1 Department of Integrative Structural & Computational Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA. Electronic address: millar@scripps.edu.
2 Deputy Vice-Chancellor (Research), The University of Sydney, Room 646, Jane Foss Russell Building G02, Sydney, NSW 2006, Australia. Electronic address: jill.trewhella@sydney.edu.au.