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PDBsum entry 2ih1
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Membrane protein
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PDB id
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2ih1
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Contents |
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219 a.a.
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212 a.a.
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101 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 selectivity in a semisynthetic k+ channel locked in the conductive conformation.
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Authors
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F.I.Valiyaveetil,
M.Leonetti,
T.W.Muir,
R.Mackinnon.
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Ref.
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Science, 2006,
314,
1004-1007.
[DOI no: ]
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PubMed id
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Abstract
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Potassium channels are K+-selective protein pores in cell membrane. The
selectivity filter is the functional unit that allows K+ channels to distinguish
potassium (K+) and sodium (Na+) ions. The filter's structure depends on whether
K+ or Na+ ions are bound inside it. We synthesized a K+ channel containing the
d-enantiomer of alanine in place of a conserved glycine and found by x-ray
crystallography that its filter maintains the K+ (conductive) structure in the
presence of Na+ and very low concentrations of K+. This channel conducts Na+ in
the absence of K+ but not in the presence of K+. These findings demonstrate that
the ability of the channel to adapt its structure differently to K+ and Na+ is a
fundamental aspect of ion selectivity, as is the ability of multiple K+ ions to
compete effectively with Na+ for the conductive filter.
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Figure 1.
Fig. 1. Dependence of the conformation of the selectivity
filter of K^+ channels on K^+ concentration. (A) Close-up view
of the selectivity filter of wild-type KcsA channel in the
presence of high K^+ concentrations [K^+]. Two of the diagonally
opposite subunits are shown in stick representation. K^+ ions
are depicted as green spheres and water molecules as red
spheres. The K^+ binding sites in the selectivity filter are
labeled. (B) The structure of the selectivity filter in low
[K^+], represented as in (A). (C and D) Superposition of the
selectivity filter of wild-type KcsA in the presence of high
[K^+](blue) and low[K^+] (red). (C) shows a side view; (D)
depicts a top view extending  15 Å out from
the center of the filter. Aromatic residues that undergo
conformation changes are indicated.
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Figure 2.
Fig. 2. Structure of the selectivity filter of KcsA^D-Ala77 in
the presence of high [K^+]. (A) Stereo view of the electron
density of the selectivity filter of KcsA^D-Ala77. The 2F[obs]
– F[calc] electron density map contoured at 2.0  for the
diagonally opposite subunits is shown. (B) Structure of the
selectivity filter of KcsA^D-Ala77 in high [K^+] represented as
in Fig. 1. (C) Superposition of the selectivity filter of
KcsA^D-Ala77 (blue) and the wild-type KcsA channel (red) in the
presence of high [K^+].
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The above figures are
reprinted
by permission from the AAAs:
Science
(2006,
314,
1004-1007)
copyright 2006.
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