Electron cryo-microscopy (cryo-EM) is a versatile technique to visualize the three-dimensional (3D) structure of macromolecules and their assemblies. With this technique, it is now becoming possible to study the atomic structure of assemblies with molecular masses as low as ~200 kDa (for example, a membrane protein) or as high as hundreds of MDa (for example, a large virus). The assemblies can be visualized single-fold, thus avoiding the need for crystals. This "single-particle" approach requires extremely small amounts of material, typically only a few tens of picomoles.
Our laboratory develops new methods for cryo-EM to achieve the highest possible resolution (4 Å or better). We have recently established a new movie imaging protocol  that makes use of a new type of camera, the direct electron detector. Using this detector, the total electron dose used for an image can be distributed over many short movie frames rather than a single long exposure. Any sample movement that occurs during the exposure (for example, beam-induced motion) can subsequently be tracked in the movies and “undone” by aligning the movie frames to each other, thereby producing a final image that is free of blurring.
We apply the single-particle technique to assemblies that are difficult to study by more traditional techniques such as X-ray crystallography and nuclear magnetic resonance (NMR). For example, membrane proteins are usually too large for NMR analysis or are difficult to crystallize for X-ray crystallography. Large protein assemblies pose additional problems because they can undergo constant changes in composition and conformation. An example is the spliceosome, which forms from a number of smaller RNA-protein assemblies called snRNPs. Another class of protein assemblies that do not usually form crystals includes fibers and filaments, such as amyloid fibrils. We also study highly symmetrical viruses that represent ideal test specimens for the development of new image processing techniques.