Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, United States.
Department of Structural Biology, Van Andel Institute, Grand Rapids, United States.
Elife. 2023 Jan 12;12:e83935. doi: 10.7554/eLife.83935.
Proton-activated chloride (PAC) channel is a ubiquitously expressed pH-sensing ion channel, encoded by (). PAC regulates endosomal acidification and macropinosome shrinkage by releasing chloride from the organelle lumens. It is also found at the cell surface, where it is activated under pathological conditions related to acidosis and contributes to acid-induced cell death. However, the pharmacology of the PAC channel is poorly understood. Here, we report that phosphatidylinositol (4,5)-bisphosphate (PIP) potently inhibits PAC channel activity. We solved the cryo-electron microscopy structure of PAC with PIP at pH 4.0 and identified its putative binding site, which, surprisingly, locates on the extracellular side of the transmembrane domain (TMD). While the overall conformation resembles the previously resolved PAC structure in the desensitized state, the TMD undergoes remodeling upon PIP-binding. Structural and electrophysiological analyses suggest that PIP inhibits the PAC channel by stabilizing the channel in a desensitized-like conformation. Our findings identify PIP as a new pharmacological tool for the PAC channel and lay the foundation for future drug discovery targeting this channel.
质子激活氯离子（PAC）通道是一种广泛表达的 pH 感应离子通道，由编码。PAC 通过从细胞器腔室释放氯离子来调节内体酸化和巨胞饮泡收缩。它也存在于细胞表面，在与酸中毒相关的病理条件下被激活，并有助于酸诱导的细胞死亡。然而，PAC 通道的药理学特性知之甚少。在这里，我们报告磷脂酰肌醇（4,5）-二磷酸（PIP）强烈抑制 PAC 通道活性。我们在 pH 值为 4.0 时解决了 PAC 与 PIP 的冷冻电镜结构，并确定了其假定的结合位点，令人惊讶的是，该位点位于跨膜域（TMD）的细胞外侧。虽然整体构象类似于先前在脱敏状态下解析的 PAC 结构，但在 PIP 结合后 TMD 会发生重塑。结构和电生理分析表明，PIP 通过将通道稳定在类似脱敏的构象中来抑制 PAC 通道。我们的发现将 PIP 鉴定为 PAC 通道的一种新的药理学工具，并为针对该通道的未来药物发现奠定了基础。
