Cloning and Characterization of a Novel Ca2+/Calmodulin-Dependent Protein Kinase I Homologue in Xenopus laevis

Biochemical characterization of four splice variants of mouse Ca2+/calmodulin-dependent protein kinase Iδ

Ca2+/calmodulin (CaM)-dependent protein kinase Iδ (CaMKIδ) is a Ser/Thr kinase that plays pivotal roles in Ca2+ signalling. CaMKIδ is activated by Ca2+/CaM-binding and phosphorylation at Thr180 by CaMK kinase (CaMKK). In this study, we characterized four splice variants of mouse CaMKIδ (mCaMKIδs: a, b, c and d) found by in silico analysis. Recombinant mCaMKIδs expressed in Escherichia coli were phosphorylated by CaMKK; however, only mCaMKIδ-a and c showed protein kinase activities towards myelin basic protein in vitro, with mCaMKIδ-b and mCaMKIδ-d being inactive. Although mCaMKIδ-a and mCaMKIδ-c underwent autophosphorylation in vitro, only mCaMKIδ-c underwent autophosphorylation in 293T cells. Site-directed mutagenesis showed that the autophosphorylation site is Ser349, which is found in the C-terminal region of only variants c and b (Ser324). Furthermore, phosphorylation of these sites (Ser324 and Ser349) in mCaMKIδ-b and c was more efficiently catalyzed by cAMP-dependent protein kinase in vitro and in cellulo as compared to the autophosphorylation of mCaMKIδ-c. Thus, variants of mCaMKIδ possess distinct properties in terms of kinase activities, autophosphorylation and phosphorylation by another kinase, suggesting that they play physiologically different roles in murine cells.

Dual phosphorylation of protein phosphatase PPM1H promotes dephosphorylation of Smad1 in cellulo

Protein phosphatase PPM1H is known to participate in various biological or pathophysiological mechanisms. However, little is known about the molecular mechanisms of its regulation. In this study, we investigated the protein kinases that directly phosphorylate PPM1H, identifying them as cAMP-dependent protein kinase (PKA) and Ca²⁺/calmodulin-dependent protein kinase I (CaMKI). In vitro and in silico analyses showed that the phosphorylation sites of PPM1H by PKA and CaMKI were Ser-123 and Ser-210, respectively. The phosphorylation state of PPM1H in cells exhibited the kinase activator- and inhibitor-dependent changes. In mouse neuroblastoma Neuro2a cells, phosphorylation of Ser-210 was much higher in the phospho-mimetic mutant (S123D) than in the non-phosphorylatable mutant (S123A) when they were treated with ionomycin. This suggests that a hierarchical phosphorylation, with initial phosphorylation of Ser-123 promoting subsequent phosphorylation of Ser-210, occurs in these neuron-like cells. Moreover, in cell-based assay a PPM1H(S123A/S210A) double mutant barely dephosphorylated Smad1, a transcription factor known as an endogenous substrate of PPM1H. These results suggest that cAMP and Ca²⁺/calmodulin regulate dephosphorylation of Smad1 through the dual phosphorylation of PPM1H at Ser-123 and Ser-210.

Multi-PK antibodies: Powerful analytical tools to explore the protein kinase world

Diverse biological events are regulated through protein phosphorylation mediated by protein kinases. Some of these protein kinases are known to be involved in the pathogenesis of various diseases. Although 518 protein kinase genes were identified in the human genome, it remains unclear how many and what kind of protein kinases are expressed and activated in cells and tissues under varying situations. To investigate cellular signaling by protein kinases, we developed monoclonal antibodies, designated as Multi-PK antibodies, that can recognize multiple protein kinases in various biological species. These Multi-PK antibodies can be used to profile the kinases expressed in cells and tissues, identify the kinases of special interest, and analyze protein kinase expression and phosphorylation state. Here we introduce some applications of Multi-PK antibodies to identify and characterize the protein kinases involved in epigenetics, glucotoxicity in type 2 diabetes, and pathogenesis of ulcerative colitis. In this review, we focus on the recently developed technologies for kinomics studies using the powerful analytical tools of Multi-PK antibodies.

