Reconstruction of 3D structure for nanoscale biological objects from experiments data on super-bright X-ray free electron lasers (XFELs): dependence of the 3D resolution on the experiment parameters

Abstract

The ability to investigate 3D structure of biomolecules, such as proteins and viruses, is essential in biology and medicine. With the invention of super-bright X-ray free electron lasers (e.g. European XFEL and Linac Coherent Light Source (LCLS)) the Single Particle Imaging (SPI) approach allows to reconstruct 3D structures from many 2D diffraction images produced in the experiment by X-rays scattered on the biomolecule exposed in different orientations. In the same time, there are still many challenging problems in experiment setup, sample preparation and injection, which limit number and quality of obtained diffraction patterns and, consequently, limit achievable resolution of recovered 3D structure. However even with the current experimental limitations it is possible to reconstruct 3D structures of some large biomolecules. An important question arises: what range of 3D resolution is possible to achieve under experimental conditions available now. We investigated how the number and quality of diffraction images affect the 3D resolution. First the SPI experiment was simulated and reconstructed with the Dragonfly software. Then we analyzed how the number of diffraction images and the beam intensity affect the final 3D resolution. We come to the following conclusions:1) starting from the beam intensity value (fluence) equal to 3×1012photons/μm2 the resolution becomes to be almost constant;2) the resolution strongly depends on the number of diffraction patterns. More than 10 000 diffraction images are required to get 4 nm resolution.