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Two-component Systems (two-component + system)
Selected AbstractsListeria monocytogenes response regulators important for stress tolerance and pathogenesisFEMS MICROBIOLOGY LETTERS, Issue 1 2001Birgitte H. Kallipolitis Abstract Environmental sensing by two-component signal transduction systems is likely to play a role for growth and survival of Listeria monocytogenes both during transmission in food products and within a host organism. Two-component systems typically consist of a membrane-associated sensor histidine kinase and a gene regulatory protein, the response regulator (RR). We have identified seven putative RR genes in L. monocytogenes LO28 by PCR using degenerate oligonucleotide primers. By insertional inactivation we obtained data suggesting that three of the putative RRs contribute to the pathogenicity of L. monocytogenes in mice. Strikingly, the mutants that were attenuated in virulence also had a decreased ability to grow in the presence of various stress conditions potentially encountered in an infection process. Thus, our data point to a connection between the ability of the putative two-component systems to sense and respond to certain environmental stimuli, and the virulence of L. monocytogenes. [source] Identification and characterization of KvgAS, a two-component system in Klebsiella pneumoniae CG43FEMS MICROBIOLOGY LETTERS, Issue 1 2003Yi-Chyi Lai Abstract A two-component system encoding gene cluster kvgAS that is present only in virulent Klebsiella pneumoniae CG43 was isolated and its sequence determined. RT-PCR and Southern analysis demonstrated that kvgAS is organized as an operon. No apparent effect of a kvgS deletion on bacterial virulence was observed in a mouse peritonitis model. In the presence of paraquat or 2,2-dipyridyl, the activity of kvgAS promoter in the kvgS mutant was found to be reduced to half of the level in the wild-type strain. The data suggest that the KvgAS system is autoregulated and plays a role in countering free radical stresses and sensing iron-limiting conditions. [source] Three independent signalling pathways repress motility in Pseudomonas fluorescens F113MICROBIAL BIOTECHNOLOGY, Issue 4 2009Ana Navazo Summary Motility is one of the most important traits for rhizosphere colonization by pseudomonads. Despite this importance, motility is severely repressed in the rhizosphere-colonizing strain Pseudomonas fluorescens F113. This bacterium is unable to swarm under laboratory conditions and produce relatively small swimming haloes. However, phenotypic variants with the ability to swarm and producing swimming haloes up to 300% larger than the wild-type strain, arise during rhizosphere colonization. These variants harbour mutations in the genes encoding the GacA/GacS two-component system and in other genes. In order to identify genes and pathways implicated in motility repression, we have used generalized mutagenesis with transposons. Analysis of the mutants has shown that besides the Gac system, the Wsp system and the sadB gene, which have been previously implicated in cyclic di-GMP turnover, are implicated in motility repression: mutants in the gacS, sadB or wspR genes can swarm and produce swimming haloes larger than the wild-type strain. Epistasis analysis has shown that the pathways defined by each of these genes are independent, because double and triple mutants show an additive phenotype. Furthermore, GacS, SadB and WspR act at different levels. Expression of the fleQ gene, encoding the master regulator of flagella synthesis is higher in the gacS - and sadB - backgrounds than in the wild-type strain and this differential expression is reflected by a higher secretion of the flagellin protein FliC. Conversely, no differences in fleQ expression or FliC secretion were observed between the wild-type strain and the wspR - mutant. [source] Legionella pneumophila couples fatty acid flux to microbial differentiation and virulenceMOLECULAR MICROBIOLOGY, Issue 5 2009Rachel L. Edwards Summary During its life cycle, Legionella pneumophila alternates between at least two phenotypes: a resilient, infectious form equipped for transmission and a replicative cell type that grows in amoebae and macrophages. Considering its versatility, we postulated that multiple cues regulate L. pneumophila differentiation. Beginning with a Biolog Phenotype MicroArray screen, we demonstrate that excess short-chain fatty acids (SCFAs) trigger replicative cells to cease growth and activate their panel of transmissive traits. To co-ordinate their response to SCFAs, L. pneumophila utilizes the LetA/LetS two-component system, but not phosphotransacetylase or acetyl