1
|
Steiert F, Schultz P, Höfinger S, Müller TD, Schwille P, Weidemann T. Insights into receptor structure and dynamics at the surface of living cells. Nat Commun 2023; 14:1596. [PMID: 36949079 PMCID: PMC10033668 DOI: 10.1038/s41467-023-37284-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2022] [Accepted: 03/10/2023] [Indexed: 03/24/2023] Open
Abstract
Evaluating protein structures in living cells remains a challenge. Here, we investigate Interleukin-4 receptor alpha (IL-4Rα) into which the non-canonical amino acid bicyclo[6.1.0]nonyne-lysine (BCNK) is incorporated by genetic code expansion. Bioorthogonal click labeling is performed with tetrazine-conjugated dyes. To quantify the reaction yield in situ, we develop brightness-calibrated ratiometric imaging, a protocol where fluorescent signals in confocal multi-color images are ascribed to local concentrations. Screening receptor mutants bearing BCNK in the extracellular domain uncovered site-specific variations of both click efficiency and Interleukin-4 binding affinity, indicating subtle well-defined structural perturbations. Molecular dynamics and continuum electrostatics calculations suggest solvent polarization to determine site-specific variations of BCNK reactivity. Strikingly, signatures of differential click efficiency, measured for IL-4Rα in ligand-bound and free form, mirror sub-angstrom deformations of the protein backbone at corresponding locations. Thus, click efficiency by itself represents a remarkably informative readout linked to protein structure and dynamics in the native plasma membrane.
Collapse
Affiliation(s)
- Frederik Steiert
- Department of Cellular and Molecular Biophysics, Max Planck Institute of Biochemistry, Am Klopferspitz 18, 82152, Martinsried, Germany
- Department of Physics, Technical University Munich, 85748, Garching, Germany
| | - Peter Schultz
- Department of Cellular and Molecular Biophysics, Max Planck Institute of Biochemistry, Am Klopferspitz 18, 82152, Martinsried, Germany
| | - Siegfried Höfinger
- VSC Research Center, TU Wien, Operngasse 11 / E057-09, 1040, Wien, Austria
- Department of Physics, Michigan Technological University, 1400 Townsend Drive, 49931, Houghton, MI, USA
| | - Thomas D Müller
- Biozentrum, Julius-von-Sachs-Institut für Biowissenschaften, Lehrstuhl für Molekulare Pflanzenphysiologie und Biophysik - Botanik I, Julius-von-Sachs-Platz 2, 97082, Würzburg, Germany
| | - Petra Schwille
- Department of Cellular and Molecular Biophysics, Max Planck Institute of Biochemistry, Am Klopferspitz 18, 82152, Martinsried, Germany
| | - Thomas Weidemann
- Department of Cellular and Molecular Biophysics, Max Planck Institute of Biochemistry, Am Klopferspitz 18, 82152, Martinsried, Germany.
| |
Collapse
|
2
|
Lemke SB, Weidemann T, Cost AL, Grashoff C, Schnorrer F. A small proportion of Talin molecules transmit forces at developing muscle attachments in vivo. PLoS Biol 2019; 17:e3000057. [PMID: 30917109 PMCID: PMC6453563 DOI: 10.1371/journal.pbio.3000057] [Citation(s) in RCA: 48] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2018] [Revised: 04/08/2019] [Accepted: 03/08/2019] [Indexed: 11/19/2022] Open
Abstract
Cells in developing organisms are subjected to particular mechanical forces that shape tissues and instruct cell fate decisions. How these forces are sensed and transmitted at the molecular level is therefore an important question, one that has mainly been investigated in cultured cells in vitro. Here, we elucidate how mechanical forces are transmitted in an intact organism. We studied Drosophila muscle attachment sites, which experience high mechanical forces during development and require integrin-mediated adhesion for stable attachment to tendons. Therefore, we quantified molecular forces across the essential integrin-binding protein Talin, which links integrin to the actin cytoskeleton. Generating flies expressing 3 Förster resonance energy transfer (FRET)-based Talin tension sensors reporting different force levels between 1 and 11 piconewton (pN) enabled us to quantify physiologically relevant molecular forces. By measuring primary Drosophila muscle cells, we demonstrate that Drosophila Talin experiences mechanical forces in cell culture that are similar to those previously reported for Talin in mammalian cell lines. However, in vivo force measurements at developing flight muscle attachment sites revealed that average forces across Talin are comparatively low and decrease even further while attachments mature and tissue-level tension remains high. Concomitantly, the Talin concentration at attachment sites increases 5-fold as quantified by fluorescence correlation spectroscopy (FCS), suggesting that only a small proportion of Talin molecules are mechanically engaged at any given time. Reducing Talin levels at late stages of muscle development results in muscle–tendon rupture in the adult fly, likely as a result of active muscle contractions. We therefore propose that a large pool of adhesion molecules is required to share high tissue forces. As a result, less than 15% of the molecules experience detectable forces at developing muscle attachment sites at the same time. Our findings define an important new concept of how cells can adapt to changes in tissue mechanics to prevent mechanical failure in vivo. The protein Talin links the transmembrane cell adhesion molecule integrin to the actin cytoskeleton. Quantitative FRET-based force measurements across Talin in vivo reveal that only few Talin molecules are under force during the development of muscle attachment sites. Cells in our body are constantly exposed to mechanical forces, which they need to sense and react to. In previous studies, fluorescent force sensors were developed to demonstrate that individual proteins in adhesion structures of a cell experience forces in the piconewton (pN) range. However, these cells were analyzed in isolation in an artificial plastic or glass environment. Here, we explored forces on adhesion proteins in their natural environment within a developing animal and used the muscle–tendon tissue in the fruit fly Drosophila as a model system. We made genetically modified fly lines with force sensors or controls inserted into the gene that produces the essential adhesion protein Talin. Using these force sensor flies, we found that only a small proportion of all the Talin proteins (<15%) present at developing muscle–tendon attachments experience detectable forces at the same time. Nevertheless, a large amount of Talin is accumulated at these attachments during fly development. We found that this large Talin pool is important to prevent rupture of the muscle–tendon connection in adult flies that produce high muscle forces during flight. In conclusion, we demonstrated that a large pool of Talin proteins is required for stable muscle–tendon attachment, likely with the individual Talin molecules dynamically sharing the mechanical load.
