101
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Affiliation(s)
- Mikhail Y. Berezin
- Department of Radiology, Washington University School of Medicine, 4525 Scott Ave, St. Louis, USA, Tel. 314-747-0701, 314-362-8599, fax 314-747-5191
| | - Samuel Achilefu
- Department of Radiology, Washington University School of Medicine, 4525 Scott Ave, St. Louis, USA, Tel. 314-747-0701, 314-362-8599, fax 314-747-5191
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102
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Blue fluorescent cGMP sensor for multiparameter fluorescence imaging. PLoS One 2010; 5:e9164. [PMID: 20161796 PMCID: PMC2820094 DOI: 10.1371/journal.pone.0009164] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2009] [Accepted: 01/22/2010] [Indexed: 11/19/2022] Open
Abstract
Cyclic GMP (cGMP) regulates many physiological processes by cooperating with the other signaling molecules such as cyclic AMP (cAMP) and Ca(2+). Genetically encoded sensors for cGMP have been developed based on fluorescence resonance energy transfer (FRET) between fluorescent proteins. However, to analyze the dynamic relationship among these second messengers, combined use of existing sensors in a single cell is inadequate because of the significant spectral overlaps. A single wavelength indicator is an effective alternative to avoid this problem, but color variants of a single fluorescent protein-based biosensor are limited. In this study, to construct a new color fluorescent sensor, we converted the FRET-based sensor into a single wavelength indicator using a dark FRET acceptor. We developed a blue fluorescent cGMP biosensor, which is spectrally compatible with a FRET-based cAMP sensor using cyan and yellow fluorescent proteins (CFP/YFP). We cotransfected them and loaded a red fluorescent probe for Ca(2+) into cells, and accomplished triple-parameter fluorescence imaging of these cyclic nucleotides and Ca(2+), confirming the applicability of this combination to individually monitor their dynamics in a single cell. This blue fluorescent sensor and the approach using this FRET pair would be useful for multiparameter fluorescence imaging to understand complex signal transduction networks.
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103
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104
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Batters C, Zhu H, Sale JE. Visualisation of PCNA monoubiquitination in vivo by single pass spectral imaging FRET microscopy. PLoS One 2010; 5:e9008. [PMID: 20126408 PMCID: PMC2814862 DOI: 10.1371/journal.pone.0009008] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2009] [Accepted: 01/14/2010] [Indexed: 01/04/2023] Open
Abstract
Monoubiquitination of the DNA sliding clamp, PCNA, plays a central role in the control of damage bypass during replication. By combining a widely-spaced FRET donor/acceptor pair (CFP and mRFP) with spectral imaging, we have developed a simple method for the visualisation of PCNA monoubiquitination in both fixed and live cells with a single imaging pass. We validate the method with genetic controls in the avian cell line DT40 and use it to examine the intracellular dynamics of PCNA ubiquitination following subnuclear UV irradiation. This general approach is likely to be of utility for live imaging of post-translational modifications of a wide range of substrates in vivo.
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Affiliation(s)
- Christopher Batters
- Medical Research Council Laboratory of Molecular Biology, Cambridge, United Kingdom
| | - Hannah Zhu
- Medical Research Council Laboratory of Molecular Biology, Cambridge, United Kingdom
- Medical Research Council Laboratory of Molecular Biology, Division of Protein & Nucleic Acid Chemistry, Cambridge, United Kingdom
| | - Julian E. Sale
- Medical Research Council Laboratory of Molecular Biology, Cambridge, United Kingdom
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105
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Morris JR, Boutell C, Keppler M, Densham R, Weekes D, Alamshah A, Butler L, Galanty Y, Pangon L, Kiuchi T, Ng T, Solomon E. The SUMO modification pathway is involved in the BRCA1 response to genotoxic stress. Nature 2010; 462:886-90. [PMID: 20016594 DOI: 10.1038/nature08593] [Citation(s) in RCA: 335] [Impact Index Per Article: 23.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2009] [Accepted: 10/19/2009] [Indexed: 12/27/2022]
Abstract
Mutations in BRCA1 are associated with a high risk of breast and ovarian cancer. BRCA1 participates in the DNA damage response and acts as a ubiquitin ligase. However, its regulation remains poorly understood. Here we report that BRCA1 is modified by small ubiquitin-like modifier (SUMO) in response to genotoxic stress, and co-localizes at sites of DNA damage with SUMO1, SUMO2/3 and the SUMO-conjugating enzyme Ubc9. PIAS SUMO E3 ligases co-localize with and modulate SUMO modification of BRCA1, and are required for BRCA1 ubiquitin ligase activity in cells. In vitro SUMO modification of the BRCA1/BARD1 heterodimer greatly increases its ligase activity, identifying it as a SUMO-regulated ubiquitin ligase (SRUbL). Further, PIAS SUMO ligases are required for complete accumulation of double-stranded DNA (dsDNA) damage-repair proteins subsequent to RNF8 accrual, and for proficient double-strand break repair. These data demonstrate that the SUMOylation pathway plays a significant role in mammalian DNA damage response.
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Affiliation(s)
- Joanna R Morris
- Department of Medical and Molecular Genetics, King's College London, Guy's Medical School Campus, London SE1 9RT, UK.
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106
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Kaláb P, Soderholm J. The design of Förster (fluorescence) resonance energy transfer (FRET)-based molecular sensors for Ran GTPase. Methods 2010; 51:220-32. [PMID: 20096786 DOI: 10.1016/j.ymeth.2010.01.022] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2010] [Accepted: 01/19/2010] [Indexed: 01/01/2023] Open
Abstract
The application of FRET-based molecular biosensors provided confirmation of the central model of Ran GTPase function and led to important new insights into its physiological role. In many fields of cell biology, methods employing FRET are a standard approach that is becoming increasingly accessible due to advances in instrumentation and available fluorophores. However, the optimal design of a FRET sensor remains to be the cornerstone of any successful FRET application. Utilizing the recent literature on FRET applications and our studies on Ran, we outline the basic considerations involved in designing molecular FRET sensors. We point to several broadly applicable principles that were used in many different FRET sensors that can detect a wide range of molecular events. Using the FRET sensors for Ran that we created as examples, we then focus on the practical aspects of FRET assays. We describe the preparation of a bipartite FRET sensor consisting of ECFP-Ran and EYFP-importin beta and its validation as a reporter for FRET-based high throughput screening in small molecule libraries. Finally, we review the design and optimization of monomolecular FRET sensors that monitor the RanGTP-RanBP1 interaction, and of sensors detecting the RanGTP-regulated importin beta cargo release.
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Affiliation(s)
- Petr Kaláb
- National Cancer Institute, NIH, Bethesda, MD 20892-4256, USA.
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107
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Laptenok SP, Borst JW, Mullen KM, van Stokkum IHM, Visser AJWG, van Amerongen H. Global analysis of Förster resonance energy transfer in live cells measured by fluorescence lifetime imaging microscopy exploiting the rise time of acceptor fluorescence. Phys Chem Chem Phys 2010; 12:7593-602. [DOI: 10.1039/b919700a] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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108
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Carlin LM, Makrogianneli K, Keppler M, Fruhwirth GO, Ng T. Visualisation of signalling in immune cells. Methods Mol Biol 2010; 616:97-113. [PMID: 20379871 DOI: 10.1007/978-1-60761-461-6_7] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/20/2023]
Abstract
Currently, a great number of approaches are employed in investigation of the immune system. These range from experiments in live animals and biochemical techniques to investigate whole organs or cell populations down to single cell and molecular techniques to look at dynamics in specific cell-cell interactions. It is the latter approach that this chapter focusses on. The use of Förster resonance energy transfer (FRET) techniques to probe protein-protein interactions that are involved in receptor signalling to the cytoskeleton in intact cells is now well established. Various FRET biosensors are available to visualise several critical cell processes, giving information about activity and the location of key signalling molecules. As a specific set of examples in this chapter, we have generated variants of the original Rho, Rac and Cdc42 "Raichu" probes and improved their fluorophore combination to make them suitable for FLIM. These were employed in a number of assays to determine signal dynamics in T and NK cells. Specific protocols of how to use these probes and technical notes are described.
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Affiliation(s)
- Leo M Carlin
- Cancer Studies Division/Randall Division of Cellular and Molecular Biophysics, Richard Dimbleby Department of Cancer Research, Guy's Medical School Campus, King's College London, London, UK
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109
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Barstow B, Ando N, Kim CU, Gruner SM. Coupling of pressure-induced structural shifts to spectral changes in a yellow fluorescent protein. Biophys J 2009; 97:1719-27. [PMID: 19751677 PMCID: PMC2749779 DOI: 10.1016/j.bpj.2009.06.039] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2009] [Revised: 06/02/2009] [Accepted: 06/24/2009] [Indexed: 11/19/2022] Open
Abstract
X-ray diffraction analysis of pressure-induced structural changes in the Aequorea yellow fluorescent protein Citrine reveals the structural basis for the continuous fluorescence peak shift from yellow to green that is observed on pressurization. This fluorescence peak shift is caused by a reorientation of the two elements of the Citrine chromophore. This study describes the structural linkages in Citrine that are responsible for the local reorientation of the chromophore. The deformation of the Citrine chromophore is actuated by the differential motion of two clusters of atoms that compose the beta-barrel scaffold of the molecule, resulting in a slight bending of the beta-barrel. The high-pressure structures also show a perturbation of the hydrogen bonding network that stabilizes the excited state of the Citrine chromophore. The perturbation of this network is implicated in the reduction of fluorescence intensity of Citrine. The blue-shift of the Citrine fluorescence spectrum resulting from the bending of the beta-barrel provides structural insight into the transient blue-shifting of isolated yellow fluorescent protein molecules under ambient conditions and suggests mechanisms to alter the time-dependent behavior of Citrine under ambient conditions.
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Affiliation(s)
- Buz Barstow
- School of Applied Physics, Cornell University, Ithaca, New York
| | - Nozomi Ando
- Department of Physics, Cornell University, Ithaca, New York
| | - Chae Un Kim
- Cornell High Energy Synchrotron Source, Cornell University, Ithaca, New York
| | - Sol M. Gruner
- Cornell High Energy Synchrotron Source, Cornell University, Ithaca, New York
- Department of Physics, Cornell University, Ithaca, New York
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110
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Rickman C, Duncan RR. Munc18/Syntaxin interaction kinetics control secretory vesicle dynamics. J Biol Chem 2009; 285:3965-3972. [PMID: 19748891 PMCID: PMC2823538 DOI: 10.1074/jbc.m109.040402] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
In neuronal and hormonal release, regulated exocytosis requires an essential set of proteins: the soluble N-ethylmaleimide sensitive-factor attachment receptor proteins (SNAREs) syntaxin 1, SNAP-25, VAMP, and their regulator, Munc18. Recently, it was found that Munc18-1 can interact with syntaxin 1 through distinct mechanisms: an inhibitory mode enveloping syntaxin (mode 1), sequestering it from SNARE protein interactions, and direct binding to an evolutionarily conserved N-terminal peptide of syntaxin (mode 2/3). The latter interaction has been proposed to control "priming" of the fusion reaction, defined using electrophysiology, but it is unknown how this interaction is regulated, and any dynamic effect at the molecular or vesicular level in cells remains undiscovered. We now show that a phosphorylation site in syntaxin 1 (Ser(14)) regulates the N-terminal interaction with Munc18-1. Probing syntaxin 1 association with Munc18-1, in real-time and in living cells, we found that modification of Ser(14) modulated the dynamics of this interaction, specifically at the plasma membrane. Destabilization of this dynamic interaction enhanced vesicle immobilization at the plasma membrane with a resulting inhibition of exocytosis.
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Affiliation(s)
- Colin Rickman
- From the Centre for Integrative Physiology, University of Edinburgh, George Square, Edinburgh EH8 9XD, Scotland, United Kingdom
| | - Rory R Duncan
- From the Centre for Integrative Physiology, University of Edinburgh, George Square, Edinburgh EH8 9XD, Scotland, United Kingdom.
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111
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Kelleher MT, Fruhwirth G, Patel G, Ofo E, Festy F, Barber PR, Ameer-Beg SM, Vojnovic B, Gillett C, Coolen A, Kéri G, Ellis PA, Ng T. The potential of optical proteomic technologies to individualize prognosis and guide rational treatment for cancer patients. Target Oncol 2009; 4:235-52. [PMID: 19756916 PMCID: PMC2778706 DOI: 10.1007/s11523-009-0116-y] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2009] [Accepted: 08/28/2009] [Indexed: 12/21/2022]
Abstract
Genomics and proteomics will improve outcome prediction in cancer and have great potential to help in the discovery of unknown mechanisms of metastasis, ripe for therapeutic exploitation. Current methods of prognosis estimation rely on clinical data, anatomical staging and histopathological features. It is hoped that translational genomic and proteomic research will discriminate more accurately than is possible at present between patients with a good prognosis and those who carry a high risk of recurrence. Rational treatments, targeted to the specific molecular pathways of an individual's high-risk tumor, are at the core of tailored therapy. The aim of targeted oncology is to select the right patient for the right drug at precisely the right point in their cancer journey. Optical proteomics uses advanced optical imaging technologies to quantify the activity states of and associations between signaling proteins by measuring energy transfer between fluorophores attached to specific proteins. Förster resonance energy transfer (FRET) and fluorescence lifetime imaging microscopy (FLIM) assays are suitable for use in cell line models of cancer, fresh human tissues and formalin-fixed paraffin-embedded tissue (FFPE). In animal models, dynamic deep tissue FLIM/FRET imaging of cancer cells in vivo is now also feasible. Analysis of protein expression and post-translational modifications such as phosphorylation and ubiquitination can be performed in cell lines and are remarkably efficiently in cancer tissue samples using tissue microarrays (TMAs). FRET assays can be performed to quantify protein-protein interactions within FFPE tissue, far beyond the spatial resolution conventionally associated with light or confocal laser microscopy. Multivariate optical parameters can be correlated with disease relapse for individual patients. FRET-FLIM assays allow rapid screening of target modifiers using high content drug screens. Specific protein-protein interactions conferring a poor prognosis identified by high content tissue screening will be perturbed with targeted therapeutics. Future targeted drugs will be identified using high content/throughput drug screens that are based on multivariate proteomic assays. Response to therapy at a molecular level can be monitored using these assays while the patient receives treatment: utilizing re-biopsy tumor tissue samples in the neoadjuvant setting or by examining surrogate tissues. These technologies will prove to be both prognostic of risk for individuals when applied to tumor tissue at first diagnosis and predictive of response to specifically selected targeted anticancer drugs. Advanced optical assays have great potential to be translated into real-life benefit for cancer patients.
