1. Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, United Kingdom, Centre of Chemical Biology, Department of Chemistry, University of Sheffield, Sheffield S3 7HF, United Kingdom, Bruker BioSpin GmbH, Siberstreifen 4, 76287 Rheinstetten, Germany, Department of Biochemistry, 80 Tennis Court Road, University of Cambridge, Cambridge CB2 1GA, United Kingdom, and Department of Chemistry, MC-1460, University of California, Berkeley, California 94720