dynamics of the lipid constituents of myelin. Here, we used optical stimulated emission depletion super-resolution microscopy in combination with fluorescence correlation spectroscopy to assess the characteristics of diffusion of different fluorescent lipid analogs in myelin membrane sheets of cultured oligodendrocytes and in micrometer-sized domains that were induced by MBP in live epithelial PtK2 cells. Lipid diffusion was significantly faster and less anomalous both in oligodendrocytes and inside the MBP-rich domains of PtK2 cells compared with undisturbed live PtK2 cells. Our data show that MBP reorganizes lipid diffusion, possibly by preventing the buildup of an actin-based cytocortex and by preventing most membrane proteins from entering the myelin sheath region. Yet, in contrast to myelin sheets in oligodendrocytes, the MBP-induced domains in epithelial PtK2 cells demonstrate no change in lipid order, indicating that segregation of long-chain lipids into myelin sheets is a process specific to oligodendrocytes.
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36
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Ng XW, Teh C, Korzh V, Wohland T. The Secreted Signaling Protein Wnt3 Is Associated with Membrane Domains In Vivo: A SPIM-FCS Study. Biophys J 2017; 111:418-429. [PMID: 27463143 DOI: 10.1016/j.bpj.2016.06.021] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2016] [Revised: 06/10/2016] [Accepted: 06/16/2016] [Indexed: 10/21/2022] Open
Abstract
Wnt3 is a morphogen that activates the Wnt signaling pathway and regulates a multitude of biological processes ranging from cell proliferation and cell fate specification to differentiation over embryonic induction to neural patterning. Recent studies have shown that the palmitoylation of Wnt3 by Porcupine, a membrane-bound O-acyltransferase, plays a significant role in the intracellular membrane trafficking of Wnt3 and subsequently, its secretion in live zebrafish embryos, where chemical inhibition of Porcupine reduced the membrane-bound and secreted fractions of Wnt3 and eventually led to defective brain development. However, the membrane distribution of Wnt3 in cells remains not fully understood. Here, we determine the membrane organization of functionally active Wnt3-EGFP in cerebellar cells of live transgenic zebrafish embryos and the role of palmitoylation in its organization using single plane illumination microscopy-fluorescence correlation spectroscopy (SPIM-FCS), a multiplexed modality of FCS, which generates maps of molecular dynamics, concentration, and interaction of biomolecules. The FCS diffusion law was applied to SPIM-FCS data to study the subresolution membrane organization of Wnt3. We find that at the plasma membrane in vivo, Wnt3 is associated with cholesterol-dependent domains. This association reduces with increasing concentrations of Porcupine inhibitor (C59), confirming the importance of palmitoylation of Wnt3 for its association with cholesterol-dependent domains. Reduction of membrane cholesterol also results in a decrease of Wnt3 association with cholesterol-dependent domains in live zebrafish. This demonstrates for the first time, to our knowledge, in live vertebrate embryos that Wnt3 is associated with cholesterol-dependent domains.
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Affiliation(s)
- Xue Wen Ng
- Department of Chemistry, National University of Singapore, Singapore, Singapore; Center for BioImaging Sciences, National University of Singapore, Singapore, Singapore
| | - Cathleen Teh
- Institute of Molecular and Cell Biology, Agency for Science, Technology and Research, Singapore, Singapore
| | - Vladimir Korzh
- Institute of Molecular and Cell Biology, Agency for Science, Technology and Research, Singapore, Singapore; Department of Biological Sciences, National University of Singapore, Singapore, Singapore
| | - Thorsten Wohland
- Department of Chemistry, National University of Singapore, Singapore, Singapore; Center for BioImaging Sciences, National University of Singapore, Singapore, Singapore; Department of Biological Sciences, National University of Singapore, Singapore, Singapore.
