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)

N-Acylhomoserine lactone (acyl-HSL)-mediated gene expression, also called autoinduction, is conserved among diverse gram-negative bacteria. In the paradigm Vibrio fischeri system, bioluminescence is autoinducible, and the lux operon requires the transcriptional activator LuxR and the acyl-HSL autoinducer for expression. The production of the acyl-HSL signal molecule is conferred by the luxI gene, and luxR encodes the transcriptional regulator. We show here that Erwinia stewartii, the etiological agent of Stewart's wilt of sweet corn, synthesizes an acyl-HSL. Mass spectral analysis identified the signal molecule as N-(-3-oxohexanoyl)-L-homoserine lactone, which is identical to the V. fischeri autoinducer. We have cloned and sequenced the gene that confers acyl-HSL biosynthesis, called esaI, and the linked gene, esaR, that encodes a gene regulator. The two genes are convergently transcribed and show an unusual overlap of 31 bp at their 3' ends. Sequence analysis indicates that EsaI and EsaR are homologs of LuxI and LuxR, respectively. EsaR can repress its own expression but seems not to regulate the expression of esaI. The untranslated 5' region of esaR contains an inverted repeat with similarity to the lux box-like elements located in the promoter regions of other gene systems regulated by autoinduction. However, unlike the other systems, in which the inverted repeats are located upstream of the -35 promoter elements, the esaR-associated repeat overlaps a putative -10 element. We mutagenized the esaI gene in E. stewartii by gene replacement. The mutant no longer produced detectable levels of the acyl-HSL signal, leading to a concomitant loss of extracellular polysaccharide capsule production and pathogenicity. Both phenotypes were restored by complementation with esal or by exogenous addition of the acyl-HSL.
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PMID:Capsular polysaccharide biosynthesis and pathogenicity in Erwinia stewartii require induction by an N-acylhomoserine lactone autoinducer. 766 77

The production of phenazine (Ph) antibiotics in Pseudomonas aureofaciens (Pau) 30-84 is positively regulated by PhzR, a protein belonging to the LuxR family of transcriptional activators. We have now identified phzI, a second gene required for PH production. The product of phzI is a member of the LuxI family of N-acyl-homoserine lactone (N-acyl-HSL) synthases. Inactivation of phzI results in the loss of Ph production in Pau 30-84. The presence of phzI in Escherichia coli is sufficient for the production of a diffusible signal which activates phzB expression in Pau 30-84 and traA expression in a N-acyl-HSL-dependent reporter strain of Agrobacterium tumefaciens. In addition, synthetic N-(3-oxohexanoyl)-L-HSL induces phzB expression in Pau 30-84. These results suggest that Pau 30-84 produces a N-acyl-HSL signal that regulates Ph production, and that phzI plays a central role in this signaling pathway.
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PMID:The phzI gene of Pseudomonas aureofaciens 30-84 is responsible for the production of a diffusible signal required for phenazine antibiotic production. 862 64

Bacteria employ autoinduction systems to sense the onset of appropriate cell density for expression of developmental genes. In many gram-negative bacteria, autoinduction involves the production of and response to diffusible acylated-homoserine lactones (acyl-HSLs) and is mediated by members of the LuxR and LuxI families. Ralstonia (Pseudomonas) solanacearum, a phytopathogenic bacterium that appears to autoregulate its virulence genes, produces compounds that promote expression of several heterologous acyl-HSL-responsive reporter gene constructs. High-pressure liquid chromatography of highly concentrated ethyl acetate extracts revealed that culture supernatants of strain AW1 contained two compounds with retention times similar to N-hexanoyl- and N-octanoyl-HSL. To investigate the role of these acyl-HSLs in R. solanacearum virulence gene expression, transposon mutants that were deficient for inducing an acyl-HSL-responsive reporter in Agrobacterium tumefaciens were generated. Three loci involved in normal acyl-HSL production were identified, one of which was shown to contain the divergently transcribed solR and solI genes, the luxR and luxI homologs, respectively. A 4.1-kb fragment containing solR and solI enabled all of the mutants (regardless of the locus inactivated) and a naturally acyl-HSL-defective strain of R. solanacearum to produce acyl-HSLs. Inactivation of solI abolished production of all detectable acyl-HSLs but affected neither the expression of virulence genes in culture nor the ability to wilt tomato plants. AW1 has a functional autoinduction system, because (i) expression of solI required SolR and acyl-HSL and (ii) expression of a gene linked to solR and solI, designated aidA, was acyl-HSL dependent. Because AidA has no homologs in the protein databases, its discovery provided no clues as to the role of acyl-HSLs in R. solanacearum gene regulation. However, expression of solR and solI required the global LysR-type virulence regulator PhcA, and both solR and solI exhibited a cell density-associated pattern of expression similar to other PhcA-regulated genes. The acyl-HSL-dependent autoinduction system in R. solanacearum is part of a more complex autoregulatory hierarchy, since the transcriptional activity of PhcA is itself controlled by a novel autoregulatory system that responds to 3-hydroxypalmitic acid methyl ester.
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PMID:Hierarchical autoinduction in Ralstonia solanacearum: control of acyl-homoserine lactone production by a novel autoregulatory system responsive to 3-hydroxypalmitic acid methyl ester. 937 57

