Figure 11. Hypothetical dimensions of the open pore.

(a) The closed pore from the 3.35 Å resolution structure of the quiescent conformation of Orai (PDB 4HKR) (Hou et al., 2012). The gray surface represents the radial distance to the nearest van der Waals contact. Ca²⁺ is represented as a green sphere. Red spheres represent the iron complex and anion binding sites in the closed pore. (b) Hypothetical dimensions of the open pore, which is depicted as in (a), based on the atomic coordinates of the H206A Orai_cryst structure. There is a large amount of uncertainty in the pore dimensions and in the conformations of side chains due to the limited resolution of the diffraction data. A scale bar is shown for reference. Two hypothetical Ca²⁺ ions in the selectivity filter are depicted as green spheres.