kinase, two enzymes that generate high-energy phosphate intermediates. Instead, the stringent response enzyme SpoT appears to monitor fatty acid biosynthesis to govern transmission trait expression, as an altered distribution of acylated acyl carrier proteins correlated with the SpoT-dependent differentiation of cells treated with either excess SCFAs or the fatty acid biosynthesis inhibitors cerulenin and 5-(tetradecyloxy)-2-furoic acid. We postulate that, by exploiting the stringent response pathway to couple cellular differentiation to its metabolic state, L. pneumophila swiftly acclimates to stresses encountered in its host or the environment, thereby enhancing its overall fitness. [source] A novel bacterial signalling system with a combination of a Ser/Thr kinase cascade and a His/Asp two-component systemMOLECULAR MICROBIOLOGY, Issue 2 2005Renate Lux Summary Prokaryotes and eukaryotes have long been thought to use very different types of kinases (the His kinases of the ,bacterial' two-component systems versus the ,eukaryotic' Ser/Thr/Tyr kinases) to carry out signal transduction. This paradigm no longer holds true, because both systems are now found together in an increasing number of prokaryotic organisms and ,two-component' His kinase are present in eukaryotes. Pioneering work on bacterial protein serine threonine kinases (PSTKs) has been performed in Myxococcus xanthus, a soil bacterium with a complex life cycle that possesses orthologues of signalling-related kinases ,typical' of both the prokaryotic and the eukaryotic kingdoms. In the work reported in this volume of Molecular Microbiology, Nariya and Inouye describe a PSTK cascade that modulates the biochemical activity of MrpC, a CRP-like transcriptional regulator for essential developmental signalling pathways in M. xanthus whose transcription is under the control of a two-component system. This is the first report of both a functional PSTK cascade in bacteria and the use of both PSTK and two-component systems to control a single complex bacterial signalling event. [source] Cationic antimicrobial peptides activate a two-component regulatory system, PmrA-PmrB, that regulates resistance to polymyxin B and cationic antimicrobial peptides in Pseudomonas aeruginosaMOLECULAR MICROBIOLOGY, Issue 1 2003Joseph B. McPhee Summary The two-component regulatory system PhoP-PhoQ of Pseudomonas aeruginosa regulates resistance to cationic antimicrobial peptides, polymyxin B and aminoglycosides in response to low Mg2+ conditions. We have identified a second two-component regulatory system, PmrA-PmrB, that regulates resistance to polymyxin B and cationic antimicrobial peptides. This system responds to limiting Mg2+, and is affected by a phoQ, but not a phoP mutation. Inactivation of the pmrB sensor kinase and pmrA response regulator greatly decreased the expression of the operon encoding pmrA-pmrB while expression of the response regulator pmrA in trans resulted in increased activation suggesting that the pmrA-pmrB operon is autoregulated. Interposon mutants in pmrB, pmrA, or in an intergenic region upstream of pmrA-pmrB exhibited two to 16-fold increased susceptibility to polymyxin B and cationic antimicrobial peptides. The pmrA-pmrB operon was also found to be activated by a number of cationic peptides including polymyxins B and E, cattle indolicidin and synthetic variants as well as LL-37, a component of human innate immunity, whereas peptides with the lowest minimum inhibitory concentrations tended to be the weakest inducers. Additionally, we showed that the putative LPS modification operon, PA3552-PA3559, was also induced by cationic peptides, but its expression was only partially dependent on the PmrA-PmrB system. The discovery that the PmrA-PmrB two-component system regulates resistance to cationic peptides and that both it and the putative LPS modification system are induced by cationic antimicrobial peptides has major implications for the development of these antibiotics as a therapy for P. aeruginosa infections. [source] Binding of response regulator DegU to the aprE promoter is inhibited by RapG, which is counteracted by extracellular PhrG in Bacillus subtilisMOLECULAR MICROBIOLOGY, Issue 6 2003Mitsuo Ogura Summary We screened the putative rap-phr (response regulator aspartyl-phosphate phosphatase- phosphatase regulator) systems identified in the Bacillus subtilis genome for a rap gene that affects aprE (alkaline protease gene) expression by using a multicopy plasmid. We found that rapG was involved in the regulation of aprE, which belongs to the regulon of DegU, the response regulator of the DegS-DegU two-component system. Disruption of rapG and phrG resulted in enhancement and reduction of aprE-lacZ expression, respectively, suggesting that PhrG inhibits RapG activity. Addition of 1,30 nM of a synthetic pentapeptide (PhrG; NH2 -EKMIG-COOH) to the phrG disruptant completely rescued aprE-lacZ expression, indicating that the PhrG peptide is indeed involved in aprE-lacZ expression. Surprisingly, either introduction of multicopy phrG or addition of the PhrG peptide at high concentrations (100,300 nM) to the phrG cells decreased aprE-lacZ expression. These results are reminiscent of the previous observation that at higher concentrations the PhrC peptide inhibits srfA-lacZ expression directed by ComA, the regulator of the ComP-ComA two-component system. Because the Rap proteins belong to a family of aspartyl protein phosphatases, we tried to investigate the possible influence of RapG on dephosphorylation of DegU-P (phosphorylated DegU) in vitro. RapG, however, did not affect dephosphorylation of DegU-P under the adopted experimental conditions. Therefore, we hypothesized that RapG might inhibit the binding activity of DegU to the target promoters. We analysed the interaction of DegU and RapG using the aprE promoter and another target, a comK promoter. Gel shift analysis revealed that RapG served as the inhibitor of DegU binding to the promoter regions of aprE and comK and that this inhibition was counteracted by the PhrG peptide. [source] Mechanism of membrane fluidity optimization: isothermal control of the Bacillus subtilis acyl-lipid desaturaseMOLECULAR MICROBIOLOGY, Issue 5 2002Larisa E. Cybulski Summary The Des pathway of Bacillus subtilis regulates the expression of the acyl-lipid desaturase, Des, thereby controlling the synthesis of unsaturated fatty acids (UFAs) from saturated phospholipid precursors. Previously, we showed that the master switch for the Des pathway is a two-component regulatory system composed of a membrane-associated kinase, DesK, and a soluble transcriptional regulator, DesR, which stringently controls transcription of the des gene. Activation of this pathway takes place when cells are shifted to low growth temperature. Here, we report on the mechanism by which isoleucine regulates the Des pathway. We found that exogenous isoleucine sources, as well as its ,-keto acid derivative, which is a branched-chain fatty acid precursor, negatively regulate the expression of the des gene at 37°C. The DesK,DesR two-component system mediates this response, as both partners are required to sense and transduce the isoleucine signal at 37°C. Fatty acid profiles strongly indicate that isoleucine affects the signalling state of the DesK sensor protein by dramatically increasing the incorporation of the lower-melting-point anteiso-branched-chain fatty acids into membrane phospholipids. We propose that both a decrease in membrane fluidity at constant temperature and a temperature downshift induce des by the same mechanism. Thus, the Des pathway would provide a novel mechanism to optimize membrane lipid fluidity at a constant temperature. [source] The CitST two-component system regulates the expression of the Mg-citrate transporter in Bacillus subtilisMOLECULAR MICROBIOLOGY, Issue 4 2000Hiroki Yamamoto citS and citT genes encoding a new two-component system were identified in the 71° region between the pel and citM loci on the Bacillus subtilis chromosome. citS- and citT- deficient strains were unable to grow on minimal plates including citrate as a sole carbon source. In addition, a strain deficient in citM, which encodes the secondary transporter of the Mg-citrate complex, exhibited the same phenotype on this medium. Northern blot analysis revealed that citM was polycistronically transcribed with the downstream yflN gene, and that CitS and CitT were necessary for transcription of the citM,yflN operon. Upon addition of 2 mM citrate to DSM, this operon was strongly induced after the middle of the exponential growth phase in the wild type, but not in the citST double null mutant. Moreover, the transcription of this operon was completely repressed in the presence of 1% glucose. We found a sequence exhibiting homology to a catabolite-responsive element (cre) in the citM promoter region. Glucose repression was lost in ccpA and citM,cre mutants. From the result of a citM,promoter deletion experiment, putative CitT target sequences were found to be located around two regions, from ,62 to ,74 and from ,149 to ,189, relative to the citM start point. Furthermore, DNase I footprinting assays revealed that these two CitT target regions extended maximally from ,36 to ,84 and from ,168 to ,194. From these findings, we concluded that the expression of citM is positively regulated by the CitST system and negatively