Figure 3.

Ca²⁺ binding sites in the BK intracellular subunit. a, A side view of the BK gating ring with the top surface facing the membrane. The front subunit is removed for clarity. The circled positions represent the three Ca²⁺ binding sites on one subunit, and are labeled 1 for the Ca²⁺ bowl, 2 for the Asp367 site and 3 for the Glu374/Glu399 site. b, αE, the Ca²⁺ bowl, and αEF form an EF-hand like motif. The structure of the Ca²⁺ bowl (cyan loop) is disordered in the absence of Ca²⁺. c, The EF-hand structure of a Ca²⁺ binding protein (a human Calmodulin molecule with PDB code 1CLL). d and e, Structural details of the Asp367 and E374/E399 Ca²⁺ binding sites, respectively.