1. Department of Infectious Diseases and Microbiology, Centre for Molecular Microbiology and Infection, Imperial College of Science Technology and Medicine, London SW7 2AZ, UK1
2. School of Crystallography, Birkbeck College, University of London, Malet Street, London WC1E 7HX, UK2
3. Department of Medical Microbiology, St George’s Hospital Medical School, Cranmer Terrace, London SW17 0RE, UK3