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Multi-PK antibodies recognize a wide variety of protein kinases.

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New analytical methods using Multi-PK antibodies for protein kinase studies are explained.

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Kinomics studies using Multi-PK antibodies are introduced.

Expression and phosphorylation state analysis of intracellular protein kinases using Multi-PK antibody and Phos-tag SDS-PAGE

Protein kinase expression and activity play important roles in diverse cellular functions through regulation of phosphorylation signaling. The most commonly used tools for detecting the protein kinase are protein kinase-specific antibodies, and phosphorylation site-specific antibodies were used for detecting activated protein kinase. Using these antibodies, only one kinase was analyzed at a time, however, a method for analyzing the expression and activation of a panel of protein kinases in cells is not established. Therefore, we developed a combined method using Multi-PK antibody and Phos-tag SDS-PAGE for profiling the expression and phosphorylation state of intracellular protein kinases. Using the new method, changes in the expression and phosphorylation state of various protein kinases were detected in cells treated with anticancer agent which inhibit multiple tyrosine kinase activities. Therefore, the new method is a useful technique for analysis of intracellular protein kinases.•

Multi-PK antibody recognizes a wide variety of protein kinases in various species.

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Using Phos-tag SDS-PAGE, phosphorylated proteins are visualized as slower migration bands compared with corresponding non-phosphorylated proteins.

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This combined method can be used for detecting changes in the expression and phosphorylation state of various intracellular protein kinases.

Regulation of Ca(2+)/calmodulin-dependent protein kinase phosphatase (CaMKP/PPM1F) by protocadherin-γC5 (Pcdh-γC5)

Ca(2+)/calmodulin-dependent protein kinase phosphatase (CaMKP/PPM1F) is a Ser/Thr protein phosphatase that belongs to the PPM family. It is important to identify an endogenous regulator of CaMKP. Using an Escherichia coli two-hybrid screening method, we identified the C-terminal cytoplasmic fragment of protocadherin γ subfamily C5 (Pcdh-γC5), which was generated by intracellular processing, as a CaMKP-binding protein. Dephosphorylation of phosphorylated Ca(2+)/calmodulin-dependent protein kinase I (CaMKI) by CaMKP was significantly activated by the C-terminal cytoplasmic fragment, Pcdh-γC5(715-944), both in vitro and in cells, suggesting that the C-terminal fragment functions as an endogenous activator of CaMKP. The nuclear translocation of the fragment was blocked by its binding to cytoplasmic CaMKP to form a ternary complex with CaMKI. Taken together, these results strongly suggest that the C-terminal cytoplasmic fragment of Pcdh-γC5 acts as a scaffold for CaMKP and CaMKI to regulate CaMKP activity. These findings may provide new insights into the reversible regulation of CaMKP in cells.

The Phosphatase-Resistant Isoform of CaMKI, Ca²⁺/Calmodulin-Dependent Protein Kinase Iδ (CaMKIδ), Remains in Its "Primed" Form without Ca²⁺ Stimulation

Ca²⁺/calmodulin-dependent protein kinase I (CaMKI) is known to play pivotal roles in Ca²⁺ signaling pathways. Four isoforms of CaMKI (α, β, γ, and δ) have been reported so far. CaMKI is activated through phosphorylation by the upstream kinase, CaMK kinase (CaMKK), and phosphorylates downstream targets. When CaMKI was transiently expressed in 293T cells, CaMKIα was not phosphorylated at all under low-Ca²⁺ conditions in the cells. In contrast, we found that CaMKIδ was significantly phosphorylated and activated to phosphorylate cAMP response element-binding protein (CREB) under the same conditions. Herein, we report that the sustained activation of CaMKIδ is ascribed to its phosphatase resistance resulting from the structure of its N-terminal region. First, we examined whether CaMKIδ is more readily phosphorylated by CaMKK than CaMKIα, but no significant difference was observed. Next, to compare the phosphatase resistance between CaMKIα and CaMKIδ, we assessed the dephosphorylation of the phosphorylated CaMKIs by CaMK phosphatase (CaMKP/PPM1F). Surprisingly, CaMKIδ was hardly dephosphorylated by CaMKP, whereas CaMKIα was significantly dephosphorylated under the same conditions. To date, there have been no detailed reports concerning dephosphorylation of CaMKI. Through extensive analysis of CaMKP-catalyzed dephosphorylation of various chimeric and point mutants of CaMKIδ and CaMKIα, we identified the amino acid residues responsible for the phosphatase resistance of CaMKIδ (Pro-57, Lys-62, Ser-66, Ile-68, and Arg-76). These results also indicate that the phosphatase resistance of CaMKI is largely affected by only several amino acids in its N-terminal region. The phosphatase-resistant CaMKI isoform may play a physiological role under low-Ca²⁺ conditions in the cells.

