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van Zanten TS, S GP, Mayor S. Quantitative fluorescence emission anisotropy microscopy for implementing homo-fluorescence resonance energy transfer measurements in living cells. Mol Biol Cell 2023; 34:tp1. [PMID: 37144969 DOI: 10.1091/mbc.e22-09-0446] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/06/2023] Open
Abstract
Quantitative fluorescence emission anisotropy microscopy reveals the organization of fluorescently labeled cellular components and allows their characterization in terms of changes in either rotational diffusion or homo-Förster's energy transfer characteristics in living cells. These properties provide insights into molecular organization, such as orientation, confinement, and oligomerization in situ. Here we elucidate how quantitative measurements of anisotropy using multiple microscope systems may be made by bringing out the main parameters that influence the quantification of fluorescence emission anisotropy. We focus on a variety of parameters that contribute to errors associated with the measurement of emission anisotropy in a microscope. These include the requirement for adequate photon counts for the necessary discrimination of anisotropy values, the influence of extinction ratios of the illumination source, the detector system, the role of numerical aperture, and excitation wavelength. All these parameters also affect the ability to capture the dynamic range of emission anisotropy necessary for quantifying its reduction due to homo-FRET and other processes. Finally, we provide easily implementable tests to assess whether homo-FRET is a cause for the observed emission depolarization.
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Affiliation(s)
- Thomas S van Zanten
- Cell Biology Group, National Centre for Biological Sciences, UAS-GKVK Campus, Tata Institute for Fundamental Research, Bangalore 560065, India
| | - Greeshma Pradeep S
- Cell Biology Group, National Centre for Biological Sciences, UAS-GKVK Campus, Tata Institute for Fundamental Research, Bangalore 560065, India
| | - Satyajit Mayor
- Cell Biology Group, National Centre for Biological Sciences, UAS-GKVK Campus, Tata Institute for Fundamental Research, Bangalore 560065, India
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2
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Chen H, Chen TY. Probing Oxidant Effects on Superoxide Dismutase 1 Oligomeric States in Live Cells Using Single-Molecule Fluorescence Anisotropy. CHEMICAL & BIOMEDICAL IMAGING 2023; 1:49-57. [PMID: 37122833 PMCID: PMC10131266 DOI: 10.1021/cbmi.3c00002] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/04/2023] [Revised: 02/03/2023] [Accepted: 02/08/2023] [Indexed: 05/02/2023]
Abstract
The protein Cu/Zn superoxide dismutase (SOD1) is known to function as a dimer, but its concentration in cells (∼50 μM) and the dimerization constant (K d of 500 μM) results suggest that it exists in a monomer-dimer equilibrium. It is unclear how the oligomeric state of SOD1 changes when cells are initially exposed to high levels of extracellular oxidative stress. To address this problem, we introduced the single-molecule fluorescence anisotropy (smFA) assay to explore SOD1 oligomeric states in live COS7 cells. smFA specifically probes the fluorescence polarization changes caused by molecular rotations where the fast-rotating molecules (either due to smaller hydrodynamic volume or less viscous environments) deteriorate the emission polarization and thus lower the anisotropy. After validating that smFA is effective in distinguishing monomeric and dimeric fluorescence proteins, we overexpressed SOD1 in live COS7 cells and investigated how its oligomeric state changes under basal, 2 h, and 24 h 100 μM H2O2 treatments. We found that treating cells with H2O2 promotes SOD1 dimerization and decreases cellular viscosity in 2 h. Interestingly, prolonged H2O2 treatments show similar results as the basal conditions, indicating that cells return to a steady state similar to the basal state after 24 h, despite the presence of H2O2. Our results demonstrate that SOD1 changes its oligomeric state equilibrium in response to extracellular oxidative stresses. smFA will open new opportunities to explore the relationship between the SOD1 oligomer state and its H2O2-based signaling and transcription regulation roles.
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Affiliation(s)
- Huanhuan Chen
- Department of Chemistry, University
of Houston, Houston, Texas 77204, United States
| | - Tai-Yen Chen
- Department of Chemistry, University
of Houston, Houston, Texas 77204, United States
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3
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Silberberg M, Grecco HE. Robust and unbiased estimation of the background distribution for automated quantitative imaging. JOURNAL OF THE OPTICAL SOCIETY OF AMERICA. A, OPTICS, IMAGE SCIENCE, AND VISION 2023; 40:C8-C15. [PMID: 37132946 DOI: 10.1364/josaa.477468] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Background estimation is the first step in quantitative analysis of images. It has an impact on all subsequent analyses, in particular for segmentation and calculation of ratiometric quantities. Most methods recover only a single value such as the median or yield a biased estimation in non-trivial cases. We introduce, to our knowledge, the first method to recover an unbiased estimation of background distribution. It leverages the lack of local spatial correlation in background pixels to robustly select a subset that accurately represents the background. The resulting background distribution can be used to test for foreground membership of individual pixels or estimate confidence intervals in derived quantities.
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4
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Habif M, Corbat AA, Silberberg M, Grecco HE. CASPAM: A Triple-Modality Biosensor for Multiplexed Imaging of Caspase Network Activity. ACS Sens 2021; 6:2642-2653. [PMID: 34191492 DOI: 10.1021/acssensors.1c00554] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Understanding signal propagation across biological networks requires to simultaneously monitor the dynamics of several nodes to uncover correlations masked by inherent intercellular variability. To monitor the enzymatic activity of more than two components over short time scales has proven challenging. Exploiting the narrow spectral width of homo-FRET-based biosensors, up to three activities can be imaged through fluorescence polarization anisotropy microscopy. We introduce Caspase Activity Sensor by Polarization Anisotropy Multiplexing (CASPAM) a single-plasmid triple-modality reporter of key nodes of the apoptotic network. Apoptosis provides an ideal molecular framework to study interactions between its three composing pathways (intrinsic, extrinsic, and effector). We characterized the biosensor performance and demonstrated the advantages that equimolar expression has in both simplifying experimental procedure and reducing observable variation, thus enabling robust data-driven modeling. Tools like CASPAM become essential to analyze molecular pathways where multiple nodes need to be simultaneously monitored.
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Affiliation(s)
- Martín Habif
- Department of Physics, FCEN, University of Buenos Aires and IFIBA, CONICET, Buenos Aires C1428EHA, Argentina
| | - Agustín A. Corbat
- Department of Physics, FCEN, University of Buenos Aires and IFIBA, CONICET, Buenos Aires C1428EHA, Argentina
| | - Mauro Silberberg
- Department of Physics, FCEN, University of Buenos Aires and IFIBA, CONICET, Buenos Aires C1428EHA, Argentina
| | - Hernán E. Grecco
- Department of Physics, FCEN, University of Buenos Aires and IFIBA, CONICET, Buenos Aires C1428EHA, Argentina
- Department of Systemic Cell Biology, Max Planck Institute of Molecular Physiology, Dortmund 44227, Germany
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5
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Chen L, Chen X, Yang X, He C, Wang M, Xi P, Gao J. Advances of super-resolution fluorescence polarization microscopy and its applications in life sciences. Comput Struct Biotechnol J 2020; 18:2209-2216. [PMID: 32952935 PMCID: PMC7476067 DOI: 10.1016/j.csbj.2020.06.038] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2020] [Revised: 06/20/2020] [Accepted: 06/22/2020] [Indexed: 11/29/2022] Open
Abstract
Fluorescence polarization microscopy (FPM) analyzes both intensity and orientation of fluorescence dipole, and reflects the structural specificity of target molecules. It has become an important tool for studying protein organization, orientational order, and structural changes in cells. However, suffering from optical diffraction limit, conventional FPM has low orientation resolution and observation accuracy, as the polarization information is averaged by multiple fluorescent molecules within a diffraction-limited volume. Recently, novel super-resolution FPMs have been developed to break the diffraction barrier. In this review, we will introduce the recent progress to achieve sub-diffraction determination of dipole orientation. Biological applications, based on polarization analysis of fluorescence dipole, are also summarized, with focus on chromophore-target molecule interaction and molecular organization.
