title: Biosynthesis of a central intermediate in hydrogen sulfide metabolism by a novel human sulfurtransferase and its yeast ortholog.
abstract: Human sulfide:quinone oxidoreductase (SQOR) catalyzes the conversion of H2S to thiosulfate, the first step in mammalian H2S metabolism. SQOR's inability to produce the glutathione persulfide (GSS(-)) substrate for sulfur dioxygenase (SDO) suggested that a thiosulfate:glutathione sulfurtransferase (TST) was required to provide the missing link between the SQOR and SDO reactions. Although TST could be purified from yeast, attempts to isolate the mammalian enzyme were not successful. We used bioinformatic approaches to identify genes likely to encode human TST (TSTD1) and its yeast ortholog (RDL1). Recombinant TSTD1 and RDL1 catalyze a predicted thiosulfate-dependent conversion of glutathione to GSS(-). Both enzymes contain a rhodanese homology domain and a single catalytically essential cysteine, which is converted to cysteine persulfide upon reaction with thiosulfate. GSS(-) is a potent inhibitor of TSTD1 and RDL1, as judged by initial rate accelerations and ≥25-fold lower Km values for glutathione observed in the presence of SDO. The combined action of GSS(-) and SDO is likely to regulate the biosynthesis of the reactive metabolite. SDO drives to completion p-toluenethiosulfonate:glutathione sulfurtransferase reactions catalyzed by TSTD1 and RDL1. The thermodynamic coupling of the irreversible SDO and reversible TST reactions provides a model for the physiologically relevant reaction with thiosulfate as the sulfane donor. The discovery of bacterial Rosetta Stone proteins that comprise fusions of SDO and TSTD1 provides phylogenetic evidence of the association of these enzymes. The presence of adjacent bacterial genes encoding SDO-TSTD1 fusion proteins and human-like SQORs suggests these prokaryotes and mammals exhibit strikingly similar pathways for H2S metabolism.
authors: Department of Biochemistry and Molecular Biology, Drexel University College of Medicine , Philadelphia, Pennsylvania 19102, United States.
authors: Scott L
authors: SL
authors: Melideo
authors: Michael R
authors: MR
authors: Jackson
authors: Marilyn Schuman
authors: MS
authors: Jorns
mesh_terms: D006801:Humans; D006862:Hydrogen Sulfide / Q000737:chemistry* / Q000378:metabolism; D009363:Neoplasm Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D040681:Structural Homology, Protein
chemical_list: D009363:Neoplasm Proteins; D029701:Saccharomyces cerevisiae Proteins; C481306:TSTD1 protein, human; D006862:Hydrogen Sulfide