ALTERATION OF THE CYSTIC-FIBROSIS TRANSMEMBRANE CONDUCTANCE REGULATORFOLDING PATHWAY - EFFECTS OF THE DELTA-F508 MUTATION ON THE THERMODYNAMIC STABILITY AND FOLDING YIELD OF NBD1
Bh. Qu et Pj. Thomas, ALTERATION OF THE CYSTIC-FIBROSIS TRANSMEMBRANE CONDUCTANCE REGULATORFOLDING PATHWAY - EFFECTS OF THE DELTA-F508 MUTATION ON THE THERMODYNAMIC STABILITY AND FOLDING YIELD OF NBD1, The Journal of biological chemistry, 271(13), 1996, pp. 7261-7264
The cellular phenotype of the most common cystic fibrosis-causing muta
tion, deletion of phenylalanine 508 (Delta F508) in the amino-terminal
nucleotide binding domain (NBD1) of the cystic fibrosis transmembrane
conductance regulator (CFTR), is the inability of the mutant protein
to fold and transit to the apical membrane of affected epithelial cell
s. Expressed NBD1s were purified and folded in vitro into soluble mono
mers capable of binding nucleotide. Here we report that the Delta F508
mutation has little effect on the thermodynamic stability of the fold
ed NBD1. The Delta G(D,GdnHCl)(0) is 15.5 kJ/mol for the wild type NBD
1 and 14.4 kJ/mol for NBD1 Delta F. In contrast, the mutation signific
antly reduces the folding yield at a variety of temperatures, indicati
ng that Phe-508 makes crucial contacts during the folding process, but
plays little role in stabilization of the native state. Under conditi
ons that approximate the efficiency of maturation in vivo, the rate of
f-pathway is significantly increased by the disease causing mutation.
These results establish a molecular mechanism for most cases of cystic
fibrosis and provide insight into the complex processes by which prim
ary sequence encodes the three-dimensional structure.