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Elife. 2018 Oct 12;7. pii: e39122. doi: 10.7554/eLife.39122.

Calcium-dependent electrostatic control of anion access to the pore of the calcium-activated chloride channel TMEM16A.

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Department of Biochemistry, University of Zurich, Zurich, Switzerland.


TMEM16A is a ligand-gated anion channel that is activated by intracellular Ca2+. This channel comprises two independent pores and closely apposed Ca2+ binding sites that are contained within each subunit of a homodimeric protein. Previously we characterized the influence of positively charged pore-lining residues on anion conduction (Paulino et al., 2017a). Here, we demonstrate the electrostatic control of permeation by the bound calcium ions in mouse TMEM16A using electrophysiology and Poisson-Boltzmann calculations. The currents of constitutively active mutants lose their outward rectification as a function of Ca2+ concentration due to the alleviation of energy barriers for anion conduction. This phenomenon originates from Coulombic interactions between the bound Ca2+ and permeating anions and thus demonstrates that an electrostatic gate imposed by the vacant binding site present in the sterically open pore, is released by Ca2+ binding to enable an otherwise sub-conductive pore to conduct with full capacity.


anoctamins; electrophysiology; electrostatics; ion conduction; ligand-gated ion channel; molecular biophysics; mouse; structural biology

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