Journal Article

A high affinity switch for cAMP in the HCN pacemaker channels

Introini, Bianca, Castelli, Roberta, Enke, Uta, Thiel, Gerhard, Kusch, Jana, Saponaro, Andrea, Hafez Alkotob, Anahita, DiFrancesco, Dario, Moroni, Anna, Ranjbari, Golnaz, Santoro, Bina, Porro, Alessandro, Benndorf, Klaus

2024

Overview

Binding of cAMP to Hyperpolarization activated cyclic nucleotide gated (HCN) channels facilitates pore opening. It is unclear why the isolated cyclic nucleotide binding domain (CNBD) displays in vitro lower affinity for cAMP than the full-length channel in patch experiments. Here we show that HCN are endowed with an affinity switch for cAMP. Alpha helices D and E, downstream of the cyclic nucleotide binding domain (CNBD), bind to and stabilize the holo CNBD in a high affinity state. These helices increase by 30-fold cAMP efficacy and affinity measured in patch clamp and ITC, respectively. We further show that helices D and E regulate affinity by interacting with helix C of the CNBD, similarly to the regulatory protein TRIP8b. Our results uncover an intramolecular mechanism whereby changes in binding affinity, rather than changes in cAMP concentration, can modulate HCN channels, adding another layer to the complex regulation of their activity. Cyclic AMP modulation of HCN channels underlies beta adrenergic stimulation of heart rate. Here, authors describe an intramolecular mechanism that controls cAMP affinity of the cyclic nucleotide binding domain of these channels.

• Publisher: Nature Publishing Group UK,Nature Publishing Group,Nature Portfolio
• Subject: 14 / 631/1647/1453/1970 / 631/45/269 / 631/57/2272/2273 / 631/57/2283 / 82/80 / 9/74 / Affinity / Binding / Channels / Charged particles / Cyclic AMP / Heart rate / Helices / Humanities and Social Sciences / Hyperpolarization / Ion channels (cyclic nucleotide-gated) / Ligands / multidisciplinary / Nucleotides / Pacemakers / Science / Science (multidisciplinary)