Nanomechanics combined with HDX reveal allosteric drug binding sites of CFTR NBD1

Abstract

Abstract Cystic fibrosis is most frequently caused by the deletion of F508 (ΔF508) in CFTR’s nucleotide binding domain 1 (NBD1), compromising CFTR folding, stability and domain assembly. The limitation of developing a successful therapy is due to the lack of molecules that synergistically facilitate folding by targeting distinct structural defects of ΔF508-CFTR. To improve drug efficacy by targeting the ΔF508-NBD1 folding and stability, and to study potential ΔF508-NBD1 allosteric corrector binding sites at the atomic level, we combined molecular dynamics (MD) simulations, atomic force spectroscopy (AFM) and hydrogen-deuterium exchange (HDX) experiments. These methods allowed us to describe unfolding intermediates and forces acting during NBD1 mechanical unfolding and to elucidate the stabilization mechanism of ΔF508-NBD1 by 5-bromoindole-3-acetic acid (BIA). An NBD1 region, including the α-subdomain, was identified as a potentially important participant of the first folding steps, characterized by non-native interactions of F508, thus destabilized in the deletion mutant. The instability was counteracted by the low-potency corrector BIA, increasing the mechanical resistance of the ΔF508-NBD1 α-subdomain, which was confirmed as a binding site by computational modeling and HDX experiments. Our results underline the complementarity of computational and experimental methods and provide a possible strategy to improve folding correctors.