Collapse
Affiliation(s)
- Sandra B. Lemke
- Max Planck Institute of Biochemistry, Martinsried, Germany
- * E-mail: (FS); (CG); (SBL)
| | | | - Anna-Lena Cost
- Max Planck Institute of Biochemistry, Martinsried, Germany
- University of Münster, Institute for Molecular Cell Biology, Münster, Germany
| | - Carsten Grashoff
- Max Planck Institute of Biochemistry, Martinsried, Germany
- University of Münster, Institute for Molecular Cell Biology, Münster, Germany
- * E-mail: (FS); (CG); (SBL)
| | - Frank Schnorrer
- Max Planck Institute of Biochemistry, Martinsried, Germany
- Aix Marseille University, CNRS, IBDM, Marseille, France
- * E-mail: (FS); (CG); (SBL)
| |
Collapse
|
3
|
Steiert F, Petrov EP, Schultz P, Schwille P, Weidemann T. Photophysical Behavior of mNeonGreen, an Evolutionarily Distant Green Fluorescent Protein. Biophys J 2018; 114:2419-2431. [PMID: 29706225 DOI: 10.1016/j.bpj.2018.04.013] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2018] [Revised: 04/06/2018] [Accepted: 04/09/2018] [Indexed: 12/31/2022] Open
Abstract
Fluorescent proteins (FPs) feature complex photophysical behavior that must be considered when studying the dynamics of fusion proteins in model systems and live cells. In this work, we characterize mNeonGreen (mNG), a recently introduced FP from the bilaterian Branchiostoma lanceolatum, in comparison to the well-known hydrozoan variants enhanced green fluorescent protein (EGFP) and Aequorea coerulescens GFP by steady-state spectroscopy and fluorescence correlation spectroscopy in solutions of different pH. Blind spectral unmixing of sets of absorption spectra reveals three interconverting electronic states of mNG: a nonfluorescent protonated state, a bright state showing bell-shaped pH dependence, and a similarly bright state dominating at high pH. The gradual population of the acidic form by external protonation is reflected by increased flickering at low pH in fluorescence correlation spectroscopy measurements, albeit with much slower flicker rates and lower amplitudes as compared to Aequorea GFPs. In addition, increased flickering of mNG indicates a second deprotonation step above pH 10 leading to a slight decrease in fluorescence. Thus, mNG is distinguished from Aequorea GFPs by a two-step protonation response with opposite effects that reflects a chemically distinct chromophore environment. Despite the more complex pH dependence, mNG represents a superior FP under a broad range of conditions.
Collapse
Affiliation(s)
- Frederik Steiert
- Department of Cellular and Molecular Biophysics, Max Planck Institute of Biochemistry, Martinsried, Germany; Physics Department, Technical University Munich, Garching, Germany
| | - Eugene P Petrov
- Department of Cellular and Molecular Biophysics, Max Planck Institute of Biochemistry, Martinsried, Germany; Faculty of Physics, Ludwig Maximilian University of Munich, Munich, Germany
| | - Peter Schultz
- Department of Cellular and Molecular Biophysics, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - Petra Schwille
- Department of Cellular and Molecular Biophysics, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - Thomas Weidemann
- Department of Cellular and Molecular Biophysics, Max Planck Institute of Biochemistry, Martinsried, Germany.
| |
Collapse
|
4
|
Pylypenko O, Welz T, Tittel J, Kollmar M, Chardon F, Malherbe G, Weiss S, Michel CIL, Samol-Wolf A, Grasskamp AT, Hume A, Goud B, Baron B, England P, Titus MA, Schwille P, Weidemann T, Houdusse A, Kerkhoff E. Coordinated recruitment of Spir actin nucleators and myosin V motors to Rab11 vesicle membranes. eLife 2016; 5. [PMID: 27623148 PMCID: PMC5021521 DOI: 10.7554/elife.17523] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2016] [Accepted: 08/18/2016] [Indexed: 12/22/2022] Open
Abstract
There is growing evidence for a coupling of actin assembly and myosin motor activity in cells. However, mechanisms for recruitment of actin nucleators and motors on specific membrane compartments remain unclear. Here we report how Spir actin nucleators and myosin V motors coordinate their specific membrane recruitment. The myosin V globular tail domain (MyoV-GTD) interacts directly with an evolutionarily conserved Spir sequence motif. We determined crystal structures of MyoVa-GTD bound either to the Spir-2 motif or to Rab11 and show that a Spir-2:MyoVa:Rab11 complex can form. The ternary complex architecture explains how Rab11 vesicles support coordinated F-actin nucleation and myosin force generation for vesicle transport and tethering. New insights are also provided into how myosin activation can be coupled with the generation of actin tracks. Since MyoV binds several Rab GTPases, synchronized nucleator and motor targeting could provide a common mechanism to control force generation and motility in different cellular processes.
