Surface renditions of LacY G46W/G262W (PDBid 4OAA). (a) View from the periplasmic side showing the double-Trp mutant—G46W/G262W (cyan sphere model). The TDG molecule is just visible within the protein (sphere model: green: carbon, red: oxygen, and yellow: sulfur). (b) Slab view of the structure seen parallel to the membrane. (c) View from the cytoplasmic side, with the residues that form a zipper-like motif to seal that side portrayed as yellow sphere model (yellow: carbon, red; oxygen, and blue: nitrogen).