Post-translational modifications of pro-opiomelanocrtin related hormones in medaka pituitary based on mass spectrometric analyses

Direct tissue matrix-assisted laser desorption ionization with time-of-flight mass spectrometry analysis provides a selective detection of mass profile for the peptides contained into cell secretory granules. By this mass spectrometry with slice of pituitary, two novel molecular forms of pro-opimelanocrtin related hormone were found in the orange-red strain medaka (Oryzias latipes var.). The structures of [N,O-diacetyl Serine(1), O-acetyl Serine(3)]-α-melanocyte-stimulating hormone (MSH) and [hydroxyproline(15)]-β-MSH, together with [phosphoserine(15)]-corticotropin-like intermediate lobe peptide, were determined for the first time using a collision-induced dissociation with electrospray ionization mass spectrometry. A combination of mass spectrometry analyses is thus a powerful tool to lead to the elucidation of the post-translational processing from the pre-prohormone.

A distinct role for Pin1 in the induction and maintenance of pluripotency

The prominent characteristics of pluripotent stem cells are their unique capacity to self-renew and pluripotency. Although pluripotent stem cell proliferation is maintained by specific intracellular phosphorylation signaling events, it has not been well characterized how the resulting phosphorylated proteins are subsequently regulated. We here report that the peptidylprolyl isomerase Pin1 is indispensable for the self-renewal and maintenance of pluripotent stem cells via the regulation of phosphorylated Oct4 and other substrates. Pin1 expression was found to be up-regulated upon the induction of induced pluripotent stem (iPS) cells, and the forced expression of Pin1 with defined reprogramming factors was observed to further enhance the frequency of iPS cell generation. The inhibition of Pin1 activity significantly suppressed colony formation and induced the aberrant differentiation of human iPS cells as well as murine ES cells. We further found that Pin1 interacts with the phosphorylated Ser(12)-Pro motif of Oct4 and that this in turn facilitates the stability and transcriptional activity functions of Oct4. Our current findings thus uncover an atypical role for Pin1 as a putative regulator of the induction and maintenance of pluripotency via the control of phosphorylation signaling. These data suggest that the manipulation of Pin1 function could be a potential strategy for the stable induction and proliferation of human iPS cells.

High-energy electron transfer dissociation (HE-ETD) using alkali metal targets for sequence analysis of post-translational peptides

Post-translational modifications (PTMs) of proteins are important in the activation, localization, and regulation of protein function in vivo. The usefulness of electron capture dissociation (ECD) and electron-transfer dissociation (ETD) in tandem mass spectrometry (MS/MS) using low-energy (LE) trap type mass spectrometer is associated with no loss of a labile PTM group regarding peptide and protein sequencing. The experimental results of high-energy (HE) collision induced dissociation (CID) using the Xe and Cs targets and LE-ETD were compared for doubly-phosphorylated peptides TGFLT(p)EY(p)VATR (1). Although HE-CID using the Xe target did not provide information on the amino acid sequence, HE-CID using the Cs target provided all the z-type ions without loss of the phosphate groups as a result of HE-ETD process, while LE-ETD using fluoranthene anion gave only z-type ions from z(5) to z(11). The difference in the results of HE-CID between the Xe and Cs targets demonstrated that HE-ETD process with the Cs target took place much more dominantly than collisional activation. The difference between HE-ETD using Cs targets and LE-ETD using the anion demonstrated that mass discrimination was much weaker in the high-energy process. HE-ETD was also applied to three other phosphopeptides YGGMHRQEX(p)VDC (2: X = S, 3: X = T, 4: X = Y). The HE-CID spectra of the doubly-protonated phosphopeptides (= [M + 2H](2+)) of 2, 3, and 4 using the Cs target showed a very similar feature that the c-type ions from c(7) to c(11) and the z-type ions from z(7) to z(11) were formed via N-C alpha bond cleavage without a loss of the phosphate group.

Affinity-tagged phosphorylation assay by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (ATPA-MALDI): application to calcium/calmodulin-dependent protein kinase

A matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS)-based kinase assay using a peptide substrate tagged with a biotinyl group has been developed. The peptide moiety was designed to serve as an efficient substrate for calcium/calmodulin-dependent protein kinase II, based on the in vivo phosphorylation site of phosrestin I, a Drosophila homolog of arrestin. In the assay, the quantitative relationship was determined from the ratio of the peak areas between the two peaks respectively representing the unphosphorylated and the phosphorylated substrate. Attempts to assay phosphorylated peptides directly from the reaction mixture, gave inaccurate results because of the high noise level caused by the presence of salts and detergents. In contrast, after purifying the substrate peptides with the biotin affinity tag using streptavidin-coated magnetic beads, peak areas accurately represented the ratio between the unphosphorylated and phosphorylated peptide. By changing the substrate peptide to a peptide sequence that serves as a kinase substrate, it is expected that an efficient non-radioactive protein kinase assay using MALDI-TOF MS can be developed for any type of protein kinase. We call this technique "Affinity-Tagged Phosphorylation Assay by MALDI-TOF MS (ATPA-MALDI)." ATPA-MALDI should serve as a quick and efficient non-radioactive protein kinase assay by MALDI-TOF MS.

