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 DNA-binding protein that regulates transcription of ompF and ompC. The activity of OmpR is controlled by the inner membrane osmosensor, EnvZ. In order to study the signaling process between EnvZ and OmpR, we analyzed two different envZ strains: the envZ473 strain, in which OmpC is constitutively produced and OmpF is fully repressed, and the envZ3 strain, in which the production of OmpC is greatly reduced and OmpF is not fully repressed by high-osmolarity growth conditions. Using direct sequencing of DNA derived from the polymerase chain reaction amplification method, we identified the mutation in the envZ473 strain as a Val-241-to-Gly substitution and the mutation in the envZ3 as an Ala-219-to-Val substitution. The relative DNA-binding affinity of OmpR derived from the envZ473 strain was dramatically increased for the upstream sequence of both ompF and ompC. In contrast, OmpR derived from the envZ3 strain was not converted to the high-affinity form. The intracellular levels of OmpR-phosphate, as analyzed by the in vivo phosphorylation approach, significantly increased in the envZ473 strain, while in the envZ3 strain the levels were considerably reduced, relative to those found in the parent strain. The intracellular level of OmpR protein in the envZ473 strain was also found to be markedly elevated relative to that of the parent strain. These results are discussed in relation to the role of phosphorylation and relative DNA-binding affinity of OmpR in the expression of ompF and ompC.
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PMID:Molecular analysis of the signaling pathway between EnvZ and OmpR in Escherichia coli. 131 Dec 95

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

Agrobacterium tumefaciens virulence genes are induced by plant signals through the VirA-VirG two-component regulatory system. The VirA protein is a membrane-spanning sensor molecule that possesses an autophosphorylating activity, and the VirG protein is a sequence-specific DNA-binding protein. In this report, we demonstrate that the VirG protein is phosphorylated by the VirA protein and that the phosphate is directly transferred from the phosphorylated VirA molecule (phosphohistidine) to the VirG protein. The chemical stability of the phospho-VirG bond suggested that the VirG protein was phosphorylated at the aspartate and/or glutamate residue. The phosphorylated VirG protein was reduced with tritiated sodium borohydride and subjected to proteolytic digestion with the Achromobacter protease I enzyme. The resulting peptide fragments were separated by C8 reversed-phase high-pressure liquid chromatography, and the tritium-labeled peptide was sequenced. Amino acid sequence data showed that the aspartate residue at position 52 was the only site phosphorylated. Changing this aspartate into asparagine resulted in a nonphosphorylatable and biologically nonfunctional gene product. As a control, a randomly chosen aspartate was changed into an asparagine (position 72), and no effect on its phosphorylation or biological activity was observed. Unlike its homologs, including CheA-CheY, EnvZ-OmpR, and NtrB-NtrC, the phospho-VirG molecule was very stable in vitro. The possible implications of these observations and the function of VirG phosphorylation in vir gene activation are discussed.
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PMID:Phosphorylation of the VirG protein of Agrobacterium tumefaciens by the autophosphorylated VirA protein: essential role in biological activity of VirG. 239 78

The two-component regulatory system, OmpR and EnvZ, in Escherichia coli controls the differential expression of ompF and ompC in response to medium osmolarity. Previous studies suggest that EnvZ functions as a membrane sensor relaying information to the DNA-binding protein, OmpR, which in turn activates expression of the appropriate promoter. A strategy has been devised to isolate and characterize a collection of missense mutations in ompR that alter, but do not abolish protein function. Mutants were isolated using strains that contain the ompR and envZ genes in separate chromosomal locations yet maintain the production of both regulatory proteins at physiological levels. Such an arrangement facilitates ompR diploid analysis and tests of epistasis with known envZ mutations. The data obtained indicate that OmpR works in both a positive and negative fashion to control the transcription of ompF and this result forms the basis of a model for porin regulation that explains the switch from OmpF to OmpC production in response to increasing medium osmolarity.
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PMID:Genetic analysis of the switch that controls porin gene expression in Escherichia coli K-12. 255 54

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

Transcription of the genes that encode the major outer membrane porin proteins OmpF and OmpC of Escherichia coli is regulated in response to changes in medium osmolarity by EnvZ and OmpR. EnvZ functions to sense environmental conditions and to relay this information to the DNA-binding protein OmpR. We have used a truncated EnvZ protein (EnvZ115), which is defective in sensory function but able to communicate with OmpR, to study the biochemical interactions between these two proteins and their effects on transcription from the ompF promoter. We show that purified EnvZ115 can phosphorylate OmpR in the presence of ATP. In addition, EnvZ115 stimulates the ability of OmpR to activate ompF transcription in vitro. Using antibodies specific for EnvZ, we have purified the wild-type protein and have shown that it is also an OmpR kinase. These results provide a prokaryotic example of a transmembrane sensory protein that functions as a protein kinase and suggest a mechanism by which EnvZ communicates with OmpR in signal transduction.
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PMID:A bacterial environmental sensor that functions as a protein kinase and stimulates transcriptional activation. 266 43

