Allosteric coupling between PIP₂ and Ca²⁺ binding sites gates TMEM16A channels

Area of Science:

• Ion channel biophysics
• Molecular physiology
• Membrane protein structure and function

Background:

• TMEM16A channels are crucial for physiological processes like secretion and muscle contraction.
• Channel activation depends on both intracellular calcium (Ca2+) and the signaling phospholipid phosphatidylinositol 4,5-bisphosphate (PIP2).
• The precise molecular mechanism of this dual regulation remained elusive.

Purpose of the Study:

• To elucidate the molecular basis of Ca2+ and PIP2 cooperative gating in TMEM16A channels.
• To investigate the specific roles of PIP2 headgroup and acyl chain interactions in channel activation.
• To understand the interplay between lipid binding and ion permeation.

Main Methods:

• Gating molecular-dynamics simulations.
• Structure-guided electrophysiology.
• Analysis of lipid-protein interactions at the molecular level.

Main Results:

• PIP2 and Ca2+ cooperatively gate TMEM16A via an allosterically coupled electrostatic network involving the α4 helix.
• PIP2 headgroup phosphates link Ca2+ binding to channel opening.
• PIP2 acyl chains stabilize the open state by engaging hydrophobic surfaces.
• Disrupting PIP2 interactions impairs activation, while specific PIP2 variants restore function.

Conclusions:

• Both PIP2 headgroup phosphates and acyl chains play critical, complementary roles in TMEM16A gating.
• A cooperative lipid-ion activation mechanism governs TMEM16A function.
• This mechanism provides a framework for understanding phosphoinositide regulation of ion channels.
• Findings offer insights for structure-based design of TMEM16A modulators.