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At least 19 recordsLinked to original sources
PubMed1993

Anti-phosphoserine and anti-phosphothreonine antibodies modulate autophosphorylation of the insulin receptor but not EGF receptor.

We examined the effect of anti-phosphothreonine and anti-phosphoserine antibodies on insulin receptor autophosphorylation. These antibodies did not affect insulin binding activity of the receptor. These antibodies, however, inhibited insulin-stimulated autophosphorylation of insulin receptor, while did not affect EGF-stimulated autophosphorylation of EGF receptor. The inhibition was reversed by adding large amounts of phosphoserine or phosphothreonine. These data suggest that phosphoserine and phosphothreonine on insulin receptor play an important role in insulin-induced conformational change of the receptor.

Animals↗
PubMed2000

Stereoselective synthesis of CF(2)-substituted phosphothreonine mimetics and their incorporation into peptides using newly developed deprotection procedures.

Stereoselective syntheses of all four stereoisomers of CF(2)-substituted nonhydrolyzable phosphothreonine derivatives (33, 39, and their enantiomers) and their incorporation into peptides are described herein. Key to the synthesis of these amino acids was construction of secondary phosphate-mimicking difluoromethylphosphonate units along with generation of two stereocenters. The former was achieved using a Cu(I)-mediated cross-coupling reaction of BrZnCF(2)P(O)(OEt)(2) (8) and beta-iodo-alpha,beta-unsaturated ester 12, with stereochemistry of both alpha- and beta-stereocenters being established using bornane-10,2-sultam as a chiral auxiliary. Diastereoselective hydrogenation of a chiral alpha,beta-unsaturated acylsultam (for the beta-center) (e.g., 16a) and subsequent stereoselective bromination (for the alpha-center of the threo derivative) or amination (for the alpha-center of erythro (allo) derivative) were utilized. Transesterification of the bromide to the benzyl ester followed by azide displacement of the halogen, then reduction of the resulting azide, followed by Boc-protection and finally removal of the benzyl group, afforded protected both L- and D-phosphothreonine mimetics (39 and its enantiomer). On the other hand, protected both L- and D-allo-phosphothreonine mimetics (33 and its enantiomer) were synthesized via transesterification of the above-mentioned amination product, followed by hydrogenolytic removal of the benzyl group. Key to utilization of these amino acid analogues in peptide synthesis was removal of ethyl protection from the difluoromethylphosphonate moiety. A two-step deprotection methodology, consisting of a combination of a first-step reagent [0.3 M BSTFA-TBAI in CH(2)Cl(2), BF(3).Et(2)O] followed by a second-step reagent [1 M TMSOTf-thioanisole in TFA, m-cresol, EDT] was developed for use in solid-phase protocols. A 12-residue Cdc (cell division cycle) 2-peptide 41, possessing two nonhydrolyzable phosphoamino acid mimetics (F(2)Pmab 6 and F(2)Pmp 4), was subjected to this deprotection procedure and was obtained in 25% yield based on the protected resin. The present synthetic method affords nonhydrolyzable phosphoamino acid mimetics-containing peptides in high yield without accompanying side reactions.

Indicators and Reagents↗
PubMed1999

Function of WW domains as phosphoserine- or phosphothreonine-binding modules.

Protein-interacting modules help determine the specificity of signal transduction events, and protein phosphorylation can modulate the assembly of such modules into specific signaling complexes. Although phosphotyrosine-binding modules have been well-characterized, phosphoserine- or phosphothreonine-binding modules have not been described. WW domains are small protein modules found in various proteins that participate in cell signaling or regulation. WW domains of the essential mitotic prolyl isomerase Pin1 and the ubiquitin ligase Nedd4 bound to phosphoproteins, including physiological substrates of enzymes, in a phosphorylation-dependent manner. The Pin1 WW domain functioned as a phosphoserine- or phosphothreonine-binding module, with properties similar to those of SRC homology 2 domains. Phosphoserine- or phosphothreonine-binding activity was required for Pin1 to interact with its substrates in vitro and to perform its essential function in vivo.

Amino Acid Sequence↗
PubMed2002

Decreased calcineurin and increased phosphothreonine-DARPP-32 in the striatum of rats behaviorally sensitized to methamphetamine.

