Crystal Packing of E.Coli Porin (Matrix Protein)

1981 ◽  
Vol 39 ◽  
pp. 42-43
Author(s):  
D.L. Dorset ◽  
A. Engel ◽  
R.M. Garavito ◽  
J.P. Rosenbusch
Keyword(s):  
Lipid Membranes ◽  
Matrix Protein ◽  
Crystal Packing ◽  
High Resolution Electron Microscopy ◽  
Strong Interactions ◽  
Electrical Measurements ◽  
Structure Packing ◽  
Negative Stain ◽  
Resolution Electron ◽  
Plane Group

Porin, a pore-forming protein spanning the outer membrane of E. coli (MW 36,500) has been isolated in homogeneous form after extraction in detergent. Electrical measurements on planar lipid membranes containing this protein indicate that it may be regarded as a paradigm of pore-forming transmembrane proteins. Therefore, a structural elucidation appears to be useful for correlating the pore geometry with the electrical measurements.Extraction of cells with ionic detergents, with or without removal of the peptidoglycan layer, has been monitored by Steven et al. using high resolution electron microscopy. Optical and computer reconstructions of the images indicated a trimeric structure packing in plane group p3 (a = 77 Å). Three dense patches of negative stain were tentatively assigned to the pores, an arrangement corroborated later by strong interactions among triplet channels observed in the conductance studies.

Structure and composition in the superconductive Bi–Sr–Ca–Cu–O system

1988 ◽  
Vol 3 (6) ◽  
pp. 1317-1326 ◽  
Author(s):  
A. H. Carim ◽  
A. P. M. Kentgens ◽  
J. H. T. Hengst ◽  
D. M. de Leeuw ◽  
C. A. H. A. Mutsaers
Keyword(s):  
High Resolution ◽  
High Resolution Electron Microscopy ◽  
Chemical Compositions ◽  
X Ray Diffraction ◽  
Electrical Measurements ◽  
Modulated Structure ◽  
Multiphase Materials ◽  
Resolution Electron ◽  
Diffraction Patterns

Characterization of superconducting Bi–Sr–Ca–Cu oxides has been carried out by electrical measurements, x-ray diffraction, conventional and high-resolution electron microscopy, and electron microprobe analysis. Nominal starting compositions with cation ratios of 1:1:1:2 and 2:2:1:2 show considerably different superconducting behavior. In both cases multiphase materials are formed. The predominant superconducting phase occurs as thin platelets with an orthorhombic, modulated structure. These particles often have edges aligned along [110], [100], and [010] directions and contain subgrain boundaries. Electron diffraction patterns and high-resolution micrographs taken along several zone axes are consistent with an incommensurate centered modulation along the b axis with a magnitude of 4.7 ± 0.1 times b. Unexpectedly, two distinct chemical compositions were found in platelets with the same apparent structure: Bi4Sr3Ca3Cu4O16±δ for the lower Tc phase in the 1:1:1:2 material, and Bi2Sr2CaCu2O8±δ for the isomorphic higher Tc phase present in the 2:2:1:2 samples.

How Epitaxial Are Pd2Si–Si Interfaces?

1982 ◽  
Vol 18 ◽  
Author(s):  
Z. Liliental ◽  
R. W. Carpenter ◽  
R. Tuenge
Keyword(s):  
Energy Loss ◽  
High Resolution Electron Microscopy ◽  
Auger Spectroscopy ◽  
Interface Roughness ◽  
Silicon Substrates ◽  
Electrical Measurements ◽  
X Ray ◽  
Carrier Recombination ◽  
Resolution Electron ◽  
Fluorescence Energy

