title: CryoEM structure of a prokaryotic cyclic nucleotide-gated ion channel.
abstract: Cyclic nucleotide-gated (CNG) and hyperpolarization-activated cyclic nucleotide-regulated (HCN) ion channels play crucial physiological roles in phototransduction, olfaction, and cardiac pace making. These channels are characterized by the presence of a carboxyl-terminal cyclic nucleotide-binding domain (CNBD) that connects to the channel pore via a C-linker domain. Although cyclic nucleotide binding has been shown to promote CNG and HCN channel opening, the precise mechanism underlying gating remains poorly understood. Here we used cryoEM to determine the structure of the intact LliK CNG channel isolated fromLeptospira licerasiae-which shares sequence similarity to eukaryotic CNG and HCN channels-in the presence of a saturating concentration of cAMP. A short S4-S5 linker connects nearby voltage-sensing and pore domains to produce a non-domain-swapped transmembrane architecture, which appears to be a hallmark of this channel family. We also observe major conformational changes of the LliK C-linkers and CNBDs relative to the crystal structures of isolated C-linker/CNBD fragments and the cryoEM structures of related CNG, HCN, and KCNH channels. The conformation of our LliK structure may represent a functional state of this channel family not captured in previous studies.
authors.affiliation: Department of Physiology and Biophysics, University of Washington, Seattle, WA 98195.
authors.forename: Zachary M
authors.initials: ZM
authors.lastname: James
authors.affiliation: Department of Biochemistry, University of Washington, Seattle, WA 98195.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Borst
authors.affiliation: Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, 6997801, Israel.
authors.forename: Yoni
authors.initials: Y
authors.lastname: Haitin
authors.affiliation: Department of Biochemistry, University of Washington, Seattle, WA 98195.
authors.forename: Brandon
authors.initials: B
authors.lastname: Frenz
authors.affiliation: Department of Biochemistry, University of Washington, Seattle, WA 98195.
authors.forename: Frank
authors.initials: F
authors.lastname: DiMaio
authors.affiliation: Department of Physiology and Biophysics, University of Washington, Seattle, WA 98195; zagotta@uw.edu dveesler@uw.edu.
authors.forename: William N
authors.initials: WN
authors.lastname: Zagotta
authors.affiliation: Department of Biochemistry, University of Washington, Seattle, WA 98195; zagotta@uw.edu dveesler@uw.edu.
authors.forename: David
authors.initials: D
authors.lastname: Veesler
mesh_terms: D054815:Cyclic Nucleotide-Gated Cation Channels / Q000502:physiology*; D015640:Ion Channel Gating / Q000502:physiology; D007919:Leptospira / Q000378:metabolism*; D008854:Microscopy, Electron / Q000379:methods*; D008958:Models, Molecular; D011487:Protein Conformation
chemical_list: D054815:Cyclic Nucleotide-Gated Cation Channels
keywords: allostery; conformational changes; cryoEM; cyclic nucleotide; ion channel