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37
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Reiss K, Bhakdi S. The plasma membrane: Penultimate regulator of ADAM sheddase function. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2017. [PMID: 28624437 DOI: 10.1016/j.bbamcr.2017.06.006] [Citation(s) in RCA: 36] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
BACKGROUND ADAM10 and ADAM17 are the best characterized members of the ADAM (A Disintegrin and Metalloproteinase) - family of transmembrane proteases. Both are involved diverse physiological and pathophysiological processes. ADAMs are known to be regulated by posttranslational mechanisms. However, emerging evidence indicates that the plasma membrane with its unique dynamic properties may additionally play an important role in controlling sheddase function. SCOPE OF REVIEW Membrane events that could contribute to regulation of ADAM-function are summarized. MAJOR CONCLUSIONS Surface expression of peptidolytic activity should be differentiated from ADAM-sheddase function since the latter additionally requires that the protease finds its substrate in the lipid bilayer. We propose that this is achieved through horizontal and vertical reorganization of membrane nanoarchitecture coordinately occurring at the sites of sheddase activation. Reshuffling of nanodomains thereby guides traffic of enzyme and substrate to each other. For ADAM17 phosphatidylserine exposure is required to then induce its shedding function. GENERAL SIGNIFICANCE The novel concept that physicochemical properties of the lipid bilayer govern the action of ADAM-proteases may be extendable to other functional proteins that act at the cell surface. This article is part of a Special Issue entitled: Proteolysis as a Regulatory Event in Pathophysiology edited by Stefan Rose-John.
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Affiliation(s)
- Karina Reiss
- Dept. of Dermatology, University of Kiel, 24105 Kiel, Germany.
| | - Sucharit Bhakdi
- Dept. of Dermatology, University of Kiel, 24105 Kiel, Germany
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38
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Schneider F, Waithe D, Clausen MP, Galiani S, Koller T, Ozhan G, Eggeling C, Sezgin E. Diffusion of lipids and GPI-anchored proteins in actin-free plasma membrane vesicles measured by STED-FCS. Mol Biol Cell 2017; 28:1507-1518. [PMID: 28404749 PMCID: PMC5449149 DOI: 10.1091/mbc.e16-07-0536] [Citation(s) in RCA: 82] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2016] [Revised: 03/31/2017] [Accepted: 04/04/2017] [Indexed: 02/04/2023] Open
Abstract
Diffusion and interaction dynamics of molecules at the plasma membrane play an important role in cellular signaling and are suggested to be strongly associated with the actin cytoskeleton. Here we use superresolution STED microscopy combined with fluorescence correlation spectroscopy (STED-FCS) to access and compare the diffusion characteristics of fluorescent lipid analogues and GPI-anchored proteins (GPI-APs) in the live-cell plasma membrane and in actin cytoskeleton-free, cell-derived giant plasma membrane vesicles (GPMVs). Hindered diffusion of phospholipids and sphingolipids is abolished in the GPMVs, whereas transient nanodomain incorporation of ganglioside lipid GM1 is apparent in both the live-cell membrane and GPMVs. For GPI-APs, we detect two molecular pools in living cells; one pool shows high mobility with transient incorporation into nanodomains, and the other pool forms immobile clusters, both of which disappear in GPMVs. Our data underline the crucial role of the actin cortex in maintaining hindered diffusion modes of many but not all of the membrane molecules and highlight a powerful experimental approach to decipher specific influences on molecular plasma membrane dynamics.
