insight - Biophysics - # Allosteric regulation of cyclic nucleotide-gated ion channels

Structural and Energetic Insights into Ligand-Induced Conformational Changes in a Cyclic Nucleotide-Gated Ion Channel using Time-Resolved Transition Metal Ion FRET

Q: How do the structural and energetic changes observed in the isolated C-terminal fragment of SthK relate to the allosteric regulation of the full-length channel?

The structural and energetic changes observed in the isolated C-terminal fragment of SthK provide valuable insights into the allosteric regulation of the full-length channel. By investigating the conformational dynamics and energetics of the C-terminal region using a combination of steady-state and time-resolved transition metal ion Förster resonance energy transfer (tmFRET) experiments, this study sheds light on the allosteric mechanism governing channel activation upon ligand binding. The findings reveal that the binding of cyclic nucleotides induces significant structural changes in the C-terminal region, particularly in the CNBD domain. These changes, such as the rotation of the CNBD's C-helix towards the β-roll, are crucial for the activation of the channel. The energetic changes, quantified through changes in free energy (ΔG) and differences in energy change (ΔΔG) in a four-state model, provide a deeper understanding of the energetics of the conformational transitions within the channel. Understanding the structural and energetic changes in the isolated C-terminal fragment allows us to extrapolate and infer how similar changes may occur in the full-length channel. The allosteric regulation of the full-length channel, which includes the transmembrane regions with voltage sensors and pore domains in addition to the C-terminal region, likely involves coordinated conformational changes that propagate through the entire protein structure. The insights gained from studying the isolated fragment can help elucidate the overall allosteric mechanism of the full-length channel, providing a more comprehensive understanding of how ligand binding leads to channel activation.

Q: How do the potential implications of the partial agonist behavior of cGMP on the physiological functions of cyclic nucleotide-gated ion channels?

The partial agonist behavior of cGMP, as observed in the study on the isolated C-terminal fragment of SthK, has significant implications for the physiological functions of cyclic nucleotide-gated ion channels. Cyclic nucleotide-gated ion channels, such as CNG and HCN channels, play crucial roles in sensory perception, signal transduction, and cellular excitability. These channels are activated by the binding of cyclic nucleotides, such as cAMP or cGMP, to their CNBD domains, leading to conformational changes that open the ion-conducting pore. In the context of cGMP acting as a partial agonist, the study suggests that cGMP binding to the CNBD of SthK only weakly promotes the active state compared to cAMP. This partial agonist behavior of cGMP may result in a lower channel open probability and reduced activation compared to a full agonist like cAMP. In physiological terms, this could mean that the response of the channel to cGMP is suboptimal or less robust compared to cAMP, leading to weaker cellular signaling or excitability. The partial agonist behavior of cGMP may have implications for sensory perception and cellular excitability processes where cyclic nucleotide-gated ion channels are involved. For example, in sensory neurons responsible for olfactory or visual signal transduction, the differential response to cGMP compared to cAMP could modulate the sensitivity or specificity of the signaling pathway. Similarly, in cardiac cells where HCN channels regulate pacemaker activity, the partial agonist behavior of cGMP may influence the rhythmicity of the heart. Understanding the distinct effects of partial agonists like cGMP on cyclic nucleotide-gated ion channels is essential for unraveling the complexity of cellular signaling and excitability processes and may have implications for developing targeted pharmacological interventions.

Q: Could the insights gained from this study on the allosteric regulation of SthK be leveraged to develop novel pharmacological modulators of other cyclic nucleotide-gated ion channels involved in sensory perception and cellular excitability?

