Fig. 2: Competition for the aliphatic side chains of Leu124 by extended alkyl chains in the fenestrations is sufficient to disrupt the leucine collar and allow K⁺ to pass.

a (Left) Cross-sectional slice through the KirBac3.1 pore (cyan) showing the central Leu124 side chains. (Right) Accessible molecular surface demonstrating occlusion of the conduction pathway at the Leu124 collar. Side chains and surface of Leu124 are coloured yellow, lipidic alkyl chains orange, and potassium depicted as purple spheres. b Close-up representation showing the interaction of Leu124 (yellow spheres) and fenestration lipid (orange spheres). c Comparable region of a representative simulation structure extracted as a K⁺ ion passes the leucine collar. d Hexagonal bin plots of D1 against D2 (aperture diagonals) for structures extracted from unbiased non-equilibrium MD simulations. Distances are between points (red dots in the schematic) midway between Cδ1 and Cδ2. Red arrows on the plots indicate the population of highest density. (Left) Analysis of all structures. (Right) Analysis of those structures in which a K⁺ is passing the collar. e Normalized histograms of data extracted from umbrella sampling simulations enumerate the number of (water) oxygen atoms coordinating each conducted K⁺ ion as a function of linear distance from Thr96. Each column represents the number of oxygen atoms within 3.0 Å of K⁺, expressed as a percentage. Source data are provided as a Source data file.