Structure and sequence alignment of FXYD. Top: An overview of the tripartite Na,K ATPase with FXYD (cyan), α (gray), β (blue), and three sodium ions (red) in the middle of the transmembrane domain. The conserved residues of the PFXYD motif are shown as red sticks. The extracellular side is on the top and the intracellular side is on the bottom. In the inset, the transmembrane part of the pump is highlighted, and the pump is turned to position FXYD centrally. Lipid molecules identified in the structure are shown with spheres (pale cyan). PDB accession no. 3WGU. Bottom: An alignment of the transmembrane domains and C termini of seven human FXYDs. The conserved residues of the PFXYD motif are shown on red background. The FXYD2 residues resolved in the crystal structure are cyan. Basic residues in the C termini are purple.