1
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Lee HN, Lee SE, Inn KS, Seong J. Optical sensing and control of T cell signaling pathways. Front Physiol 2024; 14:1321996. [PMID: 38269062 PMCID: PMC10806162 DOI: 10.3389/fphys.2023.1321996] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2023] [Accepted: 12/20/2023] [Indexed: 01/26/2024] Open
Abstract
T cells regulate adaptive immune responses through complex signaling pathways mediated by T cell receptor (TCR). The functional domains of the TCR are combined with specific antibodies for the development of chimeric antigen receptor (CAR) T cell therapy. In this review, we first overview current understanding on the T cell signaling pathways as well as traditional methods that have been widely used for the T cell study. These methods, however, are still limited to investigating dynamic molecular events with spatiotemporal resolutions. Therefore, genetically encoded biosensors and optogenetic tools have been developed to study dynamic T cell signaling pathways in live cells. We review these cutting-edge technologies that revealed dynamic and complex molecular mechanisms at each stage of T cell signaling pathways. They have been primarily applied to the study of dynamic molecular events in TCR signaling, and they will further aid in understanding the mechanisms of CAR activation and function. Therefore, genetically encoded biosensors and optogenetic tools offer powerful tools for enhancing our understanding of signaling mechanisms in T cells and CAR-T cells.
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Affiliation(s)
- Hae Nim Lee
- Brain Science Institute, Korea Institute of Science and Technoloy, Seoul, Republic of Korea
- Department of Converging Science and Technology, Kyung Hee University, Seoul, Republic of Korea
| | - Seung Eun Lee
- Department of Pharmacology, Seoul National University College of Medicine, Seoul, Republic of Korea
| | - Kyung-Soo Inn
- Department of Converging Science and Technology, Kyung Hee University, Seoul, Republic of Korea
| | - Jihye Seong
- Department of Pharmacology, Seoul National University College of Medicine, Seoul, Republic of Korea
- Wide River Institute of Immunology, Seoul National University, Hongcheon, Republic of Korea
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2
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Ting KK, Yu P, Dow R, Floro E, Ibrahim H, Scipione CA, Hyduk SJ, Polenz CK, Zaslaver O, Karmaus PW, Fessler MB, Rӧst HL, Ohh M, Tsai S, Winer DA, Woo M, Rocheleau J, Jongstra-Bilen J, Cybulsky MI. Oxidized Low-Density Lipoprotein Accumulation Suppresses Glycolysis and Attenuates the Macrophage Inflammatory Response by Diverting Transcription from the HIF-1α to the Nrf2 Pathway. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2023; 211:1561-1577. [PMID: 37756544 PMCID: PMC10873122 DOI: 10.4049/jimmunol.2300293] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/01/2023] [Accepted: 08/28/2023] [Indexed: 09/29/2023]
Abstract
Lipid accumulation in macrophages (Mφs) is a hallmark of atherosclerosis, yet how lipid accumulation affects inflammatory responses through rewiring of Mφ metabolism is poorly understood. We modeled lipid accumulation in cultured wild-type mouse thioglycolate-elicited peritoneal Mφs and bone marrow-derived Mφs with conditional (Lyz2-Cre) or complete genetic deficiency of Vhl, Hif1a, Nos2, and Nfe2l2. Transfection studies employed RAW264.7 cells. Mφs were cultured for 24 h with oxidized low-density lipoprotein (oxLDL) or cholesterol and then were stimulated with LPS. Transcriptomics revealed that oxLDL accumulation in Mφs downregulated inflammatory, hypoxia, and cholesterol metabolism pathways, whereas the antioxidant pathway, fatty acid oxidation, and ABC family proteins were upregulated. Metabolomics and extracellular metabolic flux assays showed that oxLDL accumulation suppressed LPS-induced glycolysis. Intracellular lipid accumulation in Mφs impaired LPS-induced inflammation by reducing both hypoxia-inducible factor 1-α (HIF-1α) stability and transactivation capacity; thus, the phenotype was not rescued in Vhl-/- Mφs. Intracellular lipid accumulation in Mφs also enhanced LPS-induced NF erythroid 2-related factor 2 (Nrf2)-mediated antioxidative defense that destabilizes HIF-1α, and Nrf2-deficient Mφs resisted the inhibitory effects of lipid accumulation on glycolysis and inflammatory gene expression. Furthermore, oxLDL shifted NADPH consumption from HIF-1α- to Nrf2-regulated apoenzymes. Thus, we postulate that repurposing NADPH consumption from HIF-1α to Nrf2 transcriptional pathways is critical in modulating inflammatory responses in Mφs with accumulated intracellular lipid. The relevance of our in vitro models was established by comparative transcriptomic analyses, which revealed that Mφs cultured with oxLDL and stimulated with LPS shared similar inflammatory and metabolic profiles with foamy Mφs derived from the atherosclerotic mouse and human aorta.
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Affiliation(s)
- Kenneth K.Y. Ting
- Department of Immunology, University of Toronto, Toronto, ON M5S 1A8, Canada
- Toronto General Hospital Research Institute, University Health Network, Toronto, ON M5G 1L7, Canada
| | - Pei Yu
- Department of Immunology, University of Toronto, Toronto, ON M5S 1A8, Canada
- Toronto General Hospital Research Institute, University Health Network, Toronto, ON M5G 1L7, Canada
| | - Riley Dow
- Department of Immunology, University of Toronto, Toronto, ON M5S 1A8, Canada
- Toronto General Hospital Research Institute, University Health Network, Toronto, ON M5G 1L7, Canada
| | - Eric Floro
- Toronto General Hospital Research Institute, University Health Network, Toronto, ON M5G 1L7, Canada
- Institute of Biomedical Engineering, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Hisham Ibrahim
- Toronto General Hospital Research Institute, University Health Network, Toronto, ON M5G 1L7, Canada
- Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Corey A. Scipione
- Department of Immunology, University of Toronto, Toronto, ON M5S 1A8, Canada
- Toronto General Hospital Research Institute, University Health Network, Toronto, ON M5G 1L7, Canada
- Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Sharon J. Hyduk
- Toronto General Hospital Research Institute, University Health Network, Toronto, ON M5G 1L7, Canada
| | - Chanele K. Polenz
- Toronto General Hospital Research Institute, University Health Network, Toronto, ON M5G 1L7, Canada
- Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Olga Zaslaver
- Terrence Donnelly Centre for Cellular & Biomolecular Research, University of Toronto, Toronto, ON M5S 3E1
| | - Peer W.F. Karmaus
- Immunity, Inflammation and Disease Laboratory, National Institute of Environmental Health Sciences, NIH, Research Triangle Park, NC, USA
| | - Michael B. Fessler
- Immunity, Inflammation and Disease Laboratory, National Institute of Environmental Health Sciences, NIH, Research Triangle Park, NC, USA
| | - Hannes L. Rӧst
- Terrence Donnelly Centre for Cellular & Biomolecular Research, University of Toronto, Toronto, ON M5S 3E1
| | - Michael Ohh
- Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON M5S 1A8, Canada
- Department of Biochemistry, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Sue Tsai
- Department of Medical Microbiology and Immunology, University of Alberta, Edmonton, AB T6G 2RS, Canada
| | - Daniel A. Winer
- Department of Immunology, University of Toronto, Toronto, ON M5S 1A8, Canada
- Toronto General Hospital Research Institute, University Health Network, Toronto, ON M5G 1L7, Canada
- Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Minna Woo
- Department of Immunology, University of Toronto, Toronto, ON M5S 1A8, Canada
- Toronto General Hospital Research Institute, University Health Network, Toronto, ON M5G 1L7, Canada
- Division of Endocrinology and Metabolism, Department of Medicine, University Health Network, University of Toronto, Toronto, ON M5S 1A8, Canada
- Banting and Best Diabetes Centre, University of Toronto, Toronto, ON M5G 2C4, Canada
| | - Jonathan Rocheleau
- Toronto General Hospital Research Institute, University Health Network, Toronto, ON M5G 1L7, Canada
- Institute of Biomedical Engineering, University of Toronto, Toronto, ON M5S 1A8, Canada
- Department of Physiology, University of Toronto, Toronto, ON M5S 1A8, Canada
- Banting and Best Diabetes Centre, University of Toronto, Toronto, ON M5G 2C4, Canada
| | - Jenny Jongstra-Bilen
- Department of Immunology, University of Toronto, Toronto, ON M5S 1A8, Canada
- Toronto General Hospital Research Institute, University Health Network, Toronto, ON M5G 1L7, Canada
- Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Myron I. Cybulsky
- Department of Immunology, University of Toronto, Toronto, ON M5S 1A8, Canada
- Toronto General Hospital Research Institute, University Health Network, Toronto, ON M5G 1L7, Canada
- Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, ON M5S 1A8, Canada
- Peter Munk Cardiac Centre, University Health Network, Toronto, ON M5G 2N2, Canada
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3
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Bui CV, Boswell CW, Ciruna B, Rocheleau JV. Apollo-NADP + reveals in vivo adaptation of NADPH/NADP + metabolism in electrically activated pancreatic β cells. SCIENCE ADVANCES 2023; 9:eadi8317. [PMID: 37792934 PMCID: PMC10550227 DOI: 10.1126/sciadv.adi8317] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/23/2023] [Accepted: 08/31/2023] [Indexed: 10/06/2023]
Abstract
Several genetically encoded sensors have been developed to study live cell NADPH/NADP+ dynamics, but their use has been predominantly in vitro. Here, we developed an in vivo assay using the Apollo-NADP+ sensor and microfluidic devices to measure endogenous NADPH/NADP+ dynamics in the pancreatic β cells of live zebrafish embryos. Flux through the pentose phosphate pathway, the main source of NADPH in many cell types, has been reported to be low in β cells. Thus, it is unclear how these cells compensate to meet NADPH demands. Using our assay, we show that pyruvate cycling is the main source of NADP+ reduction in β cells, with contributions from folate cycling after acute electrical activation. INS1E β cells also showed a stress-induced increase in folate cycling and further suggested that this cycling requires both increased glycolytic intermediates and cytosolic NAD+. Overall, we show in vivo application of the Apollo-NADP+ sensor and reveal that β cells are capable of adapting NADPH/NADP+ redox during stress.