Two forms of secreted and thermostable luciferases from the marine copepod crustacean, Metridia pacifica

We cloned two forms of the secreted and thermostable luciferase genes, MpLuc1 and MpLuc2, from the marine copepod, Metridia pacifica. The 840-bp MpLuc1 cDNA comprised a 630-bp open reading frame encoding a 210-amino acid polypeptide (22.7 kDa). MpLuc1 had the closest homology with Metridia longa luciferase. The 753-bp MpLuc2 cDNA consisted of a 567-bp open reading frame (20.3 kDa), and it had the closest homology with Gaussia princeps luciferase. Single-specimen genomic PCR confirmed the presence of two luciferase genes in M. pacifica, and single-specimen RT-PCR revealed that both luciferase mRNAs were expressed. Both MpLuc1 and MpLuc2 (MpLucs) specifically reacted with the substrate coelenterazine producing identical bioluminescent spectra (lambdamax, 485 nm), but with different kinetics. Adding salt such as MgCl2 and CaCl2 to the reaction mixture significantly enhanced MpLuc1 and MpLuc2 activities. Wild-type MpLucs were remarkably thermostable; MpLuc1 retained about 60% of the original activity even after incubation at 90 degrees C for 30 min. MpLucs expressed in NIH-3T3 and HeLa cells were largely secreted into the culture medium. Continuous monitoring of secreted MpLuc1 driven by the c-fos promoter demonstrated the potential usefulness of MpLuc1 in nondisruptive reporter assays.

Negative regulation of multifunctional Ca2+/calmodulin-dependent protein kinases: physiological and pharmacological significance of protein phosphatases

Multifunctional Ca2+/calmodulin-dependent protein kinases (CaMKs) play pivotal roles in intracellular Ca2+ signaling pathways. There is growing evidence that CaMKs are involved in the pathogenic mechanisms underlying various human diseases. In this review, we begin by briefly summarizing our knowledge of the involvement of CaMKs in the pathogenesis of various diseases suggested to be caused by the dysfunction/dysregulation or aberrant expression of CaMKs. It is widely known that the activities of CaMKs are strictly regulated by protein phosphorylation/dephosphorylation of specific phosphorylation sites. Since phosphorylation status is balanced by protein kinases and protein phosphatases, the mechanism of dephosphorylation/deactivation of CaMKs, corresponding to their 'switching off', is extremely important, as is the mechanism of phosphorylation/activation corresponding to their 'switching on'. Therefore, we focus on the regulation of multifunctional CaMKs by protein phosphatases. We summarize the current understanding of negative regulation of CaMKs by protein phosphatases. We also discuss the biochemical properties and physiological significance of a protein phosphatase that we designated as Ca2+/calmodulin-dependent protein kinase phosphatase (CaMKP), and those of its homologue CaMKP-N. Pharmacological applications of CaMKP inhibitors are also discussed. These compounds may be useful not only for exploring the physiological functions of CaMKP/CaMKP-N, but also as novel chemotherapies for various diseases.

Chemical reactivities and physical effects in comparison between tocopherols and tocotrienols: physiological significance and prospects as antioxidants

Vitamin E is a generic term for all tocopherol and tocotrienol derivatives. The most abundant and active form of vitamin E isoforms in vivo is alpha-tocopherol, but recently the roles of other forms of vitamin E have received renewed attention. In this review, we summarize the differences among alpha-, beta-, gamma-, delta-tocopherols and tocotrienols specifically regarding the following points; (i) their radical-scavenging efficacies and chemical reactivity with metal ions in solution, (ii) their physical effects at the liposomal membrane interior, and (iii) their protective effects against cell toxicity. Moreover, the physiological significance and future prospects for using vitamin E, especially tocotrienols, for the prevention and treatment of disease are discussed.