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Affiliation(s)
- Long Chen
- Department of Automation, Tsinghua University, 100084 Beijing, China.,MOE Key Laboratory of Bioinformatics; Bioinformatics Division, Center for Synthetic & Systems Biology, BNRist; Center for Synthetic & Systems Biology, Tsinghua University, 100084 Beijing, China
| | - Xingye Chen
- Department of Automation, Tsinghua University, 100084 Beijing, China
| | - Xusan Yang
- Department of Biomedical Engineering, College of Engineering, Peking University, Beijing 100871, China
| | - Chao He
- Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, UK
| | - Miaoyan Wang
- Department of Biomedical Engineering, College of Engineering, Peking University, Beijing 100871, China
| | - Peng Xi
- Department of Biomedical Engineering, College of Engineering, Peking University, Beijing 100871, China
| | - Juntao Gao
- Department of Automation, Tsinghua University, 100084 Beijing, China.,MOE Key Laboratory of Bioinformatics; Bioinformatics Division, Center for Synthetic & Systems Biology, BNRist; Center for Synthetic & Systems Biology, Tsinghua University, 100084 Beijing, China
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6
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Heckmeier PJ, Agam G, Teese MG, Hoyer M, Stehle R, Lamb DC, Langosch D. Determining the Stoichiometry of Small Protein Oligomers Using Steady-State Fluorescence Anisotropy. Biophys J 2020; 119:99-114. [PMID: 32553128 DOI: 10.1016/j.bpj.2020.05.025] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2019] [Revised: 04/24/2020] [Accepted: 05/04/2020] [Indexed: 11/19/2022] Open
Abstract
A large fraction of soluble and membrane-bound proteins exists as non-covalent dimers, trimers, and higher-order oligomers. The experimental determination of the oligomeric state or stoichiometry of proteins remains a nontrivial challenge. In one approach, the protein of interest is genetically fused to green fluorescent protein (GFP). If a fusion protein assembles into a non-covalent oligomeric complex, exciting their GFP moiety with polarized fluorescent light elicits homotypic Förster resonance energy transfer (homo-FRET), in which the emitted radiation is partially depolarized. Fluorescence depolarization is associated with a decrease in fluorescence anisotropy that can be exploited to calculate the oligomeric state. In a classical approach, several parameters obtained through time-resolved and steady-state anisotropy measurements are required for determining the stoichiometry of the oligomers. Here, we examined novel approaches in which time-resolved measurements of reference proteins provide the parameters that can be used to interpret the less expensive steady-state anisotropy data of candidates. In one approach, we find that using average homo-FRET rates (kFRET), average fluorescence lifetimes (τ), and average anisotropies of those fluorophores that are indirectly excited by homo-FRET (rET) do not compromise the accuracy of calculated stoichiometries. In the other approach, fractional photobleaching of reference oligomers provides a novel parameter a whose dependence on stoichiometry allows one to quantitatively interpret the increase of fluorescence anisotropy seen after photobleaching the candidates. These methods can at least reliably distinguish monomers from dimers and trimers.
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Affiliation(s)
- Philipp J Heckmeier
- Center for Integrated Protein Science Munich (CIPSM), Lehrstuhl für Chemie der Biopolymere, Technische Universität München, Freising, Germany
| | - Ganesh Agam
- Physical Chemistry, Department of Chemistry, Center for Nano Science (CENS), Center for Integrated Protein Science (CIPSM) and Nanosystems Initiative München (NIM), Ludwig-Maximilians-Universität Munich, Munich, Germany
| | - Mark G Teese
- Center for Integrated Protein Science Munich (CIPSM), Lehrstuhl für Chemie der Biopolymere, Technische Universität München, Freising, Germany
| | - Maria Hoyer
- Physical Chemistry, Department of Chemistry, Center for Nano Science (CENS), Center for Integrated Protein Science (CIPSM) and Nanosystems Initiative München (NIM), Ludwig-Maximilians-Universität Munich, Munich, Germany
| | - Ralf Stehle
- Institute of Structural Biology, Helmholtz Zentrum München, Neuherberg, Germany; Center for Integrated Protein Science Munich (CIPSM), Chair Biomolecular NMR Spectroscopy, Department Chemie, Technische Universität München, Garching, Germany
| | - Don C Lamb
- Physical Chemistry, Department of Chemistry, Center for Nano Science (CENS), Center for Integrated Protein Science (CIPSM) and Nanosystems Initiative München (NIM), Ludwig-Maximilians-Universität Munich, Munich, Germany.
| | - Dieter Langosch
- Center for Integrated Protein Science Munich (CIPSM), Lehrstuhl für Chemie der Biopolymere, Technische Universität München, Freising, Germany.
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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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8
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Böhm I, Gehrke S, Kleb B, Hungerbühler M, Müller R, Klose KJ, Alfke H. Monitoring of tumor burden in vivo by optical imaging in a xenograft SCID mouse model: evaluation of two fluorescent proteins of the GFP-superfamily. Acta Radiol 2019; 60:315-326. [PMID: 29890843 DOI: 10.1177/0284185118780896] [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] [Indexed: 12/19/2022]
Abstract
BACKGROUND Mouse models of human-malignant-melanoma (MM) are important tools to study tumor dynamics. The enhanced green fluorescent protein (EGFP) is widely used in molecular imaging approaches, together with optical scanners, and fluorescence imaging. PURPOSE Currently, there are no data available as to whether other fluorescent proteins are more suitable. The goal of this preclinical study was to analyze two fluorescent proteins of the GFP superfamily under real-time in vivo conditions using fluorescence reflectance imaging (FRI). MATERIAL AND METHODS The human melanoma cell line MeWo was stable transfected with one plasmid: pEGFP-C1 or pDsRed1-N1. We investigated two severe combined immunodeficiency (SCID)-mice groups: A (solid xenografts) and B (xenografts as metastases). After three weeks, the animals were weekly imaged by FRI. Afterwards the mice were euthanized and metastases were imaged in situ: to quantify the cutis-dependent reduction of emitted light, we compared signal intensities obtained by metastases in vivo with signal intensities obtained by in situ liver parenchyma preparations. RESULTS More than 90% of cells were stable transfected. EGFP-/DsRed-xenograft tumors had identical growth kinetics. In vivo the emitted light by DsRed tumors/metastases was much brighter than by EGFP. DsRed metastases were earlier (3 vs. 5 weeks) and much more sensitive detectable than EGFP metastases. Cutis-dependent reduction of emitted light was greater in EGFP than in DsRed mice (tenfold). Autofluorescence of DsRed was lower than of EGFP. CONCLUSION We established an in vivo xenograft mouse model (DsRed-MeWo) that is reliable, reproducible, and superior to the EGFP model as a preclinical tool to study innovative therapies by FRI under real-time in vivo conditions.
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Affiliation(s)
- Ingrid Böhm
- Department of Diagnostic, Interventional, and Pediatric Radiology, Inselspital, University of Bern, Bern, Switzerland
- Radiology Laboratory, Department for BioMedical Research, University of Bern, Bern, Switzerland
| | - Stephan Gehrke
- Department of Pathology, Stanford University School of Medicine, Stanford, CA, USA
| | - Beate Kleb
- Department of Experimental Ophthalmology, Philipps University of Marburg, Marburg, Germany
| | - Martin Hungerbühler
- Department of Diagnostic, Interventional, and Pediatric Radiology, Inselspital, University of Bern, Bern, Switzerland
- Radiology Laboratory, Department for BioMedical Research, University of Bern, Bern, Switzerland
| | - Rolf Müller
- Institute of Molecular Tumor Biology and Cancer Gene Therapy (IMT), Philipps University of Marburg, Marburg, Germany
| | - Klaus J Klose
- Deans Office, Faculty of Medicine, Philipps University of Marburg, Marburg, Germany
| | - Heiko Alfke
- Department of Diagnostic Radiology and Interventional Radiology, Klinikum Lüdenscheid, Lüdenscheid, Germany
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9
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Baumdick M, Gelléri M, Uttamapinant C, Beránek V, Chin JW, Bastiaens PIH. A conformational sensor based on genetic code expansion reveals an autocatalytic component in EGFR activation. Nat Commun 2018; 9:3847. [PMID: 30242154 PMCID: PMC6155120 DOI: 10.1038/s41467-018-06299-7] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2018] [Accepted: 08/10/2018] [Indexed: 12/26/2022] Open
Abstract
Epidermal growth factor receptor (EGFR) activation by growth factors (GFs) relies on dimerization and allosteric activation of its intrinsic kinase activity, resulting in trans-phosphorylation of tyrosines on its C-terminal tail. While structural and biochemical studies identified this EGF-induced allosteric activation, imaging collective EGFR activation in cells and molecular dynamics simulations pointed at additional catalytic EGFR activation mechanisms. To gain more insight into EGFR activation mechanisms in living cells, we develop a Förster resonance energy transfer (FRET)-based conformational EGFR indicator (CONEGI) using genetic code expansion that reports on conformational transitions in the EGFR activation loop. Comparing conformational transitions, self-association and auto-phosphorylation of CONEGI and its Y845F mutant reveals that Y845 phosphorylation induces a catalytically active conformation in EGFR monomers. This conformational transition depends on EGFR kinase activity and auto-phosphorylation on its C-terminal tail, generating a looped causality that leads to autocatalytic amplification of EGFR phosphorylation at low EGF dose. Upon ligand binding epidermal growth factor receptor (EGFR) dimerizes and activates its intrinsic kinase to auto-phosphorylate EGFR. Here, the authors engineer and image a FRET-based conformational EGFR indicator which reveals that activation loop phosphorylation induces a catalytically active conformation in EGFR monomers.
