Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.13.3 (histidine kinase)
 2,405 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

OmpR is a transcriptional activator for the expression of outer membrane porin genes ompF and ompC in Escherichia coli. Its C-terminal half has been identified as the DNA-binding domain (K. Tsung, R. Brissette, and M. Inouye, J. Biol. Chem. 264:10104-10109, 1989). Recent studies have indicated that the N-terminal non-DNA-binding domain of OmpR is involved in modulating OmpR function through interaction with the EnvZ protein, a kinase and phosphatase for OmpR. We isolated and characterized two mutations, G94D and E111K, in the N-terminal domain of OmpR and one mutation, R182C, in the DNA-binding domain of OmpR. All three mutations abolished the ability of OmpR to bind to the ompF and ompC promoters in vivo, thus giving an OmpF- OmpC- phenotype. The decreased DNA-binding ability of the mutant OmpRs was not due to diminished phosphorylation of their N termini, since all the mutant OmpRs were found to be normally phosphorylated by EnvZ in vitro. The mutant OmpRs produced from multicopy plasmids were also found to inhibit completely the production of OmpF and OmpC in wild-type cells, and the complete inhibition depended on the function of EnvZ which was produced in cis or in trans from plasmids. The relationship of the possible alterations in OmpR by the mutations with the observed diminished binding ability is discussed.
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PMID:Mutations in a central highly conserved non-DNA-binding region of OmpR, an Escherichia coli transcriptional activator, influence its DNA-binding ability. 132 Nov 17

OmpR is a transcriptional activator for the ompF and ompC genes of Escherichia coli. Its phosphorylation is mediated by a transmembrane sensory-receptor protein, EnvZ, and is essential for transcriptional activation. In a previous study, when the aspartic acid residue at position 55, the putative phosphorylation site, was replaced with glutamine (D55Q), ompF and ompC expression were completely lost. In this study two pseudorevertants of the D55Q mutation were isolated and identified to be the replacement of threonine at position 83 with alanine (T83A) and glycine at position 94 with serine (G94S). The revertant OmpRs no longer responded to EnvZ function when ompF and ompC expression were examined. The purified D55Q-T83A OmpR was unable to be phosphorylated by EnvZ in vitro. The role of EnvZ as an osmosensor for the environmentally regulated expression of OmpF and OmpC has been indicated in previous studies. The isolation of seemingly EnvZ-independent OmpR revertants in this study, however, made it possible to examine the osmolarity-regulated expression of OmpF and OmpC in the absence of effects exerted by EnvZ. We found that the expression of OmpF and OmpC supported by these revertant OmpRs was clearly regulated in accordance with the change in osmolarity of the growth media. These results indicate that another EnvZ-independent mechanism(s) may also contribute to the regulated expression of the ompF and ompC genes.
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PMID:Intramolecular second-site revertants to the phosphorylation site mutation in OmpR, a kinase-dependent transcriptional activator in Escherichia coli. 164 88

Taz1 is a hybrid signal-transducing membrane receptor between Tar, an aspartate chemoreceptor, and EnvZ, an osmosensor of Escherichia coli that is able to induce ompC expression by phosphorylating OmpR (a transcriptional activator) in response to aspartate. When the Taz1 His-277, the proposed autophosphorylation site in the cytoplasmic EnvZ domain, was replaced with a valine residue, the mutant Taz1 was unable to induce ompC expression. Similarly, when approximately two-thirds of the EnvZ domain was deleted, Taz1 was nonfunctional. However, when these two defective Taz1 proteins were coexpressed in a cell, ompC was constitutively expressed. Coinciding with this result, two mutant Taz1 molecules were able to intermolecularly complement each other to restore the OmpR kinase activity but not phosphatase activity in vitro. The identical result was also obtained with EnvZ. The present results suggest that the autophosphorylation of Taz1 and EnvZ is an intermolecular phosphorylation reaction, requiring formation of a dimer (or oligomer), and that ligand-dependent ompC expression requires not only kinase but also phosphatase activity.
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PMID:Intermolecular complementation between two defective mutant signal-transducing receptors of Escherichia coli. 166 80

