1. Diamond Light Source, University College London, 17–19 Gordon Street, London WC1H 0AH, UK
2. London Centre for Nanotechnology, University College London, 17–19 Gordon Street, London WC1H 0AH, UK
3. Division of Structural Biology, University of Oxford, The Henry Wellcome Building for Genomic Medicine, Headington, Oxford OX3 7BN, UK