Fig. 5

Refined transport cycle of AdiC showing different conformational states and gating residue movements during substrate translocation. In the outward-open, substrate-free state (state a, observed), the gating residue W202 (in red) is mobile, whereas the mobility of the buried gating residue W293 (in green) is restrained. In the inward-open, substrate-free state (state g, hypothetical), the features of the gating residues are inverted, i.e., W293 mobile and W202 restrained mobility. For states a and g, AdiC monomer models are displayed as gray volume with vertical cut through the structure. The membrane region is displayed as gray bar and the sidedness indicated. Gating residues W202 and W293 are shown as red and green sticks, respectively. For states b to f, AdiC monomers are displayed in blue, and gating residues W202 and W293 are shown as red and green bars. The substrates L-arginine and agmatine are colored in orange and yellow, respectively. AdiC conformational states are outward-open, substrate-free (a); outward-open, substrate-bound (b); outward-facing, substrate occluded (c); substrate-bound, fully occluded (d); inward-facing, substrate occluded (e); inward-open, substrate-bound (f); and inward-open, substrate-free (g)