The S4-S5 linker couples voltage sensing and activation of pacemaker channels

摘要: Abstract Voltage-gated channels are normally opened by depolarization and closed repolarization of the membrane. Despite sharing significant sequence homology with voltage-gated K+ channels, gating hyperpolarization-activated, cyclic-nucleotide-gated (HCN) pacemaker has opposite dependence on membrane potential: hyperpolarization opens, whereas closes, these channels. The mechanism structural basis process that couples voltage sensor movement to HCN channel opening closing is not understood. On our previous studies a mutant HERG (human ether-a-go-go-related gene) channel, we hypothesized intracellular linker connects fourth fifth transmembrane domains (S4–S5 linker) might be important for gating. Here, used alanine-scanning mutagenesis HCN2 S4–S5 identify three residues, E324, Y331, R339, when mutated disrupted normal closing. Mutation basic residue in S4 domain (R318Q) prevented opening, presumably disrupting movement. However, R318Q Y331S mutations were constitutively open, suggesting can open without functioning domain. We conclude mediates coupling between sensing activation. Our findings also suggest related corresponds activation gate located near inner pore, rather than recovery from C-type inactivated state.