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Affiliation(s)
- Muireann T. Kelleher
- Richard Dimbleby Department of Cancer Research, Randall Division & Division of Cancer Studies, Kings College London, 2nd Floor, New Hunt House, Guy’s Medical School Campus, London, SE1 1UL UK
- Department Medical Oncology, Guy’s Hospital, London, SE1 9RT UK
| | - Gilbert Fruhwirth
- Richard Dimbleby Department of Cancer Research, Randall Division & Division of Cancer Studies, Kings College London, 2nd Floor, New Hunt House, Guy’s Medical School Campus, London, SE1 1UL UK
| | - Gargi Patel
- Richard Dimbleby Department of Cancer Research, Randall Division & Division of Cancer Studies, Kings College London, 2nd Floor, New Hunt House, Guy’s Medical School Campus, London, SE1 1UL UK
| | - Enyinnaya Ofo
- Richard Dimbleby Department of Cancer Research, Randall Division & Division of Cancer Studies, Kings College London, 2nd Floor, New Hunt House, Guy’s Medical School Campus, London, SE1 1UL UK
| | - Frederic Festy
- Biomaterial, Biomimetics & Biophotonics Research Group, King’s College London, London, UK
| | - Paul R. Barber
- Gray Institute for Radiation Oncology & Biology, University of Oxford, Old Road Campus Research Building, Roosevelt Drive, Oxford, OX3 7DQ UK
| | - Simon M. Ameer-Beg
- Richard Dimbleby Department of Cancer Research, Randall Division & Division of Cancer Studies, Kings College London, 2nd Floor, New Hunt House, Guy’s Medical School Campus, London, SE1 1UL UK
| | - Borivoj Vojnovic
- Richard Dimbleby Department of Cancer Research, Randall Division & Division of Cancer Studies, Kings College London, 2nd Floor, New Hunt House, Guy’s Medical School Campus, London, SE1 1UL UK
- Gray Institute for Radiation Oncology & Biology, University of Oxford, Old Road Campus Research Building, Roosevelt Drive, Oxford, OX3 7DQ UK
| | - Cheryl Gillett
- Guy’s & St Thomas’ Breast Tissue & Data Bank, King’s College London, Guy’s Hospital, London, SE1 9RT UK
| | - Anthony Coolen
- Department of Mathematics, King’s College London, Strand Campus, London, WC2R 2LS UK
| | - György Kéri
- Vichem Chemie Research Ltd., Herman Ottó utca 15, Budapest, Hungary
- Pathobiochemistry Research Group of Hungarian Academy of Science, Semmelweis University, Budapest, 1444 Bp 8. POB 260, Hungary
| | - Paul A. Ellis
- Department Medical Oncology, Guy’s Hospital, London, SE1 9RT UK
| | - Tony Ng
- Richard Dimbleby Department of Cancer Research, Randall Division & Division of Cancer Studies, Kings College London, 2nd Floor, New Hunt House, Guy’s Medical School Campus, London, SE1 1UL UK
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112
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Day RN, Davidson MW. The fluorescent protein palette: tools for cellular imaging. Chem Soc Rev 2009; 38:2887-921. [PMID: 19771335 DOI: 10.1039/b901966a] [Citation(s) in RCA: 559] [Impact Index Per Article: 37.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
This critical review provides an overview of the continually expanding family of fluorescent proteins (FPs) that have become essential tools for studies of cell biology and physiology. Here, we describe the characteristics of the genetically encoded fluorescent markers that now span the visible spectrum from deep blue to deep red. We identify some of the novel FPs that have unusual characteristics that make them useful reporters of the dynamic behaviors of proteins inside cells, and describe how many different optical methods can be combined with the FPs to provide quantitative measurements in living systems (227 references).
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Affiliation(s)
- Richard N Day
- Department of Cellular and Integrative Physiology, Indiana University School of Medicine, 635 Barnhill Dr., Indianapolis, IN 46202, USA.
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113
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Vuojola J, Lamminmäki U, Soukka T. Resonance Energy Transfer from Lanthanide Chelates to Overlapping and Nonoverlapping Fluorescent Protein Acceptors. Anal Chem 2009; 81:5033-8. [DOI: 10.1021/ac9005793] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Affiliation(s)
- Johanna Vuojola
- Department of Biotechnology, University of Turku, Tykistökatu 6A, FI-20520 Turku, Finland
| | - Urpo Lamminmäki
- Department of Biotechnology, University of Turku, Tykistökatu 6A, FI-20520 Turku, Finland
| | - Tero Soukka
- Department of Biotechnology, University of Turku, Tykistökatu 6A, FI-20520 Turku, Finland
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114
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Activation of CaMKII in single dendritic spines during long-term potentiation. Nature 2009; 458:299-304. [PMID: 19295602 PMCID: PMC2719773 DOI: 10.1038/nature07842] [Citation(s) in RCA: 496] [Impact Index Per Article: 33.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2008] [Accepted: 01/29/2009] [Indexed: 11/10/2022]
Abstract
Ca2+ / Calmodulin-dependent kinase II (CaMKII) plays a central role in long-term potentiation (LTP), which underlies some forms of learning and memory. Here we monitored the spatiotemporal dynamics of CaMKII activation in individual dendritic spines during LTP using 2-photon fluorescence lifetime imaging microscopy in combination with 2-photon glutamate uncaging. Induction of LTP and associated spine enlargement in single spines triggered transient (∼ 1 min) CaMKII activation restricted to the stimulated spines. CaMKII in spines was specifically activated by NMDA receptors and L-type voltage sensitive calcium channels, presumably via nanodomain Ca2+ near the channels, in response to glutamate uncaging and depolarization, respectively. The high degree of compartmentalization and channel specificity of CaMKII signalling allow stimuli-specific spatiotemporal patterns of CaMKII signalling and may be important for synapse-specificity of synaptic plasticity.
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115
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Harbaugh S, Kelley-Loughnane N, Davidson M, Narayanan L, Trott S, Chushak YG, Stone MO. FRET-Based Optical Assay for Monitoring Riboswitch Activation. Biomacromolecules 2009; 10:1055-60. [DOI: 10.1021/bm801117f] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Affiliation(s)
- Svetlana Harbaugh
- Applied Biotechnology Branch, Human Effectiveness Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base, Dayton, Ohio 45433, and Biotechnology HPC Software Applications Institute, Telemedicine and Advanced Technology Research Center, U.S. Army Medical Research and Material Command, Fort Detrick, Maryland 21702
| | - Nancy Kelley-Loughnane
- Applied Biotechnology Branch, Human Effectiveness Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base, Dayton, Ohio 45433, and Biotechnology HPC Software Applications Institute, Telemedicine and Advanced Technology Research Center, U.S. Army Medical Research and Material Command, Fort Detrick, Maryland 21702
| | - Molly Davidson
- Applied Biotechnology Branch, Human Effectiveness Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base, Dayton, Ohio 45433, and Biotechnology HPC Software Applications Institute, Telemedicine and Advanced Technology Research Center, U.S. Army Medical Research and Material Command, Fort Detrick, Maryland 21702
| | - Latha Narayanan
- Applied Biotechnology Branch, Human Effectiveness Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base, Dayton, Ohio 45433, and Biotechnology HPC Software Applications Institute, Telemedicine and Advanced Technology Research Center, U.S. Army Medical Research and Material Command, Fort Detrick, Maryland 21702
| | - Sandra Trott
- Applied Biotechnology Branch, Human Effectiveness Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base, Dayton, Ohio 45433, and Biotechnology HPC Software Applications Institute, Telemedicine and Advanced Technology Research Center, U.S. Army Medical Research and Material Command, Fort Detrick, Maryland 21702
| | - Yaroslav G. Chushak
- Applied Biotechnology Branch, Human Effectiveness Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base, Dayton, Ohio 45433, and Biotechnology HPC Software Applications Institute, Telemedicine and Advanced Technology Research Center, U.S. Army Medical Research and Material Command, Fort Detrick, Maryland 21702
| | - Morley O. Stone
- Applied Biotechnology Branch, Human Effectiveness Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base, Dayton, Ohio 45433, and Biotechnology HPC Software Applications Institute, Telemedicine and Advanced Technology Research Center, U.S. Army Medical Research and Material Command, Fort Detrick, Maryland 21702
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116
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Gralle M, Botelho MG, Wouters FS. Neuroprotective secreted amyloid precursor protein acts by disrupting amyloid precursor protein dimers. J Biol Chem 2009; 284:15016-25. [PMID: 19336403 DOI: 10.1074/jbc.m808755200] [Citation(s) in RCA: 102] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
The amyloid precursor protein (APP) is implied both in cell growth and differentiation and in neurodegenerative processes in Alzheimer disease. Regulated proteolysis of APP generates biologically active fragments such as the neuroprotective secreted ectodomain sAPPalpha and the neurotoxic beta-amyloid peptide. Furthermore, it has been suggested that the intact transmembrane APP plays a signaling role, which might be important for both normal synaptic plasticity and neuronal dysfunction in dementia. To understand APP signaling, we tracked single molecules of APP using quantum dots and quantitated APP homodimerization using fluorescence lifetime imaging microscopy for the detection of Förster resonance energy transfer in living neuroblastoma cells. Using selective labeling with synthetic fluorophores, we show that the dimerization of APP is considerably higher at the plasma membrane than in intracellular membranes. Heparan sulfate significantly contributes to the almost complete dimerization of APP at the plasma membrane. Importantly, this technique for the first time structurally defines the initiation of APP signaling by binding of a relevant physiological extracellular ligand; our results indicate APP as receptor for neuroprotective sAPPalpha, as sAPPalpha binding disrupts APP dimers, and this disruption of APP dimers by sAPPalpha is necessary for the protection of neuroblastoma cells against starvation-induced cell death. Only cells expressing reversibly dimerized wild-type, but not covalently dimerized mutant APP are protected by sAPPalpha. These findings suggest a potentially beneficial effect of increasing sAPPalpha production or disrupting APP dimers for neuronal survival.
