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:2.7.11.1 (protein kinase)
81,284 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In C(4) plants, phosphoenolpyruvate carboxylase (PEPC; EC 4.1.1.31), a key enzyme in C(4) photosynthesis, is controlled by reversible phosphorylation of a conserved Ser residue near the N-terminus. We now report the first cloning of a cDNA from a C(4) plant, Flaveria trinervia, which encodes the specific protein kinase (FtPEPC-PK) involved in the phosphorylation of C(4)-form PEPC. Several lines of supportive evidence are: strict substrate specificity of the recombinant enzyme, prominent light/dark response of the transcript level and abundant expression in leaves of C(4) plant (F. trinervia) but very low expression in a C(3) plant of the same genus (Flaveria pringlei). We also discuss the possibility that the FtPEPC-PK gene has co-evolved with the PEPC gene to participate in C(4) photosynthesis.
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PMID:Phosphoenolpyruvate carboxylase kinase involved in C(4) photosynthesis in Flaveria trinervia: cDNA cloning and characterization. 1169 63

The activity of phosphoenolpyruvate carboxylase (PEPC, EC4.1.1.31) for the C4 photosynthesis is known to be regulated mainly in response to light/dark transitions through reversible phosphorylation by a specific protein kinase (PK). PEPC-PK with an M(r) of 30 kDa was purified about 1.4 million-fold to homogeneity from maize leaves and characterized. The purified PEPC-PK was readily inactivated under mild oxidative conditions, but the activity could be recovered by dithiothreitol (DTT). The recovery by DTT was strongly accelerated by thioredoxin (Trx) from E. coli. Trxs of plant origin such as Trx-m from spinach chloroplast and Trx-h from rice cytoplasm were also effective. These results suggest the possibility of PEPC-PK being redox-regulated via Trx in vivo.
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PMID:Thioredoxin-mediated reductive activation of a protein kinase for the regulatory phosphorylation of C4-form phosphoenolpyruvate carboxylase from maize. 1177 21

In most Gram-positive bacteria, catabolite repression is mediated by a bifunctional enzyme, the histidine-containing protein kinase/phosphatase (HprK/P). Based either on its primary sequence or on its recently solved three-dimensional structure, no straightforward homology with other known proteins was found. However, we showed here that HprK/P exhibits a restricted homology with an unrelated phosphotransferase, the phosphoenolpyruvate carboxykinase. This includes notably two consecutive Asp residues from the phosphoenolpyruvate carboxykinase active site, whose equivalent residues were mutated in Bacillus subtilis HprK/P. Characterization of the corresponding mutants emphasizes the crucial role of these Asp residues in the HprK/P functioning. Furthermore, superimposition of HprK/P and phosphoenolpyruvate carboxykinase active sites supports the view that both enzymes bear significant resemblance in their overall mechanism of functioning showing that these two enzymes constitute a new family of phosphotransferases.
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PMID:A new family of phosphotransferases with a P-loop motif. 1179 14

In C4 plants, the photosynthetic enzyme phosphoenolpyruvate carboxylase (PEPCase; EC 4.1.1.31) is subjected to a phosphorylation process via the light-dependent up-regulation of a Ca2+-independent PEPCase-kinase. The present work aimed to study the effect of salt stress on PEPCase phosphorylation in Sorghum vulgare Pers. leaves. The growth of salt-treated plants was reduced compared with that of the control plants. PEPCase activity modestly increased (around 20-40%) whereas PEPCase phosphorylation was markedly enhanced, on a protein basis, in extracts from illuminated leaves. The enhanced protein kinase activity was found to display a low molecular mass in the range 32-35 kDa, to be independent of Ca2+ and to be up-regulated by light. Furthermore, up-regulation was blocked in vivo by the cytosolic protein synthesis inhibitor cycloheximide. Collectively, these data demonstrated that salinity stress altered the Ca2+-independent PEPCase-kinase, presumably by increasing the mesophyll content of the enzyme. Potassium chloride, but not abscisic acid, mimicked the effect of NaCl on PEPCase-kinase activity.
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PMID:Salt stress increases the Ca2+-independent phosphoenolpyruvate carboxylase kinase activity in Sorghum leaves. 1180 Mar 93

