Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: 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)

An insertion mutation in the Escherichia coli dsbA gene, coding for periplasmic disulfide oxidoreductase, dramatically reduces the level of OmpF porin protein in the cell envelope. Studies with chromosomal ompF-lacZ operon and gene fusions indicate that this is due to reduced ompF transcription. Identical effects resulted from growth in medium containing the reducing agent dithiothreitol, but the combined effects of the reducing agent and dsbA were no greater than the effects of each individually. The dsbA mutation did not prevent normal regulation of ompF transcription by the local anaesthetic procaine or by osmolarity. OmpF does not contain a cysteine residue, and the sole cysteine residue in the cytoplasmic membrane regulator of ompF transcription, EnvZ, is predicted to be located on the cytoplasmic side of the membrane, and is therefore unlikely to be involved in the effects of the dsbA mutation. The effects of the dsbA mutation and of the reducing agent on ompF transcription may be due to the failure to from an essential disulfide bond in an as yet unidentified envelope protein that affects ompF transcription.
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PMID:A mutation in the dsbA gene coding for periplasmic disulfide oxidoreductase reduces transcription of the Escherichia coli ompF gene. 848 56

Osmoregulation of the porin genes, ompF and ompC of Escherichia coli, occurs at the level of transcription through the action of EnvZ and OmpR proteins as well as at the level of translation through micF antisense RNA. In this study, we used a genetic screening approach to identify new genes which interfere with the expression of ompC or ompF. Using an E. coli genomic library in pUC19, we identified three clones whose products altered expression of ompC and ompF in response to medium osmolarity. One clone carrying the secB gene was found to block ompC and inhibit ompF expression. One clone carrying gcvA, a transcriptional regulator for the gvcA operon, was found to block ompF expression at high osmolarity and elevate ompC expression at low osmolarity. One clone carrying rbsR, a repressor for the rbs operon, was found to block ompF expression at both low and high osmolarities and elevate ompC expression at low osmolarity. These results suggest that ompF and ompC expression is associated with other physiological regulating systems in addition to osmoregulation.
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PMID:Identification of the genes in multicopy plasmids affecting ompC and ompF expression in Escherichia coli. 852 38

In Escherichia coli, levels of the two major outer membrane porin proteins, OmpF and OmpC, are regulated in response to a variety of environmental parameters, and numerous factors have been shown to influence porin synthesis. EnvZ and OmpR control porin-gene transcription in response to osmolarity, and the antisense RNA, MicF, influences ompF translation. In contrast to these characterized factors, some of the components reported to influence porin expression have only modest effects and/or act indirectly. For others, potential regulatory roles, although intriguing, remain elusive. Here we review many of the components that have been reported to influence porin expression, address the potential regulatory nature of these components, and discuss how they may contribute to a regulatory network controlling porin synthesis.
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PMID:From acids to osmZ: multiple factors influence synthesis of the OmpF and OmpC porins in Escherichia coli. 880 44

In Escherichia coli, EnvZ senses changes in the osmotic conditions of the growth environment and controls the phosphorylated state of the regulatory protein, OmpR. OmpR-phosphate regulates the expression of the porin genes, ompF and ompC. To investigate the role of the periplasmic domain of EnvZ in sensing of osmolarity signals, portions of this domain were deleted. Cells containing the EnvZ mutant proteins were able to regulate normally the production of OmpF and OmpC in response to changes in osmolarity. The periplasmic domain of EnvZ was also replaced with the non-homologous periplasmic domain of the histidine kinase PhoR of Bacillus subtilis. Osmoregulation of OmpF and OmpC production in cells containing the PhoR-EnvZ hybrid protein was indistinguishable from that in cells containing wild-type EnvZ. Identical results were obtained with an envZ-pta/ack strain, which could not synthesize acetyl phosphate. Thus, acetyl phosphate was not involved in the regulation of ompF and ompC observed in this study. These results indicate that the periplasmic domain of EnvZ is not essential for sensing of osmolarity signals.
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PMID:Re-examination of the role of the periplasmic domain of EnvZ in sensing of osmolarity signals in Escherichia coli. 893 25

Nucleoside-diphosphate kinase (NDP kinase), a key enzyme in nucleotide metabolism, is also known to be involved in growth and developmental control and tumor metastasis suppression. Interestingly, we find that coexpression of NDP kinase with Taz1, a Tar/EnvZ chimera, in the absence of its native signal, can activate a porin gene ompC-lacZ expression in Escherichia coli. Further studies show that NDP kinase can act as a protein kinase to phosphorylate histidine protein kinases such as EnvZ and CheA which are members of the His-Asp phosphorelay signal transduction systems in E. coli. Instead of ATP, the exclusive phosphodonor for histidine kinases, GTP can be utilized in vitro in the presence of NDP kinase to phosphorylate EnvZ and CheA, which then transfer the phosphoryl group to OmpR and CheY, the respective response regulators. The direct involvement of GTP for the phosphorylation of EnvZ through NDP kinase was further demonstrated by the use of a mutant EnvZ, which lost ability to be autophosphorylated with ATP. Phospho-OmpR thus formed can bind specifically to an ompF promoter sequence. These results suggest that NDP kinase may play a physiological role in signal transduction.
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PMID:Nucleoside-diphosphate kinase-mediated signal transduction via histidyl-aspartyl phosphorelay systems in Escherichia coli. 895 29