Collapse
Affiliation(s)
- Olena Pylypenko
- Institut Curie, PSL Research University, CNRS, UMR 144, F-75005, Paris, France
| | - Tobias Welz
- University Hospital Regensburg, Regensburg, Germany
| | - Janine Tittel
- Max Planck Institute of Biochemistry, Martinsried, Germany
| | - Martin Kollmar
- Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Florian Chardon
- Institut Curie, PSL Research University, CNRS, UMR 144, F-75005, Paris, France
| | - Gilles Malherbe
- Institut Curie, PSL Research University, CNRS, UMR 144, F-75005, Paris, France
| | - Sabine Weiss
- University Hospital Regensburg, Regensburg, Germany
| | | | | | | | - Alistair Hume
- University of Nottingham, Nottingham, United Kingdom
| | - Bruno Goud
- Institut Curie, PSL Research University, CNRS, UMR 144, F-75005, Paris, France
| | - Bruno Baron
- Institut Pasteur, Biophysics of Macromolecules and their Interactions, Paris, France.,CNRS, UMR 3528, Paris, France
| | - Patrick England
- Institut Pasteur, Biophysics of Macromolecules and their Interactions, Paris, France.,CNRS, UMR 3528, Paris, France
| | - Margaret A Titus
- Department of Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, United States
| | - Petra Schwille
- Max Planck Institute of Biochemistry, Martinsried, Germany
| | | | - Anne Houdusse
- Institut Curie, PSL Research University, CNRS, UMR 144, F-75005, Paris, France
| | | |
Collapse
|
5
|
Heusermann W, Ludin B, Pham NT, Auer M, Weidemann T, Hintersteiner M. A Wide-Field Fluorescence Microscope Extension for Ultrafast Screening of One-Bead One-Compound Libraries Using a Spectral Image Subtraction Approach. ACS Comb Sci 2016; 18:209-19. [PMID: 27057765 DOI: 10.1021/acscombsci.5b00175] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
The increasing involvement of academic institutions and biotech companies in drug discovery calls for cost-effective methods to identify new bioactive molecules. Affinity-based on-bead screening of combinatorial one-bead one-compound libraries combines a split-mix synthesis design with a simple protein binding assay operating directly at the bead matrix. However, one bottleneck for academic scale on-bead screening is the unavailability of a cheap, automated, and robust screening platform that still provides a quantitative signal related to the amount of target protein binding to individual beads for hit bead ranking. Wide-field fluorescence microscopy has long been considered unsuitable due to significant broad spectrum autofluorescence of the library beads in conjunction with low detection sensitivity. Herein, we demonstrate how such a standard microscope equipped with LED-based excitation and a modern CMOS camera can be successfully used for selecting hit beads. We show that the autofluorescence issue can be overcome by an optical image subtraction approach that yields excellent signal-to-noise ratios for the detection of bead-associated target proteins. A polymer capillary attached to a semiautomated bead-picking device allows the operator to efficiently isolate individual hit beads in less than 20 s. The system can be used for ultrafast screening of >200,000 bead-bound compounds in 1.5 h, thereby making high-throughput screening accessible to a wider group within the scientific community.
Collapse
Affiliation(s)
- Wolf Heusermann
- IMCF
Biozentrum, Universität Basel, Klingelbergstrasse 50/70, 4056 Basel, Switzerland
| | - Beat Ludin
- Life Imaging Services, Efringerstrasse
79, 4057 Basel, Switzerland
| | - Nhan T Pham
- School
of Biological Sciences and School of Biomedical Sciences, University of Edinburgh, CH Waddington Building, Max Born Crescent, The King's
Buildings, Edinburgh, EH9
3BF, United Kingdom
| | - Manfred Auer
- School
of Biological Sciences and School of Biomedical Sciences, University of Edinburgh, CH Waddington Building, Max Born Crescent, The King's
Buildings, Edinburgh, EH9
3BF, United Kingdom
| | - Thomas Weidemann
- Max Planck Institute of Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany
| | | |
Collapse
|
6
|
Sánchez MF, Levi V, Weidemann T, Carrer DC. Agonist mobility on supported lipid bilayers affects Fas mediated death response. FEBS Lett 2015; 589:3527-33. [PMID: 26484594 DOI: 10.1016/j.febslet.2015.10.009] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2015] [Revised: 10/07/2015] [Accepted: 10/08/2015] [Indexed: 11/29/2022]
Abstract
Extrinsic apoptosis is initiated by recognition and clustering of the single-pass transmembrane proteins Fas ligand and Fas expressed at the surface of closely apposed lymphocytes and target cells, respectively. Since Fas-mediated death response was mainly studied with soluble antibodies, the mobility constraints for receptor activation by a membrane embedded agonist is not well understood. We explored this influence by stimulating apoptosis on functionalized supported lipid bilayers, where we quantified agonist mobility by z-scan fluorescence correlation spectroscopy. Using different lipid compositions, we show that the apoptotic response correlates with increased lateral mobility of the agonist in the lipid bilayer.
Collapse
Affiliation(s)
- M Florencia Sánchez
- Instituto de Investigación Médica Mercedes y Martín Ferreyra (INIMEC), CONICET-Universidad Nacional de Córdoba, Friuli 2434, CC389, 5000 Córdoba, Argentina
| | - Valeria Levi
- Departamento de Química Biológica-IQUIBICEN, Facultad de Ciencias Exactas, Universidad de Buenos Aires, Ciudad Universitaria, Buenos Aires, Argentina
| | - Thomas Weidemann
- Max Planck Institute of Biochemistry, Cellular and Molecular Biophysics, Am Klopferspitz 18, 82152 Martinsried, Germany.
| | - Dolores C Carrer
- Instituto de Investigación Médica Mercedes y Martín Ferreyra (INIMEC), CONICET-Universidad Nacional de Córdoba, Friuli 2434, CC389, 5000 Córdoba, Argentina.
| |
Collapse
|
7
|
Tittel J, Welz T, Czogalla A, Dietrich S, Samol-Wolf A, Schulte M, Schwille P, Weidemann T, Kerkhoff E. Membrane targeting of the Spir·formin actin nucleator complex requires a sequential handshake of polar interactions. J Biol Chem 2015; 290:6428-44. [PMID: 25564607 DOI: 10.1074/jbc.m114.602672] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
Spir and formin (FMN)-type actin nucleators initiate actin polymerization at vesicular membranes necessary for long range vesicular transport processes. Here we studied in detail the membrane binding properties and protein/protein interactions that govern the assembly of the membrane-associated Spir·FMN complex. Using biomimetic membrane models we show that binding of the C-terminal Spir-2 FYVE-type zinc finger involves both the presence of negatively charged lipids and hydrophobic contributions from the turret loop that intrudes the lipid bilayer. In solution, we uncovered a yet unknown intramolecular interaction between the Spir-2 FYVE-type domain and the N-terminal kinase non-catalytic C-lobe domain (KIND) that could not be detected in the membrane-bound state. Interestingly, we found that the intramolecular Spir-2 FYVE/KIND and the trans-regulatory Fmn-2-FSI/Spir-2-KIND interactions are competitive. We therefore characterized co-expressed Spir-2 and Fmn-2 fluorescent protein fusions in living cells by fluorescence cross-correlation spectroscopy. The data corroborate a model according to which Spir-2 exists in two different states, a cytosolic monomeric conformation and a membrane-bound state in which the KIND domain is released and accessible for subsequent Fmn-2 recruitment. This sequence of interactions mechanistically couples membrane binding of Spir to the recruitment of FMN, a pivotal step for initiating actin nucleation at vesicular membranes.
