1
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Smid AI, Garforth SJ, Obaid MS, Bollons HR, James JR. Pre-T cell receptor localization and trafficking are independent of its signaling. J Cell Biol 2023; 222:e202212106. [PMID: 37516909 PMCID: PMC10373305 DOI: 10.1083/jcb.202212106] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2022] [Revised: 06/08/2023] [Accepted: 07/06/2023] [Indexed: 07/31/2023] Open
Abstract
Expression of the pre-T cell receptor (preTCR) is an important checkpoint during the development of T cells, an essential cell type of our adaptive immune system. The preTCR complex is only transiently expressed and rapidly internalized in developing T cells and is thought to signal in a ligand-independent manner. However, identifying a mechanistic basis for these unique features of the preTCR compared with the final TCR complex has been confounded by the concomitant signaling that is normally present. Thus, we have reconstituted preTCR expression in non-immune cells to uncouple receptor trafficking dynamics from its associated signaling. We find that all the defining features of the preTCR are intrinsic properties of the receptor itself, driven by exposure of an extracellular hydrophobic region, and are not the consequence of receptor activation. Finally, we show that transitory preTCR cell surface expression can sustain tonic signaling in the absence of ligand binding, suggesting how the preTCR can nonetheless drive αβTCR lineage commitment.
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Affiliation(s)
- Andrei I. Smid
- Molecular Immunity Unit, Department of Medicine, Medical Research Council–Laboratory of Molecular Biology, University of Cambridge, Cambridge, UK
| | - Sam J. Garforth
- Division of Biomedical Sciences, Warwick Medical School, University of Warwick, Coventry, UK
| | - Maryam S. Obaid
- Division of Biomedical Sciences, Warwick Medical School, University of Warwick, Coventry, UK
| | - Hannah R. Bollons
- Division of Biomedical Sciences, Warwick Medical School, University of Warwick, Coventry, UK
| | - John R. James
- Molecular Immunity Unit, Department of Medicine, Medical Research Council–Laboratory of Molecular Biology, University of Cambridge, Cambridge, UK
- Division of Biomedical Sciences, Warwick Medical School, University of Warwick, Coventry, UK
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2
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Abstract
T cell activation is initiated by the recognition of specific antigenic peptides and subsequently accomplished by complex signaling cascades. These aspects have been extensively studied for decades as pivotal factors in the establishment of adaptive immunity. However, how receptors or signaling molecules are organized in the resting state prior to encountering antigens has received less attention. Recent advancements in super-resolution microscopy techniques have revealed topographically controlled pre-formed organization of key molecules involved in antigen recognition and signal transduction on microvillar projections of T cells before activation and substantial effort has been dedicated to characterizing the topological structure of resting T cells over the past decade. This review will summarize our current understanding of how key surface receptors are pre-organized on the T-cell plasma membrane and discuss the potential role of these receptors, which are preassembled prior to ligand binding in the early activation events of T cells.
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Affiliation(s)
- Yunmin Jung
- Department of Nano-Biomedical Engineering, Advanced Science Institute, Yonsei University, Seoul, Republic of Korea
- Center for Nanomedicine, Institute for Basic Science, Seoul, Republic of Korea
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3
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Rochussen AM, Lippert AH, Griffiths GM. Imaging the T-cell receptor: new approaches, new insights. Curr Opin Immunol 2023; 82:102309. [PMID: 37011462 DOI: 10.1016/j.coi.2023.102309] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2023] [Revised: 03/02/2023] [Accepted: 03/03/2023] [Indexed: 04/03/2023]
Abstract
T cells recognize pathogenic antigens via the T-cell antigen receptor (TCR). This protein complex binds to antigen fragments on the surface of antigen-presenting cells. To understand how cellular activation can ensue rapidly from molecular recognition, the localization and distribution of the TCR on the surface of the resting T cell are of particular importance. Conflicting results regarding TCR distribution have emerged from recent studies using a range of imaging techniques, including total internal reflection and single-molecule localization microscopy modalities. Here, we review the differing results and the potential biases inherent in differing imaging approaches. In addition, we review studies showing the impact of differing imaging surfaces on T-cell activation.
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4
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McColl J, Klenerman D. Surfaces for Study of Receptor Dynamics on T Cells. Methods Mol Biol 2023; 2654:41-50. [PMID: 37106174 DOI: 10.1007/978-1-0716-3135-5_3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/29/2023]
Abstract
Microscopy developments since the turn of the decade have seen an abundance of imaging modalities emerge that are revolutionizing the way we image the immune system. We are now able to image faster and utilize techniques that can image individual receptors, in real time, on live T cells. Total internal reflection fluorescence (TIRF) microscopy is one such technique, although it has one problem. The imaging must be carried out close to the glass interface. There are clearly issues with live cell imaging at glass surfaces as these are not biologically relevant. Manipulating the surface is key for maintaining biologically relevant imaging conditions. Here, we describe a simple approach to generate substrates for cell attachment and imaging of receptor dynamics and outline a guide for imaging and tracking T cell, surface receptors using TIRF microscopy.
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Affiliation(s)
- James McColl
- Department of Chemistry, University of Cambridge, Cambridge, UK
| | - David Klenerman
- Department of Chemistry, University of Cambridge, Cambridge, UK.
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5
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Sušac L, Vuong MT, Thomas C, von Bülow S, O'Brien-Ball C, Santos AM, Fernandes RA, Hummer G, Tampé R, Davis SJ. Structure of a fully assembled tumor-specific T cell receptor ligated by pMHC. Cell 2022; 185:3201-3213.e19. [PMID: 35985289 PMCID: PMC9630439 DOI: 10.1016/j.cell.2022.07.010] [Citation(s) in RCA: 36] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2021] [Revised: 04/05/2022] [Accepted: 07/15/2022] [Indexed: 12/12/2022]
Abstract
The T cell receptor (TCR) expressed by T lymphocytes initiates protective immune responses to pathogens and tumors. To explore the structural basis of how TCR signaling is initiated when the receptor binds to peptide-loaded major histocompatibility complex (pMHC) molecules, we used cryogenic electron microscopy to determine the structure of a tumor-reactive TCRαβ/CD3δγε2ζ2 complex bound to a melanoma-specific human class I pMHC at 3.08 Å resolution. The antigen-bound complex comprises 11 subunits stabilized by multivalent interactions across three structural layers, with clustered membrane-proximal cystines stabilizing the CD3-εδ and CD3-εγ heterodimers. Extra density sandwiched between transmembrane helices reveals the involvement of sterol lipids in TCR assembly. The geometry of the pMHC/TCR complex suggests that efficient TCR scanning of pMHC requires accurate pre-positioning of T cell and antigen-presenting cell membranes. Comparisons of the ligand-bound and unliganded receptors, along with molecular dynamics simulations, indicate that TCRs can be triggered in the absence of spontaneous structural rearrangements.
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Affiliation(s)
- Lukas Sušac
- Institute of Biochemistry, Biocenter, Goethe University Frankfurt, Max-von-Laue-Str. 9, 60438 Frankfurt am Main, Germany
| | - Mai T Vuong
- Radcliffe Department of Medicine, John Radcliffe Hospital, University of Oxford, Oxford OX3 9DS, UK; Medical Research Council Human Immunology Unit, John Radcliffe Hospital, University of Oxford, Oxford OX3 9DS, UK
| | - Christoph Thomas
- Institute of Biochemistry, Biocenter, Goethe University Frankfurt, Max-von-Laue-Str. 9, 60438 Frankfurt am Main, Germany
| | - Sören von Bülow
- Department of Theoretical Biophysics, Max Planck Institute of Biophysics, Max-von-Laue-Str. 3, 60438 Frankfurt am Main, Germany
| | - Caitlin O'Brien-Ball
- Radcliffe Department of Medicine, John Radcliffe Hospital, University of Oxford, Oxford OX3 9DS, UK; Medical Research Council Human Immunology Unit, John Radcliffe Hospital, University of Oxford, Oxford OX3 9DS, UK
| | - Ana Mafalda Santos
- Radcliffe Department of Medicine, John Radcliffe Hospital, University of Oxford, Oxford OX3 9DS, UK; Medical Research Council Human Immunology Unit, John Radcliffe Hospital, University of Oxford, Oxford OX3 9DS, UK
| | - Ricardo A Fernandes
- Radcliffe Department of Medicine, John Radcliffe Hospital, University of Oxford, Oxford OX3 9DS, UK; Medical Research Council Human Immunology Unit, John Radcliffe Hospital, University of Oxford, Oxford OX3 9DS, UK
| | - Gerhard Hummer
- Department of Theoretical Biophysics, Max Planck Institute of Biophysics, Max-von-Laue-Str. 3, 60438 Frankfurt am Main, Germany; Institute of Biophysics, Goethe University Frankfurt, Max-von-Laue-Str. 1, 60438 Frankfurt am Main, Germany
| | - Robert Tampé
- Institute of Biochemistry, Biocenter, Goethe University Frankfurt, Max-von-Laue-Str. 9, 60438 Frankfurt am Main, Germany.
| | - Simon J Davis
- Radcliffe Department of Medicine, John Radcliffe Hospital, University of Oxford, Oxford OX3 9DS, UK; Medical Research Council Human Immunology Unit, John Radcliffe Hospital, University of Oxford, Oxford OX3 9DS, UK.
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6
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Nieves DJ, Pandzic E, Gunasinghe SD, Goyette J, Owen DM, Justin Gooding J, Gaus K. The T cell receptor displays lateral signal propagation involving non-engaged receptors. NANOSCALE 2022; 14:3513-3526. [PMID: 35171177 DOI: 10.1039/d1nr05855j] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
T cells are highly sensitive to low levels of antigen, but how this sensitivity is achieved is currently unknown. Here, we imaged proximal TCR-CD3 signal propagation with single molecule localization microscopy (SMLM) in T cells activated with nanoscale clusters of TCR stimuli. We observed the formation of large TCR-CD3 clusters that exceeded the area of the ligand clusters, and required multivalent interactions facilitated by TCR-CD3 phosphorylation for assembly. Within these clustered TCR-CD3 domains, TCR-CD3 signaling spread laterally for ∼500 nm, far beyond the activating site, via non-engaged receptors. Local receptor density determined the functional cooperativity between engaged and non-engaged receptors, but lateral signal propagation was not influenced by the genetic deletion of ZAP70. Taken together, our data demonstrates that clustered ligands induced the clustering of non-ligated TCR-CD3 into domains that cooperatively facilitate lateral signal propagation.
