Basic concepts of cryo-EM image processing in single particle analysis and relevant modern softwares

Bum Han Ryu

Electron Microscopy Research Center

Korea Basic Science Institute

E-mail: psryubh@gmail.com

For last decades X-ray crystallography was a major technique to obtain high-resolution structure of biological macromolecules, though there are some critical limits due to its high dependency on sample crystallization. As an alternative, single particle cryo-electron microscopy has drawn a huge attention since it allows us to solve near-native structures of challenging macromolecules. This technique can be summarized into the following two steps: 1) collection of 2D projection image data from cyro-EM experiments, 2) 3D reconstruction of structure from the processing of 2D images. Both steps are tricky in many terms. Particularly, the latter part entails complicated computation procedures with certain risks that lead to an improper 3D reconstruction or an erroneous resolution estimation. Therefore, a robust understanding of related fundamental theories is very important in order to perform each stage of image processing properly. Here, basic concepts of single particle image processing and relevant modern softwares are introduced briefly.

Keyword: cryo-EM, image processing, single particle analysis, protein structure