The nicotinic acetylcholine receptor (nAChR) is a ligand-gated ion channel protein that mediates fast excitatory synaptic transmission in the peripheral and central nervous systems. Changes in the structure and function of the AChR can lead to serious impairment of physiological processes. In this study, we combined site-directed mutagenesis, radioligand binding assays, electrophysiological recordings and Fourier analyses to characterize the functional role and structural aspects of the betaM4 transmembrane domain of the Torpedo AChR. We performed tryptophan replacements, from residues L438 through F455, along the betaM4 transmembrane domain. Expression levels of mutants F439W-G450W and F452W-I454W produced peak currents similar to or lower than those in wild-type (WT). Tryptophan substitutions at positions L438 and T451 led to a deficiency in either subunit expression or receptor assembly. Mutations L440W, V442W, C447W and S453W produced a gain-of-function response. Mutation F455W produced a loss of ion channel function. The periodicity profile of the normalized expression level (closed state) and EC(50) (open state) revealed a minor conformational change of 0.4 residues/turn of the betaM4 domain. These findings suggest that a minor movement of the betaM4 domain occurs during channel activation.

中文翻译：

---

乙酰胆碱受体 betaM4 跨膜结构域的色氨酸扫描：用离子通道门控解码脂质-蛋白质界面的变构连接。

烟碱型乙酰胆碱受体 (nAChR) 是一种配体门控离子通道蛋白，可介导外周和中枢神经系统中的快速兴奋性突触传递。AChR 结构和功能的变化会导致生理过程的严重损害。在这项研究中，我们结合定点诱变、放射性配体结合测定、电生理记录和傅里叶分析来描述鱼雷 AChR 的 betaM4 跨膜结构域的功能作用和结构方面。我们沿着 betaM4 跨膜结构域进行了从残基 L438 到 F455 的色氨酸置换。突变体 F439W-G450W 和 F452W-I454W 的表达水平产生的峰值电流与野生型 (WT) 相似或更低。L438 和 T451 位置的色氨酸取代导致亚基表达或受体组装缺陷。突变 L440W、V442W、C447W 和 S453W 产生了功能增益响应。突变 F455W 导致离子通道功能丧失。标准化表达水平（关闭状态）和 EC(50)（打开状态）的周期性配置文件显示 betaM4 域的 0.4 个残基/转的微小构象变化。这些发现表明在通道激活过程中发生了 betaM4 域的轻微移动。4 个残基/转 betaM4 结构域。这些发现表明在通道激活过程中发生了 betaM4 域的轻微移动。4 个残基/转 betaM4 结构域。这些发现表明在通道激活过程中发生了 betaM4 域的轻微移动。