Pd2Si layers produced by evaporation or sputtering onto silicon substrates were examined by high resolution electron microscopy, microdiffraction, X-ray, energy loss and Auger spectroscopy. The Si-Pd2Si interfaces produced by evaporation were in all cases rougher and more polycrystalline than those produced by sputtering. X-ray microanalysis showed the predictable variation in palladium distribution across the interface but quantification did not produce the expected palladium–to–silicon ratios, primarily because of probe broadening and X-rayinduced fluorescence. Energy loss spectra showed plasmon energy shifts and changes in Si L edge shape due to bond formation with palladium. Auger data provided evidence for a small amount of oxygen at the Si-Pd2Si interface. Electrical measurements of the ideality factor for Schottky barriers made from these materials produced higher values for the rougher evaporation-formed interfaces consistent with interface-roughness-induced scattering and carrier recombination.

scholarly journals Yeast pex1 cells contain peroxisomal ghosts that import matrix proteins upon reintroduction of Pex1

2015 ◽  
Vol 211 (5) ◽  
pp. 955-962 ◽  
Author(s):  
Kèvin Knoops ◽  
Rinse de Boer ◽  
Anita Kram ◽  
Ida J. van der Klei
Keyword(s):  
Cross Sections ◽  
Matrix Protein ◽  
Protein Import ◽  
Electron Tomography ◽  
High Resolution Electron Microscopy ◽  
Matrix Proteins ◽  
Peroxisomal Membrane ◽  
Resolution Electron ◽  
Microscopy Techniques ◽  
Aaa Atpases

Pex1 and Pex6 are two AAA-ATPases that play a crucial role in peroxisome biogenesis. We have characterized the ultrastructure of the Saccharomyces cerevisiae peroxisome-deficient mutants pex1 and pex6 by various high-resolution electron microscopy techniques. We observed that the cells contained peroxisomal membrane remnants, which in ultrathin cross sections generally appeared as double membrane rings. Electron tomography revealed that these structures consisted of one continuous membrane, representing an empty, flattened vesicle, which folds into a cup shape. Immunocytochemistry revealed that these structures lack peroxisomal matrix proteins but are the sole sites of the major peroxisomal membrane proteins Pex2, Pex10, Pex11, Pex13, and Pex14. Upon reintroduction of Pex1 in Pex1-deficient cells, these peroxisomal membrane remnants (ghosts) rapidly incorporated peroxisomal matrix proteins and developed into peroxisomes. Our data support earlier views that Pex1 and Pex6 play a role in peroxisomal matrix protein import.

Recent Applications of High Resolution Electron Microscopy to Crystalline Arrays of Virus Particles

1978 ◽  
Vol 36 (3) ◽  
pp. 470-482 ◽  
Author(s):  
R.W. Horne
Keyword(s):  
Electron Microscopy ◽  
Image Processing ◽  
Analytical Techniques ◽  
Staining Technique ◽  
High Resolution Electron Microscopy ◽  
Optical Diffraction ◽  
Full Potential ◽  
Virus Particles ◽  
Resolution Electron ◽  
Wide Range

The technique of surrounding virus particles with a neutralised electron dense stain was described at the Fourth International Congress on Electron Microscopy, Berlin 1958 (see Home & Brenner, 1960, p. 625). For many years the negative staining technique in one form or another, has been applied to a wide range of biological materials. However, the full potential of the method has only recently been explored following the development and applications of optical diffraction and computer image analytical techniques to electron micrographs (cf. De Hosier & Klug, 1968; Markham 1968; Crowther et al., 1970; Home & Markham, 1973; Klug & Berger, 1974; Crowther & Klug, 1975). These image processing procedures have allowed a more precise and quantitative approach to be made concerning the interpretation, measurement and reconstruction of repeating features in certain biological systems.

