Opportunities for Structure Determination Using X-ray Free-electron Laser Pulses

Abstract

One of the exciting prospects enabled by the short, intense pulses of X-ray free-electron lasers (XFELs) is the determination of near-atomic resolution structures of biomolecules and their complexes without the need of crystallisation or cryo-cooling. Using femtosecond pulses that freeze all atomic motion could open up entirely new capabilities and insights into the dynamics, function and interaction of many systems in structural biology. Meeting this goal requires methodological advances beyond those that have already been recently made at XFEL facilities. Here, some of the challenges and opportunities are discussed, starting from considerations of the interactions of X-rays with materials. The destructive nature of XFEL pulses restricts high-resolution imaging experiments to a single shot from a single sample, yet three-dimensional information is needed to properly interpret images from unsectioned samples. This requires the means to obtain multiple-view images of a unique object, such as a cell, in a single pulse or to average data from many reproducible objects as in crystallography or single-particle diffractive imaging. A potential method is presented for the former case and, in addition to the requirement of high peak brightness, the performance in the latter case is dependent on the highest average brightness achievable with future XFEL sources