TMEM16A is a ligand-gated anion channel that is activated by intracellular Ca2+. This channel contains 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 C. et. al., 2017). 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.
- Raimund Dutzler
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
- Baron Chanda, University of Wisconsin-Madison, United States
© 2018, Lam & Dutzler
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