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At least 1,531 records · Page 85Linked to original sources
PubMed2004

Antioxidant defense of the midgut epithelium by the peritrophic envelope in caterpillars.

The peritrophic envelope (PE) is an extracellular matrix that is secreted by the midgut epithelium in most arthropods. In addition to protecting the midgut epithelium from abrasive food particles and microbial pathogens, in vitro experiments have suggested that the PE functions as a radical-scavenging antioxidant in caterpillars. This study tested the hypothesis that the PE is a "sacrificial antioxidant" in vivo in caterpillars. As a sacrificial antioxidant, the PE would (1) bind catalytic metal ions, (2) become oxidized itself, and (3) protect the midgut epithelium from oxidative damage. Each of these functions was supported by our results: the PE in Malacosoma disstria adsorbed increased amounts of iron as the concentration of iron was increased in its diet. Iron adsorption by the PE helped protect the midgut epithelium of M. disstria from oxidative damage over a wide range of ingested iron concentrations. Secondly, while the midgut epithelium was protected, protein oxidation in the PE increased 108% when tannic acid was oxidized in the endoperitrophic space. Finally, when the formation of the PE was inhibited by Calcofluor, protein carbonyls in the midgut epithelia of M. disstria and Orgyia leucostigma increased by two- to threefold. We conclude that the PE functions as an effective iron-binding and radical-scavenging antioxidant that protects the midgut epithelia of caterpillars.

Animals↗
PubMed2006

Alanine racemase from Helicobacter pylori NCTC 11637: purification, characterization and gene cloning.

The Helicobacter pylori NCTC 11637 alanine racemase gene, alr1, was cloned based on a putative alanine racemase gene, alr, of H. pylori 26695. The protein, Alr1, was purified to homogeneity from Escherichia coli MB2795 cells harboring the alr1 gene. The protein exclusively catalyzes the conversion of l-alanine to the d-isomer with K(m) and V(max) values of 100 mM and 909 mumol min(-1) mg(-1), respectively. The values are 16-fold higher than those for the reaction in the reverse direction. The molecular weight of Alr1 is 42,000 by SDS-PAGE, and 68,000 by gel-filtration analysis. The optimal pH and temperature are pH 8.3 and 37 degrees C, respectively, in good accordance with the characteristics shown by the alanine racemase purified from H. pylori NCTC 11637 cells. Pyridoxal 5'-phosphate was suggested to be the cofactor. The physiological function of Alr1 is discussed regarding energy production in the microbial cells.

Alanine↗
PubMed2006

p130Cas: a versatile scaffold in signaling networks.

The Cas family of multiadaptor and scaffold molecules has an essential role in intracellular signaling events. Although these proteins do not have enzymatic or transcriptional activity, they spatially and temporally control signaling events through their ability to undergo changes in phosphorylation and to associate with effectors proteins in multimolecular complexes. The involvement of p130Cas in cell motility as a component of the integrin signaling machinery is well established. Here, we discuss recent developments that highlight a fundamental role in cell transformation and microbial pathogenesis and the implications of these developments on p130Cas function under normal and pathological conditions.

Animals↗
PubMed1984

Siderophore reduction catalyzed by higher plant NADH:nitrate reductase.

Squash cotyledon NADH:nitrate reductase catalyzes the reduction of the siderophore ferrioxamine B. The enzyme also reduced ferric ion in a buffer system containing the chelators oxalate and maleate. Ferrioxamine B reduction was maximal at pH 4; ferric ion reduction was maximal at pH 8. The present study indicates that iron assimilation by higher plants may occur with microbial siderophores serving as ferric ion sources and nitrate reductase functioning as the siderophore reductase.

Antibodies↗
PubMed2003

Tautomeric state of alpha-sarcin histidines. Ndelta tautomers are a common feature in the active site of extracellular microbial ribonucleases.

Extracellular fungal RNases, including ribotoxins such as alpha-sarcin, constitute a family of structurally related proteins represented by RNase T1. The tautomeric preferences of the alpha-sarcin imidazole side chains have been determined by nuclear magnetic resonance and electrostatic calculations. Histidine residues at the active site, H50 and H137, adopt the Ndelta tautomer, which is less common in short peptides, as has been found for RNase T1. Comparison with tautomers predicted from crystal structures of other ribonucleases suggests that two active site histidine residues with the Ndelta tautomer are a conserved feature of microbial ribonucleases and that this is related to their ribonucleolytic function.

