Figure 6: The helix-turn S_Ca binding motif

(a) Superimposition of the Ca²⁺ binding motif of 47 PDB structures (grey cartoon) out of 369 hits obtained by analysis using the Metal3 database⁴³, and the pore helix (green), selectivity filter (yellow) and the calcium ion at site S_Ca of the NaKTs structure. (b) Superimposition of the NaKTs structure (pore helix—green; main chain atoms of selectivity filter—yellow sticks; Ca²⁺ at site S_Ca—purple sphere) with representative motifs of PDB id 3K28 and 2IZ7 (grey cartoon) with <1.0 Å RMSD and their respective Ca²⁺ ions are shown in green spheres.