1
|
Lata K, Charles S, Mangala Prasad V. Advances in computational approaches to structure determination of alphaviruses and flaviviruses using cryo-electron microscopy. J Struct Biol 2023; 215:107993. [PMID: 37414374 DOI: 10.1016/j.jsb.2023.107993] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2023] [Revised: 05/15/2023] [Accepted: 07/03/2023] [Indexed: 07/08/2023]
Abstract
Advancements in the field of cryo-electron microscopy (cryo-EM) have greatly contributed to our current understanding of virus structures and life cycles. In this review, we discuss the application of single particle cryo-electron microscopy (EM) for the structure elucidation of small enveloped icosahedral viruses, namely, alpha- and flaviviruses. We focus on technical advances in cryo-EM data collection, image processing, three-dimensional reconstruction, and refinement strategies for obtaining high-resolution structures of these viruses. Each of these developments enabled new insights into the alpha- and flavivirus architecture, leading to a better understanding of their biology, pathogenesis, immune response, immunogen design, and therapeutic development.
Collapse
Affiliation(s)
- Kiran Lata
- Molecular Biophysics Unit, Indian Institute of Science, Bengaluru, Karnataka 560012, India
| | - Sylvia Charles
- Molecular Biophysics Unit, Indian Institute of Science, Bengaluru, Karnataka 560012, India
| | - Vidya Mangala Prasad
- Molecular Biophysics Unit, Indian Institute of Science, Bengaluru, Karnataka 560012, India; Center for Infectious Disease Research, Indian Institute of Science, Bengaluru, Karnataka 560012, India
| |
Collapse
|
2
|
Hettler S, Arenal R. Comparative image simulations for phase-plate transmission electron microscopy. Ultramicroscopy 2021; 227:113319. [PMID: 34024662 DOI: 10.1016/j.ultramic.2021.113319] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2021] [Revised: 04/27/2021] [Accepted: 05/09/2021] [Indexed: 11/19/2022]
Abstract
Numerous physical phase plates (PP) for phase-contrast enhancement in transmission electron microscopy (TEM) have been proposed and studied with the hole-free or Volta PP having a high impact and interest in recent years. This study is concerned with comparative TEM image simulations considering realistic descriptions of various PP approaches and samples from three different fields of application covering a large range of object sizes. The simulated images provide an illustrative characterization of the typical image appearance and common artifacts of the different PPs and the influence of simulation parameters especially important for PP simulations. A quantitative contrast analysis shows the superior phase-shifting properties of the hole-free phase plate for biological applications and the benefits of adjustable phase plates. The application of PPs in high-resolution TEM imaging, especially of weak-phase objects such as (atomically thin) 2D materials, is shown to increase image interpretability. The software with graphical user interface written and used for the presented simulations is available for free usage.
Collapse
Affiliation(s)
- Simon Hettler
- Laboratorio de Microscopías Avanzadas (LMA), Universidad de Zaragoza, Zaragoza, Spain.
| | - Raul Arenal
- Laboratorio de Microscopías Avanzadas (LMA), Universidad de Zaragoza, Zaragoza, Spain; Instituto de Nanociencia y Materiales de Aragón (INMA), CSIC-Universidad de Zaragoza, Zaragoza, Spain; ARAID Foundation, Zaragoza, Spain
| |
Collapse
|
3
|
Gilbert RJC. Electron microscopy as a critical tool in the determination of pore forming mechanisms in proteins. Methods Enzymol 2021; 649:71-102. [PMID: 33712203 DOI: 10.1016/bs.mie.2021.01.034] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Electron microscopy has consistently played an important role in the description of pore-forming protein systems. The discovery of pore-forming proteins has depended on visualization of the structural pores formed by their oligomeric protein complexes, and as electron microscopy has advanced technologically so has the degree of insight it has been able to give. This review considers a large number of published studies of pore-forming complexes in prepore and pore states determined using single-particle cryo-electron microscopy. Sample isolation and preparation, imaging and image analysis, structure determination and optimization of results are all discussed alongside challenges which pore-forming proteins particularly present. The review also considers the use made of cryo-electron tomography to study pores within their membrane environment and which will prove an increasingly important approach for the future.
