1M8Q

Molecular Models of Averaged Rigor Crossbridges from Tomograms of Insect Flight Muscle

ELECTRON MICROSCOPY

Starting Model(s)

Initial Refinement Model(s)
Type	Source	Accession Code	Details
experimental model	PDB	2MYS
experimental model	PDB	1ATN

Sample
Insect flight muscle of the large water bug Lethocerus maximus

Specimen Preparation
Sample Aggregation State	TISSUE
Vitrification Instrument
Cryogen Name
Sample Vitrification Details	No vitrification. Samples were viewed at room temperature.
Staining Type	NEGATIVE
Staining Material	Osmium tetroxide, Uranyl Acetate
Staining Details

3D Reconstruction
Reconstruction Method	TOMOGRAPHY
Number of Particles
Reported Resolution (Å)	70
Resolution Method
Other Details	3-D motifs were identified in the tomogram by first producing a cross correlation map from which peak coordinates were determined from their center of ...	3-D motifs were identified in the tomogram by first producing a cross correlation map from which peak coordinates were determined from their center of gravity. We define a 3-D motif as one, entire 38.7 nm crossbridge repeat along actin. These motifs usually contain at least four myosin heads in two paired crossbridges (single chevrons) and sometimes contain as many as six myosin heads in four paired crossbridges (double chevrons). The reference for the analysis was selected to be centered between successive troponin densities which could be identified from the in-plane projection. The individual crossbridge motifs were then subjected to multivariate statistical analysis to identify clusters of motifs showing similar crossbridge structure. These clusters formed the class averages. The choice of structure to be classified was decided by the resolution and the later process of model building. Averaging was done according to the heirarchical ascendent method. The resolution in each of the class averages was 7 nm by the spectral signal to noise ratio.
Refinement Type
Symmetry Type	POINT
Point Symmetry	C1

Map-Model Fitting and Refinement
Id	1 (2MYS, 1ATN)
Refinement Space	REAL
Refinement Protocol	RIGID BODY FIT
Refinement Target	Best correlation coefficient and fewest poor contacts
Overall B Value
Fitting Procedure
Details	METHOD--Initial models were fit by hand using O. The fit was then refined using real space refinement. REFINEMENT PROTOCOL--rigid body

Data Acquisition
Detector Type	KODAK SO-163 FILM
Electron Dose (electrons/Å**2)

Imaging Experiment	1
Date of Experiment
Temperature (Kelvin)
Microscope Model	FEI/PHILIPS EM400
Minimum Defocus (nm)
Maximum Defocus (nm)
Minimum Tilt Angle (degrees)
Maximum Tilt Angle (degrees)
Nominal CS
Imaging Mode	BRIGHT FIELD
Specimen Holder Model
Nominal Magnification	17000
Calibrated Magnification
Source	TUNGSTEN HAIRPIN
Acceleration Voltage (kV)	100
Imaging Details

EM Software
Task	Software Package	Version
MODEL FITTING	RSRef
RECONSTRUCTION	Custom

Image Processing
CTF Correction Type	CTF Correction Details	Number of Particles Selected	Particle Selection Details
	none

RCSB PDB Core Operations are funded by the U.S. National Science Foundation (DBI-2321666), the US Department of Energy (DE-SC0019749), and the National Cancer Institute, National Institute of Allergy and Infectious Diseases, and National Institute of General Medical Sciences of the National Institutes of Health under grant R01GM157729.