Gating effects of membrane potential on TMEM16A analyzed using molecular dynamics simulations combined with external electric field

TMEM16A is the molecular basis of calcium-activated chloride channels (CaCCs) and is dual regulated by intracellular calcium ion and membrane potential. It is widely expressed and participates in important physiological processes. At present, although the cryo-EM structures of several states of TMEM16A protein are obtained, none of them shows a fully activated pore, and the role of membrane potential in regulation of the channel cannot be explained in these static structures. Here, based on the stereo structure of TMEM16A we used molecular dynamics (MD)with applied external electric field (EE-MD) simulations to understand how membrane potential regulates the gating process of TMEM16A channels. Our results indicate that the transmembrane helices TM3 and TM4, which constitute the ion-conducting pore, are strongly influenced by the membrane potential and expand outward, resulting in a clear separation of the hydrophobic-gated amino acids of TM4 and TM6, increasing the space for chloride ions (Cl−) to pass through. The membrane potential breaks the hydrogen bond between K645 and E705, directing the K645 side chain to the neck region, which lowers the energy barrier for chloride ion conduction by affecting the static electricity in the neck region. Furthermore, the simulation results indicate that the dual coupling of calcium ions and membrane potential can lead to the spontaneous diffusion of Cl− ions from the extracellular side through the pore. Our molecular dynamics simulations and analyses provide new dynamic, and energetic information of the gating mechanism by which membrane potential affects TMEM16A channels and to guide functional studies of the TMEM16A channels and development of its regulators.