Collapse
Affiliation(s)
- Robert J C Gilbert
- Division of Structural Biology, Wellcome Centre for Human Genetics, University of Oxford, Oxford, United Kingdom.
| |
Collapse
|
4
|
Malac M, Hettler S, Hayashida M, Kano E, Egerton RF, Beleggia M. Phase plates in the transmission electron microscope: operating principles and applications. Microscopy (Oxf) 2020; 70:75-115. [DOI: 10.1093/jmicro/dfaa070] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2020] [Revised: 10/30/2020] [Accepted: 12/11/2020] [Indexed: 01/19/2023] Open
Abstract
Abstract
In this paper, we review the current state of phase plate imaging in a transmission electron microscope. We focus especially on the hole-free phase plate design, also referred to as the Volta phase plate. We discuss the implementation, operating principles and applications of phase plate imaging. We provide an imaging theory that accounts for inelastic scattering in both the sample and in the hole-free phase plate.
Collapse
Affiliation(s)
- Marek Malac
- NRC-NANO, National Research Council, 11421 Saskatchewan Drive, Edmonton, Alberta T6G 2M9, Canada
- Department of Physics, University of Alberta, Edmonton, Alberta T6G 2E1, Canada
| | - Simon Hettler
- Laboratorio de Microscopías Avanzadas (LMA), Instituto de Nanociencia y Materiales de Aragon (INMA), Universidad de Zaragoza, Campus Río Ebro, 50018 Zaragoza, España
| | - Misa Hayashida
- NRC-NANO, National Research Council, 11421 Saskatchewan Drive, Edmonton, Alberta T6G 2M9, Canada
| | - Emi Kano
- Institute of Materials and Systems for Sustainability, Nagoya University, Nagoya, Aichi 464-8601, Japan
| | - Ray F Egerton
- Department of Physics, University of Alberta, Edmonton, Alberta T6G 2E1, Canada
| | - Marco Beleggia
- DTU Nanolab, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark
| |
Collapse
|
5
|
Verbeeck J, Béché A, Müller-Caspary K, Guzzinati G, Luong MA, Den Hertog M. Demonstration of a 2 × 2 programmable phase plate for electrons. Ultramicroscopy 2018; 190:58-65. [DOI: 10.1016/j.ultramic.2018.03.017] [Citation(s) in RCA: 59] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2017] [Revised: 03/16/2018] [Accepted: 03/24/2018] [Indexed: 02/03/2023]
|
6
|
Dries M, Hettler S, Schulze T, Send W, Müller E, Schneider R, Gerthsen D, Luo Y, Samwer K. Thin-Film Phase Plates for Transmission Electron Microscopy Fabricated from Metallic Glasses. MICROSCOPY AND MICROANALYSIS : THE OFFICIAL JOURNAL OF MICROSCOPY SOCIETY OF AMERICA, MICROBEAM ANALYSIS SOCIETY, MICROSCOPICAL SOCIETY OF CANADA 2016; 22:955-963. [PMID: 27681223 DOI: 10.1017/s143192761601165x] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Thin-film phase plates (PPs) have become an interesting tool to enhance the contrast of weak-phase objects in transmission electron microscopy (TEM). The thin film usually consists of amorphous carbon, which suffers from quick degeneration under the intense electron-beam illumination. Recent investigations have focused on the search for alternative materials with an improved material stability. This work presents thin-film PPs fabricated from metallic glass alloys, which are characterized by a high electrical conductivity and an amorphous structure. Thin films of the zirconium-based alloy Zr65.0Al7.5Cu27.5 (ZAC) were fabricated and their phase-shifting properties were evaluated. The ZAC film was investigated by different TEM techniques, which reveal beneficial properties compared with amorphous carbon PPs. Particularly favorable is the small probability for inelastic plasmon scattering, which results from the combined effect of a moderate inelastic mean free path and a reduced film thickness due to a high mean inner potential. Small probability plasmon scattering improves contrast transfer at high spatial frequencies, which makes the ZAC alloy a promising material for PP fabrication.