regulated by CcpA. [source] Block replacement policies for a two-component system with failure dependenceNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 1 2003Philip A. Scarf Abstract Block replacement and modified block replacement policies for two-component systems with failure dependence and economic dependence are considered in this paper. Opportunistic maintenance policies are also considered. Where tractable, long-run costs per unit time are calculated using renewal theory based arguments; otherwise simulation studies are carried out. The management implications for the adoption of the various policies are discussed. The usefulness of the results in the paper is illustrated through application to a particular two-component system. © 2002 Wiley Periodicals, Inc. Naval Research Logistics, 2003 [source] Proteomic analysis of Agrobacterium tumefaciens response to the vir gene inducer acetosyringonePROTEINS: STRUCTURE, FUNCTION AND BIOINFORMATICS, Issue 14 2006Erh-Min Lai Dr. Abstract Agrobacterium tumefaciens causes crown gall disease in a wide range of plants by transforming plants through the transfer and integration of its transferred DNA,(T-DNA) into the host genome. In the present study, we used two-dimensional gel electrophoresis to examine the protein expression profiles of A.,tumefaciens in response to the phenolic compound acetosyringone,(AS), a known plant-released virulence (vir) gene inducer. Using mass spectrometry, we identified 11,proteins consisting of 9,known AS-induced Vir proteins and 2,newly discovered AS-induced proteins, an unknown protein Y4mC (Atu6162) and a small heat shock protein HspL (Atu3887). Further expression analysis revealed that the AS-induced expression of Y4mC and HspL is regulated by the VirA/VirG two-component system. This report presents the first proteomics study successfully identifying both known and new AS-induced proteins that are implicated in Agrobacterium virulence. [source] Dynamics of protein uptake within the adsorbent particle during packed bed chromatographyBIOTECHNOLOGY & BIOENGINEERING, Issue 4 2002Jürgen Hubbuch Abstract A new experimental set-up for on-line visualization of the intra-particle uptake kinetics during packed bed chromatography has been designed and tested. Confocal laser scanning microscopy was used to analyze the dynamics of protein adsorption to porous stationary phases. In combination with this, a flow cell was developed that could be packed with chromatography media and operated as a fully functional mini-scale chromatography column. Adsorption profiles of single- and two-component mixtures containing BSA and IgG 2a during packed bed cation-exchange chromatography were investigated. The two proteins appear to exhibit different transport characteristics. For BSA a classical "shrinking core" behavior could be detected. The profiles obtained during IgG 2a adsorption point toward a different transport mode, which deviates from the classical pore-diffusion picture. For the two-component system, a superposition of the single-component profiles combined with a classical displacement of the weaker bound protein species was found. The results indicate that depending on the adsorbed protein the uptake can vary tremendously, even for adsorption to the same chromatographic support. It is clearly shown that the new microcolumn allows in situ quantitative investigations of protein adsorption dynamics within a single particle, which adds a new tool to the available methods for characterizing and optimizing protein adsorption chromatography. © 2002 Wiley Periodicals, Inc. Biotechnol Bioeng 80: 359,368, 2002. [source] Cadmium-regulated gene fusions in Pseudomonas fluorescensENVIRONMENTAL MICROBIOLOGY, Issue 4 2000Silvia Rossbach To study the mechanisms soil bacteria use to cope with elevated concentrations of heavy metals in the environment, a mutagenesis with the lacZ -based reporter gene transposon Tn5 -B20 was performed. Random gene fusions in the genome of the common soil bacterium Pseudomonas fluorescens strain ATCC 13525 were used to create a bank of 5000 P. fluorescens mutants. This mutant bank was screened for differential gene expression in the presence of the toxic metal cadmium. Fourteen mutants were identified that responded with increased or reduced gene expression to the presence of cadmium. The mutants were characterized with respect to their metal-dependent gene expression and their metal tolerance. Half the identified mutants reacted with differential gene expression specifically to the metal cadmium, whereas some of the other mutants also responded to elevated concentrations of copper and zinc ions. One of the mutants, strain C8, also showed increased