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Affiliation(s)
- Daniel J Nieves
- EMBL Australia Node in Single Molecule Science, School of Medical Sciences and the ARC Centre of Excellence in Advanced Molecular Imaging, University of New South Wales, Sydney, Australia
- Institute of Immunology and Immunotherapy, School of Mathematics, and Centre of Membrane Proteins and Receptors (COMPARE), University of Birmingham, Birmingham, UK.
| | - Elvis Pandzic
- Katharina Gaus Light Microscopy Facility, Mark Wainwright Analytical Centre, University of New South Wales, Sydney, Australia
| | - Sachith D Gunasinghe
- EMBL Australia Node in Single Molecule Science, School of Medical Sciences and the ARC Centre of Excellence in Advanced Molecular Imaging, University of New South Wales, Sydney, Australia
| | - Jesse Goyette
- EMBL Australia Node in Single Molecule Science, School of Medical Sciences and the ARC Centre of Excellence in Advanced Molecular Imaging, University of New South Wales, Sydney, Australia
| | - Dylan M Owen
- Institute of Immunology and Immunotherapy, School of Mathematics, and Centre of Membrane Proteins and Receptors (COMPARE), University of Birmingham, Birmingham, UK.
| | - J Justin Gooding
- School of Chemistry and Australian Centre for NanoMedicine, University of New South Wales, Sydney, Australia
| | - Katharina Gaus
- EMBL Australia Node in Single Molecule Science, School of Medical Sciences and the ARC Centre of Excellence in Advanced Molecular Imaging, University of New South Wales, Sydney, Australia
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7
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Feher K, Graus MS, Coelho S, Farrell MV, Goyette J, Gaus K. K-Neighbourhood Analysis: A Method for Understanding SMLM Images as Compositions of Local Neighbourhoods. FRONTIERS IN BIOINFORMATICS 2021; 1:724127. [PMID: 36303786 PMCID: PMC9581049 DOI: 10.3389/fbinf.2021.724127] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2021] [Accepted: 10/04/2021] [Indexed: 11/30/2022] Open
Abstract
Single molecule localisation microscopy (SMLM) is a powerful tool that has revealed the spatial arrangement of cell surface signalling proteins, producing data of enormous complexity. The complexity is partly driven by the convolution of technical and biological signal components, and partly by the challenge of pooling information across many distinct cells. To address these two particular challenges, we have devised a novel algorithm called K-neighbourhood analysis (KNA), which emphasises the fact that each image can also be viewed as a composition of local neighbourhoods. KNA is based on a novel transformation, spatial neighbourhood principal component analysis (SNPCA), which is defined by the PCA of the normalised K-nearest neighbour vectors of a spatially random point pattern. Here, we use KNA to define a novel visualisation of individual images, to compare within and between groups of images and to investigate the preferential patterns of phosphorylation. This methodology is also highly flexible and can be used to augment existing clustering methods by providing clustering diagnostics as well as revealing substructure within microclusters. In summary, we have presented a highly flexible analysis tool that presents new conceptual possibilities in the analysis of SMLM images.
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Affiliation(s)
- Kristen Feher
- School of Medical Sciences, EMBL Australia Node in Single Molecule Science, University of New South Wales, Kensington, NSW, Australia
- ARC Centre of Excellence in Advanced Molecular Imaging, University of New South Wales, Sydney, NSW, Australia
| | - Matthew S. Graus
- School of Medical Sciences, EMBL Australia Node in Single Molecule Science, University of New South Wales, Kensington, NSW, Australia
- ARC Centre of Excellence in Advanced Molecular Imaging, University of New South Wales, Sydney, NSW, Australia
| | - Simao Coelho
- School of Medical Sciences, EMBL Australia Node in Single Molecule Science, University of New South Wales, Kensington, NSW, Australia
- ARC Centre of Excellence in Advanced Molecular Imaging, University of New South Wales, Sydney, NSW, Australia
- Structural Biology Program, Memorial Sloan Kettering Cancer Center, New York, NY, United States
| | - Megan V. Farrell
- School of Medical Sciences, EMBL Australia Node in Single Molecule Science, University of New South Wales, Kensington, NSW, Australia
- ARC Centre of Excellence in Advanced Molecular Imaging, University of New South Wales, Sydney, NSW, Australia
| | - Jesse Goyette
- School of Medical Sciences, EMBL Australia Node in Single Molecule Science, University of New South Wales, Kensington, NSW, Australia
- ARC Centre of Excellence in Advanced Molecular Imaging, University of New South Wales, Sydney, NSW, Australia
| | - Katharina Gaus
- School of Medical Sciences, EMBL Australia Node in Single Molecule Science, University of New South Wales, Kensington, NSW, Australia
- ARC Centre of Excellence in Advanced Molecular Imaging, University of New South Wales, Sydney, NSW, Australia
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8
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Yang X, Annaert W. The Nanoscopic Organization of Synapse Structures: A Common Basis for Cell Communication. MEMBRANES 2021; 11:248. [PMID: 33808285 PMCID: PMC8065904 DOI: 10.3390/membranes11040248] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/20/2021] [Revised: 03/26/2021] [Accepted: 03/27/2021] [Indexed: 11/16/2022]
Abstract
Synapse structures, including neuronal and immunological synapses, can be seen as the plasma membrane contact sites between two individual cells where information is transmitted from one cell to the other. The distance between the two plasma membranes is only a few tens of nanometers, but these areas are densely populated with functionally different proteins, including adhesion proteins, receptors, and transporters. The narrow space between the two plasma membranes has been a barrier for resolving the synaptic architecture due to the diffraction limit in conventional microscopy (~250 nm). Various advanced super-resolution microscopy techniques, such as stimulated emission depletion (STED), structured illumination microscopy (SIM), and single-molecule localization microscopy (SMLM), bypass the diffraction limit and provide a sub-diffraction-limit resolving power, ranging from 10 to 100 nm. The studies using super-resolution microscopy have revealed unprecedented details of the nanoscopic organization and dynamics of synaptic molecules. In general, most synaptic proteins appear to be heterogeneously distributed and form nanodomains at the membranes. These nanodomains are dynamic functional units, playing important roles in mediating signal transmission through synapses. Herein, we discuss our current knowledge on the super-resolution nanoscopic architecture of synapses and their functional implications, with a particular focus on the neuronal synapses and immune synapses.
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Affiliation(s)
| | - Wim Annaert
- VIB Center for Brain and Disease Research and KU Leuven, Department of Neurosciences, Gasthuisberg, B-3000 Leuven, Belgium;
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9
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Zhang X, Mariano CF, Ando Y, Shen K. Bioengineering tools for probing intracellular events in T lymphocytes. WIREs Mech Dis 2020; 13:e1510. [PMID: 33073545 DOI: 10.1002/wsbm.1510] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2020] [Revised: 09/14/2020] [Accepted: 09/16/2020] [Indexed: 11/11/2022]
Abstract
T lymphocytes are the central coordinator and executor of many immune functions. The activation and function of T lymphocytes are mediated through the engagement of cell surface receptors and regulated by a myriad of intracellular signaling network. Bioengineering tools, including imaging modalities and fluorescent probes, have been developed and employed to elucidate the cellular events throughout the functional lifespan of T cells. A better understanding of these events can broaden our knowledge in the immune systems biology, as well as accelerate the development of effective diagnostics and immunotherapies. Here we review the commonly used and recently developed techniques and probes for monitoring T lymphocyte intracellular events, following the order of intracellular events in T cells from activation, signaling, metabolism to apoptosis. The techniques introduced here can be broadly applied to other immune cells and cell systems. This article is categorized under: Immune System Diseases > Molecular and Cellular Physiology Immune System Diseases > Biomedical Engineering Infectious Diseases > Biomedical Engineering.
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Affiliation(s)
- Xinyuan Zhang
- Department of Biomedical Engineering, University of Southern California, Los Angeles, California, USA
| | - Chelsea F Mariano
- Department of Biomedical Engineering, University of Southern California, Los Angeles, California, USA
| | - Yuta Ando
- Department of Biomedical Engineering, University of Southern California, Los Angeles, California, USA
| | - Keyue Shen
- Department of Biomedical Engineering, University of Southern California, Los Angeles, California, USA.,Norris Comprehensive Cancer Center, University of Southern California, Los Angeles, California, USA.,USC Stem Cell, University of Southern California, Los Angeles, California, USA
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10
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Davis SJ, O’Brien-Ball C. T-Cell Receptor Ligands: Every which Way They Can. Biophys J 2020; 118:2867-2869. [PMID: 32492373 PMCID: PMC7300379 DOI: 10.1016/j.bpj.2020.05.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2020] [Revised: 05/10/2020] [Accepted: 05/11/2020] [Indexed: 10/24/2022] Open
Affiliation(s)
- Simon J. Davis
- Radcliffe Department of Medicine, University of Oxford, Oxford, United Kingdom,Medical Research Council Human Immunology Unit, University of Oxford, Oxford, United Kingdom,Corresponding author
| | - Caitlin O’Brien-Ball
- Medical Research Council Human Immunology Unit, University of Oxford, Oxford, United Kingdom
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11
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Kaitao L, William R, Zhou Y, Cheng Z. Single-molecule investigations of T-cell activation. CURRENT OPINION IN BIOMEDICAL ENGINEERING 2019; 12:102-110. [PMID: 32296738 PMCID: PMC7158867 DOI: 10.1016/j.cobme.2019.10.005] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
T-cell activation is the central event governing its development, differentiation, and effector functions. T-cell activation is initiated by the direct physical interaction of the T cell antigen receptor (TCR) with cognate peptide presented by the major histocompatibility complex (pMHC) molecule expressed on the antigen presenting cell (APC) surface. Since the identification of TCR as the only receptor for antigen on T cells three decades ago, studies have elucidated the major molecular players and signaling events responding to TCR stimulation. However, the question of how the physical event of pMHC binding is converted across the membrane into chemical events to initiate signal transduction remains elusive. Here we review recent investigations of T-cell activation using single-molecule force and fluorescence techniques that shed new light on this key question.
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Affiliation(s)
- Li Kaitao
- Wallace H. Coulter Department of Biomedical Engineering
- Institute for Bioengineering and Biosciences, Georgia Institute of Technology, Atlanta, GA 30332
| | - Rittase William
- Wallace H. Coulter Department of Biomedical Engineering
- Institute for Bioengineering and Biosciences, Georgia Institute of Technology, Atlanta, GA 30332
| | - Yuan Zhou
- George W. Woodruff School of Mechanical Engineering
- Institute for Bioengineering and Biosciences, Georgia Institute of Technology, Atlanta, GA 30332
| | - Zhu Cheng
- Wallace H. Coulter Department of Biomedical Engineering
- George W. Woodruff School of Mechanical Engineering
- Institute for Bioengineering and Biosciences, Georgia Institute of Technology, Atlanta, GA 30332
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12
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Can single molecule localization microscopy detect nanoclusters in T cells? Curr Opin Chem Biol 2019; 51:130-137. [DOI: 10.1016/j.cbpa.2019.05.019] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2018] [Revised: 05/10/2019] [Accepted: 05/21/2019] [Indexed: 11/21/2022]
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13
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Fernandes RA, Ganzinger KA, Tzou JC, Jönsson P, Lee SF, Palayret M, Santos AM, Carr AR, Ponjavic A, Chang VT, Macleod C, Lagerholm BC, Lindsay AE, Dushek O, Tilevik A, Davis SJ, Klenerman D. A cell topography-based mechanism for ligand discrimination by the T cell receptor. Proc Natl Acad Sci U S A 2019; 116:14002-14010. [PMID: 31221762 PMCID: PMC6628812 DOI: 10.1073/pnas.1817255116] [Citation(s) in RCA: 45] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The T cell receptor (TCR) initiates the elimination of pathogens and tumors by T cells. To avoid damage to the host, the receptor must be capable of discriminating between wild-type and mutated self and nonself peptide ligands presented by host cells. Exactly how the TCR does this is unknown. In resting T cells, the TCR is largely unphosphorylated due to the dominance of phosphatases over the kinases expressed at the cell surface. However, when agonist peptides are presented to the TCR by major histocompatibility complex proteins expressed by antigen-presenting cells (APCs), very fast receptor triggering, i.e., TCR phosphorylation, occurs. Recent work suggests that this depends on the local exclusion of the phosphatases from regions of contact of the T cells with the APCs. Here, we developed and tested a quantitative treatment of receptor triggering reliant only on TCR dwell time in phosphatase-depleted cell contacts constrained in area by cell topography. Using the model and experimentally derived parameters, we found that ligand discrimination likely depends crucially on individual contacts being ∼200 nm in radius, matching the dimensions of the surface protrusions used by T cells to interrogate their targets. The model not only correctly predicted the relative signaling potencies of known agonists and nonagonists but also achieved this in the absence of kinetic proofreading. Our work provides a simple, quantitative, and predictive molecular framework for understanding why TCR triggering is so selective and fast and reveals that, for some receptors, cell topography likely influences signaling outcomes.