Collapse
Affiliation(s)
- Manuel Dries
- 1Laboratorium für Elektronenmikroskopie (LEM),Karlsruher Institut für Technologie (KIT),Engesserstraße 7,D-76131 Karlsruhe,Germany
| | - Simon Hettler
- 1Laboratorium für Elektronenmikroskopie (LEM),Karlsruher Institut für Technologie (KIT),Engesserstraße 7,D-76131 Karlsruhe,Germany
| | - Tina Schulze
- 1Laboratorium für Elektronenmikroskopie (LEM),Karlsruher Institut für Technologie (KIT),Engesserstraße 7,D-76131 Karlsruhe,Germany
| | - Winfried Send
- 1Laboratorium für Elektronenmikroskopie (LEM),Karlsruher Institut für Technologie (KIT),Engesserstraße 7,D-76131 Karlsruhe,Germany
| | - Erich Müller
- 1Laboratorium für Elektronenmikroskopie (LEM),Karlsruher Institut für Technologie (KIT),Engesserstraße 7,D-76131 Karlsruhe,Germany
| | - Reinhard Schneider
- 1Laboratorium für Elektronenmikroskopie (LEM),Karlsruher Institut für Technologie (KIT),Engesserstraße 7,D-76131 Karlsruhe,Germany
| | - Dagmar Gerthsen
- 1Laboratorium für Elektronenmikroskopie (LEM),Karlsruher Institut für Technologie (KIT),Engesserstraße 7,D-76131 Karlsruhe,Germany
| | - Yuansu Luo
- 2I. Physikalisches Institut,Universität Göttingen,Friedrich-Hund-Platz 1,D-37077 Göttingen,Germany
| | - Konrad Samwer
- 2I. Physikalisches Institut,Universität Göttingen,Friedrich-Hund-Platz 1,D-37077 Göttingen,Germany
| |
Collapse
|
7
|
Rhinow D. Towards an optimum design for thin film phase plates. Ultramicroscopy 2016; 160:1-6. [DOI: 10.1016/j.ultramic.2015.09.003] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2014] [Revised: 08/27/2015] [Accepted: 09/03/2015] [Indexed: 01/18/2023]
|
8
|
Hettler S, Wagner J, Dries M, Oster M, Wacker C, Schröder RR, Gerthsen D. On the role of inelastic scattering in phase-plate transmission electron microscopy. Ultramicroscopy 2015; 155:27-41. [DOI: 10.1016/j.ultramic.2015.04.001] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2014] [Revised: 03/02/2015] [Accepted: 04/01/2015] [Indexed: 01/22/2023]
|
9
|
Towards an optimum design for electrostatic phase plates. Ultramicroscopy 2015; 153:22-31. [PMID: 25697462 DOI: 10.1016/j.ultramic.2015.01.005] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2014] [Revised: 01/21/2015] [Accepted: 01/31/2015] [Indexed: 11/20/2022]
Abstract
Charging of physical phase plates is a problem that has prevented their routine use in transmission electron microscopy of weak-phase objects. In theory, electrostatic phase plates are superior to thin-film phase plates since they do not attenuate the scattered electron beam and allow freely adjustable phase shifts. Electrostatic phase plates consist of multiple layers of conductive and insulating materials, and are thus more prone to charging than thin-film phase plates, which typically consist of only one single layer of amorphous material. We have addressed the origins of charging of Boersch phase plates and show how it can be reduced. In particular, we have performed simulations and experiments to analyze the influence of the insulating Si3N4 layers and surface charges on electrostatic charging. To optimize the performance of electrostatic phase plates, it would be desirable to fabricate electrostatic phase plates, which (i) impart a homogeneous phase shift to the unscattered electrons, (ii) have a low cut-on frequency, (iii) expose as little material to the intense unscattered beam as possible, and (iv) can be additionally polished by a focused ion-beam instrument to eliminate carbon contamination accumulated during exposure to the unscattered electron beam (Walter et al., 2012, Ultramicroscopy, 116, 62-72). We propose a new type of electrostatic phase plate that meets the above requirements and would be superior to a Boersch phase plate. It consists of three free-standing coaxial rods converging in the center of an aperture (3-fold coaxial phase plate). Simulations and preliminary experiments with modified Boersch phase plates indicate that the fabrication of a 3-fold coaxial phase plate is feasible.
