bluuebunny/crossref_metadata_2025_split huggingface dataset:
Helicobacter pylori
Urease Suppresses Bactericidal Activity of Peroxynitrite via Carbon Dioxide Production
Authors: Kuwahara Hideo , Miyamoto Yoichi , Akaike Takaaki , Kubota Tatsuo , Sawa Tomohiro , Okamoto Shinichiro , Maeda Hiroshi 
Published: July 2002

ABSTRACT

Helicobacter pylori
can produce a persistent infection in the human stomach, where chronic and active inflammation, including the infiltration of phagocytes such as neutrophils and monocytes, is induced.
H. pylori
may have a defense system against the antimicrobial actions of phagocytes. We studied the defense mechanism of
H. pylori
against host-derived peroxynitrite (ONOO
−
), a bactericidal metabolite of nitric oxide, focusing on the role of
H. pylori
urease, which produces CO
2
and NH
3
from urea and is known to be an essential factor for colonization. The viability of
H. pylori
decreased in a time-dependent manner with continuous exposure to 1 μM ONOO
−
, i.e., 0.2% of the initial bacteria remained after a 5-min treatment without urea. The bactericidal action of ONOO
−
against
H. pylori
was significantly attenuated by the addition of 10 mM urea, the substrate for urease, whereas ONOO
−
-induced killing of a urease-deficient mutant of
H. pylori
or
Campylobacter jejuni
, another microaerophilic bacterium lacking urease, was not affected by the addition of urea. Such a protective effect of urea was potentiated by supplementation with exogenous urease, and it was almost completely nullified by 10 μM flurofamide, a specific inhibitor of urease. The bactericidal action of ONOO
−
was also suppressed by the addition of 20 mM NaHCO
3
but not by the addition of 20 mM NH
3
. In addition, the nitration of
l
-tyrosine of
H. pylori
after treatment with ONOO
−
was significantly reduced by the addition of urea or NaHCO
3
, as assessed by high-performance liquid chromatography with electrochemical detection. These results suggest that
H. pylori
-associated urease functions to produce a potent ONOO
−
scavenger, CO
2
/HCO
3
−
, that defends the bacteria from ONOO
−
cytotoxicity. The protective effect of urease may thus facilitate sustained bacterial colonization in the infected gastric mucosa.
Antiviral Activity of Shiga Toxin 1: Suppression of Bovine Leukemia Virus-Related Spontaneous Lymphocyte Proliferation
Authors: Ferens Witold A. , Hovde Carolyn J. 
Published: July 2002

ABSTRACT

Human infections with Shiga toxin (Stx)-producing
Escherichia coli
(STEC) cause hemorrhagic colitis. The Stxs belong to a large family of ribosome-inactivating proteins (RIPs) that are found in a variety of higher plants and some bacteria. Many RIPs have potent antiviral activity for the plants that synthesize them. STEC strains, both virulent and nonvirulent to humans, are frequently isolated from healthy cattle. Interestingly, despite intensive investigations, it is not known why cattle carry STEC. We tested the hypothesis that Stx has antiviral properties for bovine viruses by assessing the impact of Stx type 1 (Stx1) on bovine peripheral blood mononuclear cells (PBMC) from cows infected with bovine leukemia virus (BLV). PBMC from BLV-positive animals invariably displayed spontaneous lymphocyte proliferation (SLP) in vitro. Stx1 or the toxin A subunit (Stx1A) strongly inhibited SLP. Toxin only weakly reduced the pokeweed mitogen- or interleukin-2-induced proliferation of PBMC from normal (BLV-negative) cows and had no effect on concanavalin A-induced proliferation. The toxin activity in PBMC from BLV-positive cattle was selective for viral SLP and did not abrogate cell response to pokeweed mitogen- or interleukin-2-induced proliferation. Antibody to virus or Stx1A was most effective at inhibiting SLP if administered at the start of cell culture, indicating that both reagents likely interfere with BLV-dependent initiation of SLP. Stx1A inhibited expression of BLV p24 protein by PBMC. A well-defined mutant Stx1A (E167D) that has decreased catalytic activity was not effective at inhibiting SLP, suggesting the inhibition of protein synthesis is likely the mechanism of toxin antiviral activity. Our data suggest that Stx has potent antiviral activity and may serve an important role in BLV-infected cattle by inhibiting BLV replication and thus slowing the progression of infection to its malignant end stage.
Modulation of Cardiocyte Functional Activity by Antibodies againstTrypanosoma cruziRibosomal P2 Protein C Terminus
Authors: Sepulveda P. , Liegeard P. , Wallukat G. , Levin M. J. , Hontebeyrie M. 
Published: July 2002

