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PDBsum entry 2ez0
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Membrane protein
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PDB id
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2ez0
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Contents |
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444 a.a.
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221 a.a.
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211 a.a.
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References listed in PDB file
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Key reference
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Title
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Ion-Binding properties of the clc chloride selectivity filter.
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Authors
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S.Lobet,
R.Dutzler.
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Ref.
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EMBO J, 2006,
25,
24-33.
[DOI no: ]
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PubMed id
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Abstract
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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.
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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.
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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.
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The above figures are
reprinted
by permission from Macmillan Publishers Ltd:
EMBO J
(2006,
25,
24-33)
copyright 2006.
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