Collapse
|
10
|
Fu X, Himes BA, Ke D, Rice WJ, Ning J, Zhang P. Controlled bacterial lysis for electron tomography of native cell membranes. Structure 2014; 22:1875-1882. [PMID: 25456413 DOI: 10.1016/j.str.2014.09.017] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2014] [Revised: 09/22/2014] [Accepted: 09/27/2014] [Indexed: 11/16/2022]
Abstract
Cryo-electron tomography (cryoET) has become a powerful tool for direct visualization of 3D structures of native biological specimens at molecular resolution, but its application is limited to thin specimens (<300 nm). Recently, vitreous sectioning and cryoFIB milling technologies were developed to physically reduce the specimen thickness; however, cryoET analysis of membrane protein complexes within native cell membranes remains a great challenge. Here, we use phage ΦX174 lysis gene E to rapidly produce native, intact, bacterial cell membranes for high resolution cryoET. We characterized E gene-induced cell lysis using FIB/SEM and cryoEM and showed that the bacteria cytoplasm was largely depleted through spot lesion, producing ghosts with the cell membranes intact. We further demonstrated the utility of E-gene-induced lysis for cryoET using the bacterial chemotaxis receptor signaling complex array. The described method should have a broad application for structural and functional studies of native, intact cell membranes and membrane protein complexes.
Collapse
Affiliation(s)
- Xiaofeng Fu
- Department of Structural Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260, USA
| | - Benjamin A Himes
- Department of Structural Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260, USA
| | - Danxia Ke
- Department of Structural Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260, USA
| | - William J Rice
- New York Structural Biology Center, 89 Convent Avenue, New York, NY 10027, USA
| | - Jiying Ning
- Department of Structural Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260, USA
| | - Peijun Zhang
- Department of Structural Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15260, USA; Department of Mechanical Engineering and Materials Science, Swanson School of Engineering, University of Pittsburgh, Pittsburgh, PA 15260, USA.
| |
Collapse
|
11
|
Zernike phase-contrast electron cryotomography applied to marine cyanobacteria infected with cyanophages. Nat Protoc 2014; 9:2630-42. [PMID: 25321408 DOI: 10.1038/nprot.2014.176] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Advances in electron cryotomography have provided new opportunities to visualize the internal 3D structures of a bacterium. An electron microscope equipped with Zernike phase-contrast optics produces images with markedly increased contrast compared with images obtained by conventional electron microscopy. Here we describe a protocol to apply Zernike phase plate technology for acquiring electron tomographic tilt series of cyanophage-infected cyanobacterial cells embedded in ice, without staining or chemical fixation. We detail the procedures for aligning and assessing phase plates for data collection, and methods for obtaining 3D structures of cyanophage assembly intermediates in the host by subtomogram alignment, classification and averaging. Acquiring three or four tomographic tilt series takes ∼12 h on a JEM2200FS electron microscope. We expect this time requirement to decrease substantially as the technique matures. The time required for annotation and subtomogram averaging varies widely depending on the project goals and data volume.
Collapse
|
12
|
Glaeser RM. Invited review article: Methods for imaging weak-phase objects in electron microscopy. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2013; 84:111101. [PMID: 24289381 PMCID: PMC3855062 DOI: 10.1063/1.4830355] [Citation(s) in RCA: 62] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/05/2013] [Accepted: 10/26/2013] [Indexed: 05/21/2023]
Abstract
Contrast has traditionally been produced in electron-microscopy of weak phase objects by simply defocusing the objective lens. There now is renewed interest, however, in using devices that apply a uniform quarter-wave phase shift to the scattered electrons relative to the unscattered beam, or that generate in-focus image contrast in some other way. Renewed activity in making an electron-optical equivalent of the familiar "phase-contrast" light microscope is based in part on the improved possibilities that are now available for device microfabrication. There is also a better understanding that it is important to take full advantage of contrast that can be had at low spatial frequency when imaging large, macromolecular objects. In addition, a number of conceptually new phase-plate designs have been proposed, thus increasing the number of options that are available for development. The advantages, disadvantages, and current status of each of these options is now compared and contrasted. Experimental results that are, indeed, superior to what can be accomplished with defocus-based phase contrast have been obtained recently with two different designs of phase-contrast aperture. Nevertheless, extensive work also has shown that fabrication of such devices is inconsistent, and that their working lifetime is short. The main limitation, in fact, appears to be electrostatic charging of any device that is placed into the electron diffraction pattern. The challenge in fabricating phase plates that are practical to use for routine work in electron microscopy thus may be more in the area of materials science than in the area of electron optics.
