1 Institute of Structural and Molecular Biology, Birkbeck College, London, WC1E 7HX, UK.
2 Department of Biochemistry, University of Oxford, Oxford, OX1 3QU, UK.
3 School of Life Sciences, University of Nottingham, Nottingham, NG7 2UH, UK.
4 Department of Infection Biology, Faculty of Infectious & Tropical Diseases, London School of Hygiene & Tropical Medicine, Keppel Street, London, WC1E 7HT, UK.
5 Institute of Structural and Molecular Biology, Birkbeck College, London, WC1E 7HX, UK. c.moores@bbk.ac.uk.