X-Ray Lasers in Biology Structure and Dynamics

The recent invention of the X-ray laser (XFEL), with its high spatial coherence and ability to outrun radiation damage, has provided unprecedented new opportunities for structural biology. Here, we review the challenges and advances which have occurred over the past 7 years since the first beamtimes, provide their historical context, and describe the underlying principles of the new techniques used and the XFEL. The main focus is on the achievements and prospects for imaging protein dynamics at near-atomic spatial resolution under physiological and controlled chemical conditions, in the correct thermal bath, and a summary of the many approaches to this aim. Radiation damage, comparisons of XFEL and synchrotron work, single-particle diffraction, fast solution scattering, pump-probe studies on photosensitive proteins, mixing jets, caged molecules, pH jump, and other reaction initiation methods, and the thermodynamics of molecular machines are all discussed, in addition to data analysis methods for all the instrumental modes. The ability of the XFEL to separate chemical reaction effects in dynamical imaging from radiation-induced effects (by minimizing these), while imaging at the physiological temperatures required for molecular machines, is highlighted.