Department of Biochemistry, Duke University Medical Center, Durham, NC, USA.
Department of Chemistry, University of Massachusetts, Amherst, MA, USA.
Nat Commun. 2019 Aug 21;10(1):3769. doi: 10.1038/s41467-019-11784-8.
The calcium-activated chloride channel (CaCC) TMEM16A plays crucial roles in regulating neuronal excitability, smooth muscle contraction, fluid secretion and gut motility. While opening of TMEM16A requires binding of intracellular Ca, prolonged Ca-dependent activation results in channel desensitization or rundown, the mechanism of which is unclear. Here we show that phosphatidylinositol (4,5)-bisphosphate (PIP) regulates TMEM16A channel activation and desensitization via binding to a putative binding site at the cytosolic interface of transmembrane segments (TMs) 3-5. We further demonstrate that the ion-conducting pore of TMEM16A is constituted of two functionally distinct modules: a Ca-binding module formed by TMs 6-8 and a PIP-binding regulatory module formed by TMs 3-5, which mediate channel activation and desensitization, respectively. PIP dissociation from the regulatory module results in ion-conducting pore collapse and subsequent channel desensitization. Our findings thus provide key insights into the mechanistic understanding of TMEM16 channel gating and lipid-dependent regulation.
钙激活氯离子通道（CaCC）TMEM16A 在调节神经元兴奋性、平滑肌收缩、液体分泌和肠道蠕动方面发挥着关键作用。虽然 TMEM16A 的开放需要细胞内 Ca 的结合，但 Ca 依赖性的持续激活会导致通道脱敏或失活，其机制尚不清楚。本研究表明，磷脂酰肌醇（4,5）-二磷酸（PIP）通过与跨膜片段（TM）3-5 胞质界面上的假定结合位点结合，调节 TMEM16A 通道的激活和脱敏。进一步证明 TMEM16A 的离子通道由两个功能上不同的模块组成：由 TM6-8 形成的 Ca 结合模块和由 TM3-5 形成的 PIP 结合调节模块，它们分别介导通道的激活和脱敏。PIP 从调节模块解离会导致离子通道孔坍塌，随后通道脱敏。因此，这些发现为 TMEM16 通道门控和脂质依赖性调节的机制理解提供了关键见解。
