It is also evident that the presence of the POPE donor substrate does not exert any significant effect upon the overall structure of either domain. The largest differences between equivalent sets of simulations in the absence and presence of POPE are observed for the "resting" (i.e. with Thr285 unmodified) state of the catalytic domain, and for the transmembrane domain in the PEtN-bound intermediate state, both in the mono-zinc form. In both cases we consider these differences to arise from stochastic variations between individual simulations in each set of triplicate repeats. For the unmodified mono-zinc system this variation is due to a reorientation of the two domains relative to one another in one of the three POPE-bound simulations, while in the intermediate (PEtN-bound) system the major differences involve unstructured loop regions, far from the active site, in both catalytic and transmembrane domains. Less pronounced (≤ 4.0 Å) differences are also evident in all four helices of the transmembrane domain which interact with the POPE molecule (below). Overall, we conclude that increases in fluctuations within the MCR-1 structure in the presence or absence of docked POPE are due to stochastic variations between repeat simulations, and/or minor rearrangements within the transmembrane domain local to the POPE molecule, and do not indicate long-distance or larger scale conformational changes.