Study of the dissociation of a charge-reduced phosphopeptide formed by electron transfer from an alkali metal target

Doubly protonated phosphopeptide (YGGMHRQET(p)VDC) ions obtained by electrospray ionization were collided with Xe and Cs targets to give singly and doubly charged positive ions via collision-induced dissociation (CID). The resulting ions were analyzed and detected by using an electrostatic analyzer (ESA). Whereas doubly charged fragment ions resulting from collisionally activated dissociation (CAD) were dominant in the CID spectrum with the Xe target, singly charged fragment ions resulting from electron transfer dissociation (ETD) were dominant in the CID spectrum with the Cs target. The most intense peak resulting from ETD was estimated to be associated with the charge-reduced ion with H2 lost from the precursor. Five c-type fragment ions with amino acid residues detached consecutively from the C-terminal were clearly observed without a loss of the phosphate group. These ions must be formed by N--Calpha bond cleavage, in a manner similar to the cases of electron capture dissociation (ECD) and ETD from negative ions. Although the accuracy in m/z of the CID spectra was about +/-1 Th because of the mass analysis using the ESA, it is supposed from the m/z values of the c-type ions that these ions were accompanied by the loss of a hydrogen atom. Four z-type (or y--NH3, or y--H2O) ions analogously detached consecutively from the N-terminal were also observed. The fragmentation processes took place within the time scale of 4.5 micros in the high-energy collision. The present results demonstrated that high-energy ETD with the alkali metal target allowed determination of the position of phosphorylation and the amino acid sequence of post-translational peptides.

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.

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.

Knockdown of nuclear Ca2+/calmodulin-dependent protein kinase phosphatase causes developmental abnormalities in zebrafish

Nuclear Ca2+/calmodulin-dependent protein kinase phosphatase (CaMKP-N) is an enzyme that dephosphorylates and concomitantly downregulates multifunctional Ca2+/calmodulin-dependent protein kinases (CaMKs) in vitro. However, the functional roles of this enzyme in vivo are not well understood. To investigate the biological significance of CaMKP-N during zebrafish embryogenesis, we cloned and characterized zebrafish CaMKP-N (zCaMKP-N). Based on the nucleotide sequences in the zebrafish whole genome shotgun database, we isolated a cDNA clone for zCaMKP-N, which encoded a protein of 633 amino acid residues. Transiently expressed full-length zCaMKP-N in mouse neuroblastoma, Neuro2a cells, was found to be localized in the nucleus. In contrast, the C-terminal truncated mutant lacking RKKRRLDVLPLRR (residues 575-587) had cytoplasmic staining, suggesting that the nuclear localization signal of zCaMKP-N exists in the C-terminal region. Ionomycin treatment of CaMKIV-transfected Neuro2a cells resulted in a marked increase in the phosphorylated form of CaMKIV. However, cotransfection with zCaMKP-N significantly decreased phospho-CaMKIV in ionomycin-stimulated cells. Whole mount in situ hybridization analysis of zebrafish embryos showed that zCaMKP-N is exclusively expressed in the head and neural tube regions. Gene knockdown of zCaMKP-N using morpholino-based antisense oligonucleotides induced significant morphological abnormalities in zebrafish embryos. A number of apoptotic cells were observed in brain and spinal cord of the abnormal embryos. These results suggest that zCaMKP-N plays a crucial role in the early development of zebrafish.

Characterization of the tritium-labeled analog of L-threo-beta-benzyloxyaspartate binding to glutamate transporters

L-Glutamate is the major excitatory neurotransmitter in the mammalian central nervous system. Termination of glutamate receptor activation and maintenance of low extracellular glutamate concentrations are primarily achieved by glutamate transporters (excitatory amino acid transporters 1-5, EAATs1-5) located on both the nerve endings and the surrounding glial cells. To identify the physiological roles of each subtype, subtype-selective EAAT ligands are required. In this study, we developed a binding assay system to characterize EAAT ligands for all EAAT subtypes. We recently synthesized novel analogs of threo-beta-benzyloxyaspartate (TBOA) and reported that they blocked glutamate uptake by EAATs 1-5 much more potently than TBOA. The strong inhibitory activity of the TBOA analogs suggested that they would be suitable to use as radioisotope-labeled ligands, and we therefore synthesized a tritiated derivative of (2S,3S)-3-{3-[4-ethylbenzoylamino]benzyloxy}aspartate ([3H]ETB-TBOA). [3H]ETB-TBOA showed significant high-affinity specific binding to EAAT-transfected COS-1 cell membranes with each EAAT subtype. The Hill coefficient for the Na+-dependence of [3H]ETB-TBOA binding revealed a single class of noncooperative binding sites for Na+, suggesting that Na+ binding in the ligand binding step is different from Na+ binding in the substrate uptake process. The binding was displaced by known substrates and blockers. The rank order of inhibition by these compounds was consistent with glutamate uptake assay results reported previously. Thus, the [3H]ETB-TBOA binding assay will be useful to screen novel EAAT ligands for all EAAT subtypes.