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Affiliation(s)
- Ricardo A Fernandes
- Radcliffe Department of Medicine, John Radcliffe Hospital, University of Oxford, OX3 9DS Oxford, United Kingdom
- Medical Research Council Human Immunology Unit, John Radcliffe Hospital, University of Oxford, OX3 9DS Oxford, United Kingdom
| | - Kristina A Ganzinger
- Department of Chemistry, University of Cambridge, CB2 1EW Cambridge, United Kingdom
| | - Justin C Tzou
- Department of Applied & Computational Mathematics & Statistics, University of Notre Dame, Notre Dame, IN 46556
| | - Peter Jönsson
- Department of Chemistry, University of Cambridge, CB2 1EW Cambridge, United Kingdom
| | - Steven F Lee
- Department of Chemistry, University of Cambridge, CB2 1EW Cambridge, United Kingdom
| | - Matthieu Palayret
- Department of Chemistry, University of Cambridge, CB2 1EW Cambridge, United Kingdom
| | - Ana Mafalda Santos
- Radcliffe Department of Medicine, John Radcliffe Hospital, University of Oxford, OX3 9DS Oxford, United Kingdom
- Medical Research Council Human Immunology Unit, John Radcliffe Hospital, University of Oxford, OX3 9DS Oxford, United Kingdom
| | - Alexander R Carr
- Department of Chemistry, University of Cambridge, CB2 1EW Cambridge, United Kingdom
| | - Aleks Ponjavic
- Department of Chemistry, University of Cambridge, CB2 1EW Cambridge, United Kingdom
| | - Veronica T Chang
- Radcliffe Department of Medicine, John Radcliffe Hospital, University of Oxford, OX3 9DS Oxford, United Kingdom
- Medical Research Council Human Immunology Unit, John Radcliffe Hospital, University of Oxford, OX3 9DS Oxford, United Kingdom
| | - Charlotte Macleod
- Department of Chemistry, University of Cambridge, CB2 1EW Cambridge, United Kingdom
| | - B Christoffer Lagerholm
- Radcliffe Department of Medicine, John Radcliffe Hospital, University of Oxford, OX3 9DS Oxford, United Kingdom
| | - Alan E Lindsay
- Mathematics Department, University of British Columbia, Vancouver, BC V6T 1Z2, Canada
| | - Omer Dushek
- Sir William Dunn School of Pathology, University of Oxford, OX1 3RE Oxford, United Kingdom
- Wolfson Centre for Mathematical Biology, University of Oxford, OX1 3RE Oxford, United Kingdom
| | - Andreas Tilevik
- School of Bioscience, University of Skövde, 541 28 Skövde, Sweden
| | - Simon J Davis
- Radcliffe Department of Medicine, John Radcliffe Hospital, University of Oxford, OX3 9DS Oxford, United Kingdom;
- Medical Research Council Human Immunology Unit, John Radcliffe Hospital, University of Oxford, OX3 9DS Oxford, United Kingdom
| | - David Klenerman
- Department of Chemistry, University of Cambridge, CB2 1EW Cambridge, United Kingdom;
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14
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Abstract
T cells initiate and regulate adaptive immune responses that can clear infections. To do this, they use their T cell receptors (TCRs) to continually scan the surfaces of other cells for cognate peptide antigens presented on major histocompatibility complexes (pMHCs). Experimental work has established that as few 1-10 pMHCs are sufficient to activate T cells. This sensitivity is remarkable in light of a number of factors, including the observation that the TCR and pMHC are short molecules relative to highly abundant long surface molecules, such as CD45, that can hinder initial binding, and moreover, the TCR/pMHC interaction is of weak affinity with solution lifetimes of approximately 1 second. Here, we review experimental and mathematical work that has contributed to uncovering molecular mechanisms of T cell sensitivity. We organize the mechanisms by where they act in the pathway to activate T cells, namely mechanisms that (a) promote TCR/pMHC binding, (b) induce rapid TCR signaling, and (c) amplify TCR signaling. We discuss work showing that high sensitivity reduces antigen specificity unless molecular feedbacks are invoked. We conclude by summarizing a number of open questions.
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Affiliation(s)
| | - Omer Dushek
- Sir William Dunn School of Pathology, University of Oxford, Oxford, UK
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15
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Pettmann J, Santos AM, Dushek O, Davis SJ. Membrane Ultrastructure and T Cell Activation. Front Immunol 2018; 9:2152. [PMID: 30319617 PMCID: PMC6167458 DOI: 10.3389/fimmu.2018.02152] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2018] [Accepted: 08/31/2018] [Indexed: 11/13/2022] Open
Abstract
The immune system serves as a crucial line of defense from infection and cancer, while also contributing to tissue homeostasis. Communication between immune cells is mediated by small soluble factors called cytokines, and also by direct cellular interactions. Cell-cell interactions are particularly important for T cell activation. T cells direct the adaptive immune response and therefore need to distinguish between self and foreign antigens. Even though decades have passed since the discovery of T cells, exactly why and how they are able to recognize and discriminate between antigens is still not fully understood. Early imaging of T cells was very successful in capturing the early stages of conjugate formation of T cells with antigen-presenting cells upon recognition of peptide-loaded major histocompatibility complexes by the T cell receptor (TCR). These studies lead to the discovery of a “supramolecular activation cluster” now known as the immunological synapse, followed by the identification of microclusters of TCRs formed upon receptor triggering, that eventually coalesce at the center of the synapse. New developments in light microscopy have since allowed attention to turn to the very earliest stages of T cell activation, and to resting cells, at high resolution. This includes single-molecule localization microscopy, which has been applied to the question of whether TCRs are pre-clustered on resting T cells, and lattice light-sheet microscopy that has enabled imaging of whole cells interacting with antigen-presenting cells. The utilization of lattice light-sheet microscopy has yielded important insights into structures called microvilli, which are small membrane protrusions on T cells that seem likely to have a large impact on T cell recognition and activation. Here we consider how imaging has shaped our thinking about T cell activation. We summarize recent findings obtained by applying more advanced microscopy techniques and discuss some of the limitations of these methods.
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Affiliation(s)
- Johannes Pettmann
- Sir William Dunn School of Pathology, University of Oxford, Oxford, United Kingdom.,Radcliffe Department of Medicine, Medical Research Council Human Immunology Unit, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, United Kingdom
| | - Ana Mafalda Santos
- Radcliffe Department of Medicine, Medical Research Council Human Immunology Unit, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, United Kingdom
| | - Omer Dushek
- Sir William Dunn School of Pathology, University of Oxford, Oxford, United Kingdom
| | - Simon J Davis
- Radcliffe Department of Medicine, Medical Research Council Human Immunology Unit, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, United Kingdom
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16
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Ponjavic A, McColl J, Carr AR, Santos AM, Kulenkampff K, Lippert A, Davis SJ, Klenerman D, Lee SF. Single-Molecule Light-Sheet Imaging of Suspended T Cells. Biophys J 2018; 114:2200-2211. [PMID: 29742413 PMCID: PMC5961759 DOI: 10.1016/j.bpj.2018.02.044] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2017] [Revised: 02/01/2018] [Accepted: 02/02/2018] [Indexed: 11/26/2022] Open
Abstract
Adaptive immune responses are initiated by triggering of the T cell receptor. Single-molecule imaging based on total internal reflection fluorescence microscopy at coverslip/basal cell interfaces is commonly used to study this process. These experiments have suggested, unexpectedly, that the diffusional behavior and organization of signaling proteins and receptors may be constrained before activation. However, it is unclear to what extent the molecular behavior and cell state is affected by the imaging conditions, i.e., by the presence of a supporting surface. In this study, we implemented single-molecule light-sheet microscopy, which enables single receptors to be directly visualized at any plane in a cell to study protein dynamics and organization in live, resting T cells. The light sheet enabled the acquisition of high-quality single-molecule fluorescence images that were comparable to those of total internal reflection fluorescence microscopy. By comparing the apical and basal surfaces of surface-contacting T cells using single-molecule light-sheet microscopy, we found that most coated-glass surfaces and supported lipid bilayers profoundly affected the diffusion of membrane proteins (T cell receptor and CD45) and that all the surfaces induced calcium influx to various degrees. Our results suggest that, when studying resting T cells, surfaces are best avoided, which we achieve here by suspending cells in agarose.
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Affiliation(s)
- Aleks Ponjavic
- Department of Chemistry, University of Cambridge, Cambridge, United Kingdom
| | - James McColl
- Department of Chemistry, University of Cambridge, Cambridge, United Kingdom
| | - Alexander R Carr
- Department of Chemistry, University of Cambridge, Cambridge, United Kingdom
| | - Ana Mafalda Santos
- Radcliffe Department of Medicine and MRC Human Immunology Unit, John Radcliffe Hospital, University of Oxford, Oxford, United Kingdom
| | - Klara Kulenkampff
- Department of Chemistry, University of Cambridge, Cambridge, United Kingdom
| | - Anna Lippert
- Department of Chemistry, University of Cambridge, Cambridge, United Kingdom
| | - Simon J Davis
- Radcliffe Department of Medicine and MRC Human Immunology Unit, John Radcliffe Hospital, University of Oxford, Oxford, United Kingdom.
| | - David Klenerman
- Department of Chemistry, University of Cambridge, Cambridge, United Kingdom.
| | - Steven F Lee
- Department of Chemistry, University of Cambridge, Cambridge, United Kingdom.
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17
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Brameshuber M, Kellner F, Rossboth BK, Ta H, Alge K, Sevcsik E, Göhring J, Axmann M, Baumgart F, Gascoigne NRJ, Davis SJ, Stockinger H, Schütz GJ, Huppa JB. Monomeric TCRs drive T cell antigen recognition. Nat Immunol 2018; 19:487-496. [PMID: 29662172 DOI: 10.1038/s41590-018-0092-4] [Citation(s) in RCA: 91] [Impact Index Per Article: 15.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2017] [Accepted: 03/15/2018] [Indexed: 11/09/2022]
Abstract
T cell antigen recognition requires T cell antigen receptors (TCRs) engaging MHC-embedded antigenic peptides (pMHCs) within the contact region of a T cell with its conjugated antigen-presenting cell. Despite micromolar TCR:pMHC affinities, T cells respond to even a single antigenic pMHC, and higher-order TCRs have been postulated to maintain high antigen sensitivity and trigger signaling. We interrogated the stoichiometry of TCRs and their associated CD3 subunits on the surface of living T cells through single-molecule brightness and single-molecule coincidence analysis, photon-antibunching-based fluorescence correlation spectroscopy and Förster resonance energy transfer measurements. We found exclusively monomeric TCR-CD3 complexes driving the recognition of antigenic pMHCs, which underscores the exceptional capacity of single TCR-CD3 complexes to elicit robust intracellular signaling.