One Million Direct Magnification Microscopy

1971 ◽  
Vol 29 ◽  
pp. 166-167
Author(s):  
J. A. Hugo ◽  
V. A. Phillips
Keyword(s):  
Electron Microscopy ◽  
High Resolution Electron Microscopy ◽  
Illumination Level ◽  
Level Of Detail ◽  
Photographic Emulsion ◽  
Low Contrast ◽  
Fluorescent Screen ◽  
Resolution Electron ◽  
Lattice Images ◽  
Electron Microscopes

A continuing problem in high resolution electron microscopy is that the level of detail visible to the microscopist while he is taking a picture is inferior to that obtainable by the microscope, readily readable on a photographic emulsion and visible in an enlargement made from the plate. Line resolutions, of 2Å or better are now achievable with top of the line 100kv microscopes. Taking the resolution of the human eye as 0.2mm, this indicates a need for a direct viewing magnification of at least one million. However, 0.2mm refers to optimum viewing conditions in daylight or the equivalent, and certainly does not apply to a (colored) image of low contrast and illumination level viewed on a fluorescent screen through a glass window by the dark-adapted eye. Experience indicates that an additional factor of 5 to 10 magnification is needed in order to view lattice images with line spacings of 2 to 4Å. Fortunately this is provided by the normal viewing telescope supplied with most electron microscopes.

Lattice Imaging of Twin, Lath and α/Martensite Boundaries in Duplex Low Carbon Steels

1977 ◽  
Vol 35 ◽  
pp. 118-119
Author(s):  
J. Y. Koo ◽  
G. Thomas
Keyword(s):  
High Resolution Electron Microscopy ◽  
Ferrite Matrix ◽  
Carbon Steels ◽  
Bright Field Image ◽  
Low Carbon ◽  
Lattice Imaging ◽  
Bright Field ◽  
Lattice Image ◽  
New Information ◽  
Resolution Electron

High resolution electron microscopy has been shown to give new information on defects(1) and phase transformations in solids (2,3). In a continuing program of lattice fringe imaging of alloys, we have applied this technique to the martensitic transformation in steels in order to characterize the atomic environments near twin, lath and αmartensite boundaries. This paper describes current progress in this program.Figures A and B show lattice image and conventional bright field image of the same area of a duplex Fe/2Si/0.1C steel described elsewhere(4). The microstructure consists of internally twinned martensite (M) embedded in a ferrite matrix (F). Use of the 2-beam tilted illumination technique incorporating a twin reflection produced {110} fringes across the microtwins.

Structural analysis of the surface-layer protein of spirillum serpens by high-resolution electron microscopy

1983 ◽  
Vol 41 ◽  
pp. 738-739
Author(s):  
W. H. Wu ◽  
R. M. Glaeser
Keyword(s):  
Electron Microscopy ◽  
Surface Layer ◽  
Structural Analysis ◽  
High Resolution ◽  
Low Dose ◽  
High Resolution Electron Microscopy ◽  
Optical Diffraction ◽  
Surface Layer Protein ◽  
Morphological Unit ◽  
Resolution Electron

Spirillum serpens possesses a surface layer protein which exhibits a regular hexagonal packing of the morphological subunits. A morphological model of the structure of the protein has been proposed at a resolution of about 25 Å, in which the morphological unit might be described as having the appearance of a flared-out, hollow cylinder with six ÅspokesÅ at the flared end. In order to understand the detailed association of the macromolecules, it is necessary to do a high resolution structural analysis. Large, single layered arrays of the surface layer protein have been obtained for this purpose by means of extensive heating in high CaCl2, a procedure derived from that of Buckmire and Murray. Low dose, low temperature electron microscopy has been applied to the large arrays.As a first step, the samples were negatively stained with neutralized phosphotungstic acid, and the specimens were imaged at 40,000 magnification by use of a high resolution cold stage on a JE0L 100B. Low dose images were recorded with exposures of 7-9 electrons/Å2. The micrographs obtained (Fig. 1) were examined by use of optical diffraction (Fig. 2) to tell what areas were especially well ordered.