The insights gained from the study on the allosteric regulation of SthK have the potential to be leveraged for the development of novel pharmacological modulators of other cyclic nucleotide-gated ion channels involved in sensory perception and cellular excitability. Cyclic nucleotide-gated ion channels, including CNG and HCN channels, are key players in sensory perception, signal transduction, and cellular excitability, making them attractive targets for pharmacological intervention. By elucidating the structural and energetic changes that occur during the allosteric regulation of SthK, researchers can gain a deeper understanding of the mechanisms underlying channel activation and modulation by ligands. This knowledge can be applied to other cyclic nucleotide-gated ion channels to design specific pharmacological agents that target the allosteric sites involved in channel activation. The study's findings on the differential effects of full agonists like cAMP and partial agonists like cGMP on SthK provide valuable information on how ligands can modulate channel activity. This knowledge can guide the development of novel pharmacological modulators that mimic or enhance the effects of full agonists to potentiate channel activation or inhibit the effects of partial agonists to regulate channel activity. Overall, the insights gained from studying the allosteric regulation of SthK can serve as a foundation for the design and development of targeted pharmacological modulators for other cyclic nucleotide-gated ion channels, offering new opportunities for therapeutic interventions in sensory perception and cellular excitability processes.

Conceitos Básicos

Binding of the full agonist cAMP induces large structural changes and favorable energetics in the C-terminal region of the cyclic nucleotide-gated ion channel SthK, while the partial agonist cGMP promotes a smaller fraction of the active conformation.

Resumo

This study investigates the conformational dynamics and energetics of the C-terminal region of the prokaryotic cyclic nucleotide-gated ion channel SthK using a combination of steady-state and time-resolved transition metal ion Förster resonance energy transfer (tmFRET) experiments.

Key highlights:

Binding of the full agonist cAMP produces large structural changes in the C-helix of the cyclic nucleotide-binding domain (CNBD), with a very favorable change in free energy (ΔΔG).
In contrast, the partial agonist cGMP only weakly promotes the active state, exhibiting a smaller fraction of the same active conformation observed with cAMP.
Time-resolved tmFRET allowed the determination of distance distributions and quantification of the energetics of the conformational transitions between resting and active states in the four-state allosteric model.
Oligomerization and ionic strength were found to impact the energetics of the conformational changes in the isolated SthK C-terminal fragment.
The time-resolved tmFRET approach provides valuable structural insights and quantification of the energetic landscape, contributing to a deeper understanding of the allosteric regulation in cyclic nucleotide-gated ion channels.

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Estatísticas

The binding of cAMP to SthK causes robust channel currents with a high degree of cooperativity (Hill slope, h: 2.9 ± 0.2).
Fractional activation by 1 mM cGMP was 0.002 ± 0.003.
The average distances (r̄) for the resting and active states were 40.9 Å and 29.5 Å, respectively, with standard deviations (σ) of 4.3 Å and 0.84 Å.
In the absence of ligand, the fraction of the active state (A2) was 0.12.
For saturating cAMP, the fraction of the active state (A2) was 1.0.
For saturating cGMP, the fraction of the active state (A2) was 0.34.
The change in free energy (ΔΔG) for cAMP was more favorable than -3.9 kcal/mol, while for cGMP it was -0.82 kcal/mol.

Citações

"Binding of cAMP to SthK causes robust channel currents in E.coli spheroplasts with a high degree of cooperativity (Hill slope, h: 2.9 ± 0.2)."
"Fractional activation by 1 mM cGMP was 0.002 ± 0.003."
"The average distances (r̄) for the resting and active states were 40.9 Å and 29.5 Å, respectively, with standard deviations (σ) of 4.3 Å and 0.84 Å."
"In the absence of ligand, the fraction of the active state (A2) was 0.12."
"For saturating cAMP, the fraction of the active state (A2) was 1.0."
"For saturating cGMP, the fraction of the active state (A2) was 0.34."
"The change in free energy (ΔΔG) for cAMP was more favorable than -3.9 kcal/mol, while for cGMP it was -0.82 kcal/mol."

Principais Insights Extraídos De

Ligand-Coupled Conformational Changes in a Cyclic Nucleotide-Gated Ion Channel Revealed by Time-Resolved Transition Metal Ion FRET

by Eggan,P., Go... às www.biorxiv.org 04-27-2024

https://www.biorxiv.org/content/10.1101/2024.04.25.591185v1

Perguntas Mais Profundas

How do the structural and energetic changes observed in the isolated C-terminal fragment of SthK relate to the allosteric regulation of the full-length channel?

