Molecular mechanism underlying desensitization of the proton-activated chloride channel PAC.
Molecular mechanism underlying desensitization of the proton-activated chloride channel PAC.
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作者：
Osei-Owusu J;Ruan Z;Mihaljević L;Matasic DS;Chen KH;Lü W;Qiu Z
脱敏是包括离子通道在内的膜受体的共同特性。新近发现的质子激活氯(PAC)通道在调节细胞内吞途径中细胞器的pH和大小方面起着重要作用，也参与了酸诱导的细胞死亡。然而，PAC通道如何脱敏在很大程度上是未知的。在这里，我们通过膜片钳电生理研究表明，PAC(也称为TMEM206/ASOR)在长时间的酸暴露下经历pH依赖的脱敏。通过结构导向和综合诱变，我们确定了几个对PAC脱敏至关重要的残基，包括跨膜螺旋1(TM1)胞外延伸处的组氨酸(H)98、谷氨酸(E)94和天冬氨酸(D)91，以及胞外区(ECD)-跨膜区(TMD)界面的E107、D109和E250。结构分析和分子动力学模拟表明，TM1延伸处的残基与ECD-TMD界面上的残基之间存在广泛的相互作用。这些相互作用可能通过稳定TM1的脱敏构象来促进PAC的脱敏，TM1经历了从静息和激活状态到脱敏状态的特征旋转运动。我们的研究建立了在这种普遍表达的离子通道中通道脱敏的新范式，并为未来研究其在细胞生理学和疾病中的相关性铺平了道路。
Desensitization is a common property of membrane receptors, including ion channels. The newly identified proton-activated chloride (PAC) channel plays an important role in regulating the pH and size of organelles in the endocytic pathway, and is also involved in acid-induced cell death. However, how the PAC channel desensitizes is largely unknown. Here, we show by patch-clamp electrophysiological studies that PAC (also known as TMEM206/ASOR) undergoes pH-dependent desensitization upon prolonged acid exposure. Through structure-guided and comprehensive mutagenesis, we identified several residues critical for PAC desensitization, including histidine (H) 98, glutamic acid (E) 94, and aspartic acid (D) 91 at the extracellular extension of the transmembrane helix 1 (TM1), as well as E107, D109, and E250 at the extracellular domain (ECD)–transmembrane domain (TMD) interface. Structural analysis and molecular dynamic simulations revealed extensive interactions between residues at the TM1 extension and those at the ECD–TMD interface. These interactions likely facilitate PAC desensitization by stabilizing the desensitized conformation of TM1, which undergoes a characteristic rotational movement from the resting and activated states to the desensitized state. Our studies establish a new paradigm of channel desensitization in this ubiquitously expressed ion channel and pave the way for future investigation of its relevance in cellular physiology and disease.