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Affiliation(s)
- Falk Schneider
- MRC Human Immunology Unit, University of Oxford, Oxford OX39DS, United Kingdom
| | - Dominic Waithe
- Wolfson Imaging Centre Oxford, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford OX39DS, United Kingdom
| | - Mathias P Clausen
- MRC Human Immunology Unit, University of Oxford, Oxford OX39DS, United Kingdom
- MEMPHYS-Center for Biomembrane Physics, Department of Physics, Chemistry, and Pharmacy, University of Southern Denmark, 5230 Odense M, Denmark
| | - Silvia Galiani
- MRC Human Immunology Unit, University of Oxford, Oxford OX39DS, United Kingdom
| | - Thomas Koller
- MRC Human Immunology Unit, University of Oxford, Oxford OX39DS, United Kingdom
| | - Gunes Ozhan
- Izmir International Biomedicine and Genome Institute, Dokuz Eylul University Medical School, Inciralti-Balcova, 35340 Izmir, Turkey
- Department of Medical Biology and Genetics, Dokuz Eylul University Medical School, Inciralti-Balcova, 35340 Izmir, Turkey
| | - Christian Eggeling
- MRC Human Immunology Unit, University of Oxford, Oxford OX39DS, United Kingdom
- Wolfson Imaging Centre Oxford, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford OX39DS, United Kingdom
| | - Erdinc Sezgin
- MRC Human Immunology Unit, University of Oxford, Oxford OX39DS, United Kingdom
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39
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PKCα diffusion and translocation are independent of an intact cytoskeleton. Sci Rep 2017; 7:475. [PMID: 28352102 PMCID: PMC5428563 DOI: 10.1038/s41598-017-00560-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2016] [Accepted: 03/03/2017] [Indexed: 01/04/2023] Open
Abstract
Translocation of cytosolic cPKC to the plasma membrane is a key event in their activation process but its exact nature is still unclear with particular dispute whether sole diffusion or additional active transport along the cell’s cytoskeleton contributes to cPKC’s dynamics. This was addressed by analyzing the recruitment behavior of PKCα while manipulating the cytoskeleton. Photolytic Ca2+ uncaging allowed us to quantify the kinetics of PKCα redistribution to the plasma membrane when fused to monomeric, dimeric and tetrameric fluorescence proteins. Results indicated that translocation kinetics were modulated by the state of oligomerization as expected for varying Stokes’ radii of the participating proteins. Following depolymerization of the microtubules and the actin filaments we found that Ca2+ induced membrane accumulation of PKCα was independent of the filamentous state of the cytoskeleton. Fusion of PKCα to the photo-convertible fluorescent protein Dendra2 enabled the investigation of PKCα-cytoskeleton interactions under resting conditions. Redistribution following spatially restricted photoconversion showed that the mobility of the fusion protein was independent of the state of the cytoskeleton. Our data demonstrated that in living cells neither actin filaments nor microtubules contribute to PKCα’s cytosolic mobility or Ca2+-induced translocation to the plasma membrane. Instead translocation is a solely diffusion-driven process.
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40
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Lagerholm BC, Andrade DM, Clausen MP, Eggeling C. Convergence of lateral dynamic measurements in the plasma membrane of live cells from single particle tracking and STED-FCS. JOURNAL OF PHYSICS D: APPLIED PHYSICS 2017; 50:063001. [PMID: 28458397 PMCID: PMC5390782 DOI: 10.1088/1361-6463/aa519e] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/21/2016] [Revised: 11/15/2016] [Accepted: 12/05/2016] [Indexed: 05/06/2023]
Abstract
Fluorescence correlation spectroscopy (FCS) in combination with the super-resolution imaging method STED (STED-FCS), and single-particle tracking (SPT) are able to directly probe the lateral dynamics of lipids and proteins in the plasma membrane of live cells at spatial scales much below the diffraction limit of conventional microscopy. However, a major disparity in interpretation of data from SPT and STED-FCS remains, namely the proposed existence of a very fast (unhindered) lateral diffusion coefficient, ⩾5 µm2 s-1, in the plasma membrane of live cells at very short length scales, ≈⩽ 100 nm, and time scales, ≈1-10 ms. This fast diffusion coefficient has been advocated in several high-speed SPT studies, for lipids and membrane proteins alike, but the equivalent has not been detected in STED-FCS measurements. Resolving this ambiguity is important because the assessment of membrane dynamics currently relies heavily on SPT for the determination of heterogeneous diffusion. A possible systematic error in this approach would thus have vast implications in this field. To address this, we have re-visited the analysis procedure for SPT data with an emphasis on the measurement errors and the effect that these errors have on the measurement outputs. We subsequently demonstrate that STED-FCS and SPT data, following careful consideration of the experimental errors of the SPT data, converge to a common interpretation which for the case of a diffusing phospholipid analogue in the plasma membrane of live mouse embryo fibroblasts results in an unhindered, intra-compartment, diffusion coefficient of ≈0.7-1.0 µm2 s-1, and a compartment size of about 100-150 nm.
