Figure 6.

Left: core domain, viewed from the gate/dimerization domain, showing the relationship between the probable substrate binding pocket (gray circle between the helical portions of TM3 and TM10) and covalently bound 4,4′-diisothiocyanatodihydrostilbene-2,2′-disulfonate (H₂DIDS) (black sticks). The side chains of R730 and E681 are on either side of the substrate pocket. One of the H₂DIDS sulfonate groups is near the side chain of R730. The positions of other polar side chains (S465, S725, T727, and T728) are indicated. The 3 links between core and gate domains (portion of TM7-TM8 loop and surface helices H2 and H3) are viewed end-on. Right: same structure, rotated to show the view from the extracellular medium. The only gate domain amino acid residues shown are those covalently bound to H₂DIDS. The helical portion of TM10 is behind TM1 in this view. H₂DIDS is between core and gate, near but not in the substrate binding pocket.