High-resolution structural biology – that is, imaging and analysis of proteins and macromolecular complexes at resolutions that allow one to draw conclusions about structural mechanism – has long been the province of techniques like X-ray crystallography and NMR. However, it is now possible to achieve these types of resolutions by cryo-electron microscopy, which does not require crystallization, and can be applied to complexes large and small alike. At the Center for Molecular Microscopy, our cryo-EM section is focused on determining structures of proteins and macromolecular complexes to high resolution.
Although electron microscopy has been used to image biological materials for decades, the use of cryogenic temperatures, which reduces the damage from electrons during imaging, allows for the study of unfixed, unstained proteins and molecular complexes. Nevertheless, even with the protection of cryogenic temperatures, the electron dose still needs to be very low in order to avoid damaging sensitive biological samples.
Within the last few years, several key advances have allowed for better and better resolution: first, a new type of camera (direct electron detectors) has been introduced, which allows for much better signal detection; and second, more computing power coupled with new algorithms for processing images has allowed researchers to tease more information out of existing electron microscopic images. For the first time, it is possible to acquire near-atomic resolution information from cryo-electron microscopy.
At the Center for Molecular Microscopy, we use both single particle analysis with cryo-electron microscopy, as well as cryo-electron tomography coupled with sub-tomogram averaging, to determine structures of protein complexes.