Cyclic nucleotide–gated (CNG) channels convert cyclic nucleotide (CN) binding and unbinding into electrical signals in sensory receptors and neurons. The molecular conformational changes underpinning ligand activation are largely undefined. We report both closed- and open-state atomic cryo-EM structures of a full-length Caenorhabditis elegans cyclic GMP−activated channel TAX-4, reconstituted in lipid nanodiscs. These structures, together with computational and functional analyses and a mutant channel structure, reveal a double-barrier hydrophobic gate formed by two S6 amino acids in the central cavity. cGMP binding produces global conformational changes that open the cavity gate located ~52 Å away but do not alter the structure of the selectivity filter—the commonly presumed activation gate. Our work provides mechanistic insights into the allosteric gating and regulation of CN-gated and nucleotide-modulated channels and CNG channel−related channelopathies.

环核苷酸门控 (CNG) 通道将环核苷酸 (CN) 的结合和解除结合转化为感觉受体和神经元中的电信号。支撑配体激活的分子构象变化在很大程度上是不确定的。我们报告了全长秀丽隐杆线虫的封闭态和开放态原子冷冻电镜结构环状 GMP 激活通道 TAX-4，在脂质纳米圆盘中重组。这些结构，连同计算和功能分析以及突变通道结构，揭示了由中央空腔中的两个 S6 氨基酸形成的双屏障疏水门。cGMP 结合产生全局构象变化，打开位于约 52 Å 外的腔门，但不会改变选择性过滤器的结构——通常假定的激活门。我们的工作提供了对 CN 门控和核苷酸调节通道的变构门控和调节以及 CNG 通道相关通道病的机制见解。