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Affiliation(s)
- Cindy V. Bui
- Institute of Biomedical Engineering, University of Toronto, Toronto, Ontario, Canada
- Toronto General Hospital Research Institute, University Health Network, Toronto, Ontario, Canada
| | - Curtis W. Boswell
- Program in Developmental and Stem Cell Biology, Hospital for Sick Children, Toronto, Ontario, Canada
- Department of Molecular Genetics, University of Toronto, Toronto, Ontario, Canada
- Department of Genetics, Yale University School of Medicine, New Haven, CT, USA
| | - Brian Ciruna
- Program in Developmental and Stem Cell Biology, Hospital for Sick Children, Toronto, Ontario, Canada
- Department of Molecular Genetics, University of Toronto, Toronto, Ontario, Canada
| | - Jonathan V. Rocheleau
- Institute of Biomedical Engineering, University of Toronto, Toronto, Ontario, Canada
- Toronto General Hospital Research Institute, University Health Network, Toronto, Ontario, Canada
- Banting and Best Diabetes Centre, University of Toronto, Toronto, Ontario, Canada
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4
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Chang H, Bennett AM, Cameron WD, Floro E, Au A, McFaul CM, Yip CM, Rocheleau JV. Targeting Apollo-NADP + to Image NADPH Generation in Pancreatic Beta-Cell Organelles. ACS Sens 2022; 7:3308-3317. [PMID: 36269889 PMCID: PMC9706804 DOI: 10.1021/acssensors.2c01174] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
NADPH/NADP+ redox state supports numerous reactions related to cell growth and survival; yet the full impact is difficult to appreciate due to organelle compartmentalization of NADPH and NADP+. To study glucose-stimulated NADPH production in pancreatic beta-cell organelles, we targeted the Apollo-NADP+ sensor by first selecting the most pH-stable version of the single-color sensor. We subsequently targeted mTurquoise2-Apollo-NADP+ to various organelles and confirmed activity in the cytoplasm, mitochondrial matrix, nucleus, and peroxisome. Finally, we measured the glucose- and glutamine-stimulated NADPH responses by single- and dual-color imaging of the targeted sensors. Overall, we developed multiple organelle-targeted Apollo-NADP+ sensors to reveal the prominent role of beta-cell mitochondria in determining NADPH production in the cytoplasm, nucleus, and peroxisome.
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Affiliation(s)
- Huntley
H. Chang
- Institute
of Biomedical Engineering, University of
Toronto, Toronto, Ontario M5S 3G9, Canada,Toronto
General Hospital Research Institute, University
Health Network, Toronto, Ontario M5G 2C4, Canada
| | - Alex M. Bennett
- Institute
of Biomedical Engineering, University of
Toronto, Toronto, Ontario M5S 3G9, Canada,Toronto
General Hospital Research Institute, University
Health Network, Toronto, Ontario M5G 2C4, Canada
| | - William D. Cameron
- Institute
of Biomedical Engineering, University of
Toronto, Toronto, Ontario M5S 3G9, Canada,Toronto
General Hospital Research Institute, University
Health Network, Toronto, Ontario M5G 2C4, Canada
| | - Eric Floro
- Institute
of Biomedical Engineering, University of
Toronto, Toronto, Ontario M5S 3G9, Canada,Toronto
General Hospital Research Institute, University
Health Network, Toronto, Ontario M5G 2C4, Canada
| | - Aaron Au
- Institute
of Biomedical Engineering, University of
Toronto, Toronto, Ontario M5S 3G9, Canada
| | - Christopher M. McFaul
- Institute
of Biomedical Engineering, University of
Toronto, Toronto, Ontario M5S 3G9, Canada
| | - Christopher M. Yip
- Institute
of Biomedical Engineering, University of
Toronto, Toronto, Ontario M5S 3G9, Canada
| | - Jonathan V. Rocheleau
- Institute
of Biomedical Engineering, University of
Toronto, Toronto, Ontario M5S 3G9, Canada,Toronto
General Hospital Research Institute, University
Health Network, Toronto, Ontario M5G 2C4, Canada,Department
of Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada,Banting
and Best Diabetes Centre, University of
Toronto, Toronto, Ontario M5G 2C4, Canada,
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5
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Myšková J, Rybakova O, Brynda J, Khoroshyy P, Bondar A, Lazar J. Directionality of light absorption and emission in representative fluorescent proteins. Proc Natl Acad Sci U S A 2020; 117:32395-32401. [PMID: 33273123 PMCID: PMC7768707 DOI: 10.1073/pnas.2017379117] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2020] [Accepted: 10/30/2020] [Indexed: 12/13/2022] Open
Abstract
Fluorescent molecules are like antennas: The rate at which they absorb light depends on their orientation with respect to the incoming light wave, and the apparent intensity of their emission depends on their orientation with respect to the observer. However, the directions along which the most important fluorescent molecules in biology, fluorescent proteins (FPs), absorb and emit light are generally not known. Our optical and X-ray investigations of FP crystals have now allowed us to determine the molecular orientations of the excitation and emission transition dipole moments in the FPs mTurquoise2, eGFP, and mCherry, and the photoconvertible FP mEos4b. Our results will allow using FP directionality in studies of molecular and biological processes, but also in development of novel bioengineering and bioelectronics applications.
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Affiliation(s)
- Jitka Myšková
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, 16610 Prague 6, Czech Republic
| | - Olga Rybakova
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, 16610 Prague 6, Czech Republic
- Institute of Microbiology, Czech Academy of Sciences, 37333 Nové Hrady, Czech Republic
| | - Jiří Brynda
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, 16610 Prague 6, Czech Republic
- Institute of Molecular Genetics, Czech Academy of Sciences, 14220 Prague 4, Czech Republic
| | - Petro Khoroshyy
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, 16610 Prague 6, Czech Republic
- Institute of Microbiology, Czech Academy of Sciences, 37333 Nové Hrady, Czech Republic
| | - Alexey Bondar
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, 16610 Prague 6, Czech Republic
- Institute of Microbiology, Czech Academy of Sciences, 37333 Nové Hrady, Czech Republic
| | - Josef Lazar
- Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, 16610 Prague 6, Czech Republic;
- Institute of Microbiology, Czech Academy of Sciences, 37333 Nové Hrady, Czech Republic
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6
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Sparks H, Dent L, Bakal C, Behrens A, Salbreux G, Dunsby C. Dual-view oblique plane microscopy (dOPM). BIOMEDICAL OPTICS EXPRESS 2020; 11:7204-7220. [PMID: 33408991 PMCID: PMC7747899 DOI: 10.1364/boe.409781] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/11/2020] [Revised: 10/26/2020] [Accepted: 10/28/2020] [Indexed: 05/02/2023]
Abstract
We present a new folded dual-view oblique plane microscopy (OPM) technique termed dOPM that enables two orthogonal views of the sample to be obtained by translating a pair of tilted mirrors in refocussing space. Using a water immersion 40× 1.15 NA primary objective, deconvolved image volumes of 200 nm beads were measured to have full width at half maxima (FWHM) of 0.35 ± 0.04 µm and 0.39 ± 0.02 µm laterally and 0.81 ± 0.07 µm axially. The measured z-sectioning value was 1.33 ± 0.45 µm using light-sheet FWHM in the frames of the two views of 4.99 ± 0.58 µm and 4.89 ± 0.63 µm. To qualitatively demonstrate that the system can reduce shadow artefacts while providing a more isotropic resolution, a multi-cellular spheroid approximately 100 µm in diameter was imaged.
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Affiliation(s)
- Hugh Sparks
- Photonics Group, Department of Physics,
Imperial College London, London, SW7 2AZ, UK
| | - Lucas Dent
- Dynamical Cell Systems Team, The Institute
of Cancer Research, London, SW3 6JB, UK
| | - Chris Bakal
- Dynamical Cell Systems Team, The Institute
of Cancer Research, London, SW3 6JB, UK
| | - Axel Behrens
- Cancer Stem Cell Team, The Institute of
Cancer Research, London, SW3 6JB, UK
| | - Guillaume Salbreux
- The Theoretical Physics of Biology
Laboratory, The Francis Crick Institute, London, NW1 1AT, UK
| | - Chris Dunsby
- Photonics Group, Department of Physics,
Imperial College London, London, SW7 2AZ, UK
- Centre for Pathology, Imperial College
London, London, SW7 2AZ, UK
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7
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Bartle EI, Rao TC, Beggs RR, Dean WF, Urner TM, Kowalczyk AP, Mattheyses AL. Protein exchange is reduced in calcium-independent epithelial junctions. J Cell Biol 2020; 219:151763. [PMID: 32399559 PMCID: PMC7265307 DOI: 10.1083/jcb.201906153] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2019] [Revised: 01/29/2020] [Accepted: 03/11/2020] [Indexed: 12/29/2022] Open
Abstract
Desmosomes are cell–cell junctions that provide mechanical integrity to epithelial and cardiac tissues. Desmosomes have two distinct adhesive states, calcium-dependent and hyperadhesive, which balance tissue plasticity and strength. A highly ordered array of cadherins in the adhesive interface is hypothesized to drive hyperadhesion, but how desmosome structure confers adhesive state is still elusive. We employed fluorescence polarization microscopy to show that cadherin order is not required for hyperadhesion induced by pharmacologic and genetic approaches. FRAP experiments in cells treated with the PKCα inhibitor Gö6976 revealed that cadherins, plakoglobin, and desmoplakin have significantly reduced exchange in and out of hyperadhesive desmosomes. To test whether this was a result of enhanced keratin association, we used the desmoplakin mutant S2849G, which conferred reduced protein exchange. We propose that inside-out regulation of protein exchange modulates adhesive function, whereby proteins are “locked in” to hyperadhesive desmosomes while protein exchange confers plasticity on calcium-dependent desmosomes, thereby providing rapid control of adhesion.
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Affiliation(s)
- Emily I Bartle
- Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL
| | - Tejeshwar C Rao
- Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL
| | - Reena R Beggs
- Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL
| | - William F Dean
- Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL
| | - Tara M Urner
- Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL
| | - Andrew P Kowalczyk
- Departments of Cell Biology and Dermatology, Emory University, Atlanta, GA
| | - Alexa L Mattheyses
- Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL
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8
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Imaging of fluorescence anisotropy during photoswitching provides a simple readout for protein self-association. Nat Commun 2020; 11:21. [PMID: 31911590 PMCID: PMC6946710 DOI: 10.1038/s41467-019-13843-6] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2019] [Accepted: 12/03/2019] [Indexed: 12/02/2022] Open
Abstract
Monitoring of protein oligomerization has benefited greatly from Förster Resonance Energy Transfer (FRET) measurements. Although donors and acceptors are typically fluorescent molecules with different spectra, homo-FRET can occur between fluorescent molecules of the same type if the emission spectrum overlaps with the absorption spectrum. Here, we describe homo-FRET measurements by monitoring anisotropy changes in photoswitchable fluorescent proteins while photoswitching to the off state. These offer the capability to estimate anisotropy in the same specimen during homo-FRET as well as non-FRET conditions. We demonstrate photoswitching anisotropy FRET (psAFRET) with a number of test chimeras and example oligomeric complexes inside living cells. We also present an equation derived from FRET and anisotropy equations which converts anisotropy changes into a factor we call delta r FRET (drFRET). This is analogous to an energy transfer efficiency and allows experiments performed on a given homo-FRET pair to be more easily compared across different optical configurations. Performing homo-FRET measurements in cells using a fluorescence microscope is challenging, especially when using high numerical aperture objective lenses. Here the authors present a method for improved homo-FRET measurements based on anisotropy changes in photoswitchable fluorescent proteins.
