1. MRC London Institute of Medical Sciences, Imperial College London, Hammersmith Hospital, London W12 0NN, U.K.
2. Structure Biophysics and Fragments, Discovery Sciences, Biopharmaceuticals R&D, AstraZeneca, Cambridge, U.K.
3. Institute of Clinical Sciences, Imperial College London, Hammersmith Hospital, London W12 0NN, U.K.