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J Biol Chem. 2017 Jul 28;292(30):12412-12423. doi: 10.1074/jbc.M117.779090. Epub 2017 Jun 6.

Molecular simulations and free-energy calculations suggest conformation-dependent anion binding to a cytoplasmic site as a mechanism for Na+/K+-ATPase ion selectivity.

Author information

1
From the Department of Chemistry and.
2
Institute for Computational Molecular Science, Temple University, Philadelphia, Pennsylvania 19122.
3
Science for Life Laboratory, Department of Theoretical Physics, KTH Royal Institute of Technology, Stockholm 11428, Sweden, and.
4
the Department of Pharmacology, Physiology and Neuroscience, New Jersey Medical School, Rutgers University, Newark, New Jersey 07103.
5
From the Department of Chemistry and vincenzo.carnevale@temple.edu.
6
From the Department of Chemistry and voelz@temple.edu.

Abstract

Na+/K+-ATPase transports Na+ and K+ ions across the cell membrane via an ion-binding site becoming alternatively accessible to the intra- and extracellular milieu by conformational transitions that confer marked changes in ion-binding stoichiometry and selectivity. To probe the mechanism of these changes, we used molecular simulation and free-energy perturbation approaches to identify probable protonation states of Na+- and K+-coordinating residues in E1P and E2P conformations of Na+/K+-ATPase. Analysis of these simulations revealed a molecular mechanism responsible for the change in protonation state: the conformation-dependent binding of an anion (a chloride ion in our simulations) to a previously unrecognized cytoplasmic site in the loop between transmembrane helices 8 and 9, which influences the electrostatic potential of the crucial Na+-coordinating residue Asp926 This mechanistic model is consistent with experimental observations and provides a molecular-level picture of how E1P to E2P enzyme conformational transitions are coupled to changes in ion-binding stoichiometry and selectivity.

KEYWORDS:

Na+/K+-ATPase; anion binding site; free energy perturbation; membrane transport; membrane transporter; molecular dynamics; potassium transport; protonation; selectivity; sodium transport

PMID:
28588025
PMCID:
PMC5535017
DOI:
10.1074/jbc.M117.779090
[Indexed for MEDLINE]
Free PMC Article

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