Fig. 5.

Transport cycle. To shuttle ions between the inward-open (left) and outward-open conformations (right), the six-helix-bundle transporter domain (blue) translates along z, normal to the membrane, and rotates relative to the core domain (gray) around an axis in the membrane plane. Although the scheme shows the inward transport of Na⁺ (yellow), and the outward transport of H⁺ (green), both carried by Asp159, the transport cycle is fully reversible, and its direction determined by the respective gradients of H⁺ and Na⁺ across the membrane. Coupled to the domain motion, closing of the hydrophobic gate (magenta) prevents ion leakage