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)

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

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

Taz1-1 is Tar-EnvZ chimeric receptor that is able to induce ompC-lacZ expression in response to aspartate. Previous studies indicated that aspartate binding to the receptor domain of the Taz1-1 receptor modulated the ratio of kinase and phosphatase activities of the cytoplasmic signaling domain. The 80-residue segment of chemoreceptors that is located between the second transmembrane domain and the signaling domain was defined as the linker region. The Taz1-1 chimeric receptor contains 43 amino acid residues of the Tar linker region. In order to understand further the function of the linker region in transmembrane signaling, site-directed random mutagenesis was carried out on the conserved Ala231 in the linker region. Substitution mutations with Val, Glu, Gly, Thr, Lys and His gave the locked "off-mode" form (low ompC-lacZ expression), and substitution mutations with Ile and Leu resulted in the locked "on-mode" form (constitutive ompC-lacZ expression). All the mutant Taz1-1 receptors still retained both OmpR kinase and phospho-OmpR phosphatase activities. Interestingly Taz1N6, a kinase defective mutant, was able to complement with Taz1H1, a phosphatase defective mutant, carrying an off-mode mutant at position 231 to restore Asp-inducible ompC-lacZ expression, but not with Taz1H1 carrying an on-mode mutation. These results suggest that the residue at position 231 in Taz1-1 plays a key role in signal transduction.
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PMID:Transmembrane signaling. Mutational analysis of the cytoplasmic linker region of Taz1-1, a Tar-EnvZ chimeric receptor in Escherichia coli. 799 Jan 35

Taz1 is a hybrid receptor in the Escherichia coli cytoplasmic membrane, consisting of the N-terminal ligand binding domain of Tar (a chemoreceptor for aspartate) and the C-terminal signaling domain of EnvZ (an osmosensor). The binding of aspartate to an extra cytoplasmic domain induces the transmembrane signal to the cytoplasmic signaling domain. The signaling domain functioning as a protein kinase evokes a response by transferring a phosphate from an intracellular histidine to OmpR. This domain also encodes an OmpR-specific phosphatase whose action is crucial in completing the OmpR phosphorylation cycle. Phosphorylated OmpR acts as a transcriptional activator for the ompC gene. A number of mutations were introduced into the signaling domain in conserved sequences of the prokaryotic histidine kinase family. All Taz1 mutants lost the ability to both autophosphorylate the histidine residue and transfer the phosphate to OmpR. These mutated receptors were unable to activate ompC-lacZ expression. However, ompC-lacZ was able to be activated by complementation of Taz1 mutants. In some combinations, two different defective Taz1 mutants could restore both OmpR kinase and phosphatase activities when co-expressed. In other combinations only kinase activity was restored. Aspartate-inducible ompC-lacZ expression was restored only in the former cases, while in the latter cases ompC-lacZ expression became constitutive. These results indicate that the kinase activity is essential to activate ompC expression while the phosphatase activity is required to regulate ompC gene expression in a ligand-dependent manner.
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PMID:Requirement of both kinase and phosphatase activities of an Escherichia coli receptor (Taz1) for ligand-dependent signal transduction. 838 84

Taz1 is a hybrid receptor, in which the periplasmic receptor domain of Tar, an aspartate chemoreceptor, is fused with the cytoplasmic signaling domain of EnvZ, an osmosensor. Taz1 is able to induce ompC-lacZ expression in response to aspartate added to the medium. We introduced amino acid substitution mutations in the highly conserved region of the signaling domain of Tar near the Tar-EnvZ junction. The same mutations in Tsr, a serine chemoreceptor, are known to lock the flagella rotation in either a clockwise (CW) or in a counter-clockwise (CCW) mode. It was found that a CW-biased mutation in Taz1 resulted in ompC-lacZ expression in the "off mode", or low ompC-lacZ expression in both the absence and presence of aspartate, while CCW-biased mutations caused ompC-lacZ expression in the "on mode", or constitutive expression regardless of aspartate. The OmpR kinase and phospho-OmpR phosphatase activities of the wild-type and mutant Taz proteins were also examined in response to aspartate. The phosphatase activity of the wild-type Taz1 was found to decrease in the presence of aspartate, while the OmpR kinase activity remained constant. This indicated that aspartate binding to the Taz1 receptor domain modulates the ratio of kinase to phosphatase activity of the signaling domain. An increased kinase to phosphatase ratio in the presence of aspartate resulted in higher levels of phospho-OmpR in the cell and therefore induced ompC-lacZ expression. In contrast to the wild-type Taz1 protein, the enzymatic activities of CW as well as CCW mutants did not change in response to aspartate, indicating that mutant Taz proteins are incapable of transducing the signal across the membrane as a result of a locked conformation of the signaling domain in either the on or off mode.
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PMID:Ligand binding to the receptor domain regulates the ratio of kinase to phosphatase activities of the signaling domain of the hybrid Escherichia coli transmembrane receptor, Taz1. 839 37

