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Piston DW, Kremers GJ. Fluorescent protein FRET: the good, the bad and the ugly. Trends Biochem Sci 2007; 32:407-14. [PMID: 17764955 DOI: 10.1016/j.tibs.2007.08.003] [Citation(s) in RCA: 590] [Impact Index Per Article: 34.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2007] [Revised: 06/21/2007] [Accepted: 08/15/2007] [Indexed: 10/22/2022]
Abstract
Dynamic protein interactions play a significant part in many cellular processes. A technique that shows considerable promise in elucidating such interactions is Förster resonance energy transfer (FRET). When combined with multiple, colored fluorescent proteins, FRET permits high spatial resolution assays of protein-protein interactions in living cells. Because FRET signals are usually small, however, their measurement requires careful interpretation and several control experiments. Nevertheless, the use of FRET in cell biological experiments has exploded over the past few years. Here we describe the physical basis of FRET and the fluorescent proteins appropriate for these experiments. We also review the approaches that can be used to measure FRET, with particular emphasis on the potential artifacts associated with each approach.
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Affiliation(s)
- David W Piston
- Department of Molecular Physiology and Biophysics, Vanderbilt University, 702 Light Hall, Nashville, TN 37232-0615, USA.
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52
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Fooksman DR, Edidin M, Barisas BG. Measuring rotational diffusion of MHC class I on live cells by polarized FPR. Biophys Chem 2007; 130:10-6. [PMID: 17656002 PMCID: PMC2094112 DOI: 10.1016/j.bpc.2007.06.013] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2007] [Revised: 06/26/2007] [Accepted: 06/26/2007] [Indexed: 11/17/2022]
Abstract
Clustering of membrane proteins is a dynamic process which can regulate cellular function and signaling. The size of receptor and other membrane protein clusters can in principle be measured in terms of their rotational diffusion. However, in practice, measuring rotation of membrane proteins of live cells has been difficult, largely because of the difficulty of rigidly attaching reporter groups to the molecules of interest. Here we show that polarized photobleaching recovery can detect rotation of membrane proteins genetically tagged with yellow fluorescent protein, YFP. MHC class I molecules were engineered with a rigid, in-sequence, YFP tag followed at the C-terminus by a pair of crosslinkable domains. When crosslinker was added we could detect changes in rotational anisotropy decay consistent with clustering of the MHC molecules. This result points the way to use of engineered fluorescent fusion proteins to measure rotational diffusion in native cell membranes.
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Affiliation(s)
- David R Fooksman
- Department of Chemistry, Colorado State University, Ft. Collins, CO 80523, USA.
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53
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Vrabioiu AM, Mitchison TJ. Structural insights into yeast septin organization from polarized fluorescence microscopy. Nature 2006; 443:466-9. [PMID: 17006515 DOI: 10.1038/nature05109] [Citation(s) in RCA: 168] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2006] [Accepted: 07/24/2006] [Indexed: 11/09/2022]
Abstract
Septins are polymerizing GTPases that function in cortical organization and cell division. In Saccharomyces cerevisiae they localize at the isthmus between the mother and the daughter cells, where they undergo a transition from a non-dynamic hourglass-shaped assembly to two separate rings, at the onset of cytokinesis. Septins form filaments as pure protein and in vivo, but the filament organization within the hourglass and ring structures is controversial. Here, we use polarized fluorescence microscopy of orientationally constrained green fluorescent protein to determine septin filament organization and dynamics in living yeast. We found that the hourglass is made of filaments aligned along the yeast bud neck. During the transition from hourglass to rings the filaments rotate through 90 degrees in the membrane plane and become circumferential. These data resolve a long-standing controversy in the field and provide strong evidence that septins have a mechanical function in cell division.
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Affiliation(s)
- Alina M Vrabioiu
- Department of Systems Biology, Harvard Medical School, 200 Longwood Avenue, Boston, Massachusetts 02115, USA.