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Affiliation(s)
- Matthias Gralle
- Laboratory for Molecular and Cellular Systems, Department of Neurophysiology and Sensory Physiology, University of Göttingen, Humboldtallee 23, 37073 Göttingen, Germany.
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117
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Integrating receptor signal inputs that influence small Rho GTPase activation dynamics at the immunological synapse. Mol Cell Biol 2009; 29:2997-3006. [PMID: 19307303 DOI: 10.1128/mcb.01008-08] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The Rho GTPase Cdc42 regulates cytoskeletal changes at the immunological synapse (IS) that are critical to T-cell activation. By imaging fluorescent activity biosensors (Raichu) using fluorescence lifetime imaging microscopy, Cdc42 activation was shown to display kinetics that are conditional on the specific receptor input (through two IS-associated receptors, CD3 and beta1 integrin). CD3-triggered Cdc42 activity is dependent on the cyto-2 (NPIY) motif of the beta1 integrin cytoplasmic domain. Perturbations of the ezrin-radixin-moesin (ERM) function blocked CD3- and beta1-dependent increases in Cdc42 activity. Both IS-associated receptors probably lie on a serial molecular pathway and transduce signals through the ERM-dependent machinery that is responsible for the remodeling and stabilization of the synapse. Cdc42 activity is impaired in beta1 integrin-deficient T cells that form conjugates with antigen-presenting cells but is partially restored in the context of an antigen-specific synapse. This restoration of Cdc42 activity is due, at least in part, to the recruitment and activation of beta2 integrin.
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118
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119
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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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120
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Chapter 12 Reflections on FRET imaging. ACTA ACUST UNITED AC 2009. [DOI: 10.1016/s0075-7535(08)00012-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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121
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Chapter 5 Visible fluorescent proteins for FRET. ACTA ACUST UNITED AC 2009. [DOI: 10.1016/s0075-7535(08)00005-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/29/2023]
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122
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Lee SJR, Yasuda R. Spatiotemporal Regulation of Signaling in and out of Dendritic Spines: CaMKII and Ras. THE OPEN NEUROSCIENCE JOURNAL 2009; 3:117-127. [PMID: 20463853 PMCID: PMC2867484 DOI: 10.2174/1874082000903020117] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Recent advances in 2-photon fluorescence lifetime imaging microscopy (2pFLIM) in combination with 2-photon photochemistry have enabled the visualization of neuronal signaling during synaptic plasticity at the level of single dendritic spines in light scattering tissue. Using these techniques, the activity of Ca(2+)/Calmodulin-dependent kinase II (CaMKII) and Ras have been imaged in single spines during synaptic plasticity and associated spine enlargement. These provide two contrasting examples of spatiotemporal regulation of spine signaling: Ras signaling is diffusive and spread over ~10 μm along the dendrites, while CaMKII activation is restricted to the spine undergoing plasticity. In this review, we will discuss the mechanisms and roles of the different spatiotemporal regulation of signaling in neurons, and the impact of the spine structure upon these biochemical signaling processes.
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Affiliation(s)
- Seok-Jin R. Lee
- Department of Neurobiology, Duke University Medical Center, Durham, NC 27710
| | - Ryohei Yasuda
- Department of Neurobiology, Duke University Medical Center, Durham, NC 27710
- Howard Hughes Medical Institute, Duke University Medical Center, Durham, NC 27710
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123
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Shkrob MA, Mishin AS, Chudakov DM, Labas IA, Luk'ianov KA. [Chromoproteins of the green fluorescent protein family: properties and applications]. RUSSIAN JOURNAL OF BIOORGANIC CHEMISTRY 2008; 34:581-90. [PMID: 19060933 DOI: 10.1134/s1068162008050014] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The distribution in nature and the spectral and structural properties of chromoproteins of the green fluorescent protein (GFP) family and their differences from one another and other fluorescent proteins of this family are considered. Discussed in detail are practical applications of the chromoproteins and their mutant variants that have unique characteristics not found among natural proteins of the GFP family, such as far-red or photoconvertible fluorescence, a large Stokes shift, enhanced phototoxicity, etc.
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124
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Bennett RP, Salter JD, Liu X, Wedekind JE, Smith HC. APOBEC3G subunits self-associate via the C-terminal deaminase domain. J Biol Chem 2008; 283:33329-36. [PMID: 18842592 PMCID: PMC2586250 DOI: 10.1074/jbc.m803726200] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2008] [Revised: 10/03/2008] [Indexed: 11/06/2022] Open
Abstract
Human APOBEC3G (hA3G) is a cytidine deaminase active on HIV single-stranded DNA. Small angle x-ray scattering and molecular envelope restorations predicted a C-terminal dimeric model for RNA-depleted hA3G in solution. Each subunit was elongated, suggesting that individual domains of hA3G are solvent-exposed and therefore may interact with other macromolecules even as isolated substructures. In this study, co-immunoprecipitation and in-cell quenched fluorescence resonance energy transfer assays reveal that hA3G forms RNA-independent oligomers through interactions within its C terminus. Residues 209-336 were necessary and sufficient for homoligomerization. N-terminal domains of hA3G were unable to multimerize but remained functional for Gag and viral infectivity factor (Vif) interactions when expressed apart from the C terminus. These findings corroborate the small angle x-ray scattering structural model and are instructive for development of high throughput screens that target specific domains and their functions to identify HIV/AIDS therapeutics.
