Molecular Dynamics Study of the Gating Mechanism of CFTR

Abstract

Cystic fibrosis transmembrane conductance regulator (CFTR) is an ATP-gated chloride channel found on the apical membrane of epithelial cells. Loss-of-function mutations in CFTR are known to cause the lethal disease cystic fibrosis. CFTR is the only known member of the ATP-binding cassette (ABC) transporter superfamily that functions as an ion channel. Unique structural features of CFTR revealed by recent cryo-EM structures have been speculated to be responsible for its function as a channel. Despite that ATP-binding and dimerization of nucleotide-binding domains lead to opening of the channel, the structure of CFTR with dimerized nucleotide-binding domains appears to be closed at its extracellular gate. Our research aims to study the molecular events relevant to gating of CFTR. To refine the structure of CFTR experimentally determined in detergent micelles, we performed microsecond atomistic molecular dynamics simulations on the ATP-bound structure of zebrafish CFTR as well as on a homology model of human CFTR, both embedded inside phospholipid bilayers. The ATP-bound CFTR remains in a closed state in most simulation repeats. However, a few trajectories show the presence of hydrated pathways through a putative extracellular gate, fulfilling a necessary condition for ion conduction. The conformational changes of CFTR correlated with hydration of the putative pore are analyzed. The simulations with hydrated pathways are extended, and the capacity of these pathways to mediate chloride conduction is evaluated. Results provide insight into the molecular basis of CFTR gating and permeation.