1. Faculty of Applied Sciences, De Montfort University, The Gateway, Leicester, LE1 9BH, United Kingdom, Molecular Biophysics Group, CCLRC Daresbury Laboratory, Warrington, WA4 4AD, United Kingdom, Biological Chemistry Department, John Innes Centre, Norwich NR4 7UH, United Kingdom, and Molecular Microbiology Department, John Innes Centre, Norwich, NR4 7UH, United Kingdom