1. Department of Chemistry Structural Biology Laboratory, The University of York, Heslington, York YO10 5YW, United Kingdom, Department of Chemistry, 2036 Main Mall, University of British Columbia, Vancouver, Canada V6T 1Z1, School of Biomedical and Chemical Sciences, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009 Australia, and Biochemisches Institut, Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland