title: Regulation of hyperpolarization-activated HCN channels by cAMP through a gating switch in binding domain symmetry.
abstract: Recent X-ray structures show that the binding domains of tetrameric ligand-gated channels form either a 4-fold symmetric gating ring or a 2-fold symmetric dimer of dimers. To determine how such structures function to coordinate the binding of multiple ligands during channel activation, we examined the action of cAMP to enhance the opening of the hyperpolarization-activated HCN2 channels, whose cytoplasmic C terminus forms a gating ring in the presence of cAMP. Using tandem dimers and tetramers in which cAMP binding to selected HCN2 subunits was prevented by a point mutation or deletion, we provide the first direct determination of the energetic effects on gating of each of four ligand binding events and demonstrate the importance of the gating ring for cAMP regulation. We suggest that cAMP binding enhances channel opening by promoting assembly of the gating ring from an unliganded state in which the four subunits interact as a 2-fold symmetric dimer of dimers.
authors.affiliation: Center for Neurobiology and Behavior, Department of Pharmacology, Howard Hughes Medical Institute, Columbia University, 722 West 168 Street, New York, NY 10032, USA.
authors.forename: Chris
authors.initials: C
authors.lastname: Ulens
authors.forename: Steven A
authors.initials: SA
authors.lastname: Siegelbaum
mesh_terms: D000818:Animals; D001665:Binding Sites / Q000187:drug effects / Q000502:physiology; D000242:Cyclic AMP / Q000378:metabolism* / Q000494:pharmacology; D054815:Cyclic Nucleotide-Gated Cation Channels; D005260:Female; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D007473:Ion Channels / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D009124:Muscle Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009419:Nerve Tissue Proteins; D015221:Potassium Channels; D014981:Xenopus
chemical_list: D054815:Cyclic Nucleotide-Gated Cation Channels; C578711:Hcn2 protein, mouse; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D007473:Ion Channels; D009124:Muscle Proteins; D009419:Nerve Tissue Proteins; D015221:Potassium Channels; D000242:Cyclic AMP