Sulfurtransferases, including mercaptopyruvate sulfurtransferase and rhodanese, are widely distributed in living organisms. Mercaptopyruvate sulfurtransferase and rhodanese catalyze the transfer of sulfur from mercaptopyruvate and thiosulfate, respectively, to sulfur acceptors such as thiols or cyanide. There is evidence to suggest that rhodanese can mobilize sulfur from thiosulfate for in vitro formation of iron-sulfur clusters. Additionally, primary sequence analysis reveals that MoeB from some organisms, as well as ThiI of Escherichia coli, contain a C-terminal sulfurtransferase domain. MoeB is required for molybdopterin biosynthesis, whereas ThiI is necessary for biosynthesis of thiamin and 4-thiouridine in transfer ribonucleic acid. These observations led to the hypothesis that sulfurtransferases might be involved in sulfur transfer for biosynthesis of some sulfur-containing cofactors (e.g., biotin, lipoic acid, thiamin and molybdopterin). Results of a BLAST search revealed that E. coli has at least eight potential sulfurtransferases, besides ThiI. Previously, a glpE-encoded rhodanese of E. coli was characterized in our laboratory. In this dissertation, a mercaptopyruvate sulfurtransferase and corresponding gene (sseA) of E. coli were identified. In addition, the possibility that mercaptopyruvate sulfurtransferase could participate or work in concert with a cysteine desulfurase, IscS, in the biosynthesis of cofactors was examined. Cloning of the sseA gene and biochemical characterization of the corresponding protein were used to show that SseA is a mercaptopyruvate sulfurtransferase of E. coli. A strain with a chromosomal insertion mutation in sseA was constructed in order to characterize the physiological function of mercaptopyruvate sulfurtransferase. However, the lack of SseA did not result in a discernable phenotypic change. Redundancy of sulfurtransferases in E. coli may prevent the appearance of a phenotypic change due to the loss of a single sulfurtransferase. Subsequently, other paralogous genes for putative sulfurtransferases, including ynjE and yceA, were cloned. Strains with individual deletions of the chromosomal ynjE and yceA genes were also constructed. Finally, strains with multiple deficiency in potential sulfurtransferase genes, including sseA, ynjE and glpE, as well as iscS, were created. However, no phenotype associated with combinations of sseA, glpE and/or ynjE deficiency was identified. Therefore, the physiological functions of mercaptopyruvate sulfurtransferase and related sulfurtransferases remain unknown. / Ph. D.

PspE, encoded by the last gene of the phage shock protein operon, is one of the nine proteins of Escherichia coli that contain a rhodanese homology domain. PspE is synthesized as a precursor with a 19-amino acid signal sequence and secreted to the periplasm. Mature PspE is the smallest rhodanese of E. coli (85 amino acids) and catalyzes the transfer of sulfur from thiosulfate to cyanide forming thiocyanate and sulfite. Cation exchange chromatography of a freeze-thaw extract of a PspE-overexpressing strain yielded two major peaks of active, homogeneous PspE. The two peaks contained two forms of PspE (PspE1 and PspE2) of distinct size and/or charge that were distinguished by native polyacrylamide gel electrophoresis and gel chromatography. PspE2 was converted to the more compact PspE1 by treatment with thiosulfate, which suggested that PspE1 is the persulfide form. One equivalent of cyanizable sulfur was associated with PspE1, with much less present in PspE2. Consistent with the conclusion that the single active site cysteine of PspE1 contains a persulfide sulfur was the observation that this form was much more tolerant to chemical inactivation by thiol-specific modifying reagent DTNB (5,5′-dithiobis(2-nitrobenzoic acid)). Rhodanese activity was subject to inhibition by anions (sulfite, sulfate, chloride, phosphate and arsenate), suggesting PspE has a cationic site for substrate binding. Kinetic analysis revealed that PspE employs a double-displacement mechanism, as is the case for other rhodaneses. The Kms for SSO32- and CN- were 3.0 and 43 mM, respectively. PspE exhibited a kcat of 72 s-1. To aid in understanding the physiological role of PspE, a strain with a pspE gene disruption was constructed. Comparison of rhodanese activity in extracts of wild-type and mutant strains revealed that PspE is a major contributor of rhodanese activity in E. coli. The pspE mutant displayed no obvious growth defect or auxotrophies, and was capable of molybdopterin biosynthesis, indicating that pspE is not essential for production of sulfur-containing amino acid or cofactors. Growth of wild-type and mutant strains deficient in pspE and other sulfurtransferase paralogs in medium with cyanide or cadmium was compared. The results indicated that neither PspE nor other E. coli rhodanese paralogs play roles in cyanide or cadmium detoxification. The physiological role of PspE remains to be determined. / Master of Science