Collapse
Affiliation(s)
- Janine Tittel
- From the Max Planck Institute of Biochemistry, Am Klopferspitz 18, D-82152 Martinsried, Germany, Biotechnology Center (BIOTEC), Biophysics Research Group and
| | - Tobias Welz
- Molecular Cell Biology Laboratory, Department of Neurology, University Hospital Regensburg, Franz-Josef-Strauss-Allee 11, D-93053 Regensburg, Germany, and
| | - Aleksander Czogalla
- Paul Langerhans Institute, Technische Universität (TU) Dresden, Tatzberg 47-51, D-01307 Dresden, Germany, German Center for Diabetes Research (Deutsches Zentrum für Diabetesforschung), 85764 Neuherberg, Germany
| | - Susanne Dietrich
- Molecular Cell Biology Laboratory, Department of Neurology, University Hospital Regensburg, Franz-Josef-Strauss-Allee 11, D-93053 Regensburg, Germany, and
| | - Annette Samol-Wolf
- Molecular Cell Biology Laboratory, Department of Neurology, University Hospital Regensburg, Franz-Josef-Strauss-Allee 11, D-93053 Regensburg, Germany, and
| | - Markos Schulte
- Molecular Cell Biology Laboratory, Department of Neurology, University Hospital Regensburg, Franz-Josef-Strauss-Allee 11, D-93053 Regensburg, Germany, and
| | - Petra Schwille
- From the Max Planck Institute of Biochemistry, Am Klopferspitz 18, D-82152 Martinsried, Germany, Biotechnology Center (BIOTEC), Biophysics Research Group and
| | - Thomas Weidemann
- From the Max Planck Institute of Biochemistry, Am Klopferspitz 18, D-82152 Martinsried, Germany, Biotechnology Center (BIOTEC), Biophysics Research Group and
| | - Eugen Kerkhoff
- Molecular Cell Biology Laboratory, Department of Neurology, University Hospital Regensburg, Franz-Josef-Strauss-Allee 11, D-93053 Regensburg, Germany, and
| |
Collapse
|
8
|
Kurgonaite K, Gandhi H, Kurth T, Pautot S, Schwille P, Weidemann T, Bökel C. Essential role of endocytosis for Interleukin-4 receptor mediated JAK/STAT signalling. J Cell Sci 2015; 128:3781-95. [DOI: 10.1242/jcs.170969] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2015] [Accepted: 08/21/2015] [Indexed: 01/15/2023] Open
Abstract
Many important signalling cascades operate through specialized signalling endosomes, but a corresponding mechanism has as yet not been described for hematopoietic cytokine receptors. Based on live cell affinity measurements we recently proposed that ligand induced Interleukin-4 receptor (IL-4R) complex formation and thus JAK/STAT pathway activation requires a local, subcellular increase in receptor density. Here we show that this concentration step is provided by the internalization of IL-4R subunits through a constitutive, Rac1/Pak and actin mediated endocytosis route that causes IL-4R subunits to become enriched by about two orders of magnitude within a population of cortical endosomes. Consistently, ligand induced receptor dimers are preferentially detected within these endosomes. IL-4 signalling can be blocked by pharmacological inhibitors targeting the actin polymerization machinery driving receptor internalization, placing endocytosis unambigously upstream of receptor activation. Together these observations demonstrate a role for endocytosis that is mechanistically distinct from the scaffolding function of signalling endosomes in other pathways.
Collapse
Affiliation(s)
- Kristina Kurgonaite
- Center for Regenerative Therapies Dresden (CRTD), Technische Universität Dresden, Fetscherstr. 105, 01307 Dresden, Germany
| | - Hetvi Gandhi
- BIOTEC/Biophysics, Technische Universität Dresden, Tatzberg 47-51, 01307 Dresden, Germany
| | - Thomas Kurth
- BIOTEC/Biophysics, Technische Universität Dresden, Tatzberg 47-51, 01307 Dresden, Germany
| | - Sophie Pautot
- BIOTEC/Biophysics, Technische Universität Dresden, Tatzberg 47-51, 01307 Dresden, Germany
| | - Petra Schwille
- Center for Regenerative Therapies Dresden (CRTD), Technische Universität Dresden, Fetscherstr. 105, 01307 Dresden, Germany
| | - Thomas Weidemann
- BIOTEC/Biophysics, Technische Universität Dresden, Tatzberg 47-51, 01307 Dresden, Germany
| | - Christian Bökel
- Center for Regenerative Therapies Dresden (CRTD), Technische Universität Dresden, Fetscherstr. 105, 01307 Dresden, Germany
| |
Collapse
|
9
|
Gandhi H, Worch R, Kurgonaite K, Hintersteiner M, Schwille P, Bökel C, Weidemann T. Dynamics and interaction of interleukin-4 receptor subunits in living cells. Biophys J 2014; 107:2515-27. [PMID: 25468331 DOI: 10.1016/j.bpj.2014.07.077] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2014] [Revised: 07/08/2014] [Accepted: 07/24/2014] [Indexed: 11/19/2022] Open
Abstract
It has long been established that dimerization of Interleukin-4 receptor (IL-4R) subunits is a pivotal step for JAK/STAT signal transduction. However, ligand-induced complex formation at the surface of living cells has been challenging to observe. Here we report an experimental assay employing trisNTA dyes for orthogonal, external labeling of eGFP-tagged receptor constructs that allows the quantification of receptor heterodimerization by dual-color fluorescence cross-correlation spectroscopy. Fluorescence cross-correlation spectroscopy analysis at the plasma membrane shows that IL-4R subunit dimerization is indeed a strictly ligand-induced process. Under conditions of saturating cytokine occupancy, we determined intramembrane dissociation constants (K(d,2D)) of 180 and 480 receptors per μm(2) for the type-2 complexes IL-4:IL-4Rα/IL-13Rα1 and IL-13:IL-13Rα1/IL-4Rα, respectively. For the lower affinity type-1 complex IL-4:IL-4Rα/IL-2Rγ, we estimated a K(d,2D) of ∼1000 receptors per μm(2). The receptor densities required for effective dimerization thus exceed the typical, average expression levels by several orders of magnitude. In addition, we find that all three receptor subunits accumulate rapidly within a subpopulation of early sorting and recycling endosomes stably anchored just beneath the plasma membrane (cortical endosomes, CEs). The receptors, as well as labeled IL-4 and trisNTA ligands are specifically trafficked into CEs by a constitutive internalization mechanism. This may compensate for the inherent weak affinities that govern ligand-induced receptor dimerization at the plasma membrane. Consistently, activated receptors are also concentrated at the CEs. Our observations thus suggest that receptor trafficking may play an important role for the regulation of IL-4R-mediated JAK/STAT signaling.
