1. Department of Biomolecular Mechanisms, Max Planck Institute for Medical Research, Jahnstrasse 29, 69120 Heidelberg, Germany.
2. Department of Structural Biology, Max Planck Institute of Biophysics, Max-von-Laue-Strasse 3, 60438 Frankfurt am Main, Germany.
3. Department of Microbiology, Radboud University, Heyendaalseweg 135, 6525 AJ Nijmegen, Netherlands.