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Query: UMLS:C0038187 (starvation)
 24,951 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Inorganic polyphosphate (poly P) is a chain of tens or many hundreds of phosphate (Pi) residues linked by high-energy phosphoanhydride bonds. Despite inorganic polyphosphate's ubiquity--found in every cell in nature and likely conserved from prebiotic times--this polymer has been given scant attention. Among the reasons for this neglect of poly P have been the lack of sensitive, definitive, and facile analytical methods to assess its concentration in biological sources and the consequent lack of demonstrably important physiological functions. This review focuses on recent advances made possible by the introduction of novel, enzymatically based assays. The isolation and ready availability of Escherichia coli polyphosphate kinase (PPK) that can convert poly P and ADP to ATP and of a yeast exopolyphosphatase that can hydrolyze poly P to Pi, provide highly specific, sensitive, and facile assays adaptable to a high-throughput format. Beyond the reagents afforded by the use of these enzymes, their genes, when identified, mutated, and overexpressed, have offered insights into the physiological functions of poly P. Most notably, studies in E. coli reveal large accumulations of poly P in cellular responses to deficiencies in an amino acid, Pi, or nitrogen or to the stresses of a nutrient downshift or high salt. The ppk mutant, lacking PPK and thus severely deficient in poly P, also fails to express RpoS (a sigma factor for RNA polymerase), the regulatory protein that governs > or = 50 genes responsible for stationary-phase adaptations to resist starvation, heat and oxidant stresses, UV irradiation, etc. Most dramatically, ppk mutants die after only a few days in stationary phase. The high degree of homology of the PPK sequence in many bacteria, including some of the major pathogenic species (e.g. Mycobacterium tuberculosis, Neisseria meningitidis, Helicobacter pylori, Vibrio cholerae, Salmonella typhimurium, Shigella flexneri, Pseudomonas aeruginosa, Bordetella pertussis, and Yersinia pestis), has prompted the knockout of their ppk gene to determine the dependence of virulence on poly P and the potential of PPK as a target for antimicrobial drugs. In yeast and mammalian cells, exo- and endopolyphosphatases have been identified and isolated, but little is known about the synthesis of poly P or its physiologic functions. Whether microbe or human, all species depend on adaptations in the stationary phase, which is truly a dynamic phase of life. Most research is focused on the early and reproductive phases of organisms, which are rather brief intervals of rapid growth. More attention needs to be given to the extensive period of maturity. Survival of microbial species depends on being able to manage in the stationary phase. In view of the universality and complexity of basic biochemical mechanisms, it would be surprising if some of the variety of poly P functions observed in microorganisms did not apply to aspects of human growth and development, to aging, and to the aberrations of disease. Of theoretical interest regarding poly P is its antiquity in prebiotic evolution, which along with its high energy and phosphate content, make it a plausible precursor to RNA, DNA, and proteins. Practical interest in poly P includes many industrial applications, among which is the microbial removal of Pi in aquatic environments.
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PMID:Inorganic polyphosphate: a molecule of many functions. 1087 45

The enteropathogenic Yersinia enterocolitica strains have several systems for scavenging iron from their environment. We have studied the expression of the fyuA gene, which encodes the outer membrane receptor for the siderophore yersiniabactin (Ybt), and the hemR gene, which encodes the receptor for heme, using the reporter genes gfp (encoding green fluorescent protein) and luc (encoding firefly luciferase). To study gene expression in vitro as well as in vivo, we have constructed several translational reporter gene fusions to monitor simultaneously expression of fyuA and hemR or expression of one gene by a gfp-luc tandem reporter. Results of the in vitro expression analysis (liquid media) indicated that fyuA and hemR are strongly derepressed under iron starvation conditions, resulting in strong fluorescence and/or luminescence at 27 degrees C. In the in vivo BALB/C mouse infection model, tissue-specific expression of fyuA and hemR reporter fusions was observed. Surprisingly, fyuA and hemR reporter constructs were weakly expressed by yersiniae located in the liver and intestinal lumen, whereas strong expression was found for yersiniae in the peritoneal cavity and moderate expression was found in the spleen. Strikingly, yersiniae carrying fyuA or hemR reporter fusions exhibited threefold-stronger signals when grown in the peritoneal cavity of mice than those growing under iron derepression in vitro. This hyperexpression suggests that besides Fur derepression, additional activators may be involved in the enhanced expression of fyuA and hemR under peritoneal growth conditions. Differential expression of the fyuA and hemR reporter fusions could not be observed, suggesting similar regulation of fyuA and hemR in the mouse infection model.
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PMID:Expression analysis of the yersiniabactin receptor gene fyuA and the heme receptor hemR of Yersinia enterocolitica in vitro and in vivo using the reporter genes for green fluorescent protein and luciferase. 1170 59