Collapse
Affiliation(s)
- Hetvi Gandhi
- BIOTEC/Biophysics, Technische Universität Dresden, Dresden, Germany
| | - Remigiusz Worch
- BIOTEC/Biophysics, Technische Universität Dresden, Dresden, Germany; Institute of Physics, Polish Academy of Sciences, Warsaw, Poland
| | - Kristina Kurgonaite
- Center for Regenerative Therapies Dresden, Technische Universität Dresden, Dresden, Germany
| | | | - Petra Schwille
- BIOTEC/Biophysics, Technische Universität Dresden, Dresden, Germany; Max Planck Institute of Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany
| | - Christian Bökel
- Center for Regenerative Therapies Dresden, Technische Universität Dresden, Dresden, Germany
| | - Thomas Weidemann
- BIOTEC/Biophysics, Technische Universität Dresden, Dresden, Germany; Max Planck Institute of Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany.
| |
Collapse
|
10
|
Weidemann T, Mücksch J, Schwille P. Fluorescence fluctuation microscopy: a diversified arsenal of methods to investigate molecular dynamics inside cells. Curr Opin Struct Biol 2014; 28:69-76. [DOI: 10.1016/j.sbi.2014.07.008] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2014] [Accepted: 07/11/2014] [Indexed: 11/26/2022]
|
11
|
Abstract
Summary: We present a graphical user interface (PyCorrFit) for the fitting of theoretical model functions to experimental data obtained by fluorescence correlation spectroscopy (FCS). The program supports many data file formats and features a set of tools specialized in FCS data evaluation. Availability and implementation: The Python source code is freely available for download from the PyCorrFit web page at http://pycorrfit.craban.de. We offer binaries for Ubuntu Linux, Mac OS X and Microsoft Windows. Contact:paul.mueller@biotec.tu-dresden.de and weidemann@biochem.mpg.de
Collapse
Affiliation(s)
- Paul Müller
- Biotechnology Center, Technische Universität Dresden, 01307 Dresden and Max Planck Institute of Biochemistry, Cellular and Molecular Biophysics, 82152 Martinsried, Germany
| | - Petra Schwille
- Biotechnology Center, Technische Universität Dresden, 01307 Dresden and Max Planck Institute of Biochemistry, Cellular and Molecular Biophysics, 82152 Martinsried, Germany
| | - Thomas Weidemann
- Biotechnology Center, Technische Universität Dresden, 01307 Dresden and Max Planck Institute of Biochemistry, Cellular and Molecular Biophysics, 82152 Martinsried, Germany
| |
Collapse
|
12
|
Abstract
Fluorescence correlation spectroscopy (FCS) can add dynamic molecular information to images of live cells. For example, a confocal laser scanning microscope (CLSM) equipped with an accessory FCS unit provides the possibility to first image the spatial distribution of a fluorescent protein before probing its mobility within defined regions of interest. Whereas specific protein-protein interactions are preferably assayed with a dual-color approach, single-color FCS can still provide valuable information about the size of the diffusing entities and potential interactions with other, nonfluorescent, proteins or subcellular structures. Because number fluctuations are measured, the concentrations of freely diffusing complexes and their state of oligomerization are accessible.
Collapse
Affiliation(s)
- Thomas Weidemann
- BIOTEC, Biophysics, Technische Universität Dresden, Dresden, Germany
| |
Collapse
|
13
|
Abstract
Scanning fluorescence correlation spectroscopy (SFCS) with a scan path perpendicular to the membrane plane was introduced to measure diffusion and interactions of fluorescent components in free-standing biomembranes. Using a confocal laser scanning microscope (CLSM), the open detection volume is repeatedly scanned through the membrane at a kHz frequency. The fluorescence photons emitted from the detection volume are continuously recorded and stored in a file. While the accessory hardware requirements for a conventional CLSM are minimal, data evaluation can pose a bottleneck. The photon events must be assigned to each scan, in which the maximum signal intensities have to be detected, binned, and aligned between the scans, in order to derive the membrane-related intensity fluctuations of one spot. Finally, this time-dependent signal must be correlated and evaluated by well-known FCS model functions. Here we provide two platform-independent, open source software tools (PyScanFCS and PyCorrFit) that allow to perform all of these steps and to establish perpendicular SFCS in its one- or two-focus as well as its single- or dual-color modality.
