Fig. 1.

(A) Overlapping structures of modeled ECD (orange) and determined structure (PDB ID 5FBK). Mg²⁺ and putative Ca²⁺ are shown in yellow and red spheres respectively. (B) X-ray Structure of CaSR ECD (PDB ID 5FBK) and key areas to be studied with zoomed Mg²⁺ Site I, Mg²⁺ Site II, Mg²⁺ new Site, hinge ligand binding site and anion binding site. Green spheres represent Ca²⁺. bicarbonate is shown in orange sticks. TNCA is indicated by magenta sticks.