1. Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany
2. Institute of Biotechnology, P.O. Box 65, 00014 University of Helsinki, Helsinki, Finland
3. Peptide and Protein Laboratory, Department of Virology, Infection Biology Research Program, Haartman Institute, P.O. Box 21, 00014 University of Helsinki, Helsinki, Finland
4. Department of Biological and Environmental Sciences, P.O. Box 65, 00014 University of Helsinki, Helsinki, Finland