Local anesthetics are known to reduce the level of OmpF and increase the synthesis of OmpC in the outer membrane of Escherichia coli K-12. It has been shown that the anesthetics procaine and phenethyl alcohol (PEA) act at the transcriptional level for ompF and ompC and that in the case of procaine, its action is dependent on EnvZ, the membrane-bound signal transducer required for ompF and ompC expression. In an effort to further understand how anesthetics regulate ompF and ompC expression, we have analyzed the DNA binding properties of OmpR (the transcriptional activator protein for ompF and ompC genes) from cells treated with procaine or PEA. Treatment of a wild-type cell with either anesthetic converted OmpR from a low-affinity DNA binding form to a high-affinity DNA binding form. The change in DNA binding affinity was correlated with alterations in outer membrane porin profiles and could occur in the absence of protein synthesis. A strain lacking EnvZ was unable to respond to procaine to produce either the shift in the OmpR DNA binding property or cause any change in the outer membrane porin profile. PEA treatment was also dependent on EnvZ for the alteration in the OmpR DNA binding property, but it could induce ompC expression in the absence of EnvZ. Further studies suggest that the amino-terminal region of EnvZ is responsible for the procaine signalling. Our results indicate that procaine and PEA regulate ompF and ompC expression by modifying the DNA binding properties of OmpR through EnvZ signal transduction.
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PMID:Procaine, a local anesthetic, signals through the EnvZ receptor to change the DNA binding affinity of the transcriptional activator protein OmpR. 171 43

The Tar-EnvZ hybrid molecule (Taz1) is an inner membrane transducer that activates OmpR, a transcriptional activator for porin gene expression (ompC), in response to an aspartic acid signal. Signal transduction by Taz1 most likely involves a phosphorylated Taz1 intermediate that donates its phosphate to OmpR. Phosphorylated OmpR has already been implicated in transcriptional activation of porin genes. Using a cell-free system containing Taz1-enriched membrane fractions, we have examined the phosphorylation properties of Taz1 and the stimulatory effects of divalent and monovalent ions. Highest activation of Taz1 phosphorylation was observed with CaCl2, and its stimulation could be observed with as low as 60 microM of CaCl2. Phosphorylated Taz1 could readily donate its phosphate group to OmpR in the presence of calcium. CaCl2 was also able to enhance phosphorylation of intact membrane-bound EnvZ and a cytoplasmic fragment of EnvZ lacking the receptor and transmembrane domains. These results indicate that the site for CaCl2 stimulation is within the cytoplasmic region of EnvZ and probably involves an enhanced rate of EnvZ phosphorylation.
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PMID:Ca2(+)-enhanced phosphorylation of a chimeric protein kinase involved with bacterial signal transduction. 185 Apr 14

A new paradigm, termed two-component regulatory systems, is emerging from the study of signal transduction in bacteria. A simple example of such a system is provided by the Omp regulon of Escherichia coli. This regulon, which controls the expression of the major outer membrane porin proteins OmpF and OmpC in response to changes in osmolarity, includes the inner membrane protein EnvZ (a receptor kinase) and the DNA-binding protein OmpR (a transcriptional activator). Although we do not know what "ligand" is sensed in the Omp system, we can trace the signal transduction pathway from the receptor at the cell surface directly to regulatory sequences within the DNA. Perhaps signal transduction in bacteria can serve as a simple archetype for understanding certain functions performed by receptor kinases and phosphorylated DNA-binding proteins in higher organisms.
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PMID:Signal transduction in bacteria: kinases that control gene expression. 196 84

The Tar chemoreceptor of Escherichia coli is a membrane-bound sensory protein that facilitates bacterial chemotaxis in response to aspartate. The EnvZ molecule has a membrane topology similar to Tar and is a putative osmosensor that is required for osmoregulation of the genes for the major outer membrane porin proteins, OmpF and OmpC. The cytoplasmic signaling domain of Tar was replaced with the carboxyl portion of EnvZ, and the resulting chimeric receptor activated transcription of the ompC gene in response to aspartate. The activation of ompC by the chimeric receptor was absolutely dependent on OmpR, a transcriptional activator for ompF and ompC.
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PMID:Activation of bacterial porin gene expression by a chimeric signal transducer in response to aspartate. 247 47

