1. Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, U.K.
2. Department of Structural and Computational Biology, Max Perutz Laboratories, University of Vienna, Campus Vienna Biocenter 5, Vienna A-1030, Austria
3. UCB Pharma, 208 Bath Road, Slough SL1 3WE, U.K.