Acyl homoserine lactones (acyl-HSLs) are important intercellular signaling molecules used by many bacteria to monitor their population density in quorum-sensing control of gene expression. These signals are synthesized by members of the LuxI family of proteins. To understand the mechanism of acyl-HSL synthesis we have purified the Pseudomonas aeruginosa RhlI protein and analyzed the kinetics of acyl-HSL synthesis by this enzyme. Purified RhlI catalyzes the synthesis of acyl-HSLs from acyl-acyl carrier proteins and S-adenosylmethionine. An analysis of the patterns of product inhibition indicated that RhlI catalyzes signal synthesis by a sequential, ordered reaction mechanism in which S-adenosylmethionine binds to RhlI as the initial step in the enzymatic mechanism. Because pathogenic bacteria such as P. aeruginosa use acyl-HSL signals to regulate virulence genes, an understanding of the mechanism of signal synthesis and identification of inhibitors of signal synthesis has implications for development of quorum sensing-targeted antivirulence molecules.
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PMID:Acyl homoserine-lactone quorum-sensing signal generation. 1020 Feb 67

The rhi genes of Rhizobium leguminosarum biovar viciae are expressed in the rhizosphere and play a role in the interaction with legumes, such as the pea. Previously (K. M. Gray, J. P. Pearson, J. A. Downie, B. E. A. Boboye, and E. P. Greenberg, J. Bacteriol. 178:372-376, 1996) the rhiABC operon had been shown to be regulated by RhiR and to be induced by added N-(3-hydroxy-7-cis-tetradecenoyl)-L-homoserine lactone (3OH, C14:1-HSL). Mutagenesis of a cosmid carrying the rhiABC and rhiR gene region identified a gene (rhiI) that affects the level of rhiA expression. Mutation of rhiI slightly increased the number of nodules formed on the pea. The rhiI gene is (like rhiA) regulated by rhiR in a cell density-dependent manner. RhiI is similar to LuxI and other proteins involved in the synthesis of N-acyl-homoserine lactones (AHLs). Chemical analyses of spent culture supernatants demonstrated that RhiI produces N-(hexanoyl)-L-homoserine lactone (C6-HSL) and N-(octanoyl)-L-homoserine lactone (C8-HSL). Both of these AHLs induced rhiA-lacZ and rhiI-lacZ expression on plasmids introduced into an Agrobacterium strain that produces no AHLs, showing that rhiI is positively regulated by autoinduction. However, in this system no induction of rhiA or rhiI with 3OH,C14:1-HSL was observed. Analysis of the spent culture supernatant of the wild-type R. leguminosarum bv. viciae revealed that at least seven different AHLs are made. Mutation of rhiI decreased the amounts of C6-HSL and C8-HSL but did not block their formation, and in this background the rhiI mutation did not significantly affect the expression levels of the rhiI gene or rhiABC genes or the accumulation of RhiA protein. These observations suggest that there are additional loci involved in AHL production in R. leguminosarum bv. viciae and that they affect rhiI and rhiABC expression. We postulate that the previously observed induction of rhiA by 3OH,C14:1-HSL may be due to an indirect effect caused by induction of other AHL production loci.
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PMID:Analysis of quorum-sensing-dependent control of rhizosphere-expressed (rhi) genes in Rhizobium leguminosarum bv. viciae. 1036 58

