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  • Cryo‐electron microscopy of...
    Kanai, Ryuta; Cornelius, Flemming; Vilsen, Bente; Toyoshima, Chikashi

    FEBS letters, October 2022, Volume: 596, Issue: 19
    Journal Article

    Na+,K+‐ATPase (NKA) is one of the most important members of the P‐type ion‐translocating ATPases and plays a pivotal role in establishing electrochemical gradients for Na+ and K+ across the cell membrane. Presented here is a 3.3 Å resolution structure of NKA in the E2·2K+ state solved by cryo‐electron microscopy. It is a stable state with two occluded K+ after transferring three Na+ into the extracellular medium and releasing inorganic phosphate bound to the cytoplasmic P domain. We describe how the extracellular ion pathway wide open in the E2P state becomes closed and locked in E2·2K+, linked to events at the phosphorylation site more than 50 Å away. We also show, although at low resolution, how ATP binding to NKA in E2·2K+ relaxes the gating machinery and thereby accelerates the transition into the next step, that is, the release of K+ into the cytoplasm, more than 100 times. Na+,K+‐ATPase establishes concentration gradients of Na+ and K+ across the plasma membrane. Cryo‐EM structures of Na+,K+‐ATPase in the E2·2K+ state and after addition of ATP explain how the release of inorganic phosphate locks the extracellular gate to occlude bound K+, and why the addition of ATP prompts the release of K+ into the cytoplasm.