The protein kinase 60S is a free catalytic CK2alpha' subunit and forms an inactive complex with superoxide dismutase SOD1

Changes in a Protein Profile Can Account for the Altered Phenotype of the Yeast Saccharomyces cerevisiae Mutant Lacking the Copper-Zinc Superoxide Dismutase

Copper-zinc superoxide dismutase (SOD1) is an antioxidant enzyme that catalyzes the disproportionation of superoxide anion to hydrogen peroxide and molecular oxygen (dioxygen). The yeast Saccharomyces cerevisiae lacking SOD1 (Δsod1) is hypersensitive to the superoxide anion and displays a number of oxidative stress-related alterations in its phenotype. We compared proteomes of the wild-type strain and the Δsod1 mutant employing two-dimensional gel electrophoresis and detected eighteen spots representing differentially expressed proteins, of which fourteen were downregulated and four upregulated. Mass spectrometry-based identification enabled the division of these proteins into functional classes related to carbon metabolism, amino acid and protein biosynthesis, nucleotide biosynthesis, and metabolism, as well as antioxidant processes. Detailed analysis of the proteomic data made it possible to account for several important morphological, biochemical, and physiological changes earlier observed for the SOD1 mutation. An example may be the proposed additional explanation for methionine auxotrophy. It is concluded that protein comparative profiling of the Δsod1 yeast may serve as an efficient tool in the elucidation of the mutation-based systemic alterations in the resultant S. cerevisiae phenotype.

A proteomic screen of Ty1 integrase partners identifies the protein kinase CK2 as a regulator of Ty1 retrotransposition

Background

Transposable elements are ubiquitous and play a fundamental role in shaping genomes during evolution. Since excessive transposition can be mutagenic, mechanisms exist in the cells to keep these mobile elements under control. Although many cellular factors regulating the mobility of the retrovirus-like transposon Ty1 in Saccharomyces cerevisiae have been identified in genetic screens, only very few of them interact physically with Ty1 integrase (IN).

Results

Here, we perform a proteomic screen to establish Ty1 IN interactome. Among the 265 potential interacting partners, we focus our study on the conserved CK2 kinase. We confirm the interaction between IN and CK2, demonstrate that IN is a substrate of CK2 in vitro and identify the modified residues. We find that Ty1 IN is phosphorylated in vivo and that these modifications are dependent in part on CK2. No significant change in Ty1 retromobility could be observed when we introduce phospho-ablative mutations that prevent IN phosphorylation by CK2 in vitro. However, the absence of CK2 holoenzyme results in a strong stimulation of Ty1 retrotransposition, characterized by an increase in Ty1 mRNA and protein levels and a high accumulation of cDNA.

Conclusion

Our study shows that Ty1 IN is phosphorylated, as observed for retroviral INs and highlights an important role of CK2 in the regulation of Ty1 retrotransposition. In addition, the proteomic approach enabled the identification of many new Ty1 IN interacting partners, whose potential role in the control of Ty1 mobility will be interesting to study.

Proteomic response of Trichoderma aggressivum f. europaeum to Agaricus bisporus tissue and mushroom compost

A cellular proteomic analysis was performed on Trichoderma aggressivum f. europaeum. Thirty-four individual protein spots were excised from 2-D electropherograms and analysed by ESI-Trap Liquid Chromatography Mass Spectrometry (LC/MS). Searches of the NCBInr and SwissProt protein databases identified functions for 31 of these proteins based on sequence homology. A differential expression study was performed on the intracellular fraction of T. aggressivum f. europaeum grown in media containing Agaricus bisporus tissue and Phase 3 mushroom compost compared to a control medium. Differential expression was observed for seven proteins, three of which were upregulated in both treatments, two were down regulated in both treatments and two showed qualitatively different regulation under the two treatments. No proteins directly relating to fungal cell wall degradation or other mycoparasitic activity were observed. Functions of differentially produced intracellular proteins included oxidative stress tolerance, cytoskeletal structure, and cell longevity. Differential production of these proteins may contribute to the growth of T. aggressivum in mushroom compost and its virulence toward A. bisporus.

