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Abstract
The formation of a persulfide group (-SSH) on cysteine residues has gained attention as a reversible posttranslational modification contributing to protein regulation or protection. The widely distributed 3-mercaptopyruvate sulfurtransferases (MSTs) are implicated in the generation of persulfidated molecules and H2S biogenesis through transfer of a sulfane sulfur atom from a suitable donor to an acceptor. Arabidopsis has two MSTs, named STR1 and STR2, but they are poorly characterized. To learn more about these enzymes, we conducted a series of biochemical experiments including a variety of possible reducing systems. Our kinetic studies, which used a combination of sulfur donors and acceptors revealed that both MSTs use 3-mercaptopyruvate efficiently as a sulfur donor while thioredoxins, glutathione, and glutaredoxins all served as high-affinity sulfane sulfur acceptors. Using the redox-sensitive GFP (roGFP2) as a model acceptor protein, we showed that the persulfide-forming MSTs catalyze roGFP2 oxidation and more generally trans-persulfidation reactions. However, a preferential interaction with the thioredoxin system and glutathione was observed in case of competition between these sulfur acceptors. Moreover, we observed that MSTs are sensitive to overoxidation but are protected from an irreversible inactivation by their persulfide intermediate and subsequent reactivation by thioredoxins or glutathione. This work provides significant insights into Arabidopsis STR1 and STR2 catalytic properties and more specifically emphasizes the interaction with cellular reducing systems for the generation of H2S and glutathione persulfide and reactivation of an oxidatively modified form.
Highlights
An ever-growing body of evidence indicates that hydrogen sulfide (H2S) plays a role in cellular signaling as other gaseous molecules such as nitric oxide (NO) and carbon monoxide (CO)
Different sulfur-containing compounds were tested as substrates to examine which sulfur donor is preferentially used by STR1 and STR2 in vitro
The present biochemical study of Arabidopsis STR1 and STR2 indicates that both mercaptopyruvate sulfurtransferase (MST) use 3-MP as canonical substrate and are able to transfer the persulfide to various acceptors
Summary
An ever-growing body of evidence indicates that hydrogen sulfide (H2S) plays a role in cellular signaling as other gaseous molecules such as nitric oxide (NO) and carbon monoxide (CO). Signaling by H2S is proposed to occur via the posttranslational modification (PTM) of critical cysteine residues (RSH) to persulfides (RSSH), called persulfidation, resulting in a cysteine whose thiol group is covalently bound to sulfur (sulfane sulfur) [1] Oxidized thiol species such as sulfenic acids (RSOH), but not reduced thiols, are the direct targets of H2S reactivity [2,3,4]. Sulfide is primarily produced in chloroplasts through the action of sulfite reductase during the reductive assimilation of sulfate It is incorporated into the amino acid skeleton of O-acetylserine to form cysteine, the biosynthesis of which can occur in the cytosol, plastids, and mitochondria [9]. It is suggested that STR1 persulfide is transferred to GSH [28] In accordance with their catalytic mechanism, both Arabidopsis MSTs were isolated as persulfidated proteins from leaf extracts [13]. In addition to these functions, an interaction of both MSTs was observed with TRXs through bimolecular fluorescence complementation (BiFC), but no further investigation of the implication of these two systems in H2S biosynthesis and protein persulfidation has been performed [31]
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