Vx-770 potentiates CFTR function by promoting decoupling between the gating cycle and ATP hydrolysis cycle

Area of Science:

• Biochemistry
• Molecular Biology
• Pharmacology

Background:

• Cystic fibrosis (CF) is caused by defects in the CFTR chloride channel.
• Vx-770 (Ivacaftor) is an FDA-approved drug that targets CFTR, but its mechanism of action is not fully understood.
• Vx-770 affects both wild-type (WT) and mutant CFTR channels, including G551D-CFTR.

Purpose of the Study:

• To elucidate the unified mechanism underlying Vx-770's dual effect on CFTR channel activity.
• To investigate how Vx-770 modulates both ATP-dependent and ATP-independent gating of CFTR.
• To propose a new gating model for CFTR that explains Vx-770's action.

Main Methods:

• Electrophysiological recordings of WT-CFTR and mutant CFTR channels (G551D and R352C).
• Analysis of CFTR gating kinetics in the presence and absence of ATP and Vx-770.
• Development of a novel CFTR gating model incorporating ATP hydrolysis and reentry mechanisms.

Main Results:

• Vx-770 enhances spontaneous, ATP-independent activity of WT-CFTR.
• Vx-770 increases the open time of WT-CFTR in an ATP-dependent manner.
• Vx-770 stabilizes a posthydrolytic open state, decoupling gating from ATP hydrolysis, as observed with R352C-CFTR.

Conclusions:

• Vx-770 acts through a unified mechanism involving enhanced spontaneous activity and prolonged open time.
• A novel ATP-dependent reentry mechanism explains Vx-770's effect on CFTR gating.
• This understanding can guide the development of new strategies to improve CFTR function.