SINGLE PARTICLE cryo-EM OF BIOLOGICAL MACROMOLECULES
Electron Microscopy Unit, Weizmann Institute of Science, Rehovot, Israel
Single particle cryo-electron microscopy (cryo-EM) involves the 3D visualization of biological macromolecules in solution. Substantial improvements in the technique now enable to determine macromolecular structures to atomic resolution, attracting great interest in the structural biology field. These breakthroughs have awarded the 2017 Nobel Prize in Chemistry to Jacques Dubochet, Joachim Frank and Richard Henderson, who played a major role in the development of the method over the past 5 decades.
In order to resolve the structure of a macromolecule, it is first purified from the cellular environment and imaged at cryogenic temperatures using a transmission electron microscope (TEM). The resulting images, formed from the interaction of the electrons with the sample, are 2D projections of the macromolecule. Then, many 2D projections of the same macromolecule viewed from different orientations are combined in silico to form a 3D reconstruction. The reconstruction provides detailed information on the macromolecule and can be used for different purposes such as understanding protein function, interactions and dynamics, and for drug design.
Several technological advances have contributed to the improvement in map resolution, including advances in imaging quality and throughput, direct detection, new algorithms and computation power. Notably, although the improvement in map resolution has been major driving force, cryo-EM experiments entail additional elaborate information about the investigated macromolecule, such as the existence of multiple populations in the solution, oligomeric states and conformational heterogeneity. In my talk, I will introduce the theory and practice of single particle cryo-EM, and explain how recent ideas and technology have revolutionized the field.