Fig. 6: Cryo-EM structure of NKA-like SPWC-ngHKA.

a, b EM potential maps (colored surfaces indicate higher contour level, while transparent surfaces indicate lower levels with micelle and cytoplasmic domains visible) and cartoon models of the SPWC-ngHKA mutant in the presence of 300 mM Na⁺ and 5 mM AMPPCP to induce the 3Na⁺·E1-ATP state (a), and with 100 mM KCl and 1 mM AlF₄⁻ to lock the pump in the E2-P_i state (b). The β-subunit is shown in gray and the α-subunit in pink, for E1, and purple, for E2. Bound ions are shown as orange (Na⁺) or purple (K⁺) spheres. See Fig. 7 for comparison with NKA structures. c Cytoplasmic view of the ion-binding sites region in E1-ATP showing the densities likely representing the three bound Na⁺ (orange spheres) and several waters (red spheres, w1-4). d Cytoplasmic view of the cation-binding sites in the (2 K⁺)E2-P_i state with two occluded K⁺ ions (purple spheres). e Overall structure of SPWC mutant in 3Na⁺·E1-ATP state in ribbon representations, and close-up view around its cation-binding site. The four point mutations (cyan) and other amino acids involved in Na⁺ coordination are displayed as sticks. Bound AMPPCP and the three Na⁺ ions (site I, II, and III) are shown as spheres.