Interactions between S4-S5 linker and S6 transmembrane domain modulate gating of HERG K+ channels.
Outward movement of the voltage sensor is coupled to activation in voltage-gated ion channels; however, the precise mechanism and structural basis of this gating event are poorly understood. Potential insight into the coupling mechanism was provided by our previous finding that mutation to Lys of a single residue (Asp(540)) located in the S4-S5 linker endowed HERG (human ether-a-go-go-related gene) K(+) channels with the unusual ability to open in response to membrane depolarization and hyperpolarization in a voltage-dependent manner. We hypothesized that the unusual hyperpolarization-induced gating occurred through an interaction between Lys(540) and the C-terminal end of the S6 domain, the region proposed to form the activation gate. Therefore, we mutated six residues located in this region of S6 (Ile(662)-Tyr(667)) to Ala in D540K HERG channels. Mutation of Arg(665), but not the other five residues, prevented hyperpolarization-dependent reopening of D540K HERG channels. Mutation of Arg(665) to Gln or Asp also prevented reopening. In addition, D540R and D540K/R665K HERG reopened in response to hyperpolarization. Together these findings suggest that a single residue (Arg(665)) in the S6 domain interacts with Lys(540) by electrostatic repulsion to couple voltage sensing to hyperpolarization-dependent opening of D540K HERG K(+) channels. Moreover, our findings suggest that the C-terminal ends of S4 and S6 are in close proximity at hyperpolarized membrane potentials.
Tristani-Firouzi
Martin
M
Department of Pediatrics, University of Utah School of Medicine, Salt Lake City, Utah 84112, USA. mfirouzi@hmbg.utah.edu
Chen
Jun
J
Sanguinetti
Michael C
MC
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D027682:Cation Transport Proteins; D051638:Ether-A-Go-Go Potassium Channels; D015640:Ion Channel Gating; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D015221:Potassium Channels / Q000737:chemistry / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D024642:Potassium Channels, Voltage-Gated; D014982:Xenopus laevis
D027682:Cation Transport Proteins; D051638:Ether-A-Go-Go Potassium Channels; C092509:KCNH6 protein, human; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated