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
(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.