Orthologous proteins can be beneficial for X-ray crystallographic studies when a protein from an organism of choice fails to crystallize or the crystals are not suitable for structure determination. Their amino-acid sequences should be similar enough that they will share the same fold, but different enough so that they may crystallize under alternative conditions and diffract to higher resolution. This multi-species approach was employed to obtain diffraction-quality crystals of the RNA polymerase (RNAP) associated stringent starvation protein A (SspA). Although Escherichia coli SspA could be crystallized, the crystals failed to diffract well enough for structure determination. Therefore, SspA proteins from Yersinia pestis, Vibrio cholerae and Pseudomonas aeruginosa were cloned, expressed, purified and subjected to crystallization trials. The V. cholerae SspA protein failed to crystallize under any conditions tested and the P. aeruginosa SspA protein did not form crystals suitable for data collection. On the other hand, Y. pestis SspA crystallized readily and the crystals diffracted to 2.0 A.
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PMID:Characterization of four orthologs of stringent starvation protein A. 1277 5

Stringent starvation protein A (SspA) of Escherichia coli is an RNA polymerase-associated transcriptional activator for the lytic development of phage P1 and is essential for stationary phase-induced acid tolerance of E. coli. We report the crystal structure of Yersinia pestis SspA, which is 83% identical to E. coli SspA in amino acid sequence and is functionally complementary in supporting the lytic growth of phage P1 and acid resistance of an E. coli sspA mutant. The structure reveals that SspA assumes the characteristic fold of glutathione S-transferase (GST). However, SspA lacks GST activity and does not bind glutathione. Three regions of SspA are flexible, the N and C termini and the alpha2-helix. The structure also reveals a conserved surface-exposed pocket composed of residues from a loop between helices alpha3 and alpha4. The functional roles of these structural features were investigated by assessing the ability of deletion and site-directed mutants to confer acid resistance of E. coli and to activate transcription from a phage P1 late promoter, thereby supporting the lytic growth of phage P1. The results indicate that the flexible regions are not critical for SspA function, whereas the surface pocket is important for both transcriptional activation of the phage P1 late promoter and acid resistance of E. coli. The size, shape, and property of the pocket suggest that it mediates protein-protein interactions. SspA orthologs from Y. pestis, Vibrio cholerae, and Pseudomonas aeruginosa are all functional in acid resistance of E. coli, whereas only Y. pestis SspA supports phage P1 growth.
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PMID:Structural basis for the function of stringent starvation protein a as a transcription factor. 1573 7

It was found that at low temperature (6-8 degrees C) in the absence of nitrogen supply and at the presence of phosphate ions in the medium, Yersinia pseudotuberculosis and Listeria monocytogenes are able to actively synthesize reserve substances as polyphosphates. Most of the bacterial polyphosphates are alkali-soluble, especially at the preliminary stage of cell growth (lag-phase). This is proved by electron microscopic studies of ultrastructure of model microorganisms. During a long starvation period under conditions of carbon and energy source deficit, L. monocytogenes and Y. pseudotuberculosis consume this biopolymer for biosynthetic and bioenergetic processes.
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PMID:Effect of temperature on synthesis of polyphosphates in Yersinia pseudotuberculosis and Listeria monocytogenes under starvation conditions. 1661 64

Using DNA microarray analysis, mRNA levels from wild-type Yersinia pestis cells treated with the iron chelator 2,2'-dipyridyl were compared with those supplemented with excessive iron, and subsequent to this, gene expression in the fur mutant was compared with that in the wild-type strain under iron rich conditions. The microarray analysis revealed many iron transport or storage systems that had been induced in response to the iron starvation, which is mediated by the Fur protein, using the iron as a co-repressor. The iron-Fur complex also affected some genes involved in various non-iron functions (ribonucleoside-diphosphate reductase, membrane proteins, electron transport and oxidative defense, etc.). The Fur protein still participated in the regulation of genes involved in broad cellular processes (virulence factors, pesticin activity, haemin storage and many proteins with unknown functions) that were not affected by iron depletion conditions. In addition to its classical negative regulatory activities, the Fur protein activates gene transcription. Using bioinformatics tools, we were able to predict the Y. pestis Fur box sequence that was clearly the over-presented motif in the promoter regions of members of the iron-Fur modulon.
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PMID:Global analysis of iron assimilation and fur regulation in Yersinia pestis. 1663 Feb 48

