scholarly journals Tubular crystals of acetylcholine receptor.

1984 ◽  
Vol 99 (4) ◽  
pp. 1202-1211 ◽  
Author(s):  
A Brisson ◽  
P N Unwin
Keyword(s):  
Acetylcholine Receptor ◽  
Cross Sections ◽  
Asymmetric Distribution ◽  
Torpedo Marmorata ◽  
Oriented Molecules ◽  
Cell Dimensions ◽  
Average Unit ◽  
Plane Group ◽  
Unit Cell Dimensions ◽  
Tubular Crystals

Well-ordered tubular crystals of acetylcholine receptor were obtained from suspensions of Torpedo marmorata receptor-rich vesicles. They are composed of pairs of oppositely oriented molecules arranged on the surface lattice with the symmetry of the plane group p2 (average unit cell dimensions: a = 90 A, b = 162 A, gamma = 117 degrees). The receptor in this lattice has an asymmetric distribution of mass around its perimeter, yet a regular pentagonal shape; thus its five transmembrane subunits appear to have different lengths, but approximately equal cross sections. The tubes grow by lateral aggregation on the vesicle surface of ribbons of the paired molecules. Both ribbons and tubes were sensitive to dispersal by the disulphide reductant, dithiothreitol. This observation and other evidence suggest that the basic pairing interaction in the tubes may be that of the physiological dimer, involving contact between delta-subunits.

SECTION– a computer program for the graphic display of cross sections through a unit cell

1999 ◽  
Vol 32 (2) ◽  
pp. 353-354 ◽  
Author(s):  
Leonard J. Barbour
Keyword(s):  
Crystal Structure ◽  
Computer Program ◽  
Cross Sections ◽  
Unit Cell ◽  
Graphic Display ◽  
Cross Sectional ◽  
Cell Dimensions ◽  
Unit Cell Dimensions ◽  
Microsoft Windows ◽  
Symmetry Operations

SECTIONis a 32-bit Microsoft Windows-based program that displays cross-sectional slices through a packed crystal structure. Unit-cell dimensions as well as the unique atomic positions and symmetry operations are read fromSHELXinstruction files.

Selective contrast in images of crystalline cytochrome oxidase dimers

1983 ◽  
Vol 41 ◽  
pp. 442-443
Author(s):  
T. G. Frey ◽  
M. J. Costello ◽  
J. E. Reardon ◽  
P. A. Frey
Keyword(s):  
Cytochrome Oxidase ◽  
Three Dimensional ◽  
Phospholipid Bilayer ◽  
Specimen Preparation ◽  
Inner Mitochondrial Membrane ◽  
Entire Structure ◽  
Beef Heart Mitochondria ◽  
Cell Dimensions ◽  
Plane Group ◽  
Unit Cell Dimensions

Vesicle crystals of cytochrome oxidase dimers embedded in the phospholipid bilayer of a collapsed vesicle are produced when beef heart mitochondria are treated with Triton detergents. The crystals have the symmetry of plane group p22121 with unit cell dimensions of a=95 A, b=125 A, and c=210 A. The molecules protrude 60 A beyond the lipid bilayer on the inside of the vesicle, but very little beyond the bilayer on the outside. Decoration of crys- stals with subunit-specific antibodies identified the outside surface of the vesicle crystals as corresponding to the M-side (matrix) of the inner mitochondrial membrane and the inside surface as the C-side (cytoplasmic).We have used various methods of specimen preparation to selectively image different regions of the dimer crystals in order to correlate the structure of dimers with that of 'Y'-shaped monomers. Electron micrographs of negatively stained specimens (Fig. 1a, 2a) give a two-dimensional projection of the three-dimensional stain replica of the entire structure.

scholarly journals Asynchronous assembly of the acetylcholine receptor and of the 43-kD nu1 protein in the postsynaptic membrane of developing Torpedo marmorata electrocyte.

1989 ◽  
Vol 108 (1) ◽  
pp. 127-139 ◽  
Author(s):  
E Kordeli ◽  
J Cartaud ◽  
H O Nghiêm ◽  
A Devillers-Thiéry ◽  
J P Changeux
Keyword(s):  
Plasma Membrane ◽  
Acetylcholine Receptor ◽  
Postsynaptic Membrane ◽  
Synaptic Membrane ◽  
Asymmetric Distribution ◽  
Subsequent Stage ◽  
Torpedo Marmorata ◽  
Intracellular Compartments ◽  
Membrane Compartments