The Pseudomonas aeruginosa fabI structural gene, encoding enoyl-acyl carrier protein (ACP) reductase, was cloned and sequenced. Nucleotide sequence analysis revealed that fabI is probably the last gene in a transcriptional unit that includes a gene encoding an ATP-binding protein of an ABC transporter of unknown function. The FabI protein was similar in size and primary sequence to other bacterial enoyl-ACP reductases, and it contained signature motifs for the FAD-dependent pyridine nucleotide reductase and glucose/ribitol dehydrogenase families, respectively. The chromosomal fabI gene was disrupted, and the resulting mutant was viable but possessed only 62% of the total enoyl-ACP reductase activity found in wild-type cell extracts. The fabI-encoded enoyl-ACP reductase activity was NADH dependent and inhibited by triclosan; the residual activity in the fabI mutant was also NADH dependent but not inhibited by triclosan. An polyhistidine-tagged FabI protein was purified and characterized. Purified FabI (i) could use NADH but not NADPH as a cofactor; (ii) used both crotonyl-coenzyme A and crotonyl-ACP as substrates, although it was sixfold more active with crotonyl-ACP; and (iii) was efficiently inhibited by low concentrations of triclosan. A FabI Gly95-to-Val active-site amino acid substitution was generated by site-directed mutagenesis, and the mutant protein was purified. The mutant FabI protein retained normal enoyl-ACP reductase activity but was highly triclosan resistant. When coupled to FabI, purified P. aeruginosa N-butyryl-L-homoserine lactone (C4-HSL) synthase, RhlI, could synthesize C4-HSL from crotonyl-ACP and S-adenosylmethionine. This reaction was NADH dependent and inhibited by triclosan. The levels of C4-HSL and N-(3-oxo)-dodecanoyl-L-homoserine lactones were reduced 50% in a fabI mutant, corroborating the role of FabI in acylated homoserine lactone synthesis in vivo.
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PMID:Characterization of Pseudomonas aeruginosa enoyl-acyl carrier protein reductase (FabI): a target for the antimicrobial triclosan and its role in acylated homoserine lactone synthesis. 1046 25

Pseudomonas aeruginosa LasB elastase gene (lasB) transcription is controlled by the two-component quorum-sensing system of LasR, and the autoinducer, 3OC(12)-HSL (N-3-[oxododecanoyl]homoserine lactone). LasR and 3OC(12)-HSL-mediated lasB activation requires a functional operator sequence (OP1) in the lasB promoter region. Optimal activation of lasB, however, requires a second sequence of 70% identity to OP1, named OP2, located 43 bp upstream of OP1. In this study, we used sequence substitutions and insertion mutations in lasBp-lacZ fusion plasmids to explore the role of OP2 in lasB activation. Our results demonstrate that (i) OP1 and OP2 synergistically mediate lasB activation; (ii) OP2, like OP1, responds to LasR and 3OC(12)-HSL; and (iii) the putative autoinducer-binding domain of LasR is not required for synergistic activation from OP1 and OP2.
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PMID:A second operator is involved in Pseudomonas aeruginosa elastase (lasB) activation. 1051 13

Luminescence in Vibrio fischeri is controlled by a population density-responsive regulatory mechanism called quorum sensing. Elements of the mechanism include: LuxI, an acyl-homoserine lactone (acyl-HSL) synthase that directs synthesis of the diffusible signal molecule, 3-oxo-hexanoyl-HSL (V. fischeri autoinducer-1, VAI-1); LuxR, a transcriptional activator protein necessary for response to VAI-1; GroEL, which is necessary for production of active LuxR; and AinS, an acyl-HSL synthase that catalyzes the synthesis of octanoyl-HSL (VAI-2). The population density-dependent accumulation of VAI-1 triggers induction of lux operon (luxICDABEG; genes for luminescence enzymes and for LuxI) transcription and luminescence by binding to LuxR, forming a complex that facilitates the association of RNA polymerase with the luxoperon promoter. VAI-2, which apparently interferes with VAI-1 binding to LuxR, operates to limit premature luxoperon induction. Hierarchical control is imposed on the system by 3':5'-cyclic AMP (cAMP) and cAMP receptor protein (CRP), which are necessary for activated expression of luxR. Several non-lux genes in V. fischeri are controlled by LuxR and VAI-1. Quorum regulation in V. fischeri serves as a model for LuxI/LuxR-type quorum sensing systems in other gram-negative bacteria.
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PMID:Quorum regulation of luminescence in Vibrio fischeri. 1094 79