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Affiliation(s)
- Martin Baumdick
- Department of Systemic Cell Biology, Max Planck Institute of Molecular Physiology, Otto-Hahn-Street 11, 44227, Dortmund, Germany
| | - Márton Gelléri
- Department of Systemic Cell Biology, Max Planck Institute of Molecular Physiology, Otto-Hahn-Street 11, 44227, Dortmund, Germany.,Faculty of Chemistry and Chemical Biology, Technical University Dortmund, Otto-Hahn-Street 6, 44227, Dortmund, Germany
| | - Chayasith Uttamapinant
- Medical Research Council Laboratory of Molecular Biology, Cambridge Biomedical Campus, Francis Crick Avenue, Cambridge, CB2 0QH, UK
| | - Václav Beránek
- Medical Research Council Laboratory of Molecular Biology, Cambridge Biomedical Campus, Francis Crick Avenue, Cambridge, CB2 0QH, UK
| | - Jason W Chin
- Medical Research Council Laboratory of Molecular Biology, Cambridge Biomedical Campus, Francis Crick Avenue, Cambridge, CB2 0QH, UK.
| | - Philippe I H Bastiaens
- Department of Systemic Cell Biology, Max Planck Institute of Molecular Physiology, Otto-Hahn-Street 11, 44227, Dortmund, Germany. .,Faculty of Chemistry and Chemical Biology, Technical University Dortmund, Otto-Hahn-Street 6, 44227, Dortmund, Germany.
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10
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Co-imaging extrinsic, intrinsic and effector caspase activity by fluorescence anisotropy microscopy. Redox Biol 2018; 19:210-217. [PMID: 30176560 PMCID: PMC6120609 DOI: 10.1016/j.redox.2018.07.023] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2018] [Revised: 07/23/2018] [Accepted: 07/31/2018] [Indexed: 01/08/2023] Open
Abstract
In order to overcome intercellular variability and thereby effectively assess signal propagation in biological networks it is imperative to simultaneously quantify multiple biological observables in single living cells. While fluorescent biosensors have been the tool of choice to monitor the dynamics of protein interaction and enzymatic activity, co-measuring more than two of them has proven challenging. In this work, we designed three spectrally separated anisotropy-based Förster Resonant Energy Transfer (FRET) biosensors to overcome this difficulty. We demonstrate this principle by monitoring the activation of extrinsic, intrinsic and effector caspases upon apoptotic stimulus. Together with modelling and simulations we show that time of maximum activity for each caspase can be derived from the anisotropy of the corresponding biosensor. Such measurements correlate relative activation times and refine existing models of biological signalling networks, providing valuable insight into signal propagation.
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11
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Bene L, Bagdány M, Ungvári T, Damjanovich L. Dual-Laser Tetra-Polarization FRET (4polFRET) for Site-Selective Control of Homo-FRET in Hetero-FRET Systems on the Cell Surface: The Homo-FRET Gate. Anal Chem 2018; 90:10159-10170. [DOI: 10.1021/acs.analchem.7b05441] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- László Bene
- Department of Surgery, Faculty of Medicine, University of Debrecen P.O. Box 400, Debrecen H-4002, Hungary
| | - Miklós Bagdány
- Department of Physiology, McGill University, 3655 Promenade Sir William Osler, Montreal H3G1Y6, Canada
| | - Tamás Ungvári
- Department of Biophysics and Cell Biology, Faculty of Medicine, University of Debrecen, P.O. Box 400, Debrecen H-4002, Hungary
| | - László Damjanovich
- Department of Surgery, Faculty of Medicine, University of Debrecen P.O. Box 400, Debrecen H-4002, Hungary
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Masip ME, Huebinger J, Christmann J, Sabet O, Wehner F, Konitsiotis A, Fuhr GR, Bastiaens PIH. Reversible cryo-arrest for imaging molecules in living cells at high spatial resolution. Nat Methods 2016; 13:665-672. [PMID: 27400419 PMCID: PMC5038880 DOI: 10.1038/nmeth.3921] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2015] [Accepted: 06/13/2016] [Indexed: 12/11/2022]
Abstract
The dynamics of molecules in living cells hampers precise imaging of molecular patterns by functional and super-resolution microscopy. We developed a method that circumvents lethal chemical fixation and allows on-stage cryo-arrest for consecutive imaging of molecular patterns within the same living, but arrested, cells. The reversibility of consecutive cryo-arrests was demonstrated by the high survival rate of different cell lines and by intact growth factor signaling that was not perturbed by stress response. Reversible cryo-arrest was applied to study the evolution of ligand-induced receptor tyrosine kinase activation at different scales. The nanoscale clustering of epidermal growth factor receptor (EGFR) in the plasma membrane was assessed by single-molecule localization microscopy, and endosomal microscale activity patterns of ephrin receptor A2 (EphA2) were assessed by fluorescence lifetime imaging microscopy. Reversible cryo-arrest allows the precise determination of molecular patterns while conserving the dynamic capabilities of living cells.
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Affiliation(s)
- Martin E Masip
- Department of Systemic Cell Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany
| | - Jan Huebinger
- Department of Systemic Cell Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany
| | - Jens Christmann
- Department of Systemic Cell Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany
- Faculty of Chemistry and Chemical Biology, TU Dortmund, Dortmund, Germany
| | - Ola Sabet
- Department of Systemic Cell Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany
| | - Frank Wehner
- Department of Systemic Cell Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany
| | - Antonios Konitsiotis
- Department of Systemic Cell Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany
| | - Günther R Fuhr
- Fraunhofer Institute for Biomedical Engineering, St. Ingbert, Germany
| | - Philippe I H Bastiaens
- Department of Systemic Cell Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany
- Faculty of Chemistry and Chemical Biology, TU Dortmund, Dortmund, Germany
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13
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Tanaka K, Kelly CE, Goh KY, Lim KB, Ibáñez CF. Death Domain Signaling by Disulfide-Linked Dimers of the p75 Neurotrophin Receptor Mediates Neuronal Death in the CNS. J Neurosci 2016; 36:5587-95. [PMID: 27194337 PMCID: PMC6601771 DOI: 10.1523/jneurosci.4536-15.2016] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2015] [Revised: 04/11/2016] [Accepted: 04/12/2016] [Indexed: 11/21/2022] Open
Abstract
UNLABELLED The p75 neurotrophin receptor (p75(NTR)) mediates neuronal death in response to neural insults by activating a caspase apoptotic pathway. The oligomeric state and activation mechanism that enable p75(NTR) to mediate these effects have recently been called into question. Here, we have investigated mutant mice lacking the p75(NTR) death domain (DD) or a highly conserved transmembrane (TM) cysteine residue (Cys(259)) implicated in receptor dimerization and activation. Neuronal death induced by proneurotrophins or epileptic seizures was assessed and compared with responses in p75(NTR) knock-out mice and wild-type animals. Proneurotrophins induced apoptosis of cultured hippocampal and cortical neurons from wild-type mice, but mutant neurons lacking p75(NTR), only the p75(NTR) DD, or just Cys(259) were all equally resistant to proneurotrophin-induced neuronal death. Homo-FRET anisotropy experiments demonstrated that both NGF and proNGF induce conformational changes in p75(NTR) that are dependent on the TM cysteine. In vivo, neuronal death induced by pilocarpine-mediated seizures was significantly reduced in the hippocampus and somatosensory, piriform, and entorhinal cortices of all three strains of p75(NTR) mutant mice. Interestingly, the levels of protection observed in mice lacking the DD or only Cys(259) were identical to those of p75(NTR) knock-out mice even though the Cys(259) mutant differed from the wild-type receptor in only one amino acid residue. We conclude that, both in vitro and in vivo, neuronal death induced by p75(NTR) requires the DD and TM Cys(259), supporting the physiological relevance of DD signaling by disulfide-linked dimers of p75(NTR) in the CNS. SIGNIFICANCE STATEMENT A detailed understanding of the physiological significance of distinct structural determinants in the p75 neurotrophin receptor (p75(NTR)) is crucial for the identification of suitable drug targets in this receptor. We have tested the relevance of the p75(NTR) death domain (DD) and the highly conserved transmembrane residue Cys(259) for the ability of p75(NTR) to induce apoptosis in neurons of the CNS using gene-targeted mutant mice. The physiological importance of these determinants had been contested in some recent in vitro studies. Our results indicate a requirement for DD signaling by disulfide-linked dimers of p75(NTR) for neuronal death induced by proneurotrophins and epileptic seizures. These new mouse models will be useful for clarifying different aspects of p75(NTR) physiology.
