Self-S-sulfonation in a bacterial persulfide dioxygenase mediates thiol persulfide detoxification

A ubiquitous class of non-heme Fe(II) enzymes, the persulfide dioxygenases (PDOs), provide protection against hydrogen sulfide (H₂S) poisoning. The PDO in humans is a single-domain enzyme, while bacterial PDOs, such as CstB of Staphylococcus aureus, are often fused to a sulfurtransferase (rhodanese) module. Canonical PDOs cleave the S-S bond of glutathione persulfide (GSSH) to produce GSH and sulfite (SO₃ ^2-). In contrast, CstB, via an unknown mechanism, converts two RSSH to thiosulfate (S₂O₃ ^2-) without the release of sulfite. Six crystallographic structures of S. aureus CstB reveal that a Cys-Gly sequence (C201-G202) in a CstB-unique dynamic loop functions as a glutathione mimic, occupying one face of the hemifacial octahedral Fe(II) coordination site. We establish that CstB self-S-sulfonates C201 in a thiol persulfide, Fe(II) and O₂-dependent manner, which is then shuttled to a persulfidated C408 in the rhodanese domain ≈27 Å away via electrostatic steering to generate thiosulfate as the sole oxidation product. Both C201A and C408A CstBs are inactive in O₂-consumption. Self-S-sulfonation ensures rapid clearance of diverse reactive sulfur species under conditions where these species accumulate, permitting S. aureus to harness their cytoprotective effects while avoiding cellular toxicity.