The assembly of the nicotinic acetylcholine receptor (AchR) and the 43-kD protein (v1), the two major components of the post synaptic membrane of the electromotor synapse, was followed in Torpedo marmorata electrocyte during embryonic development by immunocytochemical methods. At the first developmental stage investigated (45-mm embryos), accumulation of AchR at the ventral pole of the newly formed electrocyte was observed within columns before innervation could be detected. No concomitant accumulation of 43-kD immunoreactivity in AchR-rich membrane domains was observed at this stage, but a transient asymmetric distribution of the extracellular protein, laminin, which paralleled that of the AchR, was noticed. At the subsequent stage studied (80-mm embryos), codistribution of the two proteins was noticed on the ventral face of the cell. Intracellular pools of AchR and 43-kD protein were followed at the EM level in 80-mm electrocytes. AchR immunoreactivity was detected within membrane compartments, which include the perinuclear cisternae of the endoplasmic reticulum and the plasma membrane. On the other hand, 43-kD immunoreactivity was not found associated with the AchR in the intracellular compartments of the cell, but codistributed with the AchR at the level of the plasma membrane. The data reported in this study suggest that AchR clustering in vivo is not initially determined by the association of the AchR with the 43-kD protein, but rather relies on AchR interaction with extracellular components, for instance from the basement membrane, laid down in the tissue before the entry of the electromotor nerve endings.

Short-range order, thermal vibration and expansion, and other properties of pseudosymmetric and mixed crystals of small organic molecules - Mixed crystals of phenzaine and n -oxyphenazine: refinement of crystal structures

1970 ◽  
Vol 266 (1180) ◽  
pp. 593-622 ◽  
Keyword(s):  
Unit Cell ◽  
Mixed Crystals ◽  
X Ray Diffraction ◽  
Small Organic Molecules ◽  
Anisotropic Temperature ◽  
Cell Dimensions ◽  
Average Unit ◽  
Unit Cell Dimensions ◽  
Temperature Factors ◽  
Atomic Coordinates

Compositions (accurate to about 1%) of mixed crystals of phenazine (P) and N -oxyphenazine (NOP) were determined from their u.v. absorption spectra. Densities, habit and unit-cell dimensions were found at 20 °C for crystals containing respectively 0, 8, 52, 81 and 100 mole % NOP relative to P; and X-ray diffraction data (F obs ) were obtained for all these and also at — 90 °C for NOP. All are isostructural (NOP being pseudocentrosymmetric) in P2 1 / a with two molecules per average unit cell. Atomic coordinates, bond lengths and anisotropic temperature factors are listed, site-occupation factors for the oxygen atoms being used for the 8, 52 and 81 mole % compositions. A qualitative explanation, in terms of structure, is offered for the anisotropic thermal expansion of NOP.

Location of subunits in the acetylcholine receptor by analysis of electron images of tubular crystals from Torpedo marmorata

1996 ◽  
Vol 54 ◽  
pp. 70-71
Author(s):  
David A. Burkwall ◽  
Robert Josephs ◽  
Jennifer Holly ◽  
David Richman ◽  
Robert Fairclough
Keyword(s):  
Acetylcholine Receptor ◽  
Torpedo Marmorata ◽  
Central Cavity ◽  
Α Subunit ◽  
Γ Subunit ◽  
Disulphide Bonds ◽  
Selective Channel ◽  
Polypeptide Chains ◽  
Tubular Crystals ◽  
Α Subunits

The nicotinic acetylcholine receptor(AChR) is a membrane protein containing four different homologous polypeptide chains (two copies of an α-subunit and single copies of β, γ, and δ). These subunits assemble about a central cavity, which is thought to delineate the ion-selective channel. In tubular crystals from T. marmorata receptors normally exist as dimers, paired through disulphide bonds between the δ-subunits. Conflicting reports still arise concerning the relative locations of these subunits around the central axis. It has been proposed that the β-subunit lies between the two α-subunits or that the γ subunit lies between the two α-subunits. Here we examine the locus of two subunit-specific labels, mAb 383C and 247G, bound to receptors and averaged in each case from over 5,000 molecules.