Cellular localization of CoPK12, a Ca(2+)/calmodulin-dependent protein kinase in mushroom Coprinopsis cinerea, is regulated by N-myristoylation

Multifunctional Ca(2+)/calmodulin-dependent protein kinases (CaMKs) have been extensively studied in mammals, whereas fungus CaMKs still remain largely uncharacterized. We previously obtained CaMK homolog in Coprinopsis cinerea, designated CoPK12, and revealed its unique catalytic properties in comparison with the mammalian CaMKs. To further clarify the regulatory mechanisms of CoPK12, we investigated post-translational modification and subcellular localization of CoPK12 in this study. In C. cinerea, full-length CoPK12 (65 kDa) was fractionated in the membrane fraction, while the catalytically active fragment (46 kDa) of CoPK12 was solely detected in the soluble fraction by differential centrifugation. Expressed CoPK12-GFP was localized on the cytoplasmic and vacuolar membranes as visualized by green fluorescence in yeast cells. In vitro N-myristoylation assay revealed that CoPK12 is N-myristoylated at Gly-2 in the N-terminal position. Furthermore, calmodulin could bind not only to CaM-binding domain but also to the N-terminal myristoyl moiety of CoPK12. These results, taken together, suggest that the cellular localization and function of CoPK12 are regulated by protein N-myristoylation and limited proteolysis.

Calcium/calmodulin-dependent kinases are involved in growth, thermotolerance, oxidative stress survival, and fertility in Neurospora crassa

Calcium/calmodulin-dependent kinases (Ca(2+)/CaMKs) are Ser/Thr protein kinases that respond to change in cytosolic free Ca(2+) ([Ca(2+)]c) and play multiple cellular roles in organisms ranging from fungi to humans. In the filamentous fungus Neurospora crassa, four Ca(2+)/CaM-dependent kinases, Ca(2+)/CaMK-1 to 4, are encoded by the genes NCU09123, NCU02283, NCU06177, and NCU09212, respectively. We found that camk-1 and camk-2 are essential for full fertility in N. crassa. The survival of ∆camk-2 mutant was increased in induced thermotolerance and oxidative stress conditions. In addition, the ∆camk-1 ∆camk-2, ∆camk-4 ∆camk-2, and ∆camk-3 ∆camk-2 double mutants display slow growth phenotype, reduced aerial hyphae, decreased thermotolerance, and increased sensitivity to oxidative stress, revealing the genetic interactions among these kinases. Therefore, Ca(2+)/CaMKs are involved in growth, thermotolerance, oxidative stress tolerance, and fertility in N. crassa.

In-gel phosphatase assay using fluorogenic and radioactive substrates

To investigate the regulatory mechanisms of cellular signaling by protein phosphorylation, it is important to analyze protein phosphatases, as well as protein kinases expressed in cells and tissues. In this unit, two different types of in-gel phosphatase assays are described. The first is an in-gel phosphatase assay using fluorogenic substrates. Protein samples containing phosphatase activities are resolved by native polyacrylamide gel electrophoresis (native-PAGE) and phosphatase activities detected in situ using fluorogenic substrates, such as 4-methylumbelliferyl phosphate (MUP) or 6,8-difluoro-4-methylumbelliferyl phosphate (DiFMUP). The other assay is an in-gel phosphatase assay using (32)P-labeled substrates. In this method, protein samples are resolved by SDS-polyacrylamide gel electrophoresis (SDS-PAGE) using polyacrylamide gels containing (32)P -labeled substrates, renatured in situ, and the dephosphorylating activities detected by autoradiography. Each method has advantages and disadvantages that are discussed in the commentary.

