Cryo-electron Microscopy

Cryo-electron microscopy (cryo-EM) examines frozen biological samples at cryogenic temperatures below −150 °C, preserving their native state without fixing or dehydrating. Unlike conventional electron microscopy, which requires sample preparation that distorts biological structures, cryo-EM uses gentler electron beams and frozen samples to prevent chemical bond damage and obtain near atomic-resolution images.

Vitrification rapidly freezes small biological samples in liquid ethane, fixing them in their native state within a thin water layer. The water forms a glass-like state without ice crystal formation, preventing high-energy electron damage to chemical bonds and enabling preservation of native biological structures for high-resolution imaging.

Thicker samples cannot be vitrified in thin liquid layers, so cryo-EM of vitreous sections is used instead. The sample is first vitrified by high-pressure freezing, then cut into ultrathin sections at −140 °C before observation using cryo-EM, allowing study of larger biological structures.

Cryo-EM does not require crystallization, which may alter biomolecular structure or be impossible for some molecules. Unlike NMR, which is limited to small soluble proteins, cryo-EM enables visualization of larger proteins, membrane-bound receptors, and biomolecular complexes in their native state without structural distortion.

Cryo-EM is extensively used in biochemistry to study biomolecular structure, function, and interactions. It enables identification and analysis of infectious agents like viruses. During the Zika virus outbreak, cryo-EM created three-dimensional images of virus structures to identify potential anti-viral drug targets for therapeutic development.

High-energy electrons used in electron microscopy damage chemical bonds in samples. Freezing samples at cryogenic temperatures below −150 °C slows molecular motion and prevents this damage, allowing for detailed near atomic-resolution imaging while preserving the native biological structure and molecular integrity.

Conventional electron microscopy involves dehydration, fixation, and staining, which distort native biological molecules and create artifacts. Cryo-EM avoids these preparation steps by rapidly freezing samples in their native aqueous state, enabling visualization of molecular movements and biomolecular interactions as they naturally occur without structural alteration.