Molecular underpinning of intracellular pH regulation on TMEM16F

TMEM16F, a dual functional phospholipid scramblase and ion channel, is important in blood coagulation, skeleton development, HIV infection and cell fusion. Despite advances in understanding its structure and activation mechanism, how TMEM16F is regulated by intracellular factors remains largely elusive. Here we report that TMEM16F lipid scrambling and ion channel activities are strongly influenced by intracellular pH (pHi). We found that low pHi attenuates, whereas high pHi potentiates, TMEM16F channel and scramblase activation under physiological concentrations of intracellular Ca2+ ([Ca2+]i). We further demonstrate that TMEM16F pHi sensitivity depends on [Ca2+]i and exhibits a bell-shaped relationship with [Ca2+]i: TMEM16F channel activation becomes increasingly pHi sensitive from the resting [Ca2+]i to micromolar [Ca2+]i, but when [Ca2+]i increases beyond 15µM, the pHi sensitivity gradually diminishes. The mutation of a Ca2+-binding residue that markedly reduces TMEM16F Ca2+ sensitiv...跨膜蛋白16F（TMEM16F）是一种兼具磷脂 scramblase（phospholipid scramblase）与离子通道功能的双功能蛋白，在凝血、骨骼发育、HIV感染及细胞融合过程中发挥关键作用。尽管目前针对其结构与激活机制的研究已取得显著进展，但细胞内因子调控TMEM16F的具体机制仍在很大程度上不明晰。本研究在此报道，TMEM16F的脂质翻转活性与离子通道活性会受到细胞内pH（pHi）的显著调控。我们发现，在生理浓度的细胞内钙离子（[Ca²+]i）条件下，低pHi会抑制TMEM16F的通道与脂质翻转活性，而高pHi则会增强其激活效应。进一步研究表明，TMEM16F对pHi的敏感性依赖于[Ca²+]i，并与[Ca²+]i呈现钟形曲线关系：从静息[Ca²+]i到微摩尔级[Ca²+]i时，TMEM16F的通道激活对pHi的敏感性逐渐升高；但当[Ca²+]i超过15μM时，其pHi敏感性会逐渐减弱。针对一个可显著降低TMEM16F钙离子敏感性的钙离子结合残基进行突变...