Projection structures of biological cells and organelles

The diffraction apparatus for X-ray diffraction imaging (XDI) and the specimen preparation methods allow us to collect diffraction patterns from frozen-hydrated noncrystalline biological particles, such as cells and organelles, at 66–80 K. From high-quality diffraction patterns, phase retrieval (PR) calculations reconstruct electron density maps of specimen particles projected along the direction of the incident X-rays. Here, the application of XDI to structural studies of cells and cellular components is presented. Topics in synchrotron XDI include structural analyses of the chloroplasts of spinach and the small eukaryote Cyanidioschyzon merolae. In XDI experiments using X-ray free electron laser (XFEL) pulses, the structure of cyanobacteria cells and the chloroplasts of C. merolae are investigated. In addition, because XFEL-XDI experiments can provide a large number of diffraction patterns within a short time, the size distribution of targeted particles can be constructed with statistical significance. As examples, the size distributions of cuprous oxide particles, cyanobacteria cells, and amyloid aggregates are presented.