Hydrogen sulfide (H2S) is an endogenous gasotransmitter that regulates vascular function and blood pressure, and also protects the heart from injury associated with myocardial infarction (MI). The mitochondrial enzyme thiosulfate sulfurtransferase (TST) has a putative role in the breakdown of H2S but its role in the cardiovascular system is unknown. I hypothesised that TST reduces cardiovascular H2S availability and that inhibiting TST activity may therefore ameliorate cardiovascular pathology. In the heart, TST was expressed by cardiomyocytes and vascular smooth muscle cells. Tst-/- mice all survived to adulthood and had normal cardiac structure and function. Cardiac and hepatic H2S breakdown rates were reduced and H2S levels were higher in the blood of Tst-/- mice. However, in heart tissue, protein levels for the H2S-activated Nrf2 downstream targets, thioredoxin (Trx1) and heme oxygenase-1 (HO-1) were comparable. In contrast, protein levels for the cardiac specific H2S-synthetic enzyme, cystathionine gamma lyase (CSE) was reduced, suggesting a homeostatic negative feedback mechanism to maintain H2S at non-toxic levels. Respiration, measured using an oxygen-sensing electrode was normal in isolated mitochondria from whole Tst-/- compared to control C57BL6 hearts. Endothelial nitric oxide synthase (eNOS) protein expression was lower in Tst-/- hearts, highlighting potential cross talk between H2S and nitric oxide (NO) signalling. TST was expressed in whole aorta homogenates and in isolated endothelial cells from aorta and small intramuscular vessels of the hindlimb from C57BL/6N control mice. Myography and western blotting revealed a greater influence of NO in aorta from Tst-/- mice that was associated with increased phosphorylation of the activating serine1177 residue of eNOS (PeNOSSer1177). NO plays a lesser role in resistance arteries, but in comparison to control vessels, small mesenteric vessels from Tst-/- mice was more reliant on small and intermediate calcium activated potassium channels for relaxation. Tst-/- mice were normotensive, despite this alteration in the regulation of vascular tone. However, metabolic cage experiments identified that Tst-/- mice presented with diuresis, polydipsia, and increased urinary electrolyte excretion of sodium, potassium and chloride, possibly to compensate for increased vascular tone in order to maintain stable blood pressure. To investigate the role of TST in regulating the response to pathological challenge, MI was induced by coronary artery ligation (CAL). In control mice, gene expression of CSE was downregulated by 2 days after CAL, but TST expression was 12-fold increased, suggesting regulation of H2S bioavailability during the acute MI-healing phase. Tst-/- male mice had a 40% greater incidence of cardiac rupture during infarct healing and surviving Tst-/- mice had greater left ventricular dilatation and impaired function compared to controls. Ex vivo, isolated perfused hearts from Tst-/- mice were more susceptible to ischaemia/ reperfusion injury, suggesting an additional role of TST in determining cardiomyocyte susceptibility to injury. In conclusion, these data indicate that cardiovascular H2S bioavailability is regulated through degradation by TST. The data presented here provide evidence for significant tissue specific crosstalk between H2S synthetic and degradative mechanisms and between H2S and other local regulatory mechanisms, including ion channels and NOS. We infer TST has a physiological role in the kidney where its loss leads to changes in renal electrolyte and water handling, although other compensatory mechanisms prevent a change in blood pressure. Under conditions of pathological challenge following MI, loss of TST is detrimental, illustrating its key role in removal of H2S. The data refute the original hypothesis that TST inhibition would be protective against cardiovascular pathology. Further studies in mice with tissue specific deletion of TST are now required to more fully reveal the cardiovascular role of TST.

