Fig 2.

(a) Fully atomistic KcsA ion channel system (protein as yellow ribbons, lipid tails as chains, water as sticks and K⁺ and Cl⁻ ions as red and grey balls, respectively). (b) Differing multi-ion barriers for K⁺ and Na⁺. The low barrier to K⁺ outward conduction results from the ability of a K⁺ ion (red) to bind to the entrance of the selectivity filter. (c) The shift of binding site for Na⁺ (green), eliminates this process and requires a substantial amount of energy. Based on (Nimigean & Allen, 2011).