101
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Kedrov A, Müller DJ. Characterizing folding, structure, molecular interactions and ligand gated activation of single sodium/proton antiporters. Naunyn Schmiedebergs Arch Pharmacol 2006; 372:400-12. [PMID: 16544108 DOI: 10.1007/s00210-005-0027-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2005] [Accepted: 12/02/2005] [Indexed: 01/21/2023]
Abstract
Using the example of sodium/proton antiporter from Escherichia coli NhaA, we review the capabilities of single-molecule atomic force microscopy and force spectroscopy to observe structural and functional insights of a membrane protein, which are not attainable by other traditional methods. While atomic force microscopy provides high-resolution topographs of single membrane proteins, their oligomeric state and assembly, single-molecule force spectroscopy experiments detect molecular interactions of the protein. The sensitivity of this method makes it possible to detect and locate interactions that stabilize secondary structures such as transmembrane alpha-helices, polypeptide loops and segments within them. Controlled refolding experiments using single-molecule force spectroscopy observed individual secondary structure segments folding into the functional protein. Various folding pathways of NhaA were detected, each one exhibiting a certain probability to be taken. Time-lapse refolding experiments enabled determining the folding kinetics and hierarchy of individual secondary structural elements. Recent examples detected and located the ligand binding of an antiporter. Similarly, inhibitor binding and location can be detected which in future may guide towards comparative studies of agonist and antagonist altering the functional state of a membrane protein. We review current and future potentials of these approaches to characterize the action of pharmacological molecules on the antiporter function.
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Affiliation(s)
- Alexej Kedrov
- BioTechnological Center, University of Technology, Tatzberg 49, 01307, Dresden, Germany
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102
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Scheuring S, Lévy D, Rigaud JL. Watching the components of photosynthetic bacterial membranes and their in situ organisation by atomic force microscopy. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2005; 1712:109-27. [PMID: 15919049 DOI: 10.1016/j.bbamem.2005.04.005] [Citation(s) in RCA: 97] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/03/2005] [Revised: 04/04/2005] [Accepted: 04/15/2005] [Indexed: 11/18/2022]
Abstract
The atomic force microscope has developed into a powerful tool in structural biology allowing information to be acquired at submolecular resolution on the protruding structures of membrane proteins. It is now a complementary technique to X-ray crystallography and electron microscopy for structure determination of individual membrane proteins after extraction, purification and reconstitution into lipid bilayers. Moving on from the structures of individual components of biological membranes, atomic force microscopy has recently been demonstrated to be a unique tool to identify in situ the individual components of multi-protein assemblies and to study the supramolecular architecture of these components allowing the efficient performance of a complex biological function. Here, recent atomic force microscopy studies of native membranes of different photosynthetic bacteria with different polypeptide contents are reviewed. Technology, advantages, feasibilities, restrictions and limits of atomic force microscopy for the acquisition of highly resolved images of up to 10 A lateral resolution under native conditions are discussed. From a biological point of view, the new insights contributed by the images are analysed and discussed in the context of the strongly debated organisation of the interconnected network of membrane-associated chlorophyll-protein complexes composing the photosynthetic apparatus in different species of purple bacteria.
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Affiliation(s)
- Simon Scheuring
- Institut Curie, UMR-CNRS 168 and LRC-CEA 34V, 11 rue Pierre et Marie Curie, 75231 Paris Cedex 05, France
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103
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Horn C, Steinem C. Photocurrents generated by bacteriorhodopsin adsorbed on nano-black lipid membranes. Biophys J 2005; 89:1046-54. [PMID: 15908580 PMCID: PMC1366590 DOI: 10.1529/biophysj.105.059550] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Purple membranes were adsorbed on freestanding lipid bilayers, termed nano-black lipid membranes (nano-BLMs), suspending the pores of porous alumina substrates with average pore diameters of 280 nm. Nano-BLMs were obtained by first coating the upper surface of the highly ordered porous alumina substrates with a thin gold layer followed by chemisorption of 1,2-dipalmitoyl-sn-glycero-3-phosphothioethanol and subsequent addition of a droplet of 1,2-diphytanoyl-sn-glycero-3-phosphocholine and octadecylamine dissolved in n-decane onto the hydrophobic submonolayer. By means of impedance spectroscopy, the quality of the nano-BLMs was verified. The electrical parameters confirm the formation of single lipid bilayers with high membrane resistances covering the porous matrix. Adsorption of purple membranes on the nano-BLMs was followed by recording the photocurrents generated by bacteriorhodopsin upon continuous light illumination. The membrane system exhibits a very high long-term stability with the advantage that not only transient but also stationary currents are recordable. By adding the proton ionophore carbonyl cyanide-m-chlorophenylhydrazone the conductivity of the nano-BLMs increases, resulting in a higher stationary current, which proves that proton conductance occurs across the nano-BLMs.
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Affiliation(s)
- Christian Horn
- Institut für Analytische Chemie, Chemo- und Biosensorik, Universität Regensburg, Germany
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104
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Kienberger F, Kada G, Mueller H, Hinterdorfer P. Single Molecule Studies of Antibody–Antigen Interaction Strength Versus Intra-molecular Antigen Stability. J Mol Biol 2005; 347:597-606. [PMID: 15755453 DOI: 10.1016/j.jmb.2005.01.042] [Citation(s) in RCA: 95] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2004] [Accepted: 01/18/2005] [Indexed: 11/21/2022]
Abstract
We investigated molecular recognition of antibodies to membrane-antigens and extraction of the antigens out of membranes at the single molecule level. Using dynamic force microscopy imaging and enzyme immunoassay, binding of anti-sendai antibodies to sendai-epitopes genetically fused into bacteriorhodopsin molecules from purple membranes were detected under physiological conditions. The antibody/antigen interaction strength of 70-170 pN at loading rates of 2-50 nN/second yielded a barrier width of x = 0.12 nm and a kinetic off-rate (corresponding to the barrier height) of k(off) = 6s(-1), respectively. Bacteriorhodopsin unfolding revealed a characteristic intra-molecular force pattern, in which wild-type and sendai-bacteriorhodopsin molecules were clearly distinguishable in their length distributions, originating from the additional 13 amino acid residues epitope in sendai purple membranes. The inter-molecular antibody/antigen unbinding force was significantly lower than the force required to mechanically extract the binding epitope-containing helix pair out of the membrane and unfold it (126 pN compared to 204 pN at the same loading rate), meeting the expectation that inter-molecular unbinding forces are weaker than intra-molecular unfolding forces responsible for stabilizing native conformations of proteins.
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Affiliation(s)
- Ferry Kienberger
- Institute for Biophysics, University of Linz, Altenbergerstr. 69, A-4040 Linz, Austria
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105
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Zhang H, Zhang D, He Y. A novel atomic force microscope operating in liquid for in situ investigation of electrochemical preparation of porous alumina. Microsc Res Tech 2005; 66:126-31. [PMID: 15880512 DOI: 10.1002/jemt.20143] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
A novel atomic force microscope (AFM) operating in liquid is described in this article. The specially designed AFM probe involves a tip attached to a cantilever, a tip holder, and a circular Plexiglas window. When the probe dives into the fluid, a circular meniscus is established around the Plexiglas window, preventing the tip from being affected or destroyed by surface tension of the liquid. In this setup, the whole scanning probe and the sample can completely dive into fluid. Meanwhile, the probe tip scans over the sample surface when the instrument works. These advantages enable the instrument to scan comparatively large or heavy samples with a high speed. The highest scan rate is about 30 lines/s or 14 s for a 400 x 400-pixel, 3 x 3 microm image. Using the new AFM, we carry out in-situ investigation of the formation processes of porous alumina during electrochemical anodic oxidation. A lead ring and an aluminum foil serve as cathode and anode, respectively. They are entirely immersed in the bath electrolyte, which is oxalic acid solution. During anodic oxidation, the AFM images of the sample surface are successively acquired without elevating the sample out of the solution. Experiments reveal that electrochemical reactions take place soon after the power supply is switched on, and with the progression of anodization, nanostructures of porous alumina gradually occur on the aluminum substrate, finally yielding ordered arrays of nanopores. As a typical example of applications, the results of this work show that the new AFM is an ideal and powerful tool for in-situ observation and study of materials or samples in aqueous solutions.
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Affiliation(s)
- Haijun Zhang
- Department of Optical Engineering, Zhejiang University, Hangzhou 310027, People's Republic of China.
