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The selectivity of K+ ion channels: testing the hypotheses
Philip W Fowler1, Kaihsu Tai, Mark S P Sansom
1Department of Biochemistry, University of Oxford, Oxford, United Kingdom.
Biophysical Journal
|September 16, 2008
Summary
Molecular dynamics simulations reveal how ion channels distinguish between potassium (K+) and sodium (Na+) ions. The over-coordination hypothesis best explains K+ channel selectivity, while the snug-fit hypothesis is refuted.
Area of Science:
- Biophysics
- Structural Biology
- Computational Biology
Background:
- Understanding ion channel selectivity is crucial for cellular function.
- The structural basis for potassium (K+) channel selectivity remains incompletely understood.
- The NaK channel, conducting both Na+ and K+ ions, provides a model for studying selectivity.
Purpose of the Study:
- To test hypotheses explaining K+ ion channel selectivity.
- To compare the K+ selective channel KcsA and the NaK channel using molecular dynamics simulations.
- To investigate the structural basis of ion permeation and selectivity.
Main Methods:
- Classical molecular dynamics simulations.
- Simulations of KcsA and NaK ion channels embedded in lipid bilayers.
- Comparison of simulation results with snug-fit, field-strength, and over-coordination hypotheses.
Main Results:
- Simulation results contradict the strong snug-fit hypothesis for K+ channel selectivity.
- Results support the over-coordination hypothesis.
- In NaK simulations, K+ ions and water molecules adopt a new conformation, narrowing the selectivity filter and allowing ion binding at site S2.
Conclusions:
- The over-coordination hypothesis provides a viable explanation for K+ channel selectivity.
- The snug-fit hypothesis, in its strong form, is inconsistent with simulation data.
- Observed conformational changes in the NaK channel suggest a dynamic mechanism for ion selectivity at physiological temperatures.
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