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MESH Headings
- APOBEC-3G Deaminase
- Cell Line
- Cytidine Deaminase/chemistry
- Cytidine Deaminase/genetics
- Cytidine Deaminase/metabolism
- DNA, Single-Stranded/chemistry
- DNA, Single-Stranded/genetics
- DNA, Single-Stranded/metabolism
- DNA, Viral/chemistry
- DNA, Viral/genetics
- DNA, Viral/metabolism
- Dimerization
- HIV Core Protein p24/chemistry
- HIV Core Protein p24/genetics
- HIV Core Protein p24/metabolism
- HIV-1/chemistry
- HIV-1/genetics
- HIV-1/metabolism
- Humans
- Models, Molecular
- Protein Structure, Quaternary
- Protein Structure, Tertiary/physiology
- vif Gene Products, Human Immunodeficiency Virus/chemistry
- vif Gene Products, Human Immunodeficiency Virus/genetics
- vif Gene Products, Human Immunodeficiency Virus/metabolism
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Affiliation(s)
- Ryan P Bennett
- Department of Biochemistry and Biophysics, University of Rochester School of Medicine and Dentistry, Rochester, New York 14642, USA
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125
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Roda A, Guardigli M, Michelini E, Mirasoli M. Nanobioanalytical luminescence: Förster-type energy transfer methods. Anal Bioanal Chem 2008; 393:109-23. [DOI: 10.1007/s00216-008-2435-8] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2008] [Revised: 09/22/2008] [Accepted: 09/23/2008] [Indexed: 12/21/2022]
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126
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Dinant C, van Royen ME, Vermeulen W, Houtsmuller AB. Fluorescence resonance energy transfer of GFP and YFP by spectral imaging and quantitative acceptor photobleaching. J Microsc 2008; 231:97-104. [PMID: 18638193 DOI: 10.1111/j.1365-2818.2008.02020.x] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
To study protein-protein interactions by fluorescence energy transfer (FRET), the proteins of interest are tagged with either a donor or an acceptor fluorophore. For efficient FRET, fluorophores need to have a reasonable overlap of donor emission and acceptor excitation spectra. However, given the relatively small Stokes shift of conventional fluorescent proteins, donor and acceptor pairs with high FRET efficiencies have emission spectra that are difficult to separate. GFP and YFP are widely used in fluorescence microscopy studies. The spectral qualities of GFP and YFP make them one of the most efficient FRET donor-acceptor couples available. However, the emission peaks of GFP (510 nm) and YFP (527 nm) are spectrally too close for separation by conventional fluorescence microscopy. Difficulties in simultaneous detection of GFP and YFP with a fluorescence microscope are eliminated when spectral imaging and subsequent linear unmixing are applied. This allows FRET microscopy using these tags to study protein-protein interactions. We adapted the linear unmixing procedure from commercially available software (Zeiss) for use with acceptor photobleaching FRET using GFP and YFP as FRET pair. FRET efficiencies up to 52% for a GFP-YFP fusion protein were measured. To investigate the applicability of the procedure, we used two constituents of the nucleotide excision repair system, which removes UV-induced single-strand DNA damage. ERCC1 and XPF form a heterodimeric 5' endonuclease in nucleotide excision repair. FRET between ERCC1-GFP and XPF-YFP occurs with an efficiency of 30%.
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Affiliation(s)
- C Dinant
- Department of Pathology, Josephine Nefkens Institute, Erasmus MC, PO Box 2040, 3000 CA Rotterdam, The Netherlands
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127
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Highly sensitive and quantitative FRET-FLIM imaging in single dendritic spines using improved non-radiative YFP. ACTA ACUST UNITED AC 2008; 36:31-42. [PMID: 18512154 DOI: 10.1007/s11068-008-9024-9] [Citation(s) in RCA: 105] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2008] [Accepted: 04/28/2008] [Indexed: 01/20/2023]
Abstract
Two-photon fluorescence lifetime imaging microscopy (TPFLIM) enables the quantitative measurements of fluorescence resonance energy transfer (FRET) in small subcellular compartments in light scattering tissue. We evaluated and optimized the FRET pair of mEGFP (monomeric EGFP with the A206K mutation) and REACh (non-radiative YFP variants) for TPFLIM. We characterized several mutants of REACh in terms of their "darkness," and their ability to act as a FRET acceptor for mEGFP in HeLa cells and hippocampal neurons. Since the commonly used monomeric mutation A206K increases the brightness of REACh, we introduced a different monomeric mutation (F223R) which does not affect the brightness. Also, we found that the folding efficiency of original REACh, as measured by the fluorescence lifetime of a mEGFP-REACh tandem dimer, was low and variable from cell to cell. Introducing two folding mutations (F46L, Q69M) into REACh increased the folding efficiency by approximately 50%, and reduced the variability of FRET signal. Pairing mEGFP with the new REACh (super-REACh, or sREACh) improved the signal-to-noise ratio compared to the mEGFP-mRFP or mEGFP-original REACh pair by approximately 50%. Using this new pair, we demonstrated that the fraction of actin monomers in filamentous and globular forms in single dendritic spines can be quantitatively measured with high sensitivity. Thus, the mEGFP-sREACh pair is suited for quantitative FRET measurement by TPFLIM, and enables us to measure protein-protein interactions in individual dendritic spines in brain slices with high sensitivity.
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128
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Kwok S, Lee C, Sánchez SA, Hazlett TL, Gratton E, Hayashi Y. Genetically encoded probe for fluorescence lifetime imaging of CaMKII activity. Biochem Biophys Res Commun 2008; 369:519-25. [PMID: 18302935 PMCID: PMC2396457 DOI: 10.1016/j.bbrc.2008.02.070] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2008] [Accepted: 02/12/2008] [Indexed: 11/16/2022]
Abstract
Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) is highly enriched in excitatory synapses in the central nervous system and is critically involved in synaptic plasticity, learning, and memory. However, the precise temporal and spatial regulation of CaMKII activity in living cells has not been well described, due to lack of a specific method. Here, based on our previous work, we attempted to generate an optical probe for fluorescence lifetime imaging (FLIM) of CaMKII activity by fusing the protein with donor and acceptor fluorescent proteins at its amino- and carboxyl-termini. We first optimized the combinations of fluorescent proteins by taking advantage of expansion of fluorescent proteins towards longer wavelength in fluorospectrometric assay. Then using digital frequency domain FLIM (DFD-FLIM), we demonstrated that the resultant protein can indeed detect CaMKII activation in living cells. These FLIM versions of Camui could be useful for elucidating the function of CaMKII both in vitro and in vivo.
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Affiliation(s)
- Showming Kwok
- RIKEN-MIT Neuroscience Research Center, The Picower Institute for Learning and Memory, Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Claudia Lee
- Laboratory for Fluorescence Dynamics, Department of Biomedical Engineering, 3120 Natural Sciences II, University of California, Irvine, Irvine, CA 697-2715, USA
| | - Susana A. Sánchez
- Laboratory for Fluorescence Dynamics, Department of Biomedical Engineering, 3120 Natural Sciences II, University of California, Irvine, Irvine, CA 697-2715, USA
| | - Theodore L. Hazlett
- Laboratory for Fluorescence Dynamics, Department of Biomedical Engineering, 3120 Natural Sciences II, University of California, Irvine, Irvine, CA 697-2715, USA
| | - Enrico Gratton
- Laboratory for Fluorescence Dynamics, Department of Biomedical Engineering, 3120 Natural Sciences II, University of California, Irvine, Irvine, CA 697-2715, USA
| | - Yasunori Hayashi
- RIKEN-MIT Neuroscience Research Center, The Picower Institute for Learning and Memory, Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
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129
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van der Krogt GNM, Ogink J, Ponsioen B, Jalink K. A comparison of donor-acceptor pairs for genetically encoded FRET sensors: application to the Epac cAMP sensor as an example. PLoS One 2008; 3:e1916. [PMID: 18382687 PMCID: PMC2271053 DOI: 10.1371/journal.pone.0001916] [Citation(s) in RCA: 130] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2008] [Accepted: 02/26/2008] [Indexed: 11/18/2022] Open
Abstract
We recently reported on CFP-Epac-YFP, an Epac-based single polypeptide FRET reporter to resolve cAMP levels in living cells. In this study, we compared and optimized the fluorescent protein donor/acceptor pairs for use in biosensors such as CFP-Epac-YFP. Our strategy was to prepare a wide range of constructs consisting of different donor and acceptor fluorescent proteins separated by a short linker. Constructs were expressed in HEK293 cells and tested for FRET and other relevant properties. The most promising pairs were subsequently used in an attempt to improve the FRET span of the Epac-based cAMP sensor. The results show significant albeit not perfect correlation between performance in the spacer construct and in the Epac sensor. Finally, this strategy enabled us to identify improved sensors both for detection by sensitized emission and by fluorescent lifetime imaging. The present overview should be helpful in guiding development of future FRET sensors.
