Removing the need for cumbersome and often near-impossible crystallization attempts for imaging biological samples has had such a dramatic impact on structural biology that the 2017 Nobel Prize was awarded to Jacques Dubochet, Joachim Frank, and Richard Henderson for their development of cryo-electron microscopy (cryo-EM).1
Standard transmission electron microscopy (TEM) methods often rely on the staining or dehydration of biological samples to image them.2 While one advantage is that proteins do not need to be crystallized for structural analysis, sample preparation techniques can distort the biological structure from what it would be in its natural environment. Furthermore, staining techniques limit the resolution achievable by these methods.
Cryo-EM involves flash-freezing a sample to cryogenic temperatures. While the freezing process in cryo-EM means that a biological molecule, or “particle”, is trapped in a single configuration, the ability to image thousands of individual particles allows compiling these single “snapshots” into a single high-resolution 3D structure, or multiple structures if a biological sample is dynamic.
The huge drive for understanding structure and dynamics of biomolecules comes from the relationship between structure and function. Many proteins have sites with specific geometric constraints for the selective binding of ligands. Understanding the structural configuration of those sites and how they adapt dynamically to the binding of ligands can help refine drug design leading to the development of potent therapeutics.
New Structures
The impact of cryo-EM has been so profound that it is predicted to surpass X-ray crystallography as the predominant structural biology method by 2024.3 There have already been 10,000 new structures solved by cryo-EM, making it possible to look at new classes of proteins, such as membrane proteins, that were previously impossible.
The resolution achievable with electron microscopy has also helped propel cryo-EM on its runaway success leading to what many have coined a “resolution-revolution”. Structures currently are routinely solved at atomic resolution, mirroring the resolution possible by X-ray crystallography.4
Finally, what has made cryo-EM so important in structural biology is that it can resolve multiple conformational states in dynamic biomolecules. Proteins for example often undergo interconversion between several different conformations or have significant structural changes when interacting with ligands. As modern cryo-EM automated data collection software can help capture thousands of images containing millions of particles, data processing programs can distinguish between different conformation states leading to multiple structures and insights into a range of possible conformers. In this way, cryo-EM can be used for both structural and dynamical analysis of biomolecules.
JEOL cryo-EM instruments
At the heart of a successful cryo-EM experiment is the electron microscope itself. JEOL has extensive expertise in the design of electron microscopy for biological imaging applications.
Contact JEOL today to find out how their
cryo-EM and electron microscopy instruments could help provide unparalleled structural information on your biological samples.
EMDB entry: EMD-13906
Resolution: 2.9 Å
Sample name: Cryo-EM structure of Tn4430 TnpA transposase from Tn3 family in complex with 100 bp long transposon end DNA
Data collected on JEOL cryoARM300
References
- 1. Shen, P. S. (2018). The 2017 Nobel Prize in Chemistry: cryo-EM comes of age. Analytical and Bioanalytical Chemistry, 410(8), 2053–2057. https://doi.org/10.1007/s00216-018-0899-8
- 2. Ayache, J., Beaunier, L., Boumendil, J., Ehret, G., & Laub, D. (2010). Sample preparation handbook for transmission electron microscopy: techniques (Vol. 2). Springer Science & Business Media.
- 3. Callaway, E. (2020). Revolutionary cryo-EM is taking over structural biology. Nature, 578(7794), 201. https://doi.org/10.1038/d41586-020-00341-9
- 4. Nwanochie, E., & Uversky, V. N. (2019). Structure Determination by Single-Particle Cryo-Electron Microscopy : Only the Sky ( and Intrinsic Disorder ) is the Limit. International Journal of Molecular Sciences, 20, 4186. https://doi.org/doi:10.3390/ijms20174186