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Affiliation(s)
| | - Florian Kellner
- Center for Pathophysiology, Infectiology and Immunology, Institute for Hygiene and Applied Immunology, Medical University of Vienna, Vienna, Austria
| | | | - Haisen Ta
- Department of NanoBiophotonics, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Kevin Alge
- Center for Pathophysiology, Infectiology and Immunology, Institute for Hygiene and Applied Immunology, Medical University of Vienna, Vienna, Austria
| | - Eva Sevcsik
- Institute of Applied Physics, TU Wien, Vienna, Austria
| | - Janett Göhring
- Institute of Applied Physics, TU Wien, Vienna, Austria.,Center for Pathophysiology, Infectiology and Immunology, Institute for Hygiene and Applied Immunology, Medical University of Vienna, Vienna, Austria
| | - Markus Axmann
- Center for Pathobiochemistry and Genetics, Institute of Medical Chemistry and Pathobiochemistry, Medical University of Vienna, Vienna, Austria
| | | | - Nicholas R J Gascoigne
- Department of Microbiology and Immunology, Yong Loo Lin School of Medicine, National University of Singapore, Singapore, Singapore
| | - Simon J Davis
- Radcliffe Department of Medicine and MRC Human Immunology Unit, John Radcliffe Hospital, University of Oxford, Oxford, UK
| | - Hannes Stockinger
- Center for Pathophysiology, Infectiology and Immunology, Institute for Hygiene and Applied Immunology, Medical University of Vienna, Vienna, Austria
| | | | - Johannes B Huppa
- Center for Pathophysiology, Infectiology and Immunology, Institute for Hygiene and Applied Immunology, Medical University of Vienna, Vienna, Austria.
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18
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Santos AM, Ponjavic A, Fritzsche M, Fernandes RA, de la Serna JB, Wilcock MJ, Schneider F, Urbančič I, McColl J, Anzilotti C, Ganzinger KA, Aßmann M, Depoil D, Cornall RJ, Dustin ML, Klenerman D, Davis SJ, Eggeling C, Lee SF. Capturing resting T cells: the perils of PLL. Nat Immunol 2018; 19:203-205. [PMID: 29476188 PMCID: PMC7612954 DOI: 10.1038/s41590-018-0048-8] [Citation(s) in RCA: 46] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2017] [Accepted: 12/13/2017] [Indexed: 11/09/2022]
Affiliation(s)
- Ana Mafalda Santos
- Radcliffe Department of Medicine, University of Oxford, Oxford, UK
- MRC Human Immunology Unit, John Radcliffe Hospital, University of Oxford, Oxford, UK
| | - Aleks Ponjavic
- Department of Chemistry, University of Cambridge, Cambridge, UK
| | - Marco Fritzsche
- Radcliffe Department of Medicine, University of Oxford, Oxford, UK
- MRC Human Immunology Unit, John Radcliffe Hospital, University of Oxford, Oxford, UK
- Kennedy Institute of Rheumatology, University of Oxford, Oxford, UK
| | - Ricardo A Fernandes
- Radcliffe Department of Medicine, University of Oxford, Oxford, UK
- MRC Human Immunology Unit, John Radcliffe Hospital, University of Oxford, Oxford, UK
| | - Jorge Bernardino de la Serna
- Radcliffe Department of Medicine, University of Oxford, Oxford, UK
- MRC Human Immunology Unit, John Radcliffe Hospital, University of Oxford, Oxford, UK
| | - Martin J Wilcock
- Radcliffe Department of Medicine, University of Oxford, Oxford, UK
- MRC Human Immunology Unit, John Radcliffe Hospital, University of Oxford, Oxford, UK
| | - Falk Schneider
- Radcliffe Department of Medicine, University of Oxford, Oxford, UK
- MRC Human Immunology Unit, John Radcliffe Hospital, University of Oxford, Oxford, UK
| | - Iztok Urbančič
- Radcliffe Department of Medicine, University of Oxford, Oxford, UK
- MRC Human Immunology Unit, John Radcliffe Hospital, University of Oxford, Oxford, UK
| | - James McColl
- Department of Chemistry, University of Cambridge, Cambridge, UK
| | - Consuelo Anzilotti
- Radcliffe Department of Medicine, University of Oxford, Oxford, UK
- MRC Human Immunology Unit, John Radcliffe Hospital, University of Oxford, Oxford, UK
| | | | - Meike Aßmann
- Radcliffe Department of Medicine, University of Oxford, Oxford, UK
- MRC Human Immunology Unit, John Radcliffe Hospital, University of Oxford, Oxford, UK
| | - David Depoil
- Kennedy Institute of Rheumatology, University of Oxford, Oxford, UK
| | - Richard J Cornall
- MRC Human Immunology Unit, John Radcliffe Hospital, University of Oxford, Oxford, UK
- Nuffield Department of Clinical Medicine, University of Oxford, Oxford, UK
| | - Michael L Dustin
- Kennedy Institute of Rheumatology, University of Oxford, Oxford, UK
| | - David Klenerman
- Department of Chemistry, University of Cambridge, Cambridge, UK
| | - Simon J Davis
- Radcliffe Department of Medicine, University of Oxford, Oxford, UK
- MRC Human Immunology Unit, John Radcliffe Hospital, University of Oxford, Oxford, UK
| | - Christian Eggeling
- Radcliffe Department of Medicine, University of Oxford, Oxford, UK.
- MRC Human Immunology Unit, John Radcliffe Hospital, University of Oxford, Oxford, UK.
| | - Steven F Lee
- Department of Chemistry, University of Cambridge, Cambridge, UK.
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19
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Taylor MJ, Husain K, Gartner ZJ, Mayor S, Vale RD. A DNA-Based T Cell Receptor Reveals a Role for Receptor Clustering in Ligand Discrimination. Cell 2017; 169:108-119.e20. [PMID: 28340336 DOI: 10.1016/j.cell.2017.03.006] [Citation(s) in RCA: 131] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2016] [Revised: 02/02/2017] [Accepted: 03/03/2017] [Indexed: 12/18/2022]
Abstract
A T cell mounts an immune response by measuring the binding strength of its T cell receptor (TCR) for peptide-loaded MHCs (pMHC) on an antigen-presenting cell. How T cells convert the lifetime of the extracellular TCR-pMHC interaction into an intracellular signal remains unknown. Here, we developed a synthetic signaling system in which the extracellular domains of the TCR and pMHC were replaced with short hybridizing strands of DNA. Remarkably, T cells can discriminate between DNA ligands differing by a single base pair. Single-molecule imaging reveals that signaling is initiated when single ligand-bound receptors are converted into clusters, a time-dependent process requiring ligands with longer bound times. A computation model reveals that receptor clustering serves a kinetic proofreading function, enabling ligands with longer bound times to have disproportionally greater signaling outputs. These results suggest that spatial reorganization of receptors plays an important role in ligand discrimination in T cell signaling.
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Affiliation(s)
- Marcus J Taylor
- Department of Cellular and Molecular Pharmacology, University of California San Francisco, San Francisco, CA 94143, USA; National Centre for Biological Sciences, Bangalore 560065, India; HHMI Summer Institute, Woods Hole, MA 02543, USA
| | - Kabir Husain
- National Centre for Biological Sciences, Bangalore 560065, India; The Simons Centre for the Study of Living Machines, Bangalore 560065, India
| | - Zev J Gartner
- Department of Pharmaceutical Chemistry, University of California San Francisco, San Francisco, CA 94143, USA
| | - Satyajit Mayor
- National Centre for Biological Sciences, Bangalore 560065, India; HHMI Summer Institute, Woods Hole, MA 02543, USA.
| | - Ronald D Vale
- Department of Cellular and Molecular Pharmacology, University of California San Francisco, San Francisco, CA 94143, USA; Howard Hughes Medical Institute, University of California San Francisco, San Francisco, CA 94143, USA; HHMI Summer Institute, Woods Hole, MA 02543, USA.
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20
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Carr AR, Ponjavic A, Basu S, McColl J, Santos AM, Davis S, Laue ED, Klenerman D, Lee SF. Three-Dimensional Super-Resolution in Eukaryotic Cells Using the Double-Helix Point Spread Function. Biophys J 2017; 112:1444-1454. [PMID: 28402886 PMCID: PMC5390298 DOI: 10.1016/j.bpj.2017.02.023] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2016] [Revised: 02/07/2017] [Accepted: 02/21/2017] [Indexed: 02/02/2023] Open
Abstract
Single-molecule localization microscopy, typically based on total internal reflection illumination, has taken our understanding of protein organization and dynamics in cells beyond the diffraction limit. However, biological systems exist in a complicated three-dimensional environment, which has required the development of new techniques, including the double-helix point spread function (DHPSF), to accurately visualize biological processes. The application of the DHPSF approach has so far been limited to the study of relatively small prokaryotic cells. By matching the refractive index of the objective lens immersion liquid to that of the sample media, we demonstrate DHPSF imaging of up to 15-μm-thick whole eukaryotic cell volumes in three to five imaging planes. We illustrate the capabilities of the DHPSF by exploring large-scale membrane reorganization in human T cells after receptor triggering, and by using single-particle tracking to image several mammalian proteins, including membrane, cytoplasmic, and nuclear proteins in T cells and embryonic stem cells.
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Affiliation(s)
- Alexander R. Carr
- Department of Chemistry, University of Cambridge, Cambridge, United Kingdom
| | - Aleks Ponjavic
- Department of Chemistry, University of Cambridge, Cambridge, United Kingdom
| | - Srinjan Basu
- Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom
| | - James McColl
- Department of Chemistry, University of Cambridge, Cambridge, United Kingdom
| | - Ana Mafalda Santos
- Radcliffe Department of Clinical Medicine and Medical Research Council Human Immunology Unit, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, United Kingdom
| | - Simon Davis
- Radcliffe Department of Clinical Medicine and Medical Research Council Human Immunology Unit, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, United Kingdom
| | - Ernest D. Laue
- Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom
| | - David Klenerman
- Department of Chemistry, University of Cambridge, Cambridge, United Kingdom
| | - Steven F. Lee
- Department of Chemistry, University of Cambridge, Cambridge, United Kingdom,Corresponding author
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21
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Janeczek AA, Scarpa E, Horrocks MH, Tare RS, Rowland CA, Jenner D, Newman TA, Oreffo RO, Lee SF, Evans ND. PEGylated liposomes associate with Wnt3A protein and expand putative stem cells in human bone marrow populations. Nanomedicine (Lond) 2017; 12:845-863. [PMID: 28351228 DOI: 10.2217/nnm-2016-0386] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
AIM To fabricate PEGylated liposomes which preserve the activity of hydrophobic Wnt3A protein, and to demonstrate their efficacy in promoting expansion of osteoprogenitors from human bone marrow. METHODS PEGylated liposomes composed of several synthetic lipids were tested for their ability to preserve Wnt3A activity in reporter and differentiation assays. Single-molecule microspectroscopy was used to test for direct association of protein with liposomes. RESULTS Labeled Wnt3A protein directly associated with all tested liposome preparations. However, Wnt3A activity was preserved or enhanced in PEGylated 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) liposomes but not in PEGylated 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) liposomes. PEGylated Wnt3A liposomes associated with skeletal stem cell populations in human bone marrow and promoted osteogenesis. CONCLUSION Active Wnt protein-containing PEGylated liposomes may have utility for systemic administration for bone repair.
