Figure 5
From: Structural insights into the elevator-like mechanism of the sodium/citrate symporter CitS
Alternating access mechanism of the KpCitS. (a) In the outward-facing conformation, the transport pathway is blocked by I121, L408 and M417. In the inward-facing conformation, these residues move and citrate is released to the cytoplasm. The citrate is shown in orange and red. The release of citrate in the inward-facing conformation is marked by a black arrow. (b) Role of the polar residues in the alternating access mechanism. In the inward-facing conformation, D112, E195, R205 and Y348 form a salt bridge network at the membrane/periplasm interface, by virtue of which the substrate transport pathway is open only towards the cytoplasm. The view is rotated by 30 degrees along the vertical axis from that of (a).
