1. Department of Biochemistry and Biophysics, Stockholm University, SE-106 91 Stockholm, Sweden
2. Center for Integrated Protein Science Munich at the Department of Chemistry, Technical University of Munich, Lichtenbergstrasse 4, D85748 Garching, Germany
3. Institut für Biochemie, Albert-Ludwigs-Universität Freiburg, Albertstrasse 21, 79104 Freiburg, Germany