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9
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Taneja S, Rutenberg AD. Photobleaching of randomly rotating fluorescently decorated particles. J Chem Phys 2018; 147:104105. [PMID: 28915751 DOI: 10.1063/1.4989673] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Randomly rotating particles that have been isotropically labeled with rigidly linked fluorophores will undergo non-isotropic (patchy) photobleaching under illumination due to the dipole coupling of fluorophores with light. For a rotational diffusion rate D of the particle and a photobleaching time scale τ of the fluorophores, the dynamics of this process are characterized by the dimensionless combination Dτ. We find significant interparticle fluctuations at intermediate Dτ. These fluctuations vanish at both large and small Dτ or at small or large elapsed times t. Associated with these fluctuations between particles, we also observe transient non-monotonicities of the brightness of individual particles. These non-monotonicities can be as much as 20% of the original brightness. We show that these novel photobleach-fluctuations dominate over variability of single-fluorophore orientation when there are at least 103 fluorophores on individual particles.
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Affiliation(s)
- Swadhin Taneja
- Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada
| | - Andrew D Rutenberg
- Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia B3H 4R2, Canada
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10
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Bene L, Gralle M, Damjanovich L. Confocal microscopic dual-laser dual-polarization FRET (2polFRET) at the acceptor side for correlating rotations at different distances on the cell surface. Biochim Biophys Acta Gen Subj 2018; 1862:1050-1068. [PMID: 29292190 DOI: 10.1016/j.bbagen.2017.12.013] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2017] [Revised: 12/16/2017] [Accepted: 12/22/2017] [Indexed: 10/18/2022]
Abstract
Relationship of donor and acceptor fluorescence anisotropies as well as efficiency of fluorescence resonance energy transfer (FRET) has been investigated in a confocal microscope in the context of FRET systems comprised of donor and acceptor-labeled MHCI and MHCII receptors on the surface of Kit-225 K6 human T-cells. The measurements have been carried out in a 2-laser, 5-signal platform where the total donor fluorescence intensity and 2 acceptor fluorescence intensities with their anisotropies - one at the donor's excitation wavelength, the other at the acceptor's excitation wavelength - have been detected. This configuration enabled the determination of FRET efficiency and correlating it with the two acceptor fluorescence anisotropies as a kind of calibration. Estimations for the FRET-enhanced donor fluorescence anisotropy, the directly excited acceptor fluorescence anisotropy, and the fluorescence anisotropy of sensitized emission have been obtained. Procedures for determining FRET by measuring only the total donor intensity and the acceptor intensity and its anisotropy, or two acceptor intensities and their anisotropies have been elaborated, the errors of which have been estimated based on the fluorescence anisotropy values obtained in the calibration with the method of flow cytometric energy transfer (FCET). The combined detection of the donor and acceptor fluorescence anisotropies enabled also the determination of the lower and upper limits of the orientation factor for FRET (κ2). An increase in range for κ2 with increasing FRET efficiency has been observed, with average κ2 values different from the dynamic random average of 2/3. These observations call for the need of κ2 determination in proximity measurements, where the donor and acceptor orientations are not predictable. An increasing range of κ2 with increasing intermolecular proximity of the MHCI and MHCII receptors has been observed. This indicates that molecular flexibility in the clusters of the MHCI and MHCII receptors reduces with increasing cluster density, i.e. a "fluidity gradient" exists in the clusters. More specifically, the local density dependent flexibility can also be taken as a direct proof for that the association of these receptors is non-random, but mediated by some type of physical interaction, a finding as a benefit of FRET detection by polarization spectroscopy. Two new quantities - the quenched donor fluorescence anisotropy and a fluorescence anisotropy analogue, the "dissymmetry index" of the polarized FRET efficiency components - have also been introduced for the characterization of the orientational dynamics of the excited state during FRET.
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Affiliation(s)
- László Bene
- Department of Surgery, Faculty of Medicine, University of Debrecen, Debrecen, Hungary.
| | - Matthias Gralle
- Departamento de Bioquímica Médica Leopoldo de Meis, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - László Damjanovich
- Department of Surgery, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
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11
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Bartle EI, Urner TM, Raju SS, Mattheyses AL. Desmoglein 3 Order and Dynamics in Desmosomes Determined by Fluorescence Polarization Microscopy. Biophys J 2018; 113:2519-2529. [PMID: 29212005 DOI: 10.1016/j.bpj.2017.09.028] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2017] [Revised: 09/18/2017] [Accepted: 09/21/2017] [Indexed: 11/24/2022] Open
Abstract
Desmosomes are macromolecular cell-cell junctions that provide adhesive strength in epithelial tissue. Desmosome function is inseparably linked to structure, and it is hypothesized that the arrangement, or order, of desmosomal cadherins in the intercellular space is critical for adhesive strength. However, due to desmosome size, molecular complexity, and dynamics, the role that order plays in adhesion is challenging to study. Herein, we present an excitation resolved fluorescence polarization microscopy approach to measure the spatiotemporal dynamics of order and disorder of the desmosomal cadherin desmoglein 3 (Dsg3) in living cells. Simulations were used to establish order factor as a robust metric for quantifying the spatiotemporal dynamics of order and disorder. Order factor measurements in keratinocytes showed the Dsg3 extracellular domain is ordered at the individual desmosome, single cell, and cell population levels compared to a series of disordered controls. Desmosomal adhesion is Ca2+ dependent, and reduction of extracellular Ca2+ leads to a loss of adhesion measured by dispase fragmentation assay (λ = 15.1 min). Live cell imaging revealed Dsg3 order decreased more rapidly (λ = 5.5 min), indicating that cadherin order is not required for adhesion. Our results suggest that rapid disordering of cadherins can communicate a change in extracellular Ca2+ concentration to the cell, leading to a downstream loss of adhesion. Fluorescence polarization is an effective bridge between protein structure and complex dynamics and the approach presented here is broadly applicable to studying order in macromolecular structures.
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Affiliation(s)
- Emily I Bartle
- Department of Cell Biology, Emory University, Atlanta, Georgia
| | - Tara M Urner
- Department of Cell Biology, Emory University, Atlanta, Georgia
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12
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Banerjee P, Wehle M, Lipowsky R, Santer M. A molecular dynamics model for glycosylphosphatidyl-inositol anchors: “flop down” or “lollipop”? Phys Chem Chem Phys 2018; 20:29314-29324. [DOI: 10.1039/c8cp04059a] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Computational model for GPI anchors tested in DMPC and POPC bilayers. The free anchor rarely occurs as an erected “lollipop-like” conformation, it rather “flops down” onto the bilayer surface. Yet an attached protein (here green fluorescent protein) exhibits extensive orientational flexibility due to the phospho-ethanolamine linker.
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Affiliation(s)
- Pallavi Banerjee
- Department of Theory and Biosystems
- Max Planck Institute for Colloids and Interfaces
- 14424 Potsdam
- Germany
| | - Marko Wehle
- Department of Theory and Biosystems
- Max Planck Institute for Colloids and Interfaces
- 14424 Potsdam
- Germany
| | - Reinhard Lipowsky
- Department of Theory and Biosystems
- Max Planck Institute for Colloids and Interfaces
- 14424 Potsdam
- Germany
| | - Mark Santer
- Department of Theory and Biosystems
- Max Planck Institute for Colloids and Interfaces
- 14424 Potsdam
- Germany
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13
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Nordenfelt P, Moore TI, Mehta SB, Kalappurakkal JM, Swaminathan V, Koga N, Lambert TJ, Baker D, Waters JC, Oldenbourg R, Tani T, Mayor S, Waterman CM, Springer TA. Direction of actin flow dictates integrin LFA-1 orientation during leukocyte migration. Nat Commun 2017; 8:2047. [PMID: 29229906 PMCID: PMC5725580 DOI: 10.1038/s41467-017-01848-y] [Citation(s) in RCA: 67] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2017] [Accepted: 10/20/2017] [Indexed: 12/31/2022] Open
Abstract
Integrin αβ heterodimer cell surface receptors mediate adhesive interactions that provide traction for cell migration. Here, we test whether the integrin, when engaged to an extracellular ligand and the cytoskeleton, adopts a specific orientation dictated by the direction of actin flow on the surface of migrating cells. We insert GFP into the rigid, ligand-binding head of the integrin, model with Rosetta the orientation of GFP and its transition dipole relative to the integrin head, and measure orientation with fluorescence polarization microscopy. Cytoskeleton and ligand-bound integrins orient in the same direction as retrograde actin flow with their cytoskeleton-binding β-subunits tilted by applied force. The measurements demonstrate that intracellular forces can orient cell surface integrins and support a molecular model of integrin activation by cytoskeletal force. Our results place atomic, Å-scale structures of cell surface receptors in the context of functional and cellular, μm-scale measurements. Integrin αβ heterodimer cell surface receptors mediate adhesive interactions that provide traction for cell migration. Here the authors show that actin flow can orient cell surface integrins during leukocyte migration, suggesting integrin activation by cytoskeletal force.