We investigated changes in signal transduction via calcineurin (CaN) in the striatum of rats behaviorally sensitized to methamphetamine (Meth). The rats were injected with Meth (4 mg/kg, s.c.) five times a week for 3 weeks and then were given a challenge dose of Meth (2 mg/kg, s.c.). Seven days after the challenge test, we determined the levels of CaN Aalpha and Abeta by Western blotting. We further immunoquantified DARPP-32 (dopamine- and cAMP-regulated phosphoprotein, mw 32,000) and phosphothreonine-DARPP-32, which can be dephosphorylated at threonine sites by CaN. We found that both CaN Aalpha and Abeta were significantly decreased in the particulate fractions but were not changed in the soluble fractions from the striatum of Meth-sensitized rats as compared with control rats. The same findings were observed in the striatum of rats 6 h after the injection of PCP (10 mg/kg, s.c.). In the striatum of Meth-sensitized rats, phosphothreonine-DARPP-32 immunoreactivities significantly increased, but DARPP-32 immunoreactivities were not significantly different from those of the control rats. These results indicate that the activity of signal transduction via CaN is functionally decreased in the striatum of Meth-sensitized rats.

Animals↗
PubMed1986

Resolution and identification of O-phosphoserine, O-phosphothreonine, O-phosphotyrosine, and gamma-carboxyglutamic acid as their fluorescent o-phthalaldehyde derivatives by high performance liquid chromatography.

High performance liquid chromatography was used to resolve O-phosphoserine, O-phosphothreonine, and O-phosphotyrosine as their fluorescent o-phthalaldehyde derivatives. By adjusting the buffer system, very small amounts of O-phosphothreonine could be detected and quantitated in the presence of very large amounts of O-phosphoserine. In addition, gamma-carboxyglutamic acid and glutamic acid were also separated and quantitated. Depending on the buffer used, various combinations of these amino acids could be resolved in a single run.

1-Carboxyglutamic Acid↗
PubMed1983

A rapid microdetermination of phosphoserine, phosphothreonine, and phosphotyrosine in proteins by automatic cation exchange on a conventional amino acid analyzer.

A cation-exchange chromatographic method for the separation and determination of phosphoserine, phosphothreonine, and phosphotyrosine in proteins after partial acid hydrolysis is described. The short column (0.6 X 8 cm) of an automatic amino acid analyzer was used and elution was carried out isocratically with 10 mM trifluoroacetic acid. The method is highly sensitive and each of the three O-phosphoamino acids can be accurately determined down to the 50-pmol level. Higher sensitivity may be obtained by the use of [32P]phosphate-labeled proteins. A correction factor for the decomposition of phosphoserine or phosphothreonine during acid hydrolysis can be deduced from the amount of inorganic phosphate recovered at the column void volume. The method is sensitive enough to be used for 32P-labeled proteins isolated by two-dimensional gel electrophoresis.

Animals↗
PubMed1989

Thin-layer chromatography can resolve phosphotyrosine, phosphoserine, and phosphothreonine in a protein hydrolyzate.

A solution of propionic acid, 1 M ammonium hydroxide, and isopropyl alcohol (45/17.5/17.5, v/v) was the ascending solvent in the separation of phosphotyrosine, phosphothreonine, and phosphoserine by thin-layer chromatography. The immobile phase was cellulose. The relative migrations were 0.44, 0.38, and 0.2, respectively. A previously described thin-layer system consisting of isobutyric acid and 0.5 M ammonium hydroxide (50/30, v/v) gave very similar relative migrations. To determine the usefulness of thin-layer chromatography in phosphoamino acid analysis, the propionic acid/ammonium hydroxide/isopropyl alcohol solution was used to characterize phosphorylated residues in a plasma membrane protein which is a substrate for the insulin receptor kinase, in insulin receptor phosphorylated histone H2B, and in an in vivo phosphorylated 90000-Da protein from IM9 cells. 32P-labeled proteins were separated by dodecyl sulfate-gel electrophoresis, digested with trypsin, and then hydrolyzed with 6 N HCl, 2 h, 110 degrees C. Following thin-layer chromatography of the hydrolyzates and autoradiography, phosphotyrosine was detected in insulin receptor substrates, and phosphoserine and phosphothreonine were found in the in vivo-phosphorylated protein. This study supports previous reports about the practicality of thin-layer chromatography in phosphoamino acid analysis and it demonstrates that a propionic acid, ammonium hydroxide, isoprophyl alcohol solution may be a useful ascending solvent mixture for this purpose.