Functional characterization of protein kinase CK2 regulatory subunits regulating Penicillium oxalicum asexual development and hydrolytic enzyme production

Casein kinase CK2 is a ubiquitous and conserved phosphate transferase that is critical for the growth and development of eukaryotic cells. In Penicillium oxalicum, one catalytic subunit (CK2A) and two regulatory subunits (CK2B1 and CK2B2) of CK2 were annotated. In this study, CK2 regulatory subunit-defective mutants Δck2B1 and Δck2B2 were constructed to investigate the biological function of CK2 in P. oxalicum. The Δck2B1 strain exhibited minimal changes in morphogenesis and conidiation, whereas the Δck2B2 strain showed delayed conidial germination and drastically reduced conidiation compared with the parent strain. The defect in conidiation in Δck2B2 could be attributed to the reduced expression of transcription factor BrlA. Both Δck2B1 and Δck2B2 showed delayed autolysis in carbon-starvation medium compared with the parent strain. Cellulase and amylase production were decreased considerably in both mutants. The transcript abundances of the main extracellular glycoside hydrolase genes cel7A-2, bgl1, and amy15A, as well as those of three related transcriptional activators (i.e., ClrB, XlnR, and AmyR), were reduced or delayed in the mutants. Epistasis analysis suggested that CK2B1 and CK2B2 might function upstream of transcription factor CreA by inhibiting its repressing activity. In summary, CK2 plays important roles in development and extracellular enzyme production in P. oxalicum, with both unique and overlapping functions performed by the two regulatory subunits.

Isolation of a CK2α subunit and the holoenzyme from the mussel Mytilus galloprovincialis and construction of the CK2α and CK2β cDNAs

Protein kinase CK2 is a ubiquitous, highly pleiotropic, and constitutively active phosphotransferase that phosphorylates mainly serine and threonine residues. CK2 has been studied and characterized in many organisms, from yeast to mammals. The holoenzyme is generally composed of two catalytic (α and/or α') and two regulatory (β) subunits, forming a differently assembled tetramer. The free and catalytically active α/α' subunits can be present in cells under some circumstances. We present here the isolation of a putative catalytic CK2α subunit and holoenzyme from gills of the mussel Mytilus galloprovincialis capable of phosphorylating the purified recombinant ribosomal protein rMgP1. For further analysis of M. galloprovincialis protein kinase CK2, the cDNA molecules of CK2α and CK2β subunits were constructed and cloned into expression vectors, and the recombinant proteins were purified after expression in Escherichia coli. The recombinant MgCK2β subunit and MgP1 were phosphorylated by the purified recombinant MgCK2α subunit. The mussel enzyme presented features typical for CK2: affinity for GTP, inhibition by both heparin and ATP competitive inhibitors (TBBt, TBBz), and sensitivity towards NaCl. Predicted amino acid sequence comparison showed that the M. galloprovincialis MgCK2α and MgCK2β subunits have similar features to their mammalian orthologs.

Casein Kinase II: an attractive target for anti-cancer drug design

Casein Kinase II (CK2) is a ubiquitous serine/threonine kinase that is highly conserved in eukaryotic cells. CK2 has been shown to impact cell growth and proliferation, as numerous growth-related proteins are substrates of CK2. More importantly, experimental evidence linking increased expression and activity of CK2 to human cancers underscores the relevance of CK2 biology to cellular transformation and carcinogenesis. Due to the critical regulatory role CK2 plays in cell fate determination in cancer cells, there is a tremendous interest in the development of CK2-specific therapies. Supporting this, recent reports have demonstrated that genetic manipulation of CK2 expression as well as pharmacological inhibition of its enzymatic activity sensitizes cancers to apoptotic stimuli. Here we provide a succinct account of the biology of CK2, its cellular substrates, its pro-survival and pro-proliferation activity, and highlight evidence for its involvement in human cancer.

Differential phosphorylation of plant translation initiation factors by Arabidopsis thaliana CK2 holoenzymes

