Chemistry of ion coordination and hydration revealed by a K+ channel–Fab complex at 2.0 Å resolution

@article{Zhou2001ChemistryOI,
  title={Chemistry of ion coordination and hydration revealed by a K+ channel–Fab complex at 2.0 Å resolution},
  author={Yufeng Zhou and J. H. Morais-Cabral and Amelia Kaufman and Roderick MacKinnon},
  journal={Nature},
  year={2001},
  volume={414},
  pages={43-48}
}
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 Å 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… 
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TLDR
A simple theoretical analysis of K+ and Na+ complexation with water in the context of simplified binding site models and bulk solution reveals that water molecules and carbonyl groups can both provide K+ selective environments if equivalent constraints are imposed on the coordination number of the complex.
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TLDR
It is concluded 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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TLDR
In this issue, Varma and Rempe provide a novel explanation for K+ and Na+ binding to clusters of water and of a few other ligands, and find that preferred solvation structures are sensitive to their environment, providing new insight into factors controlling selectivity.
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TLDR
The ability of the NaK filter to bind both Na+ and K+ ions seemingly arises from the ions' ability to use the existing environment in unique ways, rather than from any structural rearrangements of the filter itself.
The predominant role of coordination number in potassium channel selectivity.
TLDR
It is demonstrated that the number of carbonyl oxygen atoms that surround permeating ions is the most important factor in determining ion selectivity rather than the size of the pore or the strength of the coordinating dipoles.
Structural basis for ion permeation mechanism in pentameric ligand-gated ion channels
TLDR
Simulations and electrostatics calculations complemented the description of hydration in the pore and suggest that the water pentagons observed in the crystal are important for the ion to cross hydrophobic constriction barriers.
Ion selectivity in potassium channels.
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