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Affiliation(s)
| | - Janneke Ogink
- Division of Cell Biology, The Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Bas Ponsioen
- Division of Cell Biology, The Netherlands Cancer Institute, Amsterdam, The Netherlands
- Division of Cellular Biochemistry, The Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Kees Jalink
- Division of Cell Biology, The Netherlands Cancer Institute, Amsterdam, The Netherlands
- * To whom correspondence should be addressed. E-mail:
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130
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Quantitative lifetime unmixing of multiexponentially decaying fluorophores using single-frequency fluorescence lifetime imaging microscopy. Biophys J 2008; 95:378-89. [PMID: 18359789 DOI: 10.1529/biophysj.107.125229] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Fluorescence lifetime imaging microscopy (FLIM) is a quantitative microscopy technique for imaging nanosecond decay times of fluorophores. In the case of frequency-domain FLIM, several methods have been described to resolve the relative abundance of two fluorescent species with different fluorescence decay times. Thus far, single-frequency FLIM methods generally have been limited to quantifying two species with monoexponential decay. However, multiexponential decays are the norm rather than the exception, especially for fluorescent proteins and biological samples. Here, we describe a novel method for determining the fractional contribution in each pixel of an image of a sample containing two (multiexponentially) decaying species using single-frequency FLIM. We demonstrate that this technique allows the unmixing of binary mixtures of two spectrally identical cyan or green fluorescent proteins, each with multiexponential decay. Furthermore, because of their spectral identity, quantitative images of the relative molecular abundance of these fluorescent proteins can be generated that are independent of the microscope light path. The method is rigorously tested using samples of known composition and applied to live cell microscopy using cells expressing multiple (multiexponentially decaying) fluorescent proteins.
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131
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Fitzsimons CP, Ahmed S, Wittevrongel CFW, Schouten TG, Dijkmans TF, Scheenen WJJM, Schaaf MJM, de Kloet ER, Vreugdenhil E. The microtubule-associated protein doublecortin-like regulates the transport of the glucocorticoid receptor in neuronal progenitor cells. Mol Endocrinol 2008; 22:248-62. [PMID: 17975023 PMCID: PMC5419639 DOI: 10.1210/me.2007-0233] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2007] [Accepted: 10/23/2007] [Indexed: 02/05/2023] Open
Abstract
In neuronal cells, activated glucocorticoid receptor (GR) translocates to the nucleus guided by the cytoskeleton. However, the detailed mechanisms underlying GR translocation remain unclear. Using gain and loss of function studies, we report here for the first time that the microtubule-associated protein doublecortin-like (DCL) controls GR translocation to the nucleus. DCL overexpression in COS-1 cells, neuroblastoma cells, and rat hippocampus organotypic slice cultures impaired GR translocation and decreased GR-dependent transcriptional activity, measured by a specific reporter gene assay, in COS-1 cells. Moreover, DCL and GR directly interact on microtubule bundles formed by DCL overexpression. A C-terminal truncated DCL with conserved microtubule-bundling activity did not influence GR translocation. In N1E-115 mouse neuroblastoma cells and neuronal progenitor cells in rat hippocampus organotypic slice cultures, laser-scanning confocal microscopy showed colabeling of endogenously expressed DCL and GR. In these systems, RNA-interference-mediated DCL knockdown hampered GR translocation. Thus, we conclude that DCL expression is tightly regulated to adequately control GR transport. Because DCL is primarily expressed in neuronal progenitor cells, our results introduce this microtubule-associated protein as a new modulator of GR signaling in this cell type and suggest the existence of cell-specific mechanisms regulating GR translocation to the nucleus.
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Affiliation(s)
- Carlos P Fitzsimons
- Leiden/Amsterdam Center for Drug Research/Medical Pharmacology Department, Einsteinweg 55, Leiden, The Netherlands
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132
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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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133
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Kalab P, Pralle A. Chapter 21 Quantitative Fluorescence Lifetime Imaging in Cells as a Tool to Design Computational Models of Ran‐Regulated Reaction Networks. Methods Cell Biol 2008; 89:541-68. [DOI: 10.1016/s0091-679x(08)00621-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
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134
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Application of novel imaging techniques for early clinical trials. EJC Suppl 2007. [DOI: 10.1016/j.ejcsup.2007.09.020] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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135
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Abstract
Mutant superoxide dismutase 1 (mtSOD1) causes dominantly inherited amyotrophic lateral sclerosis (ALS). The mechanism for mtSOD1 toxicity remains unknown. Two main hypotheses are the impairment of proteasomal function and chaperone depletion by misfolded mtSOD1. Here, we employed FRET/FLIM and biosensor imaging to quantitatively localize ubiquitination, as well as chaperone binding of mtSOD1, and to assess their effect on proteasomal and protein folding activities. We found large differences in ubiquitination and chaperone interaction levels for wild-type (wt) SOD1 versus mtSOD1 in intact single cells. Moreover, SOD1 ubiquitination levels differ between proteasomal structures and cytoplasmic material. Hsp70 binding and ubiquitination of wt and mtSOD1 species are highly correlated, demonstrating the coupled upregulation of both cellular detoxification mechanisms upon mtSOD1 expression. Biosensor imaging in single cells revealed that mtSOD1 expression alters cellular protein folding activity but not proteasomal function in the neuronal cell line examined. Our results provide the first cell-by-cell-analysis of SOD1 ubiquitination and chaperone interaction. Moreover, our study opens new methodological avenues for cell biological research on ALS.
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136
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Müller-Taubenberger A, Anderson KI. Recent advances using green and red fluorescent protein variants. Appl Microbiol Biotechnol 2007; 77:1-12. [PMID: 17704916 DOI: 10.1007/s00253-007-1131-5] [Citation(s) in RCA: 88] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2007] [Revised: 07/12/2007] [Accepted: 07/14/2007] [Indexed: 11/28/2022]
Abstract
Fluorescent proteins have proven to be excellent tools for live-cell imaging. In addition to green fluorescent protein (GFP) and its variants, recent progress has led to the development of monomeric red fluorescent proteins (mRFPs) that show improved properties with respect to maturation, brightness, and the monomeric state. This review considers green and red spectral variants, their paired use for live-cell imaging in vivo, in vitro, and in fluorescence resonance energy transfer (FRET) studies, in addition to other recent "two-color" advances including photoswitching and bimolecular fluorescence complementation (BiFC). It will be seen that green and red fluorescent proteins now exist with nearly ideal properties for dual-color microscopy and FRET.
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Affiliation(s)
- Annette Müller-Taubenberger
- Institut für Zellbiologie (ABI), Ludwig-Maximilians-Universität München, Schillerstrasse 42, Munich, Germany.
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137
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Goedhart J, Vermeer JEM, Adjobo-Hermans MJW, van Weeren L, Gadella TWJ. Sensitive detection of p65 homodimers using red-shifted and fluorescent protein-based FRET couples. PLoS One 2007; 2:e1011. [PMID: 17925859 PMCID: PMC1995760 DOI: 10.1371/journal.pone.0001011] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2007] [Accepted: 09/20/2007] [Indexed: 11/17/2022] Open
Abstract
BACKGROUND Fluorescence Resonance Energy Transfer (FRET) between the green fluorescent protein (GFP) variants CFP and YFP is widely used for the detection of protein-protein interactions. Nowadays, several monomeric red-shifted fluorescent proteins are available that potentially improve the efficiency of FRET. METHODOLOGY/PRINCIPAL FINDINGS To allow side-by-side comparison of several fluorescent protein combinations for detection of FRET, yellow or orange fluorescent proteins were directly fused to red fluorescent proteins. FRET from yellow fluorescent proteins to red fluorescent proteins was detected by both FLIM and donor dequenching upon acceptor photobleaching, showing that mCherry and mStrawberry were more efficient acceptors than mRFP1. Circular permutated yellow fluorescent protein variants revealed that in the tandem constructs the orientation of the transition dipole moment influences the FRET efficiency. In addition, it was demonstrated that the orange fluorescent proteins mKO and mOrange are both suitable as donor for FRET studies. The most favorable orange-red FRET pair was mKO-mCherry, which was used to detect homodimerization of the NF-kappaB subunit p65 in single living cells, with a threefold higher lifetime contrast and a twofold higher FRET efficiency than for CFP-YFP. CONCLUSIONS/SIGNIFICANCE The observed high FRET efficiency of red-shifted couples is in accordance with increased Förster radii of up to 64 A, being significantly higher than the Förster radius of the commonly used CFP-YFP pair. Thus, red-shifted FRET pairs are preferable for detecting protein-protein interactions by donor-based FRET methods in single living cells.
