RJR conceived of and directed the project. DJT constructed (or supervised the construction of) the mutants, purified the proteins and carried out the kinetic assays and analysis. Both authors contributed to the interpretation of the data and have read and approved the contents of this manuscript.
We thank David Rice (University of Sheffield, UK) and Hazel Holden (University of Wisconsin, USA) for sharing data prior to publication. We also thank Alison Swinnerton who constructed the E43G mutant as part of her undergraduate project. This work was funded by the BBSRC and the Leverhulme Trust.