gene expression in the presence of the solvent ethanol, but otherwise no overlap between cadmium-induced gene expression and general stress response was detected. Molecular analysis of the corresponding genetic loci was performed using arbitrary polymerase chain reaction (PCR), DNA sequencing and comparison of the deduced protein products with sequences deposited in genetic databases. Some of the genetic loci targeted by the transposon did not show any similarities to any known genes; thus, they may represent ,novel' loci. The hypothesis that genes that are differentially expressed in the presence of heavy metals play a role in metal tolerance was verified for one of the mutants. This mutant, strain C11, was hypersensitive to cadmium and zinc ions. In mutant C11, the transposon had inserted into a genetic region displaying similarity to genes encoding the sensor/regulator protein pairs of two-component systems that regulate gene expression in metal-resistant bacteria, including czcRS of Ralstonia eutropha, czrRS of Pseudomonas aeruginosa and copRS of Pseudomonas syringae. Although the P. fluorescens strain used in this study had not been isolated from a metal-rich environment, it nevertheless contained at least one genetic region enabling it to cope with elevated concentrations of heavy metals. [source] Listeria monocytogenes response regulators important for stress tolerance and pathogenesisFEMS MICROBIOLOGY LETTERS, Issue 1 2001Birgitte H. Kallipolitis Abstract Environmental sensing by two-component signal transduction systems is likely to play a role for growth and survival of Listeria monocytogenes both during transmission in food products and within a host organism. Two-component systems typically consist of a membrane-associated sensor histidine kinase and a gene regulatory protein, the response regulator (RR). We have identified seven putative RR genes in L. monocytogenes LO28 by PCR using degenerate oligonucleotide primers. By insertional inactivation we obtained data suggesting that three of the putative RRs contribute to the pathogenicity of L. monocytogenes in mice. Strikingly, the mutants that were attenuated in virulence also had a decreased ability to grow in the presence of various stress conditions potentially encountered in an infection process. Thus, our data point to a connection between the ability of the putative two-component systems to sense and respond to certain environmental stimuli, and the virulence of L. monocytogenes. [source] Regulation of virulence and antibiotic resistance by two-component regulatory systems in Pseudomonas aeruginosaFEMS MICROBIOLOGY REVIEWS, Issue 2 2009W. James Gooderham Abstract The Gram-negative opportunistic pathogen Pseudomonas aeruginosa ubiquitously inhabits soil and water habitats and also causes serious, often antibiotic resistant, infections in immunocompromised patients (e.g. cystic fibrosis). This versatility is mediated in part by a large repertoire of two-component regulatory systems that appear instrumental in the regulation of both virulence processes and resistance to antimicrobials. Major two-component regulatory system proteins demonstrated to regulate these diverse processes include PhoP,PhoQ, GacA,GacS, RetS, LadS, and AlgR, among others. Here, we summarize the current body of knowledge of these and other two-component systems that provides insight into the complex regulation of virulence and resistance in P. aeruginosa. [source] Impact of Thermal Diffusion on Densification During SPSJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 2009Eugene A. Olevsky Spark-plasma sintering (SPS) has the potential for rapid (with heating rates reaching several hundred K/min) and efficient consolidation of a broad spectrum of powder materials. Possible mechanisms of the enhancement of consolidation in SPS versus conventional techniques of powder processing are categorized with respect to their thermal and athermal nature. This paper analyzes the influence of thermal diffusion, which is an SPS consolidation enhancement factor of a thermal nature. The Ludwig,Soret effect of thermal diffusion causes concentration gradients in two-component systems subjected to a temperature gradient. The thermal diffusion-based constitutive mechanism of sintering results from the additional driving force instigated by spatial temperature gradients, which cause vacancy diffusion. This mechanism is a commonly omitted addition to the free-surface curvature-driven diffusion considered in conventional sintering theories. The interplay of three mechanisms of material transport during SPS is considered: surface tension- and external stress-driven grain-boundary diffusion, surface tension- and