Sulfhemoglobin formation in human erythrocytes by cystalysin, an L-cysteine desulfhydrase from Treponema denticola

Low level exposure to hydrogen sulfide: a review of emissions, community exposure, health effects, and exposure guidelines

Hydrogen sulfide (H2S) is a toxic gas that is well-known for its acute health risks in occupational settings, but less is known about effects of chronic and low-level exposures. This critical review investigates toxicological and experimental studies, exposure sources, standards, and epidemiological studies pertaining to chronic exposure to H2S from both natural and anthropogenic sources. H2S releases, while poorly documented, appear to have increased in recent years from oil and gas and possibly other facilities. Chronic exposures below 10 ppm have long been associated with odor aversion, ocular, nasal, respiratory and neurological effects. However, exposure to much lower levels, below 0.03 ppm (30 ppb), has been associated with increased prevalence of neurological effects, and increments below 0.001 ppm (1 ppb) in H2S concentrations have been associated with ocular, nasal, and respiratory effects. Many of the studies in the epidemiological literature are limited by exposure measurement error, co-pollutant exposures and potential confounding, small sample size, and concerns of representativeness, and studies have yet to consider vulnerable populations. Long-term community-based studies are needed to confirm the low concentration findings and to refine exposure guidelines. Revised guidelines that incorporate both short- and long-term limits are needed to protect communities, especially sensitive populations living near H2S sources.

Virulence factors of Streptococcus anginosus - a molecular perspective

Streptococcus anginosus together with S. constellatus and S. intermedius constitute the Streptococcus anginosus group (SAG), until recently considered to be benign commensals of the human mucosa isolated predominantly from oral cavity, but also from upper respiratory, intestinal, and urogenital tracts. For years the virulence potential of SAG was underestimated, mainly due to complications in correct species identification and their assignment to the physiological microbiota. Still, SAG representatives have been associated with purulent infections at oral and non-oral sites resulting in abscesses formation and empyema. Also, life threatening blood infections caused by SAG have been reported. However, the understanding of SAG as potential pathogen is only fragmentary, albeit certain aspects of SAG infection seem sufficiently well described to deserve a systematic overview. In this review we summarize the current state of knowledge of the S. anginosus pathogenicity factors and their mechanisms of action.

Role of Hydrogen Sulfide in Oral Disease

Oral diseases are among the most common human diseases yet less studied. These diseases affect both the physical, mental, and social health of the patients resulting in poor quality of life. They affect all ages, although severe stages are mostly observed in older individuals. Poor oral hygiene, genetics, and environmental factors contribute enormously to the development and progression of these diseases. Although there are available treatment options for these diseases, the recurrence of the diseases hinders their efficiency. Oral volatile sulfur compounds (VSCs) are highly produced in oral cavity as a result of bacteria activities. Together with bacteria components such as lipopolysaccharides, VSCs participate in the progression of oral diseases by regulating cellular activities and interfering with the immune response. Hydrogen sulfide (H2S) is a gaseous neurotransmitter primarily produced endogenously and is involved in the regulation of cellular activities. The gas is also among the VSCs produced by oral bacteria. In numerous diseases, H2S have been reported to have dual effects depending on the cell, concentration, and donor used. In oral diseases, high production and subsequent utilization of this gas have been reported. Also, this high production is associated with the progression of oral diseases. In this review, we will discuss the production of H2S in oral cavity, its interaction with cellular activities, and most importantly its role in oral diseases.

H2S Donors and Their Use in Medicinal Chemistry

Hydrogen sulfide (H2S) is a ubiquitous gaseous signaling molecule that has an important role in many physiological and pathological processes in mammalian tissues, with the same importance as two others endogenous gasotransmitters such as NO (nitric oxide) and CO (carbon monoxide). Endogenous H2S is involved in a broad gamut of processes in mammalian tissues including inflammation, vascular tone, hypertension, gastric mucosal integrity, neuromodulation, and defense mechanisms against viral infections as well as SARS-CoV-2 infection. These results suggest that the modulation of H2S levels has a potential therapeutic value. Consequently, synthetic H2S-releasing agents represent not only important research tools, but also potent therapeutic agents. This review has been designed in order to summarize the currently available H2S donors; furthermore, herein we discuss their preparation, the H2S-releasing mechanisms, and their -biological applications.

Role of the oral microbiome, metabolic pathways, and novel diagnostic tools in intra-oral halitosis: a comprehensive update

Halitosis or oral malodor is one of the most common reasons for the patients' visit to the dental clinic, ranking behind only dental caries and periodontitis. In the present times, where social and professional communications are becoming unavoidable, halitosis has become a concern of growing importance. Oral malodor mostly develops due to the putrefaction of substrates by the indigenous bacterial populations. Although culture-based studies have provided adequate information on halitosis, the high throughput omics technologies have amplified the resolution at which oral microbial community can be examined and has led to the detection of a broader range of taxa associated with intra-oral halitosis (IOH). These microorganisms are regulated by the interactions of their ecological processes. Thus to develop effective treatment strategies, it is important to understand the microbial basis of halitosis. In the current review, we provide an update on IOH in context to the role of the oral microbiome, metabolic pathways involved, and novel diagnostic tools, including breathomics. Understanding oral microbiota associated with halitosis from a broader ecological perspective can provide novel insights into one's oral and systemic health. Such information can pave the way for the emergence of diagnostic tools that can revolutionize the early detection of halitosis and various associated medical conditions.

