First, we will consider the effect of binding ATP to the apo system. By careful analysis of the "bands" in figure , we can see that an overall loss of correlation occurs in many regions of the protein -which implies a sort of "loosening" of motion, or an "unfreezing" of the protein itself. Among the regions that experienced an overall loss of correlation upon ATP binding to the apo structure, the A and N cytosolic domains, which are fairly close to and encompass the ATP binding site itself, experienced such a "loosening". This finding agrees well with previous results showing an increase in A-N domain distance with ATP binding . Additionally, and significantly, the transmembrane region close to the calcium binding domain experienced a "loosening" phenomenon upon ATP binding, a result that corroborates our observation in Fig. , where a low correlated motion was also observed between the ATP and the calciumbinding residues. In contrast, some of the "bands" indicate that several regions gained correlated motion upon ATP binding, implying a sort of "freezing up" or "stiffening" of regions of the protein. Among the regions that "stiffened", a few parts of the A cytosolic domain, as well as a few residues (556 to 563) near the back of the ATP binding site, were included. Additionally, a few parts of the P cytosolic domain, as well as the lumenal domain of the transmembrane region. In the case of the "stiffening" of the lumenal domain, our data supports the idea of a "disorder gradient" from a high amount of disordered motion within the calcium-binding region, gradually shifting towards a region of low disorder in the lumenal portion, where the calcium is released. We hypothesize that this "disorder gradient" provides the mechanism that promotes the traversal of calcium across the membrane, thereby contributing to the pumping mechanism of SERCA.