1. Macromolecular Structure Laboratory, The Francis Crick Institute, 1 Midland Road, London NW1 1AT, U.K.
2. Structural Biology Science Technology Platform, The Francis Crick Institute, 1 Midland Road, London NW1 1AT, U.K.
3. The Medical Research Council Biomedical NMR Centre, The Francis Crick Institute, 1 Midland Road, London NW1 1AT, U.K.