Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.3.1.184 (LasR)
 897 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The elastolytic activity of the opportunistic pathogen Pseudomonas aeruginosa is due to the combined activities of at least three secreted proteins: elastase, LasA and alkaline protease. Transcription of both the lasA gene and the elastase structural gene, lasB, requires the transcriptional activator LasR. In order to localize the promoter elements involved in lasA expression, the transcription start point (tsp) for lasA was localized by S1 protection and primer extension analysis. The DNA sequence of the region upstream from the tsp was determined, and a putative sigma promoter was identified. Sequence comparison with the lasB promoter region revealed two areas of considerable homology which could act as potential binding sites for LasR or other, as yet unidentified, regulatory proteins.
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PMID:Pseudomonas aeruginosa lasA gene: determination of the transcription start point and analysis of the promoter/regulatory region. 833 50

The lasR gene of Pseudomonas aeruginosa is required for transcription of the genes for elastase (lasB) and LasA protease (lasA), two proteases associated with virulence. We report here that the alkaline protease gene (apr) also requires the lasR gene for transcription. Alkaline protease mRNA was absent in the lasR mutant PAO-R1 and present when an intact lasR gene was supplied in trans as determined by Northern (RNA) analysis. The lasR gene also enhances exotoxin A production. Exotoxin A activity in supernatants of PAO-R1 were 30% less than in supernatants of the parental strain, PAO-SR. Multiple copies of lasR in trans in PAO-R1 in increased toxin A activity to twice the parental levels. Analysis of PAO-R1 containing the toxA promoter fused to beta-galactosidase suggests that LasR acts at the toxA promoter or at upstream toxA mRNA sequences. beta-Galactosidase activity was approximately 40% lower in PAO-R1 than in the parental strain, PAO-SR. Furthermore, the effect of LasR on the toxA promoter is not due to the stimulation of transcription of regA, a transcriptional activator of toxA. No difference in chloramphenicol acetyltransferase (CAT) activity was noted between PAO-SR and PAO-R1 containing transcriptional regA promoter-CAT gene fusions. These results broaden the regulatory dominion of lasR and suggest that the lasR gene plays a global role in P. aeruginosa pathogenesis.
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PMID:LasR of Pseudomonas aeruginosa is a transcriptional activator of the alkaline protease gene (apr) and an enhancer of exotoxin A expression. 845 22

Pseudomonas aeruginosa is an opportunistic human pathogen that causes a variety of infections in immunocompromised hosts and individuals with cystic fibrosis. Expression of elastase, one of the virulence factors produced by this organism, requires the transcriptional activator LasR. Experiments with gene fusions show that gene lasl is essential for high expression of elastase. The lasl gene is involved in the synthesis of a diffusible molecule termed Pseudomonas autoinducer (PAI). PAI provides P. aeruginosa with a means of cell-to-cell communication that is required for the expression of virulence genes and may provide a target for therapeutic approaches.
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PMID:Expression of Pseudomonas aeruginosa virulence genes requires cell-to-cell communication. 849 56

A series of structural analogs of the Pseudomonas aeruginosa autoinducer [PAI, N-3-oxo-dodecanoyl homoserine lactone] were obtained and tested for their ability to act as autoinducers in stimulating the expression of the gene for elastase (lasB) by measuring beta-galactosidase production from a lasB-lacZ gene fusion in the presence of the transcriptional activator LasR. The data suggest that the length of the acyl side chain of the autoinducer molecule is the most critical factor for activity. Replacement of the ring O by S in the homoserine lactone moiety can be tolerated. Tritium-labelled PAI ([3H]PAI) was synthesized and used to demonstrate the association of [3H]PAI with cells overexpressing LasR. The PAI analogs were also tested for their ability to compete with [3H]PAI for binding of LasR. Results from the competition assays suggest that once again the length of the acyl side chain appears to be crucial for antagonist activity. The presence of the 3-oxo moiety also plays a significant role in binding since analogs which lacked this moiety were much less effective in blocking binding of [3H]PAI. All analogs demonstrating competition with PAI in binding to LasR also exhibited the ability to activate lasB expression, suggesting that they are functional analogs of PAI.
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PMID:Functional analysis of the Pseudomonas aeruginosa autoinducer PAI. 883 Jun 97