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Affiliation(s)
- Kazuhiro Tanaka
- Department of Physiology, National University of Singapore, Singapore 117597, Singapore, Life Sciences Institute, National University of Singapore, Singapore 117456, Singapore
| | - Claire E Kelly
- Department of Neuroscience, Karolinska Institute, Stockholm S-17177, Sweden, and
| | - Ket Yin Goh
- Department of Physiology, National University of Singapore, Singapore 117597, Singapore, Life Sciences Institute, National University of Singapore, Singapore 117456, Singapore
| | - Kim Buay Lim
- Department of Physiology, National University of Singapore, Singapore 117597, Singapore, Life Sciences Institute, National University of Singapore, Singapore 117456, Singapore
| | - Carlos F Ibáñez
- Department of Physiology, National University of Singapore, Singapore 117597, Singapore, Life Sciences Institute, National University of Singapore, Singapore 117456, Singapore, Department of Neuroscience, Karolinska Institute, Stockholm S-17177, Sweden, and Stellenbosch Institute for Advanced Study, Wallenberg Research Centre at Stellenbosch University, Stellenbosch 7600, South Africa
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14
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Multiplexed imaging of intracellular protein networks. Cytometry A 2016; 89:761-75. [DOI: 10.1002/cyto.a.22876] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2015] [Revised: 04/21/2016] [Accepted: 04/26/2016] [Indexed: 12/19/2022]
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15
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Weber’s Red-Edge Effect that Changed the Paradigm in Photophysics and Photochemistry. ACTA ACUST UNITED AC 2016. [DOI: 10.1007/4243_2016_14] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/17/2023]
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16
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Baumdick M, Brüggemann Y, Schmick M, Xouri G, Sabet O, Davis L, Chin JW, Bastiaens PIH. EGF-dependent re-routing of vesicular recycling switches spontaneous phosphorylation suppression to EGFR signaling. eLife 2015; 4. [PMID: 26609808 PMCID: PMC4716840 DOI: 10.7554/elife.12223] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2015] [Accepted: 11/25/2015] [Indexed: 11/17/2022] Open
Abstract
Autocatalytic activation of epidermal growth factor receptor (EGFR) coupled to dephosphorylating activity of protein tyrosine phosphatases (PTPs) ensures robust yet diverse responses to extracellular stimuli. The inevitable tradeoff of this plasticity is spontaneous receptor activation and spurious signaling. We show that a ligand-mediated switch in EGFR trafficking enables suppression of spontaneous activation while maintaining EGFR’s capacity to transduce extracellular signals. Autocatalytic phosphorylation of tyrosine 845 on unliganded EGFR monomers is suppressed by vesicular recycling through perinuclear areas with high PTP1B activity. Ligand-binding results in phosphorylation of the c-Cbl docking tyrosine and ubiquitination of the receptor. This secondary signal relies on EGF-induced EGFR self-association and switches suppressive recycling to directional trafficking. The re-routing regulates EGFR signaling response by the transit-time to late endosomes where it is switched-off by high PTP1B activity. This ubiquitin-mediated switch in EGFR trafficking is a uniquely suited solution to suppress spontaneous activation while maintaining responsiveness to EGF. DOI:http://dx.doi.org/10.7554/eLife.12223.001 In living tissue, the ability of individual cells to grow is influenced by signal molecules in the environment around each cell. For example, after an injury, a molecule called epidermal growth factor can stimulate cells to grow to repair the wound. Epidermal growth factor binds to and activates a receptor protein called EGFR, which faces outwards from the cell surface. However, this signal needs to be switched off again afterwards to prevent the cells from growing too much. Epidermal growth factor activates EGFR by triggering a process called “autophosphorylation”, in which EGFR attaches molecules called phosphates to itself. To quench the signal, EGFRs that are bound to growth factors are removed from the cell surface and taken into the cell in small membrane bubbles called vesicles. Enzymes called phosphatases near the cell nucleus remove the phosphate groups and thereby switch the receptors off, before the receptors are ultimately destroyed. However, EGFR autophosphorylation can also happen spontaneously in the absence of growth factor, so it was not clear how the cell is able to distinguish between this spontaneous activation and a genuine signal. Baumdick, Brüggemann, Schmick, Xouri et al. used biochemical techniques to address this question. The experiments show that EGFRs that have become spontaneously active are also removed from the cell surface in vesicles. However, unlike the EGFRs that are bound to growth factors, the spontaneously active receptors are recycled back to the membrane. On the way, their activity is also switched off by encountering phosphatases so that they are not active when they reach the cell surface again. The experiments also show that EGFRs are targeted for destruction by the presence of a tag called ubiquitin, which is added to the receptor in response to the binding of growth factor. Therefore, Baumdick et al.’s findings show that epidermal growth factor controls a switch that alters the way active EGFRs are processed in cells. This system acts to suppress the spontaneous activation of EGFRs, whilst maintaining the ability of the cell to respond to epidermal growth factor. The next challenge is to understand how the location of the phosphatases inside the cell influences when and how the EGFRs respond to this external signal. DOI:http://dx.doi.org/10.7554/eLife.12223.002
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Affiliation(s)
- Martin Baumdick
- Department of Systemic Cell Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany
| | - Yannick Brüggemann
- Department of Systemic Cell Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany.,Faculty of Chemistry and Chemical Biology, Technical University of Dortmund, Dortmund, Germany
| | - Malte Schmick
- Department of Systemic Cell Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany
| | - Georgia Xouri
- Department of Systemic Cell Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany
| | - Ola Sabet
- Department of Systemic Cell Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany
| | - Lloyd Davis
- Medical Research Council Laboratory of Molecular Biology, Cambridge, United Kingdom
| | - Jason W Chin
- Medical Research Council Laboratory of Molecular Biology, Cambridge, United Kingdom
| | - Philippe I H Bastiaens
- Department of Systemic Cell Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany.,Faculty of Chemistry and Chemical Biology, Technical University of Dortmund, Dortmund, Germany
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17
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Levitt JA, Morton PE, Fruhwirth GO, Santis G, Chung PH, Parsons M, Suhling K. Simultaneous FRAP, FLIM and FAIM for measurements of protein mobility and interaction in living cells. BIOMEDICAL OPTICS EXPRESS 2015; 6:3842-54. [PMID: 26504635 PMCID: PMC4605044 DOI: 10.1364/boe.6.003842] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/29/2015] [Revised: 08/16/2015] [Accepted: 08/18/2015] [Indexed: 05/23/2023]
Abstract
We present a novel integrated multimodal fluorescence microscopy technique for simultaneous fluorescence recovery after photobleaching (FRAP), fluorescence lifetime imaging (FLIM) and fluorescence anisotropy imaging (FAIM). This approach captures a series of polarization-resolved fluorescence lifetime images during a FRAP recovery, maximizing the information available from a limited photon budget. We have applied this method to analyse the behaviour of GFP-labelled coxsackievirus and adenovirus receptor (CAR) in living human epithelial cells. Our data reveal that CAR exists in oligomeric states throughout the cell, and that these complexes occur in conjunction with high immobile fractions of the receptor at cell-cell junctions. These findings shed light on previously unknown molecular associations between CAR receptors in intact cells and demonstrate the power of combined FRAP, FLIM and FAIM microscopy as a robust method to analyse complex multi-component dynamics in living cells.