Oral Microbiome and Gingival Tissue Apoptosis and Autophagy Transcriptomics

Objective: This study focused on documenting characteristics of the gingival transcriptome during various stages of periodontitis targeting genes associated with apoptotic and autophagic pathways and changes that specifically associate with features of the oral microbiome.

Methods:Macaca mulatta (n = 18; 12–23 years) were examined at baseline and 0.5, 1, and 3 months of disease progression, as well as 5 months with clinical disease resolution. 16S sequencing and microarray analyses examined changes in the microbiome and gingival transcriptome, respectively, at each time point from every animal.

Results: Specific patterns of apoptotic and autophagic genes were identified related to the initiation and progression of disease. The analysis also provided insights on the principal bacteria within the complex microbiome whose abundance was significantly correlated with differences in apoptotic and autophagic gene expression. Bacteria were identified that formed associated complexes with similar effects on the host gene expression profiles. A complex of Leptotrichia_unclassifed, Capnocytophaga_unclassified, Prevotella sp. 317, and Veillonellaceae_[G-1] sp. 155 were significantly negatively correlated with both apoptosis and autophagy. Whereas, Veillonellaceae_[G-1], Porphyromonadaceae, and F. alocis 539 were significantly positively correlated with both pathways, albeit this relationship was primarily associated with pro-apoptotic genes.

Conclusions: The findings provide evidence for specific bacteria/bacterial complexes within the oral microbiome that appear to have a more substantive effect on regulating apoptotic and autophagic pathways in the gingival tissues with periodontitis.

Multiple enzymes can make hydrogen sulfide from cysteine in Treponema denticola

Treponema denticola is a spirochete that is involved in causing periodontal diseases. This bacterium can produce H2S from thiol compounds found in the gingival crevicular fluid. Determining how H2S is made by oral bacteria is important since this molecule is present at high levels in periodontally-diseased pockets and the biological effects of H2S can explain some of the pathologies seen in periodontitis. Thus, it is of interest to identify the enzyme, or enzymes, involved in the synthesis of H2S by T. denticola. We, and others, have previously identified and characterized a T. denticola cystalysin, called HlyA, which hydrolyzes cysteine into H2S (and pyruvate and ammonia). However, there have been no studies to show that HlyA is, or is not, the only pathway that T. denticola can use to make H2S. To address this question, allelic replacement mutagenesis was used to make a deletion mutant (ΔhlyA) in the gene encoding HlyA. The mutant produces the same amount of H2S from cysteine as do wild type spirochetes, indicating that T. denticola has at least one other enzyme that can generate H2S from cysteine. To identify candidates for this other enzyme, a BLASTp search of T. denticola strain 33520 was done. There was one gene that encoded an HlyA homolog so we named it HlyB. Recombinant His-tagged HlyB was expressed in E. coli and partially purified. This enzyme was able to make H2S from cysteine in vitro. To test the role of HlyB in vivo, an HlyB deletion mutant (ΔhlyB) was constructed in T. denticola. This mutant still made normal levels of H2S from cysteine, but a strain mutated in both hly genes (ΔhlyA ΔhlyB) synthesizes significantly less H2S from cysteine. We conclude that the HlyA and HlyB enzymes perform redundant functions in vivo and are the major contributors to H2S production in T. denticola. However, at least one other enzyme can still convert cysteine to H2S in the ΔhlyA ΔhlyB mutant. An in silico analysis that identifies candidate genes for this other enzyme is presented.

Glutathione catabolism by Treponema denticola impacts its pathogenic potential

Treponema denticola is a spirochete that is etiologic for periodontal diseases. This bacterium is one of two periodontal pathogens that have been shown to have a complete three step enzymatic pathway (GTSP) that catabolizes glutathione to H2S. This pathway may contribute to the tissue pathology seen in periodontitis since diseased periodontal pockets have lower glutathione levels than healthy sites with a concomitant increase in H2S concentration. In order to be able to demonstrate that glutathione catabolism by the GTSP is critical for the pathogenic potential of T. denticola, allelic replacement mutagenesis was used to make a deletion mutant (Δggt) in the gene encoding the first enzyme in the GTSP. The mutant cannot produce H2S from glutathione since it lacks gamma-glutamyltransferase (GGT) activity. The hemolytic and hemoxidation activities of wild type T. denticola plus glutathione are reduced to background levels with the Δggt mutant and the mutant has lost the ability to grow aerobically when incubated with glutathione. The Δggt bacteria with glutathione cause less cell death in human gingival fibroblasts (hGFs) in vitro than do wild type T. denticola and the levels of hGF death correlate with the amounts of H2S produced. Importantly, the mutant spirochetes plus glutathione make significantly smaller lesions than wild type bacteria plus glutathione in a mouse back lesion model that assesses soft tissue destruction, a major symptom of periodontal diseases. Our results are the first to prove that T. denticola thiol-compound catabolism by its gamma-glutamyltransferase can play a significant role in the in the types of host tissue damage seen in periodontitis.

