1. Department of Structural Biology Weizmann Institute of Science Herzl St. 234 7610001 Rehovot Israel
2. Centre for Structural Systems Biology (CSSB) DESY and European Molecular Biology Laboratory Hamburg Notkestrasse 85 22607 Hamburg Germany
3. Department of Chemical and Biological Physics Weizmann Institute of Science Herzl St. 234 7610001 Rehovot Israel
4. Department of Medical Biochemistry and Biophysics Karolinska Institutet 17177 Stockholm Sweden