title: Structures of closed and open states of a voltage-gated sodium channel.
abstract: Bacterial voltage-gated sodium channels (BacNavs) serve as models of their vertebrate counterparts. BacNavs contain conserved voltage-sensing and pore-forming domains, but they are homotetramers of four identical subunits, rather than pseudotetramers of four homologous domains. Here, we present structures of two NaVAb mutants that capture tightly closed and open states at a resolution of 2.8-3.2 Å. Introduction of two humanizing mutations in the S6 segment (NaVAb/FY: T206F and V213Y) generates a persistently closed form of the activation gate in which the intracellular ends of the four S6 segments are drawn tightly together to block ion permeation completely. This construct also revealed the complete structure of the four-helix bundle that forms the C-terminal domain. In contrast, truncation of the C-terminal 40 residues in NavAb/1-226 captures the activation gate in an open conformation, revealing the open state of a BacNav with intact voltage sensors. Comparing these structures illustrates the full range of motion of the activation gate, from closed with its orifice fully occluded to open with an orifice of ∼10 Å. Molecular dynamics and free-energy simulations confirm designation of NaVAb/1-226 as an open state that allows permeation of hydrated Na+, and these results also support a hydrophobic gating mechanism for control of ion permeation. These two structures allow completion of a closed-open-inactivated conformational cycle in a single voltage-gated sodium channel and give insight into the structural basis for state-dependent binding of sodium channel-blocking drugs.
authors.affiliation: Department of Pharmacology, University of Washington, Seattle, WA 98195.|Department of Medicine, Division of General Internal Medicine, University of Washington, Seattle, WA 98195.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Lenaeus
authors.affiliation: Department of Pharmacology, University of Washington, Seattle, WA 98195.
authors.forename: Tamer M
authors.initials: TM
authors.lastname: Gamal El-Din
authors.affiliation: Molecular Medicine, Hospital for Sick Children, Toronto, ON, Canada M5G 0A4.|Department of Biochemistry, University of Toronto, Toronto, ON, Canada M5S 1A8.
authors.forename: Christopher
authors.identifier: 0000-0001-6947-5731
authors.initials: C
authors.lastname: Ing
authors.affiliation: Department of Pharmacology, University of Washington, Seattle, WA 98195.|Department of Biology, École Normal Supérieure, 94230 Cachan, France.
authors.forename: Karthik
authors.initials: K
authors.lastname: Ramanadane
authors.affiliation: Molecular Medicine, Hospital for Sick Children, Toronto, ON, Canada M5G 0A4.|Department of Biochemistry, University of Toronto, Toronto, ON, Canada M5S 1A8.
authors.forename: Régis
authors.initials: R
authors.lastname: Pomès
authors.affiliation: Department of Pharmacology, University of Washington, Seattle, WA 98195.|Howard Hughes Medical Institute, University of Washington, Seattle, WA 98195.
authors.forename: Ning
authors.initials: N
authors.lastname: Zheng
authors.affiliation: Department of Pharmacology, University of Washington, Seattle, WA 98195; wcatt@uw.edu.
authors.forename: William A
authors.initials: WA
authors.lastname: Catterall
mesh_terms: D018360:Crystallography, X-Ray; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D015640:Ion Channel Gating / Q000502:physiology*; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D009154:Mutation; D011487:Protein Conformation; D061566:Voltage-Gated Sodium Channels / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D061566:Voltage-Gated Sodium Channels
keywords: action potential; activation gate; sodium channels; sodium conductance