The Drug Developments of Hydrogen Sulfide on Cardiovascular Disease

The recognition of hydrogen sulfide (H₂S) has been evolved from a toxic gas to a physiological mediator, exhibiting properties similar to NO and CO. On the one hand, H₂S is produced from L-cysteine by enzymes of cystathionine γ-lyase (CSE) and cystathionine β-synthase (CBS), 3-mercaptopyruvate sulfurtransferase (3MST) in combination with aspartate aminotransferase (AAT) (also called as cysteine aminotransferase, CAT); on the other hand, H₂S is produced from D-cysteine by enzymes of D-amino acid oxidase (DAO). Besides sulfide salt, several sulfide-releasing compounds have been synthesized, including organosulfur compounds, Lawesson's reagent and analogs, and plant-derived natural products. Based on garlic extractions, we synthesized S-propargyl-L-cysteine (SPRC) and its analogs to contribute our endeavors on drug development of sulfide-containing compounds. A multitude of evidences has presented H₂S is widely involved in the roles of physiological and pathological process, including hypertension, atherosclerosis, angiogenesis, and myocardial infarcts. This review summarizes current sulfide compounds, available H₂S measurements, and potential molecular mechanisms involved in cardioprotections to help researchers develop further applications and therapeutically drugs.

Molecular pathogenicity of Streptococcus anginosus

Streptococcus anginosus and the closely related species Streptococcus constellatus and Streptococcus intermedius, are primarily commensals of the mucosa. The true pathogenic potential of this group has been under-recognized for a long time because of difficulties in correct species identification as well as the commensal nature of these species. In recent years, streptococci of the S. anginosus group have been increasingly found as relevant microbial pathogens in abscesses and blood cultures and they play a pathogenic role in cystic fibrosis. Several international studies have shown a surprisingly high frequency of infections caused by the S. anginosus group. Recent studies and a genome-wide comparative analysis suggested the presence of multiple putative virulence factors that are well-known from other streptococcal species. However, very little is known about the molecular basis of pathogenicity in these bacteria. This review summarizes our current knowledge of pathogenicity factors and their regulation in S. anginosus.

Effects of pH and lactate on hydrogen sulfide production by oral Veillonella spp

Indigenous oral bacteria in the tongue coating such as Veillonella have been identified as the main producers of hydrogen sulfide (H2S), one of the major components of oral malodor. However, there is little information on the physiological properties of H2S production by oral Veillonella such as metabolic activity and oral environmental factors which may affect H2S production. Thus, in the present study, the H2S-producing activity of growing cells, resting cells, and cell extracts of oral Veillonella species and the effects of oral environmental factors, including pH and lactate, were investigated. Type strains of Veillonella atypica, Veillonella dispar, and Veillonella parvula were used. These Veillonella species produced H2S during growth in the presence of l-cysteine. Resting cells of these bacteria produced H2S from l-cysteine, and the cell extracts showed enzymatic activity to convert l-cysteine to H2S. H2S production by resting cells was higher at pH 6 to 7 and lower at pH 5. The presence of lactate markedly increased H2S production by resting cells (4.5- to 23.7-fold), while lactate had no effect on enzymatic activity in cell extracts. In addition to H2S, ammonia was produced in cell extracts of all the strains, indicating that H2S was produced by the catalysis of cystathionine γ-lyase (EC 4.4.1.1). Serine was also produced in cell extracts of V. atypica and V. parvula, suggesting the involvement of cystathionine β-synthase lyase (EC 4.2.1.22) in these strains. This study indicates that Veillonella produce H2S from l-cysteine and that their H2S production can be regulated by oral environmental factors, namely, pH and lactate.

Targeting cystalysin, a virulence factor of treponema denticola-supported periodontitis

Cystalysin from Treponema denticola is a pyridoxal 5'-phosphate dependent lyase that catalyzes the formation of pyruvate, ammonia, and sulfide from cysteine. It is a virulence factor in adult periodontitis because its reaction contributes to hemolysis, which sustains the pathogen. Therefore, it was proposed as a potential antimicrobial target. To identify specific inhibitors by structure-based in silico methods, we first validated the crystal structure of cystalysin as a reliable starting point for the design of ligands. By using single-crystal absorption microspectrophotometry, we found that the enzyme in the crystalline state, with respect to that in solution, exhibits: 1) the same absorption spectra for the catalytic intermediates, 2) a close pKa value for the residue controlling the keto enamine ionization, and 3) similar reactivity with glycine, L-serine, L-methionine, and the nonspecific irreversible inhibitor aminoethoxyvinylglycine. Next, we screened in silico a library of 9357 compounds with the Fingerprints for Ligands and Proteins (FLAP) software, by using the three-dimensional structure of cystalysin as a template. From the library, 17 compounds were selected and experimentally evaluated by enzyme assays and spectroscopic methods. Two compounds were found to competitively inhibit recombinant T. denticola cystalysin, with inhibition constant (Ki ) values of 25 and 37 μM. One of them exhibited a minimum inhibitory concentration (MIC) value of 64 μg mL(-1) on Moraxella catarrhalis ATCC 23246, which proves its ability to cross bacterial membranes.