external stress-driven power-law creep, and temperature gradient-driven thermal diffusion. It is shown that the effect of thermal diffusion can be significant for ceramic powder systems. Besides SPS, the results obtained are applicable to the ample range of powder consolidation techniques, which involve high local temperature gradients. The case study conducted on the alumina powder SPS demonstrates the correlation between the modeling and experimental data. It is noted that this study considers only one of many possible mechanisms of the consolidation enhancement during SPS. Further efforts on the modeling of field-assisted powder processing are necessary. [source] Asymmetric cross-regulation between the nitrate-responsive NarX,NarL and NarQ,NarP two-component regulatory systems from Escherichia coli K-12MOLECULAR MICROBIOLOGY, Issue 2 2010Chris E. Noriega Summary The NarX,NarL and NarQ,NarP sensor,response regulator pairs control Escherichia coli gene expression in response to nitrate and nitrite. Previous analysis suggests that the Nar two-component systems form a cross-regulation network in vivo. Here we report on the kinetics of phosphoryl transfer between different sensor,regulator combinations in vitro. NarX exhibited a noticeable kinetic preference for NarL over NarP, whereas NarQ exhibited a relatively slight kinetic preference for NarL. These findings were substantiated in reactions containing one sensor and both response regulators, or with two sensors and a single response regulator. We isolated 21 NarX mutants with missense substitutions in the cytoplasmic central and transmitter modules. These confer phenotypes that reflect defects in phospho-NarL dephosphorylation. Five of these mutants, all with substitutions in the transmitter DHp domain, also exhibited NarP-blind phenotypes. Phosphoryl transfer assays in vitro confirmed that these NarX mutants have defects in catalysing NarP phosphorylation. By contrast, the corresponding NarQ mutants conferred phenotypes indicating comparable interactions with both NarP and NarL. Our overall results reveal asymmetry in the Nar cross-regulation network, such that NarQ interacts similarly with both response regulators, whereas NarX interacts preferentially with NarL. [source] Threonine phosphorylation prevents promoter DNA binding of the Group B Streptococcus response regulator CovRMOLECULAR MICROBIOLOGY, Issue 6 2009Wan-Jung Lin Summary All living organisms communicate with the external environment for their survival and existence. In prokaryotes, communication is achieved by two-component systems (TCS) comprising histidine kinases and response regulators. In eukaryotes, signalling is accomplished by serine/threonine and tyrosine kinases. Although TCS and serine/threonine kinases coexist in prokaryotes, direct cross-talk between these families was first described in Group B Streptococcus (GBS). A serine/threonine kinase (Stk1) and a TCS (CovR/CovS) co-regulate toxin expression in GBS. Typically, promoter binding of regulators like CovR is controlled by phosphorylation of the conserved active site aspartate (D53). In this study, we show that Stk1 phosphorylates CovR at threonine 65. The functional consequence of threonine phosphorylation of CovR in GBS was evaluated using phosphomimetic and silencing substitutions. GBS encoding the phosphomimetic T65E allele are deficient for CovR regulation unlike strains encoding the non-phosphorylated T65A allele. Further, compared with wild-type or T65A CovR, the T65E CovR is unable to bind promoter DNA and is decreased for phosphorylation at D53, similar to Stk1-phosphorylated CovR. Collectively, we provide evidence for a novel mechanism of response regulator control that enables GBS (and possibly other prokaryotes) to fine-tune gene expression for environmental adaptation. [source] Bacitracin sensing in Bacillus subtilisMOLECULAR MICROBIOLOGY, Issue 3 2008Eva Rietkötter Summary The extracellular presence of antibiotics is a common threat in microbial life. Their sensitive detection and subsequent induction of appropriate resistance mechanisms is therefore a prerequisite for survival. The bacitracin stress response network of Bacillus subtilis consists of four signal-transducing systems, the two-component systems (TCS) BceRS, YvcPQ and LiaRS, and the extracytoplasmic function (ECF) , factor ,M. Here, we investigated the mechanism of bacitracin perception and the response hierarchy within this network. The BceRS,BceAB TCS/ABC transporter module is the most sensitive and efficient bacitracin resistance determinant. The ABC transporter BceAB not only acts as a bacitracin detoxification pump, but is also crucial for bacitracin sensing, indicative