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Affiliation(s)
- Agnieszka A Janeczek
- Human Development & Health Academic Unit, Faculty of Medicine, Centre for Human Development, Stem Cells & Regeneration, Bone & Joint Research Group & Institute for Life Sciences, Institute for Developmental Sciences, University of Southampton, Tremona Road, Southampton, SO16 6YD, UK
| | - Edoardo Scarpa
- Human Development & Health Academic Unit, Faculty of Medicine, Centre for Human Development, Stem Cells & Regeneration, Bone & Joint Research Group & Institute for Life Sciences, Institute for Developmental Sciences, University of Southampton, Tremona Road, Southampton, SO16 6YD, UK
| | - Mathew H Horrocks
- Department of Chemistry, University of Cambridge, Cambridge, CB2 1EW, UK
| | - Rahul S Tare
- Human Development & Health Academic Unit, Faculty of Medicine, Centre for Human Development, Stem Cells & Regeneration, Bone & Joint Research Group & Institute for Life Sciences, Institute for Developmental Sciences, University of Southampton, Tremona Road, Southampton, SO16 6YD, UK
| | - Caroline A Rowland
- Microbiology Group, Chemical, Biological & Radiological Division, Dstl, Porton Down, Salisbury, SP4 0JQ, UK
| | - Dominic Jenner
- Microbiology Group, Chemical, Biological & Radiological Division, Dstl, Porton Down, Salisbury, SP4 0JQ, UK
| | - Tracey A Newman
- Clinical & Experimental Sciences, Faculty of Medicine, Institute for Life Sciences, University of Southampton, Building 85, Life Sciences Building, Highfield Campus, Southampton, SO17 1BJ, UK
| | - Richard Oc Oreffo
- Human Development & Health Academic Unit, Faculty of Medicine, Centre for Human Development, Stem Cells & Regeneration, Bone & Joint Research Group & Institute for Life Sciences, Institute for Developmental Sciences, University of Southampton, Tremona Road, Southampton, SO16 6YD, UK
| | - Steven F Lee
- Department of Chemistry, University of Cambridge, Cambridge, CB2 1EW, UK
| | - Nicholas D Evans
- Human Development & Health Academic Unit, Faculty of Medicine, Centre for Human Development, Stem Cells & Regeneration, Bone & Joint Research Group & Institute for Life Sciences, Institute for Developmental Sciences, University of Southampton, Tremona Road, Southampton, SO16 6YD, UK
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22
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Sasmal DK, Pulido LE, Kasal S, Huang J. Single-molecule fluorescence resonance energy transfer in molecular biology. NANOSCALE 2016; 8:19928-19944. [PMID: 27883140 PMCID: PMC5145784 DOI: 10.1039/c6nr06794h] [Citation(s) in RCA: 61] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/19/2023]
Abstract
Single-molecule fluorescence resonance energy transfer (smFRET) is a powerful technique for studying the conformation dynamics and interactions of individual biomolecules. In this review, we describe the concept and principle of smFRET, illustrate general instrumentation and microscopy settings for experiments, and discuss the methods and algorithms for data analysis. Subsequently, we review applications of smFRET in protein conformational changes, ion channel open-close properties, receptor-ligand interactions, nucleic acid structure regulation, vesicle fusion, and force induced conformational dynamics. Finally, we discuss the main limitations of smFRET in molecular biology.
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Affiliation(s)
- Dibyendu K Sasmal
- The Institute for Molecular Engineering, The University of Chicago, Chicago, IL 60637, USA.
| | - Laura E Pulido
- The Institute for Molecular Engineering, The University of Chicago, Chicago, IL 60637, USA.
| | - Shan Kasal
- The Institute for Molecular Engineering, The University of Chicago, Chicago, IL 60637, USA.
| | - Jun Huang
- The Institute for Molecular Engineering, The University of Chicago, Chicago, IL 60637, USA.
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23
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Functional role of T-cell receptor nanoclusters in signal initiation and antigen discrimination. Proc Natl Acad Sci U S A 2016; 113:E5454-63. [PMID: 27573839 DOI: 10.1073/pnas.1607436113] [Citation(s) in RCA: 147] [Impact Index Per Article: 18.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Antigen recognition by the T-cell receptor (TCR) is a hallmark of the adaptive immune system. When the TCR engages a peptide bound to the restricting major histocompatibility complex molecule (pMHC), it transmits a signal via the associated CD3 complex. How the extracellular antigen recognition event leads to intracellular phosphorylation remains unclear. Here, we used single-molecule localization microscopy to quantify the organization of TCR-CD3 complexes into nanoscale clusters and to distinguish between triggered and nontriggered TCR-CD3 complexes. We found that only TCR-CD3 complexes in dense clusters were phosphorylated and associated with downstream signaling proteins, demonstrating that the molecular density within clusters dictates signal initiation. Moreover, both pMHC dose and TCR-pMHC affinity determined the density of TCR-CD3 clusters, which scaled with overall phosphorylation levels. Thus, TCR-CD3 clustering translates antigen recognition by the TCR into signal initiation by the CD3 complex, and the formation of dense signaling-competent clusters is a process of antigen discrimination.
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Jahan AS, Lestra M, Swee LK, Fan Y, Lamers MM, Tafesse FG, Theile CS, Spooner E, Bruzzone R, Ploegh HL, Sanyal S. Usp12 stabilizes the T-cell receptor complex at the cell surface during signaling. Proc Natl Acad Sci U S A 2016; 113:E705-14. [PMID: 26811477 PMCID: PMC4760780 DOI: 10.1073/pnas.1521763113] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Posttranslational modifications are central to the spatial and temporal regulation of protein function. Among others, phosphorylation and ubiquitylation are known to regulate proximal T-cell receptor (TCR) signaling. Here we used a systematic and unbiased approach to uncover deubiquitylating enzymes (DUBs) that participate during TCR signaling in primary mouse T lymphocytes. Using a C-terminally modified vinyl methyl ester variant of ubiquitin (HA-Ub-VME), we captured DUBs that are differentially recruited to the cytosol on TCR activation. We identified ubiquitin-specific peptidase (Usp) 12 and Usp46, which had not been previously described in this pathway. Stimulation with anti-CD3 resulted in phosphorylation and time-dependent translocation of Usp12 from the nucleus to the cytosol. Usp12(-/-) Jurkat cells displayed defective NFκB, NFAT, and MAPK activities owing to attenuated surface expression of TCR, which were rescued on reconstitution of wild type Usp12. Proximity-based labeling with BirA-Usp12 revealed several TCR adaptor proteins acting as interactors in stimulated cells, of which LAT and Trat1 displayed reduced expression in Usp12(-/-) cells. We demonstrate that Usp12 deubiquitylates and prevents lysosomal degradation of LAT and Trat1 to maintain the proximal TCR complex for the duration of signaling. Our approach benefits from the use of activity-based probes in primary cells without any previous genome modification, and underscores the importance of ubiquitin-mediated regulation to refine signaling cascades.
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Affiliation(s)
- Akhee S Jahan
- HKU-Pasteur Research Pole and Center for Influenza Research, School of Public Health, LKS Faculty of Medicine, University of Hong Kong, Hong Kong
| | - Maxime Lestra
- HKU-Pasteur Research Pole and Center for Influenza Research, School of Public Health, LKS Faculty of Medicine, University of Hong Kong, Hong Kong
| | - Lee Kim Swee
- Whitehead Institute for Biomedical Research, Cambridge, MA 02142
| | - Ying Fan
- HKU-Pasteur Research Pole and Center for Influenza Research, School of Public Health, LKS Faculty of Medicine, University of Hong Kong, Hong Kong
| | - Mart M Lamers
- HKU-Pasteur Research Pole and Center for Influenza Research, School of Public Health, LKS Faculty of Medicine, University of Hong Kong, Hong Kong
| | - Fikadu G Tafesse
- Whitehead Institute for Biomedical Research, Cambridge, MA 02142
| | | | - Eric Spooner
- Whitehead Institute for Biomedical Research, Cambridge, MA 02142
| | - Roberto Bruzzone
- HKU-Pasteur Research Pole and Center for Influenza Research, School of Public Health, LKS Faculty of Medicine, University of Hong Kong, Hong Kong; Department of Cell Biology and Infection, Institut Pasteur, 75015 Paris, France
| | - Hidde L Ploegh
- Whitehead Institute for Biomedical Research, Cambridge, MA 02142; Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02142
| | - Sumana Sanyal
- HKU-Pasteur Research Pole and Center for Influenza Research, School of Public Health, LKS Faculty of Medicine, University of Hong Kong, Hong Kong; Department of Cell Biology and Infection, Institut Pasteur, 75015 Paris, France;
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25
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Wong K, Briddon SJ, Holliday ND, Kerr ID. Plasma membrane dynamics and tetrameric organisation of ABCG2 transporters in mammalian cells revealed by single particle imaging techniques. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2016; 1863:19-29. [DOI: 10.1016/j.bbamcr.2015.10.002] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/31/2015] [Revised: 09/17/2015] [Accepted: 10/06/2015] [Indexed: 10/22/2022]
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26
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Garcia-Parajo MF, Cambi A, Torreno-Pina JA, Thompson N, Jacobson K. Nanoclustering as a dominant feature of plasma membrane organization. J Cell Sci 2015; 127:4995-5005. [PMID: 25453114 DOI: 10.1242/jcs.146340] [Citation(s) in RCA: 196] [Impact Index Per Article: 21.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Early studies have revealed that some mammalian plasma membrane proteins exist in small nanoclusters. The advent of super-resolution microscopy has corroborated and extended this picture, and led to the suggestion that many, if not most, membrane proteins are clustered at the plasma membrane at nanoscale lengths. In this Commentary, we present selected examples of glycosylphosphatidyl-anchored proteins, Ras family members and several immune receptors that provide evidence for nanoclustering. We advocate the view that nanoclustering is an important part of the hierarchical organization of proteins in the plasma membrane. According to this emerging picture, nanoclusters can be organized on the mesoscale to form microdomains that are capable of supporting cell adhesion, pathogen binding and immune cell-cell recognition amongst other functions. Yet, a number of outstanding issues concerning nanoclusters remain open, including the details of their molecular composition, biogenesis, size, stability, function and regulation. Notions about these details are put forth and suggestions are made about nanocluster function and why this general feature of protein nanoclustering appears to be so prevalent.
