Single Molecule Imaging and the First Results from LCLS

The ultrafast pulses from X-ray free-electron lasers are of high enough intensity and of sufficiently short duration that individual single-shot diffraction patterns can be obtained from a sample before significant damage occurs. This “diffraction before destruction” method may enable the determination of structures of proteins that cannot be grown into large enough crystals or are too radiation sensitive for high-resolution crystallography. In order to address the many challenges that we face in attempting molecular diffraction, we have carried out experiments in coherent diffraction from membrane protein nanocrystals at the Linac Coherent Light Source (LCLS) at SLAC. The periodicity of these objects gives us strong high-angle scattering signals in order to determine the effects of pulse duration and fluence on the high-resolution structure of single objects. The crystals are filtered to sizes less than 2 micron, and are delivered to the pulsed X-ray beam in a liquid jet. Snapshot diffraction patterns were recorded from individual crystals as small as 300 nm at the LCLS repetition rate with pnCCD detectors. It was possible to record millions of diffraction patterns, and we are assembling these data into 3D pattern for structure determination. This new form of protein nanocrystallography may open a new avenue for high-throughput membrane protein crystallography. These experiments were carried out as part of a large international collaboration between CFEL, ASU, SLAC PULSE institute, SLAC LCLS, University of Uppsala, Max Planck Institute for Medical Research and others, using the CAMP apparatus which was designed and built by the Max Planck Advanced Study Group at CFEL. The LCLS is operated by Stanford University on behalf of the U.S. Department of Energy, Office of Basic Energy Sciences.