Bacterial Proteins↗
PubMed2005

Culture-independent microbial community analysis with terminal restriction fragment length polymorphism.

Terminal restriction fragment length polymorphism is a polymerase chain reaction (PCR)-based technique that has been used to effectively interrogate microbial communities to determine the diversity of both phylogenetic and functional markers. It requires the isolation of community DNA and knowledge of the target sequence. PCR amplification, performed with fluorescently labeled primers, is followed with restriction digestion and size selection on automated sequencing systems. The fluorescent tag identifies the terminal fragment, and the length polymorphism of the terminal fragments reveals a fraction of the phylogenetic diversity within the target sequence. Because the technique has high-throughput capabilities, it performs well in surveys where a large number of samples must be interrogated to ascertain spatial or temporal changes in community structure.

Bacteriolysis↗
PubMed2000

Genes that fight infection: what the Drosophila genome says about animal immunity.

From deciphering the principles of heredity to identifying the genes that control development, the fruit fly Drosophila melanogaster is being used to deconstruct an increasing number of biological processes. Genetic studies of Drosophila responses to microbial infection have identified regulators of innate immunity that are functionally conserved in mammals. These recent findings highlight the ancient origins of animal immune responses and demonstrate the potential of Drosophila for dissecting host-pathogen interactions. The sequencing of the Drosophila genome both enhances genetic approaches and provides new clues for the identification of key components of innate immunity. This article summarizes how information gained from genomic analysis contributes to our understanding of how animals cope with infectious disease.

Adaptation, Physiological↗
PubMed2000

Reactive oxygen and reactive nitrogen intermediates in innate and specific immunity.

Nitric oxide, nitric oxide derivatives and reactive oxygen intermediates are toxic molecules of the immune system which contribute to the control of microbial pathogens and tumors. There is recent evidence for additional functions of these oxygen metabolites in innate and adaptive immunity; these functions include the modulation of the cytokine response of lymphocytes and the regulation of immune cell apoptosis, as well as immunodeviating effects. Components of several signal transduction pathways have been identified as intracellular targets for reactive nitrogen and oxygen intermediates.

Anti-Infective Agents↗
PubMed1998

Surface plasmon resonance biosensors as a tool in antibody engineering.

Modern gene technology combined with efficient microbial expression systems provides tools to produce antibodies with reduced functional size and improved binding properties as well as antibody fusions or novel antibodies. Surface plasmon resonance based biosensors, which measure antigen-antibody interactions in real-time, can be used for a diverse characterization of the modified antibodies. To date, the majority of published work originates from real-time biospecific interaction analysis based on the BIAcore instruments. This article describes the range of applications in antibody engineering in which BIAcore has been applied.

Animals↗
PubMed2005

Tigecycline is modified by the flavin-dependent monooxygenase TetX.

The clinical use of tetracycline antibiotics has decreased due to the emergence of efflux and ribosomal protection-based resistance mechanisms. Currently in phase III clinical trials, the glycylcycline derivative tigecycline (GAR-936) containing a 9-tert-butylglycylamido group is part of a new generation of tetracycline antibiotics developed during the 1990s. Tigecycline displays a broad spectrum of antibacterial activity and circumvents the efflux and ribosomal protection resistance mechanisms. The TetX protein is a flavin-dependent monooxygenase that modifies first and second generation tetracyclines and requires NADPH, Mg(2+), and O(2) for activity. We report that tigecycline is a substrate for TetX and that bacterial strains containing the tet(X) gene are resistant to tigecycline. The resistance is due to the modification of tigecycline by TetX to form 11a-hydroxytigecycline, which we have shown has a weakened ability to inhibit protein translation compared with tigecycline. We have explored the basis of this decreased ability to block translation and found that hydroxylation occurs in the region of the molecule important for coordinating magnesium. 11a-Hydroxytigecycline forms a weaker complex with magnesium than tigecycline; the crystal structure of tetracycline in complex with the ribosome has shown that magnesium coordination is critical for binding tetracycline. Although tet(X) has not been isolated from any clinically resistant strains, our report demonstrates the first enzymatic resistance mechanism to tigecycline and provides an alert for the surveillance of resistant strains that may contain tet(X).