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Affiliation(s)
- B Christoffer Lagerholm
- Wolfson Imaging Centre Oxford, Weatherall Institute of Molecular Medicine, University of Oxford, Headley Way, Oxford OX3 9DS, UK
| | - Débora M Andrade
- Centre for Neural Circuits and Behaviour, University of Oxford, Mansfield Road, Oxford OX1 3SR, UK
| | - Mathias P Clausen
- MEMPHYS-Center for Biomembrane Physics, University of Southern Denmark, Campusvej 55, Odense M DK-5230, Denmark
- MRC Human Immunology Unit, Weatherall Institute of Molecular Medicine, University of Oxford, Headley Way, Oxford OX3 9DS, UK
| | - Christian Eggeling
- Wolfson Imaging Centre Oxford, Weatherall Institute of Molecular Medicine, University of Oxford, Headley Way, Oxford OX3 9DS, UK
- MRC Human Immunology Unit, Weatherall Institute of Molecular Medicine, University of Oxford, Headley Way, Oxford OX3 9DS, UK
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41
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Mailfert S, Hamon Y, Bertaux N, He HT, Marguet D. A user's guide for characterizing plasma membrane subdomains in living cells by spot variation fluorescence correlation spectroscopy. Methods Cell Biol 2017; 139:1-22. [PMID: 28215331 DOI: 10.1016/bs.mcb.2016.12.002] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/05/2022]
Abstract
Due to the intrinsic molecular Brownian agitation within plasma membrane and the vast diversity of membrane components, it is expected that the plasma membrane organization is highly heterogeneous with the formation of local complex multicomponent assemblies of lipids and proteins on different time scales. Still, deciphering this lateral organization on living cells and on the appropriate length and temporal scales has been challenging but is crucial to advance our knowledge on the biological function of the plasma membrane. Among the methodological developments based on biophotonics, the spot variation FCS (svFCS), a fluorescent correlation spectroscopy (FCS)-based method, has allowed the significant progress in the characterization of cell membrane lateral organization at the suboptical level, including to providing compelling evidence for the in vivo existence of lipid-dependent nanodomains. The aim of this chapter is to serve as a guide for setting and applying the svFCS methodology to study the plasma membrane of both adherent and nonadherent cell types.
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Affiliation(s)
- S Mailfert
- Centre d'Immunologie de Marseille Luminy, Aix Marseille Université, Inserm, CNRS, Marseille, France
| | - Y Hamon
- Centre d'Immunologie de Marseille Luminy, Aix Marseille Université, Inserm, CNRS, Marseille, France
| | - N Bertaux
- Institut Fresnel, Aix Marseille Université, Centrale Marseille, CNRS, Marseille, France
| | - H-T He
- Centre d'Immunologie de Marseille Luminy, Aix Marseille Université, Inserm, CNRS, Marseille, France
| | - D Marguet
- Centre d'Immunologie de Marseille Luminy, Aix Marseille Université, Inserm, CNRS, Marseille, France
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42
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Kordyukova L. Structural and functional specificity of Influenza virus haemagglutinin and paramyxovirus fusion protein anchoring peptides. Virus Res 2017; 227:183-199. [DOI: 10.1016/j.virusres.2016.09.014] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2016] [Revised: 09/21/2016] [Accepted: 09/23/2016] [Indexed: 02/08/2023]
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43
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The use of fluorescence correlation spectroscopy to characterize the molecular mobility of fluorescently labelled G protein-coupled receptors. Biochem Soc Trans 2016; 44:624-9. [PMID: 27068980 PMCID: PMC5264494 DOI: 10.1042/bst20150285] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2016] [Indexed: 01/10/2023]
Abstract
The membranes of living cells have been shown to be highly organized into distinct microdomains, which has spatial and temporal consequences for the interaction of membrane bound receptors and their signalling partners as complexes. Fluorescence correlation spectroscopy (FCS) is a technique with single cell sensitivity that sheds light on the molecular dynamics of fluorescently labelled receptors, ligands or signalling complexes within small plasma membrane regions of living cells. This review provides an overview of the use of FCS to probe the real time quantification of the diffusion and concentration of G protein-coupled receptors (GPCRs), primarily to gain insights into ligand–receptor interactions and the molecular composition of signalling complexes. In addition we document the use of photon counting histogram (PCH) analysis to investigate how changes in molecular brightness (ε) can be a sensitive indicator of changes in molecular mass of fluorescently labelled moieties.
