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Article

Cation Binding in Na,K-ATPase, Investigated by ²⁰⁵Tl Solid-State NMR Spectroscopy^†

Louise Odgaard Jakobsen,^‡ Anders Malmendal,^§ Niels Chr. Nielsen,^§ and Mikael Esmann*^‡

Department of Biophysics, Institute of Physiology and Biophysics, University of Aarhus, DK-8000 Aarhus, Denmark, and Center for Insoluble Protein Structures (inSPIN), Interdisciplinary Nanoscience Center (iNANO) and Department of Chemistry, University of Aarhus, DK-8000 Aarhus, Denmark

Biochemistry, 2006, 45 (35), pp 10768–10776

DOI: 10.1021/bi060642k

Publication Date (Web): August 9, 2006

†

This work was supported by the Danish Medical Research Council, the Danish National Research Foundation, the Danish Natural Science Research Council (SNF), the Danish Biotechnological Instrument Centre (DABIC), Aarhus University Research Foundation, and Carlsbergfondet.

‡

Department of Biophysics.

Center for Insoluble Protein Structures (inSPIN).

Corresponding author. Tel: +45 8942 2930. Fax: +45 8612 9599. E-mail: me@biophys.au.dk.

Abstract

Cation binding to Na,K-ATPase is characterized in native membranes at room temperature by solid-state NMR spectroscopy using the K⁺ congener ²⁰⁵Tl. It has been demonstrated that the signals from occluded Tl⁺ and nonspecifically bound Tl⁺ can be detected and distinguished by NMR. Effects of dipole−dipole coupling between ¹H and ²⁰⁵Tl in the occlusion sites show that the ions are rigidly bound, rather than just occluded. Furthermore, a low chemical shift suggests occlusion site geometries with a relatively small contribution from carboxylate and hydroxyl groups. Nonspecific binding of Tl⁺ is characterized by rapid chemical exchange, in agreement with the observed low binding affinity.

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