1. Institute of Biochemistry and Molecular Biology, ZBMZ, University of Freiburg, Stefan-Meier-Strasse 17, D-79104 Freiburg, Germany
2. Institute of Organic Chemistry and Biochemistry, University of Freiburg, Albert-Strasse 21, D-79104 Freiburg, Germany
3. Department of Medical Genome Sciences, Graduate School of Frontier Sciences, The University of Tokyo, Chiba 277-8562, Japan
4. Unité Biochimie Structurale, CNRS URA 2185, Institut Pasteur, 75724 Paris cedex 15, France