CFTR corrector efficacy is associated with occupancy of distinct binding sites

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. ### Competing Interest Statement NB, AhE, JPM, BC, IP, NS, RZ, JLD, AlE, IC and AH declare no competing interests. ISG reports grants from Vertex Therapeutics, Eloxx Pharmaceuticals and participation to scientific board of Proteostasis Therapeutics; outside the submitted work.