title: The S4-S5 linker directly couples voltage sensor movement to the activation gate in the human ether-a'-go-go-related gene (hERG) K+ channel.
abstract: A key unresolved question regarding the basic function of voltage-gated ion channels is how movement of the voltage sensor is coupled to channel opening. We previously proposed that the S4-S5 linker couples voltage sensor movement to the S6 domain in the human ether-a'-go-go-related gene (hERG) K+ channel. The recently solved crystal structure of the voltage-gated Kv1.2 channel reveals that the S4-S5 linker is the structural link between the voltage sensing and pore domains. In this study, we used chimeras constructed from hERG and ether-a'-go-go (EAG) channels to identify interactions between residues in the S4-S5 linker and S6 domain that were critical for stabilizing the channel in a closed state. To verify the spatial proximity of these regions, we introduced cysteines in the S4-S5 linker and at the C-terminal end of the S6 domain and then probed for the effect of oxidation. The D540C-L666C channel current decreased in an oxidizing environment in a state-dependent manner consistent with formation of a disulfide bond that locked the channel in a closed state. Disulfide bond formation also restricted movement of the voltage sensor, as measured by gating currents. Taken together, these data confirm that the S4-S5 linker directly couples voltage sensor movement to the activation gate. Moreover, rather than functioning simply as a mechanical lever, these findings imply that specific interactions between the S4-S5 linker and the activation gate stabilize the closed channel conformation.
authors.affiliation: Department of Pediatrics, University of Utah, Salt Lake City, Utah 94113, USA.
authors.forename: Tania
authors.initials: T
authors.lastname: Ferrer
authors.forename: Jason
authors.initials: J
authors.lastname: Rupp
authors.forename: David R
authors.initials: DR
authors.lastname: Piper
authors.forename: Martin
authors.initials: M
authors.lastname: Tristani-Firouzi
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D004594:Electrophysiology; D051638:Ether-A-Go-Go Potassium Channels / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D008969:Molecular Sequence Data; D009865:Oocytes / Q000378:metabolism; D010100:Oxygen / Q000737:chemistry / Q000378:metabolism; D011188:Potassium / Q000378:metabolism; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000737:chemistry; D014982:Xenopus laevis
chemical_list: D051638:Ether-A-Go-Go Potassium Channels; C092509:KCNH6 protein, human; D011993:Recombinant Fusion Proteins; D011188:Potassium; D010100:Oxygen