1. Division of Structural Biology, Wellcome Trust Centre for Human Genetics, University of Oxford, Roosevelt Drive, Oxford, OX3 7BN, UK.
2. Department of Cell Biology and Program in Neuroscience, Harvard Medical School, Boston, MA 02115, USA.
3. Motor Neuron Center, Columbia University, New York, NY 10032, USA.
4. School of Cancer and Imaging Sciences, Faculty of Medical and Health Sciences, University of Manchester, Paterson Institute for Cancer Research, Manchester M20 4BX, UK.
5. Iduron, Paterson Institute for Cancer Research, University of Manchester, Manchester M20 4BX, UK.