A previously described wheat germ protein kinase (Yan, T. F., and Tao, M. (1982) J. Biol. Chem. 257, 7037-7043) was identified unambiguously as CK2 using mass spectrometry. CK2 is a ubiquitous eukaryotic protein kinase that phosphorylates a wide range of substrates. In previous studies, this wheat germ kinase was shown to phosphorylate eIF2alpha, eIF3c, and three large subunit (60 S) ribosomal proteins (Browning, K. S., Yan, T. F., Lauer, S. J., Aquino, L. A., Tao, M., and Ravel, J. M. (1985) Plant Physiol. 77, 370-373). To further characterize the role of CK2 in the regulation of translation initiation, Arabidopsis thaliana catalytic (alpha1 and alpha2) and regulatory (beta1, beta2, beta3, and beta4) subunits of CK2 were cloned and expressed in Escherichia coli. Recombinant A. thaliana CK2beta subunits spontaneously dimerize and assemble into holoenzymes in the presence of either CK2alpha1 or CK2alpha2 and exhibit autophosphorylation. The purified CK2 subunits were used to characterize the properties of the individual subunits and their ability to phosphorylate various plant protein substrates. CK2 was shown to phosphorylate eIF2alpha, eIF2beta, eIF3c, eIF4B, eIF5, and histone deacetylase 2B but did not phosphorylate eIF1, eIF1A, eIF4A, eIF4E, eIF4G, eIFiso4E, or eIFiso4G. Differential phosphorylation was exhibited by CK2 in the presence of various regulatory beta-subunits. Analysis of A. thaliana mutants either lacking or overexpressing CK2 subunits showed that the amount of eIF2beta protein present in extracts was affected, which suggests that CK2 phosphorylation may play a role in eIF2beta stability. These results provide evidence for a potential mechanism through which the expression and/or subcellular distribution of CK2 beta-subunits could participate in the regulation of the initiation of translation and other physiological processes in plants.

Surface-enhanced Raman scattering and DFT computational studies of a benzotriazole derivative

Here, we report the surface-enhanced Raman scattering (SERS) spectrum of 2-(2'-hydroxy-5'-methylphenyl)benzotriazole (Tinuvin P), a benzotriazole derivative that is the most widely used commercially available UV absorber or stabilizer and is used representatively for the research of photostability mechanism. A full assignment of the Raman spectrum has been made based on the scaled-DFT analysis of the normal vibrational modes. Through the comparative studies on the ordinary Raman spectrum and the SERS spectrum of Tinuvin P, we propose that this molecule binds the Au atom, via the O atom of the hydroxyl or the N1 atom of the benzotriazole moiety, with a perpendicular geometry.

Yeast surviving factor Svf1 as a new interacting partner, regulator and in vitro substrate of protein kinase CK2

Since Svf1 is phosphoprotein, we investigated whether it was a substrate for protein kinase CK2. According to the amino acid sequence Svf1 harbours 20 putative CK2 phosphorylation sites. Here, we have reported cloning, overexpression, purification and characterization of yeast Svf1 as a substrate for three forms of yeast CK2. Svf1 serves as a substrate for both the recombinant CK2alpha (Km 0.35 microM) and CK2alpha' (Km 0.18 microM) as well as CK2 holoenzyme (Km 1.1 microM). Different Km values argue that CK2beta(beta') subunit has an inhibitory effect on the activity of both CK2alpha and CK2alpha' towards surviving factor Svf1. Reconstitution of alpha'2betabeta' isoform of CK2 holoenzyme shows that beta/beta' subunits have regulatory effect depending on the kind of CK2 catalytic subunit. This effect was not observed in the case of alpha2betabeta' isoform, which may be due to interaction between Svf1 and regulatory CK2beta subunit (shown by co-immunoprecipitation experiments). Interactions between CK2 subunits and Svf1 protein may have influence on ATP as well as ATP-competitive inhibitors (TBBt and TBBz) binding. CK2 phosphorylates up to six serine residues in highly acidic peptide K199EVIPESDEEESSADEDDNEDEDEESGDSEEESGSEEESDSEEVEITYED248 of the Svf1 protein in vitro. Presented data may help to elucidate the role of protein kinase CK2 and Svf1 in the regulation of cell survival pathways.

Mass spectrometry analysis of a protein kinase CK2beta subunit interactome isolated from mouse brain by affinity chromatography

CK2, an acronym derived from the misnomer "casein kinase 2", denotes a ubiquitous and extremely pleiotropic Ser/Thr protein kinase, the holoenzyme of which is composed of two catalytic (alpha and/or alpha') and two noncatalytic beta subunits acting as a docking platform and the multifarious functions of which are still incompletely understood. By combining affinity chromatography and mass spectrometry, we have identified 144 mouse brain proteins that associate with immobilized CK2beta. A large proportion (60%) of the identified proteins had been previously reported to be functionally related to CK2, and a similar proportion have been classified as phosphoproteins with approximately half of these having the features of CK2 targets. A large number of the identified proteins ( approximately 40%) either are nuclear or shuttle between the nucleus and cytoplasm, and the biggest functional classes of CK2beta interactors are committed to protein synthesis and degradation (32 proteins) and RNA/DNA interaction (20 proteins). Also well represented are the categories of cytoskeletal/structural proteins (19), trafficking proteins (17), and signaling proteins (14). The identified proteins are examined in relation to their functions and potential as targets and/or regulators of CK2, disclosing in some cases unanticipated links between this kinase and a variety of biochemical events.

