ELECTRON MICROSCOPY Experimental Data



EM Sample
Sample Vitrification Details LIQUID ETHANE
Sample Aggregation State FILAMENT
Sample Reconstruction Method HELICAL
Name of Sample POSTSYNAPTIC MEMBRANE
EM Data Acquisition
Date of Experiment 2002-10-01
Temperature (Kelvin) 4.2
Microscope Model JEOL 3000SFF
Detector Type KODAK SO-163 FILM
Minimum Defocus (nm) 800.0
Maximum Defocus (nm) 1800.0
Minimum Tilt Angle (degrees) --
Maximum Tilt Angle (degrees) --
Nominal CS 1.3
Imaging Mode BRIGHT FIELD
Electron Dose (electrons per Å**-2) 20.0
Illumination Mode FLOOD BEAM
Nominal Magnification 40000
Calibrated Magnification 36800
Source FIELD EMISSION GUN
Acceleration Voltage (kV) 300
Imaging Details THE SPECIMENS WERE TUBULAR CRYSTALS GROWN IN LOW SALT BUFFER FROM ISOLATED TORPEDO POSTSYNAPTIC MEMBRANES. THEY WERE APPLIED TO THE THE MICROSCOPE GRIDS AND FROZEN IN THE SAME SOLUTION. THESE CRYSTALS WERE TOO SMALL AND DISTORTED TO YIELD MEANINGFUL ELECTRON DIFFRACTION PATTERNS, SO BOTH THE AMPLITUDE AND THE PHASE TERMS HAD TO BE MEASURED FROM FOURIER TRANSFORMS OF THE IMAGES. THE IMAGES WERE RECORDED USING A DOSE OF 2000 ELECTRONS/NM2 DURING THE PERIOD: JAN-1996 TO OCT-2002. THE DATASETS INVOLVED 4 HELICAL FAMILIES OF TUBES, WHICH WERE ANALYSED (INCLUDING CORRECTIONS FOR DISTORTIONS) AS DESCRIBED IN THE REFERENCES. STRUCTURES WERE SYNTHESISED FROM THE AMPLITUDE AND PHASE TERMS DERIVED FROM EACH HELICAL FAMILY. THE FINAL DATASET WAS OBTAINED BY AVERAGING THESE 4 STRUCTURES IN REAL SPACE.
3D Reconstruction
Software Package(s) --
Reconstruction Method(s) --
EM Image Reconstruction Statistics
Number of Particles --
Other Details NO REFINEMENT WAS CARRIED OUT ON THE MODEL. THE COORDINATES ARE PRELIMINARY. INCLUDED ARE ALL RESIDUES IN THE TRANSMEMBRANE SEGMENTS M1-M3 AND M4, AND THE CONNECTING LINKS M1-M2 AND M2-M3. THE EXTENDED LOOP BETWEEN M3 AND M4, FORMING THE INTRACELLULAR DOMAIN OF THE RECEPTOR, AND SEVERAL OF THE C -TERMINAL RESIDUES ON M4 (CHAINS B, C AND E) ARE OMITTED. THE LINK BETWEEN M1 AND M2 WAS POORLY RESOLVED AND THE TRACE HERE IS ALMOST CERTAINLY WRONG IN DETAIL. IT IS HOPED THAT WITH IMPROVED DATA AND WITH REFINEMENT A MORE ACCURATE MODEL WILL BE OBTAINED. THESE COORDINATES, INCLUDING ESTIMATES OF SIDE CHAIN POSITIONS, ARE BEING MADE AVAILABLE IN THE HOPE THAT THEY WILL BE USEFUL. USERS SHOULD BEAR IN MIND THAT BECAUSE OF THE LIMITED RESOLUTION THE CONFORMATIONS OF THE SIDE CHAINS AND THEIR ATOMIC COORDINATES ARE NOT INDIVIDUALLY RELIABLE. ALSO THE ENDS OF THE HELICES ARE UNCERTAIN BY AT LEAST ONE RESIDUE. THE SURFACE LATTICE OF THE TUBULAR CRYSTALS HAS P2 SYMMETRY. THE FOUR HELICAL FAMILIES, DEFINED BY THE NUMBERS OF THE TWO PRINCIPAL HELICES REQUIRED TO FILL 360 DEGREES OF AZIMUTH, WERE: (-16,6),(-18,6),(-17,5),(-15,7). NEGATIVE INDICATES LEFT-HANDED. TO COMPARE AND COMBINE FOURIER TERMS FROM WITHIN A FAMILY IT WAS USUALLY NECESSARY TO REASSIGN LAYER-LINES TO MATCH THOSE CORRESPONDING TO A STANDARD HELICAL SELECTION RULE DEFINING A TYPICAL SET OF POSITIONS IN THE TRANSFORM. THE STANDARD SELECTION RULES WERE: L = 113N' + 314M (N = 2N') (-16,6) L = 25N' + 112M (N = 6N') (-18,6) L = 247N + 605M (-17,5) L = -91N + 662M (-15,7) WHERE L IS THE LAYER-LINE NUMBER, M IS AN INTEGER, N IS THE START NUMBER (I.E. NUMBER AROUND THE CIRCUMFERENCE) OF THE CONTRIBUTING HELIX, AND N=2N' INDICATES THAT THE START NUMBERS OCCUR IN MULTIPLES OF 2.
Effective Resolution 4.0