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Affiliation(s)
- James A. Levitt
- Department of Physics, King’s College London, Strand, London WC2R 2LS, UK
| | - Penny E. Morton
- Division of Asthma, Allergy, and Lung Biology, Guys Campus, King’s College London, London, UK
- Randall Division of Cell and Molecular Biophysics, Guys Campus, King’s College London, London, SE1 1UL, UK
| | - Gilbert O. Fruhwirth
- Department of Imaging Chemsitry and Biology, Division of Imaging Sciences and Biomedical Engineering, St. Thomas Hospital, King's College London, SE1 7EH, UK
| | - George Santis
- Division of Asthma, Allergy, and Lung Biology, Guys Campus, King’s College London, London, UK
| | - Pei-Hua Chung
- Department of Physics, King’s College London, Strand, London WC2R 2LS, UK
| | - Maddy Parsons
- Randall Division of Cell and Molecular Biophysics, Guys Campus, King’s College London, London, SE1 1UL, UK
| | - Klaus Suhling
- Department of Physics, King’s College London, Strand, London WC2R 2LS, UK
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18
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Ubiquitination switches EphA2 vesicular traffic from a continuous safeguard to a finite signalling mode. Nat Commun 2015; 6:8047. [PMID: 26292967 PMCID: PMC4560775 DOI: 10.1038/ncomms9047] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2015] [Accepted: 07/11/2015] [Indexed: 01/15/2023] Open
Abstract
Autocatalytic phosphorylation of receptor tyrosine kinases (RTKs) enables diverse, context-dependent responses to extracellular signals but comes at the price of autonomous, ligand-independent activation. Using a conformational biosensor that reports on the kinase activity of the cell guidance ephrin receptor type-A (EphA2) in living cells, we observe that autonomous EphA2 activation is suppressed by vesicular recycling and dephosphorylation by protein tyrosine phosphatases 1B (PTP1B) near the pericentriolar recycling endosome. This spatial segregation of catalytically superior PTPs from RTKs at the plasma membrane is essential to preserve ligand responsiveness. Ligand-induced clustering, on the other hand, promotes phosphorylation of a c-Cbl docking site and ubiquitination of the receptor, thereby redirecting it to the late endosome/lysosome. We show that this switch from cyclic to unidirectional receptor trafficking converts a continuous suppressive safeguard mechanism into a transient ligand-responsive signalling mode.
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19
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Warren SC, Margineanu A, Katan M, Dunsby C, French PMW. Homo-FRET Based Biosensors and Their Application to Multiplexed Imaging of Signalling Events in Live Cells. Int J Mol Sci 2015; 16:14695-716. [PMID: 26133241 PMCID: PMC4519867 DOI: 10.3390/ijms160714695] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2015] [Revised: 06/15/2015] [Accepted: 06/17/2015] [Indexed: 12/20/2022] Open
Abstract
Multiplexed imaging of Förster Resonance Energy Transfer (FRET)-based biosensors potentially presents a powerful approach to monitoring the spatio-temporal correlation of signalling pathways within a single live cell. Here, we discuss the potential of homo-FRET based biosensors to facilitate multiplexed imaging. We demonstrate that the homo-FRET between pleckstrin homology domains of Akt (Akt-PH) labelled with mCherry may be used to monitor 3'-phosphoinositide accumulation in live cells and show how global analysis of time resolved fluorescence anisotropy measurements can be used to quantify this accumulation. We further present multiplexed imaging readouts of calcium concentration, using fluorescence lifetime measurements of TN-L15-a CFP/YFP based hetero-FRET calcium biosensor-with 3'-phosphoinositide accumulation.
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Affiliation(s)
- Sean C Warren
- Photonics Group, Department of Physics, Imperial College London, London SW7 2AZ, UK.
| | - Anca Margineanu
- Photonics Group, Department of Physics, Imperial College London, London SW7 2AZ, UK.
| | - Matilda Katan
- Structural and Molecular Biology, University College London, London WC1E 6BT, UK.
| | - Chris Dunsby
- Photonics Group, Department of Physics, Imperial College London, London SW7 2AZ, UK.
| | - Paul M W French
- Photonics Group, Department of Physics, Imperial College London, London SW7 2AZ, UK.
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20
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Bene L, Ungvári T, Fedor R, Nagy I, Damjanovich L. Dual-laser homo-FRET on the cell surface. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2015; 1853:1096-112. [DOI: 10.1016/j.bbamcr.2015.02.001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/24/2014] [Revised: 01/19/2015] [Accepted: 02/02/2015] [Indexed: 10/24/2022]
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21
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22
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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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23
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Erdelyi M, Simon J, Barnard EA, Kaminski CF. Analyzing receptor assemblies in the cell membrane using fluorescence anisotropy imaging with TIRF microscopy. PLoS One 2014; 9:e100526. [PMID: 24945870 PMCID: PMC4063901 DOI: 10.1371/journal.pone.0100526] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2014] [Accepted: 05/28/2014] [Indexed: 11/19/2022] Open
Abstract
Signaling within and between animal cells is controlled by the many receptor proteins in their membrane. They variously operate as trans-membrane monomers and homo- or hetero-dimers, and may assemble with ion-channels: analyses thereof are needed in studies of receptor actions in tissue physiology and pathology. Interactions between membrane proteins are detectable when pre-labeled with fluorophores, but a much fuller analysis is achievable via advanced optical techniques on living cells. In this context, the measurement of polarization anisotropy in the emitted fluorescence has been the least exploited. Here we demonstrate its methodology and particular advantages in the study of receptor protein assembly. Through excitation in both TIRF and EPI fluorescence illumination modes we are able to quantify and suppress contributions to the signal from extraneous intra-cellular fluorescence, and we show that the loss of fluorescence-polarization measured in membrane proteins reports on receptor protein assembly in real time. Receptor monomers and homo-dimers in the cell membrane can be analyzed quantitatively and for homo-dimers only a single fluorescent marker is needed, thus suppressing ambiguities that arise in alternative assays, which require multiple label moieties and which are thus subject to stoichiometric uncertainty.
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Affiliation(s)
- Miklos Erdelyi
- Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge, United Kingdom
- Analytical Science Division, National Physical Laboratory, Teddington, Middlesex, United Kingdom
- Department of Optics and Quantum Electronics, University of Szeged, Szeged, Hungary
| | - Joseph Simon
- Department of Pharmacology, University of Cambridge, Cambridge, United Kingdom
| | - Eric A. Barnard
- Department of Pharmacology, University of Cambridge, Cambridge, United Kingdom
| | - Clemens F. Kaminski
- Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge, United Kingdom
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24
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Bhardwaj V, Panicker MM, Udgaonkar JB. Fluorescence anisotropy uncovers changes in protein packing with inclusion growth in a cellular model of polyglutamine aggregation. Biochemistry 2014; 53:3621-36. [PMID: 24819723 DOI: 10.1021/bi500383h] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The aggregation of polyglutamine-rich proteins is closely linked with numerous neurodegenerative disorders. In pathological and cellular models, the appearance of protein-rich inclusions in cells acts as a read out of protein aggregation. The precise organization of aggregated protein in these inclusions and their mode of growth are still poorly understood. Here, fluorescence anisotropy-based measurements have been used to probe protein packing across inclusions of varying brightness, formed by an monomeric enhanced green fluorescent protein (mEGFP)-tagged polyglutamine model peptide in cells. High-resolution, confocal-based steady-state anisotropy measurements report a large depolarization, consistent with extensive homo-Förster (fluorescence) resonance energy transfer (FRET) between the sequestered mEGFP-tagged protein molecules. An inverse correlation of fluorescence anisotropy with intensity is seen across inclusions, which becomes emphasized when the observed fluorescence anisotropy values of inclusions are corrected for the fluorescence contribution of the diffusible protein, present within and around smaller inclusions. Homo-FRET becomes enhanced as inclusion size increases. This enhancement is confirmed by two-photon excitation-based time-resolved fluorescence anisotropy decay measurements, which also suggest that the mEGFP-tagged protein molecules are arranged in multiple ways within inclusions. Bright inclusions display faster FRET rates with a larger number of mEGFP moieties participating in homo-FRET than faint inclusions do. These results are consistent with a model in which the protein is more closely packed in the brighter inclusions. In such a possible mechanism, the higher packing density of protein molecules in brighter inclusions would suggest that inclusion growth could involve an intermolecular compaction event within the inclusion, as more monomers and aggregates are recruited into the growing inclusion.