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44
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González Bardeci N, Angiolini JF, De Rossi MC, Bruno L, Levi V. Dynamics of intracellular processes in live-cell systems unveiled by fluorescence correlation microscopy. IUBMB Life 2016; 69:8-15. [PMID: 27896901 DOI: 10.1002/iub.1589] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2016] [Accepted: 11/07/2016] [Indexed: 11/12/2022]
Abstract
Fluorescence fluctuation-based methods are non-invasive microscopy tools especially suited for the study of dynamical aspects of biological processes. These methods examine spontaneous intensity fluctuations produced by fluorescent molecules moving through the small, femtoliter-sized observation volume defined in confocal and multiphoton microscopes. The quantitative analysis of the intensity trace provides information on the processes producing the fluctuations that include diffusion, binding interactions, chemical reactions and photophysical phenomena. In this review, we present the basic principles of the most widespread fluctuation-based methods, discuss their implementation in standard confocal microscopes and briefly revise some examples of their applications to address relevant questions in living cells. The ultimate goal of these methods in the Cell Biology field is to observe biomolecules as they move, interact with targets and perform their biological action in the natural context. © 2016 IUBMB Life, 69(1):8-15, 2017.
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Affiliation(s)
- Nicolás González Bardeci
- Departamento de Química Biológica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Argentina, IQUIBICEN, UBA-CONICET
| | - Juan Francisco Angiolini
- Departamento de Química Biológica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Argentina, IQUIBICEN, UBA-CONICET
| | - María Cecilia De Rossi
- Departamento de Química Biológica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Argentina, IQUIBICEN, UBA-CONICET
| | | | - Valeria Levi
- Departamento de Química Biológica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Argentina, IQUIBICEN, UBA-CONICET
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45
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Bernardino de la Serna J, Schütz GJ, Eggeling C, Cebecauer M. There Is No Simple Model of the Plasma Membrane Organization. Front Cell Dev Biol 2016; 4:106. [PMID: 27747212 PMCID: PMC5040727 DOI: 10.3389/fcell.2016.00106] [Citation(s) in RCA: 96] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2016] [Accepted: 09/14/2016] [Indexed: 12/29/2022] Open
Abstract
Ever since technologies enabled the characterization of eukaryotic plasma membranes, heterogeneities in the distributions of its constituents were observed. Over the years this led to the proposal of various models describing the plasma membrane organization such as lipid shells, picket-and-fences, lipid rafts, or protein islands, as addressed in numerous publications and reviews. Instead of emphasizing on one model we in this review give a brief overview over current models and highlight how current experimental work in one or the other way do not support the existence of a single overarching model. Instead, we highlight the vast variety of membrane properties and components, their influences and impacts. We believe that highlighting such controversial discoveries will stimulate unbiased research on plasma membrane organization and functionality, leading to a better understanding of this essential cellular structure.
