* Corresponding authors

^a Division of Chemistry & Structural Biology, Institute for Molecular Bioscience, The University of Queensland, St. Lucia 4072, Brisbane, Australia

^b Department of Molecular, Microbial, and Structural Biology, University of Connecticut Health Center, 263 Farmington Ave, Farmington, CT 06030-3305, USA
E-mail: hoch@uchc.edu

^c Rowland Institute at Harvard, 100 Edwin H. Land Blvd, Cambridge, MA 02139, USA