Figure 8.

Summary and model of the role of glutamate 418 to stabilize the channel voltage sensor in the conductiving conformation. A section of a K⁺ channel is shown with the pore region in white containing the negative charges of the carbonyl dipoles lining the selectivity filter. The negatively charged side chain of residue 418 located at the base of the turret is represented inside a circle. Two of the four S4 helices with seven positive charges, connected to the activation gates, are shown. The channel is shown at the closed, open, and C-inactivated states. The open state resulting from the movement of the S4 voltage sensors is stabilized by the charge in residue 418. Transition from the open to the C-inactivated state involves reorganization of the pore and rearrangement of the S4 helices, which is favored by either removal of extracellular K⁺ or neutralization of the charge at position 418. Destabilization of the open state in channel E418Q accelerates the closing of the channels. See text for further details.