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Ion permeation through the Na+,K+-ATPase

Nature volume 443, pages 470–474 (2006)Cite this article

Abstract

P-type ATPase pumps generate concentration gradients of cations across membranes in nearly all cells. They provide a polar transmembrane pathway, to which access is strictly controlled by coupled gates that are constrained to open alternately, thereby enabling thermodynamically uphill ion transport (for example, see ref. 1). Here we examine the ion pathway through the Na+,K+-ATPase, a representative P-type pump, after uncoupling its extra- and intracellular gates with the marine toxin palytoxin2. We use small hydrophilic thiol-specific reagents3 as extracellular probes and we monitor their reactions, and the consequences, with cysteine residues introduced along the anticipated cation pathway through the pump. The distinct effects of differently charged reagents indicate that a wide outer vestibule penetrates deep into the Na+,K+-ATPase, where the pathway narrows and leads to a charge-selectivity filter. Acidic residues in this region, which are conserved to coordinate pumped ions, allow the approach of cations but exclude anions. Reversing the charge at just one of those positions converts the pathway from cation selective to anion selective. Close structural homology among the catalytic subunits of Ca2+-, Na+,K+- and H+,K+-ATPases4,5,6 argues that their extracytosolic cation exchange pathways all share these physical characteristics.

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Figure 1: Homology model of the Na + ,K + -ATPase transmembrane domain.
Figure 2: Effects of MTSET + and MTSES - on E321C, G805C, T806C and G337C mutants.
Figure 3: Analysis of MTS-reagent action on G805C and T806C mutants.
Figure 4: Charge selectivity in palytoxin-bound pump–channels.

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Acknowledgements

We thank P. Artigas for advice and discussion; M. Mense and P. Vergani for discussion; and R.F. Rakowski for cDNAs encoding the Xenopus α1 and β Na+,K+-ATPase subunits. This work was supported by a grant from the NIH (to D.C.G.).

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  1. Laboratory of Cardiac/Membrane Physiology, The Rockefeller University, New York, New York, 10021, USA

    Nicolás Reyes & David C. Gadsby

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  1. Nicolás Reyes
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Correspondence to David C. Gadsby.

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Supplementary information

Supplementary Figures

Supplementary Figures 1 and 3 provide stereo views of Figs. 1b and 4b, respectively. Supplementary Figure 2 shows accessibility of differently charged MTS reagents in mutant V807C. Supplementary Figure 4 illustrates likely arrangements of ion-coordinating residues in different functional states of the Na+,K+-ATPase. (PDF 456 kb)

Supplementary Methods

Supplementary methodological details of our experimental approach are appended (PDF 75 kb)

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Reyes, N., Gadsby, D. Ion permeation through the Na+,K+-ATPase. Nature 443, 470–474 (2006). https://doi.org/10.1038/nature05129

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