The selectivity of the Na+/K+-pump is controlled by binding site protonation and self-correcting occlusion
Abstract
The Na+/K+-pump maintains the physiological K+ and Na+ electrochemical gradients across the cell membrane. It operates via an 'alternating-access' mechanism, making iterative transitions between inward-facing (E1) and outward-facing (E2) conformations. Although the general features of the transport cycle are known, the detailed physicochemical factors governing the binding site selectivity remain mysterious. Free energy molecular dynamics simulations show that the ion binding sites switch their binding specificity in E1 and E2. This is accompanied by small structural arrangements and changes in protonation states of the coordinating residues. Additional computations on structural models of the intermediate states along the conformational transition pathway reveal that the free energy barrier toward the occlusion step is considerably increased when the wrong type of ion is loaded into the binding pocket, prohibiting the pump cycle from proceeding forward. This self-correcting mechanism strengthens the overall transport selectivity and protects the stoichiometry of the pump cycle.
Article and author information
Author details
Funding
National Institutes of Health (U54-GM087519)
- Benoît Roux
National Science Foundation (MCB-1515434)
- Pablo Artigas
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Reviewing Editor
- Nir Ben-Tal, Tel Aviv University, Israel
Version history
- Received: April 2, 2016
- Accepted: August 3, 2016
- Accepted Manuscript published: August 4, 2016 (version 1)
- Version of Record published: September 16, 2016 (version 2)
Copyright
© 2016, Rui et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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