Collapse
Affiliation(s)
- Paul Müller
- BIOTEC, Biophysics, Technische Universität Dresden, Dresden, Germany
| | | | | |
Collapse
|
14
|
Kupinski AP, Raabe I, Michel M, Ail D, Brusch L, Weidemann T, Bökel C. Phosphorylation of the Smo tail is controlled by membrane localisation and is dispensable for clustering. Development 2013. [DOI: 10.1242/dev.105163] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
|
15
|
Kotlarz D, Ziętara N, Uzel G, Weidemann T, Braun CJ, Diestelhorst J, Krawitz PM, Robinson PN, Hecht J, Puchałka J, Gertz EM, Schäffer AA, Lawrence MG, Kardava L, Pfeifer D, Baumann U, Pfister ED, Hanson EP, Schambach A, Jacobs R, Kreipe H, Moir S, Milner JD, Schwille P, Mundlos S, Klein C. Loss-of-function mutations in the IL-21 receptor gene cause a primary immunodeficiency syndrome. ACTA ACUST UNITED AC 2013; 210:433-43. [PMID: 23440042 PMCID: PMC3600901 DOI: 10.1084/jem.20111229] [Citation(s) in RCA: 161] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
A primary immunodeficiency syndrome caused by loss-of-function mutations in the IL-21 receptor exhibits impaired B, T, and NK cell function. Primary immunodeficiencies (PIDs) represent exquisite models for studying mechanisms of human host defense. In this study, we report on two unrelated kindreds, with two patients each, who had cryptosporidial infections associated with chronic cholangitis and liver disease. Using exome and candidate gene sequencing, we identified two distinct homozygous loss-of-function mutations in the interleukin-21 receptor gene (IL21R; c.G602T, p.Arg201Leu and c.240_245delCTGCCA, p.C81_H82del). The IL-21RArg201Leu mutation causes aberrant trafficking of the IL-21R to the plasma membrane, abrogates IL-21 ligand binding, and leads to defective phosphorylation of signal transducer and activator of transcription 1 (STAT1), STAT3, and STAT5. We observed impaired IL-21–induced proliferation and immunoglobulin class-switching in B cells, cytokine production in T cells, and NK cell cytotoxicity. Our study indicates that human IL-21R deficiency causes an immunodeficiency and highlights the need for early diagnosis and allogeneic hematopoietic stem cell transplantation in affected children.
Collapse
Affiliation(s)
- Daniel Kotlarz
- Department of Pediatric Hematology/Oncology, Hannover Medical School, 30625 Hannover, Germany
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
16
|
Kupinski AP, Raabe I, Michel M, Ail D, Brusch L, Weidemann T, Bökel C. Phosphorylation of the Smo tail is controlled by membrane localization and is dispensable for clustering. J Cell Sci 2013; 126:4684-97. [DOI: 10.1242/jcs.128926] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
The Hedgehog (Hh) signalling cascade is highly conserved and involved in development and disease throughout evolution. Nevertheless, in comparison with other pathways our mechanistic understanding of Hh signal transduction is remarkably incomplete. In the absence of ligand, the Hh receptor Patched (Ptc) represses the key signal transducer Smoothened (Smo) through an unknown mechanism. Hh binding to Ptc alleviates this repression, causing Smo redistribution to the plasma membrane, phosphorylation and opening of the Smo cytoplasmic tail, and Smo oligomerization. However, the order and interdependence of these events is as yet poorly understood. We have mathematically modelled and simulated Smo activation for two alternative modes of pathway activation, with Ptc primarily affecting either Smo localization or phosphorylation. Visualizing Smo activation through a novel, fluorescence based reporter allowed us to test these competing models. Here we show that Smo localization to the plasma membrane is sufficient for phosphorylation of the cytoplasmic tail in the presence of Ptc. Using fluorescence cross-correlation spectroscopy (FCCS) we furthermore demonstrate that inactivation of Ptc by Hh induces Smo clustering irrespective of Smo phosphorylation. Our observations therefore support a model of Hh signal transduction whereby Smo subcellular localization and not phosphorylation is the primary target of Ptc function.
Collapse
|
17
|
Abstract
Fluorescence correlation spectroscopy evaluates local signal fluctuations arising from stochastic movements of fluorescent particles in solution. The measured fluctuating signal is correlated in time and analyzed with appropriate model functions containing the parameters that describe the underlying molecular behavior. The dual-color extension, fluorescence cross-correlation spectroscopy (FCCS) allows for a comparison between spectrally well-separated channels to extract codiffusion events that reflect interactions between differently labeled molecules. In addition to solution measurements, FCCS can be applied with subcellular resolution and is therefore a very promising approach for a quantitative biochemical assessment of molecular networks in living cells. To derive thermodynamic and kinetic reaction parameters, the influence of a number of other factors like background noise, illumination intensity profiles, photophysical processes, and cross talk between the channels have to be treated. Here, we provide a roadmap to derive binding reaction data with dual-color FCCS using continuous wave laser excitation, as it is now accessible with many state-of-the-art confocal microscopes.
Collapse
Affiliation(s)
- Thomas Weidemann
- Biophysics/BIOTEC, Technische Universität Dresden, Dresden, Germany.
| | | |
Collapse
|
18
|
Weidemann T, Worch R, Kurgonaite K, Hintersteiner M, Bökel C, Schwille P. Single cell analysis of ligand binding and complex formation of interleukin-4 receptor subunits. Biophys J 2011; 101:2360-9. [PMID: 22098734 DOI: 10.1016/j.bpj.2011.10.014] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2011] [Revised: 09/27/2011] [Accepted: 10/11/2011] [Indexed: 10/15/2022] Open
Abstract
Interleukin-4 (IL-4) is an important class I cytokine involved in adaptive immunity. IL-4 binds with high affinity to the single-pass transmembrane receptor IL-4Rα. Subsequently, IL-4Rα/IL-4 is believed to engage a second receptor chain, either IL-2Rγ or IL-13Rα1, to form type I or II receptor complexes, respectively. This ternary complex formation then triggers downstream signaling via intracellular Janus kinases bound to the cytoplasmic receptor tails. Here, we study the successive steps of complex formation at the single cell level with confocal fluorescence imaging and correlation spectroscopy. We characterize binding and signaling of fluorescently labeled IL-4 by flow cytometry of IL-4-dependent BaF3 cells. The affinity to ectopically expressed IL-4Rα was then measured by single-color fluorescence correlation spectroscopy in adherent HEK293T cells that express the components of the type II IL-4R but not type I. Finally, IL-4-induced complex formation was tested by dual-color fluorescence cross-correlation spectroscopy. The data provide evidence for codiffusion of IL-4-A647 bound IL-4Rα and the type II subunit IL-13Rα1 fused to enhanced green fluorescent protein, whereas type I complexes containing IL-2Rγ and JAK3 were not detected at the cell surface. This behavior may reflect hitherto undefined differences in the mode of receptor activation between type I (lymphoid) and type II (epithelial) receptor expressing cells.
