Crystal structure of the high-affinity Na+,K+-ATPase–ouabain complex with Mg2+ bound in the cation binding site

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The Na+,K+-ATPase maintains electrochemical gradients for Na+ and K+ that are critical for animal cells. Cardiotonic steroids (CTSs), widely used in the clinic and recently assigned a role as endogenous regulators of intracellular processes, are highly specific inhibitors of the Na+,K+-ATPase. Here we describe a crystal structure of the phosphorylated pig kidney Na+,K+-ATPase in complex with the CTS representative ouabain, extending to 3.4 Å resolution. The structure provides key details on CTS binding, revealing an extensive hydrogen bonding network formed by the β-surface of the steroid core of ouabain and the side chains of αM1, αM2, and αM6. Furthermore, the structure reveals that cation transport site II is occupied by Mg2+, and crystallographic studies indicate that Rb+ and Mn2+, but not Na+, bind to this site. Comparison with the low-affinity [K2]E2–MgFx–ouabain structure [Ogawa et al. (2009) Proc Natl Acad Sci USA 106(33):13742–13747) shows that the CTS binding pocket of [Mg]E2P allows deep ouabain binding with possible long-range interactions between its polarized five-membered lactone ring and the Mg2+. K+ binding at the same site unwinds a turn of αM4, dragging residues Ile318–Val325 toward the cation site and thereby hindering deep ouabain binding. Thus, the structural data establish a basis for the interpretation of the biochemical evidence pointing at direct K+–Mg2+ competition and explain the well-known antagonistic effect of K+ on CTS binding.
Original languageEnglish
JournalProceedings of the National Academy of Sciences of the United States of America
Volume110
Issue27
Pages (from-to)10958–10963
Number of pages6
ISSN0027-8424
DOIs
Publication statusPublished - Jul 2013
EventInternational Plant & Animal Genome XXI (PAG XXI) - San Diego, CA, United States
Duration: 12 Jan 201316 Jan 2013

Conference

ConferenceInternational Plant & Animal Genome XXI (PAG XXI)
CountryUnited States
CitySan Diego, CA
Period12/01/201316/01/2013

    Research areas

  • membrane proteins, crystallography, cardiac glycosides, phosphoenzyme

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