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PDBsum entry 2itc
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Membrane protein
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PDB id
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2itc
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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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References listed in PDB file
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Key reference
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Title
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Structural and thermodynamic properties of selective ion binding in a k+ channel.
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Authors
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S.W.Lockless,
M.Zhou,
R.Mackinnon.
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Ref.
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Plos Biol, 2007,
5,
e121.
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PubMed id
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Abstract
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Thermodynamic measurements of ion binding to the Streptomyces lividans K(+)
channel were carried out using isothermal titration calorimetry, whereas atomic
structures of ion-bound and ion-free conformations of the channel were
characterized by x-ray crystallography. Here we use these assays to show that
the ion radius dependence of selectivity stems from the channel's recognition of
ion size (i.e., volume) rather than charge density. Ion size recognition is a
function of the channel's ability to adopt a very specific conductive structure
with larger ions (K(+), Rb(+), Cs(+), and Ba(2+)) bound and not with smaller
ions (Na(+), Mg(2+), and Ca(2+)). The formation of the conductive structure
involves selectivity filter atoms that are in direct contact with bound ions as
well as protein atoms surrounding the selectivity filter up to a distance of 15
A from the ions. We conclude that ion selectivity in a K(+) channel is a
property of size-matched ion binding sites created by the protein structure.
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