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Affiliation(s)
- Pontus Nordenfelt
- Whitman Center, Marine Biological Laboratory, Woods Hole, MA, 02543, USA.,Physiology Course, Marine Biological Laboratory, Woods Hole, MA, 02543, USA.,Program in Cellular and Molecular Medicine, Children's Hospital, and Department of Biological Chemistry and Molecular Pharmacology and Medicine, Harvard Medical School, Boston, MA, 02115, USA.,Division of Infection Medicine, Department of Clinical Sciences Lund, Faculty of Medicine, Lund University, Lund, 221 84, Sweden
| | - Travis I Moore
- Whitman Center, Marine Biological Laboratory, Woods Hole, MA, 02543, USA.,Program in Cellular and Molecular Medicine, Children's Hospital, and Department of Biological Chemistry and Molecular Pharmacology and Medicine, Harvard Medical School, Boston, MA, 02115, USA
| | - Shalin B Mehta
- Eugene Bell Center, Marine Biological Laboratory, Woods Hole, MA, 02543, USA.,Chan Zuckerberg Biohub, San Francisco, CA, 94158, USA
| | - Joseph Mathew Kalappurakkal
- Whitman Center, Marine Biological Laboratory, Woods Hole, MA, 02543, USA.,Physiology Course, Marine Biological Laboratory, Woods Hole, MA, 02543, USA.,National Center for Biological Sciences, Bangalore, 560065, India
| | - Vinay Swaminathan
- Whitman Center, Marine Biological Laboratory, Woods Hole, MA, 02543, USA.,Physiology Course, Marine Biological Laboratory, Woods Hole, MA, 02543, USA.,Cell Biology and Physiology Center, NHLBI, NIH, Bethesda, MD, 20824, USA
| | - Nobuyasu Koga
- Howard Hughes Medical Institute, University of Washington, Seattle, WA, 98195, USA.,Institute for Molecular Science, Myodaiji, Okazaki, 444-8585, Japan
| | - Talley J Lambert
- Department of Cell Biology, Harvard Medical School, Boston, MA, 02115, USA
| | - David Baker
- Howard Hughes Medical Institute, University of Washington, Seattle, WA, 98195, USA
| | - Jennifer C Waters
- Department of Cell Biology, Harvard Medical School, Boston, MA, 02115, USA
| | - Rudolf Oldenbourg
- Eugene Bell Center, Marine Biological Laboratory, Woods Hole, MA, 02543, USA
| | - Tomomi Tani
- Eugene Bell Center, Marine Biological Laboratory, Woods Hole, MA, 02543, USA
| | - Satyajit Mayor
- Whitman Center, Marine Biological Laboratory, Woods Hole, MA, 02543, USA.,Physiology Course, Marine Biological Laboratory, Woods Hole, MA, 02543, USA.,National Center for Biological Sciences, Bangalore, 560065, India
| | - Clare M Waterman
- Whitman Center, Marine Biological Laboratory, Woods Hole, MA, 02543, USA.,Physiology Course, Marine Biological Laboratory, Woods Hole, MA, 02543, USA.,Cell Biology and Physiology Center, NHLBI, NIH, Bethesda, MD, 20824, USA
| | - Timothy A Springer
- Whitman Center, Marine Biological Laboratory, Woods Hole, MA, 02543, USA. .,Physiology Course, Marine Biological Laboratory, Woods Hole, MA, 02543, USA. .,Program in Cellular and Molecular Medicine, Children's Hospital, and Department of Biological Chemistry and Molecular Pharmacology and Medicine, Harvard Medical School, Boston, MA, 02115, USA.
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14
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Swaminathan V, Kalappurakkal JM, Mehta SB, Nordenfelt P, Moore TI, Koga N, Baker DA, Oldenbourg R, Tani T, Mayor S, Springer TA, Waterman CM. Actin retrograde flow actively aligns and orients ligand-engaged integrins in focal adhesions. Proc Natl Acad Sci U S A 2017; 114:10648-10653. [PMID: 29073038 PMCID: PMC5635867 DOI: 10.1073/pnas.1701136114] [Citation(s) in RCA: 75] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Integrins are transmembrane receptors that, upon activation, bind extracellular ligands and link them to the actin filament (F-actin) cytoskeleton to mediate cell adhesion and migration. Cytoskeletal forces in migrating cells generated by polymerization- or contractility-driven "retrograde flow" of F-actin from the cell leading edge have been hypothesized to mediate integrin activation for ligand binding. This predicts that these forces should align and orient activated, ligand-bound integrins at the leading edge. Here, polarization-sensitive fluorescence microscopy of GFP-αVβ3 integrins in fibroblasts shows that integrins are coaligned in a specific orientation within focal adhesions (FAs) in a manner dependent on binding immobilized ligand and a talin-mediated linkage to the F-actin cytoskeleton. These findings, together with Rosetta modeling, suggest that integrins in FA are coaligned and may be highly tilted by cytoskeletal forces. Thus, the F-actin cytoskeleton sculpts an anisotropic molecular scaffold in FAs, and this feature may underlie the ability of migrating cells to sense directional extracellular cues.
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Affiliation(s)
- Vinay Swaminathan
- Whitman Center, Marine Biological Laboratory, Woods Hole, MA 02543
- Physiology Course, Marine Biological Laboratory, Woods Hole, MA 02543
- Cell Biology and Physiology Center, National Heart, Lung, and Blood Institute, NIH, Bethesda, MD 20892
| | - Joseph Mathew Kalappurakkal
- Whitman Center, Marine Biological Laboratory, Woods Hole, MA 02543
- Physiology Course, Marine Biological Laboratory, Woods Hole, MA 02543
- National Centre for Biological Sciences, Bangalore 560065, Karnataka, India
| | - Shalin B Mehta
- Eugene Bell Center, Marine Biological Laboratory, Woods Hole, MA 02543
| | - Pontus Nordenfelt
- Whitman Center, Marine Biological Laboratory, Woods Hole, MA 02543
- Physiology Course, Marine Biological Laboratory, Woods Hole, MA 02543
- Division of Infection Medicine, Lund University, SE-221 84 Lund, Sweden
- Program in Cellular and Molecular Medicine, Children's Hospital, Boston, MA 02115
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115
| | - Travis I Moore
- Whitman Center, Marine Biological Laboratory, Woods Hole, MA 02543
- Program in Cellular and Molecular Medicine, Children's Hospital, Boston, MA 02115
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115
| | - Nobuyasu Koga
- Department of Biochemistry, University of Washington, Seattle, WA 98195
- Howard Hughes Medical Institute, University of Washington, Seattle, WA 98195
- Institute for Molecular Science, Okazaki 444-8585, Japan
| | - David A Baker
- Department of Biochemistry, University of Washington, Seattle, WA 98195
- Howard Hughes Medical Institute, University of Washington, Seattle, WA 98195
| | - Rudolf Oldenbourg
- Eugene Bell Center, Marine Biological Laboratory, Woods Hole, MA 02543
| | - Tomomi Tani
- Eugene Bell Center, Marine Biological Laboratory, Woods Hole, MA 02543
| | - Satyajit Mayor
- Whitman Center, Marine Biological Laboratory, Woods Hole, MA 02543
- Physiology Course, Marine Biological Laboratory, Woods Hole, MA 02543
- National Centre for Biological Sciences, Bangalore 560065, Karnataka, India
| | - Timothy A Springer
- Whitman Center, Marine Biological Laboratory, Woods Hole, MA 02543
- Program in Cellular and Molecular Medicine, Children's Hospital, Boston, MA 02115
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115
| | - Clare M Waterman
- Whitman Center, Marine Biological Laboratory, Woods Hole, MA 02543;
- Physiology Course, Marine Biological Laboratory, Woods Hole, MA 02543
- Cell Biology and Physiology Center, National Heart, Lung, and Blood Institute, NIH, Bethesda, MD 20892
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15
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Boothe T, Lim GE, Cen H, Skovsø S, Piske M, Li SN, Nabi IR, Gilon P, Johnson JD. Inter-domain tagging implicates caveolin-1 in insulin receptor trafficking and Erk signaling bias in pancreatic beta-cells. Mol Metab 2016; 5:366-378. [PMID: 27110488 PMCID: PMC4837300 DOI: 10.1016/j.molmet.2016.01.009] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/03/2016] [Revised: 01/18/2016] [Accepted: 01/25/2016] [Indexed: 01/04/2023] Open
Abstract
OBJECTIVE The role and mechanisms of insulin receptor internalization remain incompletely understood. Previous trafficking studies of insulin receptors involved fluorescent protein tagging at their termini, manipulations that may be expected to result in dysfunctional receptors. Our objective was to determine the trafficking route and molecular mechanisms of functional tagged insulin receptors and endogenous insulin receptors in pancreatic beta-cells. METHODS We generated functional insulin receptors tagged with pH-resistant fluorescent proteins between domains. Confocal, TIRF and STED imaging revealed a trafficking pattern of inter-domain tagged insulin receptors and endogenous insulin receptors detected with antibodies. RESULTS Surprisingly, interdomain-tagged and endogenous insulin receptors in beta-cells bypassed classical Rab5a- or Rab7-mediated endocytic routes. Instead, we found that removal of insulin receptors from the plasma membrane involved tyrosine-phosphorylated caveolin-1, prior to trafficking within flotillin-1-positive structures to lysosomes. Multiple methods of inhibiting caveolin-1 significantly reduced Erk activation in vitro or in vivo, while leaving Akt signaling mostly intact. CONCLUSIONS We conclude that phosphorylated caveolin-1 plays a role in insulin receptor internalization towards lysosomes through flotillin-1-positive structures and that caveolin-1 helps bias physiological beta-cell insulin signaling towards Erk activation.
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Affiliation(s)
- Tobias Boothe
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, BC, Canada
| | - Gareth E Lim
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, BC, Canada
| | - Haoning Cen
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, BC, Canada
| | - Søs Skovsø
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, BC, Canada
| | - Micah Piske
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, BC, Canada
| | - Shu Nan Li
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, BC, Canada
| | - Ivan R Nabi
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, BC, Canada
| | - Patrick Gilon
- Pôle d'endocrinologie, diabète et nutrition, Institut de recherche expérimentale et clinique, Université catholique de Louvain, Brussels, Belgium
| | - James D Johnson
- Department of Cellular and Physiological Sciences, University of British Columbia, Vancouver, BC, Canada.
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16
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Bene L, Gogolák P, Ungvári T, Bagdány M, Nagy I, Damjanovich L. Depolarized FRET (depolFRET) on the cell surface: FRET control by photoselection. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2015; 1863:322-34. [PMID: 26657258 DOI: 10.1016/j.bbamcr.2015.12.003] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/15/2015] [Revised: 11/23/2015] [Accepted: 12/02/2015] [Indexed: 11/16/2022]
Abstract
Sensitivity of FRET in hetero- and homo-FRET systems on the photoselected orientation distribution of donors has been proven by using polarized and depolarized light for excitation. FRET as well as donor and acceptor anisotropies have been simultaneously measured in a dual emission-polarization scheme realized in a conventional flow cytometer by using single laser excitation and applying fluorophore-conjugated mAbs against the MHCI and MHCII cell surface receptors. Depolarization of the originally polarized light have been achieved by using crystal depolarizers based on Cornu's principle, a quarter-wave plate for circular polarization, and a parallel beam splitter acting as a diagonal-polarizer for dual-polarization excitation. Simultaneous analysis of intensity-based FRET efficiency and acceptor depolarization equivocally report that depolarization of light may increase FRET in an amount depending on the acceptor-to-donor concentration ratio. Acceptor depolarization turned to be more sensitive to FRET than donor hyper-polarization and even than intensity-based FRET efficiency. It can be used as a sensitive tool for monitoring changes in the dynamics of the donor-acceptor pairs. The basic observations of FRET enhancement and increased acceptor depolarization obtained for hetero-FRET are paralleled by analog observations of homo-FRET enhancements under depolarized excitation. In terms of the orientation factor for FRET, the FRET enhancements on depolarization in the condition of the macroscopically isotropic orientation distributions such as those of the cell surface bound fluorophores report on the presence of local orientation mismatches of the donor and acceptor preventing the optimal FRET in the polarized case, which may be eliminated by the excitation depolarization. A theory of fluorescence anisotropy for depolarized excitation is also presented.
