ABC-transporter CFTR folds with high fidelity through a modular, stepwise pathway

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Biology

Background:

• Protein folding is crucial for cellular function, particularly for complex membrane proteins like the ABC transporter CFTR.
• Understanding CFTR folding is essential for deciphering the molecular basis of cystic fibrosis, a disease linked to protein misfolding.

Purpose of the Study:

• To elucidate the precise sequence of events in the proper folding of the CFTR protein within live cells.
• To analyze the impact of mutations and therapeutic interventions on CFTR folding pathways.

Main Methods:

• Combined kinetic radiolabeling with protease-susceptibility assays to track CFTR folding at the amino-acid level.
• Investigated folding and domain assembly by probing protein resistance to proteases at high resolution.

Main Results:

• CFTR folding occurs in two distinct stages: a co-translational stage involving TMD1, TMD2, and NBD1, followed by a post-translational stage of domain assembly.
• The F508del mutation causes co-translational misfolding of NBD1, preventing stage-2 folding and leading to cystic fibrosis.
• Corrector drugs improved stage-2 folding but did not fully rescue NBD1 misfolding; the DxD motif in NBD1 is critical for early folding events.

Conclusions:

• CFTR folding is a modular and stepwise process, contributing to its high fidelity and potential for correction.
• The study provides a detailed mechanistic understanding of CFTR folding, essential for developing targeted therapies for cystic fibrosis.