1. Department of Biochemistry and Molecular Biology, University of Parma, 43100 Parma, Italy
2. Institute of Chemistry, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands
3. Institute of Biochemistry, Molecular Genetics Group, and Cluster of Excellence Macromolecular Complexes, Goethe University, D-60438 Frankfurt, Germany