AgaR, a protein in <i>Escherichia coli</i> thought to control the metabolism of N-acetylgalactosamine, is a member of the DeoR family of transcriptional regulators. Three transcriptional promoters within a cluster of genes containing the gene for AgaR were identified, specific for <i>agaR, agaZ</i> and <i>agaS</i>, and the transcription start sites mapped. Transcription from these promoters was specifically induced by N-acetylgalactosamine or galactosamine, though K-12 strains lacked the ability to utilize these as sole sources of carbon. The activity of these promoters was constitutively elevated in a strain in which <i>agaR</i> had been disrupted confirming that the promoters are subject to negative regulation by AgaR. AgaR-His6, purified using immobilized metal affinity chromatography, was used for DNase I footprint analysis of the promoter regions. Four operator sites bound by AgaR were identified. A putative consensus binding sequence for AgaR was proposed based on these four sites. <i>In vivo</i> and <i>in vitro</i> analysis of the <i>agaZ</i> promoter indicated that this promoter was activated by the cAMP-cAMP receptor protein (CRP). Expression from the <i>aga</i> promoters was less sensitive to catabolite repression in revertants capable of <i>N</i>-acetylgalactosamine utilization, suggesting that these revertants have mutation(s) that result in an elevated level of inducer for AgaR. A cluster of genes at minute 87.7 of the <i>E. coli</i> genome contains a gene that encodes another member of the DeoR family of transcriptional regulators. This protein, YihW, is more similar to GlpR, transcriptional regulator of <i>sn</i>-glycerol 3-phosphate metabolism in <i>E. coli</i>, than other members of the DeoR family. Despite the high degree of similarity, YihW lacked the ability to repress P_glpK, a promoter known to be controlled by GlpR. A variant of YihW containing substitutions in the putative recognition helix to more closely match the recognition helix of GlpR was also unable to repress P_glpK. Transcriptional promoters identified in this cluster of genes were negatively regulated by YihW. Regulation of genes involved in the metabolism of <i>sn</i>-glycerol 3-phosphate in <i>E. coli</i> by GlpR has been well characterized. However, the function of a protein (GlpE) encoded by a gene cotranscribed with that for GlpR was unknown prior to this work. GlpE was identified as a single-domain, 12-kDa rhodanese (thiosulfate:cyanide sulfurtransferase). The enzyme was purified to near homogeneity and characterized. As shown for other characterized rhodaneses, kinetic analysis revealed that catalysis occurs via an enzyme-sulfur intermediate utilizing a double-displacement mechanism requiring an active-site cysteine. K_m (SSO₃²⁻) and K_m (CN⁻) were determined to be 78 mM and 17 mM, respectively. The native molecular mass of GlpE was 22.5 kDa indicating that GlpE functions as a dimer. GlpE exhibited a kcat of 230 s-1. Thioredoxin, a small multifunctional dithiol protein, served as sulfur-acceptor substrate for GlpE with an apparent K_m of 34 mM when thiosulfate was near its K_m, suggesting thioredoxin may be a physiological substrate. / Ph. D.

