ABSTRACT
Extracellular tetraethylammonium (TEA+) inhibits the current carried out by K+ ions in potassium channels. Structural models of wild-type (WT) and Y82C KcsA K+ channel/TEA+ complexes are here built using docking procedures, electrostatics calculations and molecular dynamics simulations. The calculations are based on the structure determined by Doyle et al.11Our calculations suggest that in WT, the TEA+ cation turns binds at the outer mouth of the selectivity filter, stabilized by electrostatic and hydrophobic interactions with the four Tyr82 side chains. Replacement of Tyr82 with Cys causes a decrease of the affinity of the cation for the channel, consistently with the available site-directed mutagenesis data16. An MD simulation in which K+ replaces TEA+ provides evidence that TEA+ binding site can accommodate a potassium ion, in agreement with the high-resolution structure recently reported by Zhou et al.20
Notes
*D2d TEA+ in water. TEA+ was immersed in a water cubic box (∼40 Å edge) along with a Cl− counterion. The system was equilibrated for 0.5 ns carrying out MD calculations at room conditions.
†Standard structural parameters were imposed.
‡During the dynamics, the two ions turned out to be separated by at least 15 Å; thus, the presence of Cl− is expected not to affect the structural properties of TEA+ and its hydration sphere.
§The four Cys side-chains, initially located into the bulk aqueous solvent, approached the hydrophobic Tyr-78 aromatic rings within 0.2 ns.
**Instead, TEA+ does not form cation-π interactions with the protein, as previously postulated.Citation[4]