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Affiliation(s)
- László Bene
- Department of Surgery, Faculty of Medicine, University of Debrecen, Debrecen, Hungary.
| | - Péter Gogolák
- Department of Immunology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Tamás Ungvári
- Department of Biophysics and Cell Biology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Miklós Bagdány
- Department of Physiology, McGill University, Montreal, Canada
| | - István Nagy
- Division of Electronics, Research Center for Nuclear Physics of the Hungarian Academy of Sciences, Debrecen, Hungary
| | - László Damjanovich
- Department of Surgery, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
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17
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Benninger RKP. Fluorescence linear dichroism imaging for quantifying membrane order. Methods Mol Biol 2015; 1232:161-79. [PMID: 25331136 DOI: 10.1007/978-1-4939-1752-5_14] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/21/2023]
Abstract
The plasma membrane of a cell is an ordered environment, giving rise to anisotropic orientations and restricted motion of constituent lipids and proteins. The membrane environment is also dynamic and heterogeneous, which is important for the regulation of membrane-localized signaling. A number of fluorescent microscopy approaches enable the membrane order to be quantified with high spatial and temporal resolution. A polarization-resolved fluorescence method, termed fluorescent linear dichroism (fLD) imaging, can quantify the orientation of membrane bound fluorophores which allows spatially resolved measurement of membrane order and sub-resolution membrane topology (ruffling). Here we describe the detailed methods for performing fLD imaging in biological membrane environments such as the plasma membrane of living cells. This includes the preparation of the sample with appropriate fluorescent dyes, the requirements of the microscope system, the data collection protocol, and post-acquisition image processing, analysis, and interpretation.
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Affiliation(s)
- Richard K P Benninger
- Department of Bioengineering, University of Colorado, 1775 Aurora Court, Aurora, CO, 80045, USA,
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18
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Single-laser polarization FRET (polFRET) on the cell surface. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2014; 1843:3047-64. [PMID: 25241341 DOI: 10.1016/j.bbamcr.2014.07.011] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/21/2014] [Revised: 07/15/2014] [Accepted: 07/21/2014] [Indexed: 11/22/2022]
Abstract
A new method for the simultaneous detection of rotational mobility and proximity of cell surface receptors is presented based on cell-by-cell basis measurement of polarized fluorescence intensity components of the donor and acceptor of a FRET system. In addition to the FRET efficiency and the donor and acceptor concentrations, the method makes also possible the determination of the rotational characteristics and the associated fraction of the donors (FRET-fraction). The method is illustrated with flow cytometric and rFLIM measurements on donor-acceptor systems comprising fluorescently labeled whole antibodies and their Fab fragments against epitopes of the MHCI and MHCII cell surface receptors on human lymphoblast cells. Fluorescence anisotropy of donor and acceptor and FRET efficiency were measured for samples of different acceptor-to-donor concentration ratios. Acceptor anisotropy proved to be more sensitive than the donor anisotropy for sensing FRET. After determining the rotational constants of the donor-conjugated antibodies by measurements of FRET in the steady state, and by rFLIM as a reference, the associated fractions of the MHCI and MHCII molecules in their clusters were determined. Besides the flow cytometer and the wide-field rFLIM used in this study, the method can be applied also in other devices capable of dual-anisotropy detection.
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19
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Mapping the local organization of cell membranes using excitation-polarization-resolved confocal fluorescence microscopy. Biophys J 2014; 105:127-36. [PMID: 23823231 DOI: 10.1016/j.bpj.2013.05.043] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2012] [Revised: 04/12/2013] [Accepted: 05/21/2013] [Indexed: 12/28/2022] Open
Abstract
Fluorescence anisotropy and linear dichroism imaging have been widely used for imaging biomolecular orientational distributions in protein aggregates, fibrillar structures of cells, and cell membranes. However, these techniques do not give access to complete orientational order information in a whole image, because their use is limited to parts of the sample where the average orientation of molecules is known a priori. Fluorescence anisotropy is also highly sensitive to depolarization mechanisms such as those induced by fluorescence energy transfer. A fully excitation-polarization-resolved fluorescence microscopy imaging that relies on the use of a tunable incident polarization and a nonpolarized detection is able to circumvent these limitations. We have developed such a technique in confocal epifluorescence microscopy, giving access to new regions of study in the complex and heterogeneous molecular organization of cell membranes. Using this technique, we demonstrate morphological changes at the subdiffraction scale in labeled COS-7 cell membranes whose cytoskeleton is perturbed. Molecular orientational order is also seen to be affected by cholesterol depletion, reflecting the strong interplay between lipid-packing regions and their nearby cytoskeleton. This noninvasive optical technique can reveal local organization in cell membranes when used as a complement to existing methods such as generalized polarization.
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20
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Patel PC, Lee HSW, Ming AYK, Rath A, Deber CM, Yip CM, Rocheleau JV, Gray-Owen SD. Inside-out signaling promotes dynamic changes in the carcinoembryonic antigen-related cellular adhesion molecule 1 (CEACAM1) oligomeric state to control its cell adhesion properties. J Biol Chem 2013; 288:29654-69. [PMID: 24005674 DOI: 10.1074/jbc.m113.504639] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Cell-cell contacts are fundamental to multicellular organisms and are subject to exquisite levels of control. The carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) can engage in both cis-homophilic (parallel) oligomerization and trans-homophilic (anti-parallel) binding. In this study, we establish that the CEACAM1 transmembrane domain has a propensity to form cis-dimers via the transmembrane-embedded (432)GXXXG(436) motif and that this basal state is overcome when activated calmodulin binds to the CEACAM1 cytoplasmic domain. Although mutation of the (432)GXXXG(436) motif reduced CEACAM1 oligomerization, it did not affect surface localization of the receptor or influence CEACAM1-dependent cellular invasion by the pathogenic Neisseria. The mutation did, however, have a striking effect on CEACAM1-dependent cellular aggregation, increasing both the kinetics of cell-cell association and the size of cellular aggregates formed. CEACAM1 association with tyrosine kinase c-Src and tyrosine phosphatases SHP-1 and SHP-2 was not affected by the (432)GXXXG(436) mutation, consistent with their association with the monomeric form of wild type CEACAM1. Collectively, our results establish that a dynamic oligomer-to-monomer shift in surface-expressed CEACAM1 facilitates trans-homophilic binding and downstream effector signaling.
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21
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Heikal AA. Time-resolved fluorescence anisotropy and fluctuation correlation analysis of major histocompatibility complex class I proteins in fibroblast cells. Methods 2013; 66:283-91. [PMID: 23811298 DOI: 10.1016/j.ymeth.2013.06.023] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2013] [Revised: 06/12/2013] [Accepted: 06/18/2013] [Indexed: 11/26/2022] Open
Abstract
Major histocompatibility complex class I proteins, MHC(I), are expressed in almost all nucleated cells and synthesized in the endoplasmic reticulum (ER). The orientation and mobility of these complexes are crucial in their biological function in the immune system, i.e., the cytosolic pathogen peptides loading and their presentation to T-cell receptors at the plasma membrane, where cell destruction is triggered. Here, we investigate the structural flexibility and associations of GFP-encoded MHC(I) alleles (H2L(d)), namely H2L(d)GFPin and H2L(d)GFPout, in cultured mouse fibroblast cells. Time-resolved fluorescence anisotropy of H2L(d)GFPin in the ER indicates a dominant overall tumbling motion of 56±7 ns (ER), with a fast conformational flexibility, as compared with a restricted rotation of H2L(d)GFPout. At the single-molecule level, the diffusion coefficient of H2L(d)GFPin and H2L(d)GFPout in the ER is (1.8±0.5)×10(-9) and (2.1±0.6)×10(-9) cm(2)/s, respectively, as revealed by fluorescence correlation spectroscopy. A complementary immunoblotting of H2L(d)GFP constructs, isolated from mouse fibroblast cells, reveals band at 75 kDa as compared with 29 kDa of the free EGFP. These real-time dynamics provide new insights into the structural flexibility and intracellular associations of GFP-labeled MHC(I) alleles (H2L(d)) in living cells.
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Affiliation(s)
- Ahmed A Heikal
- Department of Chemistry and Biochemistry, Swenson College of Science and Engineering, University of Minnesota-Duluth, Duluth, MN 55812, USA; Department of Pharmacy Practice and Pharmaceutical Sciences, College of Pharmacy, University of Minnesota-Duluth, Duluth, MN 55812, USA.
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22
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Wang X, Kress A, Brasselet S, Ferrand P. High frame-rate fluorescence confocal angle-resolved linear dichroism microscopy. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2013; 84:053708. [PMID: 23742559 DOI: 10.1063/1.4807318] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Angle-resolved linear dichroism is a recent technique that exploits images recorded using an illumination field whose polarization angle is sequentially rotated during acquisition. It allows to retrieve orientation information of the fluorescent molecules, namely the average orientation angle and the amplitude of the fluctuations around this average. In order to boost up the acquisition speed without sacrificing the axial sectioning, we propose to combine a spinning disk confocal excitation scheme together with an electrooptical polarization switching and a camera acquisition. The polarization distortions induced when passing through the spinning disk system have been quantified and effectively compensated. The signal to noise features of the camera have been analyzed in detail so that the precision of the method can be quantified. The technique has been successfully tested on giant unilamellar vesicles and on living cells labeled with different fluorescent lipid probes, DiIC18 and di-8-ANEPPQ. It was able to acquire precise orientation images at full frame rates in the range of a second, ultimately limited by the fluorophore brightness and the camera sensitivity.
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Affiliation(s)
- Xiao Wang
- Aix-Marseille Université, Institut Fresnel, F-13013 Marseille, France
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23
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Parmryd I, Onfelt B. Consequences of membrane topography. FEBS J 2013; 280:2775-84. [PMID: 23438106 DOI: 10.1111/febs.12209] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2012] [Revised: 01/11/2013] [Accepted: 02/18/2013] [Indexed: 12/28/2022]
Abstract
The surface of mammalian cells is neither smooth nor flat and cells have several times more plasma membrane than the minimum area required to accommodate their shape. We discuss the biological function of this apparent excess membrane that allows the cells to migrate and undergo shape changes and probably plays a role in signal transduction. Methods for studying membrane folding and topography--atomic force microscopy, scanning ion conductance microscopy, fluorescence polarization microscopy and linear dichroism--are described and evaluated. Membrane folding and topography is frequently ignored when interpreting microscopy data. This has resulted in several misconceptions regarding for instance colocalization, membrane organization and molecular clustering. We suggest simple ways to avoid these pitfalls and invoke Occam's razor--that simple explanations are preferable to complex ones. Topography, i.e. deviations from a smooth surface, should always be ruled out as the cause of anomalous data before other explanations are presented.
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Affiliation(s)
- Ingela Parmryd
- Department of Medical Cell Biology, Uppsala University, Sweden.