Two ligand (aspartate)-binding pockets are formed at the interface between the subunits of the Tar homodimer, a bacterial chemoreceptor. Using mutant heterodimers of a hybrid receptor, Taz1, which consists of the external domain of Tar and the cytoplasmic domain of EnvZ, we disrupted either one or the other of the two ligand-binding pockets. We found that occupation of only one of the ligand-binding pockets was sufficient for induction of a transmembrane signal, and that the subunit responsible for the binding of the amino group of the ligand transduces the signal.
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PMID:Ligand binding induces an asymmetrical transmembrane signal through a receptor dimer. 839 38

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

The histidine kinase/phosphatase EnvZ helps Escherichia coli adapt to osmotic shock by controlling the phosphorylation state of the transcription factor OmpR, which regulates the levels of the outer membrane porin proteins OmpF and OmpC. We examined the effects of mutating the highly conserved Thr(247) residue in EnvZ. Using purified C-terminal domains of wild-type and mutant EnvZ proteins, we demonstrate that Thr(247) plays a vital role in EnvZ function, variously affecting its autokinase and phosphotransferase activities, but mostly its function as a phosphatase. The cytoplasmic domain of EnvZ (EnvZc) is composed of three segments: the linker domain (residues 180-222), domain A (residues 223-289), and domain B (residues 290-450). It has been shown that the isolated domain A itself can dephosphorylate phosphorylated OmpR. Here we show that mutating Thr(247) to Arg in domain A abolishes its phosphatase activity. Furthermore, using an in vivo beta-galactosidase activity assay of Taz1-1 (hybrid of the aspartate receptor Tar and EnvZ) constructs of the Thr(247) mutants in RU1012 cells expressing ompC-lacZ, we demonstrate that the external signal primarily down-regulates the phosphatase activity of EnvZ. Of the nine EnvZc(T247X) mutants (X = Ser, Ala, Cys, Lys, Asn, Glu, Gln, Tyr, or Arg) analyzed, only Ser functionally substituted for Thr at this position, whereas all the others displayed constitutive expression of beta-galactosidase.
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PMID:The critical role of the conserved Thr247 residue in the functioning of the osmosensor EnvZ, a histidine Kinase/Phosphatase, in Escherichia coli. 1097 66

Histidine kinase EnvZ, a transmembrane osmotic sensor for Escherichia coli, is a bifunctional enzyme having OmpR (its cognate response regulator) kinase and phosphorylated OmpR (OmpR-P) phosphatase activities. Its cytoplasmic domain consists of domain A responsible for dimerization of EnvZ, histidine phosphotransfer and phosphatase activities, and domain B responsible for ATP binding. Here, we have constructed a number of substitution mutations at the G2 box, one of the conserved motifs in domain B, and demonstrated that they influence the phosphatase activity of EnvZ over a wide range. The effects of ADP, a cofactor for the phosphatase activity, were found to be substantially different depending upon the mutations. The effects of these mutations were also examined in vivo using a chimeric Tar-EnvZ construct (Taz1-1), and the results agreed with the in vitro data for the phosphatase and kinase activities for all mutations. Using Taz1-1 carrying the T402A mutation, three independent intragenic suppressor mutations (T235M, S269L and E276K) were isolated, and all were found in domain A. Together, the present results demonstrate for the first time that domain A and domain B are functionally co-ordinated and topologically arranged in a specific manner. The G2 box may modulate the interaction between these two domains in response to extracellular osmolarity.
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PMID:The role of the G2 box, a conserved motif in the histidine kinase superfamily, in modulating the function of EnvZ. 1213 13

Tez1 is a chimeric protein in which the periplasmic and transmembrane domains of Tar, a chemosensor, are fused to the cytoplasmic catalytic domain of EnvZ, an osmosensing histidine kinase, through the EnvZ linker. Unlike Taz1 (a similar hybrid with the Tar linker), Tez1 could not respond to Tar ligand, aspartate, whereas single Ala insertion at the transmembrane/linker junction, as seen in Tez1A1, restored the aspartate-regulatable phenotype. Analysis of the Ala insertion site requirement and the nature of the insertion residue on the phenotype of Tez1 indicated that a junction region between the transmembrane domain and the predicted helix I in the linker is critical to signal transduction. Random mutagenesis revealed that P185Q mutation in the Tez1 linker restored the aspartate-regulatable phenotype. Substitution mutations at Pro-185 further demonstrated that specific residues are required at this site for an aspartate response. None of the hybrid receptors constructed with different Tar/EnvZ fusion sites in the linker could respond to aspartate, suggesting that specific interactions between the two predicted helices in the linker are important for the linker function. In addition, a mutation (F220D) known to cause an OmpCc phenotype in EnvZ resulted in similar OmpCc phenotypes in both Tez1A1 and Tez1, indicating the importance of the predicted helix II in signal propagation. Together, we propose that the N-terminal junction region modulates the alignment between the two helices in the linker upon signal input. In turn helix II propagates the resultant conformational signal into the downstream catalytic domain of EnvZ to regulate its bifunctional enzymatic activities.
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PMID:Analysis of the role of the EnvZ linker region in signal transduction using a chimeric Tar/EnvZ receptor protein, Tez1. 1267 98


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