Hydrogen sulfide (H2S), is a gasotransmitter with several key roles in metabolism and vascular function. The effects of H2S are dependent on concentration and target organ. For example, increased H2S concentrations impair liver metabolic function but protect against vascular dysfunction and atherosclerosis. Thiosulfate sulfurtransferase (TST), a nuclear encoded mitochondrial matrix enzyme, is proposed to be a component of the sulfide oxidising unit (SOU) which metabolises H2S. Preliminary data has shown that Tst deletion in mice (Tst-/-) increases circulating H2S levels measured in whole blood. Therefore, it was hypothesised that Tst-/- mice would exhibit worsened metabolic function in the liver but also protection of vascular function under conditions of vascular stress e.g. atherosclerosis. Liver metabolism was assessed by extensive metabolic phenotyping of Tst-/-mice fed control diet and in conditions of metabolic dysfunction induced by a high fat diet (HFD). Tst deletion altered glucose metabolism in mice; gluconeogenesis was increased in liver from Tst-/-mice fed control diet. Glucose intolerance in HFD-fed Tst-/-mice was also more severe than HFDfed C57BL/6 controls. In vitro metabolic investigations in primary hepatocytes isolated from Tst-/-mice demonstrated that mitochondrial ATP-linked and leak respiration were increased compared to controls. The effect of Tst deletion on vascular function was investigated in Tst- /-mice fed control or HFD using myography. Tst deletion did not alter vessel function when mice were maintained on a normal diet. HFD feeding (20 weeks) reduced maximal vessel constriction in the presence of endothelial nitric oxide synthase and cyclooxygenase inhibitors in C57BL/6 aorta. However, in Tst-/-mice fed HFD there was no reduction in maximal constriction suggesting a protective action of Tst deletion. The effects of Tst deletion on atherosclerotic lesions was investigated by generating double knock-out (DKO) mice by deletion of the Tst gene in ApoE-/- mice and (ApoE-/-Tst-/-). Atherosclerotic lesion formation was accelerated by feeding mice a western diet. Within the brachiocephalic branch lesion volume and total vessel volume were reduced in DKO mice fed western diet for 12 weeks, indicating that Tst deletion reduced lesion formation. Plasma cholesterol was reduced in DKO mice compared to ApoE-/- controls and a trend towards reduced systolic blood pressure was also noted. Overall this work supported the hypothesis that Tst deletion engenders metabolic dysfunction but vascular protection. The findings are consistent with the reported effects of increased H2S signalling. Overall inhibition of TST represents a novel target for treatment of atherosclerosis, with the caveat that glycaemia may be worsened due to hepatic metabolic dysfunction.

Die ubiquitär verbreitete Molybdänkofaktorbiosynthese ist in Escherichia coli (E. coli) bisher am umfassendsten untersucht. Bislang war jedoch nicht bekannt, welche physiologische Schwefelquelle im zweiten Schritt dieses Syntheseweges zur Bildung der charakteristischen Dithiolengruppe genutzt wird. Erste Untersuchungen deuteten auf eine der Cysteindesulfurasen E. colis hin, welche in Verbindung mit einem rhodaneseähnlichen Protein den Schwefel in Form eines Persulfids übertragen. Ähnliche Mechanismen wurden bereits in der humanen Moco-Biosynthese und der Thiaminbiosynthese identifiziert. In dieser Arbeit wurde das E. coli Protein YnjE näher charakterisiert. Es handelt sich bei YnjE um ein rhodaneseähnliches Protein aus drei Rhodanesedomänen. Durch Proteinkristallisation und anschliessender Röntgenstrukturanalyse wurde die Tertiärstruktur des YnjE-Proteins analysiert. Die hergestellten Kristalle konnten zur Gewinnung von Strukturdaten vermessen und eine Proteinkristallstruktur für YnjE berechnet werden. Desweiteren besitzt YnjE ein N-terminales Typ I Sekretionssystem abhängiges Sipnalpeptid. Durch Lokalisieungsexperimente wurde die Bedeutung des Signalpeptids für das YnjE-Protein untersucht. Dabei wurde festgestellt, dass endogenes YnjE sowohl im peri- als auch im cytoplasmatischen Raum lokalisiert ist. Auf Grund von vorhergehenden Studien, wurde eine Funktion des YnjE-Proteins innerhalb der Molybdänkofaktorbiosynthese in der Schwefelübertragung auf das Protein MoaD in E. coli