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24
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Probing the orientational distribution of dyes in membranes through multiphoton microscopy. Biophys J 2013; 103:907-17. [PMID: 23009840 DOI: 10.1016/j.bpj.2012.08.003] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2012] [Revised: 07/23/2012] [Accepted: 08/01/2012] [Indexed: 11/21/2022] Open
Abstract
Numerous dyes are available or under development for probing the structural and functional properties of biological membranes. Exogenous chromophores adopt a range of orientations when bound to membranes, which have a drastic effect on their biophysical behavior. Here, we present a method that employs optical anisotropy data from three polarization-imaging techniques to establish the distribution of orientations adopted by molecules in monolayers and bilayers. The resulting probability density functions, which contain the preferred molecular tilt μ and distribution breadth γ, are more informative than an average tilt angle [φ]. We describe a methodology for the extraction of anisotropy data through an image-processing technology that decreases the error in polarization measurements by about a factor of four. We use this technique to compare di-4-ANEPPS and di-8-ANEPPS, both dipolar dyes, using data from polarized 1-photon, 2-photon fluorescence and second-harmonic generation imaging. We find that di-8-ANEPPS has a lower tilt but the same distributional width. We find the distribution of tilts taken by di-4-ANEPPS in two phospholipid membrane models: giant unilamellar vesicles and water-in-oil droplet monolayers. Both models result in similar distribution functions with average tilts of 52° and 47°, respectively.
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25
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Duboisset J, Ferrand P, He W, Wang X, Rigneault H, Brasselet S. Thioflavine-T and Congo Red reveal the polymorphism of insulin amyloid fibrils when probed by polarization-resolved fluorescence microscopy. J Phys Chem B 2013; 117:784-8. [PMID: 23289901 DOI: 10.1021/jp309528f] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Amyloid fibrils are protein misfolding structures that involve a β-sheet structure and are associated with the pathologies of various neurodegenerative diseases. Here we show that Thioflavine-T and Congo Red, two major dyes used to image fibrils by fluorescence assays, can provide deep structural information when probed by means of polarization-resolved fluorescence microscopy. Unlike fluorescence anisotropy or fluorescence detected linear dichroism imaging, this technique allows to retrieve simultaneously both mean orientation and orientation dispersion of the dye, used here as a reporter of the fibril structure. We have observed that insulin amyloid fibrils exhibit a homogeneous behavior over the fibrils' length, confirming their structural uniformity. In addition, these results reveal the existence of various structures among the observed fibrils' population, in spite of a similar aspect when imaged with conventional fluorescence microscopy. This optical nondestructive technique opens perspectives for in vivo structural analyses or high throughput screening.
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Affiliation(s)
- Julien Duboisset
- Aix Marseille Université, CNRS, Ecole Centrale Marseille, Institut Fresnel, 13013 Marseille, France.
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Atkinson CE, Mattheyses AL, Kampmann M, Simon SM. Conserved spatial organization of FG domains in the nuclear pore complex. Biophys J 2013; 104:37-50. [PMID: 23332057 DOI: 10.1016/j.bpj.2012.11.3823] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2012] [Revised: 10/31/2012] [Accepted: 11/02/2012] [Indexed: 10/27/2022] Open
Abstract
Selective transport through the nuclear pore complex (NPC) requires nucleoporins containing natively unfolded phenylalanine-glycine (FG) domains. Several differing models for their dynamics within the pore have been proposed. We characterize the behavior of the FG nucleoporins in vivo using polarized fluorescence microscopy. Using nucleoporins tagged with green fluorescent protein along their FG domains, we show that some of these proteins are ordered, indicating an overall orientational organization within the NPC. This orientational ordering of the FG domains depends on their specific context within the NPC, but is independent of active transport and cargo load. For most nups, behavior does not depend on the FG motifs. These data support a model whereby local geometry constrains the orientational organization of the FG nups. Intriguingly, homologous yeast and mammalian proteins show conserved behavior, suggesting functional relevance. Our findings have implications for mechanistic models of NPC transport.
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Affiliation(s)
- Claire E Atkinson
- Laboratory of Cellular Biophysics, The Rockefeller University, New York, New York, USA
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27
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Hou Z, Hu Z, Blackwell DJ, Miller TD, Thomas DD, Robia SL. 2-Color calcium pump reveals closure of the cytoplasmic headpiece with calcium binding. PLoS One 2012; 7:e40369. [PMID: 22808146 PMCID: PMC3394785 DOI: 10.1371/journal.pone.0040369] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2012] [Accepted: 06/07/2012] [Indexed: 11/19/2022] Open
Abstract
The sarco(endo)plasmic reticulum calcium ATPase (SERCA) undergoes conformational changes while transporting calcium, but the details of the domain motions are still unclear. The objective of the present study was to measure distances between the cytoplasmic domains of SERCA2a in order to reveal the magnitude and direction of conformational changes. Using fluorescence microscopy of live cells, we measured intramolecular fluorescence resonance energy transfer (FRET) from a donor fluorescent protein fused to the SERCA N-terminus to an acceptor fluorescent protein fused to either the N-, P-, or transmembrane domain. The "2-color" SERCA constructs were catalytically active as indicated by ATPase activity in vitro and Ca uptake in live cells. All constructs exhibited dynamic FRET changes in response to the pump ligands calcium and thapsigargin (Tg). These FRET changes were quantified as an index of SERCA conformational changes. Intramolecular FRET decreased with Tg for the two N-domain fusion sites (at residue 509 or 576), while the P- (residue 661) and TM-domain (C-terminus) fusions showed increased FRET with Tg. The magnitude of the Tg-dependent conformational change was not decreased by coexpression of phospholamban (PLB), nor did PLB slow the kinetics of Tg binding. FRET in ionophore-permeabilized cells was lower in EGTA than in saturating calcium for all constructs, indicating a decrease in domain separation distance with the structural transition from E2 (Ca-free) to E1 (Ca-bound). The data suggest closure of the cytoplasmic headpiece with Ca-binding. The present results provide insight into the structural dynamics of the Ca-ATPase. In addition, the 2-color SERCA constructs developed for this study may be useful for evaluating candidate small molecule regulators of Ca uptake activity.
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Affiliation(s)
- Zhanjia Hou
- Department of Cell and Molecular Physiology, Loyola University Chicago, Maywood, Illinois, United States of America
| | - Zhihong Hu
- Department of Cell and Molecular Physiology, Loyola University Chicago, Maywood, Illinois, United States of America
| | - Daniel J. Blackwell
- Department of Cell and Molecular Physiology, Loyola University Chicago, Maywood, Illinois, United States of America
| | - Tyler D. Miller
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota, United States of America
| | - David D. Thomas
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota, United States of America
| | - Seth L. Robia
- Department of Cell and Molecular Physiology, Loyola University Chicago, Maywood, Illinois, United States of America
- * E-mail:
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28
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Brasselet S, Ferrand P, Kress A, Wang X, Ranchon H, Gasecka A. Imaging Molecular Order in Cell Membranes by Polarization-Resolved Fluorescence Microscopy. SPRINGER SERIES ON FLUORESCENCE 2012. [DOI: 10.1007/4243_2012_51] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
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DeMay BS, Noda N, Gladfelter AS, Oldenbourg R. Rapid and quantitative imaging of excitation polarized fluorescence reveals ordered septin dynamics in live yeast. Biophys J 2011; 101:985-94. [PMID: 21843491 DOI: 10.1016/j.bpj.2011.07.008] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2011] [Revised: 07/06/2011] [Accepted: 07/08/2011] [Indexed: 10/17/2022] Open
Abstract
We report an imaging method for fast, sensitive analysis of the orientation of fluorescent molecules by employing a liquid-crystal based universal polarizer in the optical path of a wide-field light microscope. We developed specific acquisition and processing algorithms for measuring the anisotropy and for correcting artifacts caused by fluorescence bleaching, background light, and differential transmission of optical components. We call this approach the Fluorescence LC-PolScope and we used it to analyze the architectural dynamics of septin-green fluorescent protein (septin-GFP) constructs in the neck region of budding yeast. We describe three different states of highly anisotropic septin arrays in which the prevailing orientation of GFP dipoles was either parallel or perpendicular to the mother-bud axis. The transitions between these ordered states were characterized by transient isotropic states. To analyze the patterns of polarized fluorescence, we modeled the alignment of septin-GFP constructs in different stages of septin ring formation. Based on our model, our experimental data are consistent with the formation of paired rather than single filaments and the axis of the α-helical septin terminus linked to a GFP molecule is likely oriented normal to the cell surface. The Fluorescence LC-PolScope combines the molecular specificity of fluorescence tagging with the structural specificity of polarized light analysis.
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Affiliation(s)
- Bradley S DeMay
- Department of Biological Sciences, Dartmouth College, Hanover, New Hampshire, USA
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31
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Probing orientational behavior of MHC class I protein and lipid probes in cell membranes by fluorescence polarization-resolved imaging. Biophys J 2011; 101:468-76. [PMID: 21767500 DOI: 10.1016/j.bpj.2011.05.021] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2010] [Revised: 05/06/2011] [Accepted: 05/11/2011] [Indexed: 11/20/2022] Open
Abstract
Steady-state polarization-resolved fluorescence imaging is used to analyze the molecular orientational order behavior of rigidly labeled major histocompatibility complex class I (MHC I) proteins and lipid probes in cell membranes of living cells. These fluorescent probes report the orientational properties of proteins and their surrounding lipid environment. We present a statistical study of the molecular orientational order, modeled as the width of the angular distribution of the molecules, for the proteins in the cell endomembrane and plasma membrane, as well as for the lipid probes in the plasma membrane. We apply this methodology on cells after treatments affecting the actin and microtubule networks. We find in particular opposite orientational order changes of proteins and lipid probes in the plasma membrane as a response to the cytoskeleton disruption. This suggests that MHC I orientational order is governed by its interaction with the cytoskeleton, whereas the plasma membrane lipid order is governed by the local cell membrane morphology.
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Nayak CR, Rutenberg AD. Quantification of fluorophore copy number from intrinsic fluctuations during fluorescence photobleaching. Biophys J 2011; 101:2284-93. [PMID: 22067169 DOI: 10.1016/j.bpj.2011.09.032] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2011] [Revised: 09/17/2011] [Accepted: 09/21/2011] [Indexed: 10/15/2022] Open
Abstract
We present a theoretical technique for quantifying the cellular copy-number of fluorophores that relies on the random nature of the photobleaching process. Our approach does not require single-molecule sensitivity, and therefore can be used with commonly used epifluorescence microscopes. Fluctuations arising from photobleaching can be used to estimate the proportionality between fluorescence intensity and copy-number, which can then be used with subsequent intensity measurements to estimate copy-number. We calculate the statistical errors of our approach and verify them with stochastic simulations. By using fluctuations over the entire photobleaching process, we obtain significantly smaller errors than previous approaches that have used fluctuations arising from cytoplasmic proteins partitioning during cellular division. From the time-dependence of the fluctuations as photobleaching proceeds, we can discriminate between desired photobleach fluctuations and background noise or photon shot noise. Our approach does not require cellular division and the photobleaching rate sets a timescale that is adjustable with respect to cellular processes. We hope that our approach will now be applied experimentally.
