1. Department of Chemistry, University of Newcastle, Newcastle-upon-Tyne NE1 7RU, UK1
2. GlaxoSmithKline Research and Development, Medicines Research Centre, Gunnels Wood Road, Stevenage, Hertfordshire SG1 2NY, UK3
3. School of Biosciences, The University of Birmingham, Edgbaston, Birmingham B15 2TT, UK2
4. Department of Microbiology, Colorado State University, Fort Collins, CO 80523-1677, USA4