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)

The Kdp system of Escherichia coli, a transport ATPase with high affinity for potassium, is expressed when turgor pressure is low. Expression requires KdpD, a 99-kDa membrane protein, and KdpE, a 25-kDa soluble cytoplasmic protein. The sequences of KdpD and KdpE show they are members of the sensor-effector class of regulatory proteins: the C-terminal half of KdpD is homologous to sensors such as EnvZ and PhoR, and KdpE is homologous to effectors such as OmpR and PhoB. The predicted structure of KdpD suggests that it is anchored to the membrane by four membrane-spanning segments near its middle, with both C- and N-terminal portions in the cytoplasm. Subcellular fractionation confirms the expected location of the protein in the inner membrane. The N-terminal region has no homology to known proteins and is the site of mutations that make Kdp expression partially constitutive; this portion may serve to sense turgor pressure. Since several other sensor-effectors have been shown to mediate control through phosphorylation, this mechanism is proposed to control expression of Kdp.
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PMID:KdpD and KdpE, proteins that control expression of the kdpABC operon, are members of the two-component sensor-effector class of regulators. 153 88

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

EnvZ is a cytoplasmic membrane protein which is involved in osmoregulatory expression of the ompF and ompC genes in Escherichia coli possibly by sensing the environmental osmotic signal. A truncated form of the EnvZ protein (EnvZ*), comprising 82% of EnvZ starting from the C terminus, was purified to homogeneity. The purified EnvZ* was autophosphorylated with ATP. The phosphoryl group on EnvZ* could then be rapidly transferred to OmpR, which is a positive regulator of the ompF and ompC genes and which was proposed to interact with EnvZ in the process of osmoregulation. In the presence of ATP, the phosphorylated OmpR was rapidly dephosphorylated. These results suggest that the transfer of the phosphoryl group between EnvZ and OmpR plays an important role in the signaling pathway in osmoregulation.
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PMID:Transfer of phosphoryl group between two regulatory proteins involved in osmoregulatory expression of the ompF and ompC genes in Escherichia coli. 265 84

The ompB operon of Salmonella typhimurium encodes a positive transcriptional regulator OmpR and an inner membrane protein EnvZ. Both proteins are needed for the proper expression of the outer membrane proteins OmpC and OmpF. We have determined the nucleotide sequence of the ompB locus and its adjacent regions. A comparison between the S. typhimurium and Escherichia coli sequences revealed that the ompB locus is highly conserved. The sequence data also showed that ompR and envZ form an operon, where the coding regions overlap by four base-pairs. Utilizing ompR-lacZ and envZ-lacZ gene fusions, the translational levels of expression of these two genes were measured, showing that ompR is considerably more efficiently expressed than envZ. Analysis of ompR frameshift mutations showed that translation of envZ is almost totally dependent on the translation of the upstream gene ompR. The mechanism of this translational coupling appears to be a reinitiation of the ribosome at the overlapping region of the two genes. The characteristics of the OmpR and EnvZ proteins were in agreement with the known functions and cellular locations of these proteins. OmpR was found to contain a putative DNA binding site, while EnvZ contained two hydrophobic stretches typical of transmembrane regions. Both OmpR and EnvZ show extensive homologies with many proteins from a number of different origins, all of which function in pairs and through which environmental signals modulate gene expression. Hence, the tightly coupled synthesis of these proteins seems to be essential in eliciting a proper response in the transmembrane regulation of gene expression.
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PMID:Structure and expression of the ompB operon, the regulatory locus for the outer membrane porin regulon in Salmonella typhimurium LT-2. 284 93

We isolated a series of delta ompR delta envZ mutants by inducing a strain carrying a lambda prophage in the closely linked gene malP and screening the bacterial survivors for loss of the major outer membrane porins OmpF and OmpC. Characterization of these deletion strains showed that both OmpR and EnvZ were necessary for transcription of ompF and ompC and that neither gene was essential for cell viability. Moreover, the deletion strains did not exhibit the pleiotropic membrane protein deficiency observed with certain envZ mutants. The method described should allow the simple isolation of deletions in any region of the chromosome.
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PMID:Isolation and characterization of delta ompB strains of Escherichia coli by a general method based on gene fusions. 315 79

