CFTR corrector efficacy is associated with occupancy of distinct binding sites

Abstract

CFTR misfolding due to cystic fibrosis causing mutations can be corrected with small molecules designated as correctors. VX-809, an investigational corrector compound, is believed to bind CFTR directly to either the first membrane-spanning domain (MSD1) and/or the first nucleotide-binding domain (NBD1). Blind docking onto the 3D structures of these domains, followed by molecular dynamics (MD) simulations, revealed the presence of two potential VX-809 binding sites which, when mutated, abrogated corrector rescue. Mutations altering protein maturation are also shown to be not equally sensitive to the occupancy of the two sites by VX-809, with the most frequent mutation F508del requiring integrity of both sites and allosteric coupling with the F508del region while L206W only requires the integrity of the MSD1 site. A network of charged amino acids in the lasso Lh2 helix and the intracellular loops ICL1 and ICL4 is involved in the allostery between MSD1 and NBD1. Corrector VX-445, which is used in combination in clinics with VX-661, a structurally close analog of VX-809, to fully correct F508del, is also shown to occupy two potential binding sites on MSD1 and NBD1, the latter being shared with VX-809. In conclusion, VX-809 and VX-445 appear to bind different CFTR domains to alleviate specific folding defects. These results provide new insights into therapeutics understanding and may help the development of efficient corrector combinations.