Exposure of residues in the cyclic nucleotide-gated channel pore: P region structure and function in gating

Neuron. 1996 Jan;16(1):141-9. doi: 10.1016/s0896-6273(00)80031-8.


In voltage-gated ion channels and in the homologous cyclic nucleotide-gated (CNG) channels, the loop between the S5 and S6 transmembrane segments (P region) is thought to form the lining of the pore. To investigate the structure and the role in gating of the P region of the bovine retinal CNG channel, we determined the accessibility of 11 cysteine-substituted P region residues to small, charged sulfhydryl reagents applied to the inside and outside of membrane patches in the open and closed states of the channel. The results suggest that the P region forms a loop that extends toward the central axis of the channel, analogous to the L3 loop of bacterial porin channels. Furthermore, the P region, in addition to forming the ion selectivity filter, functions as the channel gate, the structure of which changes when the channel opens.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Cattle
  • Cell Membrane Permeability
  • Chemical Phenomena
  • Chemistry, Physical
  • Cyclic Nucleotide-Gated Cation Channels
  • Cysteine / chemistry
  • Ethyl Methanesulfonate / analogs & derivatives
  • Ethyl Methanesulfonate / pharmacology
  • Eye Proteins / chemistry*
  • Eye Proteins / drug effects
  • Eye Proteins / genetics
  • Ion Channel Gating / drug effects
  • Ion Channel Gating / physiology*
  • Ion Channels / chemistry*
  • Ion Channels / drug effects
  • Ion Channels / genetics
  • Models, Molecular
  • Molecular Sequence Data
  • Mutagenesis, Site-Directed
  • Protein Conformation*
  • Recombinant Fusion Proteins / chemistry
  • Sequence Alignment
  • Sequence Homology, Amino Acid
  • Sulfhydryl Reagents / pharmacology


  • Cyclic Nucleotide-Gated Cation Channels
  • Eye Proteins
  • Ion Channels
  • Recombinant Fusion Proteins
  • Sulfhydryl Reagents
  • methanethiosulfonate ethylammonium
  • Ethyl Methanesulfonate
  • Cysteine