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PDBsum entry 1k4d
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Membrane protein
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PDB id
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1k4d
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Contents |
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219 a.a.
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212 a.a.
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103 a.a.
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* Residue conservation analysis
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References listed in PDB file
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Key reference
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Title
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Chemistry of ion coordination and hydration revealed by a k+ channel-Fab complex at 2.0 a resolution.
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Authors
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Y.Zhou,
J.H.Morais-Cabral,
A.Kaufman,
R.Mackinnon.
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Ref.
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Nature, 2001,
414,
43-48.
[DOI no: ]
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PubMed id
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Abstract
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Ion transport proteins must remove an ion's hydration shell to coordinate the
ion selectively on the basis of its size and charge. To discover how the K+
channel solves this fundamental aspect of ion conduction, we solved the
structure of the KcsA K+ channel in complex with a monoclonal Fab antibody
fragment at 2.0 A resolution. Here we show how the K+ channel displaces water
molecules around an ion at its extracellular entryway, and how it holds a K+ ion
in a square antiprism of water molecules in a cavity near its intracellular
entryway. Carbonyl oxygen atoms within the selectivity filter form a very
similar square antiprism around each K+ binding site, as if to mimic the waters
of hydration. The selectivity filter changes its ion coordination structure in
low K+ solutions. This structural change is crucial to the operation of the
selectivity filter in the cellular context, where the K+ ion concentration near
the selectivity filter varies in response to channel gating.
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Figure 2.
Figure 2: Stereo view of electron density in the region of the
K+ channel selectivity filter. The 2F[o] - F[c] electron
density map (contoured at 2  )
covers amino acids forming the selectivity filter (two
diagonally opposed subunits are shown), with K+ ions (green
spheres) along the ion pathway, and water molecules (red
spheres) in the vicinity.
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Figure 3.
Figure 3: Stereo view of a hydrated K+ ion in the central
cavity. Eight water molecules (red spheres) surround a single
K+ ion (green sphere) in the cavity. The 2F[o] - F[c] electron
density map is contoured at 2 .
Residues forming the cavity are shown in ball-and-stick
representation. For clarity, only backbone atoms and the side
chains facing the cavity (Thr 75, Ile 100, Phe 103, Gly 104 and
Thr 107) are shown. The subunit closest to the viewer has been
removed.
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The above figures are
reprinted
by permission from Macmillan Publishers Ltd:
Nature
(2001,
414,
43-48)
copyright 2001.
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