Characterization of protein kinase CK2 from Trypanosoma brucei

CK2 is a ubiquitous but enigmatic kinase. The difficulty in assigning a role to CK2 centers on the fact that, to date, no biologically relevant modulator of its function has been identified. One common theme revolves around a constellation of known substrates involved in growth control, compatible with its concentration in the nucleus and nucleolus. We had previously described the identification of two catalytic subunits of CK2 in Trypanosoma brucei and characterized one of them. Here we report the characterization of the second catalytic subunit, CK2alpha', and the identification and characterization of the regulatory subunit CK2beta. All three subunits are primarily localized to the nucleolus in T. brucei. We also show that CK2beta interacts with the nucleolar protein NOG1, adding to the interaction map which previously linked CK2alpha to the nucleolar protein NOPP44/46, which in turn associates with the rRNA binding protein p37. CK2 activity has four distinctive features: near equal affinity for GTP and ATP, heparin sensitivity, and stimulation by polyamines and polybasic peptides. Sequence comparison shows that the parasite orthologues have mutations in residues previously mapped as important in specifying affinity for GTP and stimulation by both polyamines and polybasic peptides. Studies of the enzymatic activity of the T. brucei CK2s show that both the affinity for GTP and stimulation by polyamines have been lost and only the features of heparin inhibition and stimulation by polybasic peptides are conserved.

Yeast holoenzyme of protein kinase CK2 requires both beta and beta' regulatory subunits for its activity

Protein kinase CK2 is a highly conserved Ser/Thr protein kinase that is ubiquitous among eucaryotic organisms and appears to play an important role in many cellular functions. This enzyme in yeast has a tetrameric structure composed of two catalytic (alpha and/or alpha') subunits and two regulatory beta and beta' subunits. Previously, we have reported isolation from yeast cells four active forms of CK2, composed of alphaalpha'betabeta', alpha2betabeta', alpha'2betabeta' and a free alpha'-catalytic subunit. Now, we report that in Saccharomyces cerevisiae CK2 holoenzyme regulatory beta subunit cannot substitute other beta' subunit and only both of them can form fully active enzymatic unit. We have examined the subunit composition of tetrameric complexes of yeast CK2 by transformation of yeast strains containing single deletion of the beta or beta' regulatory subunits with vectors carrying lacking CKB1 or CKB2 genes. CK2 holoenzyme activity was restored only in cases when both of them were present in the cell. Additional, co-immunoprecypitation experiments show that polyadenylation factor Fip1 interacts with catalytic alpha subunits of CK2 and interaction with beta subunits in the holoenzyme decreases CK2 activity towards this protein substrate. These data may help to elucidate the role of yeast protein kinase CK2beta/beta' subunits in the regulation of holoenzyme assembly and phosphotransferase activity.

TBBz but not TBBt discriminates between two molecular forms of CK2 in vivo and its implications

Two ATP-competitive inhibitors-4,5,6,7-tetrabromo-benzotriazole (TBBt) and 4,5,6,7-tetrabromo-benzimidazole (TBBz) have been shown to decrease activity of CK2 holoenzyme. Surprisingly it occurs that TBBz contrary to TBBt does not inhibit free catalytic subunit CK2 [Formula: see text]. Both inhibitors are virtually inactive against RAP protein kinase. The above-mentioned protein kinases phosphorylate in vitro a set of acidic ribosomal P-proteins of the 60S ribosomal subunit. Such a modification is one of the mechanisms regulating translational activity of ribosomes in vivo. Application of these two very selective inhibitors allows us to define the role of free catalytic [Formula: see text] subunit of CK2 in phosphorylation of ribosomal proteins. It occurs that CK2 [Formula: see text] but not CK2 holoenzyme is responsible for phosphorylation of P-proteins in vivo. Moreover, elimination of both forms of protein kinase CK2 (hCK2 and CK2 [Formula: see text] ) activity in living cells led to dramatic loss of the translational activity of the ribosome.