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54
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Davey AM, Walvick RP, Liu Y, Heikal AA, Sheets ED. Membrane order and molecular dynamics associated with IgE receptor cross-linking in mast cells. Biophys J 2006; 92:343-55. [PMID: 17040981 PMCID: PMC1697873 DOI: 10.1529/biophysj.106.088815] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Cholesterol-rich microdomains (or "lipid rafts") within the plasma membrane have been hypothesized to exist in a liquid-ordered phase and play functionally important roles in cell signaling; however, these microdomains defy detection using conventional imaging. To visualize domains and relate their nanostructure and dynamics to mast cell signaling, we use two-photon (760 nm and 960 nm) fluorescence lifetime imaging microscopy and fluorescence polarization anisotropy imaging, with comparative one-photon anisotropy imaging and single-point lifetime and anisotropy decay measurements. The inherent sensitivity of ultrafast excited-state dynamics and rotational diffusion to the immediate surroundings of a fluorophore allows for real-time monitoring of membrane structure and organization. When the high affinity receptor for IgE (FcepsilonRI) is extensively cross-linked with anti-IgE, molecules associated with cholesterol-rich microdomains (e.g., saturated lipids (the lipid analog diI-C(18) or glycosphingolipids)) and lipid-anchored proteins coredistribute with cross-linked IgE-FcepsilonRI. We find an enhancement in fluorescence lifetime and anisotropy of diI-C(18) and Alexa 488-labeled IgE-FcepsilonRI in the domains where these molecules colocalize. Our results suggest that fluorescence lifetime and, particularly, anisotropy permit us to correlate the recruitment of lipid molecules into more ordered domains that serve as platforms for IgE-mediated signaling.
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Affiliation(s)
- Angel M Davey
- Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
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55
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Yasuda R. Imaging spatiotemporal dynamics of neuronal signaling using fluorescence resonance energy transfer and fluorescence lifetime imaging microscopy. Curr Opin Neurobiol 2006; 16:551-61. [PMID: 16971112 DOI: 10.1016/j.conb.2006.08.012] [Citation(s) in RCA: 106] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2006] [Accepted: 08/30/2006] [Indexed: 11/26/2022]
Abstract
The spatiotemporal localization of neuronal signaling is important for triggering neuronal responses in specific locations at precise times. Fluorescence resonance energy transfer imaging enables measurement of spatiotemporal dynamics of signaling activity in live neurons. Although the usefulness of fluorescence resonance energy transfer is well recognized, there are many difficulties in applying it, particularly when imaging in neuronal micro-compartments in light-scattering brain tissue. Fluorescence resonance energy transfer has been imaged using several techniques including intensity-based methods, fluorescence lifetime imaging and fluorescence anisotropy imaging. These methods have different advantages and disadvantages, and thus are suitable in different applications.
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Affiliation(s)
- Ryohei Yasuda
- Neurobiology Department, Duke University Medical Center, Research Drive, Durham, NC 27710 USA.
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56
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Rizzo MA, Springer G, Segawa K, Zipfel WR, Piston DW. Optimization of pairings and detection conditions for measurement of FRET between cyan and yellow fluorescent proteins. MICROSCOPY AND MICROANALYSIS : THE OFFICIAL JOURNAL OF MICROSCOPY SOCIETY OF AMERICA, MICROBEAM ANALYSIS SOCIETY, MICROSCOPICAL SOCIETY OF CANADA 2006; 12:238-54. [PMID: 17481360 DOI: 10.1017/s1431927606060235] [Citation(s) in RCA: 106] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/2005] [Accepted: 10/26/2005] [Indexed: 05/05/2023]
Abstract
Detection of Förster resonance energy transfer (FRET) between cyan and yellow fluorescent proteins is a key method for quantifying dynamic processes inside living cells. To compare the different cyan and yellow fluorescent proteins, FRET efficiencies were measured for a set of the possible donor:acceptor pairs. FRET between monomeric Cerulean and Venus is more efficient than the ECFP:EYFP pair and has a 10% greater Förster distance. We also compared several live cell microscopy methods for measuring FRET. The greatest contrast for changes in intramolecular FRET is obtained using a combination of ratiometric and spectral imaging. However, this method is not appropriate for establishing the presence of FRET without extra controls. Accurate FRET efficiencies are obtained by fluorescence lifetime imaging microscopy, but these measurements are difficult to collect and analyze. Acceptor photobleaching is a common and simple method for measuring FRET efficiencies. However, when applied to cyan to yellow fluorescent protein FRET, this method becomes prone to an artifact that leads to overestimation of FRET efficiency and false positive signals. FRET was also detected by measuring the acceptor fluorescence anisotropy. Although difficult to quantify, this method is exceptional for screening purposes, because it provides high contrast for discriminating FRET.
