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.

Structural comparative modeling of multi-domain ΔF508 CFTR

“…Current CF drug treatment uses small molecules called correctors to stabilize F508del CFTR including the FDA approved compound VX-809 (Figure 6A). Recently, two studies converged on a putative binding site for VX-809 to the WT CFTR protein (11,12). We sought to model VX-809 in our ΔF508 comparative models to determine the energetic changes VX-809 confers to ΔF508 CFTR.…”

“…Understanding the atomic level mechanisms of CFTR correctors can facilitate computational design of improved CF therapeutics with fewer side effects. Cryo-EM (11) and computational modeling (12) revealed the binding site of FDA approved corrector VX-809 to WT CFTR. However, VX-809 binding to its primary target in the clinic, ΔF508 CFTR, remains poorly understood.…”