The nucleotide sequence of a 4.4-kilobase SacII-SspI fragment encoding the narXL operon and a part of the narK gene of Escherichia coli has been determined. The narX and narL genes encode proteins of molecular weight 67,275 and 23,927, respectively, and are transcribed from a common promoter, narXp, locating within 429 bases upstream of narX. Transcription from narXp is not significantly induced by nitrate under anaerobiosis, whereas transcription from narK promoter, which overlaps narXp region and is transcribed divergently, is fully induced by nitrate. The N-terminal two-thirds of the NarL protein has extensive homology with those of a diverse set of prokaryotic regulatory proteins, including OmpR, PhoB, SfrA, UhpA, CheY, CheB, NtrC, DctD, FixJ, VirG, SpoOF, and SpoOA. A segment locating in the C-terminal half of the NarL protein seems to have potential most likely to form the helix-turn-helix structure characteristic of a class of DNA-binding protein. The protein is considered to play a role as a transcriptional activator of the nitrate reductase operon, narCHJI, and the narK gene. The C-terminal region of the NarX protein also has homology with other regulatory proteins known as counterparts of two-component regulatory systems, such as EnvZ, PhoR, PhoM, CpxA, NtrB, DctB, FixL, and VirA. Presence of two copies of hydrophobic segments in the N-terminal half of the NarX protein suggests the role as a transmembrane receptor sensing nitrate.
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PMID:The narX and narL genes encoding the nitrate-sensing regulators of Escherichia coli are homologous to a family of prokaryotic two-component regulatory genes. 265 52

The phoB gene product of Escherichia coli is the transcriptional activator for the genes in the phosphate regulon as well as for phoB itself, all of which are induced by phosphate starvation. The phoR gene product modulates PhoB function in response to the phosphate concentrations in the medium. We quantitatively compared the levels of expression of the phoA, phoB, phoE, and pstS genes in several phoB mutants with different phenotypes by constructing operon fusions of these genes with the gene for chloramphenicol acetyltransferase. Although all the phoB mutants examined had little activator function for phoA, three among the four mutants showed various levels of the activator function for phoB, pstS, and phoE. To study the functional motifs of the PhoB and PhoR proteins, we cloned and sequenced the four classical phoB and six phoR mutant genes. All of the phoB mutations and one of the phoR mutations were missense mutations, and most of the altered amino acids were in the highly conserved amino acids among the regulatory proteins homologous to PhoB or PhoR protein, such as the OmpR, SfrA, and VirG proteins or the EnvZ, CpxA, and VirA proteins. The other five phoR mutations were nonsense mutations.
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PMID:Regulation of the phosphate regulon of Escherichia coli: analysis of mutant phoB and phoR genes causing different phenotypes. 267 81

OmpR and EnvZ, the protein products of the ompB locus, are regulatory components required for osmoexpression of outer membrane porin proteins, OmpF and OmpC, in Escherichia coli. EnvZ is considered to be an osmosensor which transmits signals across the membrane to OmpR, a transcriptional activator for ompF and ompC. We inserted the envZ gene into a high expression vector, pIN-III. Following cellular fractionation, EnvZ was found to be localized in the inner membrane. Sequence analysis revealed that the signal peptide-like N-terminal sequence was not removed from the purified EnvZ. A genetic approach using EnvZ/beta-lactamase fusion proteins was taken to determine the topology of EnvZ in the inner membrane. When beta-lactamase was fused after the N-terminal signal peptide-like sequence, ampicillin resistance, conferred by the beta-lactamase moiety of the fusion protein, was expressed. However, when beta-lactamase was fused after the second downstream apolar sequence, the cells showed very poor ampicillin resistance indicating that the enzyme was localized on the cytoplasmic side of the inner membrane. The results of this approach reveal that the hydrophilic region of EnvZ between the two apolar sequences is periplasmically localized and that the hydrophilic region downstream of the second apolar sequence is cytoplasmically directed. These results were confirmed by partial proteolysis of the fusion proteins in intact cells.
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PMID:Localization and membrane topology of EnvZ, a protein involved in osmoregulation of OmpF and OmpC in Escherichia coli. 282 92


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