FIGURE 2.

Structure of T. thermophilus SoxB and the effect of binding the substrate analogue thiosulfate. A, cartoon representation of the overall structure of SoxB using the SoxB-glycerol coordinates. The N-terminal domain is shown in blue with the N-terminal loop subdomain in green. The interdomain helix is shown in yellow, the C-terminal domain is in red, and the manganese ions are in purple. The route of access to the active site is indicated with an arrow. B, a representation of the residues that are critical for the relative orientation of the substrate analogue thiosulfate and the reactive bridging hydroxide ion based on the SoxB-Mn²⁺-thiosulfate structure. The manganese ions are in purple, and the oxygen of the reactive bridging hydroxide is in red. Thiosulfate is shown in stick representation. The footprint of the thiosulfate S–S bond on the protein surface is green. Distances between selected atoms (indicated by dashed lines) are given. C, the two conformations of loop 465–476. The closed conformation observed when the active site is empty (SoxB-Mn²⁺ structure) is shown in yellow, and the open conformation adopted upon binding of the substrate analogue thiosulfate at the active site (SoxB-Mn²⁺-thiosulfate structure) is in red. The manganese ions are shown in purple, and the thiosulfate molecule present in the open conformation in a stick representation.