Acidity and nucleophilic reactivity of glutathione persulfide

Abstract

Persulfides (RSSH/RSS-) participate in sulfur trafficking and metabolic processes, and are proposed to mediate the signaling effects of H2S. Despite their growing relevance, their chemical properties are poorly understood. Herein, we studied experimentally and computationally the formation, acidity, and nucleophilicity of glutathione persulfide (GSSH/GSS-), the derivative of the abundant cellular thiol, glutathione (GSH). We characterized the kinetics and equilibrium of GSSH formation from glutathione disulfide and H2S. A pKa of 5.45 for GSSH was determined, which is 3.49 units below that of GSH. The reactions of GSSH with the physiologically-relevant electrophiles peroxynitrite and hydrogen peroxide, as well as with the probe monobromobimane, were studied and compared with those of thiols. These reactions occurred through SN2 mechanisms. At neutral pH, GSSH reacted faster than GSH due to increased availability of the anion and, depending on the electrophile, increased reactivity. In addition, GSS- presented higher nucleophilicity with respect to a thiolate with similar basicity. This can be interpreted in terms of the so-called alpha effect, i.e. the increased reactivity of a nucleophile when the atom adjacent to the nucleophilic atom has high electron density. The magnitude of the alpha effect correlated with the Brønsted nucleophilic factor, βnuc, for the reactions with thiolates and with the ability of the leaving group. Our study constitutes the first determination of the pKa of a biological persulfide and the first examination of the alpha effect in sulfur nucleophiles, and sheds light on the chemical basis of the biological properties of persulfides.

Functional asymmetry and chemical reactivity of CsoR family persulfide sensors

“…S3). Indeed, these data suggest that Cys31 in SaCstR has a pKa of ≈8.6, or similar to that of a free thiol, 8.5-9.0, [45][46] while Cys41 in SaCsoR is elevated to ≈9.3 or higher, consistent with its decreased reactivity over the entire pH range (Fig. S3).…”

Specificity of Human Sulfiredoxin for Reductant and Peroxiredoxin Oligomeric State

“…Thus, in the absence of an enzymatic system to reduce disulfide or thiosulfinate linked Srx-Prx dimers, the studies herein suggest the possibility of a preference for H 2 S to support the repair of mitochondrial hyperoxidized Prx3 by Srx, and of combined GSH and H 2 S for the repair of cytosolic Prx2. Importantly, future detailed studies will be required to investigate the concentration and time dependence of reductants in vitro, to tease apart the contributions of these reductants in cells, and to investigate the interplay between the GSH recycling system, the appropriate Trx/TrxR system, and the enzymes that produce H 2 S. Based on the recent study by Benchoam et al, glutathione hydropersulfide (GS-SH) should also be added to the list of potential reductants, as its acidity and nucleophilicity is much greater that GSH [65].…”

Biosynthesis, Quantification and Genetic Diseases of the Smallest Signaling Thiol Metabolite: Hydrogen Sulfide

“…As is the case with other gasotransmitters, H 2 S exerts its functions by binding to biomolecules in a transient way as well as in a stable fashion via modification of their thiol groups. H 2 S can exert antioxidant functions by induction of antioxidant pathways such as Keap1/Nrf2 that control glutathione biosynthesis [141][142][143], by persulfidation of cysteine residues in proteins [144][145][146], by acting on the mitochondrial respiratory chain to control ATP synthesis [147] and by direct reaction with metal centers [148], such as hemoglobin [116] and cytochrome c oxidase [47,149]. Direct reactions of H 2 S with reactive oxygen species also occur, but given the low concentrations of H 2 S in cells and tissues, this is unlikely to be a major contribution to overall antioxidant defense [150].…”