Cryo-EM map anisotropy can be attenuated by map post-processing and a new method for its estimation

Abstract

One of the most important challenges in cryogenic electron microscopy (cryo-EM) is the substantial number of samples that exhibit preferred orientations, which leads to an uneven coverage of the projection sphere. As a result, the overall quality of the reconstructed maps can be severely affected, as manifested by the presence of anisotropy in the map resolution. Several methods have been proposed to measure the directional resolution of maps in tandem with experimental protocols to address the problem of preferential orientations in cryo-EM. Following these works, in this manuscript we show that some of the most recently proposed cryo-EM map post-processing algorithms can attenuate map anisotropy, thus offering a computational alternative for cases affected by moderate levels of preferential orientations. In addition, we identified one potential limitation that may affect most of the existing methods for anisotropic resolution estimation and we proposed an alternative method to evaluate the presence of preferential orientations in cryo-EM reconstructions.