Recent Advances in Electron Crystallography

Abstract

Electron crystallography has been used as the one of powerful tool for studying the structure of biological macromolecules at high resolution which is sufficient to provide details of intramolecular and intermolecular interactions at near-atomic level. Previously it commonly uses two-dimensional crystals that are periodic arrangement of biological molecules, however recent studies reported a novel technical approach to electron crystallography of three-dimensional crystals, called micro electron-diffraction (MicroED) which involves placing the irregular and small sized protein crystals in a transmission electron microscope to determine the atomic structure. In here, we review the advances in electron crystallography techniques with several recent studies. Furthermore, we discuss the future direction of this structural approach.

Toward High-Resolution Cryo-Electron Microscopy: Technical Review on Microcrystal-Electron Diffraction

“…This technique has been developed over recent years by many groups by using small-sized and relatively dose-insensitive compounds Unwin, 2003;Unwin & Henderson, 1975). In electron crystallography, the crystals should be thinner than those used for X-ray crystallography as electrons have much stronger interactions with the atoms and molecules in the sample than the X-ray photons (Chung et al, 2017;Kimura et al, 1997). Owing to this reason, electron diffraction has been restricted to be used with 2D crystals that comprise 1~2 thin layers of a well-ordered 2D crystalline lattice.…”

“…Traditional 3D electron crystallography produces a single diffraction pattern for a given 3D protein crystal owing to the radiation-damage issue. Hence, each diffraction pattern has to be merged into a single dataset to reconstruct the 3D model; this causes an indexing problem owing to the lack of sufficient information in a single diffraction pattern (Chung et al, 2017). One previous study solved the indexing and merging problems by using a single nanocrystal under low electrondose conditions (~10 e − /A) to collect a complete diffraction dataset (Shi et al, 2013).…”

“…However, it is still necessary to improve some factors. One of the most interesting current areas of micro-ED is the development of experimental phasing methods because the phasing information that is crucial for crystallography currently cannot be measured from electron-diffraction patterns (Chung et al, 2017). To solve this issue, accurate integrated-diffraction intensities and the development of electron-scattering tables are required (Chung et al, 2017;Scherer et al, 2014).…”

“…One of the most interesting current areas of micro-ED is the development of experimental phasing methods because the phasing information that is crucial for crystallography currently cannot be measured from electron-diffraction patterns (Chung et al, 2017). To solve this issue, accurate integrated-diffraction intensities and the development of electron-scattering tables are required (Chung et al, 2017;Scherer et al, 2014). Several strategies have been used to obtain the phase information, such as the use of heavy atoms for isomorphous replacements and changing the electron wavelengths, but unique and interesting approaches are required to solve the phasing problem (Shi et al, 2016).…”