1. Max Planck Research Unit for Enzymology of Protein Folding, Weinbergweg 22, 06120 Halle/Saale, Germany
2. Department of Microbiology, Immunology and Tropical Medicine, The George Washington University, 2300 I Street NW, Washington, D.C. 20037
3. Department of Chemistry, University of Düsseldorf, Universitätstrasse 1, D-40225 Düsseldorf, Germany