Collapse
Affiliation(s)
- Robert M Glaeser
- Life Sciences Division, Lawrence Berkeley National Laboratory, University of California, Berkeley, California 94720, USA
| |
Collapse
|
13
|
Haigh S, Jiang B, Alloyeau D, Kisielowski C, Kirkland A. Recording low and high spatial frequencies in exit wave reconstructions. Ultramicroscopy 2013; 133:26-34. [DOI: 10.1016/j.ultramic.2013.04.012] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2013] [Revised: 04/18/2013] [Accepted: 04/30/2013] [Indexed: 10/26/2022]
|
14
|
Blackburn AM, Loudon JC. Vortex beam production and contrast enhancement from a magnetic spiral phase plate. Ultramicroscopy 2013; 136:127-43. [PMID: 24128851 DOI: 10.1016/j.ultramic.2013.08.009] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2013] [Revised: 08/15/2013] [Accepted: 08/22/2013] [Indexed: 10/26/2022]
Abstract
Electron vortex beam probes offer the possibility of mapping magnetic moments with atomic resolution. In this work we consider using the stray magnetic field produced from a narrow ferromagnetic rod magnetised along its long axis to produce a vortex beam probe, as an alternative to the currently used holographic apertures or gratings. We show through numerical modelling, electron holography observations and direct imaging of the electron probe, that a long narrow ferromagnetic rod induces a phase shift in the wave-function of passing electrons that approximately describes a helix in the regions near its ends. Directing this rod towards the optical axis of a charged-particle beam probe forming system at a limiting aperture position, with the free-end sufficiently close to the axis, is shown to offer a point spread function composed of vortex modes, with evidence of this appearing in observations of the electron probe formed from inserting a micro-fabricated CoFe rod into the beam path of a 300 keV transmission electron microscope (TEM). If the rod is arranged to contain the magnetic flux of h/e, thus producing a maximum phase shift of 2π, it produces a simple spiral-like phase contrast transfer function for weak phase objects. In this arrangement the ferromagnetic rod can be used as a phase plate, positioned at the objective aperture position of a TEM, yielding enhanced image contrast which is simulated to be intermediate between comparable Zernike and Hilbert phase plates. Though this aspect of the phase plate performance is not demonstrated here, agreement between our observations and models for the probe formed from an example rod containing a magnetic flux of ~2.35h/e, indicate this phase plate arrangement could be a simple means of enhancing contrast and gaining additional information from TEM imaged weak phase samples, while also offering the capability to produce vortex beam probes. However, steps still need to be taken to either remove or improve the support membrane for the rod in our experiments to reduce any effects from charging in the phase plate.
Collapse
Affiliation(s)
- A M Blackburn
- Hitachi Cambridge Laboratory, Cavendish Laboratory, J. J. Thomson Ave., Cambridge CB3 0HE, United Kingdom.
| | | |
Collapse
|
15
|
Methods for testing Zernike phase plates and a report on silicon-based phase plates with reduced charging and improved ageing characteristics. J Struct Biol 2013; 184:237-44. [PMID: 23994351 DOI: 10.1016/j.jsb.2013.08.008] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2013] [Revised: 08/16/2013] [Accepted: 08/19/2013] [Indexed: 11/21/2022]
Abstract
Imaging with Zernike phase plates is increasingly being used in cryo-TEM tomography and cryo-EM single-particle applications. However, rapid ageing of the phase plates, together with the cost and effort in producing them, present serious obstacles to widespread adoption. We are experimenting with phase plates based on silicon chips that have thin windows; such phase plates could be mass-produced and made available at moderate cost. The windows are coated with conductive layers to reduce charging, and this considerably extends the useful life of the phase plates compared to traditional pure-carbon phase plates. However, a compromise must be reached between robustness and transmission through the phase-plate film. Details are given on testing phase-plate performance by means of imaging an amorphous thin film and evaluating the power spectra of the images.
Collapse
|
16
|
Kuo PC, Chen IH, Chen CT, Lee KP, Chen CW, Lin CC, Chiu SWY, Hsieh YF, Wang YL, Shiue J. On-chip thin film Zernike phase plate for in-focus transmission electron microscopy imaging of organic materials. ACS NANO 2013; 7:465-470. [PMID: 23268656 DOI: 10.1021/nn304511p] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
Transmission electron microscopy (TEM) is a powerful tool for imaging nanostructures, yet its capability is limited with respect to the imaging of organic materials because of the intrinsic low contrast problem. TEM phase plates have been in development for decades, yet a reliable phase plate technique has not been available because the performance of TEM phase plates deteriorates too quickly. Such an obstacle prohibits in-focus TEM phase imaging to be routinely achievable, thus limiting the technique being used in practical applications. Here we present an on-chip thin film Zernike phase plate which can effectively release charging and allow reliable in-focus TEM images of organic materials with enhanced contrast to be routinely obtained. With this stable system, we were able to characterize many polymer solar cell specimens and consequently identified and verified the existence of an unexpected nanoparticle phase. Furthermore, we were also able to observe the fine structures of an Escherichia coli specimen, without staining, using this on-chip thin film phase plate. Our system, which can be installed on a commercial TEM, opens up exciting possibilities for TEM to characterize organic materials.
