1. School of Biochemistry, University of Birmingham, Birmingham B15 2TT, UK
2. Division of Biomedical Sciences, The Randall Institute, King's College, Drury Lane, London WC28 5RL, UK
3. Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06511, USA
4. Department of Infection, Medical School, University of Birmingham, Birmingham B15 2TT, England