1. Laboratory of Biomolecular Research; Department of Biology and Chemistry; Paul Scherrer Institut; OFLC/111 5232 Villigen PSI Switzerland
2. Current address: Department of Biochemistry; University of Zürich; Winterthurerstrasse 190 8057 Zürich Switzerland
3. Chemical and Physical Biology; Centro de Investigaciones Biológicas; Consejo Superior de Investigaciones Científicas CIB-CSIC; Ramiro de Maeztu 9 28040 Madrid Spain
4. Department of Chemistry; University of Pennsylvania; 231 S. 34th Street Philadelphia PA 19104 USA
5. Department of Molecular Pharmacology; Albert Einstein College of Medicine; 1300 Morris Park Avenue Golding 201 Bronx NY 1046 USA
6. University Chemical Laboratory; Cambridge University; Lensfield Road Cambridge CB2 1EW UK