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106
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Toca-Herrera JL, Moreno-Flores S, Friedmann J, Pum D, Sleytr UB. Chemical and thermal denaturation of crystalline bacterial S-layer proteins: An atomic force microscopy study. Microsc Res Tech 2005; 65:226-34. [PMID: 15630688 DOI: 10.1002/jemt.20127] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Crystalline monomolecular cell surface layers, S-layers, are one of the most common outermost cell envelope components of the prokaryotic organisms (bacteria and archaeda) that protects them from competitive habitats. Since isolated S-protein subunits are able to re-assemble into crystalline arrays on lipid films and solid supports making biomimetic surfaces, S-layer technology is currently used in nanobiotechnology. An important aspect of the biomimetic surfaces built with S-layers is their stability under extreme solvent conditions or temperature. Chemical (pH, alcohol) and physical (thermal) denaturant conditions were employed to test the stability of S-layers. Recrystallized bacterial surface layers from Bacillus sphaericus (SbpA) on hydrophilic silicon wafers loses the crystalline structure at 80% ethanol/water mixtures, the change in structure being reversible after treating the surface with buffer solution. SbpA on silicon supports denatures at pH 3 and at 70 degrees C, and the process is irreversible. Cross-linking of SbpA enhances the stability for high ethanol and acidic conditions, but it does not improve thermal stability. Recrystallized SbpA on secondary cell wall polymer (SCWP), a natural environment for the protein layer, is more resistant to ethanol and pH exposure than recrystallized SbpA on hydrophilic silicon supports. Atomic force microscopy (AFM) was used to monitor the loss of stability and the changes in protein layer conformation.
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Affiliation(s)
- José L Toca-Herrera
- Center for NanoBiotechnology, University of Natural Resources and Applied Life Sciences, A-1180 Vienna, Austria
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107
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Zhuang W, Ecker C, Metselaar GA, Rowan AE, Nolte RJM, Samorí P, Rabe JP. SFM Characterization of Poly(isocyanodipeptide) Single Polymer Chains in Controlled Environments: Effect of Tip Adhesion and Chain Swelling. Macromolecules 2004. [DOI: 10.1021/ma048786z] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Wei Zhuang
- Department of Physics, Humboldt University Berlin, Newtonstrasse15, 12489 Berlin, Germany, Department of Organic Chemistry, NSR center, University of Nijmegen, Toernooiveld, 6525 ED Nijmegen, The Netherlands, Instituto per la Sintesi Organica e la Fotoreattività, C.N.R. Bologna, via Gobetti 101, 40129 Bologna, Italy, and Nanochemistry Laboratory, Institut de Science et d'Ingènierie Supramolèculaires (ISIS), Université Louis Pasteur of Strasbourg, 8 allée Gaspard Monge, 67083 Strasbourg, France
| | - Christof Ecker
- Department of Physics, Humboldt University Berlin, Newtonstrasse15, 12489 Berlin, Germany, Department of Organic Chemistry, NSR center, University of Nijmegen, Toernooiveld, 6525 ED Nijmegen, The Netherlands, Instituto per la Sintesi Organica e la Fotoreattività, C.N.R. Bologna, via Gobetti 101, 40129 Bologna, Italy, and Nanochemistry Laboratory, Institut de Science et d'Ingènierie Supramolèculaires (ISIS), Université Louis Pasteur of Strasbourg, 8 allée Gaspard Monge, 67083 Strasbourg, France
| | - Gerald A. Metselaar
- Department of Physics, Humboldt University Berlin, Newtonstrasse15, 12489 Berlin, Germany, Department of Organic Chemistry, NSR center, University of Nijmegen, Toernooiveld, 6525 ED Nijmegen, The Netherlands, Instituto per la Sintesi Organica e la Fotoreattività, C.N.R. Bologna, via Gobetti 101, 40129 Bologna, Italy, and Nanochemistry Laboratory, Institut de Science et d'Ingènierie Supramolèculaires (ISIS), Université Louis Pasteur of Strasbourg, 8 allée Gaspard Monge, 67083 Strasbourg, France
| | - Alan E. Rowan
- Department of Physics, Humboldt University Berlin, Newtonstrasse15, 12489 Berlin, Germany, Department of Organic Chemistry, NSR center, University of Nijmegen, Toernooiveld, 6525 ED Nijmegen, The Netherlands, Instituto per la Sintesi Organica e la Fotoreattività, C.N.R. Bologna, via Gobetti 101, 40129 Bologna, Italy, and Nanochemistry Laboratory, Institut de Science et d'Ingènierie Supramolèculaires (ISIS), Université Louis Pasteur of Strasbourg, 8 allée Gaspard Monge, 67083 Strasbourg, France
| | - Roeland J. M. Nolte
- Department of Physics, Humboldt University Berlin, Newtonstrasse15, 12489 Berlin, Germany, Department of Organic Chemistry, NSR center, University of Nijmegen, Toernooiveld, 6525 ED Nijmegen, The Netherlands, Instituto per la Sintesi Organica e la Fotoreattività, C.N.R. Bologna, via Gobetti 101, 40129 Bologna, Italy, and Nanochemistry Laboratory, Institut de Science et d'Ingènierie Supramolèculaires (ISIS), Université Louis Pasteur of Strasbourg, 8 allée Gaspard Monge, 67083 Strasbourg, France
| | - Paolo Samorí
- Department of Physics, Humboldt University Berlin, Newtonstrasse15, 12489 Berlin, Germany, Department of Organic Chemistry, NSR center, University of Nijmegen, Toernooiveld, 6525 ED Nijmegen, The Netherlands, Instituto per la Sintesi Organica e la Fotoreattività, C.N.R. Bologna, via Gobetti 101, 40129 Bologna, Italy, and Nanochemistry Laboratory, Institut de Science et d'Ingènierie Supramolèculaires (ISIS), Université Louis Pasteur of Strasbourg, 8 allée Gaspard Monge, 67083 Strasbourg, France
| | - Jürgen P. Rabe
- Department of Physics, Humboldt University Berlin, Newtonstrasse15, 12489 Berlin, Germany, Department of Organic Chemistry, NSR center, University of Nijmegen, Toernooiveld, 6525 ED Nijmegen, The Netherlands, Instituto per la Sintesi Organica e la Fotoreattività, C.N.R. Bologna, via Gobetti 101, 40129 Bologna, Italy, and Nanochemistry Laboratory, Institut de Science et d'Ingènierie Supramolèculaires (ISIS), Université Louis Pasteur of Strasbourg, 8 allée Gaspard Monge, 67083 Strasbourg, France
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108
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Janovjak H, Müller DJ, Humphris ADL. Molecular force modulation spectroscopy revealing the dynamic response of single bacteriorhodopsins. Biophys J 2004; 88:1423-31. [PMID: 15574708 PMCID: PMC1305144 DOI: 10.1529/biophysj.104.052746] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Recent advances in atomic force microscopy allowed globular and membrane proteins to be mechanically unfolded on a single-molecule level. Presented is an extension to the existing force spectroscopy experiments. While unfolding single bacteriorhodopsins from native purple membranes, small oscillation amplitudes (6-9 nm) were supplied to the vertical displacement of the cantilever at a frequency of 3 kHz. The phase and amplitude response of the cantilever-protein system was converted to reveal the elastic (conservative) and viscous (dissipative) contributions to the unfolding process. The elastic response (stiffness) of the extended parts of the protein were in the range of a few tens pN/nm and could be well described by the derivative of the wormlike chain model. Discrete events in the viscous response coincided with the unfolding of single secondary structure elements and were in the range of 1 microNs/m. In addition, these force modulation spectroscopy experiments revealed novel mechanical unfolding intermediates of bacteriorhodopsin. We found that kinks result in a loss of unfolding cooperativity in transmembrane helices. Reconstructing force-distance spectra by the integration of amplitude-distance spectra verified their position, offering a novel approach to detect intermediates during the forced unfolding of single proteins.
