Application of Hard-X-Ray Free-Electron Lasers for Static and Dynamic Processes in Structural Biology

The dream of a structural biologist is to see the biological molecule in its native conformation and to follow its structural change during fundamental biological reactions like oxidation, reduction, or excitation energy transfer. Most reactions in biology are dynamic in time domains from pico- to milliseconds. The motivation to build a hard-X-ray free-electron laser came from an in silico simulation of high-energy deposition on single molecules. This chapter reviews the pros and cons of X-ray free-electron lasers (XFEL) and serial femtosecond X-ray crystallography (SFX) over standard macromolecular X-ray crystallography and discusses the successes achieved by XFELs in structural biology to date. It talks about new challenges and prospects of time-resolved studies for ultrafast biomolecular processes, single-particle imaging, and how XFELs can revolutionize the future of structural biology. The success of the low-resolution photosystem I experiment established the premise of SFX and provided the proof of principle for damage-free structures.