Collapse
Affiliation(s)
- Thomas Weidemann
- Biophysics Research Group, Technische Universität Dresden, Dresden, Germany.
| | | | | | | | | | | |
Collapse
|
19
|
Worch R, Bökel C, Höfinger S, Schwille P, Weidemann T. Focus on composition and interaction potential of single-pass transmembrane domains. Proteomics 2010; 10:4196-208. [DOI: 10.1002/pmic.201000208] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
|
20
|
Weidemann T, Seifert JM, Hintersteiner M, Auer M. Analysis of Protein−Small Molecule Interactions by Microscale Equilibrium Dialysis and Its Application As a Secondary Confirmation Method for on-Bead Screening. ACTA ACUST UNITED AC 2010; 12:647-54. [DOI: 10.1021/cc100057e] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Thomas Weidemann
- School of Biological Sciences, University of Edinburgh, The King’s Buildings, CH Waddington Building 3.07, Mayfield Road, Edinburgh EH9 3JD, U.K., BIOTEC/Biophysics, Technische Universität Dresden, Tatzberg 47-51, 01307 Dresden, Germany, and Marinomed Biotechnology GmbH, Veterinärplatz 1, 1210 Vienna, Austria
| | - Jan-Marcus Seifert
- School of Biological Sciences, University of Edinburgh, The King’s Buildings, CH Waddington Building 3.07, Mayfield Road, Edinburgh EH9 3JD, U.K., BIOTEC/Biophysics, Technische Universität Dresden, Tatzberg 47-51, 01307 Dresden, Germany, and Marinomed Biotechnology GmbH, Veterinärplatz 1, 1210 Vienna, Austria
| | - Martin Hintersteiner
- School of Biological Sciences, University of Edinburgh, The King’s Buildings, CH Waddington Building 3.07, Mayfield Road, Edinburgh EH9 3JD, U.K., BIOTEC/Biophysics, Technische Universität Dresden, Tatzberg 47-51, 01307 Dresden, Germany, and Marinomed Biotechnology GmbH, Veterinärplatz 1, 1210 Vienna, Austria
| | - Manfred Auer
- School of Biological Sciences, University of Edinburgh, The King’s Buildings, CH Waddington Building 3.07, Mayfield Road, Edinburgh EH9 3JD, U.K., BIOTEC/Biophysics, Technische Universität Dresden, Tatzberg 47-51, 01307 Dresden, Germany, and Marinomed Biotechnology GmbH, Veterinärplatz 1, 1210 Vienna, Austria
| |
Collapse
|
21
|
Kar P, Seel M, Weidemann T, Höfinger S. Theoretical mimicry of biomembranes. FEBS Lett 2009; 583:1909-15. [DOI: 10.1016/j.febslet.2009.04.040] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2009] [Revised: 04/03/2009] [Accepted: 04/23/2009] [Indexed: 11/16/2022]
|
22
|
Carrer DC, Weidemann T, Ries J, Schwille P. Ceramide And The FasR In Plasma Membrane Spheres. Biophys J 2009. [DOI: 10.1016/j.bpj.2008.12.1843] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022] Open
|
23
|
Hintersteiner M, Weidemann T, Kimmerlin T, Filiz N, Buehler C, Auer M. Covalent fluorescence labeling of His-tagged proteins on the surface of living cells. Chembiochem 2008; 9:1391-5. [PMID: 18461582 DOI: 10.1002/cbic.200800089] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Affiliation(s)
- Martin Hintersteiner
- Novartis Institutes for BioMedical Research (NIBR), Innovative Screening Technologies, Brunnerstrasse 59, 1235 Vienna, Austria.
| | | | | | | | | | | |
Collapse
|
24
|
Weidemann T, Höfinger S, Müller K, Auer M. Beyond dimerization: a membrane-dependent activation model for interleukin-4 receptor-mediated signalling. J Mol Biol 2006; 366:1365-73. [PMID: 17223132 DOI: 10.1016/j.jmb.2006.11.095] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2006] [Revised: 11/27/2006] [Accepted: 11/28/2006] [Indexed: 10/23/2022]
Abstract
Class I cytokine receptors efficiently transfer activation signals from the extracellular space to the cytoplasm and play a dominant role in growth control and differentiation of human tissues. Although a significant body of literature is devoted to this topic, a consistent mechanistic picture for receptor activation in the membrane environment is still missing. Using the interleukin-4 receptor (IL-4R) as an example, we propose that the membrane-proximal stem-loop of the extracellular domains contains pivotal elements of a rotational switch. Interfacial energies of amino acid side-chains contained in the highly conserved WSXWS at the surface of the lipid bilayer suggest a new functional role for this motif. A generic activation mechanism for this receptor class is presented, which may impact the design of a new generation of biophysical assay systems.