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Affiliation(s)
- Vishal Bhardwaj
- National Centre for Biological Sciences, Tata Institute of Fundamental Research , Bangalore 560065, India
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25
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Single-vesicle architecture of synaptobrevin2 in astrocytes. Nat Commun 2014; 5:3780. [PMID: 24807050 DOI: 10.1038/ncomms4780] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2013] [Accepted: 04/01/2014] [Indexed: 11/08/2022] Open
Abstract
Exocytic transmitter release is regulated by the SNARE complex, which contains a vesicular protein, synaptobrevin2 (Sb2). However, Sb2 vesicular arrangement is unclear. Here we use super-resolution fluorescence microscopy to study the prevalence and distribution of endogenous and exogenous Sb2 in single vesicles of astrocytes, the most abundant glial cells in the brain. We tag Sb2 protein at C- and N termini with a pair of fluorophores, which allows us to determine the Sb2 length and geometry. To estimate total number of Sb2 proteins per vesicle and the quantity necessary for the formation of fusion pores, we treat cells with ATP to stimulate Ca2+-dependent exocytosis, increase intracellular alkalinity to enhance the fluorescence presentation of yellow-shifted pHluorin (YpH), appended to the vesicle lumen domain of Sb2, and perform photobleaching of YpH fluorophores. Fluorescence intensity analysis reveals that the total number of endogenous Sb2 units or molecules per vesicle is ≤25.
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26
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Schaupp A, Sabet O, Dudanova I, Ponserre M, Bastiaens P, Klein R. The composition of EphB2 clusters determines the strength in the cellular repulsion response. ACTA ACUST UNITED AC 2014; 204:409-22. [PMID: 24469634 PMCID: PMC3912530 DOI: 10.1083/jcb.201305037] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Graded responses to cell–cell repulsion signals mediated by Ephrin–Eph receptor interactions are specified by EphB2 cluster composition, such that the relative abundance of inactive dimers and active higher-order clusters determines the strength of the repulsive response. Trans interactions of erythropoietin-producing human hepatocellular (Eph) receptors with their membrane-bound ephrin ligands generate higher-order clusters that can form extended signaling arrays. The functional relevance of the cluster size for repulsive signaling is not understood. We used chemical dimerizers and fluorescence anisotropy to generate and visualize specific EphB2 cluster species in living cells. We find that cell collapse responses are induced by small-sized EphB2 clusters, suggesting that extended EphB2 arrays are dispensable and that EphB2 activation follows an ON–OFF switch with EphB2 dimers being inactive and trimers and tetramers being fully functional. Moreover, the strength of the collapse response is determined by the abundance of multimers over dimers within a cluster population: the more dimers are present, the weaker the response. Finally, we show that the C-terminal modules of EphB2 have negative regulatory effects on ephrin-induced clustering. These results shed new light on the mechanism and regulation of EphB2 activation and provide a model on how Eph signaling translates into graded cellular responses.
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Affiliation(s)
- Andreas Schaupp
- Department of Molecules - Signaling - Development, Max Planck Institute of Neurobiology, 82152 Martinsried, Germany
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27
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Abstract
Fluorescence can be characterized by its intensity, position, wavelength, lifetime, and polarization. The more of these features are acquired in a single measurement, the more can be learned about the sample, i.e., the microenvironment of the fluorescence probe. Polarization-resolved fluorescence lifetime imaging-time-resolved fluorescence anisotropy imaging, TR-FAIM-allows mapping of viscosity or binding or of homo-FRET which can indicate dimerization or generally oligomerization.
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Affiliation(s)
- Klaus Suhling
- Department of Physics, King's College London, London, UK
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28
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Demchenko AP. Nanoparticles and nanocomposites for fluorescence sensing and imaging. Methods Appl Fluoresc 2013; 1:022001. [DOI: 10.1088/2050-6120/1/2/022001] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
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29
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van Wijk SJL, Fiskin E, Putyrski M, Pampaloni F, Hou J, Wild P, Kensche T, Grecco HE, Bastiaens P, Dikic I. Fluorescence-based sensors to monitor localization and functions of linear and K63-linked ubiquitin chains in cells. Mol Cell 2012; 47:797-809. [PMID: 22819327 DOI: 10.1016/j.molcel.2012.06.017] [Citation(s) in RCA: 124] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2012] [Revised: 05/02/2012] [Accepted: 06/12/2012] [Indexed: 10/28/2022]
Abstract
Ubiquitin chains modify a major subset of the proteome, but detection of ubiquitin signaling dynamics and localization is limited due to a lack of appropriate tools. Here, we employ ubiquitin-binding domain (UBD)-based fluorescent sensors to monitor linear and K63-linked chains in vitro and in vivo. We utilize the UBD in NEMO and ABIN (UBAN) for detection of linear chains, and RAP80 ubiquitin-interacting motif (UIM) and TAB2 Npl4 zinc finger (NZF) domains to detect K63 chains. Linear and K63 sensors decorated the ubiquitin coat surrounding cytosolic Salmonella during bacterial autophagy, whereas K63 sensors selectively monitored Parkin-induced mitophagy and DNA damage responses in fixed and living cells. In addition, linear and K63 sensors could be used to monitor endogenous signaling pathways, as demonstrated by their ability to differentially interfere with TNF- and IL-1-induced NF-κB pathway. We propose that UBD-based biosensors could serve as prototypes to track and trace other chain types and ubiquitin-like signals in vivo.
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Affiliation(s)
- Sjoerd J L van Wijk
- Institute of Biochemistry II, Goethe University School of Medicine, Theodor-Stern-Kai 7, 60590 Frankfurt am Main, Germany
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30
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Hunt J, Keeble AH, Dale RE, Corbett MK, Beavil RL, Levitt J, Swann MJ, Suhling K, Ameer-Beg S, Sutton BJ, Beavil AJ. A fluorescent biosensor reveals conformational changes in human immunoglobulin E Fc: implications for mechanisms of receptor binding, inhibition, and allergen recognition. J Biol Chem 2012; 287:17459-17470. [PMID: 22442150 PMCID: PMC3366799 DOI: 10.1074/jbc.m111.331967] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2011] [Revised: 03/08/2012] [Indexed: 11/06/2022] Open
Abstract
IgE binding to its high affinity receptor FcεRI on mast cells and basophils is a key step in the mechanism of allergic disease and a target for therapeutic intervention. Early indications that IgE adopts a bent structure in solution have been confirmed by recent x-ray crystallographic studies of IgEFc, which further showed that the bend, contrary to expectation, is enhanced in the crystal structure of the complex with receptor. To investigate the structure of IgEFc and its conformational changes that accompany receptor binding in solution, we created a Förster resonance energy transfer (FRET) biosensor using biologically encoded fluorescent proteins fused to the N- and C-terminal IgEFc domains (Cε2 and Cε4, respectively) together with the theoretical basis for quantitating its behavior. This revealed not only that the IgEFc exists in a bent conformation in solution but also that the bend is indeed enhanced upon FcεRI binding. No change in the degree of bending was seen upon binding to the B cell receptor for IgE, CD23 (FcεRII), but in contrast, binding of the anti-IgE therapeutic antibody omalizumab decreases the extent of the bend, implying a conformational change that opposes FcεRI engagement. HomoFRET measurements further revealed that the (Cε2)(2) and (Cε4)(2) domain pairs behave as rigid units flanking the conformational change in the Cε3 domains. Finally, modeling of the accessible conformations of the two Fab arms in FcεRI-bound IgE revealed a mutual exclusion not seen in IgG and Fab orientations relative to the membrane that may predispose receptor-bound IgE to cross-linking by allergens.