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Affiliation(s)
- Mark A Rizzo
- University of Maryland School of Medicine, Baltimore, MD 21201, USA
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57
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Corry B, Jayatilaka D, Martinac B, Rigby P. Determination of the orientational distribution and orientation factor for transfer between membrane-bound fluorophores using a confocal microscope. Biophys J 2006; 91:1032-45. [PMID: 16698772 PMCID: PMC1563768 DOI: 10.1529/biophysj.106.080713] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Orientational fluorophores have been a useful tool in physical chemistry, biochemistry, and more recently structural biology due to the polarized nature of the light they emit and that fact that energy can be transferred between them. We present a practical scheme in which measurements of the intensity of emitted fluorescence can be used to determine limits on the mean and distribution of orientation of the absorption transition moment of membrane-bound fluorophores. We demonstrate how information about the orientation of fluorophores can be used to calculate the orientation factor kappa(2) required for use in FRET spectroscopy. We illustrate the method using images of AlexaFluor probes bound to MscL mechanosensitive transmembrane channel proteins in spherical liposomes.
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Affiliation(s)
- Ben Corry
- School of Biomedical, Biomolecular and Chemical Sciences, The University of Western Australia, Crawley, Australia.
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58
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Nagy P, Bene L, Hyun WC, Vereb G, Braun M, Antz C, Paysan J, Damjanovich S, Park JW, Szöllősi J. Novel calibration method for flow cytometric fluorescence resonance energy transfer measurements between visible fluorescent proteins. Cytometry A 2005; 67:86-96. [PMID: 16163690 DOI: 10.1002/cyto.a.20164] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
BACKGROUND The combination of fluorescence resonance energy transfer (FRET) and flow cytometry offers a statistically firm approach to study protein associations. Fusing green fluorescent protein (GFP) to a studied protein usually does not disturb the normal function of a protein, but quantitation of FRET efficiency calculated between GFP derivatives poses a problem in flow cytometry. METHODS We generated chimeras in which cyan fluorescent protein (CFP) was separated by amino acid linkers of different sizes from yellow fluorescent protein (YFP) and used them to calibrate the cell-by-cell flow cytometric FRET measurements carried out on two different dual-laser flow cytometers. Then, CFP-Kip1 was coexpressed in yeast cells with YFP and cyclin-dependent kinase-2 (Cdk2) and served as a positive control for FRET measurements, and CFP-Kip1 coexpressed with a random peptide fused to YFP was the negative control. RESULTS We measured donor, direct, and sensitized acceptor fluorescence intensities and developed a novel way to calculate a factor (alpha) that characterized the fluorescence intensity of acceptor molecules relative to the same number of excited donor molecules, which is essential for quantifying FRET efficiency. This was achieved by calculating FRET efficiency in two different ways and minimizing the squared difference between the two results by changing alpha. Our method reliably detected the association of Cdk2 with its inhibitor, Kip1, whereas the nonspecific FRET efficiency between Cdk2 and a random peptide was negligible. We identified and sorted subpopulations of yeast cells showing interaction between the studied proteins. CONCLUSIONS We have described a straightforward novel calibration method to accurately quantitate FRET efficiency between GFP derivatives in flow cytometry.
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Affiliation(s)
- Peter Nagy
- Department of Biophysics and Cell Biology, Medical and Health Science Center, University of Debrecen, Debrecen, Hungary
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59
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Marushchak D, Johansson LBA. On the Quantitative Treatment of Donor–Donor Energy Migration in Regularly Aggregated Proteins. J Fluoresc 2005; 15:797-803. [PMID: 16341799 DOI: 10.1007/s10895-005-2989-1] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2005] [Accepted: 07/26/2005] [Indexed: 11/29/2022]
Abstract
An algorithm is presented that quantitatively accounts for donor-donor energy migration (DDEM) among fluorophore-labeled proteins forming regular aggregates. The DDEM algorithm is based on Monte Carlo and Brownian dynamics simulations and applies to calculation of fluorescence depolarisation data, such as the fluorescence anisotropy. Thereby local orientations, as well as reorienting motions of the fluorescent group are considered in the absence and presence of DDEM and among, in principle, infinitely many proteins as they form regular aggregates. Here we apply the algorithm for calculating and illustrating the DDEM and the time-resolved fluorescence anisotropy under static as well as dynamic conditions within helical, linear and circular aggregate structures. A principal approach of the DDEM algorithm for analysing protein aggregates is also outlined.