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Affiliation(s)
- Joachim Goedhart
- Section of Molecular Cytology, Centre for Advanced Microscopy, Swammerdam Institute for Life Sciences, University of Amsterdam, Amsterdam, The Netherlands.
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138
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Piston DW, Kremers GJ. Fluorescent protein FRET: the good, the bad and the ugly. Trends Biochem Sci 2007; 32:407-14. [PMID: 17764955 DOI: 10.1016/j.tibs.2007.08.003] [Citation(s) in RCA: 590] [Impact Index Per Article: 34.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2007] [Revised: 06/21/2007] [Accepted: 08/15/2007] [Indexed: 10/22/2022]
Abstract
Dynamic protein interactions play a significant part in many cellular processes. A technique that shows considerable promise in elucidating such interactions is Förster resonance energy transfer (FRET). When combined with multiple, colored fluorescent proteins, FRET permits high spatial resolution assays of protein-protein interactions in living cells. Because FRET signals are usually small, however, their measurement requires careful interpretation and several control experiments. Nevertheless, the use of FRET in cell biological experiments has exploded over the past few years. Here we describe the physical basis of FRET and the fluorescent proteins appropriate for these experiments. We also review the approaches that can be used to measure FRET, with particular emphasis on the potential artifacts associated with each approach.
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Affiliation(s)
- David W Piston
- Department of Molecular Physiology and Biophysics, Vanderbilt University, 702 Light Hall, Nashville, TN 37232-0615, USA.
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139
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Esposito A, Dohm CP, Bähr M, Wouters FS. Unsupervised Fluorescence Lifetime Imaging Microscopy for High Content and High Throughput Screening. Mol Cell Proteomics 2007; 6:1446-54. [PMID: 17510051 DOI: 10.1074/mcp.t700006-mcp200] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Proteomics and cellomics clearly benefit from the molecular insights in cellular biochemical events that can be obtained by advanced quantitative microscopy techniques like fluorescence lifetime imaging microscopy and Förster resonance energy transfer imaging. The spectroscopic information detected at the molecular level can be combined with cellular morphological estimators, the analysis of cellular localization, and the identification of molecular or cellular subpopulations. This allows the creation of powerful assays to gain a detailed understanding of the molecular mechanisms underlying spatiotemporal cellular responses to chemical and physical stimuli. This work demonstrates that the high content offered by these techniques can be combined with the high throughput levels offered by automation of a fluorescence lifetime imaging microscope setup capable of unsupervised operation and image analysis. Systems and software dedicated to image cytometry for analysis and sorting represent important emerging tools for the field of proteomics, interactomics, and cellomics. These techniques could soon become readily available both to academia and the drug screening community by the application of new all-solid-state technologies that may results in cost-effective turnkey systems. Here the application of this screening technique to the investigation of intracellular ubiquitination levels of alpha-synuclein and its familial mutations that are causative for Parkinson disease is shown. The finding of statistically lower ubiquitination of the mutant alpha-synuclein forms supports a role for this modification in the mechanism of pathological protein aggregation.
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Affiliation(s)
- Alessandro Esposito
- Cell Biophysics Group, European Neuroscience Institute-Göttingen, Waldweg 33, 37073 Göttingen, Germany.
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140
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Ghukasyan V, Hsu YY, Kung SH, Kao FJ. Application of fluorescence resonance energy transfer resolved by fluorescence lifetime imaging microscopy for the detection of enterovirus 71 infection in cells. JOURNAL OF BIOMEDICAL OPTICS 2007; 12:024016. [PMID: 17477731 DOI: 10.1117/1.2718582] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
Timely and effective virus infection detection is critical for the clinical management and prevention of the disease spread in communities during an outbreak. A range of methods have been developed for this purpose, of which classical serological and viral nucleic acids detection are the most popular. We describe an alternative, imaging-based approach that utilizes fluorescence resonance energy transfer (FRET) resolved by fluorescence lifetime imaging microscopy (FLIM) and demonstrate it on the example of enterovirus 71 (EV71) infection detection. A plasmid construct is developed with the sequence for GFP2 and DsRed2 fluorescent proteins, linked by a 12-amino-acid-long cleavage recognition site for the 2A protease (2A(pro)), encoded by the EV71 genome and specific for the members of Picornaviridae family. In the construct expressed in HeLa cells, the linker binds the fluorophores within the Forster distance and creates a condition for FRET to occur, thus resulting in shortening of the GFP2 fluorescence lifetime. On cells infection with EV71, viral 2A(pro) released to the cytoplasm cleaves the recognition site, causing disruption of FRET through separation of the fluorophores. Thus, increased GFP2 lifetime to the native values, manifested by the time-correlated single-photon counting, serves as an efficient and specific indicator of the EV71 virus infection.
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Affiliation(s)
- Vladimir Ghukasyan
- National Yang-Ming University, Institute of Biophotonics Engineering, 155, Li-Nong St., Sec. 2, Taipei 112, Taiwan
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141
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Hsu YY, Liu YN, Wang W, Kao FJ, Kung SH. In vivo dynamics of enterovirus protease revealed by fluorescence resonance emission transfer (FRET) based on a novel FRET pair. Biochem Biophys Res Commun 2007; 353:939-45. [PMID: 17207462 DOI: 10.1016/j.bbrc.2006.12.145] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2006] [Accepted: 12/13/2006] [Indexed: 10/23/2022]
Abstract
An in vivo protease assay suitable for analysis by fluorescence resonance energy transfer (FRET) was developed on the basis of a novel FRET pair. The specifically designed fusion substrate consists of green fluorescent protein 2 (GFP2)-peptide-red fluorescent protein 2 (DsRed2), with a cleavage motif for the enterovirus 2A protease (2Apro) embedded within the peptide region. FRET can be readily visualized in real-time from cells expressing the fusion substrate until a proteolytic cleavage by 2Apro from the input virus. The level of FRET decay is a function of the amount and infection duration of the inoculated virus as measured by a fluorometer assay. The FRET biosensor also responded well to other related enteroviruses but not to a phylogenetically distant virus. Western blot analysis confirmed the physical cleavage of the fusion substrate upon the infections. The study provides proof of principle for applying the FRET technology to diagnostics, screening procedures, and cell biological research.
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Affiliation(s)
- Yueh-Ying Hsu
- Faculty of Biotechnology and Laboratory Science in Medicine, National Yang-Ming University, Taipei, Taiwan, ROC
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142
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Battad JM, Wilmann PG, Olsen S, Byres E, Smith SC, Dove SG, Turcic KN, Devenish RJ, Rossjohn J, Prescott M. A structural basis for the pH-dependent increase in fluorescence efficiency of chromoproteins. J Mol Biol 2007; 368:998-1010. [PMID: 17376484 DOI: 10.1016/j.jmb.2007.02.007] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2006] [Revised: 01/25/2007] [Accepted: 02/02/2007] [Indexed: 12/01/2022]
Abstract
Within the fluorescent protein and chromoprotein family, the phenomenon of photoswitching is both intriguing and biotechnologically useful. Illumination of particular chromoproteins with intense light results in dramatic increases in fluorescence efficiency (termed kindling) and involves cis-trans isomerization of the chromophore. Here we report that chromophore isomerization can also be driven via alteration in pH. Specifically, we demonstrate that a number of naturally occurring chromoproteins, and their engineered variants, undergo a dramatic 20-100-fold increase in fluorescence efficiency at alkaline pH (>pH9.0). We have determined to 1.8 A resolution the structure of one such chromoprotein, Rtms5(H146S), in its highly far-red fluorescent form (Phi(F), 0.11 at pH 10.7) and compared it to the structure of the non-fluorescent form (Phi(F), 0.002 at pH 8.0). At high pH, the cyclic tri-peptide chromophore was observed to be mobile and distributed between a trans non-coplanar and a cis coplanar conformation, whereas at the lower pH, only a trans non-coplanar chromophore was observed. Calculation of pK(a) values suggested that titration of the side-chain of the conserved Glu215 close to the chromophore is involved in promoting the cis-coplanar conformation. Collectively, our data establish that isomerization to form a coplanar chromophore is a basis of the increased fluorescence efficiency at high pH. The phenomenon of pH-induced fluorescence gain has similarities with photoswitching, thereby providing a model to study the mechanism of kindling.