Collapse
Affiliation(s)
- Pai-Chia Kuo
- Department of Materials Science and Engineering, National Taiwan University, Taipei 106, Taiwan
| | | | | | | | | | | | | | | | | | | |
Collapse
|
17
|
Scheres SHW. RELION: implementation of a Bayesian approach to cryo-EM structure determination. J Struct Biol 2012; 180:519-30. [PMID: 23000701 PMCID: PMC3690530 DOI: 10.1016/j.jsb.2012.09.006] [Citation(s) in RCA: 3647] [Impact Index Per Article: 303.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2012] [Revised: 09/03/2012] [Accepted: 09/06/2012] [Indexed: 11/17/2022]
Abstract
RELION, for REgularized LIkelihood OptimizatioN, is an open-source computer program for the refinement of macromolecular structures by single-particle analysis of electron cryo-microscopy (cryo-EM) data. Whereas alternative approaches often rely on user expertise for the tuning of parameters, RELION uses a Bayesian approach to infer parameters of a statistical model from the data. This paper describes developments that reduce the computational costs of the underlying maximum a posteriori (MAP) algorithm, as well as statistical considerations that yield new insights into the accuracy with which the relative orientations of individual particles may be determined. A so-called gold-standard Fourier shell correlation (FSC) procedure to prevent overfitting is also described. The resulting implementation yields high-quality reconstructions and reliable resolution estimates with minimal user intervention and at acceptable computational costs.
Collapse
Affiliation(s)
- Sjors H W Scheres
- MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 0QH, UK.
| |
Collapse
|
18
|
Walter A, Muzik H, Vieker H, Turchanin A, Beyer A, Gölzhäuser A, Lacher M, Steltenkamp S, Schmitz S, Holik P, Kühlbrandt W, Rhinow D. Practical aspects of Boersch phase contrast electron microscopy of biological specimens. Ultramicroscopy 2012; 116:62-72. [PMID: 22537744 DOI: 10.1016/j.ultramic.2012.03.009] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2011] [Revised: 03/07/2012] [Accepted: 03/10/2012] [Indexed: 10/28/2022]
Abstract
Implementation of physical phase plates into transmission electron microscopes to achieve in-focus contrast for ice-embedded biological specimens poses several technological challenges. During the last decade several phase plates designs have been introduced and tested for electron cryo-microscopy (cryoEM), including thin film (Zernike) phase plates and electrostatic devices. Boersch phase plates (BPPs) are electrostatic einzel lenses shifting the phase of the unscattered beam by an arbitrary angle. Adjusting the phase shift to 90° achieves the maximum contrast transfer for phase objects such as biomolecules. Recently, we reported the implementation of a BPP into a dedicated phase contrast aberration-corrected electron microscope (PACEM) and demonstrated its use to generate in-focus contrast of frozen-hydrated specimens. However, a number of obstacles need to be overcome before BPPs can be used routinely, mostly related to the phase plate devices themselves. CryoEM with a physical phase plate is affected by electrostatic charging, obliteration of low spatial frequencies, and mechanical drift. Furthermore, BPPs introduce single sideband contrast (SSB), due to the obstruction of Friedel mates in the diffraction pattern. In this study we address the technical obstacles in detail and show how they may be overcome. We use X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) to identify contaminants responsible for electrostatic charging, which occurs with most phase plates. We demonstrate that obstruction of low-resolution features is significantly reduced by lowering the acceleration voltage of the microscope. Finally, we present computational approaches to correct BPP images for SSB contrast and to compensate for mechanical drift of the BPP.
Collapse
Affiliation(s)
- Andreas Walter
- Max-Planck-Institute of Biophysics, Department of Structural Biology, Max-von-Laue-Str. 3, D-60439 Frankfurt, Germany
| | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|