Similarities between protein three-dimensional structures can reveal evolutionary and functional relationships not apparent from sequence comparison alone. Here we report such a similarity between the metabolic enzymes histidine phosphocarrier protein kinase (HPrK) and phosphoenolpyruvate carboxykinase (PCK), suggesting that they are evolutionarily related. Current structure classifications place PCK and other P-loop containing nucleotidyl-transferases into different folds. Our comparison of both HPrK and PCK to other P-loop containing proteins reveals that all share a common structural motif consisting of an alphabeta segment containing the P-loop flanked by an additional beta-strand that is adjacent in space, but far apart along the sequence. Analysis also shows that HPrK/PCK differ from other P-loop containing structures no more than they differ from each other. We thus suggest that HPrK and PCK should be classified with other P-loop containing proteins, and that all probably share a common ancestor that probably contained a simple P-loop motif with different protein segments being added or lost over the course of evolution. We used the structure-based sequence alignment containing residues specific to HPrK/PCK to identify additional members of this P-loop containing family.
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PMID:Evolutionary relationship between the bacterial HPr kinase and the ubiquitous PEP-carboxykinase: expanding the P-loop nucleotidyl transferase superfamily. 1206 98

Previously, we described two distinct classes of phosphoenolpyruvate carboxylase (PEPC) isoforms in the green alga Selenastrum minutum. Class 1 PEPC (PEPC1) is a homotetramer composed of 102 kDa subunits (p102), whereas Class 2 PEPCs exist as three large protein complexes (PEPC2-PEPC4) containing varying proportions of structurally dissimilar p102 and 130 kDa (p130) PEPC catalytic subunits. In the current study, a p102 calcium-independent protein kinase was shown to co-purify with PEPC1, but not PEPC2. However, the p130 subunit of PEPC2 was phosphorylated in vitro during its incubation in the presence of [gamma-(32)P]ATP and a clarified algal extract. Treatment of purified PEPC2 with protein phosphatase 2A(2) increased its apparent M(r) as judged by Superose 6 gel filtration chromatography. The presence of the protein phosphatase inhibitors NaF and microcystin-LR throughout PEPC purification significantly influenced the activity and structural organization of Class 2, but not Class 1, PEPC isoforms. The results are consistent with the notion that under the culture conditions employed: (i) Class 1 and Class 2 PEPC isoforms exist in vivo mainly in their dephosphorylated and phosphorylated forms, respectively, and (ii) phosphorylation of Class 2 PEPCs leads to a significant reduction in their activity and native M(r). We propose that protein kinase-mediated phosphorylation is involved in the control and structural organization of green algal PEPC.
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PMID:In vitro phosphorylation of phosphoenolpyruvate carboxylase from the green alga Selenastrum minutum. 1215 41

Regulation of C3 phosphoenolpyruvate carboxylase (PEPC) and its protein-serine/threonine kinase (PEPC-PK) was studied in wheat (Triticum aestivum) leaves that were excised from low-N-grown seedlings and subsequently illuminated and/or supplied with 40 mM KNO3. The apparent phosphorylation status of PEPC was assessed by its sensitivity to L-malate inhibition at suboptimal assay conditions, and the activity state of PEPC-PK was determined by the in vitro 32P labeling of purified maize dephospho-PEPC by [[gamma]-32P]ATP/Mg. Illumination ([plus or minus]NO3-) for 1 h led to about a 4.5-fold increase in the 50% inhibition constant for L-malate, which was reversed by placing the illuminated detached leaves in darkness (minus NO3-). A 1 -h exposure of excised leaves to light, KNO3, or both resulted in relative PEPC-PK activities of 205, 119, and 659%, respectively, of the dark/0 mM KNO3 control tissue. In contrast, almost no activity was observed when a recombinant sorghum phosphorylation-site mutant (S8D) form of PEPC was used as protein substrate in PEPC-PK assays of the light plus KNO3 leaf extracts. In vivo labeling of wheat-leaf PEPC by feeding 32P-labeled orthophosphate showed that PEPC from light plus KNO3 tissue was substantially more phosphorylated than the enzyme in the dark minus-nitrate immunoprecipitates. Immunoblot analysis indicated that no changes in relative PEPC-protein amount occurred within 1 h for any of the treatments. Thus, C3 PEPC activity in these detached wheat leaves appears to be regulated by phosphorylation of a serine residue near the protein's N terminus by a Ca2+ -independent protein kinase in response to a complex interaction in vivo between light and N.
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PMID:In Vivo Regulation of Wheat-Leaf Phosphoenolpyruvate Carboxylase by Reversible Phosphorylation. 1222 2

