PDBsum entry 1otu

Membrane protein

PDB id: 1otu

Contents

Protein chains

444 a.a. *

221 a.a. *

211 a.a. *

Metals

_CL ×6

* Residue conservation analysis

References listed in PDB file

Key reference

Title

Gating the selectivity filter in clc chloride channels.

Authors

R.Dutzler, E.B.Campbell, R.Mackinnon.

Ref.

Science, 2003, 300, 108-112. [DOI no: 10.1126/science.1082708]

PubMed id

12649487

Abstract

ClC channels conduct chloride (Cl-) ions across cell membranes and thereby govern the electrical activity of muscle cells and certain neurons, the transport of fluid and electrolytes across epithelia, and the acidification of intracellular vesicles. The structural basis of ClC channel gating was studied. Crystal structures of wild-type and mutant Escherichia coli ClC channels bound to a monoclonal Fab fragment reveal three Cl- binding sites within the 15-angstrom neck of an hourglass-shaped pore. The Cl- binding site nearest the extracellular solution can be occupied either by a Cl- ion or by a glutamate carboxyl group. Mutations of this glutamate residue in Torpedo ray ClC channels alter gating in electrophysiological assays. These findings reveal a form of gating in which the glutamate carboxyl group closes the pore by mimicking a Cl- ion.

Figure 2.
Fig. 2. Structure of the selectivity filter of the wild-type EcClC Fab complex. (A) Stereo view of electron density in the selectivity filter at 2.5 Å, contoured at 1 . The view is from the dimer interface within the membrane. The cytoplasm is on the bottom, the extracellular side on the top. The map was calculated from native amplitudes and solvent-flattened two-fold averaged phases. The refined protein model is shown as sticks. An (F[Br] - F[Cl]) difference Fourier map at 2.8 Å, contoured at 4 , is shown in red. (B) Stereo view of the ion-binding sites. Selected residues in the vicinity of the bound chloride ions are shown. Hydrogen bonds between the protein and chloride ions (red spheres) as well as between the side chain of Glu148 and the rest of the protein are shown as black dashed lines.

Figure 5.
Fig. 5. Schematic drawing of the closed and opened conformation of a ClC chloride channel. In the closed conformation, the ion-binding sites S[int] and S[cen] are occupied by chloride ions, and the ion-binding site S[ext] is occupied by the side chain of Glu148. In the opened conformation, the side chain of Glu148 has moved out of binding site S[ext] into the extracellular vestibule. S[ext] is occupied by a third chloride ion. Chloride ions are shown as red spheres, the Glu148 side chain is colored red, and hydrogen bonds are drawn as dashed lines.

The above figures are reprinted by permission from the AAAs: Science (2003, 300, 108-112) copyright 2003.