Middleton, David Andrew and Fedosova, Natalya U. and Esmann, Mikael (2015) Long-range effects of Na+ binding in Na,K-ATPase reported by ATP. Biochemistry, 54 (47). pp. 7041-7047. ISSN 0006-2960
acs.biochem.5b00893.pdf - Accepted Version
Available under License Creative Commons Attribution.
Download (2MB)
Abstract
This paper addresses the question of long-range interactions between the intramembranous cation binding sites and the cytoplasmic nucleotide binding site of the ubiquitous ion-transporting Na,K-ATPase using 13C cross-polarization magic-angle spinning (CP-MAS) solid-state NMR. High affinity ATP binding is induced by the presence of Na+ as well as of Na-like substances such as Tris+, and these ions are equally efficient promoters of nucleotide binding. CP-MAS analysis of bound ATP with Na,K-ATPase purified from pig kidney membranes reveals subtle differences in the nucleotide interactions within the nucleotide site depending on whether Na+ or Tris+ are used to induce binding. Differences in chemical shifts for ATP carbon atoms C1´ and C5´ observed in the presence of Na+ or Tris+ suggest alterations in the residues surrounding the bound nucleotide, hydrogen bonding and/or conformation of the ribose ring. This is taken as evidence for a long-distance communication between the Na+-filled ion sites in the membrane interior and the nucleotide binding site in the cytoplasmic domain and reflects the first conformational change ultimately leading to phosphorylation of the enzyme. Stopped-flow fluorescence measurements with the nucleotide analog eosin show that the dissociation rate constant for eosin is larger in Tris+ than in Na+, giving kinetic evidence for the difference in structural effects of Na+ and Tris+. According to the recent crystal structure of the E1•AlF4 -•ADP•3Na+-form the coupling between the ion binding sites and the nucleotide side is mediated by - among others - the M5-helix.