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Affiliation(s)
- Harald Janovjak
- BioTechnological Center, University of Technology, Dresden, Germany
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109
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Qutub Y, Reviakine I, Maxwell C, Navarro J, Landau EM, Vekilov PG. Crystallization of Transmembrane Proteins in cubo: Mechanisms of Crystal Growth and Defect Formation. J Mol Biol 2004; 343:1243-54. [PMID: 15491610 DOI: 10.1016/j.jmb.2004.09.022] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2004] [Revised: 08/26/2004] [Accepted: 09/14/2004] [Indexed: 11/17/2022]
Abstract
Crystallization of membrane proteins is a major stumbling block en route to elucidating their structure and understanding their function. The novel concept of membrane protein crystallization from lipidic cubic phases, "in cubo", has yielded well-ordered crystals and high-resolution structures of several membrane proteins, yet progress has been slow due to the lack of understanding of the molecular mechanisms of protein transport, crystal nucleation, growth, and defect formation in cubo. Here, we examine at molecular and mesoscopic resolution with atomic force microscopy the morphology of in cubo grown bacteriorhodopsin crystals in inert buffers and during etching by detergent. The results reveal that crystal nucleation occurs following local rearrangement of the highly curved lipidic cubic phase into a lamellar structure, which is akin to that of the native membrane. Crystals grow within the bulk cubic phase surrounded by such lamellar structures, whereby transport towards a growing crystalline layer is constrained to within an individual lamella. This mechanism leads to lack of dislocations, generation of new crystalline layers at numerous locations, and to voids and block boundaries. The characteristic macroscopic lengthscale of these defects suggests that the crystals grow by attachment of single molecules to the nuclei. These insights into the mechanisms of nucleation, growth and transport in cubo provide guidance en route to a rational design of membrane protein crystallization, and promise to further advance the field.
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Affiliation(s)
- Yasser Qutub
- Department of Chemical Engineering, University of Houston, Houston, TX 77204, USA
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110
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Scheuring S, Sturgis JN, Prima V, Bernadac A, Lévy D, Rigaud JL. Watching the photosynthetic apparatus in native membranes. Proc Natl Acad Sci U S A 2004; 101:11293-7. [PMID: 15273291 PMCID: PMC509197 DOI: 10.1073/pnas.0404350101] [Citation(s) in RCA: 134] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2004] [Indexed: 11/18/2022] Open
Abstract
Over the last 9 years, the structures of the various components of the bacterial photosynthetic apparatus or their homologues have been determined by x-ray crystallography to at least 4.8-A resolution. Despite this wealth of structural information on the individual proteins, there remains an urgent need to examine the architecture of the photosynthetic apparatus in intact photosynthetic membranes. Information on the arrangement of the different complexes in a native system will help us to understand the processes that ensure the remarkably high quantum efficiency of the system. In this work we report images obtained with an atomic force microscope of native photosynthetic membranes from the bacterium Rhodospirillum photometricum. Several proteins can be seen and identified at molecular resolution, allowing the analysis and modeling of the lateral organization of multiple components of the photosynthetic apparatus within a native membrane. Analysis of the distribution of the complexes shows that their arrangement is far from random, with significant clustering both of antenna complexes and core complexes. The functional significance of the observed distribution is discussed.
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Affiliation(s)
- Simon Scheuring
- Institut Curie, Unité Mixte de Recherche-Centre National de la Recherche Scientifique 168 and Laboratoire de Recherche Correspondant-Commissariat à l'Energie Atomique 34V, 11 Rue Pierre et Marie Curie, 75231 Paris 05, France.
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111
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Lesniewska E, Adrian M, Klinguer A, Pugin A. Cell wall modification in grapevine cells in response to UV stress investigated by atomic force microscopy. Ultramicroscopy 2004; 100:171-8. [PMID: 15231307 DOI: 10.1016/j.ultramic.2003.11.004] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2003] [Revised: 11/13/2003] [Accepted: 11/18/2003] [Indexed: 10/26/2022]
Abstract
Despite cell wall reinforcement being a well-known defence mechanism of plants, it remains poorly characterized from a physical point of view. The objective of this work was to further describe this mechanism. Vitis vinifera cv Gamay cells were treated with UV-light (254 nm), a well-known elicitor of defence mechanisms in grapevines, and physical cell wall modifications were observed using the atomic force microscopy (AFM) under native conditions. The grapevine cell suspensions were continuously observed in their culture medium from 30 min to 24h after elicitation. In the beginning, cellulose fibrils covered by a matrix surrounded the control and treated cells. After 3 h, the elicited cells displayed sprouted expansions around the cell wall that correspond to pectin chains. These expansions were not observed on untreated grapevine cells. The AFM tip was used to determine the average surface elastic modulus of cell wall that account for cell wall mechanical properties. The elasticity is diminished in UV-treated cells. In a comparative study, grapevine cells showed the same decrease in cell wall elasticity when treated with a fungal biotic elicitor of defence response. These results demonstrate cell wall strengthening by UV stress.
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Affiliation(s)
- E Lesniewska
- Physics Laboratory LPUB UMR CNRS 5027, University of Bourgogne, B.P. 400, F-21078 Dijon Cedex, France.
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112
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Moloney M, McDonnell L, O'Shea H. Atomic force microscopy analysis of enveloped and non-enveloped viral entry into, and egress from, cultured cells. Ultramicroscopy 2004; 100:163-9. [PMID: 15231306 DOI: 10.1016/j.ultramic.2003.12.011] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2003] [Revised: 11/28/2003] [Accepted: 12/02/2003] [Indexed: 11/22/2022]
Abstract
Since its invention, the atomic force microscope has been used to image a wide variety of biological samples, including viruses. Viral entry into, and egress from, cultured cells has been extensively studied using numerous scientific techniques and to a limited extent using atomic force microscopy. One of the main structural differences that can exist between viruses is the absence, or presence, of an envelope and this factor has consequences for the mode of viral entry and egress. In this study, the entry into, and egress from, cultured cells of enveloped and non-enveloped viruses were investigated using atomic force microscopy. No significant cell surface changes were observed following infection with enveloped or non-enveloped viruses. Although roughness analysis of viral entry revealed cell smoothing post-infection, no differences between the roughness values of enveloped and non-enveloped viral entry were observed. Line analysis of viral entry revealed minor differences between cells infected with an enveloped rather than a non-enveloped virus. These differences may represent a distinction between the uptake processes of enveloped and non-enveloped viruses. Studies of viral egress revealed that infected cells were undergoing cytopathic changes. Whilst topographic, height and roughness differences clearly occurred between virally- and mock-infected cells, no significant differences were elucidated between enveloped and non-enveloped viral egress.
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Affiliation(s)
- M Moloney
- Department of Biological Sciences, Cork Institute of Technology, Bishopstown, Cork, Ireland
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113
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Rankl C, Pastushenko V, Kienberger F, Stroh CMCM, Hinterdorfer P. Hydrodynamic damping of a magnetically oscillated cantilever close to a surface. Ultramicroscopy 2004; 100:301-8. [PMID: 15231323 DOI: 10.1016/j.ultramic.2003.12.014] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2003] [Revised: 11/28/2003] [Accepted: 12/02/2003] [Indexed: 10/26/2022]
Abstract
We studied the frequency response of a magnetically driven atomic force microscope (AFM) cantilever close to a sample surface in liquids. Amplitude-frequency (tuning) curves showed pronounced differences in dependence on the tip-sample separation (from 1 to 50 microm), with significant shifts of the resonance peak. A model was developed in which the cantilever was described in a full shape manner and the hydrodynamic forces acting on the cantilever were approximately calculated. The slight inclination of the cantilever to the surface (alpha approximately 15 degrees) leads to a force profile along the cantilever. Therefore, the mathematical problem can be strictly solved only numerically. For an approximate analytical solution, the hydrodynamic force profile was approximated by a constant force along the cantilever for large separations and by a point force acting on the tip of the cantilever for small separations. The theoretical results calculated within this model agreed well with the experimental data and allowed to determine the cantilever mass in liquid M*, the joint mass at the tip end m*t, and the coefficient of viscous interaction of the cantilever with free liquid, gamma(infinity).
