More detailed analysis of the molecular basis for the differences in stability of the loop indicated that the central portion of the WPD-loop of Chimera 2 is substantially more rigid than that of Chimera 3, and the α-helix at the C-terminus of the WPD-loop is significantly more stable in Chimera 2 (Figure ). We note that our prior computational study of wild-type YopH indicated the importance of this α-helix to being able to populate a wide-open conformation of the loop in the first instance . Our simulations also provide insight into subtle differences in the interaction networks controlling loop motion between the different enzymes, and its link to loop stability and activity. Taken together, our data provide insight into the regulation of the wideopen conformation of YopH and the implications this has for catalysis, which is an important steppingstone for both understanding the functional relevance of this conformation, and how it can be exploited for drug discovery purposes.