EnvZ is a transmembrane osmosensor which regulates the phosphorylation of OmpR, a transcription factor for ompF and ompC genes which encode the major outer membrane porin proteins, OmpF and OmpC in Escherichia coli. Autophosphorylation of EnvZ occurs through a transphosphorylation reaction between two EnvZ molecules. To elucidate the molecular mechanism of signal transduction by EnvZ, we examined the dimer formation of the EnvZ cytoplasmic domain [EnvZ(C)]. For this purpose, we developed a method to determine the complex formation between the purified EnvZ(C) and the purified His6-EnvZ(C) by means of Ni-6xhistidine tag affinity chromatography. When the mixture of EnvZ(C) and His6-EnvZ(C) was applied to Ni-NTA resin, both His6-EnvZ(C) and EnvZ(C) were bound to the resin, indicating that EnvZ can form an oligomer without the periplasmic and transmembrane domains. Binding experiments using the Ni-NTA resin revealed that EnvZ(C) forms a dimer with the Ka value for dimerization being approximately 10(5) M(-1) in the equilibrium state.
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PMID:Demonstration of dimer formation of the cytoplasmic domain of a transmembrane osmosensor protein, EnvZ, of Escherichia coli using Ni-histidine tag affinity chromatography. 900 5

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

EnvZ and OmpR are the sensor and response regulator proteins of a two-component system that controls the porin regulon of Escherichia coli in response to osmolarity. Three enzymatic activities are associated with EnvZ: autokinase, OmpR kinase, and OmpR-phosphate (OmpR-P) phosphatase. Conserved histidine-243 is critical for both autokinase and OmpR kinase activities. To investigate its involvement in OmpR-P phosphatase activity, histidine-243 was mutated to several other amino acids and the phosphatase activity of mutated EnvZ was measured both in vivo and in vitro. In agreement with previous reports, we found that certain substitutions abolished the phosphatase activity of EnvZ. However, a significant level of phosphatase activity remained when histidine-243 was replaced with certain amino acids, such as tyrosine. In addition, the phosphatase activity of a previously identified kinase- phosphatase+ mutant was not abolished by the replacement of histidine-243 with asparagine. These data indicated that although conserved histidine-243 is important for the phosphatase activity, a histidine-243-P intermediate is not required. Our data are consistent with a previous model that proposes a common transition state with histidine-243 (EnvZ) in close contact with aspartate-55 (OmpR) for both OmpR phosphorylation and dephosphorylation. Phosphotransfer occurs from histidine-243-P to aspartate-55 during phosphorylation, but water replaces the phosphorylated histidine side chain leading to hydrolysis during dephosphorylation.
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PMID:Function of conserved histidine-243 in phosphatase activity of EnvZ, the sensor for porin osmoregulation in Escherichia coli. 917 23

EnvZ is an inner membrane protein present in Escherichia coli that is important for osmosensing and required for porin gene regulation. EnvZ is phosphorylated by intracellular ATP, and EnvZ-P phosphorylates OmpR, which then binds to the porin promoters to regulate their expression. An overexpressed, truncated form of the enzyme, EnvZ115, was used to characterize the kinase reaction in vitro. Using a filter binding assay, we report the first direct measurements of the kinase activity, including the apparent affinity for ATP of 200 microM. The phosphorylation reaction is dependent on MgCl2, and the phosphoenzyme has the expected stability of a phosphohistidine; i.e., it is stable in base and less stable in acid at room temperature. The addition of OmpR and ATP to solutions containing EnvZ resulted in an OmpR-stimulated, EnvZ-dependent ATPase activity that was not vanadate-sensitive. The in vivo kinase activity of EnvZ and two mutants that were deficient in porin expression were studied using an immune complex kinase reaction. Interestingly, a mutation located in the periplasmic domain of EnvZ exhibited kinase activity that was identical to that of the wild-type enzyme, while a mutation located close to the phosphorylation site showed a significant decrease in both kinase and phosphotransferase activities. These data provide support for models of EnvZ consisting of separate sensing and kinase domains.
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PMID:Kinase activity of EnvZ, an osmoregulatory signal transducing protein of Escherichia coli. 934 78

We have generated a mutant form of the OmpR regulatory protein, OmpRD55E, that is active independent of the EnvZ kinase. Notably, the pattern of OmpF and OmpC expression can be altered simply by changing the level of this mutant protein in the cell. This result supports a key prediction of the current model of porin regulation, which states that the differential regulation of OmpF and OmpC is a direct consequence of the cellular level of the active form of OmpR.
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PMID:Differential expression of the OmpF and OmpC porin proteins in Escherichia coli K-12 depends upon the level of active OmpR. 942 9


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