title: Two salt bridges differentially contribute to the maintenance of cystic fibrosis transmembrane conductance regulator (CFTR) channel function.
abstract: Previous studies have identified two salt bridges in human CFTR chloride ion channels, Arg(352)-Asp(993) and Arg(347)-Asp(924), that are required for normal channel function. In the present study, we determined how the two salt bridges cooperate to maintain the open pore architecture of CFTR. Our data suggest that Arg(347) not only interacts with Asp(924) but also interacts with Asp(993). The tripartite interaction Arg(347)-Asp(924)-Asp(993) mainly contributes to maintaining a stable s2 open subconductance state. The Arg(352)-Asp(993) salt bridge, in contrast, is involved in stabilizing both the s2 and full (f) open conductance states, with the main contribution being to the f state. The s1 subconductance state does not require either salt bridge. In confirmation of the role of Arg(352) and Asp(993), channels bearing cysteines at these sites could be latched into a full open state using the bifunctional cross-linker 1,2-ethanediyl bismethanethiosulfonate, but only when applied in the open state. Channels remained latched open even after washout of ATP. The results suggest that these interacting residues contribute differently to stabilizing the open pore in different phases of the gating cycle.
authors.affiliation: Division of Pulmonology, Allergy/Immunology, Cystic Fibrosis, and Sleep, Department of Pediatrics, Center for Cystic Fibrosis Research, Emory University School of Medicine and Children's Healthcare of Atlanta, Atlanta, Georgia 30322, USA.
authors.forename: Guiying
authors.initials: G
authors.lastname: Cui
authors.forename: Cody S
authors.initials: CS
authors.lastname: Freeman
authors.forename: Taylor
authors.initials: T
authors.lastname: Knotts
authors.forename: Chengyu Z
authors.initials: CZ
authors.lastname: Prince
authors.forename: Christopher
authors.initials: C
authors.lastname: Kuang
authors.forename: Nael A
authors.initials: NA
authors.lastname: McCarty
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000465:Algorithms; D000595:Amino Acid Sequence; D000818:Animals; D001120:Arginine / Q000235:genetics / Q000378:metabolism*; D001224:Aspartic Acid / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites / Q000235:genetics; D002712:Chlorides / Q000494:pharmacology; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics / Q000378:metabolism*; D005260:Female; D006801:Humans; D015640:Ion Channel Gating; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009154:Mutation; D009865:Oocytes / Q000378:metabolism / Q000502:physiology; D018408:Patch-Clamp Techniques; D018075:RNA, Complementary / Q000235:genetics; D014982:Xenopus laevis
chemical_list: D002712:Chlorides; D018075:RNA, Complementary; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D001224:Aspartic Acid; D000255:Adenosine Triphosphate; D001120:Arginine
keywords: ABC Transporter; CFTR; Gating; MTS Reagents; Oocyte; Pore; Salt Bridge; Xenopus