The Sixth Transmembrane Segment Is a Major Gating Component of the TMEM16A Calcium-Activated Chloride Channel

• Published in: Neuron (Cambridge, Mass.) Mass.), 2018-03, Vol.97 (5), p.1063-1077.e4
• Main Authors: Peters, Christian J., Gilchrist, John M., Tien, Jason, Bethel, Neville P., Qi, Lijun, Chen, Tingxu, Wang, Lynn, Jan, Yuh Nung, Grabe, Michael, Jan, Lily Y.
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; Anions; Anoctamin-1 - chemistry; Anoctamin-1 - genetics; Anoctamin-1 - metabolism; Calcium; Calcium channels; Calcium channels (voltage-gated); Calcium chloride; Calcium-binding protein; Channel gating; Chloride; Chloride channels (calcium-gated); Chloride Channels - chemistry; Chloride Channels - genetics; Chloride Channels - metabolism; Exocrine glands; HEK293 Cells; Humans; Ion Channel Gating - physiology; Ions; Membranes; Mice; Mutation; Nervous system; Physiology; Protein Binding - physiology; Protein Structure, Secondary; Simulation
• ISSN: 0896-6273; 1097-4199
• DOI: 10.1016/j.neuron.2018.01.048

Calcium-activated chloride channels (CaCCs) formed by TMEM16A or TMEM16B are broadly expressed in the nervous system, smooth muscles, exocrine glands, and other tissues. With two calcium-binding sites and a pore within each monomer, the dimeric CaCC exhibits voltage-dependent calcium sensitivity. Channel activity also depends on the identity of permeant anions. To understand how CaCC regulates neuronal signaling and how CaCC is, in turn, modulated by neuronal activity, we examined the molecular basis of CaCC gating. Here, we report that voltage modulation of TMEM16A-CaCC involves voltage-dependent occupancy of calcium- and anion-binding site(s) within the membrane electric field as well as a voltage-dependent conformational change intrinsic to the channel protein. These gating modalities all critically depend on the sixth transmembrane segment. •TMEM16A is an ion channel gated by voltage, external anions, and internal calcium•Alanine scanning mutagenesis permits these gating modes to be analyzed individually•The sixth transmembrane helix has a critical role in linking TMEM16A gating modes TMEM16A is an ion channel protein with functions in a multitude of cell types. Peters et al. identified a specific domain that integrates the responses of this channel to three separable physiological stimuli.