Electron microscopy of rabbit FC crystals

1983 ◽  
Vol 41 ◽  
pp. 730-731
Author(s):  
Robert A. Grant ◽  
Laura L. Degn ◽  
Wah Chiu ◽  
John Robinson
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
High Resolution Electron Microscopy ◽  
Molecular Replacement ◽  
X Ray ◽  
X Ray Crystallography ◽  
Resolution Electron ◽  
Replacement Technique ◽  
Hydrated Crystal ◽  
Molecular Structure Analysis

Proteolytic digestion of the immunoglobulin IgG with papain cleaves the molecule into an antigen binding fragment, Fab, and a compliment binding fragment, Fc. Structures of intact immunoglobulin, Fab and Fc from various sources have been solved by X-ray crystallography. Rabbit Fc can be crystallized as thin platelets suitable for high resolution electron microscopy. The structure of rabbit Fc can be expected to be similar to the known structure of human Fc, making it an ideal specimen for comparing the X-ray and electron crystallographic techniques and for the application of the molecular replacement technique to electron crystallography. Thin protein crystals embedded in ice diffract to high resolution. A low resolution image of a frozen, hydrated crystal can be expected to have a better contrast than a glucose embedded crystal due to the larger density difference between protein and ice compared to protein and glucose. For these reasons we are using an ice embedding technique to prepare the rabbit Fc crystals for molecular structure analysis by electron microscopy.

Artefact in 20Å-Resolution Electron Images of Negatively Stained Twodimensional Membrane Protein Crystals

1982 ◽  
Vol 40 ◽  
pp. 92-93
Author(s):  
Douglas L. Dorset ◽  
Barbara Moss
Keyword(s):  
Electron Scattering ◽  
Cross Correlation ◽  
Transmission Function ◽  
Group Symmetry ◽  
Asymmetric Structure ◽  
Object Model ◽  
Phase Object ◽  
Computing Systems ◽  
Resolution Electron ◽  
Plane Group

A number of computing systems devoted to the averaging of electron images of two-dimensional macromolecular crystalline arrays have facilitated the visualization of negatively-stained biological structures. Either by simulation of optical filtering techniques or, in more refined treatments, by cross-correlation averaging, an idealized representation of the repeating asymmetric structure unit is constructed, eliminating image distortions due to radiation damage, stain irregularities and, in the latter approach, imperfections and distortions in the unit cell repeat. In these analyses it is generally assumed that the electron scattering from the thin negativelystained object is well-approximated by a phase object model. Even when absorption effects are considered (i.e. “amplitude contrast“), the expansion of the transmission function, q(x,y)=exp (iσɸ (x,y)), does not exceed the first (kinematical) term. Furthermore, in reconstruction of electron images, kinematical phases are applied to diffraction amplitudes and obey the constraints of the plane group symmetry.

Finding the Right Problems: Some HREM Applications to Interfaces

1984 ◽  
Vol 42 ◽  
pp. 376-379
Author(s):  
D. Cherns
Keyword(s):  
Grain Boundaries ◽  
High Resolution Electron Microscopy ◽  
Boundary Structure ◽  
Atomic Structures ◽  
Grain Boundary Structure ◽  
Resolution Electron ◽  
Point To Point ◽  
The Right ◽  
New Generation ◽  
Better Than

The use of high resolution electron microscopy (HREM) to determine the atomic structure of grain boundaries and interfaces is a topic of great current interest. Grain boundary structure has been considered for many years as central to an understanding of the mechanical and transport properties of materials. Some more recent attention has focussed on the atomic structures of metalsemiconductor interfaces which are believed to control electrical properties of contacts. The atomic structures of interfaces in semiconductor or metal multilayers is an area of growing interest for understanding the unusual electrical or mechanical properties which these new materials possess. However, although the point-to-point resolutions of currently available HREMs, ∼2-3Å, appear sufficient to solve many of these problems, few atomic models of grain boundaries and interfaces have been derived. Moreover, with a new generation of 300-400kV instruments promising resolutions in the 1.6-2.0 Å range, and resolutions better than 1.5Å expected from specialist instruments, it is an appropriate time to consider the usefulness of HREM for interface studies.

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