Identification and enzymic analysis of a novel protein associated with production of hydrogen sulfide and l-serine from l-cysteine in Fusobacterium nucleatum subsp. nucleatum ATCC 25586

A third enzyme that produces hydrogen sulfide from l-cysteine was identified in Fusobacterium nucleatum subsp. nucleatum. The fn1055 gene was cloned from a cosmid library constructed with genomic DNA of F. nucleatum ATCC 25586. Despite the database annotation that the product of fn1055 is a cysteine synthase, reverse-phase HPLC revealed that no l-cysteine was produced in vitro by the purified Fn1055 protein; however, the enzyme did produce l-serine. In addition, a cysteine auxotroph, Escherichia coli NK3, transformed with a plasmid containing the fn1055 gene did not grow without cysteine, which further suggests that Fn1055 does not function as a cysteine synthase. The Michaelis–Menten kinetics (K m = 0.09±0.001 mM and k cat = 5.43±0.64 s−1) of the purified enzyme showed that the capacity of Fn1055 to produce hydrogen sulfide was between that of two other enzymes, Fn0625 and Fn1220. Incubation of Fn1055 with l-cysteine resulted in the production of hydrogen sulfide, but not of pyruvate, ammonia or lanthionine, which are all byproducts produced in addition to hydrogen sulfide when Fn0625 or Fn1220 is incubated with l-cysteine. Instead, Fn1055 produced l-serine in its reaction with l-cysteine. Fn1055 produces hydrogen sulfide from l-cysteine by a mechanism that is different from that of Fn0625 or Fn1220.

Streptococcus anginosus l-cysteine desulfhydrase gene expression is associated with abscess formation in BALB/c mice

Streptococcus anginosus, an anginosus group bacterium, is frequently isolated from odontogenic abscesses, and is the oral bacterium that is primarily responsible for producing hydrogen sulfide from l-cysteine through the action of its l-cysteine desulfhydrase (βC-S lyase) enzyme. However, the relationship between its production of hydrogen sulfide and abscess formation has not been investigated. To elucidate the etiological role of hydrogen sulfide in abscess formation, we initially measured, using specific primers, expression of the lcd gene, which encodes βC-S lyase, in the pus of abscesses that formed in BALB/c mice following subcutaneous injection of S. anginosus into the dorsa. Expression of lcd was >15-fold higher when l-cysteine was present than when it was absent. A mouse virulence assay revealed that the mean diameter of abscesses caused by S. anginosus FW73 plus l-cysteine was greater than that of abscesses caused by S. anginosus FW73 in the absence of l-cysteine. These findings demonstrate that the lcd gene of S. anginosus is upregulated in mouse abscesses and that hydrogen sulfide, the product of a reaction catalyzed by βC-S lyase, plays an etiological role in odontogenic abscess formation.

Hydrogen sulphide: novel opportunity for drug discovery

Hydrogen sulphide (H(2)S) is emerging as an important endogenous modulator, which exhibits the beneficial effects of nitric oxide (NO) on the cardiovascular (CV) system, without producing toxic metabolites. H(2)S is biosynthesized in mammalian tissues by cystathionine-β-synthase and cystathionine-γ-lyase. H(2)S exhibits the antioxidant properties of inorganic and organic sulphites, behaving as a scavenger of reactive oxygen species. There is also clear evidence that H(2)S triggers other important effects, mainly mediated by the activation of ATP-sensitive potassium channels (K(ATP)). This mechanism accounts for the vasorelaxing and cardioprotective effects of H(2)S. Furthermore, H(2)S inhibits smooth muscle proliferation and platelet aggregation. In non-CV systems, H(2)S regulates the functions of the central nervous system, as well as respiratory, gastroenteric, and endocrine systems. Conversely, H(2)S deficiency contributes to the pathogenesis of hypertension. Likewise, impairment of H(2)S biosynthesis is involved in CV complications associated with diabetes mellitus. There is also evidence of a cross-talk between the H(2)S and the endothelial NO pathways. In particular, recent observations indicate a possible pathogenic link between deficiencies of H(2 S activity and the progress of endothelial dysfunction. These biological aspects of endogenous H(2)S have led several authors to look at this mediator as "the new NO" that has given attractive opportunities to develop innovative classes of drugs. In this review, the main biological actions of H(2)S are discussed. Moreover, some examples of H(2)S-donors are shown, as well as some hybrids, in which H(2)S-releasing moieties are added to well-known drugs, for improving their pharmacodynamic profile or reducing the potential for adverse effects, are reported.

