Identification of candidate Ca²⁺ binding sites by MD simulation. (a) Time evolution of the all-atom RMSD of the α7/AChBP pentamer in the presence of Ca²⁺ ions. (b) Structure of the α7/AChBP pentamer with bound Ca²⁺ ions at the conclusion of a 150-ns MD simulation. View is from the top of the pentamer, with Ca²⁺ ions shown as purple spheres at each subunit interface. (c) Ca²⁺ ion bound to one subunit interface is shown with key stabilizing residues depicted in stick representation; view is from the side of the pentamer. (d) Time evolution of the interatomic distances between the Ca²⁺ ion that ultimately associates and the oxygen atoms of key stabilizing residues from the C-loop and F-loop during the course of MD simulation.