Animals↗
PubMed1984

Insulin stimulates the dephosphorylation of phosphothreonine from fat-pad ATP-citrate lyase.

ATP-citrate lyase is phosphorylated in vivo at three amino acid residues on two peptide sequences (peptides a and b). Insulin action is known to increase the phosphorylation of peptide a. To study the effect of insulin on peptide b phosphorylation ATP-citrate lyase was radiolabeled in vivo by incubating fat pads with 32Pi. Following "cold chase", insulin action decreased the calculated specific radioactivity of peptide b to less than 30% of control whereas the specific radioactivity of peptide a increased 5-6 fold. The insulin induced decrease in peptide b phosphorylation was mainly due to a decrease in phosphothreonine phosphorylation. Isoproterenol treatment increased peptide a phosphorylation 4-6 fold but did not decrease peptide b phosphorylation. Specific radioactivity of ATP did not change significantly with hormone treatment. These results suggest that insulin action increases the dephosphorylation of peptide b by increasing the activity of a putative phosphothreonine phosphatase.

ATP Citrate (pro-S)-Lyase↗
PubMed1989

Synthesis of phosphopeptides containing O-phosphoserine or O-phosphothreonine.

Peptides containing phosphoserine or phosphothreonine were synthesized by solid phase methods. Phosphoserine and phosphothreonine were incorporated into peptides using Boc-diphenylphosphono esters of serine and threonine and standard DCC/HOBt coupling. The phenylphosphoesters were not removed when the peptides were cleaved from the resin by HF or by trifluoromethane sulfonic acid, but were subsequently removed by catalytic hydrogenation. Phosphopeptides were purified by HPLC and by Fe+3-Chelex chromatography and their identity verified by mass spectrometry. Two peptides, Leu-Arg-Arg-Ala-Ser(P)-Leu-Gly and Leu-Arg-Arg-Ala-Thr(P)-Leu-Gly, were prepared by both enzymatic and chemical methods and had identical properties.

Amino Acids↗
PubMed1989

Antibodies directed against phosphothreonine residues as potent tools for studying protein phosphorylation.

Here we report the development of novel antibodies which specifically react with phosphothreonine residues [anti-(P-Thr)antibodies]. The specificity of the antibodies was assessed in radioimmunoassays where we could demonstrate that half-maximal and maximal binding of the antibodies to plates coated with BSA - P-Thr occurred at serum dilutions of 1:4000 and 1:1000, respectively. P-Thr inhibited antibody binding with a half-maximal effect at 40 microM. P-Ser was 200-fold less potent while P-Tyr was essentially ineffective. Anti-(P-Thr) antibodies could specifically bind to phosphothreonine-containing proteins on Western blots. Using such a procedure we could demonstrate enhanced threonine phosphorylation of the EGF receptor upon treatment of intact unlabeled A431 cells with EGF. We could further demonstrate antibodies binding to proteins present in extracts of rat hepatoma cells (Fao). P-Thr at 10 microM completely inhibited antibody binding while P-Ser, P-Tyr, Thr or Ser, each present at tenfold higher concentrations, had no such inhibitory effect. Anti-(P-Thr) antibodies were also capable of specifically immunoprecipitating 32P-labeled phosphoproteins present in Triton extracts of Fao cells. Immunoprecipitation of proteins of 38 kDa, 55 kDa, 85 kDa, 100 kDa and 155 kDa was inhibited by 1 mM P-Thr but not by P-Tyr. These findings suggest that anti-(P-Thr) antibodies could be powerful tools in studies aimed at monitoring alterations in threonine phosphorylation of specific proteins as they occur under physiological conditions in response to various extracellular stimuli. Identification of such proteins can be conveniently monitored by immunoblotting.

Animals↗
PubMed1998

Changes in anti-phosphoserine and anti-phosphothreonine antibody binding during the sleep-waking cycle and after lesions of the locus coeruleus.

