Enzyme structures and dynamic behavior were characterized by X-ray crystallography, empirical valence bond simulations, and both conventional and enhanced molecular dynamics simulations, the former of which were in turn used to construct Markov State Models with which to compare loop transitions in the different enzyme variants. PTP1B is more tolerant of chimera substitutions than YopH, and these chimeras do not exhibit the structural disruptions found in the YopH-based chimeras. The combined results show how the non-catalytic amino acids within this mobile element of classical PTPs affect catalysis, particularly by altering WPDloop mobility and the equilibrium between open and closed states. More generally, the results highlight the potential for targeting non-catalytic residues as hotspots for manipulating the conformational equilibria of catalytic loops and thus regulating enzyme activity. 2 Materials and Methods