A structural, functional, and computational analysis suggests pore flexibility as the base for the poor selectivity of CNG channels

Proc Natl Acad Sci U S A. 2015 Jul 7;112(27):E3619-28. doi: 10.1073/pnas.1503334112. Epub 2015 Jun 22.

Abstract

Cyclic nucleotide-gated (CNG) ion channels, despite a significant homology with the highly selective K(+) channels, do not discriminate among monovalent alkali cations and are permeable also to several organic cations. We combined electrophysiology, molecular dynamics (MD) simulations, and X-ray crystallography to demonstrate that the pore of CNG channels is highly flexible. When a CNG mimic is crystallized in the presence of a variety of monovalent cations, including Na(+), Cs(+), and dimethylammonium (DMA(+)), the side chain of Glu66 in the selectivity filter shows multiple conformations and the diameter of the pore changes significantly. MD simulations indicate that Glu66 and the prolines in the outer vestibule undergo large fluctuations, which are modulated by the ionic species and the voltage. This flexibility underlies the coupling between gating and permeation and the poor ionic selectivity of CNG channels.

Keywords: CNG channels; MD simulations; X-ray crystallography; pore flexibility.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Bacterial Proteins / chemistry
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism
  • Cations, Monovalent / metabolism
  • Cattle
  • Cesium / metabolism
  • Crystallography, X-Ray
  • Cyclic Nucleotide-Gated Cation Channels / chemistry*
  • Cyclic Nucleotide-Gated Cation Channels / genetics
  • Cyclic Nucleotide-Gated Cation Channels / metabolism*
  • Female
  • Ion Channel Gating / genetics
  • Ion Channel Gating / physiology*
  • Ion Transport / drug effects
  • Membrane Potentials / drug effects
  • Membrane Potentials / physiology
  • Molecular Dynamics Simulation
  • Molecular Sequence Data
  • Mutant Proteins / chemistry
  • Mutant Proteins / metabolism
  • Mutation, Missense
  • Oocytes / metabolism
  • Oocytes / physiology
  • Patch-Clamp Techniques
  • Protein Conformation*
  • Sequence Homology, Amino Acid
  • Sodium / metabolism
  • Xenopus laevis

Substances

  • Bacterial Proteins
  • CNGA1 protein, bovine
  • Cations, Monovalent
  • Cyclic Nucleotide-Gated Cation Channels
  • Mutant Proteins
  • Cesium
  • Sodium

Associated data

  • PDB/4R50
  • PDB/4R6Z
  • PDB/4R7C
  • PDB/4R8C
  • PDB/4RAI
  • PDB/4RO2