Figure 3
From: Structural insights into the elevator-like mechanism of the sodium/citrate symporter CitS
The substrate binding site of KpCitS. (a) The helical hairpins, HP1 and HP2, of the transport domain in the citrate-bound outward-facing (left), citrate-bound inward-facing (middle), and citrate-free inward-facing44 states are represented in purple. Citrate is represented by an orange ball-and-stick model, sodium ions (Na1) by black spheres, and water (W) by a yellow sphere. The simulated annealing omit maps superimposed on the refined citrate, sodium ion and water were contoured at the 3σ levels. (b) Close-up view of the substrate binding site in the citrate-bound outward-facing (left), citrate-bound inward-facing (middle), and citrate-free inward-facing44 conformations. The hydrogen bonds and ionic interactions are shown by dashed lines.