ABSTRACTAntibodies against theTrypanosoma cruziribosomal P2β protein (TcP2β) have been associated with the chronic cardiac pathology of Chagas' disease in humans. Using synthetic peptides spanning the entire TcP2β molecule, we investigated their epitope recognition by antibodies from mice chronically infected withT. cruziand from mice immunized with two recombinant TcP2βs. We found clear differences in epitope recognition between antibodies fromT. cruzi-infected mice and mice immunized with two different recombinant TcP2βs associated with different schedules of immunization. Major epitopes recognized by antibodies from mice immunized with recombinant glutathioneS-transferase (GST) or histidine (Hist) fusion TcP2β (GST-TcP2β or Hist-TcP2β) are located in the central and hinge regions of the molecule. Nevertheless, mice immunized with Hist-TcP2β were also able to elicit antibodies against the TcP2β C terminus, a region which is highly conserved in bothT. cruziand mammal ribosomal P proteins. Strikingly, antibodies from infected animals recognized only the TcP2β C terminus. By using these antisera with distinct profiles of epitope recognition, it could be shown that only C terminus-specific antibodies were able to increase the beating frequency of cardiomyocytes from neonatal rats in vitro by selective stimulation of the β1-adrenergic receptor. Thus, antibodies against the TcP2β C terminus elicited in the absence of infection are able to modulate a functional activity of host cells through a molecular mimicry mechanism.
Gonococcal Nitric Oxide Reductase Is Encoded by a Single Gene,
norB
, Which Is Required for Anaerobic Growth and Is Induced by Nitric Oxide
Authors: Householder Tracey C. , Fozo Elizabeth M. , Cardinale Jean A. , Clark Virginia L. 
Published: July 2002

ABSTRACT

The gene encoding a nitric oxide reductase has been identified in
Neisseria gonorrhoeae
. The
norB
gene product shares significant identity with the nitric oxide reductases in
Ralstonia eutropha
and
Synechocystis sp.
and, like those organisms, the gonococcus lacks a
norC
homolog. The gonococcal
norB
gene was found to be required for anaerobic growth, but the absence of
norB
did not dramatically decrease anaerobic survival. In a wild-type background, induction of
norB
expression was seen anaerobically in the presence of nitrite but not anaerobically without nitrite or aerobically.
norB
expression is not regulated by FNR or NarP, but a functional
aniA
gene (which encodes an anaerobically induced outer membrane nitrite reductase) is necessary for expression. When
aniA
is constitutively expressed,
norB
expression can be induced both anaerobically and aerobically, but only in the presence of nitrite, suggesting that nitric oxide, which is likely to be produced by AniA as a product of nitrite reduction, is the inducing agent. This was confirmed with the use of the nitric oxide donor, spermine-nitric oxide complex, in an
aniA
null background both anaerobically and aerobically. NorB is important for gonococcal adaptation to an anaerobic environment, a physiologically relevant state during gonococcal infection. The presence of this enzyme, which is induced by nitric oxide, may also have implications in immune evasion and immunomodulation in the human host.
Inhibition of Caspase 3 Abrogates Lipopolysaccharide-Induced Nitric Oxide Production by Preventing Activation of NF-κB and c-Jun NH2-Terminal Kinase/Stress-Activated Protein Kinase in RAW 264.7 Murine Macrophage Cells
Authors: Chakravortty Dipshikha , Kato Yutaka , Sugiyama Tsuyoshi , Koide Naoki , Mu Mya Mya , Yoshida Tomoaki , Yokochi Takashi 
Published: July 2002