of a novel mechanism of stimulus perception, conserved in Firmicutes bacteria. The Bce system seems to respond to bacitracin directly (drug sensing), whereas the LiaRS TCS and ,M respond only at higher concentrations and indirectly to bacitracin action (damage sensing). The YvcPQ,YvcRS system is subject to cross-activation via the paralogous Bce system, and is therefore only indirectly induced by bacitracin. The bacitracin stress response network is optimized to respond to antibiotic gradients in a way that maximizes the gain and minimizes the costs of this stress response. [source] A novel bacterial signalling system with a combination of a Ser/Thr kinase cascade and a His/Asp two-component systemMOLECULAR MICROBIOLOGY, Issue 2 2005Renate Lux Summary Prokaryotes and eukaryotes have long been thought to use very different types of kinases (the His kinases of the ,bacterial' two-component systems versus the ,eukaryotic' Ser/Thr/Tyr kinases) to carry out signal transduction. This paradigm no longer holds true, because both systems are now found together in an increasing number of prokaryotic organisms and ,two-component' His kinase are present in eukaryotes. Pioneering work on bacterial protein serine threonine kinases (PSTKs) has been performed in Myxococcus xanthus, a soil bacterium with a complex life cycle that possesses orthologues of signalling-related kinases ,typical' of both the prokaryotic and the eukaryotic kingdoms. In the work reported in this volume of Molecular Microbiology, Nariya and Inouye describe a PSTK cascade that modulates the biochemical activity of MrpC, a CRP-like transcriptional regulator for essential developmental signalling pathways in M. xanthus whose transcription is under the control of a two-component system. This is the first report of both a functional PSTK cascade in bacteria and the use of both PSTK and two-component systems to control a single complex bacterial signalling event. [source] Autoinduction and signal transduction in the regulation of staphylococcal virulenceMOLECULAR MICROBIOLOGY, Issue 6 2003Richard P. Novick Summary The accessory genes of Staphylococcus aureus, in-cluding those involved in pathogenesis, are controlled by a complex regulatory network that includes at least four two-component systems, one of which, agr, is a quorum sensor, an alternative sigma factor and a large set of transcription factors, including at least two of the superantigen genes, tst and seb. These regulatory genes are hypothesized to act in a time- and population density-dependent manner to integrate signals received from the external environment with the internal metabolic machinery of the cell, in order to achieve the production of particular subsets of accessory/virulence factors at the time and in quantities that are appropriate to the needs of the organism at any given location. From the standpoint of pathogenesis, the regulatory agenda is presumably tuned to particular sites in the host organism. To address this hypothesis, it will be necessary to understand in considerable detail the regulatory interactions among the organism's numerous controlling systems. This review is an attempt to integrate a large body of data into the beginnings of a model that will hopefully help to guide research towards a full-scale test. [source] Role of two component signaling response regulators in acid tolerance of Streptococcus mutansMOLECULAR ORAL MICROBIOLOGY, Issue 2 2009M. Kawada-Matsuo Introduction:, In bacteria, two-component systems (TCS) involving the products of a histidine kinase gene (hk) and a response regulator gene (rr) play important roles in adaptation to environmental changes. Fourteen hk - rr homologs and one orphan rr homolog were identified in the Streptococcus mutans UA159 genome database. There have been no comprehensive evaluations of the roles of rr homologs in the acid tolerance of S. mutans. Methods:, The TCS genes (tcs) of S. mutans were designated smtcs01,15. Mutants of S. mutans UA159 with deletions of rr and hk-rr were constructed. Acid tolerance was evaluated by comparing the doubling times at pH 7.2 and pH 5.5 between the wild-type and mutant strains. Results:, Excluding smtcs10 and 12, for which viable mutants could not be obtained, a total of 13 rr deletion mutants were constructed. The rr deletions in smtcs03, 05, 08, and 13 resulted in diminished acid tolerance in comparison with UA159. The hk-rr double-mutants exhibited acid sensitivity levels similar to those of the corresponding rr mutants. The results of the present study reveal the involvement of the rr genes of smtcs03 and 05 in acid tolerance. Deletion of hk and/or rr in smtcs03 generated an acid-sensitive phenotype. In