Zheng Wang, Shen Chen, Wang Longfei, Rawson Shaun, Xie Wen Jun, Nist-Lund Carl, Wu Jason, Shen Zhangfei, Xia Shiyu, Holt Jeffrey R, Wu Hao, Fu Tian-Min
Departments of Otolaryngology and Neurology, Boston Children's Hospital, Harvard Medical School, Boston, MA 02115, USA.
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA.
Sci Adv. 2022 Mar 25;8(12):eabm1568. doi: 10.1126/sciadv.abm1568.
Human TMEM175, a noncanonical potassium (K) channel in endolysosomes, contributes to their pH stability and is implicated in the pathogenesis of Parkinson's disease (PD). Structurally, the TMEM175 family exhibits an architecture distinct from canonical potassium channels, as it lacks the typical TVGYG selectivity filter. Here, we show that human TMEM175 not only exhibits pH-dependent structural changes that reduce K permeation at acidic pH but also displays proton permeation. TMEM175 constitutively conducts K at pH 7.4 but displays reduced K permeation at lower pH. In contrast, proton current through TMEM175 increases with decreasing pH because of the increased proton gradient. Molecular dynamics simulation, structure-based mutagenesis, and electrophysiological analysis suggest that K ions and protons share the same permeation pathway. The M393T variant of human TMEM175 associated with PD shows reduced function in both K and proton permeation. Together, our structural and electrophysiological analysis reveals a mechanism of TMEM175 regulation by pH.
人源TMEM175是一种存在于内溶酶体中的非典型钾（K）通道，有助于维持内溶酶体的pH稳定性，并与帕金森病（PD）的发病机制有关。在结构上，TMEM175家族呈现出与典型钾通道不同的结构，因为它缺乏典型的TVGYG选择性过滤器。在此，我们表明人源TMEM175不仅表现出pH依赖性的结构变化，在酸性pH条件下降低钾离子通透，还表现出质子通透。TMEM175在pH 7.4时持续传导钾离子，但在较低pH时钾离子通透减少。相反，由于质子梯度增加，通过TMEM175的质子电流随pH降低而增加。分子动力学模拟、基于结构的诱变和电生理分析表明，钾离子和质子共享相同的通透途径。与帕金森病相关的人源TMEM175的M393T变体在钾离子和质子通透方面均表现出功能降低。总之，我们的结构和电生理分析揭示了pH对TMEM175的调节机制。
