Purification and characterization of the Pseudomonas aeruginosa NfxB protein, the negative regulator of the nfxB gene

Shiba, Toshikazu; Ishiguro, Keiko; Takemoto, Norihiro; Koibuchi, H; Sugimoto, Kazunori

doi:10.1128/jb.177.20.5872-5877.1995

Cited by 44 publications

(45 citation statements)

References 27 publications

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“…At least two pairs of inverted repeat sequences were found upstream of the pqrA gene that resemble NfxB binding sites in nfxB and mexC genes in P. aeruginosa (Fig. 6B) (38). Although the positions of the inverted repeat sequences in pqrA (IR1 and IR2) relative to the transcription start site differ from those recognized by NfxB in P. aeruginosa, we postulate that PqrA may act as an autoregulatory repressor like NfxB.…”

Section: Vol 185 2003mentioning

confidence: 93%

“…In P. aeruginosa, the nfxB gene resides immediately upstream of the mexC-mexD-oprJ operon in the opposite orientation, sharing the two inverted repeats where NfxB binds (38). As a gram-negative bacterium, P. aeruginosa possesses a resistance-nodulation-division family efflux transporter that exports various drugs.…”

Section: Discussionmentioning

confidence: 99%

“…NfxB negatively regulates the mexC-mexD-oprJ operon encoding a drug efflux system (13,29,32). NfxB also binds to the upstream region of its own gene, resulting in autorepression (38). The function of YvkB in B. subtilis is not yet known.…”

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confidence: 99%

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ThepqrABOperon Is Responsible for Paraquat Resistance inStreptomyces coelicolor

et al. 2003

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Paraquat (methyl viologen)-resistant mutants of Streptomyces coelicolor A3(2) that grew and sporulated normally in the presence of paraquat were isolated. Based on the positions of the mutant loci in the genetic map, we isolated the pqr (paraquat resistance) gene whose mutation (pqr501) caused a dominant paraquatresistant phenotype. The pqr locus consists of two genes (pqrA and pqrB) that form a transcription unit. The pqrA gene encodes a protein with a TetR-like DNA-binding motif, and the pqrB gene encodes a putative efflux pump of the major facilitator superfamily. The pqr501 mutation was a base substitution changing arginine-18 to glutamine (R18Q) near the helix-turn-helix motif in PqrA. A pqrA null mutant exhibited similar paraquat resistance, and an increase in the amount of pqrA promoter-driven transcripts of about eightfold was observed for the pqrA501 mutant. These results suggest that PqrA is a negative regulator of its own operon. Deletion of the pqrAB operon caused cells to be very sensitive to paraquat, consistent with the prediction that PqrB may function as a paraquat-efflux pump. Purified PqrA protein specifically bound to the pqrA promoter region, whereas mutant R18Q protein did not, indicating that PqrA is a direct autoregulator of its own operon.

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Section: Vol 185 2003mentioning

confidence: 93%

Section: Discussionmentioning

confidence: 99%

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ThepqrABOperon Is Responsible for Paraquat Resistance inStreptomyces coelicolor

et al. 2003

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“…1), can also confer multiantibiotic resistance on P. aeruginosa (169). NfxB autoregulates its own expression (204) and normally completely represses the mexCD-oprJ operon. Construction of P. aeruginosa strains in which three of the four mex operons are disrupted recently permitted the demonstration of mexCD-oprJ induction by acriflavine, tetraphenylphosphonium (TPP), ethidium bromide, or rhodamine 6G, all of which are substrates of this MDR pump complex (134).…”

Section: P Aeruginosa Mdr Pumps and Multiantibiotic Resistancementioning

confidence: 99%

Regulation of Bacterial Drug Export Systems

Grkovic

Brown

Skurray

2002

Microbiol Mol Biol Rev

360

339

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The active transport of toxic compounds by membrane-bound efflux proteins is becoming an increasingly frequent mechanism by which cells exhibit resistance to therapeutic drugs. This review examines the regulation of bacterial drug efflux systems, which occurs primarily at the level of transcription. Investigations into these regulatory networks have yielded a substantial volume of information that has either not been forthcoming from or complements that obtained by analysis of the transport proteins themselves. Several local regulatory proteins, including the activator BmrR from Bacillus subtilis and the repressors QacR from Staphylococcus aureus and TetR and EmrR from Escherichia coli, have been shown to mediate increases in the expression of drug efflux genes by directly sensing the presence of the toxic substrates exported by their cognate pump. This ability to bind transporter substrates has permitted detailed structural information to be gathered on protein-antimicrobial agent-ligand interactions. In addition, bacterial multidrug efflux determinants are frequently controlled at a global level and may belong to stress response regulons such as E. coli mar, expression of which is controlled by the MarA and MarR proteins. However, many regulatory systems are ill-adapted for detecting the presence of toxic pump substrates and instead are likely to respond to alternative signals related to unidentified physiological roles of the transporter. Hence, in a number of important pathogens, regulatory mutations that result in drug transporter overexpression and concomitant elevated antimicrobial resistance are often observed

