PMID:24085296

Citation	Carlson, AE, Rosenbaum, JC, Brelidze, TI, Klevit, RE and Zagotta, WN (2013) Flavonoid regulation of HCN2 channels. J. Biol. Chem. 288:33136-45
Abstract	The hyperpolarization-activated cyclic nucleotide-modulated (HCN) channels are pacemaker channels whose currents contribute to rhythmic activity in the heart and brain. HCN channels open in response to hyperpolarizing voltages, and the binding of cAMP to their cyclic nucleotide-binding domain (CNBD) facilitates channel opening. Here, we report that, like cAMP, the flavonoid fisetin potentiates HCN2 channel gating. Fisetin sped HCN2 activation and shifted the conductance-voltage relationship to more depolarizing potentials with a half-maximal effective concentration (EC50) of 1.8 μM. When applied together, fisetin and cAMP regulated HCN2 gating in a nonadditive fashion. Fisetin did not potentiate HCN2 channels lacking their CNBD, and two independent fluorescence-based binding assays reported that fisetin bound to the purified CNBD. These data suggest that the CNBD mediates the fisetin potentiation of HCN2 channels. Moreover, binding assays suggest that fisetin and cAMP partially compete for binding to the CNBD. NMR experiments demonstrated that fisetin binds within the cAMP-binding pocket, interacting with some of the same residues as cAMP. Together, these data indicate that fisetin is a partial agonist for HCN2 channels.
Links	PubMed PMC3831264 Online version:10.1074/jbc.M113.501759
Keywords	Animals; Binding Sites; Cyclic AMP/chemistry; Cyclic AMP/genetics; Cyclic AMP/metabolism; Flavonoids/chemistry; Flavonoids/pharmacology; Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels/agonists; Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels/chemistry; Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels/genetics; Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels/metabolism; Ion Channel Gating/drug effects; Ion Channel Gating/physiology; Mice; Nuclear Magnetic Resonance, Biomolecular; Potassium Channels/agonists; Potassium Channels/chemistry; Potassium Channels/genetics; Potassium Channels/metabolism; Protein Structure, Tertiary; Xenopus laevis
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
HUMAN:CAMP		GO:0001934: positive regulation of protein phosphorylation	ECO:0000266:	UniProtKB:	P		Figure 1: Fisetin potentiation of HCN2 channels resembled the channel's regulation by cAMP, thereby suggesting that fisetin and cAMP may use similar mechanisms to stabilize the channel's open state	complete CACAO 10706

References

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