Cellular responses to many extracellular signals occur through phosphorylation or dephosphorylation of intracellular proteins. To determine whether changes in protein phosphorylation accompany the electrophysiological changes occurring during the sleep-waking cycle, immunocytochemical mapping of cells labeled with anti-phosphoserine and anti-phosphothreonine antibodies was performed on brain sections of sleeping and waking rats. Animals implanted for chronic polysomnographic recordings were sacrificed after either 3h of sleep or 3h of sleep deprivation by gentle handling. Anti-phosphoserine and anti-phosphothreonine staining was mainly localized in neurons and was high in some brain regions, such as cerebral cortex and hypothalamus, and low in others, such as the thalamus. In all cases, the number of cells labeled with either antibody in the cerebral cortex was markedly higher in rats sacrificed after 3h of waking than in rats sacrificed after 3h of sleep. Unilateral lesions of the locus coeruleus by local injection of 6-hydroxydopamine were performed in other animals to determine whether the increase in protein phosphorylation during waking was influenced by the activity of the noradrenergic system, which is higher in waking than in sleep. In animals sacrificed after 3h of spontaneous or forced waking, the number of labeled neurons in the cerebral cortex was decreased on the side in which noradrenergic fibers had been lesioned. These results suggest that 1) neurons exist physiologically in different states of phosphorylation, ranging from a state of very high phosphorylation (e.g., in the cerebral cortex) to a state of very low phosphorylation (e.g., in many thalamic nuclei); 2) the fraction of highly phosphorylated neurons in cerebral cortex is higher in waking than in sleep and 3) part of the immunoreactive phosphorylation present in highly labeled cortical neurons is controlled by the locus coeruleus.

Animals↗
PubMed1990

Occurrence of free O-phosphoserine and O-phosphothreonine in porcine liver.

The occurrence of free O-phosphoserine and O-phosphothreonine in porcine liver is demonstrated. These amino acids were separated from the tissue extracts by anion- and cation-exchange chromatography and thin-layer chromatography, and were identified by gas chromatography with flame photometric detection and gas chromatography-mass spectrometry. The contents of O-phosphoserine and O-phosphothreonine in the liver were estimated to be 377 +/- 13 ng/g and 115 +/- 2 ng/g, respectively.

Animals↗
PubMed1979

Identification of organic phosphorus covalently bound to collagen and non-collagenous proteins of chicken-bone matrix. The presence of O-phosphoserine and O-phosphothreonine in non-collagenous proteins, and their absence from phosporylated collagen.

Non-collagenous phosphoproteins, almost all of which can be extracted in EDTA at neutral pH in the presence of proteinase inhibitors, are identified in the matrix of chicken bone, and are therefore not covalently bound to collagen. Similarly, all the peptides containing gamma-carboxyglutamic acid are present in the EDTA extract and none in the insoluble residue, confirming that none is covalently linked to chicken bone collagen. However, organic phosphorus is also found to be present in chicken bone collagen, principally in the alpha2-chains. Of the total protein-bound organic phosphorus present in chicken bone matrix, approx. 80% is associated with the non-collagenous proteins and 20% with collagen. The soluble non-collagenous proteins contain both O-phosphoserine and O-phosphothreonine and these account for essentially of their organic phosphorus content. In contrast, collagen contains neither O-phosphoserine nor O-phosphothreonine. Indeed, no phosphorylated hydroxy amino acid, phosphoamidated amino acid or phosphorylated sugar could be identified in purified components of collagen, which contain approximately four to five atoms of organic phosphorus per molecule of collagen. Peptides containing organic phosphorus were isolated from partial acid hydrolysates and enzymic digests of purified collagen components, which contain an as-yet-unidentified cationic amino acid. These data, the very high concentrations of glutamic acid in the phosphorylated peptides, and the pH-stability of the organic phosphorus moiety in intact collagen chains strongly suggest that at least part of the organic phosphorus in collagen is present as phosphorylated glutamic acid. This would indicate that the two major chemically different protein fractions in chicken bone matrix that contain organic phosphorus may represent two distinct metabolic pools of organic phosphorus under separate biological control.

1-Carboxyglutamic Acid↗
PubMed2006

Chemical derivatization of phosphoserine and phosphothreonine containing peptides to increase sensitivity for MALDI-based analysis and for selectivity of MS/MS analysis.

