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Proc Natl Acad Sci U S A. 2017 Apr 25;114(17):4430-4435. doi: 10.1073/pnas.1700248114. Epub 2017 Apr 10.

CryoEM structure of a prokaryotic cyclic nucleotide-gated ion channel.

Author information

1
Department of Physiology and Biophysics, University of Washington, Seattle, WA 98195.
2
Department of Biochemistry, University of Washington, Seattle, WA 98195.
3
Department of Physiology and Pharmacology, Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, 6997801, Israel.
4
Department of Physiology and Biophysics, University of Washington, Seattle, WA 98195; zagotta@uw.edu dveesler@uw.edu.
5
Department of Biochemistry, University of Washington, Seattle, WA 98195; zagotta@uw.edu dveesler@uw.edu.

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 from Leptospira 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.

KEYWORDS:

allostery; conformational changes; cryoEM; cyclic nucleotide; ion channel

PMID:
28396445
PMCID:
PMC5410850
DOI:
10.1073/pnas.1700248114
[Indexed for MEDLINE]
Free PMC Article

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