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

作者：Razavi Asghar M; Delemotte Lucie; Berlin Joshua R; Carnevale Vincenzo^*; Voelz Vincent A^*

来源：JOURNAL OF BIOLOGICAL CHEMISTRY, 2017, 292(30): 12412-12423.

DOI：10.1074/jbc.M117.779090

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

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 Asp(926). 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.

• 出版日期2017-7-28
• 单位rutgers