Figure 3.

As ion3 approaches S4 from the central cavity, the persistence time of its coordinating waters increases. (A) Illustrative snapshots showing this process. (B) Four log–linear distributions demonstrate that when ion3 is far below S4 the coordinating waters rapidly exchange with other waters in the central cavity and hence the persistence time is <140 ps. But as ion3 comes closer to the hydroxyl side chains of Thr370 that define the entrance to the filter, some waters persist for longer and longer until, when in the region −6 < z₃ ≤ −7 Å, several waters persist for the entire equilibrated region of the trajectory (400 ps).