Recent Advances in Single Particle Cryo-electron Microscopy and Cryo-electron Tomography to Determine the Structures of Biological Macromolecules

Abstract

A detailed three-dimensional structure of macromolecular assemblies is necessary to understand their function which in turn helps to understand life. Cryo-electron microscopy (cryo-EM) is a powerful method for structural studies of a wide range of different sizes biological macromolecules and their complexes. Cryo-EM has three different imaging modalities based on specimen and imaging condition: single particle analysis (SPA), cryo-electron tomography (cryo-ET) plus sub-tomogram averaging (STA)/sub-volume averaging (SVA) and electron diffraction. Richard Henderson and Nigel Unwin revealed the structure of the first membrane protein bacteriorhodopsin from electron diffraction data. This led to the beginning of understanding molecular structures of biomolecules in three-dimension. Soon after that, a unique vitrification method of biomolecules has been successfully developed by Jacques Dubochet more than two decades ago. Ordered 2D array or biomolecules with internal symmetry have long been considered for structure determination to achieve better resolution. But structure calculation by electron microscopy was at that time known as blobology to others due to low resolution Images with small number of pixels and less information and less detail. (image with less information) compared to X-ray. Since then imaging and software technologies have steadily improved and after 2013, with the development and success of direct detectors, the world witnessed a resolution revolution in cryo-EM. Now cryo-EM more specifically single particle analysis has achieved the resolution at which protein complex can be studied at near-atomic level. This once a highly skilled and difficult technique has now become a widely accepted biophysical technique in structural biology. Here the two methods of cryo-EM (SPA and cryo-ET) and recent studies are reviewed.