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Affiliation(s)
- James Hunt
- MRC and Asthma UK Centre in Allergic Mechanisms of Asthma, Guy's Hospital Campus, London SE1 1UL; The Randall Division of Cell and Molecular Biophysics, Guy's Hospital Campus, London SE1 1UL; The Division of Asthma Allergy and Lung Biology, King's College London, Guy's Hospital Campus, London SE1 1UL
| | - Anthony H Keeble
- MRC and Asthma UK Centre in Allergic Mechanisms of Asthma, Guy's Hospital Campus, London SE1 1UL; The Randall Division of Cell and Molecular Biophysics, Guy's Hospital Campus, London SE1 1UL; The Division of Asthma Allergy and Lung Biology, King's College London, Guy's Hospital Campus, London SE1 1UL
| | - Robert E Dale
- The Randall Division of Cell and Molecular Biophysics, Guy's Hospital Campus, London SE1 1UL
| | - Melissa K Corbett
- The Randall Division of Cell and Molecular Biophysics, Guy's Hospital Campus, London SE1 1UL
| | - Rebecca L Beavil
- MRC and Asthma UK Centre in Allergic Mechanisms of Asthma, Guy's Hospital Campus, London SE1 1UL; The Randall Division of Cell and Molecular Biophysics, Guy's Hospital Campus, London SE1 1UL; The Division of Asthma Allergy and Lung Biology, King's College London, Guy's Hospital Campus, London SE1 1UL
| | - James Levitt
- The Department of Physics, King's College London, Strand, London WC2R 2LS
| | - Marcus J Swann
- Farfield Group Limited, Voyager, Chicago Avenue, Manchester Airport, Manchester, M90 3DQ, United Kingdom
| | - Klaus Suhling
- The Department of Physics, King's College London, Strand, London WC2R 2LS
| | - Simon Ameer-Beg
- The Randall Division of Cell and Molecular Biophysics, Guy's Hospital Campus, London SE1 1UL
| | - Brian J Sutton
- MRC and Asthma UK Centre in Allergic Mechanisms of Asthma, Guy's Hospital Campus, London SE1 1UL; The Randall Division of Cell and Molecular Biophysics, Guy's Hospital Campus, London SE1 1UL
| | - Andrew J Beavil
- MRC and Asthma UK Centre in Allergic Mechanisms of Asthma, Guy's Hospital Campus, London SE1 1UL; The Randall Division of Cell and Molecular Biophysics, Guy's Hospital Campus, London SE1 1UL; The Division of Asthma Allergy and Lung Biology, King's College London, Guy's Hospital Campus, London SE1 1UL.
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31
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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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32
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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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Sahoo H. Förster resonance energy transfer – A spectroscopic nanoruler: Principle and applications. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY C-PHOTOCHEMISTRY REVIEWS 2011. [DOI: 10.1016/j.jphotochemrev.2011.05.001] [Citation(s) in RCA: 217] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
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Levitt JA, Chung PH, Kuimova MK, Yahioglu G, Wang Y, Qu J, Suhling K. Fluorescence anisotropy of molecular rotors. Chemphyschem 2011; 12:662-72. [PMID: 21328515 DOI: 10.1002/cphc.201000782] [Citation(s) in RCA: 96] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2010] [Revised: 01/10/2011] [Indexed: 12/12/2022]
Abstract
We present polarization-resolved fluorescence measurements of fluorescent molecular rotors 9-(2-carboxy-2-cyanovinyl)julolidine (CCVJ), 9-(2,2-dicyanovinyl)julolidine (DCVJ), and a meso-substituted boron dipyrromethene (BODIPY-C(12)). The photophysical properties of these molecules are highly dependent on the viscosity of the surrounding solvent. The relationship between their quantum yields and the viscosity of the surrounding medium is given by an equation first described and presented by Förster and Hoffmann and can be used to determine the microviscosity of the environment around a fluorophore. Herein we evaluate the applicability of molecular rotors as probes of apparent viscosity on a microscopic scale based on their viscosity dependent fluorescence depolarization. We develop a theoretical framework, combining the Förster-Hoffmann equation with the Perrin equation and compare the dynamic ranges and usable working regimes for these dyes in terms of utilising fluorescence anisotropy as a measure of viscosity. We present polarization-resolved fluorescence spectra and steady-state fluorescence anisotropy imaging data for measurements of intracellular viscosity. We find that the dynamic range for fluorescence anisotropy for CCVJ and DCVJ is significantly lower than that of BODIPY-C(12) in the viscosity range 0.6<η<600 cP. Moreover, using steady-state anisotropy measurements to probe microviscosity in the low (<3 cP) viscosity regime, the molecular rotors can offer a better dynamic range in anisotropy compared with a rigid dye as a probe of microviscosity, and a higher total working dynamic range in terms of viscosity.
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Affiliation(s)
- James A Levitt
- Department of Physics, King's College London, Strand, London, WC2R 2LS, UK
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Chan FTS, Kaminski CF, Kaminski Schierle GS. HomoFRET fluorescence anisotropy imaging as a tool to study molecular self-assembly in live cells. Chemphyschem 2010; 12:500-9. [PMID: 21344590 DOI: 10.1002/cphc.201000833] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2010] [Revised: 11/11/2010] [Indexed: 11/11/2022]
Abstract
Molecular self-assembly is a defining feature of numerous biological functions and dysfunctions, ranging from basic cell signalling to diseases mediated by protein aggregation. There is current demand for novel experimental methods to study molecular self-assembly in live cells, and thereby in its physiological context. Förster resonance energy transfer (FRET) between fluorophores of a single type, known as homoFRET, permits noninvasive detection and quantification of molecular clusters in live cells. It can thus provide powerful insights into the molecular physiology of living systems and disease. HomoFRET is detected by measuring the loss of fluorescence anisotropy upon excitation with polarised light. This article reviews recent key developments in homoFRET fluorescence anisotropy imaging for the detection and quantification of molecular self-assembly reactions in biological systems. A summary is given of the current state-of-the-art and case studies are presented of successful implementations, highlighting technical aspects which have to be mastered to bridge the gap between proof-of-concept experiments and biological discoveries.
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Affiliation(s)
- Fiona T S Chan
- Department of Chemical Engineering and Biotechnology, University of Cambridge, Pembroke Street, Cambridge, CB2 3RA, UK
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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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37
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Cytohesins are cytoplasmic ErbB receptor activators. Cell 2010; 143:201-11. [PMID: 20946980 DOI: 10.1016/j.cell.2010.09.011] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2010] [Revised: 07/13/2010] [Accepted: 08/10/2010] [Indexed: 11/24/2022]
Abstract
Signaling by ErbB receptors requires the activation of their cytoplasmic kinase domains, which is initiated by ligand binding to the receptor ectodomains. Cytoplasmic factors contributing to the activation are unknown. Here we identify members of the cytohesin protein family as such factors. Cytohesin inhibition decreased ErbB receptor autophosphorylation and signaling, whereas cytohesin overexpression stimulated receptor activation. Monitoring epidermal growth factor receptor (EGFR) conformation by anisotropy microscopy together with cell-free reconstitution of cytohesin-dependent receptor autophosphorylation indicate that cytohesins facilitate conformational rearrangements in the intracellular domains of dimerized receptors. Consistent with cytohesins playing a prominent role in ErbB receptor signaling, we found that cytohesin overexpression correlated with EGF signaling pathway activation in human lung adenocarcinomas. Chemical inhibition of cytohesins resulted in reduced proliferation of EGFR-dependent lung cancer cells in vitro and in vivo. Our results establish cytohesins as cytoplasmic conformational activators of ErbB receptors that are of pathophysiological relevance.
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Vilar M, Charalampopoulos I, Kenchappa RS, Simi A, Karaca E, Reversi A, Choi S, Bothwell M, Mingarro I, Friedman WJ, Schiavo G, Bastiaens PIH, Verveer PJ, Carter BD, Ibáñez CF. Activation of the p75 neurotrophin receptor through conformational rearrangement of disulphide-linked receptor dimers. Neuron 2009; 62:72-83. [PMID: 19376068 DOI: 10.1016/j.neuron.2009.02.020] [Citation(s) in RCA: 117] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2008] [Revised: 11/14/2008] [Accepted: 02/25/2009] [Indexed: 11/27/2022]
Abstract
Ligand-mediated dimerization has emerged as a universal mechanism of growth factor receptor activation. Neurotrophins interact with dimers of the p75 neurotrophin receptor (p75(NTR)), but the mechanism of receptor activation has remained elusive. Here, we show that p75(NTR) forms disulphide-linked dimers independently of neurotrophin binding through the highly conserved Cys(257) in its transmembrane domain. Mutation of Cys(257) abolished neurotrophin-dependent receptor activity but did not affect downstream signaling by the p75(NTR)/NgR/Lingo-1 complex in response to MAG, indicating the existence of distinct, ligand-specific activation mechanisms for p75(NTR). FRET experiments revealed a close association of p75(NTR) intracellular domains that was transiently disrupted by conformational changes induced upon NGF binding. Although mutation of Cys(257) did not alter the oligomeric state of p75(NTR), the mutant receptor was no longer able to propagate conformational changes to the cytoplasmic domain upon ligand binding. We propose that neurotrophins activate p75(NTR) by a mechanism involving rearrangement of disulphide-linked receptor subunits.