Functional processing of nuclear Ca2+/calmodulin-dependent protein kinase phosphatase (CaMKP-N): evidence for a critical role of proteolytic processing in the regulation of its catalytic activity, subcellular localization and substrate targeting in vivo

Ca(2+)/calmodulin-dependent protein kinase phosphatase (CaMKP) and its nuclear homolog CaMKP-N are Ser/Thr protein phosphatases that belong to the PPM family. These phosphatases are highly specific for multifunctional CaM kinases and negatively regulate their activities. CaMKP-N is only expressed in the brain and specifically localized in the nucleus. In this study, we found that zebrafish CaMKP-N (zCaMKP-N) underwent proteolytic processing in both the zebrafish brain and Neuro2a cells. In Neuro2a cells, the proteolytic processing was effectively inhibited by the proteasome inhibitors MG-132, Epoxomicin, and Lactacystin, suggesting that the ubiquitin-proteasome pathway was involved in this processing. Using MG-132, we found that the proteolytic processing changed the subcellular localization of zCaMKP-N from the nucleus to the cytosol. Accompanying this change, the cellular targets of zCaMKP-N in Neuro2a cells were significantly altered. Furthermore, we obtained evidence that the zCaMKP-N activity was markedly activated when the C-terminal domain was removed by the processing. Thus, the proteolytic processing of zCaMKP-N at the C-terminal region regulates its catalytic activity, subcellular localization and substrate targeting in vivo.

The DNA-binding activity of mouse DNA methyltransferase 1 is regulated by phosphorylation with casein kinase 1delta/epsilon

Dnmt1 (DNA methyltansferase 1) is an enzyme that recognizes and methylates hemimethylated DNA during DNA replication to maintain methylation patterns. The N-terminal region of Dnmt1 is known to form an independent domain structure that interacts with various regulatory proteins and DNA. In the present study, we investigated protein kinases in the mouse brain that could bind and phosphorylate the N-terminal regulatory domain of Dnmt1. A protein fraction containing protein kinase activity for phosphorylation of Dnmt1(1-290) was prepared using Dnmt1(1-290)-affinity, DNA-cellulose and gel-filtration columns. When the proteins in this fraction were analysed by LC-MS/MS (liquid chromatography tandem MS), CK1delta/epsilon (casein kinase 1delta/epsilon) was the only protein kinase identified. Recombinant CK1delta/epsilon was found to bind to the N-terminal domain of Dnmt1 and significantly phosphorylated this domain, especially in the presence of DNA. Phosphorylation analyses using various truncation and point mutants of Dnmt1 revealed that the major priming site phosphorylated by CK1delta/epsilon was Ser146, and that subsequent phosphorylation at other sites may occur after phosphorylation of the priming site. When the DNA-binding activity of phosphorylated Dnmt1 was compared with that of the non-phosphorylated form, phosphorylation of Dnmt1 was found to decrease the affinity for DNA. These results suggest that CK1delta/epsilon binds to and phosphorylates the N-terminal domain of Dnmt1 and regulates Dnmt1 function by reducing the DNA-binding activity.

