Figure 1. Distribution of epileptic encephalopathy mutations in CaM binding helices A and B of K_v7.2.

(A) K_v7.2 protein (NP_742105.1) showing functional domains including transmembrane S1–S6, a pore, an intracellular C-terminal tail containing helices A-D and ankyrin-G binding motif. Missense epileptic encephalopathy mutations are concentrated in helix A (residues 324–350), helix B (residues 532–557) and the linker between helix B and helix C (residues 568–589). The mutations (R333W, M546V, K554N) characterized in this study (red) are shown. (B) Amino acid sequence alignment of K_v7.2 (NP_742105.1) and a shorter K_v7.2 isoform (CAA_75348.1 used in this study) showing helices A and B (blue), CaM-binding consensus IQ motif in helix A (underlined), A343D mutation (purple), and epileptic encephalopathy mutations (red). (C) Amino acids (R333, M518, K526) mutated in epileptic encephalopathy and characterized in this study (red) are shown on a model of K_v7.2 helices A and B (blue) in complex with Ca²⁺-bound CaM (green). A343 (purple) is located in helix A at the CaM C-lobe contact. R532 (not shown) is located distal to the helix B of this structure. (D) The modeled structure of wild type K_v7.2 helix A-B (blue) bound to Ca²⁺-bound CaM (green) is overlaid with the lowest energy model of the mutant K_v7.2 helix A-B (mutations in red) complexed with Ca²⁺-bound CaM (grey).