1. Department of Chemical Biology, Max Planck Institute for Medical Research, 69120 Heidelberg, Germany
2. Protein Expression and Characterization Facility, Max Planck Institute for Medical Research, 69120 Heidelberg, Germany
3. Structural Biology Group, European Synchrotron Radiation Facility (ESRF), 38043 Grenoble, France
4. Institute of Chemical Sciences and Engineering, École Polytechnique Fédérale de Lausanne (EPFL), 1015 Lausanne, Switzerland
5. Chemical Biology Core Facility, European Molecular Biology Laboratory, 69117 Heidelberg, Germany
6. Department of Biomolecular Mechanisms, Max Planck Institute for Medical Research, 69120 Heidelberg, Germany