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Affiliation(s)
- Christian Rankl
- Institute for Biophysics, University of Linz, Altenbergerstr. 69, A-4040 Linz, Austria
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114
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Kienberger F, Zhu R, Moser R, Rankl C, Blaas D, Hinterdorfer P. Dynamic force microscopy for imaging of viruses under physiological conditions. Biol Proced Online 2004; 6:120-128. [PMID: 15243650 PMCID: PMC443560 DOI: 10.1251/bpo80] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2004] [Revised: 06/09/2004] [Accepted: 06/09/2004] [Indexed: 01/19/2023] Open
Abstract
Dynamic force microscopy (DFM) allows imaging of the structure and the assessment of the function of biological specimens in their physiological environment. In DFM, the cantilever is oscillated at a given frequency and touches the sample only at the end of its downward movement. Accordingly, the problem of lateral forces displacing or even destroying bio-molecules is virtually inexistent as the contact time and friction forces are reduced. Here, we describe the use of DFM in studies of human rhinovirus serotype 2 (HRV2) weakly adhering to mica surfaces. The capsid of HRV2 was reproducibly imaged without any displacement of the virus. Release of the genomic RNA from the virions was initiated by exposure to low pH buffer and snapshots of the extrusion process were obtained. In the following, the technical details of previous DFM investigations of HRV2 are summarized.
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Affiliation(s)
- Ferry Kienberger
- Institute for Biophysics, J. Kepler University, Altenbergerstr. 69, A-4040 Linz. Austria
| | - Rong Zhu
- Institute for Biophysics, J. Kepler University, Altenbergerstr. 69, A-4040 Linz, Austria and the Research Department Biomedical Nanotechnology, Upper Austrian Research GmbH, Scharitzerstr. 6-8, A-4020 Linz. Austria
| | - Rosita Moser
- Max F. Perutz Laboratories, University Departments at the Vienna Biocenter, Department of Medical Biochemistry, University of Vienna. Dr. Bohr Gasse 9/3, A-1030 Vienna. Austria
| | - Christian Rankl
- Institute for Biophysics, J. Kepler University, Altenbergerstr. 69, A-4040 Linz. Austria
| | - Dieter Blaas
- Max F. Perutz Laboratories, University Departments at the Vienna Biocenter, Department of Medical Biochemistry, University of Vienna. Dr. Bohr Gasse 9/3, A-1030 Vienna. Austria
| | - Peter Hinterdorfer
- Institute for Biophysics, J. Kepler University, Altenbergerstr. 69, A-4040 Linz. Austria
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115
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Affiliation(s)
- Yves F Dufrêne
- Unité de chimie des interfaces, Université catholique de Louvain, Croix du Sud 2/18, B-1348 Louvain-la-Neuve, Belgium.
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116
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Kienberger F, Mueller H, Pastushenko V, Hinterdorfer P. Following single antibody binding to purple membranes in real time. EMBO Rep 2004; 5:579-83. [PMID: 15143343 PMCID: PMC1299069 DOI: 10.1038/sj.embor.7400149] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2003] [Revised: 03/17/2004] [Accepted: 03/17/2004] [Indexed: 11/08/2022] Open
Abstract
Antibody binding to surface antigens in membranes is the primary event in the specific immune defence of vertebrates. Here we used force microscopy to study the dynamics of antibody recognition of mutant purple membranes from Halobacterium salinarum containing a genetically appended anti-Sendai recognition epitope. Ligation of individual anti-Sendai antibodies to their antigenic epitopes was observed over time. Their increase in number within a small selected area revealed an apparent kinetic on-rate. The membrane-bound antibodies showed many different conformations that ranged from globular to V- and Y-like shapes. The maximum distance of two Fab fragments of the same antibody was observed to be approximately 18 nm, indicating an overall strong intrinsic flexibility of the antibody hinge region. Fab fragments of bound anti-Sendai antibodies were allocated to antigenic sites of the purple membrane, allowing the identification and localization of individual recognition epitopes on the surface of purple membranes.
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Affiliation(s)
- Ferry Kienberger
- Institute for Biophysics, J. Kepler University of Linz, Altenbergerstr. 69, A-4040 Linz, Austria
| | - Harald Mueller
- Department of Microbiology, University of Kassel, Heinrich Plett Strasse 40, D-34132 Kassel, Germany
| | - Vassili Pastushenko
- Institute for Biophysics, J. Kepler University of Linz, Altenbergerstr. 69, A-4040 Linz, Austria
| | - Peter Hinterdorfer
- Institute for Biophysics, J. Kepler University of Linz, Altenbergerstr. 69, A-4040 Linz, Austria
- Tel: +43 732 2468 9265; Fax: +43 732 2468 9280; E-mail:
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117
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Janovjak H, Struckmeier J, Hubain M, Kedrov A, Kessler M, Müller DJ. Probing the Energy Landscape of the Membrane Protein Bacteriorhodopsin. Structure 2004; 12:871-9. [PMID: 15130479 DOI: 10.1016/j.str.2004.03.016] [Citation(s) in RCA: 68] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2003] [Revised: 02/26/2004] [Accepted: 03/02/2004] [Indexed: 11/29/2022]
Abstract
The folding and stability of transmembrane proteins is a fundamental and unsolved biological problem. Here, single bacteriorhodopsin molecules were mechanically unfolded from native purple membranes using atomic force microscopy and force spectroscopy. The energy landscape of individual transmembrane alpha helices and polypeptide loops was mapped by monitoring the pulling speed dependence of the unfolding forces and applying Monte Carlo simulations. Single helices formed independently stable units stabilized by a single potential barrier. Mechanical unfolding of the helices was triggered by 3.9-7.7 A extension, while natural unfolding rates were of the order of 10(-3) s(-1). Besides acting as individually stable units, helices associated pairwise, establishing a collective potential barrier. The unfolding pathways of individual proteins reflect distinct pulling speed-dependent unfolding routes in their energy landscapes. These observations support the two-stage model of membrane protein folding in which alpha helices insert into the membrane as stable units and then assemble into the functional protein.
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Affiliation(s)
- Harald Janovjak
- BIOTEC, University of Technology Dresden, 01307 Dresden, Germany
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118
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Kienberger F, Zhu R, Moser R, Blaas D, Hinterdorfer P. Monitoring RNA release from human rhinovirus by dynamic force microscopy. J Virol 2004; 78:3203-9. [PMID: 15016841 PMCID: PMC371065 DOI: 10.1128/jvi.78.7.3203-3209.2004] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Human rhinoviruses were imaged under physiological conditions by dynamic force microscopy. Topographical images revealed various polygonal areas on the surfaces of the 30-nm viral particles. RNA release was initiated by exposure to a low-pH buffer. The lengths of the RNAs that were released but still connected to the virus capsid varied between 40 and 330 nm, whereas RNA molecules that were completely released from the virus were observed with lengths up to 1 micro m. Fork-like structure elements with 30-nm extensions were sometimes resolved at one end of the RNA molecules. They possibly correspond to the characteristic multi-stem-loop conformation, the internal ribosomal entry site, located at the 5' region of the genome. This study demonstrates that dynamic force microscopy can be used to study viral RNA release in situ under physiological conditions.
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Affiliation(s)
- Ferry Kienberger
- Institute for Biophysics, J. Kepler University, A-4040 Linz, Austria
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119
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Kamruzzahan ASM, Kienberger F, Stroh CM, Berg J, Huss R, Ebner A, Zhu R, Rankl C, Gruber HJ, Hinterdorfer P. Imaging morphological details and pathological differences of red blood cells using tapping-mode AFM. Biol Chem 2004; 385:955-60. [PMID: 15551870 DOI: 10.1515/bc.2004.124] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The surface topography of red blood cells (RBCs) was investigated under near-physiological conditions using atomic force microscopy (AFM). An immobilization protocol was established where RBCs are coupled via molecular bonds of the membrane glycoproteins to wheat germ agglutinin (WGA), which is covalently and flexibly tethered to the support. This results in a tight but non-invasive attachment of the cells. Using tapping-mode AFM, which is known as gentle imaging mode and therefore most appropriate for soft biological samples like erythrocytes, it was possible to resolve membrane skeleton structures without major distortions or deformations of the cell surface. Significant differences in the morphology of RBCs from healthy humans and patients with systemic lupus erythematosus (SLE) were observed on topographical images. The surface of RBCs from SLE patients showed characteristic circular-shaped holes with approx. 200 nm in diameter under physiological conditions, a possible morphological correlate to previously published changes in the SLE erythrocyte membrane.
