1. Department for NMR-Based Structural Biology, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany
2. Max Planck Unit for Structural Molecular Biology, c/o DESY, Notkestrasse 85, 22607 Hamburg, Germany
3. Institut de Biologie Structurale Jean-Pierre Ebel, CEA-CNRS-UJF UMR 5075, 41 Rue Jules Horowitz, Grenoble 38027, France
4. DFG Research Center for the Molecular Physiology of the Brain (CMPB), Göttingen, Germany