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Cryo-EM Services

Electron microscopy (EM) has become an extremely popular method for the ultrastructural study of macromolecules, cells and tissues. An aqueous biological sample is frozen rapidly and irradiated with a beam of electrons. A detector senses how the electrons are scattered and a computer reconstructs the 3D-shape of the molecule.

Why you need this service?

  • You have small amount of materials;
  • The material is hard to crystallize;
  • You are looking into the molecules in atomic details;
  • It is a large biomolecular complex (>150 kDa, up to 2000 Å);
  • You want to observe the real "native state" structure.

See the comparison of Crystallography, NMR, and EM

Service Processes: (Take protein as an example)

Cryo-EM Services

Cryo-EM Services
Sample preparation

After protein purification, these samples will be treated with cryo-fixation. In this method, protein samples are placed on a specially treated EM grid consisting of tiny holes in a film supported by a metal frame. The grid is then plunged into liquid ethane to flash-freeze it, resulting in the protein samples being embedded in a thin layer of vitreous ice. Once the frozen-hydrated grid is prepared, it is placed in the electron microscope and kept at approximately -180 K throughout the experiment.
Cryo-EM Services
EM imaging and data processing

  • Data collection;
  • Initial 3D model calculation;
  • Beam-induced motion correction;
  • Micrograph screening;
  • Automatic particle picking and normalization;
  • 2D, 3D classification and refinement.
Cryo-EM Services
Model building and refinement

Using our high-performance computers and software packages, we are able to interpret EM maps and reconstruct them into three-dimensional structural models that satisfy principles of physics and stereochemistry. (Our scientists are also very experienced with challenging targets such as membrane proteins by manual intervention to improve the initial fit or even build de novo models.) After an initial model is built, refinement is performed to maximize the agreement between the model and experimentally observed data by adjusting atomic coordinates, B factors, and other parameters.

Your Specific Sample Types

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  1. Grassucci RA, et al. (2007) "Preparation of macromolecular complexes for cryo-electron microscopy". Nat Protoc2(12):3239-3246.
  2. Doerr A. (2016) "Single-particle cryo-electron microscopy". Nat Meth 13(1):23-23.
  3. Thompson RF, et al. (2016) "An introduction to sample preparation and imaging by cryo-electron microscopy for structural biology". Methods 100:3-15.