A conserved tripeptide in CNG and HCN channels regulates ligand gating by controlling C-terminal oligomerization.
Cyclic nucleotides directly enhance the opening of the tetrameric CNG and HCN channels, although the mechanism remains unclear. We examined why HCN and certain CNG subunits form functional homomeric channels, whereas other CNG subunits only function in heteromeric channels. The "defect" in the CNGA4 subunit that prevents its homomeric expression was localized to its C-linker, which connects the transmembrane domain to the binding domain and contains a tripeptide that decreases the efficacy of ligand gating. Remarkably, replacement of the homologous HCN tripeptide with the CNGA4 sequence transformed cAMP into an inverse agonist that inhibits HCN channel opening. Using analytical ultracentrifugation, we identified the structural basis for this gating switch: whereas cAMP normally enhances the assembly of HCN C-terminal domains into a tetrameric gating ring, inclusion of the CNGA4 tripeptide reversed this action so that cAMP now causes gating ring disassembly. Thus, ligand gating depends on the dynamic oligomerization of C-terminal binding domains.
Zhou
Lei
L
Center for Neurobiology and Behavior, Columbia University, 722 West 168 Street, New York, NY 10032, USA.
Olivier
Nelson B
NB
Yao
Huan
H
Young
Edgar C
EC
Siegelbaum
Steven A
SA
D000595:Amino Acid Sequence; D000818:Animals; D002397:Catfishes; D017124:Conserved Sequence; D054815:Cyclic Nucleotide-Gated Cation Channels; D005260:Female; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D015640:Ion Channel Gating / Q000502:physiology*; D007473:Ion Channels / Q000235:genetics / Q000502:physiology*; D008024:Ligands; D008969:Molecular Sequence Data; D009865:Oocytes; D015221:Potassium Channels; D014981:Xenopus
D054815:Cyclic Nucleotide-Gated Cation Channels; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D007473:Ion Channels; D008024:Ligands; D015221:Potassium Channels