1. M. E. Müller Institute for Structural Biology, Biozentrum, University of Basel, Klingelbergstrasse 70, 4056 Basel, Switzerland
2. Institute for Physiological Chemistry, University of Tübingen, 72076 Tübingen, Germany
3. IMB, Karl-Franzens University, Universitätsplatz 2, 8010 Graz, Austria