The importance of accurate demographic information is reflected in the United States Constitution, Article 1, which provides for a decennial census of this country's human population. Bacteria also conduct a census of their population and do so more frequently, more efficiently, and as far we know, with little if any of the political contentiousness caused by human demographers. Many examples have been found of particular bacterial genes, operons, or regulons that are expressed preferentially at high cell densities. Many of these are regulated by proteins related to the LuxR and LuxI proteins of Vibrio fischeri, and by a diffusible pheromone called an autoinducer. LuxR and LuxI and their cognate autoinducer (3-oxohexanoyl homoserine lactone, designated VAI-1) provide an important model to describe the functions of this family of proteins. LuxR is a VAI-1 receptor and a VAI-1-dependent transcriptional activator, and LuxI directs the synthesis of VAI-1. VAI-1 diffuses across the bacterial envelope, and intracellular concentrations of it are therefore strongly increased by nearby VAI-1-producing bacteria. Similar systems regulate pathogenesis factors in Pseudomonas aeruginosa and Erwinia spp., as well as T1 plasmid conjugal transfer in Agrobacterium tumefaciens, and many other genes in numerous genera of gram-negative bacteria. Genetic analyses of these systems have revealed a high degree of functional conservation, while also uncovering features that are unique to each.
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PMID:Census and consensus in bacterial ecosystems: the LuxR-LuxI family of quorum-sensing transcriptional regulators. 890 97

The production of several virulence factors by Pseudomonas aeruginosa is controlled according to cell density through two quorum-sensing systems, las and rhl. The las system is comprised of the transcriptional activator protein LasR and of LasI, which directs the synthesis of the autoinducer PAI-1. Similarly, the rhl system consists of the transcriptional activator protein RhlR and of RhlI, which directs synthesis of the autoinducer PAI-2 (formerly referred to as factor 2). To study the interrelation between the two P. aeruginosa quorum-sensing systems, we fused a lacZ reporter gene to lasR, rhlR, and rhlA and monitored expression of these three genes under various conditions. Our data indicate that lasR and rhlR are expressed in a growth-dependent manner, with activation of each gene occurring during the last half of log-phase growth. We also show that the las quorum-sensing system controls the rhl quorum-sensing system in two ways. First, we found that LasR and PAI-1 activated rhlR transcription. Second, we showed that PAI-1 blocked PAI-2 from binding to RhlR, thereby inhibiting the expression of rhlA. Our data thus indicate that the las system exerts two levels of control on RhlR, transcriptional and posttranslational.
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PMID:Regulation of las and rhl quorum sensing in Pseudomonas aeruginosa. 915 Feb 5

The global activator GacA, a highly conserved response regulator in Gram-negative bacteria, is required for the production of exoenzymes and secondary metabolites in Pseudomonas spp. The gacA gene of Pseudomonas aeruginosa PAO1 was isolated and its role in cell-density-dependent gene expression was characterized. Mutational inactivation of gacA resulted in delayed and reduced formation of the cell-density signal N-butyryl-L-homoserine lactone (BHL), of the cognate transcriptional activator RhIR (VsmR), and of the transcriptional activator LasR, which is known to positively regulate RhIR expression. Amplification of gacA on a multicopy plasmid caused precocious and enhanced production of BHL, RhIR and LasR. In parallel, the gacA gene dosage markedly influenced the BHL/RhIR-dependent formation of the cytotoxic compounds pyocyanin and cyanide and the exoenzyme lipase. However, the concentrations of another known cell-density signal of P. aeruginosa, N-oxododecanoyl-L-homoserine lactone, did not always match BHL concentrations. A model accounting for these observations places GacA function upstream of LasR and RhIR in the complex, cell-density-dependent signal-transduction pathway regulating several exoproducts and virulence factors of P. aeruginosa via BHL.
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PMID:The global activator GacA of Pseudomonas aeruginosa PAO positively controls the production of the autoinducer N-butyryl-homoserine lactone and the formation of the virulence factors pyocyanin, cyanide, and lipase. 915 18

Pseudomonas aeruginosa controls several genes in a cell density-dependent manner through a phenomenon termed quorum sensing. The transcriptional activator protein of the las quorum-sensing system is encoded for by the lasR gene, which is at the top of a quorum-sensing hierarchy. The activation of LasR as a transcriptional activator induces the expression of multiple genes that code for factors important for virulence, and rhlR, which encodes the transcriptional activator protein of the P. aeruginosa rhl quorum-sensing system. Elucidating the method of lasR regulation is crucial to understanding P. aeruginosa quorum sensing. In this report, we present studies on the transcriptional control of lasR. We identified two distinct transcriptional start sites for lasR that were located 201 bp (transcript T1) and 231 bp (transcript T2) upstream from the lasR start of translation. With the use of transcriptional lasRp-lacZ fusions, we showed that in P. aeruginosa, lasR expression is cell density dependent. This gene was expressed at a basal level until it was induced during the second half of log-phase growth, with expression becoming maximal during stationary-phase growth. We also showed that lasR expression was regulated through the cyclic AMP receptor protein (CRP)-binding consensus sequence in its promoter region. Our results from P. aeruginosa mutant studies and gel retardation assays indicated that this regulation was mediated by Vfr, a homolog of the Escherichia coli CRP.
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PMID:Vfr controls quorum sensing in Pseudomonas aeruginosa. 919 Aug 8