The External Shape of Human γ GI Immunoglobulin from Crystal Sections

1971 ◽  
Vol 29 ◽  
pp. 428-429
Author(s):  
L. W. Labaw
Keyword(s):  
Molecular Weight ◽  
Sodium Phosphate ◽  
Osmium Tetroxide ◽  
Unit Cell ◽  
Monoclinic Space Group ◽  
X Ray ◽  
Large Molecular Weight ◽  
Cell Dimensions ◽  
Unit Cell Dimensions ◽  
Crystallographic Axes

Crystals of a human γGl immunoglobulin have the external morphology of diamond shaped prisms. X-ray studies have shown them to be monoclinic, space group C2, with 2 molecules per unit cell. The unit cell dimensions are a = 194.1, b = 91.7, c = 51.6Å, 8 = 102°. The relatively large molecular weight of 151,000 and these unit cell dimensions made this a promising crystal to study in the EM.Crystals similar to those used in the x-ray studies were fixed at 5°C for three weeks in a solution of mother liquor containing 5 x 10-5M sodium phosphate, pH 7.0, and 0.03% glutaraldehyde. They were postfixed with 1% osmium tetroxide for 15 min. and embedded in Maraglas the usual way. Sections were cut perpendicular to the three crystallographic axes. Such a section cut with its plane perpendicular to the z direction is shown in Fig. 1.This projection of the crystal in the z direction shows periodicities in at least four different directions but these are only seen clearly by sighting obliquely along the micrograph.

The crystal and molecular structure of tris(pentamethylenedithiocarbamate) chromium(III)-chloroform (1 : 2)

1981 ◽  
Vol 46 (1) ◽  
pp. 6-19 ◽  
Author(s):  
Viktor Kettman ◽  
Ján Garaj ◽  
Jaroslav Majer
Keyword(s):  
Molecular Structure ◽  
Structural Analysis ◽  
Crystal And Molecular Structure ◽  
Analysis Method ◽  
Complex Molecules ◽  
Coordination Polyhedra ◽  
X Ray ◽  
Cell Dimensions ◽  
Crustal Density ◽  
Unit Cell Dimensions

The crystal and molecular structure of [Cr(S2CN(CH2)5)3].2 CHCl3 was found by the X-ray structural analysis method. The value R 0.090 was found for 1 131 observed independent reflections. The substance crystallizes in a space group of symmetry P212121 with the following unit cell dimensions: a = 0.8675 (6), b = 1.815(2), c = 2.155(3) nm. The experimentally observed crustal density was 1.48 Mgm-3 and the value calculated for Z = 4 was 1.51 Mgm-3. The CrS6 coordination polyhedron has the shape of a trigonally distorted octahedron, where the D3 symmetry is a approximately retained. The degree of trigonal distortion expressed as the projection of the chelate S-Cr-S angle onto the plane perpendicular to the C3 pseudo axis is Φ = 41.7° (Φ = 60° for an octahedron). The skeleton of the structure formed by the complex molecules contains channels filled with chloroform molecules. The specific type of complex-chloroform interaction consists of the formation of hydrogen bonds of the chloroform protons with the fully occupied pπ-orbitals of the sulphur atoms in the coordination polyhedra. The low stability and crystal decomposition can be explained by loss of chloroform from the channels.

Water Molecule Dispositions in the Cesium Sulfate α- and β-Alums: Single-Crystal Neutron Diffraction Studies of CsM(SO4)2.12H2O (M=V, Rh)

1993 ◽  
Vol 46 (9) ◽  
pp. 1337 ◽  
Author(s):  
JK Beattie ◽  
SP Best ◽  
FH Moore ◽  
BW Skelton ◽  
AH White
Keyword(s):  
Neutron Diffraction ◽  
Water Molecule ◽  
Single Crystal ◽  
Tilt Angle ◽  
Room Temperature ◽  
Bond Angle ◽  
Sulfate Salt ◽  
Cell Dimensions ◽  
Coordinated Water ◽  
Unit Cell Dimensions

Room-temperature single-crystal neutron diffraction studies are recorded for two alums, Cs( Rh /V)(SO4)2.12H2O [cubic, Pa3, a 12.357(5) ( Rh ), 12.434(1)Ǻ (V)], residuals 0.037 and 0.068 for 328 and 164 'observed' reflections, with the intention of defining water molecule hydrogen atom orientations. Whereas the two tervalent hexaaqua cations are similar in size [ rM -O = 2.010(6)Ǻ (M = V) and 2.006(2)Ǻ (M = Rh )] the vanadium salt adopts the β alum modification while rhodium gives an α alum. Significantly, the water coordination geometry is different in the two cases with the tilt angle between the plane of the water molecule and the M-O bond vector being 1° (M = V) and 35° (M = Rh ). The tilt angle for water coordinated to rhodium in CsRh (SeO4)2.12H2O is inferred from the unit cell dimensions to be similar to that of the corresponding sulfate salt and not that which generally pertains for caesium selenate alums. Significant differences in the H-O-H bond angle are found for trigonal planar and trigonal pyramidal water coordination, suggesting that differences in the metal(III)-water interaction are a determinant of the geometry of the coordinated water molecule in the caesium sulfate/ selenate alum lattices.

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