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Affiliation(s)
- A S M Kamruzzahan
- Institute of Biophysics, University of Linz, Altenbergerstr. 69, A-4040 Linz, Austria
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120
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Hategan A, Law R, Kahn S, Discher DE. Adhesively-tensed cell membranes: lysis kinetics and atomic force microscopy probing. Biophys J 2003; 85:2746-59. [PMID: 14507737 PMCID: PMC1303498 DOI: 10.1016/s0006-3495(03)74697-9] [Citation(s) in RCA: 149] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2003] [Accepted: 07/23/2003] [Indexed: 11/16/2022] Open
Abstract
Membrane tension underlies a range of cell physiological processes. Strong adhesion of the simple red cell is used as a simple model of a spread cell with a finite membrane tension-a state which proves useful for studies of both membrane rupture kinetics and atomic force microscopy (AFM) probing of native structure. In agreement with theories of strong adhesion, the cell takes the form of a spherical cap on a substrate densely coated with poly-L-lysine. The spreading-induced tension, sigma, in the membrane is approximately 1 mN/m, which leads to rupture over many minutes; and sigma is estimated from comparable rupture times in separate micropipette aspiration experiments. Under the sharpened tip of an AFM probe, nano-Newton impingement forces (10-30 nN) are needed to penetrate the tensed erythrocyte membrane, and these forces increase exponentially with tip velocity ( approximately nm/ms). We use the results to clarify how tapping-mode AFM imaging works at high enough tip velocities to avoid rupturing the membrane while progressively compressing it to a approximately 20-nm steric core of lipid and protein. We also demonstrate novel, reproducible AFM imaging of tension-supported membranes in physiological buffer, and we describe a stable, distended network consistent with the spectrin cytoskeleton. Additionally, slow retraction of the AFM tip from the tensed membrane yields tether-extended, multipeak sawtooth patterns of average force approximately 200 pN. In sum we show how adhesive tensioning of the red cell can be used to gain novel insights into native membrane dynamics and structure.
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Affiliation(s)
- Alina Hategan
- Biophysical Engineering Lab and Institute for Medicine and Engineering, School of Engineering and Applied Science, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6315, USA
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121
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Kienberger F, Stroh C, Kada G, Moser R, Baumgartner W, Pastushenko V, Rankl C, Schmidt U, Müller H, Orlova E, LeGrimellec C, Drenckhahn D, Blaas D, Hinterdorfer P. Dynamic force microscopy imaging of native membranes. Ultramicroscopy 2003; 97:229-37. [PMID: 12801675 DOI: 10.1016/s0304-3991(03)00047-0] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
We employed magnetic ACmode atomic force microscopy (MACmode AFM) as a novel dynamic force microscopy method to image surfaces of biological membranes in their native environments. The lateral resolution achieved under optimized imaging conditions was in the nanometer range, even when the sample was only weakly attached to the support. Purple membranes (PM) from Halobacterium salinarum were used as a test standard for topographical imaging. The hexagonal arrangement of the bacteriorhodopsin trimers on the cytoplasmic side of PM was resolved with 1.5nm lateral accuracy, a resolution similar to images obtained in contact and tapping-mode AFM. Human rhinovirus 2 (HRV2) particles were attached to mica surfaces via nonspecific interactions. The capsid structure and 2nm sized protein loops of HRV2 were routinely obtained without any displacement of the virus. Globular and filamentous structures on living and fixed endothelial cells were observed with a resolution of 5-20nm. These examples show that MACmode AFM is a favorable method in studying the topography of soft and weakly attached biological samples with high resolution under physiological conditions.
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Affiliation(s)
- Ferry Kienberger
- Institute for Biophysics, University of Linz, Altenbergerstr. 69, A-4040, Linz, Austria
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122
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Rossell JP, Allen S, Davies MC, Roberts CJ, Tendler SJB, Williams PM. Electrostatic interactions observed when imaging proteins with the atomic force microscope. Ultramicroscopy 2003; 96:37-46. [PMID: 12623170 DOI: 10.1016/s0304-3991(02)00379-0] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The atomic force microscope (AFM) is now an established and valuable tool for the study of biological macromolecules in aqueous environments. In this paper we form a patterned boundary via the microcontact printing of individually isolated proteins, covalently attached to a solid support. We use this boundary to investigate electrostatic interactions that can occur between an AFM tip and a protein surface during imaging in solution. The observed height variations of the protein film are found to be a combination of not only structural considerations and thickness of the protein film, but also the repulsive contribution from electrostatic interactions between the AFM tip and the sample. These variations in measured heights of the protein surface can be described by Derjaguin, Landau, Verway, Overbeek (DLVO) theory. Our experimental results show that height measurements can be manipulated either negatively or positively by adjusting the pH and concentration of the electrolyte buffer that is utilised.
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Affiliation(s)
- J P Rossell
- Laboratory of Biophysics and Surface Analysis, School of Pharmaceutical Sciences, University of Nottingham, University Park, Nottingham NG7 2RD, UK
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123
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Charras G, Lehenkari P, Horton M. Biotechnological applications of atomic force microscopy. Methods Cell Biol 2003; 68:171-91. [PMID: 12053729 DOI: 10.1016/s0091-679x(02)68009-4] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/25/2023]
Affiliation(s)
- Guillaume Charras
- Bone and Mineral Center, Department of Medicine, Rayne Institute, University College London, London, WC1E 6JJ, United Kingdom
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124
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Müller DJ, Engel A. Conformations, flexibility, and interactions observed on individual membrane proteins by atomic force microscopy. Methods Cell Biol 2003; 68:257-99. [PMID: 12053734 DOI: 10.1016/s0091-679x(02)68014-8] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/05/2022]
Affiliation(s)
- Daniel J Müller
- M. E. Müller Institute, Biocenter, University of Basel, CH-4056 Basel, Switzerland
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125
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Abstract
The investigation of biomolecules has entered a new age since the development of methodologies capable of studies at the level of single molecules. In biology, most molecules show a complex dynamical behavior, with individual motions and transitions between different states occurring highly correlated in space and time within an arrangement of various elements. Recent advances in the development of new microscopy techniques with sensitivity at the single molecule have gained access to essentially new types of information obtainable from imaging biomolecular samples. These methodologies are described here in terms of their applicability to the in vivo detection and visualization of molecular processes on surfaces, membranes, and cells. First examples of single molecule microscopy on cell membranes revealed new basic insight into the lateral organization of the plasma membrane, providing the captivating perspective of an ultra-sensitive methodology as a general tool to study local processes and heterogeneities in living cells.
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Affiliation(s)
- G J Schütz
- Institute for Biophysics, University of Linz, Altenbergerstr. 69, A-4040 Linz, Austria.
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126
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Affiliation(s)
- Yves F Dufrêne
- Unité de Chimie des Interfaces, Université Catholique de Louvain, B-1348 Louvain-la-Neuve, Belgium.
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127
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Le Grimellec C, Giocondi MC, Lenoir M, Vater M, Sposito G, Pujol R. High-resolution three-dimensional imaging of the lateral plasma membrane of cochlear outer hair cells by atomic force microscopy. J Comp Neurol 2002; 451:62-9. [PMID: 12209841 DOI: 10.1002/cne.10338] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
The outer hair cells (OHCs) from the mammalian organ of Corti are assumed to enhance the sensitivity and the selectivity of the cochlea via an electromotile response to sound stimulation. These OHC mechanical changes feed energy back into the cochlea before completion of the transduction process by inner hair cells. OHC electromotility is thought to depend on specific transmembrane motor proteins. Electron microscopy has been used previously to image the OHC lateral plasma membrane, where voltage sensors and motors are located. A very specific and regular organization of membrane particles has been described, together with an equally specific submembraneous meshwork of cytoskeleton anchored to the plasma membrane. To confirm and extend these observations, we have used, for the first time on the OHC lateral wall, atomic force microscopy (AFM). As a result of an improved tapping mode technique as well as the unique ultrastructural organization of the OHC plasma membrane, we have obtained high-resolution three-dimensional (3D) images of a markedly enhanced quality, allowing high-resolution 3D imaging. Tapping-mode AFM confirmed the presence of regularly aligned particles (presumably transmembrane proteins) on both faces of the OHC plasma membrane. It also revealed the presence of markedly different membrane domains, smooth and undulating. The differences between these zones probably are due to local differences in cytoskeleton-membrane interactions. Moreover, 3D reconstructions allowed us to distinguish between globular and pore-like particles, a distinction that may be of great functional significance.
