Fig. 1.

Putative Na⁺ ion-binding sites in glutamate transporters. (A) Model with three Na⁺ sites (Na1-Na2-Na3) suggested by the GCMC simulations. Residues are numbered as in EAAT3. Shown are two views of the C-terminal half of one subunit, rotated 90°. HP1, yellow; HP2, green; TM7, purple; TM8, blue; Na⁺, yellow balls. (B) The Na⁺ ion at Na3 interacts with the side chains of T370 and N451 and with the backbone oxygen of A409 (corresponding to T314, N401, and A353 in GltPh) and is in direct contact with the bound substrate. More details are given in SI Appendix, Fig. S3 and S4 and Tables S1–S3.