Structural characterization of a full-length heteromeric glycine receptor in multiple functional states
Structural characterization of a full-length heteromeric glycine receptor in multiple functional states
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多种功能状态下全长异聚甘氨酸受体的结构表征
DOI：
10.1016/j.bpj.2022.11.1449
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发表时间：
2023
影响因子：
3.4
通讯作者：
Gibbs E
中科院分区：
文献类型：
--
作者：
Gibbs E
甘氨酸受体（GlyR）是氯离子传导配体门控离子通道，提供抑制性神经元输入，特别是在脊髓中。Synaptic GlyR是一种异质蛋白复合物，由5个同源亚基在通道孔周围伪对称排列而成。单个亚基有α和β两种。在这里，我们展示了全长斑马鱼α1/β GlyR的结构，没有任何可能改变蛋白质功能状态的基准标记。这是在拮抗剂（士的宁），激动剂（甘氨酸）和激动剂与变构调节剂（甘氨酸和伊维菌素）存在的情况下进行的。这些结构证实了最近关于异聚GlyR （4α: 1β）化学计量学的其他发现，并揭示了细胞外和细胞内区域以前未表征的亚基特异性特征。通过分子动力学模拟评估了每个结构的功能状态。士的宁束缚的孔处于闭合状态，其大部分围绕五重轴对称。带伊维菌素和不带伊维菌素的甘氨酸结构均采用脱敏构象，但伊维菌素结构在通道孔的细胞内入口处具有明显的不对称性。与这一观察结果一致的是，伊维菌素结合袋附近的配体密度仅在鞋底的α/β界面上观察到，而不是在过去的同型GlyR结构中观察到的α/α界面。模拟显示了伊维菌素结合状态的少量渗透事件，提示通道打开的不对称机制。总之，这些结果突出了异聚体GlyR的独特结构特征，并展示了这一生理上重要的蛋白质通道的功能范围。
Glycine receptors (GlyR) are chloride-conducting ligand-gated ion channels that provide inhibitory neuronal input, particularly in the spinal cord. Synaptic GlyR is a heteromeric protein complex composed of five homologous subunits arranged pseudo-symmetrically about the channel pore. Individual subunits come in two varieties, α and β. Here, we present the structures of full-length zebrafish α1/β GlyR solved without any fiducial marker that may alter the functional state of the protein. This was done in the presence of an antagonist (strychnine), agonist (glycine) and agonist with an allosteric modulator (glycine and ivermectin). These structures confirm other recent findings regarding the stoichiometry of heteromeric GlyR (4α: 1β) and also reveal previously uncharacterized subunit-specific features in the extracellular and intracellular domain. The functional state of each structure was assessed by molecular dynamics simulations. The strychnine-bound pore is in a closed state that is mostly symmetric about the five-fold axis. The glycine structures with and without ivermectin both adopted desensitized conformations, but the ivermectin structure has significant asymmetry at the intracellular entrance to the channel pore. Consistent with this observation, ligand density near the ivermectin binding pocket was only observed at the sole α/β interface, and not at α/α interfaces as observed in past homomeric GlyR structures. Simulations show a small number of permeation events for the ivermectin-bound state, suggestive of an asymmetric mechanism for channel opening. Together, these results highlight distinct structural features of heteromeric GlyR and demonstrate the functional range of this physiologically important protein channel.