Protein phosphorylation is one of the most important and common ways of regulating protein function in cells. However, phosphopeptides are difficult to analyse, ionising poorly under standard MALDI conditions. Several methods have been developed to deal with the low sensitivity and specificity of phosphopeptide analysis. Here, we show an approach using a simple one-step beta-elimination/Michael addition reaction for the derivatization of phosphoserine and phosphothreonine. The substitution of the negatively charged phosphate group by a positively charged S-ethylpyridyl group greatly improves the ionisation of the modified peptides, especially in MALDI MS, increasing the sensitivity of the analysis. The modification allows the formation of a unique fragment ion at m/z 106 under mild collisional activation conditions, which can be used for parent (precursor) ion scanning in order to improve both the sensitivity and the selectivity of the analysis. The optimisation of the approach is described for a standard model peptide and protein and then applied to phosphorylation analysis in two biologically derived proteins purified from different experimental systems.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1993

Preparation of anti-phosphoserine and anti-phosphothreonine antibodies and their application in the study of insulin- and EGF-induced phosphorylation.

We prepared antibodies against phosphoserine (P-Ser) and phosphothreonine (P-Thr) by immunizing rabbits with P-Ser or P-Thr conjugated to bovine serum albumin. The antibodies (anti-P-Ser and anti-P-Thr) were purified using P-Ser or P-Thr affinity columns. Anti-P-Thr was highly specific for P-Thr, while anti-P-Ser showed weak cross-reactivity with P-Thr. We showed that these antibodies can immunodetect serine/threonine phosphorylated insulin and epidermal growth factor (EGF) receptors and several proteins which are phosphorylated on serine/threonine residues in response to insulin or EGF stimulation. The antibodies will certainly provide a good tool for discovering novel kinases and substrates involved in signal transduction.

Animals↗
PubMed1996

Simultaneous formation of peptides and nucleotides from N-phosphothreonine.

An intramolecular mutual activation between a phosphoryl group and carboxyl group results in the simultaneous formation of nucleotides and peptides by the reaction of nucleosides with N-(O,O-diisopropyl)phosphothreonine in anhydrous pyridine. These results suggest pathways for the simultaneous prebiotic synthesis of peptides and oligonucleotides.

Chromatography, High Pressure Liquid↗
PubMed1979

Identification of O-phosphoserine, O-phosphothreonine and gamma-carboxyglutamic acid in the non-collagenous proteins of bovine cementum; comparison with dentin, enamel and bone.

O-phosphoserine [Ser(P)], O-phosphothreonine [Thr(P)], and gamma-carboxyglutamic acid (Gla) have been identified in native, calcified cementum and in non-collagenous proteins which can be extracted from the tissue in EDTA at neutral pH. The concentrations of Ser(P) and Thr(P) and the amino acid composition of the EDTA extractable proteins are more similar to those found in bone than in dentin or enamel. The concentration of Gla in cementum is lower than it is in bone and higher than it is in enamel, which contains essentially no Gla. Based on the contents of Gla in these mineralized tissues and the distribution of alkaline and acid phosphatases in these tissues, it is speculated that Gla may be part of these or other proenzymes rather than being involved directly and structurally with the deposition of the mineral phase.

1-Carboxyglutamic Acid↗
PubMed2003

A new approach to phosphoserine and phosphothreonine analysis in peptides and proteins: chemical modification, enrichment via solid-phase reversible binding, and analysis by mass spectrometry.

beta-Elimination of the phosphate group on phosphoserine and phosphothreonine residues and addition of an alkyldithiol is a useful tool for analysis of the phosphorylation states of proteins and peptides. We have explored the influence of several conditions on the efficiency of this PO(4)(3-) elimination reaction upon addition of propanedithiol. In addition to the described influence of different bases, the solvent composition was also found to have a major effect on the yield of the reaction. In particular, an increase in the percentage of DMSO enhances the conversion rate, whereas a higher amount of protic polar solvents, such as water or isopropanol, induces the opposite effect. We have also developed a protocol for enrichment of the modified peptides, which is based on solid-phase covalent capture/release with a dithiopyridino-resin. The procedure for beta-elimination and isolation of phosphorylated peptides by solid-phase capture/release was developed with commercially available alpha-casein. Enriched peptide fragments were characterized by MALDI-TOF mass spectrometric analysis before and after alkylation with iodoacetamide, which allowed rapid confirmation of the purposely introduced thiol moiety. Sensitivity studies, carried out in order to determine the detection limit, demonstrated that samples could be detected even in the low picomolar range by mass spectrometry. The developed solid-phase enrichment procedure based on reversible covalent binding of the modified peptides is more effective and significantly simpler than methods based on the interaction between biotin and avidin, which require additional steps such as tagging the modified peptides and work-up of the samples prior to the affinity capture step.

Amino Acid Sequence↗