Cystic fibrosis transmembrane conductance regulator: Solution structures of peptides based on the Phe508 region, the most common site of disease-causing Delta F508 mutation
Ma. Massiah et al., Cystic fibrosis transmembrane conductance regulator: Solution structures of peptides based on the Phe508 region, the most common site of disease-causing Delta F508 mutation, BIOCHEM, 38(23), 1999, pp. 7453-7461
Most cases of cystic fibrosis (CF), a common inherited disease of epithelia
l cell origin, are caused by the deletion of Phe508 located in the first nu
cleotide-binding domain (NBF1) of the protein called CFTR (cystic fibrosis
transmembrane conductance regulator). To gain greater insight into the stru
cture within the Phe508 region of the wild-type protein and the change in s
tructure that occurs when this residue is deleted, we conducted nuclear mag
netic resonance (NMR) studies on representative synthetic 26 and 25 amino a
cid peptide segments. 2D H-1 NMR studies at 600 MHz of the 26-residue pepti
de consisting of Met498 to Ala523 in 10% DMSO, pH 4.0, at 25 degrees C show
a continuous but labile helix from Gly500 to Lys522, based on both NH-NH(i
,i+1) and alpha H-NH(i,i+1) NOEs. Phe508 within this helix shows only short
-range (i, less than or equal to i + 2) NOEs. The corresponding 25-residue
peptide lacking Phe508 also forms a labile helix from Gly500 to Lys522. How
ever, the relative intensities of the NH-NH(i,i+1)/alpha H-NH(i,i+1) NOEs,
fewer intermediate-range NOEs, and downfield alpha H and NH chemical shifts
indicate a lower helical propensity of the 25-mer between residues 505 and
517, surrounding the missing residue, Phe508. 2D H-1 NMR studies of both p
eptides in saturating (43%) TFE reveal stable a-helices from Gly500 to Lys5
22, based on NH-NH(i,i+1,2,3), alpha H-NH(i,i+2,3,4), alpha H-beta H-(i,H-i
+3), and weak alpha H-NH(i,i+1) NOEs. However, downfield shifts of the alph
a H resonances from residues Gly500 to Ile507 and fewer intermediate-range
NOEs suggest a less stable ex-helix in the 25-mer even in saturating TFE. T
hese findings show that the Phe508 containing region of CFTR has a propensi
ty to form an ct-helix, which is destabilized by the Delta F508 mutation fo
und in most patients with CF, These studies have direct relevance to better
understanding the CFTR misfolding problem associated with CF and to identi
fying chemical agents, which correct this problem.