title: Diffraction before destruction.
abstract: X-ray free-electron lasers have opened up the possibility of structure determination of protein crystals at room temperature, free of radiation damage. The femtosecond-duration pulses of these sources enable diffraction signals to be collected from samples at doses of 1000 MGy or higher. The sample is vaporized by the intense pulse, but not before the scattering that gives rise to the diffraction pattern takes place. Consequently, only a single flash diffraction pattern can be recorded from a crystal, giving rise to the method of serial crystallography where tens of thousands of patterns are collected from individual crystals that flow across the beam and the patterns are indexed and aggregated into a set of structure factors. The high-dose tolerance and the many-crystal averaging approach allow data to be collected from much smaller crystals than have been examined at synchrotron radiation facilities, even from radiation-sensitive samples. Here, we review the interaction of intense femtosecond X-ray pulses with materials and discuss the implications for structure determination. We identify various dose regimes and conclude that the strongest achievable signals for a given sample are attained at the highest possible dose rates, from highest possible pulse intensities.
authors.affiliation: Center for Free-Electron Laser Science, DESY, Notkestrasse 85, 22607 Hamburg, Germany Department of Physics, University of Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany Centre for Ultrafast Imaging, Luruper Chaussee 149, 22761 Hamburg, Germany henry.chapman@desy.de.
authors.forename: Henry N
authors.initials: HN
authors.lastname: Chapman
authors.affiliation: Center for Free-Electron Laser Science, DESY, Notkestrasse 85, 22607 Hamburg, Germany Department of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala, Sweden.
authors.forename: Carl
authors.initials: C
authors.lastname: Caleman
authors.affiliation: Department of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala, Sweden Laboratory of Molecular Biophysics, Department of Cell and Molecular Biology, Uppsala University, Box 596, 75124 Uppsala, Sweden.
authors.forename: Nicusor
authors.initials: N
authors.lastname: Timneanu
mesh_terms: D004583:Electrons; D007834:Lasers; D011487:Protein Conformation; D011506:Proteins / Q000648:ultrastructure*; D014961:X-Ray Diffraction / Q000295:instrumentation* / Q000379:methods*
chemical_list: D011506:Proteins
keywords: X-ray lasers; protein crystallography; radiation damage