What is the consequence of F508 mutation in CFTR?
DeltaF508, deletion of phenylalanine at position 508 in nucleotide-binding domain 1 of CFTR, is most prevalent cystic fibrosis mutation worldwide present in approximately 70 percent patients. F508 lies at interface between NBD1 and intracellular loops from transmembrane domains, crucial for domain assembly during co-translational folding. Loss destabilizes NBD1 thermally, impairs interdomain contacts, causing kinetic folding trap recognized by chaperones Hsp70 and Hsp90, ubiquitination by RNF4 and retention in endoplasmic reticulum for ER-associated degradation via proteasome. Even when manipulated to reach surface, mutant shows reduced stability and impaired channel gating with shorter open bursts. Physiological consequence is sharp reduction in apical chloride secretion in airways, intestine, pancreas and sweat ducts leading to dehydrated secretions, intestinal obstruction, pancreatic fibrosis and elevated sweat chloride. Laboratory expression studies show temperature shift or chemical chaperones partially rescue trafficking, basis for pharmacologic corrector development that improves domain assembly and membrane trafficking. Such detailed mechanistic insight is frequently examined in competitive tests including NEET, CUET, CSIR-NET and GATE where transporter classification, energetics and disease linkage are integrated into problem-solving questions.
Ref: Lukacs & Verkman, Trends Mol Med 2012, F508del processing; Riordan, Annu Rev Biochem 2008, CFTR folding.