1. Department of Molecular Biology and Biotechnology, The University of Sheffield, Sheffield S10 2TN, U.K., Centre for Chemical Biology, Krebs Institute for Biomolecular Science, Department of Chemistry, The University of Sheffield, Sheffield S3 7HF, U.K., and Faculty of Life Sciences and Manchester Interdisciplinary Biocentre, The University of Manchester, Manchester M1 7DN, U.K.