Correction of Both NBD1 Energetics and Domain Interface Is Required to Restore ΔF508 CFTR Folding and Function

The folding and misfolding mechanism of multidomain proteins remains poorly understood. Although thermodynamic instability of the first nucleotide-binding domain (NBD1) of Delta F508 CFTR (cystic fibrosis transmembrane conductance regulator) partly accounts for the mutant channel degradation in the endoplasmic reticulum and is considered as a drug target in cystic fibrosis, the link between NBD1 and CFTR misfolding remains unclear. Here, we show that Delta F508 destabilizes NBD1 both thermodynamically and kinetically, but correction of either defect alone is insufficient to restore Delta F508 CFTR biogenesis. Instead, both Delta F508-NBD1 energetic and the NBD1-MSD2 (membrane-spanning domain 2) interface stabilization are required for wild-type-like folding, processing, and transport function, suggesting a synergistic role of NBD1 energetics and topology in CFTR-coupled domain assembly. Identification of distinct structural deficiencies may explain the limited success of Delta F508 CFTR corrector molecules and suggests structure-based combination corrector therapies. These results may serve as a framework for understanding the mechanism of interface mutation in multidomain membrane proteins.