PDBsum entry 1rk4

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Ion transport/membrane protein PDB id
Protein chains
213 a.a. *
Waters ×342
* Residue conservation analysis

References listed in PDB file
Key reference
Title The intracellular chloride ion channel protein clic1 undergoes a redox-Controlled structural transition.
Authors D.R.Littler, S.J.Harrop, W.D.Fairlie, L.J.Brown, G.J.Pankhurst, S.Pankhurst, M.Z.Demaere, T.J.Campbell, A.R.Bauskin, R.Tonini, M.Mazzanti, S.N.Breit, P.M.Curmi.
Ref. J Biol Chem, 2004, 279, 9298-9305. [DOI no: 10.1074/jbc.M308444200]
PubMed id 14613939
Most proteins adopt a well defined three-dimensional structure; however, it is increasingly recognized that some proteins can exist with at least two stable conformations. Recently, a class of intracellular chloride ion channel proteins (CLICs) has been shown to exist in both soluble and integral membrane forms. The structure of the soluble form of CLIC1 is typical of a soluble glutathione S-transferase superfamily protein but contains a glutaredoxin-like active site. In this study we show that on oxidation CLIC1 undergoes a reversible transition from a monomeric to a non-covalent dimeric state due to the formation of an intramolecular disulfide bond (Cys-24-Cys-59). We have determined the crystal structure of this oxidized state and show that a major structural transition has occurred, exposing a large hydrophobic surface, which forms the dimer interface. The oxidized CLIC1 dimer maintains its ability to form chloride ion channels in artificial bilayers and vesicles, whereas a reducing environment prevents the formation of ion channels by CLIC1. Mutational studies show that both Cys-24 and Cys-59 are required for channel activity.
Figure 2.
FIG. 2. Structure of the oxidized CLIC1 dimer. A, stereo backbone of the CLIC1 dimer; green, A subunit; red, B subunit. In the A subunit every 10th residue is labeled. B, electron density of the intramolecular disulfide bond between Cys-24 and Cys-59 contoured at 1 . The CLIC1 dimer is viewed along (C) and perpendicular (D) to the pseudo 2-fold axis; are shown helices, A subunit (red) and B subunit (green), and intramolecular disulfide bonds (yellow). E, ClustalW (24) alignment of the CLIC family. The secondary structure is shown for both monomeric (red, helices; yellow, -strands) and dimeric (blue, helices) forms. Conserved regions are shaded; green, putative transmembrane regions; yellow, Cys; cream, Gly. Features unique to CLIC1 are in blue. Ramachandran distances (see "Experimental Procedures") for the monomer to dimer transition are plotted above its sequence. Figures were made with SETOR (25), MOLSCRIPT (26), RASTER3D (27), and CONSCRIPT (28).
Figure 3.
FIG. 3. Structural transition of CLIC1 between the monomeric and the dimeric forms. Representations of reduced monomeric form of CLIC1 (A) and a subunit of the oxidized dimeric form (B). C, backbone superposition of CLIC1 for the reduced monomeric (green) and the oxidized dimeric (magenta) states. Ramachandran distances for residues 23-234 are mapped onto the backbone of the monomeric (D) and dimeric (E) forms. The color gradient, from gray to pink represents Ramachandran distances from 0° to 180°. Residues not observed in the dimer are colored gold. F, Ramachandran plot of residues within the N-domain with Ramachandran distances greater than 35^0 between the two structures. Monomer - co-ordinates are plotted as orange squares, and dimer co-ordinates are in black with a connecting line. The figures were made with SETOR (25), MOLSCRIPT (26), RASTER3D (27), and GRASP (29).
The above figures are reprinted by permission from the ASBMB: J Biol Chem (2004, 279, 9298-9305) copyright 2004.
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