Automated image acquisition and processing using a new generation of 4K × 4K CCD cameras for cryo electron microscopic studies of macromolecular assemblies

Abstract

We have previously reported the development of AutoEM, a software package for semi-automated acquisition of data from a transmission electron microscope. In continuing efforts to improve the speed of structure determination of macromolecular assemblies by electron microscopy, we report here on the performance of a new generation of 4K CCD cameras for use in cryo electron microscopic applications. We demonstrate that at 120 kV, and at a nominal magnification of 67 000×, power spectra and signal-to-noise ratios for the new 4K CCD camera are comparable to values obtained for film images scanned using a Zeiss scanner to resolutions as high as ∼1/6.5 Å −1. The specimen area imaged for each exposure on the 4K CCD is about one-third of the area that can be recorded with a similar exposure on film. The CCD camera also serves the purpose of recording images at low magnification from the center of the hole to measure the thickness of vitrified ice in the hole. The performance of the camera is satisfactory under the low-dose conditions used in cryo electron microscopy, as demonstrated here by the determination of a three-dimensional map at 15 Å for the catalytic core of the 1.8 MDa Bacillus stearothermophilus icosahedral pyruvate dehydrogenase complex, and its comparison with the previously reported atomic model for this complex obtained by X-ray crystallography.