Interactions between Voltage Sensor and Pore Domains in a hERG K+ Channel Model from Molecular Simulations and the Effects of a Voltage Sensor Mutation

The hERG K+ channel is important for establishing normal electrical activity in the human heart. The channel's unique gating response to membrane potential changes indicates specific interactions between voltage sensor and pore domains that are poorly understood. In the absence of a crystal structure we constructed a homology model of the full hERG membrane domain and Performed 0.5 mu s molecular dynamics (MD) simulations in a hydrated membrane. The simulations identify potential interactions involving residues at the extracellular surface of S1 in the voltage sensor and at the N-terminal end of the pore helix in the hERG model. In addition, a diffuse interface involving hydrophobic residues on S4 (voltage sensor) and pore domain S5 of an adjacent subunit was stable during 0.5 mu s of simulation. To assess the ability of the model to give insight into the of channel mutation we simulated a hERG mutant that contains a Leu to Pro substitution in the voltage sensor S4 helical segment (hERG L532P). Consistent with the retention of gated K+ conductance, the L532P mutation was accommodated in the S4 helix with little disruption of helical structure. The mutation reduced the extent of interaction across the S4-S5 interface, suggesting a structural basis for the greatly enhanced deactivation rate in hERG L532P. The study indicates that pairwise comparison of wild-type and mutated channel models is a useful approach to interpreting functional data where uncertainty in model structures exist.