Identification of an endogenous substrate of zebrafish doublecortin-like protein kinase using a highly active truncation mutant

Doublecortin-like protein kinase (DCLK), a Ser/Thr protein kinase predominantly expressed in brain and eyes, is believed to play crucial roles in neuronal functions. However, the regulatory mechanisms for DCLK activation and its physiological targets are still unknown. In the present study, we found that a deletion mutant consisting of the catalytic domain of zebrafish DCLK, zDCLK(377-677), exhibited the highest activity among various mutants. Since fully active zDCLK(377-677) showed essentially the same substrate specificity as wild-type zDCLK, we used it to search for physiological substrates of zDCLK. When a zebrafish brain extract was resolved by isoelectric focusing and then phosphorylated by zDCLK(377-677), a highly basic protein with a molecular mass of approximately 90 kDa was detected. This protein was identified as synapsin II by mass spectrometric analysis. Synapsin II was found to interact with the catalytic domain of zDCLK and was phosphorylated at Ser-9 and Ser-58. When synaptosomes were isolated from zebrafish brain, both synapsin II and zDCLK were found to coexist in this preparation. Furthermore, synapsin II in the synaptosomes was efficiently phosphorylated by zDCLK. These results suggest that zDCLK mediates its neuronal functions through phosphorylation of physiological substrates such as synapsin II.

Cyclin-dependent kinase-like 5 binds and phosphorylates DNA methyltransferase 1

DNA methyltransferase 1 (Dnmt1) is an enzyme that recognizes and methylates hemimethylated CpG after DNA replication to maintain methylation patterns. Although the N-terminal region of Dnmt1 is known to interact with various proteins, such as methyl-CpG-binding protein 2 (MeCP2), the associations of protein kinases with this region have not been reported. In the present study, we found that a 110-kDa protein kinase in mouse brain could bind to the N-terminal domain of Dnmt1. This 110-kDa kinase was identified as cyclin-dependent kinase-like 5 (CDKL5) by LC-MS/MS analysis. CDKL5 and Dnmt1 were found to colocalize in nuclei and appeared to interact with each other. Catalytically active CDKL5, CDKL5(1-352), phosphorylated the N-terminal region of Dnmt1 in the presence of DNA. Considering that defects in the MeCP2 or CDKL5 genes cause Rett syndrome, we propose that the interaction between Dnmt1 and CDKL5 may contribute to the pathogenic processes of Rett syndrome.

Novel Ca2+/calmodulin-dependent protein kinase expressed in actively growing mycelia of the basidiomycetous mushroom Coprinus cinereus

We isolated cDNA clones for novel protein kinases by expression screening of a cDNA library from the basidiomycetous mushroom Coprinus cinereus. One of the isolated clones was found to encode a calmodulin (CaM)-binding protein consisting of 488 amino acid residues with a predicted molecular weight of 53,906, which we designated CoPK12. The amino acid sequence of the catalytic domain of CoPK12 showed 46% identity with those of rat Ca2+/CaM-dependent protein kinase (CaMK) I and CaMKIV. However, a striking difference between these kinases is that the critical Thr residue in the activating phosphorylation site of CaMKI/IV is replaced by a Glu residue at the identical position in CoPK12. As predicted from its primary sequence, CoPK12 was found to behave like an activated form of CaMKI phosphorylated by an upstream CaMK kinase, indicating that CoPK12 is a unique CaMK with different properties from those of the well-characterized CaMKI, II, and IV. CoPK12 was abundantly expressed in actively growing mycelia and phosphorylated various proteins, including endogenous substrates, in the presence of Ca2+/CaM. Treatment of mycelia of C. cinereus with KN-93, which was found to inhibit CoPK12, resulted in a significant reduction in growth rate of mycelia. These results suggest that CoPK12 is a new type of multifunctional CaMK expressed in C. cinereus, and that it may play an important role in the mycelial growth.

Inhibitors of the Ca2+/calmodulin-dependent protein kinase phosphatase family (CaMKP and CaMKP-N)

Ca(2+)/calmodulin-dependent protein kinase phosphatase (CaMKP) and its nuclear isoform CaMKP-N are unique Ser/Thr protein phosphatases that negatively regulate the Ca(2+)/calmodulin-dependent protein kinase (CaMK) cascade by dephosphorylating multifunctional CaMKI, II, and IV. However, the lack of specific inhibitors of these phosphatases has hampered studies on these enzymes in vivo. In an attempt to obtain specific inhibitors, we searched inhibitory compounds and found that Evans Blue and Chicago Sky Blue 6B served as effective inhibitors for CaMKP. These compounds also inhibited CaMKP-N, but inhibited neither protein phosphatase 2C, another member of PPM family phosphatase, nor calcineurin, a typical PPP family phosphatase. The minimum structure required for the inhibition was 1-amino-8-naphthol-4-sulfonic acid. When Neuro2a cells cotransfected with CaMKIV and CaMKP-N were treated with these compounds, the dephosphorylation of CaMKIV was strongly suppressed, suggesting that these compounds could be used as potent inhibitors of CaMKP and CaMKP-N in vivo as well as in vitro.

