Fig. 2: Na⁺ binding sites in different E1 states.

a Cross-section through the Na⁺ entry pathway in the E1·3Na·ATP state. Surface representation of the hNKA α1 subunit is coloured by vacuum electrostatics. Na⁺ are coloured yellow. b, c are the transmembrane Na⁺ binding sites in the E1·3Na and E1·3Na·ATP states, with Na⁺ (labelled I, II and III) shown in cyan and yellow, respectively. The EM density around gate residue Glu334 are shown in grey mesh. The key residues coordinated with Na⁺ within 4 Å are shown in sticks and indicated by dashed lines. The water molecules are shown as red balls. The yellow and blue triangles represent Tyr778 and Thr779 above the pictured field of view, respectively. d Binding mode comparison of Na⁺ between the E1·3Na (dark green) and E1·3Na·ATP (spectrum from blue to magenta) states. e Binding mode comparison of Na⁺ between the E1·3Na·ATP (spectrum from blue to magenta) and E1~P·[3Na]·ADP (grey) states. The gating residue Glu334 in human (Glu327 in pig) is coloured purple (E1·3Na), orange (E1·3Na·ATP), and slate (E1~P·[3Na]·ADP), respectively. Na⁺ in E1~P·[3Na]·ADP are coloured deep teal. The structures in (d) and (e) are superimposed using M7–M10.