title: Hydrophobic plug functions as a gate in voltage-gated proton channels.
abstract: Voltage-gated proton (Hv1) channels play important roles in the respiratory burst, in pH regulation, in spermatozoa, in apoptosis, and in cancer metastasis. Unlike other voltage-gated cation channels, the Hv1 channel lacks a centrally located pore formed by the assembly of subunits. Instead, the proton permeation pathway in the Hv1 channel is within the voltage-sensing domain of each subunit. The gating mechanism of this pathway is still unclear. Mutagenic and fluorescence studies suggest that the fourth transmembrane (TM) segment (S4) functions as a voltage sensor and that there is an outward movement of S4 during channel activation. Using thermodynamic mutant cycle analysis, we find that the conserved positively charged residues in S4 are stabilized by countercharges in the other TM segments both in the closed and open states. We constructed models of both the closed and open states of Hv1 channels that are consistent with the mutant cycle analysis. These structural models suggest that electrostatic interactions between TM segments in the closed state pull hydrophobic residues together to form a hydrophobic plug in the center of the voltage-sensing domain. Outward S4 movement during channel activation induces conformational changes that remove this hydrophobic plug and instead insert protonatable residues in the center of the channel that, together with water molecules, can form a hydrogen bond chain across the channel for proton permeation. This suggests that salt bridge networks and the hydrophobic plug function as the gate in Hv1 channels and that outward movement of S4 leads to the opening of this gate.
authors.affiliation: Centre for Molecular Simulation and Department of Biological Sciences, University of Calgary, Calgary, AB, Canada T2N 2N4.
authors.forename: Adam
authors.initials: A
authors.lastname: Chamberlin
authors.forename: Feng
authors.initials: F
authors.lastname: Qiu
authors.forename: Santiago
authors.initials: S
authors.lastname: Rebolledo
authors.forename: Yibo
authors.initials: Y
authors.lastname: Wang
authors.forename: Sergei Y
authors.initials: SY
authors.lastname: Noskov
authors.forename: H Peter
authors.initials: HP
authors.lastname: Larsson
mesh_terms: D001483:Base Sequence; D057927:Hydrophobic and Hydrophilic Interactions; D015640:Ion Channel Gating / Q000502:physiology*; D007473:Ion Channels / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D018408:Patch-Clamp Techniques; D011485:Protein Binding; D011487:Protein Conformation; D017422:Sequence Analysis, DNA; D013816:Thermodynamics
chemical_list: C510235:HVCN1 protein, human; D007473:Ion Channels
keywords: VSOP; blocker; molecular dynamics; mutagenesis cycle; voltage gating