Collapse
Affiliation(s)
- Thomas Weidemann
- Innovative Screening Technologies, Novartis Institutes for BioMedical Research, Brunnerstr 59, A-1235 Vienna, Austria.
| | | | | | | |
Collapse
|
25
|
Abstract
Chemical biology has emerged as a new scientific discipline to change the way scientists approach and study the interface between chemistry, biology, and physics. By integrating the knowledge base of the human genome with the power of diverse and flexible chemical technology platforms, the ultimate goal is to define the 'rules of engagement' for small molecules and their use in basic biology and in drug discovery. Herein, we highlight the current counterpoles of the chemical biology philosophy in the framework between conformational diversity and informational complexity. Expanding the growing molecular recognition information matrix into classification of diseases and immediate mechanistic in-vivo proof of concept models represent the next development phase in a field that, unlike any other due to its multidisciplinary nature, unifies basic scientists and drug discoverers.
Collapse
Affiliation(s)
- Nicole-Claudia Meisner
- Novartis Institute for Biomedical Research--Vienna Discovery Technologies, Innovative Screening Technologies Unit, A-1235, Vienna, Brunner Strasse 59, Austria
| | | | | | | | | | | | | |
Collapse
|
26
|
Weidemann T, Wachsmuth M, Knoch TA, Müller G, Waldeck W, Langowski J. Counting Nucleosomes in Living Cells with a Combination of Fluorescence Correlation Spectroscopy and Confocal Imaging. J Mol Biol 2003; 334:229-40. [PMID: 14607115 DOI: 10.1016/j.jmb.2003.08.063] [Citation(s) in RCA: 113] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Although methods for light microscopy of chromatin are well established, there are no quantitative data for nucleosome concentrations in vivo. To establish such a method we used a HeLa clone expressing the core histone H2B fused to the enhanced yellow fluorescent protein (H2B-EYFP). Quantitative gel electrophoresis and fluorescence correlation spectroscopy (FCS) of isolated oligonucleosomes show that 5% of the total H2Bs carry the fluorescent tag and an increased nucleosome repeat length of 204 bp for the fluorescent cells. In vivo, the mobility and distribution of H2B-EYFP were studied with a combination of FCS and confocal imaging. With FCS, concentration and brightness of nascent molecules were measured in the cytoplasm, while in the nucleoplasm a background of mobile fluorescent histones was determined by continuous photobleaching. Combining these results allows converting confocal fluorescence images of nuclei into calibrated nucleosome density maps. Absolute nucleosome concentrations in interphase amount up to 250 microM locally, with mean values of 140(+/-28)microM, suggesting that a condensation-controlled regulation of site accessibility takes place at length scales well below 200 nm.
Collapse
Affiliation(s)
- Thomas Weidemann
- Deutsches Krebsforschungszentrum, Division Biophysics of Macromolecules, Im Neuenheimer Feld 580, D-69120 Heidelberg, Germany
| | | | | | | | | | | |
Collapse
|
27
|
Wachsmuth M, Weidemann T, Müller G, Hoffmann-Rohrer UW, Knoch TA, Waldeck W, Langowski J. Analyzing intracellular binding and diffusion with continuous fluorescence photobleaching. Biophys J 2003; 84:3353-63. [PMID: 12719264 PMCID: PMC1302895 DOI: 10.1016/s0006-3495(03)70059-9] [Citation(s) in RCA: 110] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Transport and binding of molecules to specific sites are necessary for the assembly and function of ordered supramolecular structures in cells. For analyzing these processes in vivo, we have developed a confocal fluorescence fluctuation microscope that allows both imaging of the spatial distribution of fluorescent molecules with confocal laser scanning microscopy and probing their mobility at specific positions in the cell with fluorescence correlation spectroscopy and continuous fluorescence photobleaching (CP). Because fluorescence correlation spectroscopy is restricted to rapidly diffusing particles and CP to slower processes, these two methods complement each other. For the analysis of binding-related contributions to mobility we have derived analytical expressions for the temporal behavior of CP curves from which the bound fraction and/or the dissociation rate or residence time at binding sites, respectively, can be obtained. In experiments, we investigated HeLa cells expressing different fluorescent proteins: Although enhanced green fluorescent protein (EGFP) shows high mobility, fusions of histone H2B with the yellow fluorescent protein are incorporated into chromatin, and these nuclei exhibit the presence of a stably bound and a freely diffusing species. Nonpermanent binding was found for mTTF-I, a transcription termination factor for RNA polymerase I, fused with EGFP. The cells show fluorescent nucleoli, and binding is transient. CP yields residence times for mTTF-I-EGFP of approximately 13 s.
Collapse
Affiliation(s)
- Malte Wachsmuth
- Division Biophysics of Macromolecules, German Cancer Research Center, D-69120 Heidelberg, Germany
| | | | | | | | | | | | | |
Collapse
|
28
|
|
29
|
Sievert U, Pau HW, Weidemann T. [The "ear fever thermometer"--studies of ear thermography]. Laryngorhinootologie 1999; 78:397-400. [PMID: 10457523 DOI: 10.1055/s-2007-996895] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
BACKGROUND Though rarely mentioned in the ENT literature, the "ear thermometer" has become more and more popular in recent years, not only in hospitals but also in households. These instruments are easy to use, and their infrared technology is said to provide precise measurements. The purpose of this study was to verify these claims. PATIENTS AND METHODS Infrared thermometers were tested in various conditions, and the results were compared. We assessed the effects of "distending" the outer ear canal, different body positions, and irritation of the ear (slight external otitis, hearing aids, otitis media, etc.). We did not specifically test effects of ear wax, as it had sufficiently been studied in pediatric or anesthesiological papers before (almost no effect, except in cases of occlusion of the auditory canal). RESULTS Using the ear thermometer we found small but statistically significant differences in febrile patients in different body positions. Irritated ears always showed higher temperatures than the normal contralateral ears. The most significant differences were found in persons lying on one side. The "pillow ear" was found 0.7 degree C (average) warmer than the contralateral ear. CONCLUSIONS Ear thermometers for estimating the body temperature permit easy and fast measurements. However, they include possible sources of measurement error. This study describes possible errors that the therapists should be aware of to avoid misinterpreting the course of a disease.
Collapse
Affiliation(s)
- U Sievert
- Klinik und Poliklinik für Hals-Nasen-Ohrenheilkunde, Kopf- und Halschirurgie Otto Körner
| | | | | |
Collapse
|