ABSTRACTThe effect of caspase inhibitors on lipopolysaccharide (LPS)-induced nitric oxide (NO) production in RAW 267.4 murine macrophage cells was investigated. Pretreatment of RAW cells with a broad caspase inhibitor, benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (Z-VAD-FMK), resulted in a striking reduction in LPS-induced NO production. Z-VAD-FMK inhibited LPS-induced NF-κB activation. Furthermore, it blocked phosphorylation of c-Jun N-terminal kinase/stress-activated protein kinase (JNK/SAPK) but not that of extracellular signal-regulated kinase 1/2 and p38 mitogen-activated protein kinases. Similarly, a caspase 3-specific inhibitor, Z-Asp-Glu-Val-Asp-fluoromethylketone, inhibited NO production, NF-κB activation, and JNK/SAPK phosphorylation in LPS-stimulated RAW cells. The attenuated NO production was due to inhibition of the expression of an inducible-type NO synthase (iNOS). The overexpression of the dominant negative mutant of JNK/SAPK and the addition of a JNK/SAPK inhibitor blocked iNOS expression but did not block LPS-induced caspase 3 activation. It was therefore suggested that the inhibition of caspase 3 might abrogate LPS-induced NO production by preventing the activation of NF-κB and JNK/SAPK. The caspase family, especially caspase 3, is likely to play an important role in the signal transduction for iNOS-mediated NO production in LPS-stimulated mouse macrophages.
Antigenic Properties and Processing Requirements of 65-Kilodalton Mannoprotein, a Major Antigen Target of Anti-CandidaHuman T-Cell Response, as Disclosed by Specific Human T-Cell Clones
Authors: Nisini Roberto , Romagnoli Giulia , Gomez Maria Jesus , La Valle Roberto , Torosantucci Antonella , Mariotti Sabrina , Teloni Raffaela , Cassone Antonio 
Published: July 2002

ABSTRACTT-cell-mediated immunity is known to play a central role in the host response toCandida albicans.T-cell clones are useful tools for the exact identification of fungal T-cell epitopes and the processing requirements ofC. albicansantigens. We isolated human T-cell clones from an HLA-DRB1*1101 healthy donor by using an antigenic extract (MP-F2) of the fungus. Specific clones were T-cell receptor α/β and CD4+/CD8−and showed a T-helper type 1 cytokine profile (production of gamma interferon and not interleukin-4). The large majority of these clones recognized both the natural (highly glycosylated) and the recombinant (nonglycosylated) 65-kDa mannoprotein (MP65), an MP-F2 minor constituent that was confirmed to be an immunodominant antigen of the human T-cell response. Surprisingly, most of the clones recognized two synthetic peptides of different MP65 regions. However, the peptides shared the amino acid motif IXSXIXXL, which may be envisaged as a motif sequence representing the minimal epitope recognized by these clones. Three clones recognized natural and pronase-treated MP65 but did not detect nonglycosylated, recombinant MP65 or the peptides, suggesting a possible role for polysaccharides in T-cell recognition ofC. albicans. Finally, lymphoblastoid B-cell lines were efficient antigen-presenting cells (APC) for recombinant MP65 and peptides but failed to present natural, glycosylated antigens, suggesting that nonprofessional APC might be defective in processing highly glycosylated yeast proteins. In conclusion, this study provides the first characterization ofC. albicans-specific human T-cell clones and provides new clues for the definition of the cellular immune response againstC. albicans.
Model of Differential Susceptibility to Mucosal
Burkholderia pseudomallei
Infection
Authors: Liu Boping , Koo Ghee Chong , Yap Eu Hian , Chua Kim Lee , Gan Yunn-Hwen 
Published: July 2002

ABSTRACT

Burkholderia pseudomallei
is the causative agent of melioidosis, an infectious disease with protean clinical manifestations. The major route of infection is thought to be through subcutaneous inoculation of contaminated soil and water, although ingestion and inhalation of contaminated aerosols are also possible. This study examines infection through the intranasal route in a murine model to mimic infection through inhalation. Two strains of mice, C57BL/6 and BALB/c, exhibit differential susceptibilities to the infection, with the C57BL/6 mice being considerably more resistant. To examine host factors that could contribute to this difference, bacterial loads and cytokine profiles in the two strains of mice were compared. We found that infected BALB/c mice exhibited higher bacterial loads in the lung and spleen and that they produced significantly higher levels of gamma interferon (IFN-γ) in the serum than C57BL/6 mice. Although tumor necrosis factor alpha and interleukin-1 could be detected in the nasal washes and sera of both strains of mice, the production in serum was transient and much lower than that of IFN-γ. C57BL/6 mice also exhibited memory responses to bacteria upon reinfection, with the production of serum immunoglobulin G (IgG) and mucosal IgA antibodies. Thus, it is possible that the production of systemic and mucosal antibodies is important for protection against disease in C57BL/6 mice.
Role of Fraction 1 Antigen ofYersinia pestisin Inhibition of Phagocytosis
Authors: Du Yidong , Rosqvist Roland , Forsberg Åke 
Published: July 2002