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Affiliation(s)
- Chitra R Nayak
- Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, Canada
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33
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Ehrlich N, Christensen AL, Stamou D. Fluorescence Anisotropy Based Single Liposome Assay to Measure Molecule–Membrane Interactions. Anal Chem 2011; 83:8169-76. [DOI: 10.1021/ac2017234] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Affiliation(s)
- Nicky Ehrlich
- Bio-Nanotechnology Laboratory, Department of Neuroscience and Pharmacology, ‡Nano-Science Center, and §Lundbeck Foundation Center for Biomembranes in Nanomedicine, University of Copenhagen, 2100 Copenhagen, Denmark
| | - Andreas L. Christensen
- Bio-Nanotechnology Laboratory, Department of Neuroscience and Pharmacology, ‡Nano-Science Center, and §Lundbeck Foundation Center for Biomembranes in Nanomedicine, University of Copenhagen, 2100 Copenhagen, Denmark
| | - Dimitrios Stamou
- Bio-Nanotechnology Laboratory, Department of Neuroscience and Pharmacology, ‡Nano-Science Center, and §Lundbeck Foundation Center for Biomembranes in Nanomedicine, University of Copenhagen, 2100 Copenhagen, Denmark
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Ganguly S, Clayton AHA, Chattopadhyay A. Organization of higher-order oligomers of the serotonin₁(A) receptor explored utilizing homo-FRET in live cells. Biophys J 2011; 100:361-8. [PMID: 21244832 DOI: 10.1016/j.bpj.2010.12.3692] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2010] [Revised: 11/16/2010] [Accepted: 12/08/2010] [Indexed: 10/18/2022] Open
Abstract
The serotonin₁(A) receptor is a representative member of the GPCR superfamily and serves as an important drug target. The possible role of GPCR oligomerization in receptor function is an active area of research. We monitored the oligomerization state of serotonin₁(A) receptors using homo-FRET and fluorescence lifetime measurements. Homo-FRET is estimated by a reduction in fluorescence anisotropy and provides a superior approach for exploring oligomerization. In addition, homo-FRET offers the possibility of detecting higher-order oligomers. On the basis of an observed increase in fluorescence anisotropy upon progressive photobleaching and analysis of the difference between the extrapolated anisotropy and the predicted anisotropy of an immobile monomer, we propose the presence of constitutive oligomers of the serotonin₁(A) receptor. To the best of our knowledge, these results constitute the first report of higher-order oligomers for the serotonin₁(A) receptor. We further show that cholesterol depletion and antagonist treatment result in a reduced population of higher-order oligomers. In contrast, agonist stimulation and destabilization of the actin cytoskeleton lead to an increased contribution from higher oligomers. These results provide novel insight into the oligomerization status of the serotonin₁(A) receptor that could enhance the ability to design better therapeutic strategies to combat diseases related to malfunctioning of GPCRs.
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Affiliation(s)
- Sourav Ganguly
- Centre for Cellular and Molecular Biology, Hyderabad, India
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35
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Mapping the orientation of nuclear pore proteins in living cells with polarized fluorescence microscopy. Nat Struct Mol Biol 2011; 18:643-9. [PMID: 21499242 PMCID: PMC3109191 DOI: 10.1038/nsmb.2056] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2010] [Accepted: 02/14/2011] [Indexed: 12/12/2022]
Abstract
The nuclear pore complex (NPC) perforates the nuclear envelope to facilitate selective transport between nucleus and cytoplasm. The NPC is composed of multiple copies of ∼30 different proteins, termed nucleoporins, whose arrangement within the NPC is an important unsolved puzzle in structural biology. Various alternative models for NPC architecture have been proposed but not tested experimentally in intact NPCs. We present a method using polarized fluorescence microscopy to investigate nucleoporin orientation in live yeast and mammalian cells. Our results support an arrangement of both yeast Nic96 and human Nup133-Nup107 in which their long axes are approximately parallel to the nuclear envelope plane. The method we developed can complement X-ray crystallography and electron microscopy to generate a high-resolution map of the entire NPC, and may be able to monitor nucleoporin rearrangements during nucleocytoplasmic transport and NPC assembly. This strategy can also be adapted for other macromolecular machines.
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36
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Abstract
Ligand binding to cell membrane receptors sets off a series of protein interactions that convey the nuances of ligand identity to the cell interior. The information may be encoded in conformational changes, the interaction kinetics and, in the case of multichain immunoreceptors, by chain rearrangements. The signals may be modulated by dynamic compartmentalization of the cell membrane, cellular architecture, motility, and activation-all of which are difficult to reconstitute for studies of receptor signaling in vitro. In this paper, we will discuss how protein interactions in general and receptor signaling in particular can be studied in living cells by different fluorescence imaging techniques. Particularly versatile are methods that exploit Förster resonance energy transfer (FRET), which is exquisitely sensitive to the nanometer-range proximity and orientation between fluorophores. Fluorescence correlation microscopy (FCM) can provide complementary information about the stoichiometry and diffusion kinetics of large complexes, while bimolecular fluorescence complementation (BiFC) and other complementation techniques can capture transient interactions. A continuing challenge is extracting from the imaging data the quantitative information that is necessary to verify different models of signal transduction.
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Affiliation(s)
- Tomasz Zal
- Department of Immunology, University of Texas, MD Anderson Cancer Center, Houston TX, USA
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37
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Mattheyses AL, Kampmann M, Atkinson CE, Simon SM. Fluorescence anisotropy reveals order and disorder of protein domains in the nuclear pore complex. Biophys J 2011; 99:1706-17. [PMID: 20858414 DOI: 10.1016/j.bpj.2010.06.075] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2010] [Revised: 06/29/2010] [Accepted: 06/30/2010] [Indexed: 01/21/2023] Open
Abstract
We present a new approach for studying individual protein domains within the nuclear pore complex (NPC) using fluorescence polarization microscopy. The NPC is a large macromolecular complex, the size and complexity of which presents experimental challenges. Using fluorescence anisotropy and exploiting the symmetry of the NPC and its organization in the nuclear envelope, we have resolved order and disorder of individual protein domains. Fluorescently tagging specific domains of individual nucleoporins revealed both rigid and flexible domains: the tips of the FG domains are disordered, whereas the NPC-anchored domains are ordered. Our technique allows the collection of structural information in vivo, providing the ability to probe the organization of protein domains within the NPC. This has particular relevance for the FG domain nucleoporins, which are crucial for nucleocytoplasmic transport.
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Affiliation(s)
- Alexa L Mattheyses
- Laboratory of Cellular Biophysics, The Rockefeller University, New York, New York, USA
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38
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Bader AN, Hoetzl S, Hofman EG, Voortman J, van Bergen en Henegouwen PMP, van Meer G, Gerritsen HC. Homo‐FRET Imaging as a Tool to Quantify Protein and Lipid Clustering. Chemphyschem 2010; 12:475-83. [DOI: 10.1002/cphc.201000801] [Citation(s) in RCA: 73] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2010] [Indexed: 11/11/2022]
Affiliation(s)
- Arjen N. Bader
- Department of Molecular Biophysics, Universiteit Utrecht, Princetonplein 1, 3584 CC Utrecht (The Netherlands), Fax: (+31) 30 253 2706
| | - Sandra Hoetzl
- Department of Membrane Enzymology, Universiteit Utrecht, Padualaan 8, 3584 CH Utrecht (The Netherlands)
| | - Erik G. Hofman
- Department of Cellular Dynamics, Universiteit Utrecht, Padualaan 8, 3584 CH Utrecht (The Netherlands)
| | - Jarno Voortman
- Department of Cellular Dynamics, Universiteit Utrecht, Padualaan 8, 3584 CH Utrecht (The Netherlands)
| | | | - Gerrit van Meer
- Department of Membrane Enzymology, Universiteit Utrecht, Padualaan 8, 3584 CH Utrecht (The Netherlands)
| | - Hans C. Gerritsen
- Department of Molecular Biophysics, Universiteit Utrecht, Princetonplein 1, 3584 CC Utrecht (The Netherlands), Fax: (+31) 30 253 2706
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39
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Burghardt TP, Ajtai K. Single-molecule fluorescence characterization in native environment. Biophys Rev 2010; 2:159-167. [PMID: 21179385 PMCID: PMC3004222 DOI: 10.1007/s12551-010-0038-z] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2010] [Accepted: 10/12/2010] [Indexed: 11/29/2022] Open
Abstract
Single-molecule detection (SMD) with fluorescence is a widely used microscopic technique for biomolecule structure and function characterization. The modern light microscope with high numerical aperture objective and sensitive CCD camera can image the brightly emitting organic and fluorescent protein tags with reasonable time resolution. Single-molecule imaging gives an unambiguous bottom-up biomolecule characterization that avoids the "missing information" problem characteristic of ensemble measurements. It has circumvented the diffraction limit by facilitating single-particle localization to ~1 nm. Probes developed specifically for SMD applications extend the advantages of single-molecule imaging to high probe density regions of cells and tissues. These applications perform under conditions resembling the native biomolecule environment and have been used to detect both probe position and orientation. Native, high density SMD may have added significance if molecular crowding impacts native biomolecule behavior as expected inside the cell.
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Affiliation(s)
- Thomas P. Burghardt
- Department of Biochemistry and Molecular Biology, Mayo Clinic Rochester, Rochester, MN 55905 USA
- Department of Physiology and Biomedical Engineering, Mayo Clinic Rochester, Rochester, MN 55905 USA
| | - Katalin Ajtai
- Department of Biochemistry and Molecular Biology, Mayo Clinic Rochester, Rochester, MN 55905 USA
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40
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Spector DL, Goldman RD. Constructing and expressing fluorescent protein fusions. Cold Spring Harb Protoc 2010; 2010:pdb.top87. [PMID: 21041402 DOI: 10.1101/pdb.top87] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Fluorescent protein fusions (FPFs) have been used to address a wide range of questions in individual cells as well as in specific tissues of a particular organism. However, investigators must take extreme care when using FPFs to ensure that the resultant fusion protein is expressed at or close to the endogenous level of the parent protein, and also that it is full length, localizes correctly, and behaves normally once incorporated in the cell. Because the molecular mass of the fluorescent protein (FP) itself is 27 kDa, one must consider the potential effects of placing such a large tag in association with a protein under investigation. This article discusses how these goals can be achieved and provides examples to assist the investigator in designing and implementing experiments using FPFs.
