1. Department of Life Sciences, Imperial College London, London SW7 2AZ, U.K.
2. Center for Structural Biology, Imperial College London, London SW7 2AZ, U.K.
3. European Molecular Biology Laboratory (EMBL), Hamburg 22607, Germany
4. Department of Physics, Center for Free-Electron Laser Science, Institute for Nanostructure and Solid State Physics, University of Hamburg, Hamburg 22607, Germany
5. Scientific Support Unit Machine Physics, Max-Planck-Institute for Structure and Dynamics of Matter, Hamburg 22761, Germany
6. Max Planck Institute for the Structure and Dynamics of Matter, CFEL, Hamburg 22607, Germany
7. Institute of Chemistry─Physical Chemistry, University of Potsdam, Potsdam 14469, Germany
8. Institute for Nanostructure and Solid State Physics & The Hamburg Centre for Ultrafast Imaging, HARBOR, Universität Hamburg, Hamburg 22607, Germany