1. D.I. Godfrey is at the Dept. of Microbiology and Immunology, University of Melbourne, Parkville, Victoria 3010, Australia. J. Rossjohn is at the Dept. of Biochemistry and Molecular Biology, School of Biomedical Sciences, Protein Crystallography Unit, ARC Centre of Excellence in Structural and Functional Microbial Genomics, Monash University, Clayton, Victoria 3800, Australia