title: Tetramerization dynamics of C-terminal domain underlies isoform-specific cAMP gating in hyperpolarization-activated cyclic nucleotide-gated channels.
abstract: Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are dually activated by hyperpolarization and binding of cAMP to their cyclic nucleotide binding domain (CNBD). HCN isoforms respond differently to cAMP; binding of cAMP shifts activation of HCN2 and HCN4 by 17 mV but shifts that of HCN1 by only 2-4 mV. To explain the peculiarity of HCN1, we solved the crystal structures and performed a biochemical-biophysical characterization of the C-terminal domain (C-linker plus CNBD) of the three isoforms. Our main finding is that tetramerization of the C-terminal domain of HCN1 occurs at basal cAMP concentrations, whereas those of HCN2 and HCN4 require cAMP saturating levels. Therefore, HCN1 responds less markedly than HCN2 and HCN4 to cAMP increase because its CNBD is already partly tetrameric. This is confirmed by voltage clamp experiments showing that the right-shifted position of V(&frac12;) in HCN1 is correlated with its propensity to tetramerize in vitro. These data underscore that ligand-induced CNBD tetramerization removes tonic inhibition from the pore of HCN channels.
authors: Department of Biology and Consiglio Nazionale delle Ricerche-Istituto di Biofisica, University of Milan, Via Celoria 26, 20133 Milan, Italy.
authors: Marco
authors: M
authors: Lolicato
authors: Marco
authors: M
authors: Nardini
authors: Sabrina
authors: S
authors: Gazzarrini
authors: Stefan
authors: S
authors: Möller
authors: Daniela
authors: D
authors: Bertinetti
authors: Friedrich W
authors: FW
authors: Herberg
authors: Martino
authors: M
authors: Bolognesi
authors: Holger
authors: H
authors: Martin
authors: Marina
authors: M
authors: Fasolini
authors: Jay A
authors: JA
authors: Bertrand
authors: Cristina
authors: C
authors: Arrigoni
authors: Gerhard
authors: G
authors: Thiel
authors: Anna
authors: A
authors: Moroni
mesh_terms: D000818:Animals; D000242:Cyclic AMP / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D015640:Ion Channel Gating / Q000502:physiology*; D007473:Ion Channels / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D009865:Oocytes; D015221:Potassium Channels; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D055503:Protein Multimerization / Q000502:physiology*; D017434:Protein Structure, Tertiary; D014982:Xenopus laevis
chemical_list: C578710:HCN2 protein, human; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D007473:Ion Channels; D015221:Potassium Channels; D020033:Protein Isoforms; D000242:Cyclic AMP