Osmoregulated porin gene expression in Escherichia coli is controlled by the two-component regulatory system EnvZ and OmpR. EnvZ, the osmosensor, is an inner membrane protein and a histidine kinase. EnvZ phosphorylates OmpR, a cytoplasmic DNA-binding protein, on an aspartyl residue. Phospho-OmpR binds to the promoters of the porin genes to regulate the expression of ompF and ompC. We describe the use of limited proteolysis by trypsin and ion spray mass spectrometry to characterize phospho-OmpR and the conformational changes that occur upon phosphorylation. Our results are consistent with a two-domain structure for OmpR, an N-terminal phosphorylation domain joined to a C-terminal DNA-binding domain by a flexible linker region. In the presence of acetyl phosphate, OmpR is phosphorylated at only one site. Phosphorylation induces a conformational change that is transmitted to the C-terminal domain via the central linker. Previous genetic analysis identified a region in the C-terminal domain that is required for transcriptional activation. Our results indicate that this region is within a surface-exposed loop. We propose that this loop contacts the alpha subunit of RNA polymerase to activate transcription. Mass spectrometry also reveals an unusual dephosphorylated form of OmpR, the potential significance of which is discussed.
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PMID:Phosphorylation-dependent conformational changes in OmpR, an osmoregulatory DNA-binding protein of Escherichia coli. 756 33

The two-component regulatory system, OmpR-EnvZ, of Escherichia coli K-12 regulates the expression of the major outer membrane porin protein, OmpF. OmpR is a DNA-binding protein which acts as both an activator and a repressor to control ompF transcription. In this article, we describe a new OmpR-binding site that is located between 384 to 351 bp upstream from the ompF start point of transcription. Inactivation of this site by insertion of a 22-bp fragment prevents the repression of ompF expression conferred by the dominant negative mutation, envZ473. On the basis of the location of this binding site, the presence of bent DNA in the ompF regulatory region (T. Mizuno, Gene 54:57-64, 1987), and the fact that mutations altering integration host factor result in constitutive ompF expression (P. Tsui, V. Helu, and M. Freundlich, J. Bacteriol. 170:4950-4953, 1988), we propose that the negative regulation of ompF involves a DNA loop structure.
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PMID:A distant upstream site involved in the negative regulation of the Escherichia coli ompF gene. 811 70

The two-component regulatory proteins OmpR and EnvZ of Escherichia coli K-12 regulate expression of the major outer membrane porin protein, OmpF. OmpR is a DNA-binding protein that is involved in both the positive and negative control of ompF transcription. EnvZ is a histidine kinase that phosphorylates OmpR in response to environmental signals. We used DNA migration retardation analysis to examine the interactions of OmpR and the phosphorylated form of OmpR (OmpR-P) with the regulatory region immediately upstream of the ompF promoter. Our results indicate that the binding of OmpR to this regulatory region is cooperative and that phosphorylation significantly stimulates these cooperative interactions. Moreover, although phosphorylation increases the intrinsic binding of OmpR to a single OmpR-binding site, the primary role of phosphorylation in ompF regulation is to facilitate cooperative interactions between OmpR molecules bound at adjacent sites. Based on these results, we propose a model to explain how the phosphorylation of OmpR could stimulate the occupancy of specific sites in the ompF regulatory region, thereby resulting in the activation or repression of ompF transcription under the appropriate environmental conditions.
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PMID:Phosphorylation stimulates the cooperative DNA-binding properties of the transcription factor OmpR. 909 5

Natural competence in Streptococcus pneumoniae is regulated by a quorum-sensing mechanism consisting of a competence-stimulating peptide (CSP), its dedicated secretion apparatus (ComAB), its histidine kinase receptor (ComD) and a response regulator (ComE). In this report, we show that ComE is a DNA-binding protein that acts autocatalytically by binding to a region in its own promoter. Two additional ComE binding sites were identified in the pneumococcal genome, one in the promoter region of comAB and the other upstream of an ABC transporter of unknown function. A comparison of the ComE-binding sequences with the sequence motif previously found to be involved in the co-ordinated expression of the late genes revealed that they are unrelated. These findings indicate that ComE activates transcription of the late genes indirectly, i.e. via one or more intermediate factors.
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PMID:Identification of DNA binding sites for ComE, a key regulator of natural competence in Streptococcus pneumoniae. 1044 90


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