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41
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Chudakov DM, Matz MV, Lukyanov S, Lukyanov KA. Fluorescent proteins and their applications in imaging living cells and tissues. Physiol Rev 2010; 90:1103-63. [PMID: 20664080 DOI: 10.1152/physrev.00038.2009] [Citation(s) in RCA: 925] [Impact Index Per Article: 66.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Green fluorescent protein (GFP) from the jellyfish Aequorea victoria and its homologs from diverse marine animals are widely used as universal genetically encoded fluorescent labels. Many laboratories have focused their efforts on identification and development of fluorescent proteins with novel characteristics and enhanced properties, resulting in a powerful toolkit for visualization of structural organization and dynamic processes in living cells and organisms. The diversity of currently available fluorescent proteins covers nearly the entire visible spectrum, providing numerous alternative possibilities for multicolor labeling and studies of protein interactions. Photoactivatable fluorescent proteins enable tracking of photolabeled molecules and cells in space and time and can also be used for super-resolution imaging. Genetically encoded sensors make it possible to monitor the activity of enzymes and the concentrations of various analytes. Fast-maturing fluorescent proteins, cell clocks, and timers further expand the options for real time studies in living tissues. Here we focus on the structure, evolution, and function of GFP-like proteins and their numerous applications for in vivo imaging, with particular attention to recent techniques.
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42
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Jameson DM, Ross JA. Fluorescence polarization/anisotropy in diagnostics and imaging. Chem Rev 2010; 110:2685-708. [PMID: 20232898 DOI: 10.1021/cr900267p] [Citation(s) in RCA: 398] [Impact Index Per Article: 28.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Affiliation(s)
- David M Jameson
- Department of Cell and Molecular Biology, John A. Burns School of Medicine, University of Hawaii, 651 Ilalo Street, BSB222, Honolulu, Hawaii 96813, USA.
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43
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Rizzo MA, Davidson MW, Piston DW. Fluorescent protein tracking and detection: applications using fluorescent proteins in living cells. Cold Spring Harb Protoc 2010; 2009:pdb.top64. [PMID: 20150101 DOI: 10.1101/pdb.top64] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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44
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Gasecka A, Han TJ, Favard C, Cho BR, Brasselet S. Quantitative imaging of molecular order in lipid membranes using two-photon fluorescence polarimetry. Biophys J 2010; 97:2854-62. [PMID: 19917241 DOI: 10.1016/j.bpj.2009.08.052] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2009] [Revised: 08/18/2009] [Accepted: 08/28/2009] [Indexed: 11/26/2022] Open
Abstract
We present a polarimetric two-photon microscopy technique to quantitatively image the local static molecular orientational behavior in lipid and cell membranes. This approach, based on a tunable excitation polarization state complemented by a polarized readout, is easily implementable and does not require hypotheses on the molecular angular distribution such as its mean orientation, which is a main limitation in traditional fluorescence anisotropy measurements. The method is applied to the investigation of the molecular angular distribution in giant unilamellar vesicles formed by liquid-ordered and liquid-disordered micro-domains, and in COS-7 cell membranes. The highest order contrast between ordered and disordered domains is obtained for dyes locating within the membrane acyl chains.
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Affiliation(s)
- Alicja Gasecka
- Institut Fresnel-MOSAIC Group, UMR 6133, Centre National de la Recherche Scientifique, Université Aix Marseille III, Domaine Universitaire St Jerome, Marseille, France
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Roda A, Guardigli M, Michelini E, Mirasoli M. Nanobioanalytical luminescence: Förster-type energy transfer methods. Anal Bioanal Chem 2008; 393:109-23. [DOI: 10.1007/s00216-008-2435-8] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2008] [Revised: 09/22/2008] [Accepted: 09/23/2008] [Indexed: 12/21/2022]
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Kiss E, Nagy P, Balogh A, Szöllosi J, Matkó J. Cytometry of raft and caveola membrane microdomains: from flow and imaging techniques to high throughput screening assays. Cytometry A 2008; 73:599-614. [PMID: 18473380 DOI: 10.1002/cyto.a.20572] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
The evolutionarily developed microdomain structure of biological membranes has gained more and more attention in the past decade. The caveolin-free "membrane rafts," the caveolin-expressing rafts (caveolae), as well as other membrane microdomains seem to play an essential role in controlling and coordinating cell-surface molecular recognition, internalization/endocytosis of the bound molecules or pathogenic organisms and in regulation of transmembrane signal transduction processes. Therefore, in many research fields (e.g. neurobiology and immunology), there is an ongoing need to understand the nature of these microdomains and to quantitatively characterize their lipid and protein composition under various physiological and pathological conditions. Flow and image cytometry offer many sophisticated and routine tools to study these questions. In this review, we give an overview of the past efforts to detect and characterize these membrane microdomains by the use of classical cytometric technologies, and finally we will discuss the results and perspectives of a new line of raft cytometry, the "high throughput screening assays of membrane microdomains," based on "lipidomic" and "proteomic" approaches.
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Affiliation(s)
- Endre Kiss
- Immunology Research Group of the Hungarian Academy of Sciences at Eötvös Loránd University, Budapest, Hungary
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Winters DL, Autry JM, Svensson B, Thomas DD. Interdomain fluorescence resonance energy transfer in SERCA probed by cyan-fluorescent protein fused to the actuator domain. Biochemistry 2008; 47:4246-56. [PMID: 18338856 DOI: 10.1021/bi702089j] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We have used a biosynthetically incorporated fluorescent probe to monitor domain movements involved in ion transport by the sarcoendoplasmic reticulum Ca-ATPase (SERCA) from rabbit fast-twitch skeletal muscle. X-ray crystal structures suggest that the nucleotide-binding (N) and actuator (A) domains of SERCA move apart by several nanometers upon Ca binding. To test this hypothesis, cDNA constructs were created to fuse cyan-fluorescent protein (CFP) to the N terminus of SERCA (A domain). This CFP-SERCA fluorescent fusion protein retained activity when expressed in Sf21 insect cells using the baculovirus system. Fluorescence resonance energy transfer (FRET) was used to monitor the A-N interdomain distance for CFP-SERCA selectively labeled with fluorescein isothiocyanate (FITC) at Lys 515 in the N domain. At low [Ca (2+)] (E2 biochemical state), the measured FRET efficiency between CFP (donor in A domain) and FITC (acceptor in N domain) was 0.34 +/- 0.03, indicating a mean distance of 61.6 +/- 2.0 A between probes on the two domains. An increase of [Ca (2+)] to 0.1 mM (E1-Ca biochemical state) decreased the FRET efficiency by 0.06 +/- 0.03, indicating an increase in the mean distance by 3.0 +/- 1.2 A. Quantitative molecular modeling of dual-labeled SERCA, including an accurate calculation of the orientation factor, shows that the FRET data observed in the absence of Ca is consistent with the E2 crystal structure, but the increase in distance (decrease in FRET) induced by Ca is much less than predicted by the E1 crystal structure. We conclude that the E1 crystal structure does not reflect the predominant structure of SERCA under physiological conditions in a functional membrane bilayer.
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Affiliation(s)
- Deborah L Winters
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA
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Zal T. Visualization of protein interactions in living cells. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2008; 640:183-97. [PMID: 19065792 PMCID: PMC5788009 DOI: 10.1007/978-0-387-09789-3_14] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/09/2023]
Abstract
Ligand binding to cell membrane receptors sets off a series of protein interactions that convey the nuances ofligand identity to the cell interior. The information may be encoded in conformational changes, the interaction kinetics and, in the case of multichain immunoreceptors, by chain rearrangements. The signals may be modulated by dynamic compartmentalization of the cell membrane, cellular architecture, motility, and activation--all of which are difficult to reconstitute for studies of receptor signaling in vitro. In this chapter, we will discuss how protein interactions in general and receptor signaling in particular can be studied in living cells by different fluorescence imaging techniques. Particularly versatile are methods that exploit Förster resonance energy transfer (FRET), which is exquisitely sensitive to the nanometer-range proximity and orientation between fluorophores. Fluorescence correlation microscopy (FCM) can provide complementary information about the stoichiometry and diffusion kinetics of large complexes, while bimolecular fluorescence complementation (BiFC) and other complementation techniques can capture transient interactions. A continuing challenge is extracting from the imaging data the quantitative information that is necessary to verify different models of signal transduction.
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Affiliation(s)
- Tomasz Zal
- Department of Immunology, University of Texas, MD Anderson Cancer Center, Unit 902, 7455 Fannin, Houston TX, USA.
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Burghardt TP, Ajtai K, Chan DK, Halstead MF, Li J, Zheng Y. GFP-tagged regulatory light chain monitors single myosin lever-arm orientation in a muscle fiber. Biophys J 2007; 93:2226-39. [PMID: 17513376 PMCID: PMC1959555 DOI: 10.1529/biophysj.107.107433] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2007] [Accepted: 05/14/2007] [Indexed: 11/18/2022] Open
Abstract
Myosin is the molecular motor in muscle-binding actin and executing a power stroke by rotating its lever arm through an angle of approximately 70 degrees to translate actin against resistive force. A green fluorescent protein (GFP)-tagged human cardiac myosin regulatory light chain (HCRLC) was constructed to study in situ lever arm orientation one molecule at a time by polarized fluorescence emitted from the GFP probe. The recombinant protein physically and functionally replaced the native RLC on myosin lever arms in the thick filaments of permeabilized skeletal muscle fibers. Detecting single molecules in fibers where myosin concentration reaches 300 microM is accomplished using total internal reflection fluorescence microscopy. With total internal reflection fluorescence, evanescent field excitation, supercritical angle fluorescence detection, and CCD detector pixel size limits detection volume to just a few attoliters. Data analysis manages both the perturbing effect of the TIR interface on probe emission and the effect of high numerical aperture collection of light. The natural myosin concentration gradient in a muscle fiber allows observation of fluorescence polarization from C-term GFP-tagged HCRLC exchanged myosin from regions in the thick filament containing low and high myosin concentrations. In rigor, cross-bridges at low concentration at the end of the thick filament maintain GFP dipole moments at two distinct polar angles relative to the fiber symmetry axis. The lower angle, where the dipole is nearly parallel to fiber axis, is more highly populated than the alternative, larger angle. Cross-bridges at higher concentration in the center of the thick filament are oriented in a homogeneous band at approximately 45 degrees to the fiber axis. The data suggests molecular crowding impacts myosin conformation, implying mutual interactions between cross-bridges alter how the muscle generates force. The GFP-tagged RLC is a novel probe to assess single-lever-arm orientation characteristics in situ.
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Affiliation(s)
- Thomas P Burghardt
- Biochemistry and Molecular Biology, Mayo Clinic College of Medicine, 200 First Street SW, Rochester, MN 55905, USA.
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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: 589] [Impact Index Per Article: 34.6] [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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