Cystic Fibrosis (CF) is a genetic disorder that is caused by mutations in the gene for the CF Transmembrane Conductance Regulator (CFTR). CFTR is an ABC transporter chloride channel containing five domains: two membrane-spanning domains (MSD1 & 2) connected by two nucleotide-binding domains (NBD1 & 2) and linked by a regulatory domain. The most common CF causing mutation is the deletion of phenylalanine 508 (?F508) in NBD1. It was shown that ?F508 thermodynamically destabilizes NBD1, as a result, misfold and degrade CFTR channel in the endoplasmic reticulum and prevents its processing and translocation to the plasma membrane. An effective drug that rescue the channel enhance its folding will increase its concentration on the plasma membrane. Here, we show stabilization of ?F508-NBD1 with second site mutations was not sufficient to increase the ?F508-CFTR folding efficiency and membrane concentration to that of the wild-type level. However, the introduction of additional mutations that stabilizes the interaction between NBD1 and MSD2 of CFTR in the presence of ?F508-NBD1 stabilization mutations increased the ?F508-CFTR folding efficiency and biogenesis from ~2% to 80% of the wild-type. As a result, a two-component drug that energetically stabilizes ?F508-NBD1 and maintain the NBD1-MSD2 interface interactions are required for wild-type like folding, processing, and transport function, suggesting a two step correction process.


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