Cryoelektron

Cryoelektron, commonly known in English as cryo-electron microscopy (cryo-EM), is a form of electron microscopy that enables high-resolution imaging of biological macromolecules and other specimens while they are preserved in a frozen, hydrated state. By flash-freezing samples in vitreous ice, cryo-EM minimizes water crystallization and maintains near-native conformations, allowing structural analysis without crystallization.

Sample preparation involves applying the specimen to a perforated grid, blotting to form a thin film, and rapidly plunging it into a cryogenic liquid such as liquid ethane cooled by liquid nitrogen. The grids are kept at cryogenic temperatures and handled in controlled environments to prevent contamination. The goal is to produce uniformly thin ice that supports good particle distribution.

Imaging is performed in a transmission electron microscope at cryogenic temperatures. To limit radiation damage, a low electron dose is used and multiple frames are recorded for subsequent motion correction. Advances in direct electron detectors and optimized optics have increased signal-to-noise ratios. Micrographs are often collected at varying defocus to enable contrast transfer for downstream processing.

Data processing follows a multi-step workflow: motion correction, estimation of the contrast transfer function, automated or manual particle picking, two-dimensional classification, three-dimensional reconstruction, and refinement. Software packages such as RELION and cryoSPARC are widely used. The outcome is a three-dimensional electron density map, from which an atomic model can be built or fitted.

Cryo-EM offers advantages over X-ray crystallography, notably not requiring crystals and enabling visualization of conformational heterogeneity and large or flexible complexes. Applications include ribosomes, viral capsids, membrane proteins, and multi-protein assemblies. Challenges include sample heterogeneity, preferred orientation on grids, ice quality, and substantial computational demands. The field has seen rapid progress since the mid-2010s, achieving near-atomic resolutions for many structures.