Production of hydrogen sulfide by two enzymes associated with biosynthesis of homocysteine and lanthionine in Fusobacterium nucleatum subsp. nucleatum ATCC 25586

Fusobacterium nucleatum produces a large amount of the toxic metabolite hydrogen sulfide in the oral cavity. Here, we report the molecular basis of F. nucleatum H(2)S production, which is associated with two different enzymes: the previously reported Cdl (Fn1220) and the newly identified Lcd (Fn0625). SDS-PAGE analysis with activity staining revealed that crude enzyme extracts from F. nucleatum ATCC 25586 contained three major H(2)S-producing proteins. Two of the proteins with low molecular masses migrated similarly to purified Fn0625 and Fn1220. Their kinetic values suggested that Fn0625 had a lower enzymic capacity to produce H(2)S from L-cysteine (approximately 30%) than Fn1220. The Fn0625 protein degraded a variety of substrates containing betaC-S linkages to produce ammonia, pyruvate and sulfur-containing products. Unlike Fn0625, Fn1220 produced neither pyruvate nor ammonia from L-cysteine. Reversed-phase HPLC separation and mass spectrometry showed that incubation of L-cysteine with Fn1220 produced H(2)S and an uncommon amino acid, lanthionine, which is a natural constituent of the peptidoglycans of F. nucleatum ATCC 25586. In contrast, most of the sulfur-containing substrates tested, except L-cysteine, were not used by Fn1220. Real-time PCR analysis demonstrated that the fn1220 gene showed several-fold higher expression than fn0625 and housekeeping genes in exponential-phase cultures of F. nucleatum. Thus, we conclude that Fn0625 and Fn1220 produce H(2)S in distinct manners: Fn0625 carries out beta-elimination of L-cysteine to produce H(2)S, pyruvate and ammonia, whereas Fn1220 catalyses the beta-replacement of L-cysteine to produce H(2)S and lanthionine, the latter of which may be used for peptidoglycan formation in F. nucleatum.

Characterization of L-cysteine desulfhydrase from Prevotella intermedia

INTRODUCTION

Hydrogen sulfide is responsible for lysis of red blood cells and is a major compound for oral malodor. To clarify the production mechanism of hydrogen sulfide in Prevotella intermedia, we found an L-cysteine desulfhydrase gene (lcs) homologue on the genome database of P. intermedia ATCC25611 and characterized its gene product.

METHODS

The lcs gene homologue cloned into pGEX6p-1 vector was expressed in Escherichia coli and purified. Lcs activity was assayed by detection of the reaction products (hydrogen sulfide and pyruvate) or its derivatives from L-cysteine. Site-directed mutagenesis was used to convert an amino acid of the Lcs molecule.

RESULTS

The purified lcs gene product catalysed the degradation of L-cysteine to pyruvate, ammonia, and hydrogen sulfide, indicating that the protein is L-cysteine desulfhydrase. The enzyme required pyridoxal 5'-phosphate as a cofactor, and it was highly active at pH 7.0 and completely inhibited by ZnCl(2). The K(m) and V(max) of the enzyme were 0.7 mm and 4.2 micromol/min/mg, respectively. Replacement of Tyr-59, Tyr-118, Asp-198, and Lys-233 with any of the amino acids resulted in the complete disappearance of Lcs activity, implying that these amino acids are essential for enzyme activity. In addition, hydrogen sulfide produced by this enzyme lysed sheep red blood cells and modified hemoglobin.

CONCLUSION

These results show the enzymatic properties of L-cysteine desulfhydrase from P. intermedia ATCC25611 and also suggest that the Lcs enzyme, which produces hydrogen sulfide from L-cysteine, is closely associated with the pathogenesis of P. intermedia.

Crystallization and preliminary X-ray analysis of betaC-S lyases from two oral Streptococci

Hydrogen sulfide, which causes oral malodour, is generally produced from L-cysteine by the action of betaC-S lyase from oral bacteria. The betaC-S lyases from two oral bacteria, Streptococcus anginosus and S. gordonii, have been cloned, overproduced, purified and crystallized. X-ray diffraction data were collected from the two types of crystals using synchrotron radiation. The crystal of S. anginosus betaC-S lyase belonged to the orthorhombic space group P2(1)2(1)2(1), with unit-cell parameters a = 67.0, b = 111.1, c = 216.4 A, and the crystal of S. gordonii betaC-S lyase belonged to the same space group, with unit-cell parameters a = 58.0, b = 73.9. c = 187.6 A. The structures of the betaC-S lyases were solved by molecular-replacement techniques.

Role of Aggregatibacter actinomycetemcomitans in glutathione catabolism

INTRODUCTION

Our previous studies demonstrated that three enzymes, gamma-glutamyltransferase (GGT), cysteinylglycinase (CGase) and cystalysin, are required for the catabolism of glutathione to produce hydrogen sulfide (H(2)S) in Treponema denticola. In this study, we examined glutathione catabolism in Aggregatibacter actinomycetemcomitans.

METHODS

The GGT and CGase of A. actinomycetemcomitans were determined by biological methods and GGT was characterized using a molecular biological approach.