ABSTRACTYersinia pestis, the causative agent of plague, expresses a capsule-like antigen, fraction 1 (F1), at 37°C. F1 is encoded by thecaf1gene located on the large 100-kb pFra plasmid, which is unique toY. pestis. F1 is a surface polymer composed of a protein subunit, Caf1, with a molecular mass of 15.5 kDa. The secretion and assembly of F1 require thecaf1Mandcaf1Agenes, which are homologous to the chaperone and usher protein families required for biogenesis of pili. F1 has been implicated to be involved in the ability ofY. pestisto prevent uptake by macrophages. In this study we addressed the role of F1 antigen in inhibition of phagocytosis by the macrophage-like cell line J774. TheY. pestisstrain EV76 was found to be highly resistant to uptake by J774 cells. An in-frame deletion of thecaf1Mgene of theY. pestisstrain EV76 was constructed and found to be unable to express F1 polymer on the bacterial surface. This strain had a somewhat lowered ability to prevent uptake by J774 cells. Strain EV76C, which is cured for the virulence plasmid common to the pathogenicYersiniaspecies, was, as expected, much reduced in its ability to resist uptake. A strain lacking both the virulence plasmid andcaf1Mwas even further hampered in the ability to prevent uptake and, in this case, essentially all bacteria (95%) were phagocytosed. Thus, F1 and the virulence plasmid-encoded type III system act in concert to makeY. pestishighly resistant to uptake by phagocytes. In contrast to the type III effector proteins YopE and YopH, F1 did not have any influence on the general phagocytic ability of J774 cells. Expression of F1 also reduced the number of bacteria that interacted with the macrophages. This suggests that F1 prevents uptake by interfering at the level of receptor interaction in the phagocytosis process.
Changes in Temporal and Spatial Patterns of Outer Surface Lipoprotein Expression Generate Population Heterogeneity and Antigenic Diversity in the Lyme Disease Spirochete,
Borrelia burgdorferi
Authors: Hefty P. Scott , Jolliff Sarah E. , Caimano Melissa J. , Wikel Stephen K. , Akins Darrin R. 
Published: July 2002

ABSTRACT

Borrelia burgdorferi
differentially expresses many of the OspE/F/Elp paralogs during tick feeding. These findings, combined with the recent report that stable
B. burgdorferi
infection of mammals occurs only after 53 h of tick attachment, prompted us to further analyze the expression of the OspE/F/Elp paralogs during this critical period of transmission. Indirect immunofluorescence analysis revealed that OspE, p21, ElpB1, ElpB2, and OspF/BbK2.11 are expressed in the salivary glands of ticks allowed to feed on mice for 53 to 58 h. Interestingly, many of the spirochetes in the salivary glands that expressed abundant amounts of these antigens were negative for OspA and OspC. Although prior reports have indicated that OspE/F/Elp orthologs are surface exposed, none of the individual lipoproteins or combinations of the lipoproteins protected mice from challenge infections. To examine why these apparently surface-exposed lipoproteins were not protective, we analyzed their genetic stability during infection and their cellular locations after cultivation in vitro and within dialysis membrane chambers, mimicking a mammalian host-adapted state. Combined restriction fragment length polymorphism and nucleotide sequence analyses revealed that the genes encoding these lipoproteins are stable for at least 8 months postinfection. Interestingly, cellular localization experiments revealed that while all of these proteins can be surface localized, there were significant populations of spirochetes that expressed these lipoproteins only in the periplasm. Furthermore, host-specific signals were found to alter the expression patterns and final cellular location of these lipoproteins. The combined data revealed a remarkable heterogeneity in populations of
B. burgdorferi
during tick transmission and mammalian infection. The diversity is generated not only by temporal changes in antigen expression but also by modulation of the surface lipoproteins during infection. The ability to regulate the temporal and spatial expression patterns of lipoproteins throughout infection likely contributes to persistent infection of mammals by
B. burgdorferi
.
Identification of the
mob
Genes of Plasmid pSC101 and Characterization of a Hybrid pSC101-R1162 System for Conjugal Mobilization
Authors: Meyer Richard 
Published: July 2002