Binding of glutamate receptor delta2 to its scaffold protein, Delphilin, is regulated by PKA

The glutamate receptor delta2 (GluRdelta2) is selectively expressed in cerebellar Purkinje cells and plays an important role in motor learning, motor coordination, and long-term depression. Delphilin is identified as a GluRdelta2-interacting protein, selectively expressed in Purkinje cell-parallel fiber synapses, and specifically interacts with the GluRdelta2 C-terminus via its PDZ domain. Here, surface plasmon resonance analyses showed that Delphilin PDZ bound to GluRdelta2 C-terminal peptide (DPDRGTSI), but not to its phosphopeptides (DPDRGphosphoTSI and DPDRGTphosphoSI). We showed the incorporation of phosphate into threonine at -2 (-2T) and serine at -1 (-1S) of GluRdelta2 C-terminus by cAMP-dependent protein kinase (PKA) in vitro. In the experiments using heterologous expression system, Delphilin coimmunoprecipitated with GluRdelta2 was dramatically decreased under the condition with forskolin and isobutylmethylxanthine, which led to cAMP-dependent phosphorylation by PKA. Thus, phosphorylation of -2T and/or -1S of GluRdelta2 C-terminus by PKA may regulate the binding of GluRdelta2 to its scaffolding protein, Delphilin.

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.

Lactococcin Q, a novel two-peptide bacteriocin produced by Lactococcus lactis QU 4

A bacteriocin-producing strain, Lactococcus lactis QU 4, was isolated from corn. The bacteriocin, termed lactococcin Q, showed antibacterial activity only against L. lactis strains among a wide range of gram-positive indicator strains tested. Lactococcin Q was purified by acetone precipitation, cation exchange chromatography, and reverse-phase chromatography. Lactococcin Q consisted of two peptides, alpha and beta, whose molecular masses were determined to be 4,260.43 Da and 4,018.36 Da, respectively. Amino acid and DNA sequencing analyses revealed that lactococcin Q was a novel two-peptide bacteriocin, homologous to lactococcin G. Comparative study using chemically synthesized lactococcin Q (Qalpha plus Qbeta) and lactococcin G (Galpha plus Gbeta) clarified that hybrid combinations (Qalpha plus Gbeta and Galpha plus Qbeta) as well as original combinations showed antibacterial activity, although each single peptide showed no significant activity. These four pairs of lactococcin peptides acted synergistically at a 1:1 molar ratio and exhibited identical antibacterial spectra but differed in MIC. The MIC of Qalpha plus Gbeta was 32 times higher than that of Qalpha plus Qbeta, suggesting that the difference in beta peptides was important for the intensity of antibacterial activity.

Effective detection of peptides containing cysteine sulfonic acid using matrix-assisted laser desorption/ionization and laser desorption/ionization on porous silicon mass spectrometry

Cysteine sulfonic acid-containing peptides, being typical acidic peptides, exhibit low response in matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. In this study, matrix conditions and the effect of diammonium hydrogencitrate (DAHC) as additive were investigated for ionization of cysteine sulfonic acid-containing peptides in MALDI. A matrix-free ionization method, desorption/ionization on porous silicon (DIOS), was also utilized to evaluate the effect of DAHC. When equimolar three-component mixtures of peptides carrying free cysteine, cysteine sulfonic acid, and carbamidomethyl cysteine were measured by MALDI using a common matrix, alpha-cyano-4-hydroxycinnamic acid (CHCA), no signal corresponding to cysteine sulfonic acid-containing peptide could be observed in the mass spectrum. However, by addition of DAHC to CHCA, the peaks of cysteine sulfonic acid-containing peptides were successfully observed, as well as when using 2,4,6-trihydroxyacetophenone (THAP) and 2,6-dihydroxyacetophenone with DAHC. In the DIOS mass spectra of these analytes, the use of DAHC also enhanced the peak intensity of the cysteine sulfonic acid-containing peptides. On the basis of studies with these model peptides, tryptic digests of oxidized peroxiredoxin 6 were examined as a complex peptide mixture by MALDI and DIOS. In MALDI, the peaks of cysteine sulfonic acid-containing peptides were observed when using THAP/DAHC as the matrix, but this was not so with CHCA. In DIOS, the signal from cysteine sulfonic acid-containing peptides was suppressed; however, the use of DAHC significantly enhanced the signal intensity with an increase in the number of observed peptides and increased signal-to-noise ratio in the DIOS spectra. The results show that DAHC in the matrix or on the DIOS chip decreases discrimination and suppression effects in addition to suppressing alkali-adduct ions, which leads to a beneficial effect on protonation of peptides containing cysteine sulfonic acid.