RESULTS

A. actinomycetemcomitans showed GGT and CGase activity, but could not produce H(2)S from glutathione. The addition of recombinant T. denticola cystalysin, an l-cysteine desulfhydrase, to whole cells of A. actinomycetemcomitans resulted in the production of H(2)S from glutathione. Subsequently, we cloned A. actinomycetemcomitans GGT gene (ggt) and overexpressed the 63 kDa GGT protein. The recombinant A. actinomycetemcomitans GGT was purified and identified. The K(cat)/K(m) of the recombinant GGT from N-gamma-l-glutamyl-4-nitroaniline as substrate was 31/microm/min. The activity of GGT was optimum at pH 6.9-7.1 and enhanced by thiol-containing compounds.

CONCLUSION

The results demonstrated that A. actinomycetemcomitans had GGT and CGase activities and that the GGT was characterized. The possible role of A. actinomycetemcomitans in glutathione metabolism and H(2)S production from oral bacteria was discussed.

A 52-kDa leucyl aminopeptidase from treponema denticola is a cysteinylglycinase that mediates the second step of glutathione metabolism

The metabolism of glutathione by the periodontal pathogen Treponema denticola produces hydrogen sulfide, which may play a role in the host tissue destruction seen in periodontitis. H2S production in this organism has been proposed to occur via a three enzyme pathway, gamma-glutamyltransferase, cysteinylglycinase (CGase), and cystalysin. In this study, we describe the purification and characterization of T. denticola CGase. Standard approaches were used to purify a 52-kDa CGase activity from T. denticola, and high pressure liquid chromatography electrospray ionization tandem mass spectrometry analysis of this molecule showed that it matches the amino acid sequence of a predicted 52-kDa protein in the T. denticola genome data base. A recombinant version of this protein was overexpressed in and purified from Escherichia coli and shown to catalyze the hydrolysis of cysteinylglycine (Cys-Gly) with the same kinetics as the native protein. Surprisingly, because sequence homology indicates that this protein is a member of a family of metalloproteases called M17 leucine aminopeptidases, the preferred substrate for the T. denticola protein is Cys-Gly (k cat/Km of 8.2 microm(-1) min(-1)) not l-Leu-p-NA (k cat/Km of 1.1 microm(-1) min(-1)). The activity of CGase for Cys-Gly is optimum at pH 7.3 and is enhanced by Mn2+, Co2+, or Mg2+ but not by Zn2+ or Ca2+. Importantly, in combination with the two other previously purified T. denticola enzymes, gamma-glutamyltransferase and cystalysin, CGase mediates the in vitro degradation of glutathione into the expected end products, including H2S. These results prove that T. denticola contains the entire three-step pathway to produce H2S from glutathione, which may be important for pathogenesis.

Volatile sulfur compounds produced by Helicobacter pylori

GOALS

To assess the volatile sulfur compounds produced by three strains of Helicobacter pylori in broth cultures mixed with sulfur-containing amino acids.

BACKGROUND

Halitosis has been reported in H. pylori-positive patients, and volatile sulfur compounds such as hydrogen sulfide and methyl mercaptan are known to be responsible for inducing oral malodor. Whether H. pylori produces these volatile sulfur compounds has yet to be established.

STUDY

Three strains of H. pylori (ATCC 43504, SS 1, DSM 4867) were cultured with 5 mM cysteine and methionine. After 72 hours of incubation, the headspace air was aspirated and injected directly into a gas chromatograph. The concentrations of hydrogen sulfide and methyl mercaptan were analyzed and compared between experimental and control cultures

RESULTS

In broth containing 5 mM cysteine, hydrogen sulfide was increased by ATCC 43504 (P < 0.01) and SS 1 (P < 0.05), while methyl mercaptan was elevated only by SS 1 (P < 0.05). In broth containing 5 mM methionine, methyl mercaptan increases were significant for SS 1 (P < 0.05) and DSM 4867 (P < 0.05). In broth containing 5 mM cysteine and 5 mM methionine, the concentration of hydrogen sulfide was higher than in controls for all three strains (P < 0.01); that of methyl mercaptan was higher only for SS 1 (P < 0.01). Cysteine addition to cultures containing methionine increased hydrogen sulfide and methyl mercaptan for ATCC 43504 (P < 0.05) and SS 1 (P < 0.05). Conversely, addition of methionine to cultures containing cysteine increased methyl mercaptan only for DSM 4867 (P < 0.01).

CONCLUSIONS

The production of volatile sulfur compounds by H. pylori is not only very complicated but also strain-specific. Nevertheless, H. pylori was shown to produce hydrogen sulfide and methyl mercaptan, which suggests that this microorganism can contribute to the development of halitosis.