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128
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Yamada T, Arakawa H, Okajima T, Shimada T, Ikai A. Use of AFM for imaging and measurement of the mechanical properties of light-convertible organelles in plants. Ultramicroscopy 2002; 91:261-8. [PMID: 12211477 DOI: 10.1016/s0304-3991(02)00107-9] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
We obtained topographic images of etioplasts and chloroplasts and measured their elasticity in a physiological buffer using an atomic force microscope (AFM) and found a possible correlation between the morphological and mechanical properties during the light conversion of etioplasts to chloroplasts. Alcian blue 8GX dye was found to be effective for immobilizing the plant organelles stably on a glass surface for AFM experiments. We employed the tapping-mode AFM with a cantilever soft enough to measure the elasticity of the organelles in a liquid solution. The best images of soft, spherical organelles were obtained using the tapping-mode AFM with oscillation at the thermal vibration frequency of the cantilever of around 3 kHz. Whereas etioplasts were found to be smooth-surfaced and stiff against compression by the AFM tip, before light conversion to chloroplasts, they became rough-surfaced and mechanically soft after exposure to light. The elasticity of etioplasts was 20 times higher than that of chloroplasts, probably reflecting changes in their inner structures.
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Affiliation(s)
- Takafumi Yamada
- Laboratory of Biodynamics, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Yokohama, Japan
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129
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Moloney M, McDonnell L, O'Shea H. Immobilisation of Semliki forest virus for atomic force microscopy. Ultramicroscopy 2002; 91:275-9. [PMID: 12211479 DOI: 10.1016/s0304-3991(02)00109-2] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Semliki Forest virus (SFV), an alphavirus, is a single-stranded positive-sense RNA virus. The RNA genome is surrounded by a protein shell known as the capsid which itself is surrounded by a lipid envelope of host cell origin. In this study, SFV strain L10 enveloped virus and its capsid were immobilised onto silicon wafer supports which had been pre-coated with a monolayer of the relevant anti-viral antibody. After drying, the samples were imaged in air, using non-contact mode atomic force microscopy (AFM). Quantification of the AFM images has revealed that both the strain L10 enveloped virus and capsid collapse when immobilised in this manner. The capsid undergoes more significant collapse compared to the enveloped virus. The dimensions of the immobilised enveloped virus and capsid have been compared to a model where the free spherical particles collapse into ellipsoids during immobilisation. For the immobilised capsid the dimensions are consistent with this model whereas for the enveloped virus the model is less effective. The dimensions of the enveloped virus appear to be affected by the antibody used for immobilisation.
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130
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Wielert-Badt S, Hinterdorfer P, Gruber HJ, Lin JT, Badt D, Wimmer B, Schindler H, Kinne RKH. Single molecule recognition of protein binding epitopes in brush border membranes by force microscopy. Biophys J 2002; 82:2767-74. [PMID: 11964262 PMCID: PMC1302064 DOI: 10.1016/s0006-3495(02)75617-8] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Sidedness and accessibility of protein epitopes in intact brush border membrane vesicles were analyzed by detecting single molecule interaction forces using molecular recognition force microscopy in aqueous physiological solutions. Frequent antibody-antigen recognition events were observed with a force microscopy tip carrying an antibody directed against the periplasmically located gamma-glutamyltrans- peptidase, suggesting a right side out orientation of the vesicles. Phlorizin attached to the tips bound to NA+/D-glucose cotransporter molecules present in the vesicles. The recognition was sodium dependent and inhibited by free phlorizin and D-glucose, and revealed an apparent K(D) of 0.2 microM. Binding events were also observed with an antibody directed against the epitope aa603-aa630 close to the C terminus of the transporter. In the presence of phlorizin the probability of antibody binding was reduced but the most probable unbinding force f(u) = 100 pN remained unchanged. In the presence of D-glucose and sodium, however, both the binding probability and the most probable binding force (f(u) = 50 pN) were lower than in its absence. These studies demonstrate that molecular recognition force microscopy is a versatile tool to probe orientation and conformational changes of epitopes of membrane components during binding and trans-membrane transport.
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Affiliation(s)
- Susanne Wielert-Badt
- Max-Planck-Institute for Molecular Physiology, Department of Epithelial Cell Physiology, 44227 Dortmund, Germany
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131
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Horton M, Charras G, Lehenkari P. Analysis of ligand-receptor interactions in cells by atomic force microscopy. J Recept Signal Transduct Res 2002; 22:169-90. [PMID: 12503614 DOI: 10.1081/rrs-120014594] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
Atomic force microscopy (AFM) increasingly has been used to analyse "receptor" function, either by using purified proteins ("molecular recognition microscopy") or, more recently, in situ in living cells. The latter approach has been enabled by the use of a modified commercial AFM, linked to a confocal microscope, which has allowed adhesion forces between ligands and receptors in cells to be measured and mapped, and downstream cellular responses analysed. We review the application of AFM to cell biology and, in particular, to the study of ligand-receptor interactions and draw examples from our own work and that of others to show the utility of AFM, including for the exploration of cell surface functionalities. We also identify shortcomings of AFM in comparison to "standard" methods, such as receptor auto-radiography or immuno-detection, that are widely applied in cell biology and pharmacological analysis.
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Affiliation(s)
- Michael Horton
- Department of Medicine, University College London, London WC IE 6JJ, UK.
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132
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Tang L, Sun Q, Li Q, Huang Y, Wei Q, Zhang Y, Hu J, Zhang Z, Li M, Yang F. Imaging bacteriorhodopsinlike molecules of claretmembranes from Tibet halobacteria xz515 by atomic force microscope. ACTA ACUST UNITED AC 2001. [DOI: 10.1007/bf02901167] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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133
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Investigation of structural change of purple membrane in storage by transmission electron microscope and atomic force microscope. CHINESE SCIENCE BULLETIN-CHINESE 2001. [DOI: 10.1007/bf02900667] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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134
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Persike N, Pfeiffer M, Guckenberger R, Radmacher M, Fritz M. Direct observation of different surface structures on high-resolution images of native halorhodopsin. J Mol Biol 2001; 310:773-80. [PMID: 11453686 DOI: 10.1006/jmbi.2001.4782] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Halorhodopsin (HR) was investigated with atomic force microscopic techniques (AFM) in aqueous solution. Two-dimensional (2D) crystals of HR were obtained by purifying an HR membrane fraction with the same buoyant density as the purple membrane (HR-PM) from the overexpressing strain Halobacterium salinarum D2. The membrane patches of HR were immobilized on mica. Images with a resolution up to 14 A were recorded. Crystals showed an orthogonal structure and the orientation of the molecules showed p42(1)2 symmetry; thus, alternate tetramers are inverted in the membrane. The crystal surface was found to display different structures depending on the imaging force used, indicating that some parts of the HR molecule are more rigid but others more compressible. From samples with single tetramers missing in the crystalline patches dimensions of the unit cell could be determined. Helix-connecting loops in single molecules of halorhodopsin were assigned. The images indicate that the large extracellular BC loop covers the whole molecule and is very flexible.
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Affiliation(s)
- N Persike
- Physik Department der TU-München, Institut für Biophysik, E22, James-Franck-Str., Garching, 85747, Germany
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135
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Kienberger F, Moser R, Schindler H, Blaas D, Hinterdorfer P. Quasi-crystalline Arrangement of Human Rhinovirus 2 on Model Cell Membranes. ACTA ACUST UNITED AC 2001. [DOI: 10.1002/1438-5171(200107)2:2<99::aid-simo99>3.0.co;2-h] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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136
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Scheuring S, Fotiadis D, Möller C, Müller SA, Engel A, Müller DJ. Single Proteins Observed by Atomic Force Microscopy. ACTA ACUST UNITED AC 2001. [DOI: 10.1002/1438-5171(200107)2:2<59::aid-simo59>3.0.co;2-p] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
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137
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Scheuring S, Reiss-Husson F, Engel A, Rigaud JL, Ranck JL. High-resolution AFM topographs of Rubrivivax gelatinosus light-harvesting complex LH2. EMBO J 2001; 20:3029-35. [PMID: 11406579 PMCID: PMC150200 DOI: 10.1093/emboj/20.12.3029] [Citation(s) in RCA: 103] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2001] [Revised: 04/12/2001] [Accepted: 04/23/2001] [Indexed: 11/13/2022] Open
Abstract
Light-harvesting complexes 2 (LH2) are the accessory antenna proteins in the bacterial photosynthetic apparatus and are built up of alphabeta-heterodimers containing three bacteriochlorophylls and one carotenoid each. We have used atomic force microscopy (AFM) to investigate reconstituted LH2 from Rubrivivax gelatinosus, which has a C-terminal hydrophobic extension of 21 amino acids on the alpha-subunit. High-resolution topographs revealed a nonameric organization of the regularly packed cylindrical complexes incorporated into the membrane in both orientations. Native LH2 showed one surface which protruded by approximately 6 A and one that protruded by approximately 14 A from the membrane. Topographs of samples reconstituted with thermolysin-digested LH2 revealed a height reduction of the strongly protruding surface to approximately 9 A, and a change of its surface appearance. These results suggested that the alpha-subunit of R.gelatinosus comprises a single transmembrane helix and an extrinsic C-terminus, and allowed the periplasmic surface to be assigned. Occasionally, large rings ( approximately 120 A diameter) surrounded by LH2 rings were observed. Their diameter and appearance suggest the large rings to be LH1 complexes.
