Structural alignment and modeling illustrating the high structural similarity of different K ⁺ channels. The conformation of the pore and outer helices (TM1) is highly conserved among different K⁺ channels. The upper panel illustrates the superposition of the TM1-pore helix motif for eight homologous K⁺ channels with their PDB accession nos. in parentheses except for the predicted structure of KvKcsA (in green). For clarity, the turret loops of KvKcsA and KcsA only are shown in ribbon representation. The lower panel shows the structure-based sequence alignment for the same channels illustrating the modularity of the respective domains: first transmembrane helix (TM1), P-loop (or pore helix), and selectivity filter (SF). The turret loop is framed in an orange box.