Discovering the chloride pathway in the CFTR channel

Area of Science:

• Biophysics
• Molecular Biology
• Structural Biology

Background:

• Cystic fibrosis (CF) is a lethal monogenic disease caused by mutations in the CFTR chloride channel.
• Most CF mutations impair CFTR protein folding and stability, reducing anion conductance in epithelial cells.
• Recent cryo-electron microscopy (cryo-EM) structures offer insights into CFTR variant structure-function but lack open channel conformations.

Purpose of the Study:

• To investigate the CFTR chloride permeation pathway using computational methods.
• To identify open channel conformations and understand CFTR gating mechanisms.
• To explore the structural basis of CFTR lipid-dependency.

Main Methods:

• Performed extensive molecular dynamics (MD) simulations of the full-length human CFTR.
• Utilized channel detection algorithms to identify conformations with open ion pathways.
• Employed metadynamics simulations to investigate ion permeation through the identified pathway.

Main Results:

• Identified a primary intracellular entry point at transmembrane domains (TM) 4/6 and a secondary pore at TM10/12.
• Characterized a bottleneck region involving TM1, TM6, and TM12, consistent with experimental data.
• Revealed two potential ion exit routes, one involving hydrophobic lipid tails, suggesting a role in CFTR lipid-dependency.

Conclusions:

• The in silico study provides a detailed model of the CFTR chloride channel pathway.
• Findings contribute to understanding CFTR gating and may inform strategies for rescuing CFTR mutants.
• The identified lipid-dependent exit pathway offers new avenues for therapeutic intervention in CF.