The National Center for Macromolecular Imaging (NCMI) is a research facility primarily focused on electron cryomicroscopy (cryo-EM) of molecules and macromolecular assemblies. Using various techniques it is now possible to obtain 3-D structures of such specimens at subnanometer resolution. Our mission is to develop this technology and make it accessible to the scientific community. We are equipped with state of the art electron cryomicroscopes, sample preparation equipment, including vitrification robots and computational resources for 3-D reconstructions. A significant portion of our resources is devoted to developing software for data acquisition, 3-D reconstructions, structural analysis and visualization of the results.
In electron cryomicroscopy, numerous challenges must be overcome to achieve subnanometer resolution structures. An electron beam can very easily damage a biological specimen, thus as few electrons as possible must be used to observe high-resolution features of macromolecules. This requirement means that the signal to noise ratio of each image is also very low. To compensate for this, tens to hundreds of thousands of images of the same kind of molecule are collected to boost the signal to noise ratio in the final 3-D reconstruction. Current reconstructions require datasets on the order of tens of gigabytes, but the amount of data required to achieve higher resolutions will double for every angstrom gained in resolution. Macromolecules by their very nature are complex assemblies of proteins and/or nucleic acids. Dissecting and analyzing these 3-D reconstructions and their various components is a significant challenge in itself. Our work has resulted in a collection of software packages that work in a number of computational environments to meet the diverse challenges in pushing the limits of cryo-EM.