1. School of Chemistry and Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, UK
2. Department of Biology, University of York, York YO10 5DD, UK
3. Department of Biochemistry, University of Bristol, Bristol BS8 1QU, UK
4. Faculty of Biological Sciences, Astbury Centre for Structural Molecular Biology, University of Leeds, Leeds LS2 9JT, UK
5. GlaxoSmithKline, Medicines Research Centre, Gunnels Wood Road, Stevenage SG1 2NY, UK