The roles of the Pseudomonas aeruginosa proteases LasB (elastase) and LasA and the transcriptional activator LasR, which regulates the expression of these proteases, were evaluated in a murine model of P. aeruginosa corneal infection. In scarified corneas, P. aeruginosa PAO-A1 (LasA negative) or PAO-B1A1 (LasB and LasA negative) at a dose of 10(8) CFU per eye caused very mild or no disease following infection; however, the defect in PAO-A1 could not be complemented by supplying a functional copy of lasA either on a plasmid or inserted into the chromosome. In contrast, PAO-B1 (LasB negative) colonized the cornea and caused disease equal in severity to disease caused by the parental strain, PAO1-I. Although LasR is a known regulator of lasA expression, PAO-R1, a lasR-negative derivative of PAO1-I, was as virulent as the parental strain during corneal infection. When transcriptional fusion plasmids were used to quantify the expression of the lasB and lasA genes in P. aeruginosa PAO1-I and PAO-R1, the lasB::lacZ fusion in PAO-R1 showed only 3.5% as much activity as it did in PAO1-I, while the activity of the lasA::lacZ fusion in PAO-R1 was 27.8% of that in PAO1-I. Coadministration of 5 microg of purified LasA protease with PAO-A1 did not reconstitute a wild-type infection. This treatment produced an acute toxic reaction leading to prolonged eyelid closure without inflammatory destruction of the cornea that was similar to that observed when LasA was administered alone. These results indicate that insertional inactivation of lasA renders P. aeruginosa avirulent in a murine model of keratitis and that neither LasR nor elastase production is required for the establishment and maintenance of corneal infection. However, the lack of virulence of the LasA-deficient strains cannot be ascribed with certainty to the deficiency of LasA from the available data.
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PMID:Contribution of proteases and LasR to the virulence of Pseudomonas aeruginosa during corneal infections. 923 58

Two quorum-sensing systems (las and rhl) regulate virulence gene expression in Pseudomonas aeruginosa. The las system consists of a transcriptional activator, LasR, and LasI, which directs the synthesis of the autoinducer N-(3-oxododecanoyl) homoserine lactone (PAI-1). Induction of lasB (encoding elastase) and other virulence genes requires LasR and PAI-1. The rhl system consists of a putative transcriptional activator, RhlR, and RhlI, which directs the synthesis of N-butyryl homoserine lactone (PAI-2). Rhamnolipid production in P. aeruginosa has been reported to require both the rhl system and rhlAB (encoding a rhamnosyltransferase). Here we report the generation of a delta lasI mutant and both delta lasI delta rhlI and delta lasR rhlR::Tn501 double mutants of strain PAO1. Rhamnolipid production and elastolysis were reduced in the delta lasI single mutant and abolished in the double-mutant strains. rhlAB mRNA was not detected in these strains at mid-logarithmic phase but was abundant in the parental strain. Further RNA analysis of the wild-type strain revealed that rhlAB is organized as an operon. The rhlAB transcriptional start was mapped, and putative sigma 54 and sigma 70 promoters were identified upstream. To define components required for rhlAB expression, we developed a bioassay in Escherichia coli and demonstrated that PAI-2 and RhlR are required and sufficient for expression of rhlA. To characterize the putative interaction between PAI-2 and RhlR, we demonstrated that [3H]PAI-2 binds to E. coli cells expressing RhlR and not to those expressing LasR. Finally, the specificity of the las and rhl systems was examined in E. coli bioassays. The las system was capable of mildly activating rhlA, and similarly, the rhl system partly activated lasB. However; these effects were much less than the activation of rhlA by the rhl system and lasB by the las system. The results presented here further characterize the roles of the rhl and las quorum-sensing systems in virulence gene expression.
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PMID:Roles of Pseudomonas aeruginosa las and rhl quorum-sensing systems in control of elastase and rhamnolipid biosynthesis genes. 929 32


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