1. Department of Chemistry, Technical University of Munich, Garching, Germany
2. Max-Planck-Institut für Biochemie, Am. Klopferspitz, D-82152 Martinsried, Germany
3. Department of Medicinal Chemistry and Pharmacognosy, Purdue University, West Lafayette, Indiana 47907, U.S.A.
4. Centre for Structural Biochemistry, Karolinska Institute, S-14157 Huddinge, Sweden