1. Institute of Molecular Biology and Biophysics, Department of Biology, ETH Zürich, Zürich, Switzerland
2. Laboratory of Biomolecular Research, Biology and Chemistry Division, Paul Scherrer Institute, Villigen PSI, Switzerland
3. University of Wisconsin Milwaukee, Milwaukee, Wisconsin 53201, USA
4. Center for Free-Electron Laser Science CFEL, Deutsches Elektronen-Synchrotron DESY, 22607 Hamburg, Germany
5. Department of Physics, Universität Hamburg, 22607 Hamburg, Germany