Fig. 2

a The crystal structure of the vcCNT homotrimer (PDB id: 3TIJ) shown in the extracellular, membrane and intracellular view, respectively. b A homology model of the hCNT3 homotrimer superposed on the crystal structure of vcCNT (grey) shown in the extracellular, membrane and intracellular view, respectively. c A homology model of the hCNT3 homotrimer superposed on the low-energy structure obtained from the 1956 frame out of all 5000 frames of the 100 ns MD simulation, shown in the extracellular, membrane and intracellular view, respectively. d The binding site of the uridine molecule (shown in green) and the sodium ion (shown as a violet sphere) located inside the crystal structure of vcCNT. The polar contacts between uridine and the transporter were depicted with yellow dashed lines. The indicated Gln154 in vcCNT corresponds to Gln251 in the model of hCNT3. e The sequence alignment of the template sequence (vcCNT) and the target sequence (hCNT3). Transmembrane helices (TMHs) are shown in red, extracellular and short helices (EH) in green, amphipathic helices (IH) are shown in blue and finally helices outside the lipid bilayer (HP) are shown in grey