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[Published in 'Insight on Research' from the MRC Laboratory of Molecular Biology, February 6, 2013]
By Sjors Scheres - Determining the structure of proteins and other biomolecules at the atomic level is central to understanding many aspects of biology. X-ray crystallography is the best known technique for structural biology but, as its name suggests, it only works with samples that can be crystallized. Electron cryo-microscopy (cryo-EM) can be used to determine atomic structures of biomolecules that cannot be crystallized, but until now achieving high-resolution cryo-EM structures has been difficult.
In cryo-EM, a solution of a biomolecule of interest is frozen in a thin layer of ice, and this layer is imaged in an electron microscope. By combining images of many identical biomolecules in different orientations, it is possible to determine their three-dimensional structure. However, in order to determine this structure at high resolution, it is necessary to make many repeated measurements, often millions of images, to reduce high levels of noise. To date, cryo-EM structures with details fine enough to resolve atomic details have only been obtained for certain types of viruses.