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Affiliation(s)
- Marçal Vilar
- Division of Molecular Neurobiology, Department of Neuroscience, Karolinska Institute, 17177 Stockholm, Sweden
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40
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Levitt JA, Matthews DR, Ameer-Beg SM, Suhling K. Fluorescence lifetime and polarization-resolved imaging in cell biology. Curr Opin Biotechnol 2009; 20:28-36. [DOI: 10.1016/j.copbio.2009.01.004] [Citation(s) in RCA: 123] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2008] [Accepted: 01/23/2009] [Indexed: 10/21/2022]
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41
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Luchowski R, Sarkar P, Bharill S, Laczko G, Borejdo J, Gryczynski Z, Gryczynski I. Fluorescence polarization standard for near infrared spectroscopy and microscopy. APPLIED OPTICS 2008; 47:6257-6265. [PMID: 19023392 DOI: 10.1364/ao.47.006257] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
We present studies of polarized absorption [linear dichroism (LD)] and fluorescence polarization of the styryl derivative (LDS 798) embedded in oriented poly(vinyl alcohol) (PVA) films. These films were oriented by progressive stretching up to eight folds. Both vertical and horizontal components of absorptions and fluorescence were measured and dichroic ratios were determined for different film stretching ratios. The dichroic ratio and fluorescence anisotropy values were analyzed as a function of PVA film stretching ratio by fitting according to the previously developed theory. For maximum stretching ratios, exceptionally high anisotropy (approximately 0.8) and polarization (approximately 0.9) values have been measured. The stretched films have high polarization values also for isotropic excitation in a wide spectral range (500-700 nm). Such films can be conveniently used as high polarization standards and we envision they will also have applications in near infrared (NIR) imaging microscopy, where they can be used for correcting an instrumental factor in polarization measurements.
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Affiliation(s)
- Rafal Luchowski
- Center for Commercialization of Fluorescence Technologies (CCFT), Department of Molecular Biology & Immunology, University of North Texas Health Science Center, Fort Worth, TX 76107, USA.
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42
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Verveer PJ, Bastiaens PIH. Quantitative microscopy and systems biology: seeing the whole picture. Histochem Cell Biol 2008; 130:833-43. [DOI: 10.1007/s00418-008-0517-5] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/17/2008] [Indexed: 12/22/2022]
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43
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Quantitative characterization of the large-scale association of ErbB1 and ErbB2 by flow cytometric homo-FRET measurements. Biophys J 2008; 95:2086-96. [PMID: 18487307 DOI: 10.1529/biophysj.108.133371] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The association of receptor tyrosine kinases is a key step in the initiation of growth factor-mediated signaling. Although the ligand-induced dimerization of inactive, monomeric receptors was the central dogma of receptor tyrosine kinase activation for decades, the existence of larger oligomers is now accepted. Both homoassociations and heteroassociations are of extreme importance in the epidermal growth factor (EGF) receptor family, leading to diverse and robust signaling. We present a statistically reliable, flow-cytometric homo-fluorescence resonance energy transfer method for the quantitative characterization of large-scale receptor clusters. We assumed that a fraction of a certain protein species is monomeric, whereas the rest are present in homoclusters of N-mers. We measured fluorescence anisotropy as a function of the saturation of fluorescent antibody binding, and fitted the model to the anisotropy data yielding the fraction of monomers and the cluster size. We found that ErbB2 formed larger homoclusters than ErbB1. Stimulation with EGF and heregulin led to a decrease in ErbB2 homocluster size, whereas ErbB1 homoclusters became larger after EGF stimulation. The activation level of ErbB2 was inversely proportional to its homocluster size. We conclude that homoclusters of ErbB1 and ErbB2 behave in a fundamentally different way. Whereas huge ErbB2 clusters serve as a reservoir of inactive coreceptors and dissociate upon stimulation, small ErbB1 homoclusters form higher-order oligomers after ligand binding.
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44
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Prinz A, Reither G, Diskar M, Schultz C. Fluorescence and bioluminescence procedures for functional proteomics. Proteomics 2008; 8:1179-96. [DOI: 10.1002/pmic.200700802] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
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45
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46
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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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47
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Festy F, Ameer-Beg SM, Ng T, Suhling K. Imaging proteins in vivo using fluorescence lifetime microscopy. MOLECULAR BIOSYSTEMS 2007; 3:381-91. [PMID: 17533451 DOI: 10.1039/b617204k] [Citation(s) in RCA: 103] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Fluorescence lifetime imaging (FLIM) represents a key optical technique for imaging proteins and protein interaction in vivo. We review the principles and recent advances in the application of the technique, instrumentation and molecular probe development.
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Affiliation(s)
- Frederic Festy
- Randall Division of Cell and Molecular Biophysics, King's College London, London, UK SE1 1UL
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48
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Fletcher KA, Fakayode SO, Lowry M, Tucker SA, Neal SL, Kimaru IW, McCarroll ME, Patonay G, Oldham PB, Rusin O, Strongin RM, Warner IM. Molecular fluorescence, phosphorescence, and chemiluminescence spectrometry. Anal Chem 2006; 78:4047-68. [PMID: 16771540 PMCID: PMC2662353 DOI: 10.1021/ac060683m] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
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49
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Cohen-Kashi M, Namer Y, Deutsch M. Fluorescence resonance energy transfer imaging via fluorescence polarization measurement. JOURNAL OF BIOMEDICAL OPTICS 2006; 11:34015. [PMID: 16822065 DOI: 10.1117/1.2209955] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
Fluorescence resonance energy transfer (FRET) has become a widely used spectroscopic tool for detecting molecular interactions and molecular proximity in solution, as well as in membranes. On the other hand, fluorescence polarization (FP) is a convenient measure: ratiometric and simple to execute. This work presents a novel methodology for determining energy transfer efficiency (E) via FP measurement. The methodology is based on the fact that a donor's fluorescence lifetime is shortened due to FRET and, consequently, its FP increases. As a model, the present work evaluates the E between fluorescein and rhodamine conjugated ConA attached to the receptors in the lymphocyte membrane. It shows not only that FRET imaging via FP is possible, but also that it is inexpensive, simple to perform, conveniently adaptable to the commonly used fluorescent microscopy, and readily interpretable.
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Affiliation(s)
- Meir Cohen-Kashi
- Bar Ilan University, Department of Physics, Biophysical Interdisciplinary Schottenstein Center for the Research and the Technology of the Cellome, Ramat Gan, Israel
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50
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Nagy P, Bene L, Hyun WC, Vereb G, Braun M, Antz C, Paysan J, Damjanovich S, Park JW, Szöllősi J. Novel calibration method for flow cytometric fluorescence resonance energy transfer measurements between visible fluorescent proteins. Cytometry A 2005; 67:86-96. [PMID: 16163690 DOI: 10.1002/cyto.a.20164] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
BACKGROUND The combination of fluorescence resonance energy transfer (FRET) and flow cytometry offers a statistically firm approach to study protein associations. Fusing green fluorescent protein (GFP) to a studied protein usually does not disturb the normal function of a protein, but quantitation of FRET efficiency calculated between GFP derivatives poses a problem in flow cytometry. METHODS We generated chimeras in which cyan fluorescent protein (CFP) was separated by amino acid linkers of different sizes from yellow fluorescent protein (YFP) and used them to calibrate the cell-by-cell flow cytometric FRET measurements carried out on two different dual-laser flow cytometers. Then, CFP-Kip1 was coexpressed in yeast cells with YFP and cyclin-dependent kinase-2 (Cdk2) and served as a positive control for FRET measurements, and CFP-Kip1 coexpressed with a random peptide fused to YFP was the negative control. RESULTS We measured donor, direct, and sensitized acceptor fluorescence intensities and developed a novel way to calculate a factor (alpha) that characterized the fluorescence intensity of acceptor molecules relative to the same number of excited donor molecules, which is essential for quantifying FRET efficiency. This was achieved by calculating FRET efficiency in two different ways and minimizing the squared difference between the two results by changing alpha. Our method reliably detected the association of Cdk2 with its inhibitor, Kip1, whereas the nonspecific FRET efficiency between Cdk2 and a random peptide was negligible. We identified and sorted subpopulations of yeast cells showing interaction between the studied proteins. CONCLUSIONS We have described a straightforward novel calibration method to accurately quantitate FRET efficiency between GFP derivatives in flow cytometry.
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Affiliation(s)
- Peter Nagy
- Department of Biophysics and Cell Biology, Medical and Health Science Center, University of Debrecen, Debrecen, Hungary
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