Several different species of Pseudomonas: produce N:-acylhomoserine lactones (AHLs), quorum-sensing signal molecules which are involved in the cell-density-dependent control of secondary metabolite and virulence gene expression. When Pseudomonas fluorescens F113 was cross-streaked against AHL biosensors capable of sensitively detecting either short (C(4)-C(8)) or long (C(10)-C(14)) acyl chain AHLs, no activity was detectable. However, by extracting cell-free stationary-phase culture supernatants with dichloromethane followed by reverse-phase HPLC, three distinct fractions were obtained capable of activating the AHL biosensors. Three AHLs were subsequently characterized using high-resolution MS and chemical synthesis. These were (i) N:-(3-hydroxy-7-cis-tetradecenoyl)homoserine lactone (3OH, C(14:1)-HSL), a molecule previously known as the Rhizobium leguminosarum small bacteriocin as a consequence of its growth inhibitory properties, (ii) N:-decanoylhomoserine lactone (C(10)-HSL) and (iii) N:-hexanoylhomoserine lactone (C(6)-HSL). A gene (hdtS) capable of directing synthesis of all three P. fluorescens AHLs in Escherichia coli was cloned and sequenced. In vitro transcription/translation of hdtS yielded a protein of approximately 33 kDa capable of directing the synthesis of 3OH, C(14:1)-HSL, C(10)-HSL and C(6)-HSL in E. coli. HdtS does not belong to either of the known AHL synthase families (LuxI or LuxM) and is related to the lysophosphatidic acid acyltransferase family. HdtS may therefore constitute a member of a third protein family capable of AHL biosynthesis.
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PMID:The biocontrol strain Pseudomonas fluorescens F113 produces the Rhizobium small bacteriocin, N-(3-hydroxy-7-cis-tetradecenoyl)homoserine lactone, via HdtS, a putative novel N-acylhomoserine lactone synthase. 1102 23

In Pseudomonas aeruginosa, many exoproduct virulence determinants are regulated via a hierarchical quorum-sensing cascade involving the transcriptional regulators LasR and RhlR and their cognate activators, N-(3-oxododecanoyl)-L-homoserine lactone (3O-C12-HSL) and N-butanoyl-L-homoserine lactone (C4-HSL). In this paper, we demonstrate that the cytotoxic lectins PA-IL and PA-IIL are regulated via quorum sensing. Using immunoblot analysis, the production of both lectins was found to be directly dependent on the rhl locus while, in a lasR mutant, the onset of lectin synthesis was delayed but not abolished. The PA-IL structural gene, lecA, was cloned and sequenced. Transcript analysis indicated a monocistronic organization with a transcriptional start site 70 bp upstream of the lecA translational start codon. A lux box-type element together with RpoS (sigma(S)) consensus sequences was identified upstream of the putative promoter region. In Escherichia coli, expression of a lecA::lux reporter fusion was activated by RhlR/C4-HSL, but not by LasR/3O-C12-HSL, confirming direct regulation by RhlR/C4-HSL. Similarly, in P. aeruginosa PAO1, the expression of a chromosomal lecA::lux fusion was enhanced but not advanced by the addition of exogenous C4-HSL but not 3O-C12-HSL. Furthermore, mutation of rpoS abolished lectin synthesis in P. aeruginosa, demonstrating that both RpoS and RhlR/C4-HSL are required. Although the C4-HSL-dependent expression of the lecA::lux reporter in E. coli could be inhibited by the presence of 3O-C12-HSL, this did not occur in P. aeruginosa. This suggests that, in the homologous genetic background, 3O-C12-HSL does not function as a posttranslational regulator of the RhlR/C4-HSL-dependent activation of lecA expression.
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PMID:The Pseudomonas aeruginosa lectins PA-IL and PA-IIL are controlled by quorum sensing and by RpoS. 1105 84


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