Involvement of Ca2+/calmodulin-dependent protein kinases in mycelial growth of the basidiomycetous mushroom, Coprinus cinereus

Although multifunctional Ca(2+)/calmodulin-dependent protein kinases (CaM-kinases) are widely distributed in animal cells, the occurrence of CaM-kinases in the basidiomycetous mushroom has not previously been documented. When the extracts from various developmental stages from mycelia to the mature fruiting body of Coprinus cinereus were analyzed by Western blotting using Multi-PK antibodies, which had been generated to detect a wide variety of protein serine/threonine kinases (Ser/Thr kinases), a variety of stage-specific Ser/Thr kinases was detected. Calmodulin (CaM) overlay assay using digoxigenin-labeled CaM detected protein bands of 65 kDa, 58 kDa, 46 kDa, 42 kDa, and 38 kDa only in the presence of CaCl(2), suggesting that these bands were CaM-binding proteins. When the CaM-binding fraction was prepared from mycelial extract of C. cinereus by CaM-Sepharose and analyzed with Multi-PK antibodies, two major immunoreactive bands corresponding to 65 kDa and 46 kDa were detected. CaM-binding fraction, thus obtained, exhibited Ca(2+)/CaM-dependent protein kinase activity toward protein substrates such as histones. These CaM-kinases were found to be highly expressed in the actively growing mycelia, but not in the resting mycelial cells. Mycelial growth was enhanced by the addition of CaCl(2) in the culture media, but inhibited by the addition of EGTA or trifluoperazine, a potent CaM inhibitor. This suggested that CaM-dependent enzymes including CaM-kinases play crucial roles in mycelial growth of basidiomycete C. cinereus.

Expression, characterization, and gene knockdown of zebrafish doublecortin-like protein kinase

Doublecortin-like protein kinase (DCLK) is a protein Ser/Thr kinase expressed in brain and believed to play crucial roles in neuronal development. To investigate the biological significance of DCLK, we isolated cDNA clones for zebrafish DCLK (zDCLK) and found that there were five splice variants of the kinase. In this study, the catalytic properties of a major isoform of zDCLK, which we designated as zDCLK1, and of an N-terminal truncated mutant retaining the kinase domain were examined by expressing them in Escherichia coli. Mutational analysis of recombinant zDCLK suggested that the kinase was activated not only by phosphorylation at Thr-576 in the activation loop but also by autophosphorylation at the other site(s) in the catalytic domain. zDCLK significantly phosphorylated protein substrates such as myelin basic protein, histones, and synapsin I. Subcellular localization of zDCLK and its N-terminal deletion mutant implicated that microtubule-association of zDCLK is mediated through N-terminal doublecortin like domain of this enzyme. Western blotting analysis and whole mount in situ hybridization revealed that zDCLK was highly expressed in brain and eyes after 24-h post fertilization. Gene knockdown of zDCLK using morpholino-based antisense oligonucleotides induced significant increase of apoptotic cells in the central nervous systems and resulted in the increase of the morphologically abnormal embryos in a dose-dependent manner. These results suggest that zDCLK may play crucial roles in the central nervous systems during the early stage of embryogenesis.

Recent Advances in Technologies for Analyzing Protein Kinases

Most cellular events are regulated by protein phosphorylation mediated by protein kinases, whose malfunction is involved in the etiology of various disorders. The elucidation of the biochemical properties of the protein phosphorylation reaction will lead not only to a better understanding of the signal transduction mechanism, but also to developing new therapeutic agents. In this review, we briefly summarize the technologies to detect or characterize protein kinases with special emphasis on recently developed and/or commercially available techniques.

