title: Three charged amino acids in extracellular loop 1 are involved in maintaining the outer pore architecture of CFTR.
abstract: The cystic fibrosis (CF) transmembrane conductance regulator (CFTR) bears six extracellular loops (ECL1-6); ECL1 is the site of several mutations associated with CF. Mutation R117H has been reported to reduce current amplitude, whereas D110H, E116K, and R117C/L/P may impair channel stability. We hypothesized that these amino acids might not be directly involved in ion conduction and permeation but may contribute to stabilizing the outer vestibule architecture in CFTR. We used cRNA injected oocytes combined with electrophysiological techniques to test this hypothesis. Mutants bearing cysteine at these sites were not functionally modified by extracellular MTS reagents and were blocked by GlyH-101 similarly to WT-CFTR. These results suggest that these three residues do not contribute directly to permeation in CFTR. In contrast, mutants D110R-, E116R-, and R117A-CFTR exhibited instability of the open state and significantly shortened burst duration compared with WT-CFTR and failed to be locked into the open state by AMP-PNP (adenosine 5'-(β,γ-imido) triphosphate); charge-retaining mutants showed mainly the full open state with comparably longer open burst duration. These interactions suggest that these ECL1 residues might be involved in maintaining the outer pore architecture of CFTR. A CFTR homology model suggested that E116 interacts with R104 in both the closed and open states, D110 interacts with K892 in the fully closed state, and R117 interacts with E1126 in the open state. These interactions were confirmed experimentally. The results suggest that D110, E116, and R117 may contribute to stabilizing the architecture of the outer pore of CFTR by interactions with other charged residues.
authors.affiliation: Division of Pulmonary, Allergy and Immunology, Cystic Fibrosis, and Sleep, Department of Pediatrics, Center for Cystic Fibrosis and Airways Disease Research, Emory+Children's Pediatric Research Center, Emory University School of Medicine and Children's Healthcare of Atlanta, Atlanta, GA 30322.
authors.forename: Guiying
authors.initials: G
authors.lastname: Cui
authors.affiliation: Parker H. Petit Institute for Bioengineering and Bioscience and School of Biology, Georgia Institute of Technology, Atlanta, GA 30332 Parker H. Petit Institute for Bioengineering and Bioscience and School of Biology, Georgia Institute of Technology, Atlanta, GA 30332.
authors.forename: Kazi S
authors.initials: KS
authors.lastname: Rahman
authors.affiliation: Division of Pulmonary, Allergy and Immunology, Cystic Fibrosis, and Sleep, Department of Pediatrics, Center for Cystic Fibrosis and Airways Disease Research, Emory+Children's Pediatric Research Center, Emory University School of Medicine and Children's Healthcare of Atlanta, Atlanta, GA 30322.
authors.forename: Daniel T
authors.initials: DT
authors.lastname: Infield
authors.affiliation: Division of Pulmonary, Allergy and Immunology, Cystic Fibrosis, and Sleep, Department of Pediatrics, Center for Cystic Fibrosis and Airways Disease Research, Emory+Children's Pediatric Research Center, Emory University School of Medicine and Children's Healthcare of Atlanta, Atlanta, GA 30322.
authors.forename: Christopher
authors.initials: C
authors.lastname: Kuang
authors.affiliation: Division of Pulmonary, Allergy and Immunology, Cystic Fibrosis, and Sleep, Department of Pediatrics, Center for Cystic Fibrosis and Airways Disease Research, Emory+Children's Pediatric Research Center, Emory University School of Medicine and Children's Healthcare of Atlanta, Atlanta, GA 30322.
authors.forename: Chengyu Z
authors.initials: CZ
authors.lastname: Prince
authors.affiliation: Division of Pulmonary, Allergy and Immunology, Cystic Fibrosis, and Sleep, Department of Pediatrics, Center for Cystic Fibrosis and Airways Disease Research, Emory+Children's Pediatric Research Center, Emory University School of Medicine and Children's Healthcare of Atlanta, Atlanta, GA 30322 Parker H. Petit Institute for Bioengineering and Bioscience and School of Biology, Georgia Institute of Technology, Atlanta, GA 30332 namccar@emory.edu.
authors.forename: Nael A
authors.initials: NA
authors.lastname: McCarty
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry*; D000818:Animals; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000737:chemistry* / Q000235:genetics / Q000502:physiology*; D005110:Extracellular Space / Q000737:chemistry*; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism; D018408:Patch-Clamp Techniques; D017434:Protein Structure, Tertiary; D014981:Xenopus
chemical_list: D000596:Amino Acids; D019005:Cystic Fibrosis Transmembrane Conductance Regulator