In treating retinitis pigmentosa, a genetic disorder causing progressive vision loss, selective inhibition of rod cyclic nucleotide-gated (CNG) channels holds promise. Blocking the increased Ca²⁺-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. Although modifications at the C8 position of the guanine ring did not change the ligand efficacy, modifications at the N1 and N² positions rendered cGMP largely ineffective in activating retinal CNG channels. Notably, PET-cGMP displayed selective potential, favoring rod over cone, whereas Rp-cGMPS showed greater efficiency in activating cone over rod CNG channels. Ligand docking and molecular dynamics simulations on cyclic nucleotide-binding domains showed comparable binding energies and binding modes for cGMP and its analogues in both rod and cone CNG channels (CNGA1 vs CNGA3 subunits). Computational experiments on CNGB1a vs CNGB3 subunits showed similar binding modes albeit with fewer amino acid interactions with cGMP due to an inactivated conformation of their C-helix. In addition, no clear correlation could be observed between the computational scores and the CNG channel efficacy values, suggesting additional factors beyond binding strength determining ligand selectivity and potency. This study highlights the importance of looking beyond the cyclic nucleotide-binding domain and toward the gating mechanism when searching for selective modulators. Future efforts in developing selective modulators for CNG channels should prioritize targeting alternative channel domains.

中文翻译：

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cGMP 类似物的类似结合模式限制了通过环状核苷酸结合域调节视网膜 CNG 通道的选择性

在治疗色素性视网膜炎（一种导致进行性视力丧失的遗传性疾病）时，选择性抑制视杆细胞环核苷酸门控 (CNG) 通道有望实现这一目标。通过 CNG 通道阻断视杆光感受器中增加的 Ca ²⁺流入可能会延缓疾病进展并改善患者的生活质量。为了寻找视杆 CNG 通道的抑制剂，我们使用膜片钳技术研究了 16 种 cGMP 类似物对视杆和视锥 CNG 通道的影响。尽管鸟嘌呤环C8位置的修饰并未改变配体功效，但N1和N ²位置的修饰使得cGMP在激活视网膜CNG通道方面很大程度上无效。值得注意的是，PET-cGMP 显示出选择性潜力，有利于杆状通道而不是锥状通道，而 Rp-cGMPS 在激活锥状 CNG 通道方面表现出更高的效率。环核苷酸结合域的配体对接和分子动力学模拟显示，cGMP 及其类似物在视杆和视锥 CNG 通道（CNGA1 与 CNGA3 亚基）中具有相当的结合能和结合模式。 CNGB1a 与 CNGB3 亚基的计算实验显示出相似的结合模式，尽管由于其 C 螺旋构象失活，与 cGMP 的氨基酸相互作用较少。此外，在计算分数和 CNG 通道功效值之间没有观察到明显的相关性，这表明除了结合强度之外还有其他因素决定配体选择性和效力。这项研究强调了在寻找选择性调节剂时超越环核苷酸结合域并关注门控机制的重要性。未来为 CNG 通道开发选择性调制器的努力应优先考虑替代通道领域。