The structural and energetic changes observed in the isolated C-terminal fragment of SthK provide valuable insights into the allosteric regulation of the full-length channel. By investigating the conformational dynamics and energetics of the C-terminal region using a combination of steady-state and time-resolved transition metal ion Förster resonance energy transfer (tmFRET) experiments, this study sheds light on the allosteric mechanism governing channel activation upon ligand binding.
The findings reveal that the binding of cyclic nucleotides induces significant structural changes in the C-terminal region, particularly in the CNBD domain. These changes, such as the rotation of the CNBD's C-helix towards the β-roll, are crucial for the activation of the channel. The energetic changes, quantified through changes in free energy (ΔG) and differences in energy change (ΔΔG) in a four-state model, provide a deeper understanding of the energetics of the conformational transitions within the channel.
Understanding the structural and energetic changes in the isolated C-terminal fragment allows us to extrapolate and infer how similar changes may occur in the full-length channel. The allosteric regulation of the full-length channel, which includes the transmembrane regions with voltage sensors and pore domains in addition to the C-terminal region, likely involves coordinated conformational changes that propagate through the entire protein structure. The insights gained from studying the isolated fragment can help elucidate the overall allosteric mechanism of the full-length channel, providing a more comprehensive understanding of how ligand binding leads to channel activation.

How do the potential implications of the partial agonist behavior of cGMP on the physiological functions of cyclic nucleotide-gated ion channels?

The partial agonist behavior of cGMP, as observed in the study on the isolated C-terminal fragment of SthK, has significant implications for the physiological functions of cyclic nucleotide-gated ion channels. Cyclic nucleotide-gated ion channels, such as CNG and HCN channels, play crucial roles in sensory perception, signal transduction, and cellular excitability. These channels are activated by the binding of cyclic nucleotides, such as cAMP or cGMP, to their CNBD domains, leading to conformational changes that open the ion-conducting pore.
In the context of cGMP acting as a partial agonist, the study suggests that cGMP binding to the CNBD of SthK only weakly promotes the active state compared to cAMP. This partial agonist behavior of cGMP may result in a lower channel open probability and reduced activation compared to a full agonist like cAMP. In physiological terms, this could mean that the response of the channel to cGMP is suboptimal or less robust compared to cAMP, leading to weaker cellular signaling or excitability.
The partial agonist behavior of cGMP may have implications for sensory perception and cellular excitability processes where cyclic nucleotide-gated ion channels are involved. For example, in sensory neurons responsible for olfactory or visual signal transduction, the differential response to cGMP compared to cAMP could modulate the sensitivity or specificity of the signaling pathway. Similarly, in cardiac cells where HCN channels regulate pacemaker activity, the partial agonist behavior of cGMP may influence the rhythmicity of the heart.
Understanding the distinct effects of partial agonists like cGMP on cyclic nucleotide-gated ion channels is essential for unraveling the complexity of cellular signaling and excitability processes and may have implications for developing targeted pharmacological interventions.

Could the insights gained from this study on the allosteric regulation of SthK be leveraged to develop novel pharmacological modulators of other cyclic nucleotide-gated ion channels involved in sensory perception and cellular excitability?

The insights gained from the study on the allosteric regulation of SthK have the potential to be leveraged for the development of novel pharmacological modulators of other cyclic nucleotide-gated ion channels involved in sensory perception and cellular excitability. Cyclic nucleotide-gated ion channels, including CNG and HCN channels, are key players in sensory perception, signal transduction, and cellular excitability, making them attractive targets for pharmacological intervention.
By elucidating the structural and energetic changes that occur during the allosteric regulation of SthK, researchers can gain a deeper understanding of the mechanisms underlying channel activation and modulation by ligands. This knowledge can be applied to other cyclic nucleotide-gated ion channels to design specific pharmacological agents that target the allosteric sites involved in channel activation.
The study's findings on the differential effects of full agonists like cAMP and partial agonists like cGMP on SthK provide valuable information on how ligands can modulate channel activity. This knowledge can guide the development of novel pharmacological modulators that mimic or enhance the effects of full agonists to potentiate channel activation or inhibit the effects of partial agonists to regulate channel activity.
Overall, the insights gained from studying the allosteric regulation of SthK can serve as a foundation for the design and development of targeted pharmacological modulators for other cyclic nucleotide-gated ion channels, offering new opportunities for therapeutic interventions in sensory perception and cellular excitability processes.