The gasotransmitter role of hydrogen sulfide

A novel concept of "gasotransmitter" arrived recently. Gasotransmitters are small molecules of endogenous gases with important physiological functions. Their production and metabolism are enzymatically regulated, and their effects are not dependent on specific membrane receptors. Following the identification of nitric oxide and carbon monoxide as gasotransmitters, hydrogen sulfide (H(2)S) may be qualified as the third gasotransmitter. Recent studies have shown that H(2)S is generated from vascular smooth muscle cells (SMCs), catalyzed by specific H(2)S-generating enzyme. At physiologically relevant concentrations, H(2)S relaxes vascular tissues, an effect mediated by the activation of ATP-sensitive K(+) (K(ATP)) channels in vascular SMCs. H(2)S directly alters the activity of K(ATP) channels without the involvement of second messengers. Furthermore, the endogenous production of H(2)S in the cardiovascular system is likely regulated by nitric oxide, whereas the vasorelaxant effect of nitric oxide is inhibited by H(2)S. It is anticipated that future studies will better reveal the molecular mechanisms underlying the effect of H(2)S on K(ATP) channel proteins, the interaction of H(2)S and other gasotransmitters in cardiovascular system, the endogenous stimulators and inhibitors of H(2)S metabolism, the role of H(2)S in the regulation of heart function, and the abnormal H(2)S production and action under various pathophysiological conditions.

Differences in the betaC-S lyase activities of viridans group streptococci

betaC-S Lyase catalyzes the alpha,beta-elimination of L-cysteine to hydrogen sulfide, which is one of the main causes of oral malodor and is highly toxic to mammalian cells. We evaluated the capacity of six species of oral streptococci to produce hydrogen sulfide. The crude enzyme extract from Streptococcus anginosus had the greatest capacity. However, comparative analysis of amino acid sequences did not detect any meaningful differences in the S. anginosus betaC-S lyase. The capacity of S. anginosus purified betaC-S lyase to degrade L-cysteine was also extremely high, while its capacity to degrade L-cystathionine was unremarkable. These findings suggest that the extremely high capacity of S. anginosus to produce hydrogen sulfide is due to the unique characteristic of betaC-S lyase from that organism.

Role for recombinant gamma-glutamyltransferase from Treponema denticola in glutathione metabolism

Volatile sulfur compounds, including hydrogen sulfide (H(2)S), have been implicated in the development of periodontal disease. Glutathione is an important thiol source for H(2)S production in periodontal pockets. Our recent studies have delineated a pathway of glutathione metabolism in Treponema denticola that releases H(2)S. In this pathway, gamma-glutamyltransferase (GGT) has been proposed to catalyze the first step of glutathione degradation. We have cloned the gene of GGT from T. denticola, which contains an open reading frame of 726 bp encoding a protein of 241 amino acids. Transformation of this gene into Escherichia coli led to the expression of a recombinant protein. After purification by chromatography, the recombinant protein showed enzymatic activity typical of GGT, catalyzing the degradation of Na-gamma-glutamyl-4-nitroaniline (GNA) and the hydrolysis of glutathione, releasing glutamic acid or glutamine and cysteinylglycine. L-Cysteine is not a substrate of GGT. Importantly, GNA, when added to T. denticola, was able to compete with glutathione and inhibit the production of H(2)S, ammonia, and pyruvate. This was accompanied by the suppression of hemoxidative and hemolytic activities of the bacteria. Purified GGT was inactivated by TLCK (Nalpha-p-tosyl-L-lysine chloromethyl ketone) and proteinase K treatment. However, higher enzymatic activity was demonstrated in the presence of 2-mercaptoethanol and dithiothreitol. Our further experiments showed that the addition of recombinant GGT to Porphyromonas gingivalis, a bacterium without significant glutathione-metabolizing capacity, drastically increased the utilization of glutathione by the bacterium, producing H(2)S, ammonia, and pyruvate. This was again accompanied by enhanced bacterial hemoxidative and hemolytic activities. Together, the results suggest an important role for GGT in glutathione metabolism in oral bacteria.

lcd from Streptococcus anginosus encodes a C-S lyase with alpha,beta-elimination activity that degrades L-cysteine

Hydrogen sulfide is highly toxic to mammalian cells. It has also been postulated that hydrogen sulfide modifies haemoglobin resulting in haemolysis. The enzyme that produces hydrogen sulfide from L-cysteine was purified from Streptococcus anginosus. Using the N-terminal amino acid sequence of the purified enzyme, the lcd gene encoding L-cysteine desulfhydrase was cloned; the recombinant protein was then purified to examine its enzymic and biological characteristics. This L-cysteine desulfhydrase had the Michaelis-Menten kinetics K(m)=0.62 mM and V(max)=163 micro mol min(-1) mg(-1). DL-Cystathionine, L-cystine, S-(2-aminoethyl)-L-cysteine, 3-chloro-DL-alanine and S-methyl-L-cysteine were substrates for the enzyme, whereas D-cysteine, DL-homocysteine, L-methionine, DL-serine, DL-alanine, L-cysteine methyl ester, L-tryptophan, L-tyrosine and L-phenylalanine were not. These findings suggest that this L-cysteine desulfhydrase is a C-S lyase that catalyses the alpha,beta-elimination (alphaC-N and betaC-S) reaction. In addition, it is demonstrated that the hydrogen sulfide produced by this enzyme caused the modification and release of haemoglobin in sheep erythrocytes.

