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J. Biol. Chem., Vol. 277, Issue 39, 35896-35905, September 27, 2002
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From the Department of Biological Science, Florida State
University, Tallahassee, Florida 32306
The gene encoding the cystic fibrosis
transmembrane conductance regulator (CFTR), an ATP binding cassette
(ABC) transporter that functions as a phosphorylation- and
nucleotide-regulated chloride channel, is mutated in cystic fibrosis
(CF) patients. Deletion of a phenylalanine at amino acid position 508 (
Mutations in the Nucleotide Binding Domain 1 Signature Motif
Region Rescue Processing and Functional Defects of Cystic Fibrosis
Transmembrane Conductance Regulator
F508*
F508) in the first nucleotide binding domain (NBD1) is the most
prevalent CF-causing mutation and results in defective protein
processing and reduced CFTR function, leading to chloride
impermeability in CF epithelia and heterologous systems. Using a
STE6/CFTR
F508 chimera system in yeast, we isolated two novel
F508 revertant mutations, I539T and G550E, proximal to and within
the conserved ABC signature motif of NBD1, respectively. Western blot
and functional analysis in mammalian cells indicate that mutations
I539T and G550E each partially rescue the CFTR
F508 defect.
Furthermore, a combination of both revertant mutations resulted in a
38-fold increase in CFTR
F508-mediated chloride current, representing 29% of wild type channel activity. The G550E mutation increased the
sensitivity of CFTR
F508 and wild type CFTR to activation by cAMP
agonists and blocked the enhancement of CFTR
F508 channel activity by
2 mM 3-isobutyl-1-methylxanthine. The data show that the
F508 defect can be significantly rescued by second-site
mutations in the nucleotide binding domain 1 region, that includes the
LSGGQ consensus motif.
*
This work was supported by National Institutes of Health
Grant HL61234 and a Program Enhancement Grant from Florida State University Research Foundation (to J. L. T.).The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement" in accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
To whom correspondence should be addressed: Dept. of Biological
Science, Biounit-238, Florida State University, Tallahassee, FL 32306. Tel.: 850-644-5121; Fax: 850-644-0418; E-mail: teem@bio.fsu.edu.
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