Structural architecture of the glutamate transporter homologues. (A) Extracellular view of the Glt_Tk homotrimer; cartoon representation. The scaffold and transport domains of one of the protomers are shown in yellow and blue, respectively. (B) Cross-section of the Glt_Tk trimer in the OFC (left) and Glt_Ph in the IFC (right); protein in surface representation, the position of membrane indicated with the black lines. (C) Substrate-binding site in Glt_Tk (residue numbering for Glt_Ph in parentheses). l-Aspartate (black) and amino acid residues involved in substrate coordination are shown as sticks and sodium ions as purple spheres. HP1 and HP2 are shown in cyan and green, respectively. (D and E) Cartoon representation of protomers in OFC (D) and IFC (E). Color scheme as in A and C. PDB codes 5E9S and 3KBC, respectively.