Role of Treponema denticola in periodontal diseases

Among periodontal anaerobic pathogens, the oral spirochetes, and especially Treponema denticola, have been associated with periodontal diseases such as early-onset periodontitis, necrotizing ulcerative gingivitis, and acute pericoronitis. Basic research as well as clinical evidence suggest that the prevalence of T denticola, together with other proteolytic gram-negative bacteria in high numbers in periodontal pockets, may play an important role in the progression of periodontal disease. The accumulation of these bacteria and their products in the pocket may render the surface lining periodontal cells highly susceptible to lysis and damage. T. denticola has been shown to adhere to fibroblasts and epithelial cells, as well as to extracellular matrix components present in periodontal tissues, and to produce several deleterious factors that may contribute to the virulence of the bacteria. These bacterial components include outer-sheath-associated peptidases, chymotrypsin-like and trypsin-like proteinases, hemolytic and hemagglutinating activities, adhesins that bind to matrix proteins and cells, and an outer-sheath protein with pore-forming properties. The effects of T. denticola whole cells and their products on a variety of host mucosal and immunological cells has been studied extensively (Fig. 1). The clinical data regarding the presence of T. denticola in periodontal health and disease, together with the basic research results involving the role of T. denticola factors and products in relation to periodontal diseases, are reviewed and discussed in this article.

Role of glutathione metabolism of Treponema denticola in bacterial growth and virulence expression

Hydrogen sulfide (H(2)S) is a major metabolic end product detected in deep periodontal pockets that is produced by resident periodontopathic microbiota associated with the progression of periodontitis. Treponema denticola, a member of the subgingival biofilm at disease sites, produces cystalysin, an enzyme that catabolizes cysteine, releasing H(2)S. The metabolic pathway leading to H(2)S formation in periodontal pockets has not been determined. We used a variety of thiol compounds as substrates for T. denticola to produce H(2)S. Our results indicate that glutathione, a readily available thiol source in periodontal pockets, is a suitable substrate for H(2)S production by this microorganism. In addition to H(2)S, glutamate, glycine, ammonia, and pyruvate were metabolic end products of metabolism of glutathione. Cysteinyl glycine (Cys-Gly) was also catabolized by the bacteria, yielding glycine, H(2)S, ammonia, and pyruvate. However, purified cystalysin could not catalyze glutathione and Cys-Gly degradation in vitro. Moreover, the enzymatic activity(ies) in T. denticola responsible for glutathione breakdown was inactivated by trypsin or proteinase K, by heating (56 degrees C) and freezing (-20 degrees C), by sonication, and by exposure to N alpha-p-tosyl-L-lysine chloromethyl ketone (TLCK). These treatments had no effect on degradation of cysteine by the purified enzyme. In this study we delineated an enzymatic pathway for glutathione metabolism in the oral spirochete T. denticola; our results suggest that glutathione metabolism plays a role in bacterial nutrition and potential virulence expression.

Suppression of urease levels in Streptococcus salivarius by cysteine, related compounds and by sulfide

Urease synthesis in Streptococcus salivarius is induced by an acid environment, carbohydrate and a high growth rate. We now report that both cysteine and sulfide above 1 mM strongly suppress S. salivarius urease levels. Close structural relatives of cysteine (cysteamine, ethanedithiol and penicillamine) at 5 mM buffered to pH 7.0 also caused urease suppression, but thiols in general (2-mercaptoethanol, dithiothreitol and glutathione) did not. In cultures buffered below pH 5.9, the cysteine-induced urease suppression was lifted substantially, but the sulfide suppression increased, suggesting involvement of different processes. Urease activity was inhibited 50% by 5 mM mercaptoethanol but unaffected by 5 mM cysteine or sulfide, hence modification of enzyme activity by thiols is not directly related to suppression of their levels in culture. Cysteine, arising primarily through protein hydrolysis which also raises the pH, could be a surrogate pH feedback signal for nearby alkaline conditions, and sulfide may reflect activity of periodontopathic plaques.

Crystal structure of cystalysin from Treponema denticola: a pyridoxal 5'-phosphate-dependent protein acting as a haemolytic enzyme

Cystalysin is a C(beta)-S(gamma) lyase from the oral pathogen Treponema denticola catabolyzing L-cysteine to produce pyruvate, ammonia and H(2)S. With its ability to induce cell lysis, cystalysin represents a new class of pyridoxal 5'-phosphate (PLP)-dependent virulence factors. The crystal structure of cystalysin was solved at 1.9 A resolution and revealed a folding and quaternary arrangement similar to aminotransferases. Based on the active site architecture, a detailed catalytic mechanism is proposed for the catabolism of S-containing amino acid substrates yielding H(2)S and cysteine persulfide. Since no homologies were observed with known haemolysins the cytotoxicity of cystalysin is attributed to this chemical reaction. Analysis of the cystalysin-L-aminoethoxyvinylglycine (AVG) complex revealed a 'dead end' ketimine PLP derivative, resulting in a total loss of enzyme activity. Cystalysin represents an essential factor of adult periodontitis, therefore the structure of the cystalysin-AVG complex may provide the chemical basis for rational drug design.