CFTR misfolds during native-centric simulations due to entropic penalties of native state formation

Abstract

Cystic fibrosis (CF) is a common genetic disorder that affects approximately 70,000 people worldwide. It is caused by mutation-induced defects in synthesis, folding, processing, or function of the Cystic Fibrosis Transmembrane conductance Regulator protein (CFTR), a chloride-selective ion channel required for the proper functioning of secretory epithelia in tissues such as the lung, pancreas, and skin. The most common cause of CF is the single-residue deletion of F508 (F508del), a mutation present in one or both alleles in 90% of patients that induces severe folding defects and results in greatly reduced expression of the protein. Despite its medical importance, high-resolution mechanistic information about CFTR folding is lacking. In this study, we used molecular dynamics simulation with a native-centric force field to examine the folding and assembly of both full-length CFTR and the isolated first nucleotide-binding domain (NBD1). We observed that the protein was capable of substantial misfolding on both the intradomain and interdomain scale due to entropically favorable kinetic traps that exist on CFTRs folding free energy surface. These results suggest that even wild type CFTR, in the absence of any disease-related mutations, has suboptimal folding efficiency. We speculate that such entropically-driven misfolding also occurs in disease-prone mutants such as F508del and contributes to the proteins poor in vivo activity.