Bacterial Proteins↗
PubMed2001

On the symmetry of periodontal disease.

BACKGROUND/AIM: Symmetry is a common feature of biological systems, and can be observed in multiple aspects of the human body. The purpose of this study was to estimate the impact of symmetry on variance observed in intraoral topographic distribution patterns of chronic periodontitis. METHOD: This analysis was performed on a data set from 56 subjects, including clinical and microbiological variables, recorded at the mesial and distal aspect of every tooth in the entire dentition. The impact of contralateral conditions was determined on the level of the site, the tooth, and the quadrant. RESULTS: Significant correlations were detected between probing depths, recession, attachment levels, total cultivable bacterial counts and the plaque index recorded on the right and left side on all levels of analysis. The odds for bleeding on sampling, as well as for the presence of P. intermedia/nigrescens and A. actinomycetemcomitans increased significantly if the respective contralateral site was positive for the same parameter. In combining ipsilateral and contralateral parameters into the analysis it could be shown in several instances that this contralateral effect was stronger than the impact of other, ipsilateral factors. As an example, the odds for bleeding on sampling increased up to 10 fold if the contralateral site was bleeding, whereas the ipsilateral total cultivable count, determined at the same site, explained less than 30% of the variation in the bleeding tendency. CONCLUSION: These findings support the view that the development of periodontal disease in any site cannot be explained by the influence of local detrimental factors alone.

Adult↗
PubMed2000

Reduction of hazardous levels of the agricultural application of nitrogen and phosphorus relative to toxic ground water and toxic levels in the soil.

This paper proposes the hypothesis that microbial life chemically reduces levels of nitrogen (N(2)) and phosphorus (P) that are toxic and threaten human health and safety. Bio-remediation uses microorganisms to decontaminate a polluted system, in situ, requiring a minimal amount of space and equipment. Data strongly suggest that bio-stimulation can assist one microbe to multiply up to one billion microorganisms in 24 hours. Biochemical literature postulates that microbial life chemically biodegrades nitrates by one of two methods: (1) assimilative reduction; or (2) dissimilative reduction, also known as denitrification. Assimilative reduction results in construction of microbial cell walls, cell membranes and various forms of amino acids. It is proposed that denitrification includes the venting-off of the excess amounts of N(2)not required by the soil or needed for additional microbial development. Nitrate reduction by way of denitrification is a functional part of anaerobic respiration. Alternatively, the denitrification process supports oxidative phosphorylation, a mechanism similar to aerobic respiration. Thus, denitrification and phosphorylation may be considered as forms of respiration.

Agriculture↗
PubMed2006

Essential role of TAK1 in thymocyte development and activation.

The protein kinase TAK1 mediates the activation of NF-kappaB in response to stimulation by proinflammatory cytokines and microbial pathogens in the innate immunity pathways. However, the physiological function of TAK1 in the adaptive immunity pathways is unclear. By engineering mice lacking TAK1 in T cells, here, we show that TAK1 is essential for thymocyte development and activation in vivo. Deletion of TAK1 prevented the maturation of single-positive thymocytes displaying CD4 or CD8, leading to reduction of T cells in the peripheral tissues. Thymocytes lacking TAK1 failed to activate NF-kappaB and JNK and were prone to apoptosis upon stimulation. Our results provide the genetic evidence that TAK1 is required for the activation of NF-kappaB in thymocytes and suggest that TAK1 plays a central role in both innate and adaptive immunity.

Animals↗
PubMed2003

Fc receptor-mediated antibody regulation of T cell immunity against intracellular pathogens.