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Affiliation(s)
| | - Francoise Reiss-Husson
- M.E.Müller Institute for Microscopy at the Biozentrum, University of Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland,
Centre Génétique Moléculaire, UPR-CNRS 2167, 91198 Gif-sur-Yvette Cedex and Institut Curie, UMR-CNRS 168 and LRC-CEA 8, 11 rue Pierre et Marie Curie, 75231 Paris Cedex 05, France Corresponding author e-mail:
| | - Andreas Engel
- M.E.Müller Institute for Microscopy at the Biozentrum, University of Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland,
Centre Génétique Moléculaire, UPR-CNRS 2167, 91198 Gif-sur-Yvette Cedex and Institut Curie, UMR-CNRS 168 and LRC-CEA 8, 11 rue Pierre et Marie Curie, 75231 Paris Cedex 05, France Corresponding author e-mail:
| | - Jean-Louis Rigaud
- M.E.Müller Institute for Microscopy at the Biozentrum, University of Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland,
Centre Génétique Moléculaire, UPR-CNRS 2167, 91198 Gif-sur-Yvette Cedex and Institut Curie, UMR-CNRS 168 and LRC-CEA 8, 11 rue Pierre et Marie Curie, 75231 Paris Cedex 05, France Corresponding author e-mail:
| | - Jean-Luc Ranck
- M.E.Müller Institute for Microscopy at the Biozentrum, University of Basel, Klingelbergstrasse 70, CH-4056 Basel, Switzerland,
Centre Génétique Moléculaire, UPR-CNRS 2167, 91198 Gif-sur-Yvette Cedex and Institut Curie, UMR-CNRS 168 and LRC-CEA 8, 11 rue Pierre et Marie Curie, 75231 Paris Cedex 05, France Corresponding author e-mail:
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138
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Balashev K, Jensen TR, Kjaer K, Bjørnholm T. Novel methods for studying lipids and lipases and their mutual interaction at interfaces. Part I. Atomic force microscopy. Biochimie 2001; 83:387-97. [PMID: 11368846 DOI: 10.1016/s0300-9084(01)01264-0] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Mono-layers of lipids and their interaction with surface active enzymes (lipases) have been studied for more than a century. During the past decade new insight into this area has been obtained due to the development of scanning probe microscopy. This novel method provides direct microscopic information about the system in question and allows in situ investigations under near physiological conditions. In the present review the theory, experimental set-up and sample requirements of atomic force microscopy (AFM) are described. An overview of recent results is also presented with special emphasis on lipase hydrolysis and kinetics investigated in situ using AFM.
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Affiliation(s)
- K Balashev
- Department of Chemistry, University of Copenhagen, Universitetsparken 5, 2100, Copenhagen, Denmark
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139
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Dufrêne YF. Application of atomic force microscopy to microbial surfaces: from reconstituted cell surface layers to living cells. Micron 2001; 32:153-65. [PMID: 10936459 DOI: 10.1016/s0968-4328(99)00106-7] [Citation(s) in RCA: 113] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The application of atomic force microscopy (AFM) to probe the ultrastructure and physical properties of microbial cell surfaces is reviewed. The unique capabilities of AFM can be summarized as follows: imaging surface topography with (sub)nanometer lateral resolution; examining biological specimens under physiological conditions; measuring local properties and interaction forces. AFM is being used increasingly for: (i) visualizing the surface ultrastructure of microbial cell surface layers, including bacterial S-layers, purple membranes, porin OmpF crystals and fungal rodlet layers; (ii) monitoring conformational changes of individual membrane proteins; (iii) examining the morphology of bacterial biofilms, (iv) revealing the nanoscale structure of living microbial cells, including fungi, yeasts and bacteria, (v) mapping interaction forces at microbial surfaces, such as van der Waals and electrostatic forces, solvation forces, and steric/bridging forces; and (vi) probing the local mechanical properties of cell surface layers and of single cells.
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Affiliation(s)
- Y F Dufrêne
- Unité de chimie des interfaces, Université catholique de Louvain, Place Croix du Sud 2/18, 1348 Louvain-la-Neuve, Belgium.
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140
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Rotsch C, Jacobson K, Condeelis J, Radmacher M. EGF-stimulated lamellipod extension in adenocarcinoma cells. Ultramicroscopy 2001; 86:97-106. [PMID: 11215638 DOI: 10.1016/s0304-3991(00)00102-9] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The extension of lamellipodia has been triggered by the application of epidermal growth factor (EGF). We have used an atomic force microscope (AFM) to investigate this lamellipodial extension. During extension we could detect an increase in height from about 500 nm for the stable lamellipodium to typical values of 600-800 nm for the extending lamellipodium. The AFM was also used to determine the mechanical properties of the lamellipodium where we found a decrease of the elastic modulus by a factor of 1.4 at the same location within the same cell. Both findings are consistent with the cortical expansion hypothesis, suggesting that severing of actin filaments, leading to a swelling of the cytoskeleton, generates the protrusive force during lamellipodial extension.
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Affiliation(s)
- C Rotsch
- Lehrstuhl für Angewandte Physik, Ludwig-Maximilians Universität München, Germany
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141
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Changes in the surface structure of purple membrane upon illumination measured by atomic force microscopy. Colloids Surf B Biointerfaces 2000; 19:325-332. [PMID: 11064255 DOI: 10.1016/s0927-7765(00)00141-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Bacteriorhodopsin (BR) patches with a diameter of 1 to 3 µm were investigated in their native state by atomic force microscopy (AFM) in buffer solution. The patches were immobilized deposited and investigated on mica in 150 mM KCl and 10 mM Tris-buffer at pH 8. Under this buffer condition they adsorb preferred with their extracellular side to the solid support mica. The structure of the two-dimensional light adapted crystals was resolved with an imaging force of about 100 pN up to a resolution of 13 Å. The topography of the surface gets smoother if an imaging force of 1000 pN was applied indicating that protruding structures are compressed. Upon illumination with white light, during imaging with a force of 200 pN, the surface structure of the BR lattice changed. The force- and light-induced structural changes were reversible.
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142
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143
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Reviakine I, Bergsma-Schutter W, Mazères-Dubut C, Govorukhina N, Brisson A. Surface topography of the p3 and p6 annexin V crystal forms determined by atomic force microscopy. J Struct Biol 2000; 131:234-9. [PMID: 11052896 DOI: 10.1006/jsbi.2000.4286] [Citation(s) in RCA: 68] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Annexin V is a member of a family of structurally homologous proteins sharing the ability to bind to negatively charged phospholipid membranes in a Ca(2+)-dependent manner. The structure of the soluble form of annexin V has been solved by X-ray crystallography, while electron crystallography of two-dimensional (2D) crystals has been used to reveal the structure of its membrane-bound form. Two 2D crystal forms of annexin V have been reported to date, with either p6 or p3 symmetry. Atomic force microscopy has previously been used to investigate the growth and the topography of the p6 crystal form on supported phospholipid bilayers (Reviakine et al., 1998). The surface structure of the second crystal form, p3, is presented in this study, along with an improved topographic map of the p6 crystal form. The observed topography is correlated with the structure determined by X-ray crystallography.