C4 leaf phosphoenolpyruvate carboxylase (PEPC; EC 4.1.1.31) is subject to a day/night regulatory phosphorylation cycle. By using the cytoplasmic protein synthesis inhibitor cycloheximide (CHX), we previously reported that the reversible in vivo light activation of the C4 PEPC protein-serine kinase requires protein synthesis. In the present leaf gas-exchange study, we have examined how and to what extent the CHX-induced inhibition of PEPC protein kinase activity/PEPC phosphorylation in the light influences C4 photosynthesis. Detached Sorghum vulgare and maize (Zea mays) leaves fed 10 [mu]M CHX showed a gradual but marked decrease in photosynthetic CO2 assimilation capacity. A series of control experiments designed to assess deleterious secondary effects of the inhibitor established that this reduction in C4 leaf CO2 assimilation was not due to (a) an increased stomatal resistance to CO2 diffusion, (b) a decrease in the activation state of other photoactivated C4 cycle enzymes, and (c) a perturbation of the Benson-Calvin C3 cycle, as evidenced by the absence of an inhibitory effect of CHX on leaf photosynthesis by a C3 grass (Triticum aestivum). It is notable that the CHX-induced decrease in CO2 assimilation by illuminated Sorghum leaves was highly correlated with a decrease in the apparent phosphorylation status of PEPC and a concomitant change in carbon isotope discrimination consistent with a shift from a C4 to a C3 mode of leaf CO2 fixation. These collective findings indicate that the light-dependent activation of the PEPC protein-serine kinase and the resulting phosphorylation of serine-8 or serine-15 in Sorghum or maize PEPC, respectively, are fundamental regulatory events that influence leaf C4 photosynthesis in vivo.
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PMID:Regulatory Phosphorylation of C4 Phosphoenolpyruvate Carboxylase (A Cardinal Event Influencing the Photosynthesis Rate in Sorghum and Maize). 1223 40

The cAMP responsiveness of the phosphoenolpyruvate carboxykinase (PEPCK) gene promoter is mediated by a cAMP response unit, which includes three CCAAT/enhancer-binding protein (C/EBPs) sites, and a cAMP response element (CRE). Because both the CRE-binding protein and several C/EBP isoforms can to bind to the CRE with similar affinity, a variety of transcription factor bindings arrays in the cAMP response unit are possible that may affect the protein kinase A (PKA) responsivity of the promoter. To explore this issue, we have designed PEPCK promoter variants that have the native cis-elements within the cAMP response unit replaced with one or more LexA- and/or GAL4-binding sites. We also engineered the corresponding C/EBP and CRE-binding protein chimeras, which have their basic region leucine zipper domains replaced with LexA or GAL4 DNA-binding domains. Using this approach, we have reconstituted the PKA responsiveness of permissive PEPCK promoters in hepatoma cells and have characterized the PKA responsivity of the promoter under defined transcription factor occupancy patterns. Furthermore, analysis of deletion mutants of C/EBPalpha indicated that the domains that mediate its constitutive and PKA-inducible activities vary depending on which cis-element it occupies on the PEPCK promoter. These results suggest that promoter context may influence which domains within a transcription factor are employed to mediate transactivation.
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PMID:Different transcription factor binding arrays modulate the cAMP responsivity of the phosphoenolpyruvate carboxykinase gene promoter. 1223 88

C(4) phosphoenolpyruvate carboxylase (PEPCase: EC 4.1.1.31) is subjected to in vivo regulatory phosphorylation by a light up-regulated, calcium-independent protein kinase. Salt stress greatly enhanced phosphoenolpyruvate carboxylase-kinase (PEPCase-k) activity in leaves of Sorghum. The increase in PEPCase-k anticipated the time course of proline accumulation thereby suggesting that water stress was not involved in the kinase response to salt. Moreover, osmotic stress seemed not to be the main factor implicated, as demonstrated by the lack of effect when water availability was restricted by mannitol. In contrast, LiCl (at a concentration of 10 mM in short-term treatment of both excised leaves and whole plants) mimicked the effects of 172 mM NaCl salt-acclimation, indicating that the rise in PEPCase-k activity resulted primarily from the ionic stress. Both NaCl and LiCl treatments increased the activity of a Ca(2+)-independent, 35 kDa kinase, as demonstrated by an in-gel phosphorylation experiment. Short-term treatment of excised leaves with NaCl or LiCl partially reproduces the effects of whole plant treatments. Finally, salinization also increased PEPCase-k activity and the phosphorylation state of PEPCase in darkened Sorghum leaves. This fact, together with increased malate production during the dark period, suggests a shift towards mixed C(4) and crassulacean acid metabolism types of photosynthesis in response to salt stress.
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PMID:Characterization of salt stress-enhanced phosphoenolpyruvate carboxylase kinase activity in leaves of Sorghum vulgare: independence from osmotic stress, involvement of ion toxicity and significance of dark phosphorylation. 1256 7


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