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Affiliation(s)
- Denys Marushchak
- Department of Chemistry, University of Umeå, S-901 87, Umeå, Sweden
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60
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Rao M, Mayor S. Use of Forster's resonance energy transfer microscopy to study lipid rafts. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2005; 1746:221-33. [PMID: 16274754 DOI: 10.1016/j.bbamcr.2005.08.002] [Citation(s) in RCA: 102] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/20/2005] [Revised: 07/12/2005] [Accepted: 08/11/2005] [Indexed: 01/05/2023]
Abstract
Rafts in cell membranes have been a subject of much debate and many models have been proposed for their existence and functional significance. Recent studies using Forster's resonance energy transfer (FRET) microscopy have provided one of the first glimpses into the organization of putative raft components in living cell membranes. Here we discuss how and why FRET microscopy provides an appropriate non-invasive methodology to examine organization of raft components in cell membranes; a combination of homo and hetero-FRET microscopy in conjunction with detailed theoretical analyses are necessary for characterizing structures at nanometre scales. Implications of the physical characteristics of the organization of GPI-anchored proteins in cell membranes suggest new models of lipid-based assemblies in cell membranes based on active principles.
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Affiliation(s)
- Madan Rao
- National Centre for Biological Sciences, TIFR, UAS-GKVK Campus, GKVK PO, Bellary Road, Bangalore 560 065, India.
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61
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Griekspoor A, Zwart W, Neefjes J. Presenting antigen presentation in living cells using biophysical techniques. Curr Opin Microbiol 2005; 8:338-43. [PMID: 15939359 DOI: 10.1016/j.mib.2005.04.007] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2005] [Accepted: 04/21/2005] [Indexed: 11/19/2022]
Abstract
The combination of genetically encoded fluorescent probes and advanced microscopic techniques has dramatically propelled the understanding of cell biology. Highly complex reactions can now be studied in detail in a relatively cost-effective and easy manner and, perhaps most importantly, in the context of a single living cell. In the past decade, numerous reports have uncovered the localization of key molecules in virtually all cellular processes. However, there remains a need for more accurate determination of genuine protein-protein interactions and quantification of highly dynamic processes, which has resulted in the revival of several biophysical techniques. Recent applications of these techniques have deepened understanding of processes involved in antigen presentation to the immune system.
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Affiliation(s)
- Alexander Griekspoor
- Division of Tumor Biology, The Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands
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62
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Abstract
Current models for cellular plasma membranes focus on spatial heterogeneity and how this heterogeneity relates to cell function. In particular, putative lipid raft membrane domains have been postulated to exist based in large part on the results that a significant fraction of the membrane is detergent insoluble and that molecules facilitating key membrane processes like signal transduction are often found in the detergent-resistant membrane fraction. Yet, the in vivo existence of lipid rafts remains extremely controversial because, despite being sought for more than a decade, evidence for their presence in intact cell membranes is inconclusive. In this review, a variety of experimental techniques that have been or might be used to look for lipid microdomains in intact cell membranes are described. Experimental results are highlighted and the strengths and limitations of different techniques for microdomain identification and characterization are assessed.
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Affiliation(s)
- B Christoffer Lagerholm
- Department of Cell and Developmental Biology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA.
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63
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Bene L, Szöllosi J, Szentesi G, Damjanovich L, Gáspár R, Waldmann TA, Damjanovich S. Detection of receptor trimers on the cell surface by flow cytometric fluorescence energy homotransfer measurements. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2005; 1744:176-98. [PMID: 15950751 DOI: 10.1016/j.bbamcr.2005.02.002] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/14/2005] [Revised: 02/08/2005] [Accepted: 02/09/2005] [Indexed: 11/26/2022]
Abstract
Fluorescence energy homotransfer offers a powerful tool for the investigation of the state of oligomerization of cell surface receptors on a cell-by-cell basis by measuring the polarized components of fluorescence intensity of cells labeled with fluorescently stained antibodies. Here we describe homotransfer-based methods for the flow cytometric detection and analysis of hetero- and homo-associations of cell surface receptors. Homotransfer efficiencies for two- and three-body energy transfer interactions are defined and their frequency distribution curves are computed from the fluorescence anisotropy distributions of multiple-labeled cells. The fractions of receptors involved in homo-clustering is calculated based on the dependence of the fluorescence anisotropy on the surface concentration of the fluorescently stained antibodies. A homotransfer analysis of the homo- and hetero-clustering of the MHCI and MHCII glycoproteins, the cytokine receptor IL-2Ralpha, transferrin receptor and the receptor-type tyrosine phosphatase CD45 on JY B and Kit-225-K6 T cells is presented. We investigated how various factors such as the type of dye, rotational mobility of the dye and dye-targeting antibody, as well as the wavelength of the exciting light affect the homotransfer. We show that the homotransfer technique combined with the high statistical resolution of flow cytometry is an effective tool for detecting different oligomeric states of receptors by using fluorophores having restricted rotational mobility on the time scale of fluorescence.
