Lawrence Berkeley National Laboratory

Macromolecules, such as proteins and nucleic acids, play essential roles in cellular functions through dynamic structural changes. Understanding these functions requires detailed characterization of structural dynamics. While techniques like X-ray crystallography and cryo-EM resolve high-resolution static structures, they struggle to capture low-resolution, flexible structures and the full distribution of conformations during chemical reactions. These limitations arise from averaging processes that enhance signal-to-noise ratios (SNR) but exclude flexible regions, distort resolution, and miss rare high-energy states. To address this, we developed individual-particle electron tomography (IPET), a method for determining 3D structures of single particles at low to intermediate resolution (up to 2 nm) without averaging. By imaging a particle at multiple tilt angles, IPET reconstructs a detailed 3D density map, enabling flexible model fitting and revealing unique structures for individual particles. This approach uncovers unbiased structural distributions, advancing studies of molecular dynamics, phase transitions, and structural changes during chemical reactions and self-folding.