Specific PIP₂ Binding Promotes Calcium Activation of TMEM16A Chloride Channels

Abstract

TMEM16A is a widely expressed Ca 2+ -activated Clchannel that regulates crucial physiological functions including fluid secretion, neuronal excitability, and smooth muscle contraction. There is a critical need to understand the molecular mechanisms of TMEM16A gating and regulation.However, high-resolution TMEM16A structures have failed to reveal an activated state with unobstructed permeation pathway even with saturating Ca 2+ . This has been attributed to the requirement of PIP2 for preventing TMEM16A desensitization. Here, we show that specific binding PIP2 to TMEM16A can lead to spontaneous opening of the permeation pathway in the Ca 2+ -bound state. The predicted activated state is highly consistent with a wide range of mutagenesis and functional data. It yields a maximal Clconductance of ~1 pS, similar to experimental estimates, and recapitulates the selectivity of larger SCNover Cl -. The resulting molecular mechanism of activation provides a basis for understanding the interplay of multiple signals in controlling TMEM16A channel function.

An outer-pore gate modulates the pharmacology of the TMEM16A channel

“…S4 provides a structural alignment of our open-state TMEM16A model with the deposited TMEM16x structures and the recently developed model of the PIP 2 -bound open TMEM16A channel (28). The analysis demonstrates that our model closely resembled these structures and almost completely overlapped with the PIP 2 -bound open TMEM16A channel model (28) with C α RMSD of 1.8 Å (SI Appendix, Fig. S4 E and F).…”

Allosteric modulation of alternatively spliced Ca2+-activated Cl−channels TMEM16A by PI(4,5)P2and CaMKII

“…It is structurally established that specific PI(4,5)P 2 binding to the so-called PI(4,5)P 2 -binding module (25) promotes Ca 2+bound TMEM16A(ac) activation (48). TM6 bends toward TM4 to block the pore, and when two Ca 2+ are bound in the binding site, the TM6 helix is stretched (41,49).…”

Molecular mechanisms of activation and regulation of ANO1-Encoded Ca2+-Activated Cl- channels

“…152 Molecular dynamics (MD) simulations of ANO1 showed a dilation of the pore upon binding of PIP 2 that is consistent with an activated channel, supporting the idea that the proper lipid environment is essential to resolve a cryo-EM channel with a dilated pore. 153 However, these simulations were performed on a structure of ANO1 missing large portions of the N-and C-terminus. The N-terminus is known to be important in channel function.…”

“…Molecular dynamics simulations suggested that PIP 2 binding to this site in the Ca 2+ bound channel causes TMD4 to move away from TMD6 to contribute to a fully open pore. 153 Yu et al 190 identified three potential PIP 2 binding sites with the first located on the cytosolic side of TMD1-2 near the inter-dimer space, the second at the base of TMD6, and the third on the intracellular loop between TMD2-3 (Fig. 3F).…”