Extended Data Fig. 4: The intracellular gate in the two STP10 structures.

a) View of the STP10 outward occluded structure perpendicular to the membrane with the three key interdomain salt bridge networks highlighted in colored squares. In particular constituted by the double salt bridge from D344(M8) to the main chain nitrogen of Gly170(M5) and Ala171(M5) (network 1) and the double salt bridge from Glu162 (M4) to Arg422(M11), Thr226 (IC1) and R111(M3) (network 2) as well as and from Arg169(M5) to E415 (M10), the main chain carbonyls of Thr477 (IC5) and Val480 (IC5) (network 3). These regions are perfectly conserved in all STPs and in several bacterial symporters, and have also been observed in human sugar facilitators. b) Close-up view of the N ___domain and C ___domain at the cytosolic side in the STP10 inward open structure. In the inward open conformation, interactions between the ICH ___domain and the transmembrane N and C domains are maintained. Interactions between ICH and the two transmembrane ___domain residues are highlighted by yellow dashes. The mutant residues Q162 and N344 that broke the stabilizing networks are highlighted in red. The positions of the SP motifs are highlighted (dotted eclipses).