Genes in the phosphate regulon of Escherichia coli are positively regulated by the products of the phoB and phoR genes with limited phosphate, and negatively regulated by the product of the phoR gene with excess phosphate. We present here the complete nucleotide sequence of the phoR gene. Together with the DNA sequence of the upstream phoB gene that we determined previously, this region shows the following features. The flanking regions of the operon are abundant in A-T base-pairs. A possible stem-and-loop structure of the transcript followed by several U residues characteristic of rho-independent transcriptional terminators was distal to the phoR coding region. The operon is probably composed of only two cistrons. The nucleotide sequence of phoR indicates that its protein consists of 431 amino acid residues and has a molecular weight of 49,666. The amino acid sequence of the PhoR protein has significant homology with that of the EnvZ protein, which is a regulator for the omp regulon. Therefore, the sequences of the PhoB and PhoR proteins have considerable homologies with those of the OmpR and EnvZ proteins, respectively, indicating that the two operons share a common ancestor. The PhoR protein contains an extensive hydrophobic region in the amino-terminal portion. Thus the protein may be a membrane protein and function as a component of a signal transducer.
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PMID:Nucleotide sequence of the phoR gene, a regulatory gene for the phosphate regulon of Escherichia coli. 355 Jan 3

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

We examined the effects of hydrostatic pressure on the synthesis of Escherichia coli outer membrane proteins, particularly for the osmoregulated ImpC and OmpF porins. It was found that the expression of ompC and ompF was markedly reduced during the growth at high pressure, most likely at the transcriptional level. However, the signal transduction processes through the regulatory proteins, EnvZ and OmpR, was not influenced by the environmental pressure. It was also found that the expression of a presumed novel outer membrane protein, named OmpX, was affected by both the medium osmolarity and pressure in a manner independent of the function of EnvZ and OmpR.
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PMID:Effect of hydrostatic pressure on the synthesis of outer membrane proteins in Escherichia coli. 776 62

The fadL gene of Escherichia coli codes for an outer membrane protein that is involved in the uptake of long-chain fatty acids. Uptake is regulated by environmental osmolarity, and decreases when the cells are grown under conditions of high osmolarity. A temperature-sensitive mutant that requires fatty acid for growth at 42 degrees C was unable to grow at the high temperature even in the presence of fatty acid if the medium contained 10% sucrose. Promoter activity of the fadL gene in vivo was repressed by high osmolarity in a FadR repressor null mutant. Furthermore, in vitro transcription of the fadL gene was strongly repressed by the addition of OmpR and EnvZ proteins. The results of gel retardation and DNase I protection experiments indicated that OmpR, after incubation with the protein kinase EnvZ, specifically binds to at least four sites around the fadL promoter, two upstream and two downstream from the transcriptional start site. These results suggest that transcription of the fadL gene is osmotically regulated by the OmpR-EnvZ two-component system.
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PMID:Osmoregulation of the fatty acid receptor gene fadL in Escherichia coli. 841 82

Mouse sperm contain a tyrosine phosphorylated form of hexokinase type 1 (HK1; Kalab et al., 1994: J Biol Chem 269:3810-3817) that has properties consistent with an integral plasma membrane protein. Furthermore, this tyrosine phosphorylated form of HK1 has an extracellular domain and HK1 is localized to both the head and flagellum of nonpermeabilized cells (Visconti et al., 1995c). We have characterized HK1 in mature sperm from sterile tw32/tw5 mice (mutant sperm) that have defects in motility and sperm-egg interaction (Johnson et al., 1995: Dev Biol 168:138-149). Immunoprecipitation of mouse sperm extracts with an antiserum made against purified rat brain HK1 demonstrates the presence of HK1 in mutant sperm. Various biochemical and immunofluorescence assays indicate that at least a portion of the HK1 present in these cells is an integral membrane protein with an extracellular domain located on the sperm head and flagellum. However, immunoblot analysis with anti-phoshotyrosine antibodies demonstrates that HK1 in mutant sperm is not tyrosine phosphorylated. Northern blot and RT-PCR analysis does not indicate any obvious abnormalities in the transcription of somatic or germ cell-specific HK1 isoforms in mutant testes, and RFLP analysis of recombinant mice indicates that no genes specifying HK1 isoforms are located on chromosome 17. We have mapped the locus responsible for the lack of tyrosine phosphorylation of HK1 mutant sperm to the most proximal (to the centromere) of the four inversions within the t haplotype. A male sterility factor is located in this same inversion (Lyon, 1986: Cell 44:357-363). Since the mutant sperm are unable to complete fertilization, there could be a relationship between sterility and the lack of tyrosine phosphorylation of HK1 in these mutant sperm.
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PMID:Sperm from mice carrying two t haplotypes do not possess a tyrosine phosphorylated form of hexokinase. 872 Jan 18


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