cryoEM

Cryo-electron microscopy (cryo-EM) is a form of transmission electron microscopy in which biological specimens are studied at cryogenic temperatures to preserve native structures. It encompasses several methods, including single-particle cryo-EM, cryo-electron tomography, and microcrystal electron diffraction.

Samples are applied to grids, rapidly vitrified by plunging into liquid ethane held at cryogenic temperatures, producing vitreous ice that immobilizes molecules in a near-native state. This avoids crystalline ice and minimizes radiation damage during imaging.

Imaging is performed under low electron dose to reduce damage; thousands to millions of particle images are collected from many orientations and computationally aligned and averaged to yield a 3D electron density map. Direct electron detectors and improved software have expanded achievable resolutions.

The so-called resolution revolution in the 2010s dramatically improved attainable resolutions, enabling near-atomic structures for large proteins and complexes. The technique's developers were recognized with the 2017 Nobel Prize in Chemistry: Jacques Dubochet, Joachim Frank, and Richard Henderson.

Applications include structural biology of proteins and complexes, including membrane proteins, without the need for crystallization. Challenges include sample heterogeneity, preferred orientation, and radiation sensitivity; small or flexible targets can be difficult to resolve, and extensive computational resources are often required.

Deposited model coordinates and density maps are stored in public databases such as the Protein Data Bank and the Electron Microscopy Data Bank, with validation and community standards guiding interpretation.