Yersinia ruckeri causes the enteric redmouth disease or yersiniosis, an important systemic fish infection. In an attempt to dissect the virulence mechanisms of this bacterium, a gene encoding a putative protein involved in the secretion/activation of a haemolysin (yhlB), which had been previously identified by in vivo expression technology, was further analysed. The gene yhlB precedes another ORF (yhlA) encoding a Serratia-type haemolysin. Other toxins belonging to this group have been identified in genomic analyses of human-pathogenic yersiniae, although their role and importance in pathogenicity have not been defined yet. In spite of its being an in vivo-induced gene, the expression of yhlA can be induced under certain in vitro conditions similar to those encountered in the host, as deduced from the results obtained by using a yhlB : : lacZY fusion. Thus, higher levels of expression were obtained at 18 degrees C, the temperature of occurrence of disease outbreaks, than at 28 degrees C, the optimal growth temperature. The expression of the haemolysin also increased under iron-starvation conditions. This confirmed the decisive role of iron and temperature as environmental cues that regulate and coordinate the expression of genes encoding extracellular factors involved in the virulence of Y. ruckeri. LD(50) and cell culture experiments, using yhlB and yhlA insertional mutant strains, demonstrated the participation of the haemolysin in the virulence of Y. ruckeri and also its cytolytic properties against the BF-2 fish cell line. Finally, a screening for the production of haemolytic activity and the presence of yhlB and yhlA genes in 12 Y. ruckeri strains proved once more the genetic homogeneity of this species, since all possessed both haemolytic activity and the yhlB and yhlA genes.
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PMID:The iron- and temperature-regulated haemolysin YhlA is a virulence factor of Yersinia ruckeri. 1725 19

The ferric uptake regulator (Fur) is a predominant bacterial regulator controlling the iron assimilation functions in response to iron availability. Our previous microarray analysis on Yersinia pestis defined the iron-Fur modulon. In the present work, we reannotated the iron assimilation genes in Y. pestis, and the resulting genes in complementation with those disclosed by microarray constituted a total of 34 genome loci (putative operons) that represent the potential iron-responsive targets of Fur. The subsequent real-time reverse transcription-PCR (RT-PCR) in conjunction with the primer extension analysis showed that 32 of them were regulated by Fur in response to iron starvation. A previously predicted Fur box sequence was then used to search against the promoter regions of the 34 operons; the homologue of the above box could be predicted in each promoter tested. The subsequent electrophoretic mobility shift assay (EMSA) demonstrated that a purified His(6) tag-fused Fur protein was able to bind in vitro to each of these promoter regions. Therefore, Fur is a global regulator, both an activator and a repressor, and directly controls not only almost all of the iron assimilation functions but also a variety of genes involved in various non-iron functions for governing a complex regulatory cascade in Y. pestis. In addition, real-time RT-PCR, primer extension, EMSA, and DNase I footprinting assay were used to elucidate the Fur regulation of the ybt locus encoding a virulence-required iron uptake system. By combining the published data on the YbtA regulation of ybt, we constructed a concise Fur/YbtA regulatory network with a map of the Fur-promoter DNA interactions within the ybt locus. The data presented here give us an overview of the iron-responsive Fur regulon in Y. pestis.
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PMID:The iron-responsive Fur regulon in Yersinia pestis. 1828 95

During the course of its infection of the mammalian digestive tract, the entero-invasive, Gram-negative bacterium Yersinia pseudotuberculosis must overcome various hostile living conditions (notably, iron starvation and the presence of antimicrobial compounds produced in situ). We have previously reported that in vitro bacterial growth during iron deprivation raises resistance to the antimicrobial peptide polymyxin B; here, we show that this phenotype is mediated by a chromosomal gene (YPTB0333) encoding a transcriptional regulator from the LysR family. We determined that the product of YPTB0333 is a pleiotropic regulator which controls (in addition to its own expression) genes encoding the Yfe iron-uptake system and polymyxin B resistance. Lastly, by using a mouse model of oral infection, we demonstrated that YPTB0333 is required for colonization of Peyer's patches and mesenteric lymph nodes by Y. pseudotuberculosis.
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PMID:An iron-regulated LysR-type element mediates antimicrobial peptide resistance and virulence in Yersinia pseudotuberculosis. 1938 64

The ppGpp molecule is part of a highly conserved regulatory system for mediating the growth response to various environmental conditions. This mechanism may represent a common strategy whereby pathogens such as Yersinia pestis, the causative agent of plague, regulate the virulence gene programs required for invasion, survival and persistence within host cells to match the capacity for growth. The products of the relA and spoT genes carry out ppGpp synthesis. To investigate the role of ppGpp on growth, protein synthesis, gene expression and virulence, we constructed a Delta relA Delta spoT Y. pestis mutant. The mutant was no longer able to synthesize ppGpp in response to amino acid or carbon starvation, as expected. We also found that it exhibited several novel phenotypes, including a reduced growth rate and autoaggregation at 26 degrees C. In addition, there was a reduction in the level of secretion of key virulence proteins and the mutant was > 1,000-fold less virulent than its wild-type parent strain. Mice vaccinated subcutaneously (s.c.) with 2.5x10(4) CFU of the Delta relA Delta spoT mutant developed high anti-Y. pestis serum IgG titers, were completely protected against s.c. challenge with 1.5x10(5) CFU of virulent Y. pestis and partially protected (60% survival) against pulmonary challenge with 2.0x10(4) CFU of virulent Y. pestis. Our results indicate that ppGpp represents an important virulence determinant in Y. pestis and the Delta relA Delta spoT mutant strain is a promising vaccine candidate to provide protection against plague.
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PMID:The role of relA and spoT in Yersinia pestis KIM5 pathogenicity. 1970 61


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