Quaternary structure of NKA–FXYD complex and their interaction. (A) Lateral view of the NKA crystal structure in the E1 conformation positioning FXYD2 (γ-subunit) in the structure. (B) View of the NKA TM domain from the extracellular side. Essential subunits α (gray) and β (pink) are associated with FXYD2 (green), which interacts with the α subunit M9 (red). Three bound Na⁺ ions are blue, M9 is red, M8 is cyan, and M2 is orange. (C) Surface representation of α (gray), β (pink), and FXYD2 (green) complex. (D) Enlarged contacts between NKA subunits and FXYD2 regulator. Structures are made with PyMOL using the NKA structure (PBD accession no. 3WGU).