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Affiliation(s)
- Jorge Bernardino de la Serna
- Science and Technology Facilities Council, Rutherford Appleton Laboratory, Central Laser Facility, Research Complex at Harwell Harwell, UK
| | - Gerhard J Schütz
- Institute of Applied Physics, Technische Universität Wien Wien, Austria
| | - Christian Eggeling
- MRC Human Immunology Unit, Weatherall Institute of Molecular Medicine, University of Oxford Headley Way, UK
| | - Marek Cebecauer
- Department of Biophysical Chemistry, J.Heyrovsky Institute of Physical Chemistry, Czech Academy of Sciences Prague, Czech Republic
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46
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Li X, Xing J, Qiu Z, He Q, Lin J. Quantification of Membrane Protein Dynamics and Interactions in Plant Cells by Fluorescence Correlation Spectroscopy. MOLECULAR PLANT 2016; 9:1229-1239. [PMID: 27381442 DOI: 10.1016/j.molp.2016.06.017] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/03/2016] [Revised: 06/25/2016] [Accepted: 06/27/2016] [Indexed: 05/25/2023]
Abstract
Deciphering the dynamics of protein and lipid molecules on appropriate spatial and temporal scales may shed light on protein function and membrane organization. However, traditional bulk approaches cannot unambiguously quantify the extremely diverse mobility and interactions of proteins in living cells. Fluorescence correlation spectroscopy (FCS) is a powerful technique to describe events that occur at the single-molecule level and on the nanosecond to second timescales; therefore, FCS can provide data on the heterogeneous organization of membrane systems. FCS can also be combined with other microscopy techniques, such as super-resolution techniques. More importantly, FCS is minimally invasive, which makes it an ideal approach to detect the heterogeneous distribution and dynamics of key proteins during development. In this review, we give a brief introduction about the development of FCS and summarize the significant contributions of FCS in understanding the organization of plant cell membranes and the dynamics and interactions of membrane proteins. We also discuss the potential applications of this technique in plant biology.
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Affiliation(s)
- Xiaojuan Li
- College of Biological Sciences and Biotechnology, Beijing Forestry University, Beijing 100083, China
| | - Jingjing Xing
- Key Laboratory of Plant Resources, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China; University of Chinese Academy of Sciences, Beijing 10049, China
| | - Zongbo Qiu
- College of Life Sciences, Henan Normal University, Xinxiang 453007, China
| | - Qihua He
- The Health Science Center, Peking University, Beijing 100191, China
| | - Jinxing Lin
- College of Biological Sciences and Biotechnology, Beijing Forestry University, Beijing 100083, China.
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47
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Ozgen H, Baron W, Hoekstra D, Kahya N. Oligodendroglial membrane dynamics in relation to myelin biogenesis. Cell Mol Life Sci 2016; 73:3291-310. [PMID: 27141942 PMCID: PMC4967101 DOI: 10.1007/s00018-016-2228-8] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2015] [Accepted: 04/14/2016] [Indexed: 12/12/2022]
Abstract
In the central nervous system, oligodendrocytes synthesize a specialized membrane, the myelin membrane, which enwraps the axons in a multilamellar fashion to provide fast action potential conduction and to ensure axonal integrity. When compared to other membranes, the composition of myelin membranes is unique with its relatively high lipid to protein ratio. Their biogenesis is quite complex and requires a tight regulation of sequential events, which are deregulated in demyelinating diseases such as multiple sclerosis. To devise strategies for remedying such defects, it is crucial to understand molecular mechanisms that underlie myelin assembly and dynamics, including the ability of specific lipids to organize proteins and/or mediate protein-protein interactions in healthy versus diseased myelin membranes. The tight regulation of myelin membrane formation has been widely investigated with classical biochemical and cell biological techniques, both in vitro and in vivo. However, our knowledge about myelin membrane dynamics, such as membrane fluidity in conjunction with the movement/diffusion of proteins and lipids in the membrane and the specificity and role of distinct lipid-protein and protein-protein interactions, is limited. Here, we provide an overview of recent findings about the myelin structure in terms of myelin lipids, proteins and membrane microdomains. To give insight into myelin membrane dynamics, we will particularly highlight the application of model membranes and advanced biophysical techniques, i.e., approaches which clearly provide an added value to insight obtained by classical biochemical techniques.
