Cryo-electron microscopy

Cryo-electron microscopy (cryo-EM), or electron cryomicroscopy, is a form of transmission electron microscopy (EM) where the sample is studied at cryogenic temperatures (generally liquid nitrogen temperatures). Cryo-EM is gaining popularity in structural biology.

The popularity of cryoelectron microscopy stems from the fact that it allows the observation of specimens that have not been stained or fixed in any way, showing them in their native environment. This is in contrast to X-ray crystallography, which requires crystallizing the specimen, which can be difficult, and placing them in non-physiological environments, which can occasionally lead to functionally irrelevant conformational changes.

The resolution of cryo-EM maps is improving steadily, and in 2014 some structures at near atomic resolution had been obtained using cryoelectron microscopy, including those of viruses, ribosomes, mitochondria, ion channels, and enzyme complexes as small as 170 kD at a resolution of 4.5 Å. A 2.2 Å map of a bacterial enzyme beta-galactosidase was published in June 2015. A version of electron cryomicroscopy is cryo-electron tomography (CET) where a 3D reconstruction of a sample is created from tilted 2D images.