Biosynthesis and Reactivity of Cysteine Persulfides in Signaling

Abstract

Hydrogen sulfide (H2S) elicits pleiotropic physiological effects ranging from modulation of cardiovascular to CNS functions. A dominant method for transmission of sulfide-based signals is via posttranslational modification of reactive cysteine thiols to persulfides. However, the source of the persulfide donor and whether its relationship to H2S is as a product or precursor is controversial. The transsulfuration pathway enzymes can synthesize cysteine persulfide (Cys−SSH) from cystine and H2S from cysteine and/or homocysteine. Recently, Cys−SSH was proposed as the primary product of the transsulfuration pathway with H2S representing a decomposition product of Cys−SSH. Our detailed kinetic analyses demonstrate a robust capacity for Cys−SSH production by the human transsulfuration pathway enzymes, cystathionine beta-synthase and γ-cystathionase (CSE) and for homocysteine persulfide synthesis from homocystine by CSE only. However, in the reducing cytoplasmic milieu where the concentration of reduced thiols is significantly higher than of disulfides, substrate level regulation favors the synthesis of H2S over persulfides. Mathematical modeling at physiologically relevant hepatic substrate concentrations predicts that H2S rather than Cys−SSH is the primary product of the transsulfuration enzymes with CSE being the dominant producer. The half-life of the metastable Cys−SSH product is short and decomposition leads to a mixture of polysulfides (Cys−S−(S)n−S−Cys). These in vitro data, together with the intrinsic reactivity of Cys−SSH for cysteinyl versus sulfur transfer, are consistent with the absence of an observable increase in protein persulfidation in cells in response to exogenous cystine and evidence for the formation of polysulfides under these conditions.

A distal ligand mutes the interaction of hydrogen sulfide with human neuroglobin

“…6) and displays a low-spin ferric signal with g ϭ 3.09, 2.17, and 1.48, which is in good agreement with published data (37). The presence of a high-spin signal (g ϭ 6.0 and 1.99) could be due to the presence of a small population of Fe III -Ngb with a disulfide bridge between Cys 46 and Cys 55 , which promotes His 64 dissociation from the iron (38). In the presence of sulfide, a rhombic EPR signal was seen within 5 min with g ϭ 2.48, 2.21, and 1.85 (Fig.…”

“…Spectroscopic studies have revealed the presence of heme orientational isomers and complex kinetics for binding exogenous ligands, which is slowed by displacement of the endogenous distal heme ligand, His 64 (6,12,40,41,49). The oxidation state of a pair of cysteine residues (Cys 46 and Cys 55 in the human sequence), modulates the O 2 affinity of neuroglobin, decreasing it ϳ10-fold when the cysteines are reduced (38).…”

“…The transsulfuration pathway enzymes generate cysteine persulfide (Cys-SSH) from cystine (46), which is more reactive than H 2 S and might play a role in sulfide signaling. To test its reactivity toward neuroglobin, Cys-SSH was generated in situ by reaction of ␥-cystathionase with cystine (46).…”

“…To test its reactivity toward neuroglobin, Cys-SSH was generated in situ by reaction of ␥-cystathionase with cystine (46). Under aerobic conditions, a small decrease in the 412 nm Soret absorption was seen, which was accompanied by small increases at 538 and 575 nm (Fig.…”

Sulfide-responsive transcriptional repressor SqrR functions as a master regulator of sulfide-dependent photosynthesis

“…Despite an appreciation of sulfide signaling, the mechanisms of how H 2 S functions as a signaling molecule remain under investigation (12). Emerging evidence suggests that highly oxidized sulfur species, termed reactive sulfur species (RSS), are the actual sulfide-signaling species (13)(14)(15)(16). These include HS•, cysteine sulfenic acids, cysteine persulfides, glutathione persulfides (GSSHs), and inorganic polysulfide species, which catalyze persulfidation of specific proteins and enzymes (13,(17)(18)(19)(20), although the functional impact of this protein modification is as yet not generally clear (17).…”