ELECTRON MICROSCOPY

Sample

Ca2+-ATPase tubular crystals

Specimen Preperation
Sample Aggregation State HELICAL ARRAY
Vitrification Instrument ?
Cryogen Name ?
Sample Vitrification Details Samples at approximately 1 mg/ml were diluted 1/20 immediately prior to application to glow-discharged fenestrated carbon grids. All freezing was done in cold room. After blotting, samples were plunged into liquid ethane for freezing and stored in liquid nitrogen.
3D Reconstruction
Reconstruction Method HELICAL
Number of Particles 95
Reported Resolution (Å) 6
Resolution Method ?
Other Details Combination of Fourier and real space averaging. Helical Reconstruction: A total of 95 repeats from 58 individual tubes were used for the reconstruction. These tubes fell into 5 helical symmetries, defined by the Bessel order (n) of the principal layer lines (1,0) and (0,1). These 5 symmetries were (-23,6), (-22,6), (-21,6), (-20,6) and (-19,6). For the reference symmetry (-22,6), the unit cell parameters were: a= 56.9A, b=117.1A, gamma=64.2 deg. Data within each helical symmetry were averaged in Fourier space and distortion-correction techniques were applied (Beroukhim and Unwin, 1997). For each repeat, unit cell parameters were calculated, and repeats differing by more than 1.5% of the average value were discarded. The CTF was used to correct phases and weight amplitudes prior to averaging within each helical symmetry. Finally, maps were calculated from each of the averaged datasets. Each of the 2 molecules composing the unit cell were masked and aligned with the corresponding molecule from the reference map (-22,6). The maps were averaged in real-space then back-transformed into Fourier space. Two-fold symmetry was constrained before calculating the final map. Effective resolution of the reconstruction: The resolution of the final reconstruction was determined to be 6 A by two methods. First, the dataset was split into two equal parts and two independant reconstructions were made. After masking and aligning molecules from these maps, Fourier shell correlation coefficients and associated phase residuals were calculated. Secondly, since the crystals had p2 symmetry, two-fold phase residuals of layer lined datasets were used to monitor resolution.
Refinement Type
Symmetry Type HELICAL
Map-Model Fitting and Refinement
ID 1
Refinement Space REAL
Refinement Protocol ?
Refinement Target ?
Overall B Value ?
Fitting Procedure ?
Details DETAILS--The atomic coordinates of Ca-ATPase (1EUL) were divided into 4 domains by breaking the peptide at 3 hinge points. Each domain was separately fit into the electron density map by manual docking using the program O. Besides matching overall shape, the major criteria involved matching a-helices into strong columns of density in the map. Whereas cytoplasmic domains were treated as rigid bodies, elements of the transmembrane domain were bent or displaced to match strong densities in the cryo-em map. Finally, the loops composing the 3 hinges were rebuilt to reconnect the domains and X-PLOR was used to perform local energy minimization.
Data Acquisition
Detector Type KODAK SO-163 FILM
Electron Dose (electrons/Å2) 10
Imaging Experiment
Date of Experiment 2000-01-01
Temprature (Kelvin)
Microscope Model FEI/PHILIPS CM200FEG
Minimum Defocus (nm) 700
Maximum Defocus (nm) 1400
Minimum Tilt Angle (degrees) 0
Maximum Tilt Angle (degrees) 0
Nominal CS 2.0
Imaging Mode BRIGHT FIELD
Specimen Holder Model ?
Nominal Magnification 50000
Calibrated Magnification 51300
Source FIELD EMISSION GUN
Acceleration Voltage (kV) 200
Imaging Details ?
Imaging Experiment
Task Software Package Version
MODEL FITTING O ?
MODEL FITTING X-PLOR ?
RECONSTRUCTION Custom ?
Image Processing
CTF Correction Type CTF Correction Details Number of Particles Selected Particle Selection Details
. CTF correction of each particle with 4.6% amplitude contrast