Structures of LeuT and related transporters. Structures of LeuT in (A) an outward-open conformation (PDB accession no. 3TT1), (B) an outward-occluded state (PDB accession no. 2A65), (C) an inward-open conformation (PDB accession no. 3TT3), (D) vSGLT in an inward-open conformation (PDB accession no. 3DH4), (E) a repeat-swapped model of the inward-open conformation of LeuT (Forrest et al., 2008), and (F) SERT in an inward-open conformation (PDB accession no. 6DZZ). Bundle helices are in gold, scaffold in blue, loops in gray, and Na2 in violet. For clarity, only TM helices 1–10 are shown. Red mesh indicates the open permeation pathways.