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Affiliation(s)
- Maria F Garcia-Parajo
- ICFO-Institut de Ciencies Fotoniques, Mediterranean Technology Park, 08860 Castelldefels (Barcelona), Spain ICREA-Institució Catalana de Recerca i Estudis Avançats, 08010 Barcelona, Spain
| | - Alessandra Cambi
- Nanobiophysics, MIRA Institute for Biomedical Technology and Technical Medicine and MESA+ Institute for Nanotechnology, University of Twente, 7522 NB Enschede, The Netherlands Department of Tumor Immunology, Radboud Institute for Molecular Life Sciences, Radboud University Medical Center, 6500 HB Nijmegen, The Netherlands
| | - Juan A Torreno-Pina
- ICFO-Institut de Ciencies Fotoniques, Mediterranean Technology Park, 08860 Castelldefels (Barcelona), Spain
| | - Nancy Thompson
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-3290, USA
| | - Ken Jacobson
- Department of Cell Biology and Physiology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7090, USA Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
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Klotzsch E, Stiegler J, Ben-Ishay E, Gaus K. Do mechanical forces contribute to nanoscale membrane organisation in T cells? BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2014; 1853:822-9. [PMID: 25447546 DOI: 10.1016/j.bbamcr.2014.10.025] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/04/2014] [Revised: 09/26/2014] [Accepted: 10/25/2014] [Indexed: 12/23/2022]
Abstract
Mechanotransduction describes how a cell senses and interacts with its environment. The concept originated in adhesion biology where adhesion receptors, integrins, facilitate force transmission between the extracellular matrix and the intracellular actin cytoskeleton. Indeed, during any adhesive contacts, cells do exert mechanical force. Hence, the probing of the local environment by cells results in mechanical cues that contribute to cellular functions and cell fate decisions such as migration, proliferation, differentiation and apoptosis. On the molecular level, mechanical forces can rearrange proteins laterally within the membrane, regulate their activity by inducing conformational changes and probe the mechanical properties and bond strength of receptor-ligands. From this point of view, it appears surprising that molecular forces have been largely overlooked in membrane organisation and ligand discrimination processes in lymphocytes. During T cell activation, the T cell receptor recognises and distinguishes antigenic from benign endogenous peptides to initiate the reorganisation of membrane proteins into signalling clusters within the immunological synapse. In this review, we asked whether characteristics of fibroblast force sensing could be applied to immune cell antigen recognition and signalling, and outline state-of-the-art experimental strategies for studying forces in the context of membrane organisation. This article is part of a Special Issue entitled: Nanoscale membrane orgainisation and signalling.
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Affiliation(s)
- Enrico Klotzsch
- Centre for Vascular Research, ARC Centre of Excellence in Advanced Molecular Imaging and Australian Centre for Nanomedicine, University of New South Wales, Sydney, Australia.
| | - Johannes Stiegler
- Centre for Vascular Research, ARC Centre of Excellence in Advanced Molecular Imaging and Australian Centre for Nanomedicine, University of New South Wales, Sydney, Australia
| | - Eldad Ben-Ishay
- Centre for Vascular Research, ARC Centre of Excellence in Advanced Molecular Imaging and Australian Centre for Nanomedicine, University of New South Wales, Sydney, Australia
| | - Katharina Gaus
- Centre for Vascular Research, ARC Centre of Excellence in Advanced Molecular Imaging and Australian Centre for Nanomedicine, University of New South Wales, Sydney, Australia.
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Baumgart F, Schütz GJ. Detecting protein association at the T cell plasma membrane. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2014; 1853:791-801. [PMID: 25300585 DOI: 10.1016/j.bbamcr.2014.09.026] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/01/2014] [Revised: 09/18/2014] [Accepted: 09/29/2014] [Indexed: 10/24/2022]
Abstract
At the moment, many models on T cell signaling rely on results obtained via rather indirect methodologies, which makes direct comparison and conclusions to the in vivo situation difficult. Recently, a variety of new imaging methods were developed, which have the potential to directly shed light onto the mysteries of protein association at the T cell membrane. While the new modalities are extremely promising, for a broad readership it may be difficult to judge the results, since technological shortcomings are not always obvious. In this review article, we put key questions on the mechanism of protein interactions in the T cell plasma membrane into relation with techniques that allow to address such questions. We discuss applicability of the techniques, their strengths and weaknesses. This article is part of a Special Issue entitled: Nanoscale membrane organisation and signalling.
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Affiliation(s)
- Florian Baumgart
- Vienna University of Technology, Institute for Applied Physics, Wiedner Hauptstraße 8-10, 1040 Vienna, Austria
| | - Gerhard J Schütz
- Vienna University of Technology, Institute for Applied Physics, Wiedner Hauptstraße 8-10, 1040 Vienna, Austria.
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29
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Tracking single molecules at work in living cells. Nat Chem Biol 2014; 10:524-32. [PMID: 24937070 DOI: 10.1038/nchembio.1558] [Citation(s) in RCA: 220] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2014] [Accepted: 05/21/2014] [Indexed: 11/09/2022]
Abstract
Methods for imaging and tracking single molecules conjugated with fluorescent probes, called single-molecule tracking (SMT), are now providing researchers with the unprecedented ability to directly observe molecular behaviors and interactions in living cells. Current SMT methods are achieving almost the ultimate spatial precision and time resolution for tracking single molecules, determined by the currently available dyes. In cells, various molecular interactions and reactions occur as stochastic and probabilistic processes. SMT provides an ideal way to directly track these processes by observing individual molecules at work in living cells, leading to totally new views of the biochemical and molecular processes used by cells whether in signal transduction, gene regulation or formation and disintegration of macromolecular complexes. Here we review SMT methods, summarize the recent results obtained by SMT, including related superresolution microscopy data, and describe the special concerns when SMT applications are shifted from the in vitro paradigms to living cells.
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Dushek O, van der Merwe PA. An induced rebinding model of antigen discrimination. Trends Immunol 2014; 35:153-8. [PMID: 24636916 PMCID: PMC3989030 DOI: 10.1016/j.it.2014.02.002] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2013] [Revised: 02/10/2014] [Accepted: 02/11/2014] [Indexed: 12/01/2022]
Abstract
We propose that pMHC binding to TCR can increase (induce) pMHC rebinding. Published studies are consistent with an induced rebinding model. Induced rebinding improves the ability of T cells to discriminate antigens. Induced rebinding relates 3D to 2D TCR–pMHC binding parameters.
T cells have to detect rare high-affinity ‘foreign’ peptide MHC (pMHC) ligands among abundant low-affinity ‘self’-peptide MHC ligands. It remains unclear how this remarkable discrimination is achieved. Kinetic proofreading mechanisms can provide the required specificity but only at the expense of much reduced sensitivity. A number of recent observations suggest that pMHC engagement of T cell receptors (TCRs) induces changes such as clustering and/or conformational alterations that enhance subsequent rebinding. We show that inclusion of induced rebinding to the same pMHC in kinetic proofreading models enhances the sensitivity of TCR recognition while retaining specificity. Moreover, induced rebinding is able to reproduce the striking, and hitherto unexplained, 2D membrane-binding properties recently reported for the TCR.
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Affiliation(s)
- Omer Dushek
- Sir William Dunn School of Pathology, University of Oxford, Oxford, UK; Wolfson Centre for Mathematical Biology, University of Oxford, Oxford, UK.
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31
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Statistical denoising scheme for single molecule fluorescence microscopic images. Biomed Signal Process Control 2014. [DOI: 10.1016/j.bspc.2013.12.005] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
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32
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Abstract
Despite the low affinity of the T-cell antigen receptor (TCR) for its peptide/major histocompatibility complex (pMHC) ligand, T cells are very sensitive to their antigens. This paradox can be resolved if we consider that the TCR may be organized into pre-existing oligomers or nanoclusters. Such structures could improve antigen recognition by increasing the functional affinity (avidity) of the TCR-pMHC interaction and by allowing cooperativity between individual TCRs. Up to approximately 20 TCRs become tightly apposed in these nanoclusters, often in a linear manner, and such structures could reflect a relatively generalized phenomenon: the non-random concentration of membrane receptors in specific areas of the plasma membrane known as protein islands. The association of TCRs into nanoclusters can explain the enhanced kinetics of the pMHC-TCR interaction in two dimensional versus three dimensional systems, but also their existence calls for a revision of the TCR triggering models based on pMHC-induced TCR clustering. Interestingly, the B-cell receptor and the FcεRI have also been shown to form nanoclusters, suggesting that the formation of pre-existing receptor oligomers could be widely used in the immune system.
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Affiliation(s)
- Wolfgang W A Schamel
- Department of Molecular Immunology, Institute of Biology III, Faculty of Biology, BIOSS Centre for Biological Signaling Studies, University of Freiburg, Freiburg, Germany
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33
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Delcassian D, Depoil D, Rudnicka D, Liu M, Davis DM, Dustin ML, Dunlop IE. Nanoscale ligand spacing influences receptor triggering in T cells and NK cells. NANO LETTERS 2013; 13:5608-14. [PMID: 24125583 PMCID: PMC4288448 DOI: 10.1021/nl403252x] [Citation(s) in RCA: 85] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
Bioactive nanoscale arrays were constructed to ligate activating cell surface receptors on T cells (the CD3 component of the TCR complex) and natural killer (NK) cells (CD16). These arrays are formed from biofunctionalized gold nanospheres with controlled interparticle spacing in the range 25-104 nm. Responses to these nanoarrays were assessed using the extent of membrane-localized phosphotyrosine in T cells stimulated with CD3-binding nanoarrays and the size of cell contact area for NK cells stimulated with CD16-binding nanoarrays. In both cases, the strength of response decreased with increasing spacing, falling to background levels by 69 nm in the T cell/anti-CD3 system and 104 nm for the NK cell/anti-CD16 system. These results demonstrate that immune receptor triggering can be influenced by the nanoscale spatial organization of receptor/ligand interactions.
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MESH Headings
- CD3 Complex/chemistry
- CD3 Complex/immunology
- Humans
- Killer Cells, Natural/chemistry
- Killer Cells, Natural/immunology
- Nanoparticles/chemistry
- Nanotechnology
- Receptor-CD3 Complex, Antigen, T-Cell/chemistry
- Receptor-CD3 Complex, Antigen, T-Cell/immunology
- Receptors, Cell Surface/chemistry
- Receptors, Cell Surface/immunology
- Receptors, IgG/chemistry
- Receptors, IgG/immunology
- Receptors, Natural Killer Cell/chemistry
- Receptors, Natural Killer Cell/immunology
- T-Lymphocytes/chemistry
- T-Lymphocytes/immunology
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Affiliation(s)
- Derfogail Delcassian
- Department of Materials, Imperial College London, Exhibition Road, London SW7 2AZ, UK
| | - David Depoil
- Skirball Institute of Biomolecular Medicine, NYU School of Medicine, New York, New York, NY10016 USA
| | - Dominika Rudnicka
- Division of Cell and Molecular Biology, Imperial College London, Exhibition Road, London SW7 2AZ, UK
| | - Mengling Liu
- Department of Biostatistics, NYU School of Medicine, New York, New York, NY10016 USA
| | - Daniel M. Davis
- Division of Cell and Molecular Biology, Imperial College London, Exhibition Road, London SW7 2AZ, UK
- Manchester Collaborative Centre for Inflammation Research, University of Manchester, Grafton Street, Manchester M13 9NT, UK
| | - Michael L. Dustin
- Skirball Institute of Biomolecular Medicine, NYU School of Medicine, New York, New York, NY10016 USA
- Kennedy Institute of Rheumatology, University of Oxford, Old Road Campus, Oxford, OX3 7FY, UK
| | - Iain E. Dunlop
- Department of Materials, Imperial College London, Exhibition Road, London SW7 2AZ, UK
- To whom correspondence should be addressed:
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34
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Abstract
The recognition of peptide/MHC antigens by T-cells has continued to challenge the imagination of immunologists, biochemists, and cell biologists alike. This is at least in part because T-cell recognition connects a diversity of issues and transcends many scientific disciplines. A fundamental unsolved issue is how T-cells manage to detect even a single molecule of an agonist pMHC complex, which is vastly outnumbered by endogenous pMHCs, many of which involve the same MHC molecule. They do so although TCRs are cross-reactive and typically low in affinity when measured in isolation. Importantly, T-cell antigen recognition takes place within the contact zone between a T-cell and the antigen-presenting cell, termed the immunological synapse. This bimembrane structure sets the stage for the antigen-binding events and all subsequent molecular recognition events. There is increasing evidence that the molecular dynamics of receptor-ligand interactions are not only dependent on the intrinsic properties of the binding partners but also become transformed by cell biological parameters such as the geometrical constraints within the immune synapse, mechanical forces, and local molecular crowding. To appreciate the complete picture, we think a multidisciplinary approach is imperative, which includes genetics, biochemistry, and structure determination and also biophysical analyses and the latest molecular imaging techniques. Here, we review earlier pioneering work and also recent developments in the fascinating and interdisciplinary science of T-cell antigen recognition. In many ways, this work may present a useful "roadmap" for work in other systems of cell-cell recognition, which underlie many fundamental biological phenomenons of interest.
