Fig. 1

Cell membrane topology of a 2TM potassium (K⁺) channel: fundamental building blocks consist of multiples of transmembrane domains (M1 and M2), a pore-forming loop (P), and a signature (s) sequence of amino acids (TT V/I GYG or “ion selectivity filter”) highly conserved in K⁺ channels across taxa; intra- and extracellular segments have specific names (i.e., pre-M1, Turret and extended regions, post-M2); K⁺ ions are represented by small spheres. b Two subunits (cutaway view) of the tetrameric (4 × 2TM) structure of KcsA, one of the simpler prokaryotic K⁺ channels from the soil bacterium Streptomyces lividans, are depicted