1. Department of Biophysics, 3400 N. Charles Street, Johns Hopkins University, Baltimore, MD-21218, USA
2. Department of Microbiology, Immunobiology and Genetics, Max Perutz Labs, University of Vienna, Vienna Biocenter (VBC), Dr. Bohrgasse 9/4, 1030 Vienna, Austria
3. Department of Biochemistry, University of Cambridge, Cambridge CB2 1GA, UK