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Affiliation(s)
- I Reviakine
- Department of Biophysical Chemistry, GBB, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
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144
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Müller DJ, Heymann JB, Oesterhelt F, Möller C, Gaub H, Büldt G, Engel A. Atomic force microscopy of native purple membrane. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1460:27-38. [PMID: 10984588 DOI: 10.1016/s0005-2728(00)00127-4] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Atomic force microscopy (AFM) allows the observation of surface structures of purple membrane (PM) in buffer solution with subnanometer resolution. This offers the possibility to classify the major conformations of the native bacteriorhodopsin (BR) surfaces and to map the variability of individual polypeptide loops connecting transmembrane alpha-helices of BR. The position, the variability and the flexibility of these loops depend on the packing arrangement of BR molecules in the lipid bilayer with significant differences observed between the trigonal and orthorhombic crystal forms. Cleavage of the Schiff base bond leads to a disassembly of the trigonal PM crystal, which is restored by regenerating the bleached PM. The combination of single molecule AFM imaging and single molecule force-spectroscopy provides an unique insight into the interactions between individual BR molecules and the PM, and between secondary structure elements within BR.
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Affiliation(s)
- D J Müller
- M.E. Müller-Institute for Structural Biology, Biozentrum, University of Basel, Klingelkbergstr. 70, CH-4056 Basel, Switzerland.
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145
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Schwesinger F, Ros R, Strunz T, Anselmetti D, Güntherodt HJ, Honegger A, Jermutus L, Tiefenauer L, Pluckthun A. Unbinding forces of single antibody-antigen complexes correlate with their thermal dissociation rates. Proc Natl Acad Sci U S A 2000; 97:9972-7. [PMID: 10963664 PMCID: PMC27642 DOI: 10.1073/pnas.97.18.9972] [Citation(s) in RCA: 290] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2000] [Accepted: 06/16/2000] [Indexed: 11/18/2022] Open
Abstract
Point mutants of three unrelated antifluorescein antibodies were constructed to obtain nine different single-chain Fv fragments, whose on-rates, off-rates, and equilibrium binding affinities were determined in solution. Additionally, activation energies for unbinding were estimated from the temperature dependence of the off-rate in solution. Loading rate-dependent unbinding forces were determined for single molecules by atomic force microscopy, which extrapolated at zero force to a value close to the off-rate measured in solution, without any indication for multiple transition states. The measured unbinding forces of all nine mutants correlated well with the off-rate in solution, but not with the temperature dependence of the reaction, indicating that the same transition state must be crossed in spontaneous and forced unbinding and that the unbinding path under load cannot be too different from the one at zero force. The distance of the transition state from the ground state along the unbinding pathway is directly proportional to the barrier height, regardless of the details of the binding site, which most likely reflects the elasticity of the protein in the unbinding process. Atomic force microscopy thus can be a valuable tool for the characterization of solution properties of protein-ligand systems at the single molecule level, predicting relative off-rates, potentially of great value for combinatorial chemistry and biology.
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Affiliation(s)
- F Schwesinger
- Biochemisches Institut, Universität Zürich, CH-8057 Zürich, Switzerland
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146
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Möller C, Büldt G, Dencher NA, Engel A, Müller DJ. Reversible loss of crystallinity on photobleaching purple membrane in the presence of hydroxylamine. J Mol Biol 2000; 301:869-79. [PMID: 10966792 DOI: 10.1006/jmbi.2000.3995] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Structural changes of purple membrane during photobleaching in the presence of hydroxylamine were monitored using atomic force microscopy (AFM). The process of bleaching was associated with the disassembly of the purple membrane crystal into smaller crystals. Imaging steps of the photobleaching progress showed that disassembly proceeds until the sample is fully bleached and its crystallinity is almost lost. As revealed from high resolution AFM topographs, the loss of crystallinity was initiated by loss of lattice forming contact between the individual bacteriorhodopsin trimers. The bacteriorhodopsin molecules, however, remained assembled into trimers during the entire photobleaching process. Regeneration of the photobleached sample into intact purple membrane resulted in the reassembly of the bacteriorhodopsin trimers into the trigonal lattice of purple membrane. The data provide novel insights into factors triggering purple membrane formation and structure.
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Affiliation(s)
- C Möller
- M. E. Müller Institute for Structural Biology, Biozentrum, Klingelbergstr. 70, Basel, CH-4056, Switzerland
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147
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Baumgartner W, Hinterdorfer P, Ness W, Raab A, Vestweber D, Schindler H, Drenckhahn D. Cadherin interaction probed by atomic force microscopy. Proc Natl Acad Sci U S A 2000; 97:4005-10. [PMID: 10759550 PMCID: PMC18132 DOI: 10.1073/pnas.070052697] [Citation(s) in RCA: 355] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Single molecule atomic force microscopy was used to characterize structure, binding strength (unbinding force), and binding kinetics of a classical cadherin, vascular endothelial (VE)-cadherin, secreted by transfected Chinese hamster ovary cells as cis-dimerized full-length external domain fused to Fc-portion of human IgG. In physiological buffer, the external domain of VE-cadherin dimers is a approximately 20-nm-long rod-shaped molecule that collapses and dissociates into monomers (V-shaped structures) in the absence of Ca(2+). Trans-interaction of dimers is a low-affinity reaction (K(D) = 10(-3)-10(-5) M, k(off) = 1.8 s(-1), k(on) = 10(3)-10(5) M(-1) x s(-1)) with relatively low unbinding force (35-55 pN at retrace velocities of 200-4,000 nm x s(-1)). Higher order unbinding forces, that increase with interaction time, indicate association of cadherins into complexes with cumulative binding strength. These observations favor a model by which the inherently weak unit binding strength and affinity of cadherin trans-interaction requires clustering and cytoskeletal immobilization for amplification. Binding is regulated by low-affinity Ca(2+) binding sites (K(D) = 1.15 mM) with high cooperativity (Hill coefficient of 5.04). Local changes of free extracellular Ca(2+) in the narrow intercellular space may be of physiological importance to facilitate rapid remodeling of intercellular adhesion and communication.
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Affiliation(s)
- W Baumgartner
- Institute of Anatomy, University of Würzburg, Koellikerstrasse 6, D-97070 Würzburg, Germany
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148
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Affiliation(s)
- J G Forbes
- Department of Chemistry and Biochemistry, University of Maryland, College Park, MD 20742-2021, USA.
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149
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Abstract
Molecular recognition force microscopy (MRFM) using the magnetic AC mode (MAC mode) atomic force microscope (AFM) was recently investigated to locate and probe recognition sites. A flexible crosslinker carrying a ligand is bound to the tip for the molecular recognition of receptors on the surface of a sample. In this report, the driving frequency is calculated which optimizes the sensitivity (S). The sensitivity of MRFM is defined as the relative change of the magnetically excited cantilever deflection amplitude arising from a crosslinker/antibody/antigen connection that is characterized by a very small force constant. The sensitivity is calculated in a damped oscillator model with a certain value of quality factor Q, which, together with load, defines the frequency response (unloaded oscillator shows resonance at Q > 0.707). If Q < 1, the greatest value of S corresponds to zero driving frequency omega (measured in units of eigenfrequency). Therefore, for Q < 1, MAC-mode has no advantage in comparison with DC-mode. Two additional extremes are found at omegaL = (1 - 1/Q)(1/2) and omegaR = (1 + 1/Q)(1/2), with corresponding sensitivities S(L) = Q2/(2Q - 1), S(R) = Q2/(2Q + 1). The L-extreme exists only for Q > 1, and then S(L) > S(R), i.e. the L-extreme is the main one. For Q > 1, S(L) > 1, and for Q > 2.41, S(R) > 1. These are the critical Q-values, above which selecting driving frequency equal to sigmaL or sigmaR brings advantage to MAC mode vs. DC mode. Satisfactory quality of the oscillator model is demonstrated by comparison of some results with those calculated within the classical description of cantilevers.
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150
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Abstract
The force-distance cycle mode of the atomic force microscope (AFM) allows for detection of interaction forces between the AFM-tip and a substrate (probe). This can either be a direct tip-sample interaction or an interaction between molecules coupled to the tip and probe, respectively. The interaction forces are typically in the range of a few pN to some hundred pN. In this article we describe algorithms for the analysis of force-distance cycles, to quantify interaction forces between tip and probe. Both, the direct tip-probe interaction as well as the interaction between specifically bound molecules are analyzed. The molecules bound to tip and probe have to be either long and flexible or have to be bound via a flexible cross linker. The algorithms are exemplified on direct tip-probe interactions and on unbinding events of cadherins which are bound via PEG-spacers to the AFM-tip and to the probe.
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