Chapter 8: Crystallography with X-ray Free Electron Lasers

X-ray free electron lasers (XFELs) promise to revolutionize structural biology through serial femtosecond protein nano/microcrystallography (SFX), solution scattering and, ultimately, single particle imaging. The goals are lofty: atomic-resolution, time-resolved macromolecular structures with unprecedented time-resolution, at room temperature, without radiation damage, in the macromolecule's native liquid or lipidic environment, or in other words, experimentally-determined molecular movies. This chapter introduces XFELs and focuses on serial femtosecond crystallography. The principles of SFX, radiation damage and SFX sample delivery are described, including challenges that were overcome in order to establish SFX as a reliable technique offering unique capabilities. Achievements in the field such as the determination of undamaged, room-temperature structures of G-protein-coupled receptors and large membrane complexes, ultrafast (<100 fs) time-resolved studies of light-sensitive systems using pump-probe SFX, the first mix-and-inject experiments (the birth of SFX enzymology), and the successful development of de novo phasing from SFX data are reviewed. Finally, an overview of SFX data collection and analysis is presented, including novel methodologies undergoing most active development and outstanding challenges in SFX. We close with a brief perspective on the future of this burgeoning, exciting field.