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35
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Klenerman D, Shevchuk A, Novak P, Korchev YE, Davis SJ. Imaging the cell surface and its organization down to the level of single molecules. Philos Trans R Soc Lond B Biol Sci 2012; 368:20120027. [PMID: 23267181 DOI: 10.1098/rstb.2012.0027] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Determining the organization of key molecules on the surface of live cells in two dimensions and how this changes during biological processes, such as signalling, is a major challenge in cell biology and requires methods with nanoscale spatial resolution and high temporal resolution. Here, we review biophysical tools, based on scanning ion conductance microscopy and single-molecule fluorescence and the combination of both of these methods, which have recently been developed to address these issues. We then give examples of how these methods have been be applied to provide new insights into cell membrane organization and function, and discuss some of the issues that will need to be addressed to further exploit these methods in the future.
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Affiliation(s)
- David Klenerman
- Department of Chemistry, Cambridge University, Cambridge CB2 1EW, UK.
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36
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Rossy J, Williamson DJ, Benzing C, Gaus K. The integration of signaling and the spatial organization of the T cell synapse. Front Immunol 2012. [PMID: 23189081 PMCID: PMC3504718 DOI: 10.3389/fimmu.2012.00352] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
Engagement of the T cell antigen receptor (TCR) triggers signaling pathways that lead to T cell selection, differentiation and clonal expansion. Superimposed onto the biochemical network is a spatial organization that describes individual receptor molecules, dimers, oligomers and higher order structures. Here we discuss recent findings and new concepts that may regulate TCR organization in naïve and memory T cells. A key question that has emerged is how antigen-TCR interactions encode spatial information to direct T cell activation and differentiation. Single molecule super-resolution microscopy may become an important tool in decoding receptor organization at the molecular level.
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Affiliation(s)
- Jérémie Rossy
- Centre for Vascular Research and Australian Centre for Nanomedicine, University of New South Wales Sydney, NSW, Australia
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37
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Roda-Navarro P. Microspectroscopy reveals mechanisms of lymphocyte activation. Integr Biol (Camb) 2012; 5:300-11. [PMID: 23114860 DOI: 10.1039/c2ib20190a] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The immunological synapse (IS) regulates immune responses by integrating extracellular stimuli into intracellular signalling networks, which causes leukocyte differentiation and effector functions. The dynamic spatial organisation of molecules at the IS was initially characterised by wide-field fluorescence microscopy of cell conjugates and cells interacting with planar lipid bilayers. These methods showed stable supramolecular clusters of several microns in size, which were proposed to be responsible for sustained signalling and cell-cell adhesion. The recent emergence of microspectroscopy techniques with higher spatial and temporal resolution nonetheless reveals the complex dynamics of molecular reactions that mediate IS assembly and function. This review describes microspectroscopy-based in vitro experimental approaches for imaging the molecular dynamics at the IS, as well as their contributions and open questions in the field. It also describes experimental methods to obtain quantitative parameters of dynamic biochemical reactions in living cells, and discusses about the important role of quantitative imaging and theoretical science in our understanding of molecular mechanisms underlying lymphocyte activation.
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Affiliation(s)
- Pedro Roda-Navarro
- Department of Microbiology I, Faculty of Medicine, Universidad Complutense de Madrid, 28040 Madrid, Spain.
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38
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Molnár E, Swamy M, Holzer M, Beck-García K, Worch R, Thiele C, Guigas G, Boye K, Luescher IF, Schwille P, Schubert R, Schamel WWA. Cholesterol and sphingomyelin drive ligand-independent T-cell antigen receptor nanoclustering. J Biol Chem 2012; 287:42664-74. [PMID: 23091059 DOI: 10.1074/jbc.m112.386045] [Citation(s) in RCA: 126] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The T-cell antigen receptor (TCR) exists in monomeric and nanoclustered forms independently of antigen binding. Although the clustering is involved in the regulation of T-cell sensitivity, it is unknown how the TCR nanoclusters form. We show that cholesterol is required for TCR nanoclustering in T cells and that this clustering enhances the avidity but not the affinity of the TCR-antigen interaction. Investigating the mechanism of the nanoclustering, we found that radioactive photocholesterol specifically binds to the TCRβ chain in vivo. In order to reduce the complexity of cellular membranes, we used a synthetic biology approach and reconstituted the TCR in liposomes of defined lipid composition. Both cholesterol and sphingomyelin were required for the formation of TCR dimers in phosphatidylcholine-containing large unilamellar vesicles. Further, the TCR was localized in the liquid disordered phase in giant unilamellar vesicles. We propose a model in which cholesterol and sphingomyelin binding to the TCRβ chain causes TCR dimerization. The lipid-induced TCR nanoclustering enhances the avidity to antigen and thus might be involved in enhanced sensitivity of memory compared with naive T cells. Our work contributes to the understanding of the function of specific nonannular lipid-membrane protein interactions.
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Affiliation(s)
- Eszter Molnár
- Max Planck Institute of Immunobiology and Epigenetics, 79108 Freiburg, Germany
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39
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Klammt C, Lillemeier BF. How membrane structures control T cell signaling. Front Immunol 2012; 3:291. [PMID: 23055999 PMCID: PMC3458435 DOI: 10.3389/fimmu.2012.00291] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2012] [Accepted: 08/31/2012] [Indexed: 12/31/2022] Open
Abstract
Genetic and biochemical studies have identified a large number of molecules involved in T cell signaling. They have provided us with a comprehensive understanding of protein-protein interactions and protein modifications that take place upon antigen recognition. Diffraction limited fluorescence microscopy has been used to study the distribution of signaling molecules on a cellular level. Specifically, the discovery of microclusters and the immunological synapse demonstrates that T cell signaling cascades utilizes spatial association and segregation. Recent advancements in live cell imaging have allowed us to visualize the spatio-temporal mechanisms of T cell signaling at nanometer scale resolution. This led to the discovery that proteins are organized in distinct membrane domains prior and during T cell activation. Evidently, plasma membrane structures and signaling molecule distributions at all length scales (molecular to cellular) are intrinsic to the mechanisms that govern signaling initiation, transduction, and inhibition. Here we provide an overview of possible plasma membrane models, molecular assemblies that have been described to date, how they can be visualized and how they might contribute to T cell signaling.
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Affiliation(s)
| | - Björn F. Lillemeier
- Nomis Center for Immunobiology and Microbial Pathogenesis, Waitt Advanced Biophotonics Center, Salk Institute for Biological StudiesLa Jolla, CA, USA
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40
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Valitutti S. The Serial Engagement Model 17 Years After: From TCR Triggering to Immunotherapy. Front Immunol 2012; 3:272. [PMID: 22973273 PMCID: PMC3428561 DOI: 10.3389/fimmu.2012.00272] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2012] [Accepted: 08/08/2012] [Indexed: 12/27/2022] Open
Abstract
More than 15 years ago the serial engagement model was proposed as an attempt to solve the low affinity/high sensitivity paradox of TCR antigen recognition. Since then, the model has undergone ups and downs marked by the technical and conceptual advancements made in the field of T lymphocyte activation. Here, I describe the development of the model and survey recent literature providing evidence either for or against the idea that serial TCR/pMHC engagement might contribute to T lymphocyte activation. I also discuss how the concept of serial TCR engagement might be useful in the design of immunotherapeutic approaches aimed at potentiating T lymphocyte responses in vivo.
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Affiliation(s)
- Salvatore Valitutti
- INSERM, UMR 1043, Section Dynamique Moléculaire des Interactions Lymphocytaires, Centre de Physiopathologie de Toulouse Purpan Toulouse, France
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41
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A novel lectin from Agrocybe aegerita shows high binding selectivity for terminal N-acetylglucosamine. Biochem J 2012; 443:369-78. [PMID: 22268569 PMCID: PMC3316157 DOI: 10.1042/bj20112061] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
A novel lectin was isolated from the mushroom Agrocybe aegerita (designated AAL-2) by affinity chromatography with GlcNAc (N-acetylglucosamine)-coupled Sepharose 6B after ammonium sulfate precipitation. The AAL-2 coding sequence (1224 bp) was identified by performing a homologous search of the five tryptic peptides identified by MS against the translated transcriptome of A. aegerita. The molecular mass of AAL-2 was calculated to be 43.175 kDa from MS, which was consistent with the data calculated from the amino acid sequence. To analyse the carbohydrate-binding properties of AAL-2, a glycan array composed of 465 glycan candidates was employed, and the result showed that AAL-2 bound with high selectivity to terminal non-reducing GlcNAc residues, and further analysis revealed that AAL-2 bound to terminal non-reducing GlcNAc residues with higher affinity than previously well-known GlcNAc-binding lectins such as WGA (wheatgerm agglutinin) and GSL-II (Griffonia simplicifolia lectin-II). ITC (isothermal titration calorimetry) showed further that GlcNAc bound to AAL-2 in a sequential manner with moderate affinity. In the present study, we also evaluated the anti-tumour activity of AAL-2. The results showed that AAL-2 could bind to the surface of hepatoma cells, leading to induced cell apoptosis in vitro. Furthermore, AAL-2 exerted an anti-hepatoma effect via inhibition of tumour growth and prolongation of survival time of tumour-bearing mice in vivo.
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42
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Fernandes RA, Huo J, Lui Y, Felce JH, Davis SJ. On the Control of TCR Phosphorylation. Front Immunol 2012; 3:92. [PMID: 22566970 PMCID: PMC3345363 DOI: 10.3389/fimmu.2012.00092] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2012] [Accepted: 04/10/2012] [Indexed: 11/13/2022] Open
Affiliation(s)
- Ricardo A Fernandes
- MRC Human Immunology Unit, Nuffield Department of Clinical Medicine, John Radcliffe Hospital, University of Oxford Headington, Oxford, UK
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43
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Fernandes RA, Shore DA, Vuong MT, Yu C, Zhu X, Pereira-Lopes S, Brouwer H, Fennelly JA, Jessup CM, Evans EJ, Wilson IA, Davis SJ. T cell receptors are structures capable of initiating signaling in the absence of large conformational rearrangements. J Biol Chem 2012; 287:13324-35. [PMID: 22262845 PMCID: PMC3339974 DOI: 10.1074/jbc.m111.332783] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2011] [Revised: 01/10/2012] [Indexed: 12/18/2022] Open
Abstract
Native and non-native ligands of the T cell receptor (TCR), including antibodies, have been proposed to induce signaling in T cells via intra- or intersubunit conformational rearrangements within the extracellular regions of TCR complexes. We have investigated whether any signatures can be found for such postulated structural changes during TCR triggering induced by antibodies, using crystallographic and mutagenesis-based approaches. The crystal structure of murine CD3ε complexed with the mitogenic anti-CD3ε antibody 2C11 enabled the first direct structural comparisons of antibody-liganded and unliganded forms of CD3ε from a single species, which revealed that antibody binding does not induce any substantial rearrangements within CD3ε. Saturation mutagenesis of surface-exposed CD3ε residues, coupled with assays of antibody-induced signaling by the mutated complexes, suggests a new configuration for the complex within which CD3ε is highly exposed and reveals that no large new CD3ε interfaces are required to form during antibody-induced signaling. The TCR complex therefore appears to be a structure that is capable of initiating intracellular signaling in T cells without substantial structural rearrangements within or between the component subunits. Our findings raise the possibility that signaling by native ligands might also be initiated in the absence of large structural rearrangements in the receptor.