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Affiliation(s)
- Hande Ozgen
- Department of Cell Biology, University Medical Center Groningen, University of Groningen, Antonius Deusinglaan 1, 9713 AV, Groningen, The Netherlands
| | - Wia Baron
- Department of Cell Biology, University Medical Center Groningen, University of Groningen, Antonius Deusinglaan 1, 9713 AV, Groningen, The Netherlands.
| | - Dick Hoekstra
- Department of Cell Biology, University Medical Center Groningen, University of Groningen, Antonius Deusinglaan 1, 9713 AV, Groningen, The Netherlands
| | - Nicoletta Kahya
- Department of Cell Biology, University Medical Center Groningen, University of Groningen, Antonius Deusinglaan 1, 9713 AV, Groningen, The Netherlands
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48
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Plasma Membrane Organization of Epidermal Growth Factor Receptor in Resting and Ligand-Bound States. Biophys J 2016; 109:1925-36. [PMID: 26536269 DOI: 10.1016/j.bpj.2015.09.007] [Citation(s) in RCA: 56] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2015] [Revised: 08/24/2015] [Accepted: 09/08/2015] [Indexed: 12/21/2022] Open
Abstract
The spatial arrangement of the epidermal growth factor receptor (EGFR) on the cellular plasma membrane is one of the prime factors that control its downstream signaling pathways and related functions. However, the molecular organization, which spans the scale from nanometers to micrometer-size clusters, has not been resolved in detail, mainly due to a lack of techniques with the required spatiotemporal resolution. Therefore, we used imaging total internal reflection-fluorescence correlation spectroscopy to investigate EGFR dynamics on live CHO-K1 plasma membranes in resting and ligand-bound states. In combination with the fluorescence correlation spectroscopy diffusion law, this provides information on the subresolution organization of EGFR on cell membranes. We found that overall EGFR organization is sensitive to both cholesterol and the actin cytoskeleton. EGFR in the resting state is partly trapped in cholesterol-containing domains, whereas another fraction exhibits cholesterol independent trapping on the membrane. Disruption of the cytoskeleton leads to a broader range of EGFR diffusion coefficients and a reduction of hop diffusion. In the ligand-bound state we found a dose-dependent behavior. At 10 ng/mL EGF the EGFR is endocytosed and recycled to the membrane, whereas diffusion and organization do not change significantly. At 100 ng/mL EGF the EGFR forms clusters, which are subsequently internalized, whereas outside the clusters diffusivity increases and the organization of the receptor remains unchanged. After disruption of cholesterol-containing domains or actin cytoskeleton, EGF induces microscopic EGFR clusters on the membrane and endocytosis is inhibited.
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49
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Bag N, Ng XW, Sankaran J, Wohland T. Spatiotemporal mapping of diffusion dynamics and organization in plasma membranes. Methods Appl Fluoresc 2016; 4:034003. [PMID: 28355150 DOI: 10.1088/2050-6120/4/3/034003] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Imaging fluorescence correlation spectroscopy (FCS) and the related FCS diffusion law have been applied in recent years to investigate the diffusion modes of lipids and proteins in membranes. These efforts have provided new insights into the membrane structure below the optical diffraction limit, new information on the existence of lipid domains, and on the influence of the cytoskeleton on membrane dynamics. However, there has been no systematic study to evaluate how domain size, domain density, and the probe partition coefficient affect the resulting imaging FCS diffusion law parameters. Here, we characterize the effects of these factors on the FCS diffusion law through simulations and experiments on lipid bilayers and live cells. By segmenting images into smaller 7 × 7 pixel areas, we can evaluate the FCS diffusion law on areas smaller than 2 µm and thus provide detailed maps of information on the membrane structure and heterogeneity at this length scale. We support and extend this analysis by deriving a mathematical expression to calculate the mean squared displacement (MSDACF) from the autocorrelation function of imaging FCS, and demonstrate that the MSDACF plots depend on the existence of nanoscopic domains. Based on the results, we derive limits for the detection of domains depending on their size, density, and relative viscosity in comparison to the surroundings. Finally, we apply these measurements to bilayers and live cells using imaging total internal reflection FCS and single plane illumination microscopy FCS.
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Affiliation(s)
- Nirmalya Bag
- Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, Singapore 117543, Singapore. NUS Centre for Bio-Imaging Sciences, National University of Singapore, 14 Science Drive 4, Singapore 117557, Singapore
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50
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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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