Anomalous signal from S atoms in protein crystallographic data from an X‐ray free‐electron laser. (1st May 2013) - Barends, Thomas R. M.
Abstract X‐ray free‐electron lasers (FELs) enable crystallographic data collection using extremely bright femtosecond pulses from microscopic crystals beyond the limitations of conventional radiation damage. This diffraction‐before‐destruction approach requires a new crystal for each FEL shot and, since the crystals cannot be rotated during the X‐ray pulse, data collection requires averaging over many different crystals and a Monte Carlo integration of the diffraction intensities, making the accurate determination of structure factors challenging. To investigate whether sufficient accuracy can be attained for the measurement of anomalous signal, a large data set was collected from lysozyme microcrystals at the newly established `multi‐purpose spectroscopy/imaging instrument' of the SPring‐8 Ångstrom Compact Free‐Electron Laser (SACLA) at RIKEN Harima. Anomalous difference density maps calculated from these data demonstrate that serial femtosecond crystallography using a free‐electron laser is sufficiently accurate to measure even the very weak anomalous signal of naturally occurring S atoms in a protein at a photon energy of 7.3 keV.