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“…A second efflux system, MexCD-OprJ (41), is responsible for efflux of quinolones, erythromycin (29), and cephalosporins (12,27). Its expression is totally repressed by the transcriptional regulator NfxB (35,49). The third efflux pump, MexEFOprN, transports chloramphenicol as well as quinolones, is overexpressed in nfxC type mutants (18), and is positively regulated by the transcriptional activator MexT (16).…”

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Overexpression of the MexEF-OprN Multidrug Efflux System Affects Cell-to-Cell Signaling in Pseudomonas aeruginosa

Köhler¹,

Delden²,

Curty³

et al. 2001

J Bacteriol

258

265

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Intrinsic and acquired antibiotic resistance of the nosocomial pathogen Pseudomonas aeruginosa is mediated mainly by the expression of several efflux pumps of broad substrate specificity. Here we report that nfxC type mutants, overexpressing the MexEF-OprN efflux system, produce lower levels of extracellular virulence factors than the susceptible wild type. These include pyocyanin, elastase, and rhamnolipids, three factors controlled by the las and rhl quorum-sensing systems of P. aeruginosa. In agreement with these observations are the decreased transcription of the elastase gene lasB and the rhamnosyltransferase genes rhlAB measured in nfxC type mutants. Expression of the lasR and rhlR regulator genes was not affected in the nfxC type mutant. In contrast, transcription of the C4-homoserine lactone (C4-HSL) autoinducer synthase gene rhlI was reduced by 50% in the nfxC type mutant relative to that in the wild type. This correlates with a similar decrease in C4-HSL levels detected in supernatants of the nfxC type mutant. Transcription of an rhlAB-lacZ fusion could be partially restored by the addition of synthetic C4-HSL and Pseudomonas quinolone signal (PQS). It is proposed that the MexEF-OprN efflux pump affects intracellular PQS levels.Pseudomonas aeruginosa is an opportunistic pathogen which may cause pneumonia and bacteremia in immunocompromised hosts and is responsible for chronic destructive lung disease in patients suffering from cystic fibrosis. The pathogenicity of P. aeruginosa is attributable to an arsenal of virulence factors, some of which are cell associated (pili, nonpilus adhesins, lipopolysaccharide, and alginate) while others are secreted (proteases, rhamnolipids, exotoxin A, exoenzyme S, and pyocyanin). The production of many of these extracellular virulence factors is controlled by two cell-to-cell signaling systems, called las and rhl, which are both composed of a transcriptional regulator (LasR and RhlR, respectively) and an autoinducer synthase (LasI and RhlI, respectively). LasI and RhlI catalyze the last step in the synthesis of the cell-to-cell signaling molecules 3-oxo-C12-homoserine lactone (3-oxo-C12-HSL) and C4-HSL, respectively; each of these molecules binds to, and activates, its corresponding transcriptional regulator. The systems are connected via a hierarchical cascade (19) and allow coordinated production of extracellular virulence factors, which occurs only when the bacterial cell density has reached a threshold (quorum). Recently, a novel signaling molecule, called PQS, for Pseudomonas quinolone signal (39), has been identified. Furthermore, the published genome sequence of PAO1 (53) has revealed a new modulator of cellto-cell signaling, termed QscR (4). This protein is homologous to both LasR and RhlR and seems to prevent premature transcription of quorum-sensing regulated genes.Besides its pathogenic capabilities, P. aeruginosa is well known for its intrinsic resistance to a wide range of antimicrobial agents and its ability to develop multidrug resistance following antibi...

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Purification and characterization of the Pseudomonas aeruginosa NfxB protein, the negative regulator of the nfxB gene

Cited by 44 publications

References 27 publications

ThepqrABOperon Is Responsible for Paraquat Resistance inStreptomyces coelicolor

ThepqrABOperon Is Responsible for Paraquat Resistance inStreptomyces coelicolor

Regulation of Bacterial Drug Export Systems

Overexpression of the MexEF-OprN Multidrug Efflux System Affects Cell-to-Cell Signaling in Pseudomonas aeruginosa

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