Immunity to intracellular microbial pathogens, including Chlamydia species, is controlled primarily by cell-mediated effector mechanisms, yet, the absence of antibodies results in inefficient microbial clearance. We investigated the hypothesis that certain Fc receptor functions promote the rapid induction of elevated T helper type 1 (Th1) response, which effectively clears chlamydiae. FcR(-/-) mice exhibited a delayed and reduced frequency of Chlamydia-specific Th1 cells, compared to FcR(+/+) mice. In vitro, antichlamydial antibodies increased the rate of Th1 activation by FcR(+/+) but not FcR(-/-) antigen-presenting cells. FcR(-/-) dendritic cells and the T cell-associated IgG2A and IgA mediate enhanced Th1 activation by antibodies. Immunization with chlamydia-antibody complexes induced elevated and protective Th1 response. These results provide a mechanistic basis for requiring both T cell and humoral immune responses in protective immunity and vaccine evaluation. Findings offer a paradigm in host defense wherein different effector components function indirectly to maximize the principal effector mechanism.

Animals↗
PubMed2002

On the risk of mortality to primates exposed to anthrax spores.

Current events have heightened the importance of understanding the risks from inhalation exposure to small numbers of spores of Bacillus anthracis. Previously reported data sets have not been fully assessed using current understanding of microbial dose response. This article presents an assessment of the reported primate dose-response data. At low doses, the risk to large populations of low doses of inhaled spores (e.g., < 100) is not insignificant.

Administration, Inhalation↗
PubMed2001

A weighted composite dose-response model for human salmonellosis.

This article describes the development of a weighted composite dose-response model for human salmonellosis. Data from previously reported human challenge studies were categorized into two different groups representing low and moderately virulent/pathogenic Salmonella strains based on a disease end point. Because epidemiological data indicate that some Salmonella strains are particularly pathogenic, and in the absence of human feeding study data for such strains, Shigella dysenteriae was used as a proxy for highly virulent strains. Three single-hit dose-response models were applied to the human feeding study data and evaluated for best fit using maximum likelihood estimation: (1) the exponential (E-1pop), (2) the two-subpopulation exponential (E-2pop), and (3) the Beta-Poisson (BP). Based on the goodness-of-fit test, the E-1pop and BP were the best-fit models for low and moderately virulent/pathogenic Salmonella strains, and the E-2pop and BP models were better for highly virulent/pathogenic strains. Epistemic analysis was conducted by determining the degree of confidence associated with the selected models, which was found to be 50%/50% (E-1pop/BP) for low and moderately pathogenic Salmonella strains, and 9.8%/90.2% (E-2pop/BP) for highly virulent strains. The degree of confidence for each component model and variations in the proportion of strains within each virulence/pathogenicity category were incorporated into the overall composite model. This study describes the influence of variation in strain virulence and host susceptibility on the shape of the population dose-response relationship.

Colony Count, Microbial↗
PubMed2006

Postgenomic scan of metallo-beta-lactamase homologues in rhizobacteria: identification and characterization of BJP-1, a subclass B3 ortholog from Bradyrhizobium japonicum.

The diffusion of metallo-beta-lactamases (MBLs) among clinically important human pathogens represents a therapeutic issue of increasing importance. However, the origin of these resistance determinants is largely unknown, although an important number of proteins belonging to the MBL superfamily have been identified in microbial genomes. In this work, we analyzed the distribution and function of genes encoding MBL-like proteins in the class Rhizobiales. Among 12 released complete genomes of members of the class Rhizobiales, a total of 57 open reading frames (ORFs) were found to have the MBL conserved motif and identity scores with MBLs ranging from 8 to 40%. On the basis of the best identity scores with known MBLs, four ORFs were cloned into Escherichia coli for heterologous expression. Among their products, one (blr6230) encoded by the Bradyrhizobium japonicum USDA110 genome, named BJP-1, hydrolyzed beta-lactams when expressed in E. coli. BJP-1 enzyme is most closely related to the CAU-1 enzyme from Caulobacter vibrioides (40% amino acid sequence identity), a member of subclass B3 MBLs. A kinetic analysis revealed that BJP-1 efficiently hydrolyzed most beta-lactam substrates, except aztreonam, ticarcillin, and temocillin, with the highest catalytic efficiency measured with meropenem. Compared to other MBLs, BJP-1 was less sensitive to inactivation by chelating agents.

Agrobacterium tumefaciens↗