Figure 4.

Representative examples illustrating the structural neighborhoods of sulfonic acids (OCS), highlighting hydrogen bond interactions (orange) with Thr side chains, as well as backbone amides and Arg side chains. Peroxidatic cysteine in the sulfonylated state is located at the N-terminus of an α helix (PDB entry 2NVL) (top left). In the remaining cases, the sulfonic acid is located on a loop: (top right) LecA (PDB entry 4CPB), (bottom left) LuxS (PDB entry 1IE0), and (bottom right) TdcF domain (PDB entry 2UYJ).