CTER Rapid estimation of CTF parameters with error assessment

In structural electron microscopy, the accurate estimation of the Contrast Transfer Function (CTF) parameters, particularly defocus and astigmatism, is of utmost importance for both initial evaluation of micrograph quality and for subsequent structure determination. Due to increases in the rate of data collection on modern microscopes equipped with new generation cameras, it is also important that the CTF estimation can be done rapidly and with minimal user intervention. Finally, in order to minimize the necessity for manual screening of the micrographs by a user it is necessary to provide an assessment of the errors of fitted parameters values. In this work we introduce CTER, a CTF parameters estimation method distinguished by its computational efficiency. The efficiency of the method makes it suitable for high-LhroughpuL EM data collection, and enables the use of a statistical resampling technique, bootstrap, that yields standard deviations of estimated defocus arid astigmatism amplitude arid angle, thus facilitating the automation of the process of screening out inferior micrograph data. Furthermore. CTER also outputs the spatial frequency limit imposed by reciprocal space aliasing of the discrete form of the CTF and the finite window size. We demonstrate the efficiency and accuracy of CTER using a data set collected on a 300 kV Tecnai Polara (FEU using the K2 Summit DED camera in super resoluLion counting mode. Using CTER we obtained a structure of the 80S ribosome whose large subunit had a resolution of 4.03 angstrom without, and 3.85 angstrom with, inclusion of astigmatism parameters.(C) 2014 Elsevier B.V. All rights reserved