ABSTRACT

Similarities in DNA base sequence indicate that pSC101 and R1162 encode related systems for conjugal mobilization, although these plasmids are otherwise very different. The
mob
region of pSC101 was cloned, and two genes that are required for transfer were identified. One gene,
mobA
, encodes a protein similar in amino acid sequence to the DNA processing domain of the R1162 MobA protein. The other gene,
mobX
, is within the same transcriptional unit as the pSC101
mobA
and is located just downstream, at the same position occupied by
mobB
in R1162. Despite this, the MobB and MobX proteins do not appear to be closely related based on a comparison of their amino acid sequences. Complementation analysis indicated that neither of the pSC101 Mob proteins could substitute for, or be replaced by, their R1162 counterparts, nor were they active together at the R1162 origin of transfer (
oriT
). However, the full set of R1162 Mob proteins did recognize the pSC101
oriT
. A hybrid system for mobilization, active at the R1162
oriT
site, was constructed. This system consists of MobX and a chimeric protein made up of the DNA cleaving-ligating domain of the R1162 MobA protein joined to a fragment of pSC101 MobA. Previous results suggested that MobB and a region of MobA distinct from the DNA processing domain together formed a functional unit in transfer. The present results support this model because the chimeric MobA, although active on R1162
oriT
, requires the pSC101 protein MobX for efficient plasmid mobilization.
Regulation of Transcription of themph(A) Gene for Macrolide 2′-Phosphotransferase I inEscherichia coli: Characterization of the Regulatory GenemphR(A)
Authors: Noguchi Norihisa , Takada Katsutoshi , Katayama Jin , Emura Ayako , Sasatsu Masanori 
Published: July 2002

ABSTRACTThe synthesis of macrolide 2′-phosphotransferase I [Mph(A)], which inactivates erythromycin, is inducible by erythromycin. The expression of high-level resistance to erythromycin requires themph(A) andmrxgenes, which encode Mph(A) and an unidentified protein, respectively. We have studied themphR(A) gene, which regulates the inducible expression ofmph(A). An analysis of the synthesis of Mph(A) in minicells and results of a complementation test indicated thatmphR(A) is located downstream frommrxand that its product, MphR(A), represses the production of Mph(A). DNA sequencing indicated that themph(A),mrx, andmphR(A) genes exist as a cluster that begins withmph(A) and that the deduced amino acid sequence of MphR(A) can adopt an α-helix–turn–α-helix structure. To study the regulation of gene expression by MphR(A), we performed Northern blotting and primer extension. A transcript of 2.9 kb that corresponded to the transcript ofmph(A) throughmphR(A) was detected, and its level was elevated upon exposure of cells to erythromycin. Gel mobility shift assays and DNase I footprinting indicated that MphR(A) binds specifically to the promoter region ofmph(A), and the amount of DNA shifted as a results of the binding of MphR(A) decreased as the concentration of erythromycin was increased. These results indicate that transcription of themph(A)-mrx-mphR(A) operon is negatively regulated by the binding of a repressor protein, MphR(A), to the promoter of themph(A) gene and is activated upon inhibition of binding of MphR(A) to the promoter in the presence of erythromycin.
trp
RNA-Binding Attenuation Protein-5′ Stem-Loop RNA Interaction Is Required for Proper Transcription Attenuation Control of the
Bacillus subtilis trpEDCFBA
Operon
Authors: Du Hansen , Yakhnin Alexander V. , Dharmaraj Subramanian , Babitzke Paul 
Published: July 2002

ABSTRACT

The
trp
RNA-binding attenuation protein (TRAP) regulates expression of the
Bacillus subtilis trpEDCFBA
operon by a novel transcription attenuation mechanism. Tryptophan-activated TRAP binds to the nascent
trp
leader transcript by interacting with 11 (G/U)AG repeats, 6 of which are present in an antiterminator structure. TRAP binding to these repeats prevents formation of the antiterminator, thereby promoting formation of an overlapping intrinsic terminator. A third stem-loop structure that forms at the extreme 5′ end of the
trp
leader transcript also plays a role in the transcription attenuation mechanism. The 5′ stem-loop increases the affinity of TRAP for
trp
leader RNA. Results from RNA structure mapping experiments demonstrate that the 5′ stem-loop consists of a 3-bp lower stem, a 5-by-2 asymmetric internal loop, a 6-bp upper stem, and a hexaloop at the apex of the structure. Footprinting results indicate that TRAP interacts with the 5′ stem-loop and that this interaction differs depending on the number of downstream (G/U)AG repeats present in the transcript. Expression studies with
trpE′-′lacZ
translational fusions demonstrate that TRAP-5′ stem-loop interaction is required for proper regulation of the
trp
operon. 3′ RNA boundary experiments indicate that the 5′ structure reduces the number of (G/U)AG repeats required for stable TRAP-
trp
leader RNA association. Thus, TRAP-5′ stem-loop interaction may increase the likelihood that TRAP will bind to the (G/U)AG repeats in time to block antiterminator formation.