The S4-S5 Linker Directly Couples Voltage Sensor Movement to the Activation Gate in the Human Ether-á-go-go-related Gene (hERG) K+ Channel

• Published in: The Journal of biological chemistry 2006-05, Vol.281 (18), p.12858-12864
• Main Authors: Ferrer, Tania, Rupp, Jason, Piper, David R., Tristani-Firouzi, Martin
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; Electrophysiology; Ether-A-Go-Go Potassium Channels - chemistry; Ether-A-Go-Go Potassium Channels - metabolism; Humans; Molecular Sequence Data; Oocytes - metabolism; Oxygen - chemistry; Oxygen - metabolism; Potassium - metabolism; Protein Structure, Secondary; Protein Structure, Tertiary; Recombinant Fusion Proteins - chemistry; Xenopus laevis
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M513518200

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.