Similar Binding Modes of cGMP Analogues Limit Selectivity in Modulating Retinal CNG Channels via the Cyclic Nucleotide-Binding Domain.

In treating , a genetic disorder causing progressive vision loss, selective inhibition of rod cyclic nucleotide-gated (CNG) channels holds promise. Blocking the increased Ca-influx in rod photoreceptors through CNG channels can potentially delay disease progression and improve the quality of life for patients. To find inhibitors for rod CNG channels, we investigated the impact of 16 cGMP analogues on both rod and cone CNG channels using the patch-clamp technique.

The PKG Inhibitor CN238 Affords Functional Protection of Photoreceptors and Ganglion Cells against Retinal Degeneration.

Hereditary retinal degeneration (RD) is often associated with excessive cGMP signalling in photoreceptors. Previous research has shown that inhibition of cGMP-dependent protein kinase G (PKG) can reduce photoreceptor loss in two different RD animal models. In this study, we identified a PKG inhibitor, the cGMP analogue CN238, which preserved photoreceptor viability and functionality in and mutant mice.

cGMP Analogues with Opposing Actions on CNG Channels Selectively Modulate Rod or Cone Photoreceptor Function.

The vertebrate retina harbors rod and cone photoreceptors. Human vision critically depends on cone photoreceptor function. In the phototransduction cascade, cGMP activates distinct rod and cone isoforms of the cyclic nucleotide-gated (CNG) channel.

Redefining the role of Ca-permeable channels in photoreceptor degeneration using diltiazem.

Hereditary degeneration of photoreceptors has been linked to over-activation of Ca-permeable channels, excessive Ca-influx, and downstream activation of Ca-dependent calpain-type proteases. Unfortunately, after more than 20 years of pertinent research, unequivocal evidence proving significant and reproducible photoreceptor protection with Ca-channel blockers is still lacking. Here, we show that both D- and L-cis enantiomers of the anti-hypertensive drug diltiazem were very effective at blocking photoreceptor Ca-influx, most probably by blocking the pore of Ca-permeable channels.

Corrigendum: Deciphering the function of the CNGB1b subunit in olfactory CNG channels.

This corrects the article DOI: 10.1038/srep29378.

Corrigendum: Quantifying the cooperative subunit action in a multimeric membrane receptor.

This corrects the article DOI: 10.1038/srep20974.

Publisher Correction: Hysteresis of ligand binding in CNGA2 ion channels.

This corrects the article DOI: 10.1038/ncomms3866.

Deciphering the function of the CNGB1b subunit in olfactory CNG channels.

Olfactory cyclic nucleotide-gated (CNG) ion channels are key players in the signal transduction cascade of olfactory sensory neurons. The second messengers cAMP and cGMP directly activate these channels, generating a depolarizing receptor potential. Olfactory CNG channels are composed of two CNGA2 subunits and two modulatory subunits, CNGA4, and CNGB1b.

Quantifying the cooperative subunit action in a multimeric membrane receptor.

In multimeric membrane receptors the cooperative action of the subunits prevents exact knowledge about the operation and the interaction of the individual subunits. We propose a method that permits quantification of ligand binding to and activation effects of the individual binding sites in a multimeric membrane receptor. The power of this method is demonstrated by gaining detailed insight into the subunit action in olfactory cyclic nucleotide-gated CNGA2 ion channels.

Hysteresis of ligand binding in CNGA2 ion channels.

Tetrameric cyclic nucleotide-gated (CNG) channels mediate receptor potentials in olfaction and vision. The channels are activated by the binding of cyclic nucleotides to a binding domain embedded in the C terminus of each subunit. Here using a fluorescent cGMP derivative (fcGMP), we show for homotetrameric CNGA2 channels that ligand unbinding is ~50 times faster at saturating than at subsaturating fcGMP.

Differential regulation by cyclic nucleotides of the CNGA4 and CNGB1b subunits in olfactory cyclic nucleotide-gated channels.