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Affiliation(s)
- Jion M Battad
- Department of Biochemistry and Molecular Biology, School of Biomedical Sciences, Monash University, Clayton Campus, Victoria 3800, Australia
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143
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Duncan RR. Fluorescence lifetime imaging microscopy (FLIM) to quantify protein-protein interactions inside cells. Biochem Soc Trans 2007; 34:679-82. [PMID: 17052173 PMCID: PMC1855982 DOI: 10.1042/bst0340679] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Recent developments in cellular imaging spectroscopy now permit the minimally invasive study of protein dynamics inside living cells. These advances are of interest to cell biologists, as proteins rarely act in isolation, but rather in concert with others in forming cellular machinery. Until recently, all protein interactions had to be determined in vitro using biochemical approaches: this biochemical legacy has provided cell biologists with the basis to test defined protein-protein interactions not only inside cells, but now also with high spatial resolution. These techniques can detect and quantify protein behaviours down to the single-molecule level, all inside living cells. More recent developments in TCSPC (time-correlated single-photon counting) imaging are now also driving towards being able to determine protein interaction rates with similar spatial resolution, and together, these experimental advances allow investigators to perform biochemical experiments inside living cells.
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Affiliation(s)
- R R Duncan
- Centre for Integrative Physiology, University of Edinburgh, Hugh Robson Building, George Square, Edinburgh EH8 9XD, Scotland, UK.
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144
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Towards Imaging the Dynamics of Protein Signalling. IMAGING CELLULAR AND MOLECULAR BIOLOGICAL FUNCTIONS 2007. [DOI: 10.1007/978-3-540-71331-9_10] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/09/2023]
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145
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Medine CN, McDonald A, Bergmann A, Duncan RR. Time-correlated single photon counting FLIM: Some considerations for physiologists. Microsc Res Tech 2007; 70:420-5. [PMID: 17394229 DOI: 10.1002/jemt.20425] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Recent developments in cellular imaging now permit the minimally invasive study of protein interactions in living cells. These advances are of enormous interest to cell biologists, as proteins rarely act in isolation, but rather in concert with others in forming cellular machinery. Up until recently, all protein interactions had to be determined in vitro using biochemical approaches. This biochemical legacy has provided cell biologists with the basis to test defined protein-protein interactions not only inside cells, but now also with spatial resolution. More recent developments in TCSPC imaging are now also driving towards being able to determine protein interaction rates with similar spatial resolution, and together, these experimental advances allow investigators to perform biochemical experiments inside living cells. Here, we discuss some findings we have made along the way which may be useful for physiologists to consider.
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Affiliation(s)
- Claire N Medine
- Centre for Integrative Physiology, University of Edinburgh, Hugh Robson Building, George Square, Edinburgh EH8 9XD, Scotland, United Kingdom
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146
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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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147
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Dadke S, Cotteret S, Yip SC, Jaffer ZM, Haj F, Ivanov A, Rauscher F, Shuai K, Ng T, Neel BG, Chernoff J. Regulation of protein tyrosine phosphatase 1B by sumoylation. Nat Cell Biol 2006; 9:80-5. [PMID: 17159996 DOI: 10.1038/ncb1522] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2006] [Accepted: 10/20/2006] [Indexed: 12/30/2022]
Abstract
Protein-tyrosine phosphatase 1B (PTP1B) is an ubiquitously expressed enzyme that negatively regulates growth-factor signalling and cell proliferation by binding to and dephosphorylating key receptor tyrosine kinases, such as the insulin receptor. It is unclear how the activity of PTP1B is regulated. Using a yeast two-hybrid assay, a protein inhibitor of activated STAT1 (PIAS1) was isolated as a PTP1B-interacting protein. Here, we show that PIAS1, which functions as a small ubiquitin-like modifier (SUMO) E3 ligase, associates with PTP1B in mammalian fibroblasts and catalyses sumoylation of PTP1B. Sumoylation of PTP1B reduces its catalytic activity and inhibits the negative effect of PTP1B on insulin receptor signalling and on transformation by the oncogene v-crk. Insulin-stimulated sumoylation of endogenous PTP1B results in a transient downregulation of the enzyme; this event does not occur when the endogenous enzyme is replaced with a sumoylation-resistant mutant of PTP1B. These results suggest that sumoylation, which has been implicated primarily in processes in the nucleus and nuclear pore, also modulates a key enzyme-substrate signalling complex that regulates metabolism and cell proliferation.
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Affiliation(s)
- Shrikrishna Dadke
- Fox Chase Cancer Center, 333 Cottman Avenue, Philadelphia, PA 19111, USA
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148
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Yasuda R. Imaging spatiotemporal dynamics of neuronal signaling using fluorescence resonance energy transfer and fluorescence lifetime imaging microscopy. Curr Opin Neurobiol 2006; 16:551-61. [PMID: 16971112 DOI: 10.1016/j.conb.2006.08.012] [Citation(s) in RCA: 106] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2006] [Accepted: 08/30/2006] [Indexed: 11/26/2022]
Abstract
The spatiotemporal localization of neuronal signaling is important for triggering neuronal responses in specific locations at precise times. Fluorescence resonance energy transfer imaging enables measurement of spatiotemporal dynamics of signaling activity in live neurons. Although the usefulness of fluorescence resonance energy transfer is well recognized, there are many difficulties in applying it, particularly when imaging in neuronal micro-compartments in light-scattering brain tissue. Fluorescence resonance energy transfer has been imaged using several techniques including intensity-based methods, fluorescence lifetime imaging and fluorescence anisotropy imaging. These methods have different advantages and disadvantages, and thus are suitable in different applications.
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Affiliation(s)
- Ryohei Yasuda
- Neurobiology Department, Duke University Medical Center, Research Drive, Durham, NC 27710 USA.
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149
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Schubert W, Bonnekoh B, Pommer AJ, Philipsen L, Böckelmann R, Malykh Y, Gollnick H, Friedenberger M, Bode M, Dress AWM. Analyzing proteome topology and function by automated multidimensional fluorescence microscopy. Nat Biotechnol 2006; 24:1270-8. [PMID: 17013374 DOI: 10.1038/nbt1250] [Citation(s) in RCA: 319] [Impact Index Per Article: 17.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2006] [Accepted: 08/16/2006] [Indexed: 11/09/2022]
Abstract
Temporal and spatial regulation of proteins contributes to function. We describe a multidimensional microscopic robot technology for high-throughput protein colocalization studies that runs cycles of fluorescence tagging, imaging and bleaching in situ. This technology combines three advances: a fluorescence technique capable of mapping hundreds of different proteins in one tissue section or cell sample; a method selecting the most prominent combinatorial molecular patterns by representing the data as binary vectors; and a system for imaging the distribution of these protein clusters in a so-called toponome map. By analyzing many cell and tissue types, we show that this approach reveals rules of hierarchical protein network organization, in which the frequency distribution of different protein clusters obeys Zipf's law, and state-specific lead proteins appear to control protein network topology and function. The technology may facilitate the development of diagnostics and targeted therapies.
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Affiliation(s)
- Walter Schubert
- Molecular Pattern Recognition Research (MPRR) Group, Institute of Medical Neurobiology, Otto-von-Guericke-University Magdeburg, D-39120 Magdeburg, Germany.
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