ELECTRON MICROSCOPY Experimental Data



EM Sample
Sample pH 7.6
Sample Support Details 400 MESH COPPER, HOLEY CARBON, GLOW DISCHARGE,
Sample Vitrification Details PLUNGE VITRIFICATION SAMPLES PREPARED AS THIN LAYERS OF VITREOUS ICE MAINTAINED AT NEAR LIQUID NITROGEN TEMPERATURE IN THE ELECTRON MICROSCOPE WITH A GATAN 626-0300 CRYOTRANSFER HOLDER.
Sample Aggregation State PARTICLE
Name of Sample SEMLIKI FOREST VIRUS
EM Data Acquisition
Date of Experiment 1998-06-15
Num of Micrographs-Images Used 48
Temperature (Kelvin) 95.0
Microscope Model FEI-CM200 FEG
Detector Type KODAK SO-163 FILM
Minimum Defocus (nm) 975.0
Maximum Defocus (nm) 7600.0
Minimum Tilt Angle (degrees) 0.0
Maximum Tilt Angle (degrees) 0.0
Nominal CS 2.0
Imaging Mode LOW DOSE
Electron Dose (electrons nm**-2) 1000.0
Illumination Mode BRIGHT FIELD
Nominal Magnification 50000
Calibrated Magnification --
Source FIELD EMISSION GUN
Acceleration Voltage (kV) 200
Imaging Details --
3D Reconstruction
Software Package(s)
Reconstruction Method MODEL-BASED, POLAR-FOURIER- TRANSFORMATION (FULLER ET AL. 1996, J.STRUC.BIOL. 116, 48-55; BAKER AND CHENG 1996, J.STRUC.BIOL. 116, 120- 130) MODEL-BASED CROSS COMMOM LINES SEARCH AND REFINEMENT (CROWTHER ET AL. 1970, NATURE (LONDON) 226, 421- 425; FULLER ET AL. 1996, J.STRUC.BIOL. 11 48-55;FERLENGHI ET AL. 1998, J.MOL.BIOL. 283, 71-81)
EM Image Reconstruction Statistics
Number of Particles 5267
Nominal Pixel Size 2.64
Actual Pixel Size 2.52
Effective Resolution 9.0
EM Reconstruction Magnification Callibration THE PIXEL SIZE OF THE CRYO-EM MAP WAS CALIBRATED AGAINST A LOW RESOLUTION DENSITY MAP CALCULATED FROM THE CRYSTAL STRUCTURE OF HRV16. DENSITIES WERE COMPARED BY CROSS- CORRELATION WITHIN A SPHERICAL SHELL OF INTERNAL RADIUS 110 ANGSTROMS AND EXTERNAL RADIUS OF 145 ANGSTROMS.
Other Details THE ORIENTATIONS WERE REFINED BY THE CROSS COMMON LINES LINES METHOD (SIMPLEX) AND THE POLAR FOURIER TRANSFORM METHOD USING A PARALLEL IMPLEMENTATION (PYPFT). THE EFFECTIVE RESOLUTION OF THE FINAL RECONSTRUCTED DENSITY WAS DETERMINED TO BE AT LEAST 9 ANGSTROMS, AS MEASURED BY RANDOMLY SPLITTING THE PARTICLES INTO TWO SETS AND CALCULATING THE FOURIER SHELL CORRELATION OBTAINED FROM SEPARATE RECONSTRUCTIONS (HARAUZ AND VAN HEEL 1986, OPTIK 73, 146-156). THE EIGENVALUE SPECTRUM GAVE AN INDICATION OF THE RANDOMNESS OF THE DATA THAT WAS INCLUDED IN THE RECONSTRUCTION. THE COMPLETENESS OF THE DATA WAS VERIFIED IN THAT ALL EIGENVALUES EXCEEDED 100. THE COORDINATES ARE IN THE P, Q, R FRAME IN ANGSTROM UNITS AND CORRESPOND TO ICOSAHEDRAL SYMMETRY AXES. THE ORIGIN IS CHOSEN AT THE CENTER OF THE VIRUS WITH P, Q AND R ALONG MUTUALLY PERPENDICULAR TWO-FOLD AXES OF THE ICOSAHEDRON. THEY SHOULD REMAIN IN THAT FRAME FOR THE EASE OF THE USER IN CREATING THE BIOLOGICALLY SIGNIFICANT VIRAL COMPLEX PARTICLE USING THE 60 ICOSAHEDRAL SYMMETRY OPERATORS. RESIDUES NOT VISIBLE IN THE ORIGINAL CRYSTAL STRUCTURES ARE NOT INCLUDED IN THE CRYO-EM STRUCTURE MODEL. FOR EXAMPLE, C RESIDUES 1-118, ARE NOT VISIBLE IN THE CRYSTAL STRUCTURE (PDB ENTRY 1VCQ) AND THEREFORE ARE NOT INCLUDED IN THE COORDINATES BELOW.
EM Map-Model Fitting and Refinement
Refinement Space Refinement Protocol Refinement Target Overall B Value Fitting Procedure Fitting Software
REAL RIGID BODY REFINEMENT R-FACTOR -- THE CRYSTAL STRUCTURE OF THE CAPSID PROTEIN FROM CHOI ET AL (1997) PROTEINS 3 27:345-359 (SUBUNIT A OF PDB FILE 1VCQ) WAS PLACED INTO THE CRYO-EM DENSITY MAP. THE CAPSID PROTEIN WAS FIRST MANUALLY POSITIONED INTO THE CRYO-EM DENSITY CORRESPONDING TO POSITIONS OF THE FOUR INDEPENDENT MONOMER DENSITIES BETWEEN THE INNER LEAFLET OF THE BILAYER AND THE RNA. THESE POSITIONS WERE THEN REFINED BY RIGID BODY REFINEMENT IN REAL SPACE WITH THE PROGRAM EMFIT (CHENG ET AL. 1995, CELL 80, 621-630). THE QUALITY OF THE FIT CAN BE SEEN FROM THE MAP DENSITY WITHIN THE PROTEIN. ALL 4563 ATOMS ARE IN DENSITY OF AT LEAST 4 SIGMA (96.73) ABOVE THE AVERAGE (512.04) , 1167 ATOMS ARE IN DENSITY BETWEEN 4 AND 5 SIGMA, 3174 ATOMS ARE IN DENSITY BETWEEN 5 AND 6 SIGMA, AND 222 ATOMS ARE IN DENSTY OF 6 SIGMA OR ABOVE. THE VARIATION IN DENSITY OVER THE FITTED PROTEIN CAN BE VISUALIZED WITH THE PSEUDO TEMPERATURE FACTOR. THE DENSITY VALUE AT EACH ATOM IS GIVEN IN THE 8TH COLUM (USUALLY THE OCCUPANCY) AS THE NUMBER OF STANDARD DEVIATION ABOVE BACKGROUND. COLUMN NINE (USUALLY THE TEMPERATURE FACTOR) CONTAINS THE VALUE OF THE RELATIVE DENSITY WITHIN THE FITTED PROTEIN SCALED LINEARLY SO THAT THE MINIMUM DENSITY IS 100.0 AND THE MAXIMUM DENSITY IS 1.0. THE ATOMS THAT LIE IN THE LOWER DENSITY REGIONS WILL HAVE THE HIGHEST PSEUDO TEMPERATURE FACTORS. --