PDBsum entry 2exw

Membrane protein

PDB id: 2exw

Contents

Protein chains

444 a.a. *

221 a.a. *

211 a.a. *

* Residue conservation analysis

PDB id:

2exw

Name:

Membrane protein

Title:

Crystal structure of a ecclc-fab complex in the absence of bound ions

Structure:

H(+)/cl(-) exchange transporter clca. Chain: a, b. Synonym: clc-ec1. Engineered: yes. Fab fragment (heavy chain). Chain: c, e. Fab fragment (light chain). Chain: d, f

Source:

Escherichia coli. Organism_taxid: 562. Expressed in: escherichia coli bl21(de3). Expression_system_taxid: 469008. Mus musculus. House mouse. Organism_taxid: 10090. Cell_line: hybridoma cell line. Cell_line: hybridoma cell line

Biol. unit:

Hexamer (from PQS)

Resolution:

3.20Å R-factor: 0.268 R-free: 0.314

Authors:

S.Lobet,R.Dutzler

Key ref:

S.Lobet and R.Dutzler (2006). Ion-binding properties of the ClC chloride selectivity filter. EMBO J, 25, 24-33. PubMed id: 16341087 DOI: 10.1038/sj.emboj.7600909

Date:

09-Nov-05 Release date: 24-Jan-06

Protein chains

P37019  (CLCA_ECOLI) -  H(+)/Cl(-) exchange transporter ClcA from Escherichia coli (strain K12)

Seq: 473 a.a.

Struc: 444 a.a.

Protein chains

No UniProt id for this chain

Struc: 221 a.a.

Protein chains

No UniProt id for this chain

Struc: 211 a.a.

DOI no: 10.1038/sj.emboj.7600909

EMBO J 25:24-33 (2006)

PubMed id: 16341087

Ion-binding properties of the ClC chloride selectivity filter.

S.Lobet, R.Dutzler.

ABSTRACT

The ClC channels are members of a large protein family of chloride (Cl-) channels and secondary active Cl- transporters. Despite their diverse functions, the transmembrane architecture within the family is conserved. Here we present a crystallographic study on the ion-binding properties of the ClC selectivity filter in the close homolog from Escherichia coli (EcClC). The ClC selectivity filter contains three ion-binding sites that bridge the extra- and intracellular solutions. The sites bind Cl- ions with mM affinity. Despite their close proximity within the filter, the three sites can be occupied simultaneously. The ion-binding properties are found conserved from the bacterial transporter EcClC to the human Cl- channel ClC-1, suggesting a close functional link between ion permeation in the channels and active transport in the transporters. In resemblance to K+ channels, ions permeate the ClC channel in a single file, with mutual repulsion between the ions fostering rapid conduction.

Selected figure(s)

Figure 1.
Figure 1 Structure and ion-binding properties of the EcClC selectivity filter. (A) View of a ribbon representation of the EcClC dimer from within the membrane. The subunits are colored in green and blue. The ions are represented as red spheres. The region of the selectivity filter in one subunit is indicated by a transparent gray box. (B) Selectivity filter of wtEcClC (closed) and the EcClC mutant E148Q (open) viewed from the dimer interface. The protein backbone is shown as a ribbon, with selected residues as sticks. The N-terminal ends of -helices are colored in cyan. The ions are represented as red spheres. The Br- anomalous difference density (contoured at 6 ) is shown superimposed (red). The path for sampling the anomalous difference density is shown as gray lines (open). Aqueous cavities from the extracellular solution (out) and intracellular solution (in) are shown as cyan mesh. The ion-binding sites are labeled. (A) and (B) were prepared with DINO (www.dino3d.org). (C) One-dimensional anomalous difference electron density in the selectivity filter at high Br- concentration. The density ( ) is plotted in units of its standard deviation. The filter position is shown relative to S[cen]. The curve for the 'open conformation' is colored in blue, the curve for the 'closed conformation' in red.

Figure 5.
Figure 5 Two models for ion conduction. Schematic drawing of ion conduction in a single ion pore and a multiple-ion pore. (A) Single-ion pore: The selectivity filter binds only one ion at a time. During permeation the ion enters the selectivity filter from the solution and diffuses between the different binding sites of the channels until it dissociated from the filter. (B) Multiple-ion pore: The selectivity filter binds multiple ions, which permeate in a single file when additional ions enter the filter. The filter is depicted in its open state; the ions are drawn as spheres.

The above figures are reprinted by permission from Macmillan Publishers Ltd: EMBO J (2006, 25, 24-33) copyright 2006.

Figures were selected by an automated process.