Protein molecules and macromolecular assemblies perform the vast majority of chemical and physical actions within the cell. These tiny molecular machines perform extremely complex actions, and yet are only 10-100 nm in size. This is too small to be seen using the best possible light microscope, as they are smaller than the wavelength of visible light. In transmission electron microscopy (TEM), imaging is performed using electrons, with wavelengths of less than 0.001 nm. While the resolution of TEM is still limited due to the radiation sensitivity of biological molecules, it has now achieved resolutions ranging from 0.3 nm to 5 nm, depending on the specific technique used. TEM is capable of visualizing objects ranging from individual protein/RNA/DNA molecules to regions of cells, providing detailed information about their physical structure and function.
The National Center for Macromolecular Imaging is focused on extending the resolution, speed, and flexibility of electron cryomicroscopy (cryo-EM) for three-dimensional structure determination of biological macromolecular assemblies. The resource tackles structural problems that are too complex or too difficult for X-ray crystallography and nuclear magnetic resonance spectroscopy. Xray crystallography, the historically dominant technique in structural biology, requires the molecules under study to be rigidly locked into a single conformation. Cryo-EM, unlike crystallography, can visualize molecules under near-native conditions, and can yield images of individual molecules in a range of different conformations as they exist in solution. While these individual molecular images are highly noisy, using sophisticated computer algorithms it is possible to take tens of thousands to millions of these individual images and characterize the dynamics of these proteins in a quantitative way. Other cryo-EM techniques such as cryo-electron tomography are being developed to capture molecular structures in-situ, that is, rather than biochemically purifying a single species of molecule and studying its behavior under "artificial" conditions, actual biological molecules can be imaged within the cell at sufficient resolution to observe their conformations.
Impact on Human Health
NCMI cryo-EM hardware, software and methodologies are particularly targeted to study structures of biologically active nanomachines, which are potential drug targets for treating or preventing diseases.
NCMI collaborative research covers structures closely tied to infectious diseases. These include viruses such as Herpesvirus, and Venezuelan Equine Encephalitis Virus, which is also a bioterrorism agent; bacteria such as Salmonella and cyanobacteria; nuclear receptor superfamily protein complexes, which are a major drug target for breast cancer, and parasites such as Trypanosoma brucei, the causative agent of African Sleeping Sickness. Another focus is on neurodegenerative diseases and aging, involving the study of the misfolding of proteins found in Huntington's, Parkinson's and Alzheimer's Diseases and the potential use of molecular chaperonins to prevent their aggregation. In a third area, NCMI is contributing structural details to solve the puzzle of cardiovascular disease, investigating lipoprotein assemblies, ion channels, and the formidably complex structure of the human blood platelet, which plays a critical role in the initial stages of clot formation.
Learn more about cryo-EM - The revolution will not be crystallized from Nature