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Affiliation(s)
- László Bene
- Department of Biophysics and Cell Biology, Medical and Health Science Center, Research Center for Molecular Medicine, University of Debrecen, Hungary.
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64
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Goodwin JS, Drake KR, Remmert CL, Kenworthy AK. Ras diffusion is sensitive to plasma membrane viscosity. Biophys J 2005; 89:1398-410. [PMID: 15923235 PMCID: PMC1366624 DOI: 10.1529/biophysj.104.055640] [Citation(s) in RCA: 106] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
The cell surface contains a variety of barriers and obstacles that slow the lateral diffusion of glycosylphosphatidylinositol (GPI)-anchored and transmembrane proteins below the theoretical limit imposed by membrane viscosity. How the diffusion of proteins residing exclusively on the inner leaflet of the plasma membrane is regulated has been largely unexplored. We show here that the diffusion of the small GTPase Ras is sensitive to the viscosity of the plasma membrane. Using confocal fluorescence recovery after photobleaching, we examined the diffusion of green fluorescent protein (GFP)-tagged HRas, NRas, and KRas in COS-7 cells loaded with or depleted of cholesterol, a well-known modulator of membrane bilayer viscosity. In cells loaded with excess cholesterol, the diffusional mobilities of GFP-HRas, GFP-NRas, and GFP-KRas were significantly reduced, paralleling the behavior of the viscosity-sensitive lipid probes DiIC(16) and DiIC(18). However, the effects of cholesterol depletion on protein and lipid diffusion in cell membranes were highly dependent on the depletion method used. Cholesterol depletion with methyl-beta-cyclodextrin slowed Ras diffusion by a viscosity-independent mechanism, whereas overnight cholesterol depletion slightly increased both protein and lipid diffusion. The ability of Ras to sense membrane viscosity may represent a general feature of proteins residing on the cytoplasmic face of the plasma membrane.
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Affiliation(s)
- J Shawn Goodwin
- Department of Molecular Physiology & Biophysics, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA
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65
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Squire A, Verveer PJ, Rocks O, Bastiaens PIH. Red-edge anisotropy microscopy enables dynamic imaging of homo-FRET between green fluorescent proteins in cells. J Struct Biol 2005; 147:62-9. [PMID: 15109606 DOI: 10.1016/j.jsb.2003.10.013] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2003] [Revised: 10/07/2003] [Indexed: 11/28/2022]
Abstract
Steady-state fluorescence anisotropy measurements can be used to detect fluorescence resonance energy transfer (FRET) between identical fluorophores (homo-FRET). However, the contribution of homo-FRET to the steady-state anisotropy must be discerned from those due to the orientational distribution and rotational diffusion, which so far has required photobleaching controls, largely precluding dynamic measurements in live cells. We describe a variation of steady-state anisotropy microscopy in which the contribution of homo-FRET is dynamically isolated from the total anisotropy by exploiting the loss of energy transfer that occurs at red-edge excitation. Excitation of enhanced green fluorescent protein (EGFP) at the red-edge of its absorption band shows the shift in the emission spectrum compared to main-band excitation that is characteristic for photo-selection of static low energy S(0)-S(1) transitions that fail to exhibit FRET. An experimental setup for steady-state fluorescent anisotropy microscopy is described that can be used to acquire anisotropy images in live cells at main-band and red-edge excitation of EGFP. We demonstrate in live cells homo-FRET suppression of protein fusion constructs that consist of two and three EGFP molecules connected by short linkers. This methodology represents a novel approach for the dynamic measurement of homo-FRET in live cells that will be of utility in the biological sciences to detect oligomerization and concentration dependent interactions between identically labeled molecules.