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MESH Headings
- Animals
- Antibodies, Monoclonal/immunology
- CD3 Complex/chemistry
- CD3 Complex/genetics
- CD3 Complex/immunology
- Crystallography, X-Ray
- Dimerization
- Epitopes, T-Lymphocyte/immunology
- Humans
- Immunoglobulin Fab Fragments/immunology
- Jurkat Cells
- Mice
- Mutagenesis, Site-Directed
- Protein Conformation
- Protein Structure, Tertiary
- Receptors, Antigen, T-Cell/chemistry
- Receptors, Antigen, T-Cell/immunology
- Receptors, Antigen, T-Cell/metabolism
- Signal Transduction/immunology
- Structure-Activity Relationship
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Affiliation(s)
- Ricardo A. Fernandes
- From the Nuffield Department of Clinical Medicine and Medical Research Council Human Immunology Unit, The University of Oxford, John Radcliffe Hospital, Headington, Oxford OX3 9DU, United Kingdom and
| | - David A. Shore
- From the Nuffield Department of Clinical Medicine and Medical Research Council Human Immunology Unit, The University of Oxford, John Radcliffe Hospital, Headington, Oxford OX3 9DU, United Kingdom and
| | - Mai T. Vuong
- From the Nuffield Department of Clinical Medicine and Medical Research Council Human Immunology Unit, The University of Oxford, John Radcliffe Hospital, Headington, Oxford OX3 9DU, United Kingdom and
| | - Chao Yu
- From the Nuffield Department of Clinical Medicine and Medical Research Council Human Immunology Unit, The University of Oxford, John Radcliffe Hospital, Headington, Oxford OX3 9DU, United Kingdom and
| | - Xueyong Zhu
- the Department of Molecular Biology, The Scripps Research Institute, La Jolla, California 92037
| | - Selma Pereira-Lopes
- From the Nuffield Department of Clinical Medicine and Medical Research Council Human Immunology Unit, The University of Oxford, John Radcliffe Hospital, Headington, Oxford OX3 9DU, United Kingdom and
| | - Heather Brouwer
- From the Nuffield Department of Clinical Medicine and Medical Research Council Human Immunology Unit, The University of Oxford, John Radcliffe Hospital, Headington, Oxford OX3 9DU, United Kingdom and
| | - Janet A. Fennelly
- From the Nuffield Department of Clinical Medicine and Medical Research Council Human Immunology Unit, The University of Oxford, John Radcliffe Hospital, Headington, Oxford OX3 9DU, United Kingdom and
| | - Claire M. Jessup
- From the Nuffield Department of Clinical Medicine and Medical Research Council Human Immunology Unit, The University of Oxford, John Radcliffe Hospital, Headington, Oxford OX3 9DU, United Kingdom and
| | - Edward J. Evans
- From the Nuffield Department of Clinical Medicine and Medical Research Council Human Immunology Unit, The University of Oxford, John Radcliffe Hospital, Headington, Oxford OX3 9DU, United Kingdom and
| | - Ian A. Wilson
- the Department of Molecular Biology, The Scripps Research Institute, La Jolla, California 92037
| | - Simon J. Davis
- From the Nuffield Department of Clinical Medicine and Medical Research Council Human Immunology Unit, The University of Oxford, John Radcliffe Hospital, Headington, Oxford OX3 9DU, United Kingdom and
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44
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Illingworth JJ, Anton van der Merwe P. Dissecting T-cell activation with high-resolution live-cell microscopy. Immunology 2012; 135:198-206. [PMID: 22074058 DOI: 10.1111/j.1365-2567.2011.03537.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Results from live-cell microscopy suggest that the behaviour of isolated components of the T-cell activation machinery in vitro does not represent the reality inside cells. Understanding the cellular-scale dynamics of microcluster migration can only be accomplished by in situ observation. Developments in 'super-resolution' microscopy have permitted investigators to move beyond tracking the movements of individual molecules, allowing the recognition of protein islands and nanodomains present in quiescent and active T cells. Many high-resolution techniques have their own susceptibilities to artefacts, so it is important to take a multifaceted approach to confirm results. A major challenge for the future will be to integrate all the new information into a coherent model of antigen recognition and T-cell activation.
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Kusumi A, Fujiwara TK, Morone N, Yoshida KJ, Chadda R, Xie M, Kasai RS, Suzuki KGN. Membrane mechanisms for signal transduction: the coupling of the meso-scale raft domains to membrane-skeleton-induced compartments and dynamic protein complexes. Semin Cell Dev Biol 2012; 23:126-44. [PMID: 22309841 DOI: 10.1016/j.semcdb.2012.01.018] [Citation(s) in RCA: 106] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2012] [Accepted: 01/24/2012] [Indexed: 01/09/2023]
Abstract
Virtually all biological membranes on earth share the basic structure of a two-dimensional liquid. Such universality and peculiarity are comparable to those of the double helical structure of DNA, strongly suggesting the possibility that the fundamental mechanisms for the various functions of the plasma membrane could essentially be understood by a set of simple organizing principles, developed during the course of evolution. As an initial effort toward the development of such understanding, in this review, we present the concept of the cooperative action of the hierarchical three-tiered meso-scale (2-300 nm) domains in the plasma membrane: (1) actin membrane-skeleton-induced compartments (40-300 nm), (2) raft domains (2-20 nm), and (3) dynamic protein complex domains (3-10nm). Special attention is paid to the concept of meso-scale domains, where both thermal fluctuations and weak cooperativity play critical roles, and the coupling of the raft domains to the membrane-skeleton-induced compartments as well as dynamic protein complexes. The three-tiered meso-domain architecture of the plasma membrane provides an excellent perspective for understanding the membrane mechanisms of signal transduction.
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Affiliation(s)
- Akihiro Kusumi
- Institute for Integrated Cell-Material Sciences (iCeMS), Kyoto University, Kyoto 606-8507, Japan.
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Imaging and characterisation of the surface of live cells. Curr Opin Chem Biol 2011; 15:696-703. [DOI: 10.1016/j.cbpa.2011.04.001] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2011] [Accepted: 04/11/2011] [Indexed: 01/20/2023]
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Sako Y, Hiroshima M, Pack CG, Okamoto K, Hibino K, Yamamoto A. Live cell single-molecule detection in systems biology. WILEY INTERDISCIPLINARY REVIEWS-SYSTEMS BIOLOGY AND MEDICINE 2011; 4:183-92. [DOI: 10.1002/wsbm.161] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Dustin ML, Depoil D. New insights into the T cell synapse from single molecule techniques. Nat Rev Immunol 2011; 11:672-84. [PMID: 21904389 DOI: 10.1038/nri3066] [Citation(s) in RCA: 140] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
T cell activation depends on extracellular ligation of the T cell receptor (TCR) by peptide-MHC complexes in a synapse between the T cell and an antigen-presenting cell. The process then requires the assembly of signalling complexes between the TCR and the adaptor protein linker for activation of T cells (LAT), and subsequent filamentous actin (F-actin)-dependent TCR cluster formation. Recent progress in each of these areas, made possible by the emergence of new techniques, has forced us to rethink our assumptions and consider some radical new models. These describe the receptor interaction parameters that control T cell responses and the mechanism by which LAT is recruited to the TCR signalling machinery. This is an exciting time in T cell biology, and further innovation in imaging and genomics is likely to lead to a greater understanding of how T cells are activated.
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Affiliation(s)
- Michael L Dustin
- Helene and Martin Kimmel Center for Biology and Medicine of the Skirball Institute of Biomolecular Medicine, Department of Pathology, New York University School of Medicine, 540 First Avenue, New York, New York 10012, USA.
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James JR, McColl J, Oliveira MI, Dunne PD, Huang E, Jansson A, Nilsson P, Sleep DL, Gonçalves CM, Morgan SH, Felce JH, Mahen R, Fernandes RA, Carmo AM, Klenerman D, Davis SJ. The T cell receptor triggering apparatus is composed of monovalent or monomeric proteins. J Biol Chem 2011; 286:31993-2001. [PMID: 21757710 PMCID: PMC3173209 DOI: 10.1074/jbc.m111.219212] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Understanding the component stoichiometry of the T cell antigen receptor (TCR) triggering apparatus is essential for building realistic models of signal initiation. Recent studies suggesting that the TCR and other signaling-associated proteins are preclustered on resting T cells relied on measurements of the behavior of membrane proteins at interfaces with functionalized glass surfaces. Using fluorescence recovery after photobleaching, we show that, compared with the apical surface, the mobility of TCRs is significantly reduced at Jurkat T cell/glass interfaces, in a signaling-sensitive manner. Using two biophysical approaches that mitigate these effects, bioluminescence resonance energy transfer and two-color coincidence detection microscopy, we show that, within the uncertainty of the methods, the membrane components of the TCR triggering apparatus, i.e. the TCR complex, MHC molecules, CD4/Lck and CD45, are exclusively monovalent or monomeric in human T cell lines, implying that TCR triggering depends only on the kinetics of TCR/pMHC interactions. These analyses also showed that constraining proteins to two dimensions at the cell surface greatly enhances random interactions versus those between the membrane and the cytoplasm. Simulations of TCR-pMHC complex formation based on these findings suggest how unclustered TCR triggering-associated proteins might nevertheless be capable of generating complex signaling outputs via the differential recruitment of cytosolic effectors to the cell membrane.
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Affiliation(s)
- John R James
- Nuffield Department of Clinical Medicine and Medical Research Council Human Immunology Unit, Weatherall Institute of Molecular Medicine, University of Oxford, Oxford OX3 9DS, United Kingdom
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Quaternary structure of SecA in solution and bound to SecYEG probed at the single molecule level. Structure 2011; 19:430-9. [PMID: 21397193 DOI: 10.1016/j.str.2010.12.016] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2010] [Revised: 12/17/2010] [Accepted: 12/22/2010] [Indexed: 11/20/2022]
Abstract
Dual-color fluorescence-burst analysis (DCFBA) was applied to measure the quaternary structure and high-affinity binding of the bacterial motor protein SecA to the protein-conducting channel SecYEG reconstituted into lipid vesicles. DCFBA is an equilibrium technique that enables the direct observation and quantification of protein-protein interactions at the single molecule level. SecA binds to SecYEG as a dimer with a nucleotide- and preprotein-dependent dissociation constant. One of the SecA protomers binds SecYEG in a salt-resistant manner, whereas binding of the second protomer is salt sensitive. Because protein translocation is salt sensitive, we conclude that the dimeric state of SecA is required for protein translocation. A structural model for the dimeric assembly of SecA while bound to SecYEG is proposed based on the crystal structures of the Thermotoga maritima SecA-SecYEG and the Escherichia coli SecA dimer.
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