Mechanism of potassium ion uptake by the Na(+)/K(+)-ATPase

By Juan P. Castillo, Huan Rui, Daniel Basilio, Avisek Das, Benoît Roux, Ramon Latorre, Francisco Bezanilla, and Miguel Holmgren.

Published in Nat Commun. 2015 Jul 24;6:7622.
PMID: 26205423. PMCID: PMC4515779. Link to Pubmed page.

Project: Conformational Transitions in P-class ATPases

Figure 5. Extracellular occlusion–deocclusion of the Na⁺/K⁺-ATPase in the presence of bound K⁺.

Abstract

The Na⁺/K⁺-ATPase restores sodium (Na⁺) and potassium (K⁺) electrochemical gradients dissipated by action potentials and ion-coupled transport processes. As ions are transported, they become transiently trapped between intracellular and extracellular gates. Once the external gate opens, three Na⁺ ions are released, followed by the binding and occlusion of two K⁺ ions. While the mechanisms of Na⁺ release have been well characterized by the study of transient Na⁺ currents, smaller and faster transient currents mediated by external K⁺ have been more difficult to study. Here we show that external K⁺ ions travelling to their binding sites sense only a small fraction of the electric field as they rapidly and simultaneously become occluded. Consistent with these results, molecular dynamics simulations of a pump model show a wide water-filled access channel connecting the binding site to the external solution. These results suggest a mechanism of K⁺ gating different from that of Na⁺ occlusion.