contrast, for smtcs05, while deletion of rr resulted in reduced acid tolerance, a single-deletion of hk had no effect on acid tolerance. Conclusions:, We implicated two rr genes in the acid tolerance of S. mutans. In particular, smtcs05 is a novel tcs, the sole rr of which is involved in the acid tolerance of S. mutans. [source] Block replacement policies for a two-component system with failure dependenceNAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 1 2003Philip A. Scarf Abstract Block replacement and modified block replacement policies for two-component systems with failure dependence and economic dependence are considered in this paper. Opportunistic maintenance policies are also considered. Where tractable, long-run costs per unit time are calculated using renewal theory based arguments; otherwise simulation studies are carried out. The management implications for the adoption of the various policies are discussed. The usefulness of the results in the paper is illustrated through application to a particular two-component system. © 2002 Wiley Periodicals, Inc. Naval Research Logistics, 2003 [source] The FliK protein and flagellar hook-length controlPROTEIN SCIENCE, Issue 5 2007Richard C. Waters Abstract The bacterial flagellum is a highly complex prokaryotic organelle. It is the motor that drives bacterial motility, and despite the large amount of energy required to make and operate flagella, motile organisms have a strong adaptive advantage. Flagellar biogenesis is both complex and highly coordinated and it typically involves at least three two-component systems. Part of the flagellum is a type III secretion system, and it is via this structure that flagellar components are exported. The assembly of a flagellum occurs in a number of stages, and the "checkpoint control" protein FliK functions in this process by detecting when the flagellar hook substructure has reached its optimal length. FliK then terminates hook export and assembly and transmits a signal to begin filament export, the final stage in flagellar biosynthesis. As yet the exact mechanism of how FliK achieves this is not known. Here we review what is known of the FliK protein and discuss the evidence for and against the various hypotheses that have been proposed in recent years to explain how FliK controls hook length, FliK as a molecular ruler, the measuring cup theory, the role of the FliK N terminus, the infrequent molecular ruler theory, and the molecular clock theory. [source] Genetic analysis of response regulator activation in bacterial chemotaxis suggests an intermolecular mechanismPROTEIN SCIENCE, Issue 11 2002Sandra Da Re Abstract Response regulator proteins of two-component systems are usually activated by phosphorylation. The phosphorylated response regulator protein CheY,P mediates the chemotaxis response in Escherichia coli. We performed random mutagenesis and selected CheY mutants that are constitutively active in the absence of phosphorylation. Although a single amino acid substitution can lead to constitutive activation, no single DNA base change can effect such a transition. Numerous different sets of mutations that activate in synergy were selected in several different combinations. These mutations were all located on the side of CheY defined by ,4, ,5, ,5, and ,1. Our findings argue against the two-state hypothesis for response regulator activation. We propose an alternative intermolecular mechanism that involves a dynamic interplay between response regulators and their effector targets. [source] The maize transfer cell-specific type-A response regulator ZmTCRR-1 appears to be involved in intercellular signallingTHE PLANT JOURNAL, Issue 1 2006Luis M. Muñiz Summary Response regulators are signal-transduction molecules present in bacteria, yeast and plants, acting as relays for environmental challenges. This paper reports the characterization of a Zea mays gene, ZmTCRR-1, that codes for a member of the type-A response regulator class of proteins. The gene was found to be expressed exclusively in the endosperm transfer-cell layer 8,14 days after pollination, when transfer-cell differentiation is most active. The promoter of ZmTCRR-1 was strongly transactivated in heterologous systems by the transfer cell-specific transcription factor ZmMRP-1. The ZmTCRR-1 protein was detected not only in the transfer-cell layer, but also in the conductive tissue deep inside the endosperm, where there is no transcription of the gene. This suggests that two-component systems might be involved in intercellular signal transmission, in contrast to the generally held belief that these systems are involved only in cell-autonomous pathways. [source] | ||||||||||||||||