Olfactory cyclic nucleotide-gated (CNG) ion channels are essential contributors to signal transduction of olfactory sensory neurons. The activity of the channels is controlled by the cyclic nucleotides guanosine 3',5'-monophosphate (cGMP) and adenosine 3',5'-monophosphate (cAMP). The olfactory CNG channels are composed of two CNGA2 subunits, one CNGA4 and one CNGB1b subunit, each containing a cyclic nucleotide-binding domain.

How subunits cooperate in cAMP-induced activation of homotetrameric HCN2 channels.

Hyperpolarization-activated cyclic nucleotide-modulated (HCN) channels are tetrameric membrane proteins that generate electrical rhythmicity in specialized neurons and cardiomyocytes. The channels are primarily activated by voltage but are receptors as well, binding the intracellular ligand cyclic AMP. The molecular mechanism of channel activation is still unknown.

Role of the S4-S5 linker in CNG channel activation.

Cyclic nucleotide-gated (CNG) channels mediate sensory signal transduction in retinal and olfactory cells. The channels are activated by the binding of cyclic nucleotides to a cyclic nucleotide-binding domain (CNBD) in the C-terminus that is located at the intracellular side. The molecular events translating the ligand binding to the pore opening are still unknown.

Interdependence of receptor activation and ligand binding in HCN2 pacemaker channels.

HCN pacemaker channels are tetramers mediating rhythmicity in neuronal and cardiac cells. The activity of these channels is controlled by both membrane voltage and the ligand cAMP, binding to each of the four channel subunits. The molecular mechanism underlying channel activation and the relationship between the two activation stimuli are still unknown.

Thermodynamics of activation gating in olfactory-type cyclic nucleotide-gated (CNGA2) channels.

Olfactory-type cyclic nucleotide-gated (CNG) ion channels open by the binding of cyclic nucleotides to a binding domain in the C-terminus. Employing the Eyring rate theory, we performed a thermodynamic analysis of the activation gating in homotetrameric CNGA2 channels. Lowering the temperature shifted the concentration-response relationship to lower concentrations, resulting in a decrease of both the enthalpy DeltaH and entropy DeltaS upon channel opening, suggesting that the order of an open CNGA2 channel plus its environment is higher than that of the closed channel.

Relating ligand binding to activation gating in CNGA2 channels.

Cyclic nucleotide-gated (CNG) ion channels mediate sensory signal transduction in photoreceptors and olfactory cells. Structurally, CNG channels are heterotetramers composed of either two or three homologue subunits. Although it is well established that activation is a cooperative process of these subunits, it remains unknown whether the cooperativity is generated by the ligand binding, the gating, or both, and how the subunits interact.

Gating of cyclic nucleotide-gated (CNGA1) channels by cGMP jumps and depolarizing voltage steps.

We expressed rod-type homotetrameric cyclic nucleotide-gated (CNGA1) channels in Xenopus oocytes and studied activation by photolysis-induced jumps of the 3',5'-cyclic guanosine monophosphate (cGMP) concentration and by voltage steps. cGMP jumps to increasing concentrations up to the EC50 value of 46.5 microM decelerate the activation gating, indicative that even at concentrations of cGMP << EC50 binding is not rate limiting.

Activation of olfactory-type cyclic nucleotide-gated channels is highly cooperative.

Cyclic nucleotide-gated (CNG) ion channels play a key role in the sensory transduction of vision and olfaction. The channels are opened by the binding of cyclic nucleotides. Native olfactory CNG channels are heterotetramers of CNGA2, CNGA4, and CNGB1b subunits.

Effects of permeating ions and cGMP on gating and conductance of rod-type cyclic nucleotide-gated (CNGA1) channels.

Cyclic nucleotide-gated (CNG) channels are tetrameric non-specific cation channels. They mediate the receptor potentials in photoreceptors and cells of the olfactory epithelium and they are activated by the binding of cyclic nucleotides such as cGMP and cAMP. Previous studies in homotetrameric CNGA1 channels, activated with covalently bound cGMP, presented evidence that partially liganded channels cause partial channel opening (Ruiz & Karpen, 1997, 1999).