Functional Equilibrium of the KcsA Structure Revealed by NMR

KcsA is a tetrameric K+ channel that is activated by acidic pH. Under open conditions of the helix bundle crossing, the selectivity filter undergoes an equilibrium between permeable and impermeable conformations. Here we report that the population of the permeable conformation (pperm) positively correlates with the tetrameric stability and that the population in reconstituted high density lipoprotein, where KcsA is surrounded by the lipid bilayer, is lower than that in detergent micelles, indicating that dynamic properties of KcsA are different in these two media. Perturbation of the membrane environment by the addition of 1–3% 2,2,2-trifluoroethanol increases pperm and the open probability, revealed by NMR and single-channel recording analyses. These results demonstrate that KcsA inactivation is determined not only by the protein itself but also by the surrounding membrane environments. Background: The selectivity filter of KcsA undergoes an equilibrium between permeable and impermeable conformations under acidic conditions. Results: Truncation of the intracellular region or addition of 2,2,2-trifluoroethanol modulates the equilibrium. Conclusion: Membrane environments affect dynamics of KcsA. Significance: This is the first evidence that a structural equilibrium in the membrane is related to the inactivation of a potassium channel.