Mutational analysis of Ca2+/calmodulin-dependent protein kinase phosphatase (CaMKP)

Ca(2+)/calmodulin-dependent protein kinase phosphatase (CaMKP) is a member of the serine/threonine protein phosphatases and shares 29% sequence identity with protein phosphatase 2Calpha (PP2Calpha) in its catalytic domain. To investigate the functional domains of CaMKP, mutational analysis was carried out using various recombinant CaMKPs expressed in Escherichia coli. Analysis of N-terminal deletion mutants showed that the N-terminal region of CaMKP played important roles in the formation of the catalytically active structure of the enzyme, and a critical role in polycation stimulation. A chimera mutant, a fusion of the N-terminal domain of CaMKP and the catalytic domain of PP2Calpha, exhibited similar substrate specificity to CaMKP but not to PP2Calpha, suggesting that the N-terminal region of CaMKP is crucial for its unique substrate specificity. Point mutations at Arg-162, Asp-194, His-196, and Asp-400, highly conserved amino acid residues in the catalytic domain of PP2C family, resulted in a significant loss of phosphatase activity, indicating that these amino acid residues may play important roles in the catalytic activity of CaMKP. Although CaMKP(1-412), a C-terminal truncation mutant, retained phosphatase activity, it was found to be much less stable upon incubation at 37 degrees C than wild type CaMKP, indicating that the C-terminal region of CaMKP is important for the maintenance of the catalytically active conformation. The results suggested that the N- and C-terminal sequences of CaMKP are essential for the regulation and stability of CaMKP.

High level expression and preparation of autonomous Ca2+/calmodulin-dependent protein kinase II in Escherichia coli

The chymotryptic fragment of Ca2+/calmodulin-dependent protein kinase II (30K-CaMKII) is a constitutively active enzyme that phosphorylates a variety of protein substrates in vitro. Although 30K-CaMKII is an often used and powerful tool for protein phosphorylation, the efficient production of catalytically active 30K-CaMKII in Escherichia coli has not yet been successfully realized, probably due to its toxicity in host cells. In this study, we found that a high-level expression of 30K-CaMKII as an insoluble form was attained when the N-terminal 43 amino acid residues of Xenopus CaMKI were fused to the N-terminal end of 30K-CaMKII (CX-30K-CaMKII). The inactive CX-30K-CaMKII thus expressed in E. coli was reactivated by simple denaturation/renaturation processes and purified on a Ni2+-chelating column. The renatured CX-30K-CaMKII exhibited specific activity similar to that of rat brain CaMKII, and phosphorylated various proteins such as histones, myosin light chain, myelin basic protein, and synapsin I, as in case of 30K-CaMKII or purified CaMKII. Thus, CX-30K-CaMKII, an autonomous CaMKII, can be obtained with a simple procedure using E. coli expression system.

Generation and application of a monoclonal antibody that detects a wide variety of protein tyrosine kinases

To investigate expression profiles of the entire family of protein tyrosine kinases (PTKs), we attempted to generate an antibody that detects a variety of PTKs. For production of the antibody, antigenic peptides corresponding to amino acid sequences of a highly conserved region (subdomain VIB) of PTKs were synthesized and immunized to BALB/c mice. Among various antigens, a peptide with 11 amino acids, CYVHRDLRAAN, efficiently produced a polyclonal antibody with a broad cross-reactivity to PTKs. We established a hybridoma cell line producing a monoclonal antibody, YK34, which appeared to cross-react with at least 68 PTKs in the human genome, as evidenced by its reactivity with the recombinant Src tyrosine kinases whose subdomain VIB had been replaced by those of the other PTKs. When differentiation of HL-60 cells was induced by 12-O-tetradecanoylphorbol-13-acetate, on Western blotting we observed significant changes in immunoreactive bands with YK34 in HL-60 cell extracts along with changes in the morphology of the cells. These results suggest that the YK34 antibody will be a powerful tool for analysis of a variety of cellular PTKs.