vermutet und deshalb in dieser Arbeit näher untersucht. Es wurde eine Interaktion des YnjE-Proteins mit dem MoeB-Protein, welches für die Thiocarboxylierung des MoaD-Proteins essentiell ist, durch Tandem-Affinitätsreinigung und Antikörper-basierte Affinitätsreinigung nachgewiesen und ein signifikanter positiver Einfluss YnjEs auf die Bildung von Molybdopterin, einer Vorstufe des Molybdänkofaktors, bestätigt. Dabei wurde sowohl der Sulfurierungsgrad des MoaD-Proteins in YnjE und Cysteindesulfurase-knock-out Mutanten untersucht, als auch die Bildung von Molybdopterin in einem in vitro Ansatz in Abhängigkeit von steigenden YnjE-Konzentrationen analysiert. Im Ergebnis kann man daraus schließen, dass der Mechanismus der Schwefelübertragung ähnlich der Thiaminbiosynthese, über eine der drei Cysteindesulfurasen CsdA, SufS oder IscS geschieht, welche Schwefel in Form eines Persulfids auf YnjE übertragen können. Thiosulfat und Mercaptopyruvat, die Substrate für die beiden Familien der rhodaneseähnlichen Proteine, Thiosulfat-Sulfurtransferasen und Mercaptopyruvat-Sulfurtransferasen, dienen nicht als Substrate für eine Persulfurierung YnjEs. Durch eine Austauschmutante des Cysteinrestes der aktiven Schleife von YnjE konnte nicht bestätigt werden, dass dieser Aminosäurerest und damit die Bildung eines YnjE-gebundenen Persulfids für die positive Beeinflussung der MPT-Synthese essentiell ist. Vielmehr kann durch diese Arbeit von einer Vermittlung der Interaktionen zwischen MoeB, IscS und der MPT-Synthase durch YnjE ausgegangen werden wobei die Cysteindesulfurase IscS den Schwefel für die Thiocarboxylierung des MoaD-Proteins liefert. / The rhodanese-like protein YnjE was characterized in this study. After protein christallization the stucture of the YnjE protein was analyzed. Subzellular localization experiments revealed, that the YnjE protein is present both in cytoplasm and periplasm. Interaction studies and in vitro synthesis of Molybdopterin revealed an influence of YnjE on Molybdenum Cofactor Biosynthesis.A sulfur transfer from L-Cystein to YnjE by a Cystein desulfurase was not responsible for the the effects on Molybdenum Cofaktor Biosynthesis, since a YnjE cysteine 385 to alanine mutant showed the same effect on Molybdenum Cofaktor Biosynthesis.

Obesity is associated with dysfunction of adipose tissue due to oxidative stress and inflammation, leading to insulin resistance. Thiosulfate sulfurtransferase (Tst) was previously identified as an adipose-expressed anti-diabetic gene that protects against diet-induced metabolic impairment when upregulated in adipose tissue of mice. TST is a mitochondrial enzyme involved in the metabolism of cyanide, reactive oxygen species (ROS) and endogenous hydrogen sulfide (H2S). This thesis tested the hypothesis that TST maintains metabolic health in the face of dietary obesity. To do this, I investigated the adipose-tissue phenotypes and metabolic consequences of Tst gene deletion (Tst–/– mice) and of adipose tissue-specific overexpression of human TST (Ad-hTST mice) after exposure to high fat diet (HFD). After 20 weeks of HFD, Tst–/– mice exhibited impaired glucose tolerance despite unchanged adipose tissue inflammatory cell infiltration, protein carbonylation and unfolded protein response activation. However, levels of mRNA encoding mitochondrial antioxidant enzymes including superoxide dismutase 2 and peroxiredoxin 3 were lower in Tst–/– mice on HFD. Unexpectedly, chow-fed Tst-/- mice had lower body weight and fat mass than wild-type controls highlighting a potential effect of Tst on fat accumulation with age. A new mouse model with high expression of human TST genetically targeted to adipose tissue (Ad-hTST) was developed using the LoxP / Cre recombinase expression system, with a parent line expressing Cre under the control of the adiponectin promoter to confer adipose specificity. The Ad-hTST mice were found to gain a similar amount of weight and fat mass to control mice when exposed to 6 weeks of HFD. However, Ad-hTST mice had impaired glucose tolerance with no change in inflammatory cell infiltration, mRNA levels of antioxidant enzymes or unfolded protein response genes. Thus, unexpectedly, overexpression of human TST in adipose tissue of mice results in a detrimental metabolic phenotype. In vivo and in