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Affiliation(s)
- Anthony Squire
- Cell Biology and Cell Biophysics Program, European Molecular Biology Laboratory, Meyerhofstrasse 1, D-69117 Heidelberg, Germany
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66
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Kalinin S, Johansson LBA. Utility and considerations of donor-donor energy migration as a fluorescence method for exploring protein structure-function. J Fluoresc 2005; 14:681-91. [PMID: 15649020 DOI: 10.1023/b:jofl.0000047218.51768.59] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
This review aims at surveying the use of electronic energy transport between chemically identical fluorophores (i.e. donors) in studies of various protein systems. Applications of intra- and interprotein energy migration are presented that make use of polarised steady-state and time-resolved fluorescence spectroscopic techniques. The donor-donor energy migration (DDEM) and the partial donor-donor energy migration (PDDEM) models for calculating distances between donor groups are exposed together with the most recent development of an extended Forster theory (EFT). Synthetic fluorescence depolarisation data that mimic time-correlated single photon counting experiments were generated using the EFT, and then further re-analysed by the different models. The results obtained were compared with the known parameters used to generate EFT data. Aspects on how to adopt the EFT in the analyses of time-correlated single photon counting experiments are also presented, as well as future aspects on using energy migration for examining protein structure.
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Affiliation(s)
- Stanislav Kalinin
- Department of Chemistry, Biophysical Chemistry, University of Umeå, S-901 87 Umeå, Sweden
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67
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Photobleaching FRET Microscopy. Mol Imaging 2005. [DOI: 10.1016/b978-019517720-6.50017-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] Open
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68
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Benninger RKP, Önfelt B, Neil MAA, Davis DM, French PMW. Fluorescence imaging of two-photon linear dichroism: cholesterol depletion disrupts molecular orientation in cell membranes. Biophys J 2004; 88:609-22. [PMID: 15520272 PMCID: PMC1305038 DOI: 10.1529/biophysj.104.050096] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
The plasma membrane of cells is an ordered environment, giving rise to anisotropic orientation and restricted motion of molecules and proteins residing in the membrane. At the same time as being an organized matrix of defined structure, the cell membrane is heterogeneous and dynamic. Here we present a method where we use fluorescence imaging of linear dichroism to measure the orientation of molecules relative to the cell membrane. By detecting linear dichroism as well as fluorescence anisotropy, the orientation parameters are separated from dynamic properties such as rotational diffusion and homo energy transfer (energy migration). The sensitivity of the technique is enhanced by using two-photon excitation for higher photo-selection compared to single photon excitation. We show here that we can accurately image lipid organization in whole cell membranes and in delicate structures such as membrane nanotubes connecting two cells. The speed of our wide-field imaging system makes it possible to image changes in orientation and anisotropy occurring on a subsecond timescale. This is demonstrated by time-lapse studies showing that cholesterol depletion rapidly disrupts the orientation of a fluorophore located within the hydrophobic region of the cell membrane but not of a surface bound probe. This is consistent with cholesterol having an important role in stabilizing and ordering the lipid tails within the plasma membrane.
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Affiliation(s)
- Richard K. P. Benninger
- Department of Physics and Department of Biological Sciences, Imperial College London, London SW7 2AZ, United Kingdom
| | - Björn Önfelt
- Department of Physics and Department of Biological Sciences, Imperial College London, London SW7 2AZ, United Kingdom
| | - Mark A. A. Neil
- Department of Physics and Department of Biological Sciences, Imperial College London, London SW7 2AZ, United Kingdom
| | - Daniel M. Davis
- Department of Physics and Department of Biological Sciences, Imperial College London, London SW7 2AZ, United Kingdom
| | - Paul M. W. French
- Department of Physics and Department of Biological Sciences, Imperial College London, London SW7 2AZ, United Kingdom
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69
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Using live FRET imaging to reveal early protein–protein interactions during T cell activation. Curr Opin Immunol 2004. [DOI: 10.1016/j.coi.2004.07.018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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70
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Zal T, Gascoigne NRJ. Using live FRET imaging to reveal early protein–protein interactions during T cell activation. Curr Opin Immunol 2004; 16:418-27. [PMID: 15245734 DOI: 10.1016/j.coi.2004.05.019] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
The emerging challenge for proteomics in general and lymphocyte biology in particular is to understand protein-protein interactions in the dynamic context of the living cell. Particularly interesting are the molecular dynamics of the T cell receptor-CD3 complex and other immunoreceptors in immune synapses. Fluorescence (or Förster) resonance energy transfer (FRET) is one of the few techniques that are capable of giving dynamic information about the nanometer-range proximity between molecules, as opposed to simply the subcellular co-localization that is provided by fluorescence microscopy. Spectral changes in fluorescence intensity and down modulation of donor lifetime are the basis for rapidly developing approaches to real-time FRET imaging. With two-photon excitation, FRET can now be extended to in vivo imaging.
