Study on structural mechanism of activation by calcium of Anoctamin 1 (ANO1)/TMEM16A, calcium activated chloride channel

Abstract

Anoctamin 1 (ANO1)/TMEM16A is a key molecule known for contributing to a variety of physiological phenomena, playing a role as calcium activated chloride channel (CaCC). Despite of the importance of the activation of ANO1 by Ca2+, it is still ambiguous to identify where Ca2+ binds to a region of ANO1 and to understand how to be activated by calcium. Here, we demonstrate that Ca2+ directly binds to the third intracellular loop (ICL3) of the ANO1 and two helices, reference and Ca2+ sensor helices in the ICL3 interact directly in a Ca2+ dependent manner as facing each other with opposite charges. Moreover neutralization or deletion of the negatively and positively charged residues in the two helices significantly changes the Ca2+ sensitivity of the ANO1. Therefore we predict a new activation mechanism by which the Ca2+ sensor helix attaches to the reference helix in the resting state, and as intracellular Ca2+ rises, Ca2+ acts on the sensor helix, which repels it from the reference helix. This Ca2+-dependent push-pull conformational change would be a key electromechanical movement for gating the ANO1 channel.