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1
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Structure and functions of plant calcium-dependent protein kinases

100%
Klimecka M., Muszyńska G.
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2007
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vol. 54
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issue 2
219-233
EN
Calcium ions as second messengers play an essential role in many important cellular processes. In plants, transient changes in calcium content in the cytosol (calcium signatures) have been observed during growth, development and under stress conditions. Such diverse functions require many different calcium sensors. One of the largest and most differentiated group of calcium sensors are protein kinases, among them calcium-dependent protein kinases (CDPKs) which were identified only in plants and protists. CDPKs have a regulatory domain which is able to bind calcium ions. For regulation of CDPKs activities not only calcium ions but also specific phospholipids and autophosphorylation are responsible. CDPKs have many different substrates, which reflects the diversity of their functions. Potential protein substrates of CDPK are involved in carbon and nitrogen metabolism, phospholipid synthesis, defense responses, ion and water transport, cytoskeleton organization, transcription and hormone responses. Presently, participation of CDPKs in stress signal transduction pathways (e.g., cold, drought, high salinity, wounding) is intensively studied in many laboratories. An intriguing, but still not fully clarified problem is the cross-talk via CDPKs among different signaling pathways that enables signal integration at different levels and ensure appropriate downstream responses.
2
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Protein phosphatase 2A: Variety of forms and diversity of functions

81%
Lechward K., Awotunde O. S., Świątek W., Muszyńska G.
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2001
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vol. 48
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issue 4
921-933
EN
Protein phosphatase 2A (PP2A) comprises a diverse family of phosphoserine-and phosphothreonine-specific phosphatases present in all eukaryotic cells. All forms of PP2A contain a catalytic subunit (PP2Ac) which forms a stable complex with the structural subunit PR65/A. The heterodimer PP2Ac-PR65/A associates with regulatory proteins, termed variable subunits, in order to form trimeric holoenzymes attributed with distinct substrate specificity and targeted to different subcellular compartments. PP2Ac activity can be modulated by reversible phosphorylation on Tyr307 and methylation on C-terminal Leu309. Studies on PP2A have shown that this enzyme may be implicated in the regulation of metabolism, transcription, RNA splicing, translation, differentiation, cell cycle, oncogenic transformation and signal transduction.
3
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Interaction of maize (Zea mays) protein phosphatase 2A with tubulin

71%
Awotunde O. S., Lechward K., Krajewska K., Żołnierowicz S., Muszyńska G.
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2003
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vol. 50
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issue 1
131-138
EN
Immunological and biochemical evidence has been obtained for an interaction of maize protein phosphatase 2A (PP2A) holoenzyme with tubulin. Tubulin co-purifies with maize seedling PP2A. Affinity chromatography of the maize PP2A preparation on immobilized tubulin revealed two peaks of phosphorylase a phosphatase activity. In one of the peaks, the catalytic (C) and constant regulatory (A) subunits of PP2A were identified by Western blotting. The subunits (C and A) of PP2A were co-immunoprecipitated from maize seedlings homogenate by an anti-α-tubulin antibody. The interaction of plant PP2A with tubulin indicates a possible role of reversible protein phosphorylation in the dynamic structure of plant cytoskeleton.
4
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Characterization of dual specificity protein kinase from maize seedlings.

71%
Trojanek J. B., Klimecka M. M., Fraser A., Dobrowolska G., Muszyńska G.
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vol. 51
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issue 3
635-647
EN
A protein kinase of 57 kDa, able to phosphorylate tyrosine in synthetic substrates pol(Glu4,Tyr1) and a fragment of Src tyrosine kinase, was isolated and partly purified from maize seedlings (Zea mays). The protein kinase was able to phosphorylate exogenous proteins: enolase, caseins, histones and myelin basic protein. Amino acid analysis of phosphorylated casein and enolase, as well as of phosphorylated endogenous proteins, showed that both Tyr and Ser residues were phosphorylated. Phosphotyrosine was also immunodetected in the 57 kDa protein fraction. In the protein fraction there are present 57 kDa protein kinase and enolase. This co-purification suggests that enolase can be an endogenous substrate of the kinase. The two proteins could be resolved by two-dimensional electrophoresis. Specific inhibitors of typical protein-tyrosine kinases had essentially no effect on the activity of the maize enzyme. Staurosporine, a nonspecific inhibitor of protein kinases, effectively inhibited the 57 kDa protein kinase. Also, poly L-lysine and heparin inhibited tyrosine phosphorylation by 57 kDa maize protein kinase. The substrate and inhibitor specificities of the 57 kDa maize protein kinase phosphorylating tyrosine indicate that it is a novel plant dual-specificity protein kinase.
5
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Regulation of wound-responsive calcium-dependent protein kinase from maize (ZmCPK11) by phosphatidic acid

61%
Klimecka M., Szczegielniak J., Godecka L., Lewandowska-Gnatowska E., Dobrowolska G., Muszyńska G.
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2011
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vol. 58
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issue 4
589-595
EN
In plant cells, phospholipids are not only membrane components but also act as second messengers interacting with various proteins and regulating diverse cellular processes, including stress signal transduction. Here, we report studies on the effects of various phospholipids on the activity and expression of maize wound-responsive calcium-dependent protein kinase (ZmCPK11). Our results revealed that in leaves treated with n-butanol, a potent inhibitor of phosphatidic acid (PA) synthesis catalyzed by phospholipase D, a significant decrease of ZmCPK11 activity was observed, indicating contribution of PA in the kinase activation. Using lipid binding assays, we demonstrate that among various phospholipids only saturated acyl species (16 : 0 and 18 : 0) of phosphatidic acid are able to bind to ZmCPK11. Saturated acyl species of PA are also able to stimulate phosphorylation of exogenous substrates by ZmCPK11 and autophosphorylation of the kinase. The level of ZmCPK11 autophosphorylation is correlated with its enzymatic activity. RT-PCR analysis showed that transcript level of ZmCPK11 in maize leaves increased in response to PA treatment. The influence of PA on the activity and transcript level of ZmCPK11 suggests an involvement of this kinase in a PA-mediated wound signal transduction pathway.
6
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Phosphorylation of sucrose synthase from maize seedlings

61%
Lindblom S., Ek P., Muszyńska G., Ek B., Szczegielniak J., Engström L.
Acta Biochimica Polonica
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1997
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vol. 44
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issue 4
809-817
7
Content available remote

Chemical modification of rat liver arginase

50%
Ber E., Muszyńska G.
Acta Biochimica Polonica
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1979
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vol. 26
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issue 1-2
103-114
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