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Affiliation(s)
- Tomasz Zal
- Department of Immunology, The Scripps Research Institute, La Jolla, California 92037, USA.
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Taner SB, Onfelt B, Pirinen NJ, McCann FE, Magee AI, Davis DM. Control of Immune Responses by Trafficking Cell Surface Proteins, Vesicles and Lipid Rafts to and from the Immunological Synapse. Traffic 2004; 5:651-61. [PMID: 15296490 DOI: 10.1111/j.1600-0854.2004.00214.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Supramolecular clusters at the immunological synapse provide a mechanism for structuring complex communication networks between cells of the immune system. Regulating intra- and intercellular trafficking of proteins and lipids to and from the immunological synapse provides an additional level of complexity in determining the functional outcome of immune cell interactions. An emergent principle is that molecules requiring tightly regulated cell surface expression, e.g. negative regulators of cell activation or molecules promoting cytotoxicity, are trafficked to the immunological synapse from intracellular secretory as required lysosomes. Many molecules required for the early stages of the intercellular communication are already present at the cell surface, sometimes in lipid rafts, and are rapidly translocated laterally to the intercellular contact. Our understanding of these events critically depends on utilizing appropriate technologies for probing supramolecular recognition in live cells. Thus, we also present here a critical discussion of the technologies used to study lipid rafts and, more broadly, a map of the spatial and temporal dimensions covered by current live cell physical techniques, highlighting where advances are needed to exceed current spatial and temporal boundaries.
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Affiliation(s)
- Sabrina B Taner
- Department of Biological Sciences, Imperial College London, SW7 2AZ, UK
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Hess ST, Sheets ED, Wagenknecht-Wiesner A, Heikal AA. Quantitative analysis of the fluorescence properties of intrinsically fluorescent proteins in living cells. Biophys J 2004; 85:2566-80. [PMID: 14507719 PMCID: PMC1303480 DOI: 10.1016/s0006-3495(03)74679-7] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The main potential of intrinsically fluorescent proteins (IFPs), as noninvasive and site-specific markers, lies in biological applications such as intracellular visualization and molecular genetics. However, photophysical studies of IFPs have been carried out mainly in aqueous solution. Here, we provide a comprehensive analysis of the intracellular environmental effects on the steady-state spectroscopy and excited-state dynamics of green (EGFP) and red (DsRed) fluorescent proteins, using both one- and two-photon excitation. EGFP and DsRed are expressed either in the cytoplasm of rat basophilic leukemia (RBL-2H3) mucosal mast cells or anchored (via LynB protein) to the inner leaflet of the plasma membrane. The fluorescence lifetimes (within approximately 10%) and spectra in live cells are basically the same as in aqueous solution, which indicate the absence of both IFP aggregation and cellular environmental effects on the protein folding under our experimental conditions. However, comparative time-resolved anisotropy measurements of EGFP reveal a cytoplasmic viscosity 2.5 +/- 0.3 times larger than that of aqueous solution at room temperature, and also provide some insights into the LynB-EGFP structure and the heterogeneity of the cytoplasmic viscosity. Further, the oligomer configuration and internal depolarization of DsRed, previously observed in solution, persists upon expression in these cells. DsRed also undergoes an instantaneous three-photon induced color change under 740-nm excitation, with efficiently nonradiative green species. These results confirm the implicit assumption that in vitro fluorescence properties of IFPs are essentially valid for in vivo applications, presumably due to the beta-barrel protection of the embodied chromophore. We also discuss the relevance of LynB-EGFP anisotropy for specialized domains studies in plasma membranes.
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Affiliation(s)
- Samuel T Hess
- School of Applied and Engineering Physics, Nanobiotechnology Center, Cornell University, Ithaca, New York 14853, USA
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