Investigating the Electromechanical Coupling in voltage-gated K+ channels

Abstract

While the gating of the voltage sensor as well as the opening of the ion conducting pore in voltage-gated ion channels has been investigated extensively, the electromechanical coupling between the peripheral voltage sensors and the central ion conducting pore needs to be further elucidated. Based on previous work (Lu et al., 2002) and the crystal structure of Kv1.2 (Long et al, 2005), it has been suggested that the C-terminal S6 is coupled to the S4-S5 linker region, and that this coupling leads to opening of the pore. Here, we set out to investigate the role of this interaction in the coupling mechanism in voltage-gated Shaker K+ channels. Possible interaction sites were chosen and altered by point mutation. The Shaker channels were expressed in Xenopus oocytes and ionic and gating currents as well as fluorescence changes monitoring the S4 movement were determined using voltage-clamp fluorometry in a cut-open voltage-clamp setup.We identified two spatially distinct interactions between the S6 and the S4-S5 linker that have a significant influence on the gating properties of Shaker. One interaction acts upon the closed and open state and its disturbance accelerates voltage sensor movement while slowing ionic currents. A second interaction only acts in the open state. Exchange of the responsible residue slows closing of the channel by trapping the voltage sensor in the open state. We are interpreting the interactions in order to form a molecular model for the electromechanical coupling process.(supported by CIHR MOP-81351 and CRC 202965).