vitro experiments were conducted to test the hypothesis that TST protects against ROS accumulation. Paraquat was tested as an inducer of oxidative stress in vivo in wild-type, Tst-/- and Tst+/- mice. At the doses used (25mg/kg and under), mice became unwell and lost weight, with no increase in markers of oxidative stress in adipose or lung. The production of mitochondrial ROS in response to exogenous hydrogen peroxide (H2O2) exposure was increased in primary adipocytes from Tst-/- mice in vitro. However, primary hepatocytes showed reduced mitochondrial ROS production in response to H2O2 exposure. ROS production in hepatocytes was unaffected by pre-incubation with a H2S donor, an inhibitor of H2S-producing enzyme CSE or N-acetyl-cysteine, an antioxidant. TST may therefore influence mitochondrial ROS production differently in cell types such as adipocytes and hepatocytes. Disposal of exogenous H2O2 was unchanged in primary adipocytes from Tst-/- and Ad-hTST mice, and this was not affected by pre-incubation with sodium thiosulfate, a TST substrate. Metabolic changes in response to HFD may be influenced by alteration in TST expression, however the current data suggest it is unlikely to occur through the prevention of excessive local ROS accumulation in adipose tissue. Mice lacking the Tst gene globally and mice with adipose-specific overexpression of the human TST gene have a similarly impaired metabolic response to HFD. The phenotype of adipose-specific human TST-overexpressing mice does not recapitulate the protective metabolic phenotype produced by overexpression of the endogenous mouse Tst gene. In conclusion, TST may influence adipose tissue due to its role in the oxidation of H2S, however, by the current means, it does not appear to substantially impact the response of this tissue to oxidative stress.

Salmonella enterica is an important cause of food poisoning and is responsible for approximately a billion human infections each year. Disease manifestation in humans varies from severe systemic enteric (typhoid) fever to self-limiting gastroenteritis depending upon the infecting S. enterica serovar. S. Typhimurium is responsible for acute gastroenteritis in humans but causes a typhoid-like disease in mice and thus serves as an important model for studying the pathogenesis of systemic salmonellosis. Following ingestion, S. Typhimurium employs a variety of virulence mechanisms to survive within its host and establishes infection in the intestinal tract by invading the epithelial cells. Recent studies have revealed the importance of sulfur compounds in the intestine, such as tetrathionate and thiosulfate for the disease progression. S. Typhimurium is capable of utilising these sulfur compounds as terminal electron acceptors for its anaerobic respiration and thus gains a growth advantage over host microbiota during infection. However, the regulation of sulfur availability within S. Typhimurium and the mechanisms involved in mitigating cellular sulfide toxicity are not well-defined. During this study, we have identified the sstRA operon in S. Typhimurium encoding a deduced SmtB/ArsR family of transcriptional regulatory protein (SstR) and a deduced rhodanese-family sulfurtransferase (SstA) and demonstrated a role in mitigating the effects of cellular sulfide toxicity. SstR has been confirmed to act as a transcriptional repressor from the sstRA operator-promoter and the SstR-dependent repression is alleviated by low pH and sulfide stress (sodium thiosulfate), consistent with a role for SstR in sensing sulfide stress to trigger gene expression. Electrophoretic mobility shift assays confirm binding of purified SstR to the sstRA operator-promoter region. Furthermore, a conserved pair of cysteine residues within SstR was identified to be crucial for alleviating SstR-mediated repression, with the substitution of either cysteine causing constitutive repression. This is consistent with SstR inducer-responsiveness involving a thiol-based redox switch. Importantly, S. Typhimurium mutants lacking the sstRA operon have reduced tolerance to sulfide stress, consistent with the sstRA operon having a role in cellular sulfide detoxification. Work is continuing to further characterise the roles of sstR and sstA in S. Typhimurium on their contributions to infections.