Structural basis for anion conduction in the calcium-activated chloride channel TMEM16A

Area of Science:

• Structural Biology
• Molecular Biology
• Biophysics

Background:

• The TMEM16 family includes ion channels and lipid scramblases with distinct functions.
• Previous structures of nhTMEM16 defined the family's architecture but not channel adaptation.
• Understanding TMEM16A's structure is crucial for elucidating anion conduction mechanisms.

Purpose of the Study:

• To determine the cryo-electron microscopy structure of mouse TMEM16A.
• To understand the structural basis for TMEM16A's function as a chloride channel.
• To compare TMEM16A structure with lipid scramblase nhTMEM16 to reveal functional divergence.

Main Methods:

• Cryo-electron microscopy (cryo-EM) for high-resolution structure determination.
• Functional characterization assays to complement structural findings.
• Comparative structural analysis between TMEM16A and nhTMEM16.

Main Results:

• The structure of mouse TMEM16A was determined, revealing overall similarity to nhTMEM16.
• Key differences were identified at the catalytic site, involving transmembrane helix conformation.
• TMEM16A forms an enclosed aqueous pore, distinct from the lipid pathway in scramblases.

Conclusions:

• The study reveals the structural basis of anion conduction in TMEM16A.
• Structural adaptations explain the functional divergence between TMEM16 channels and scramblases.
• Provides a foundation for understanding the diverse roles of the TMEM16 protein family.