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

Long-range periodic sequence of the cement/silk protein of Stenopsyche marmorata: purification and biochemical characterisation

The long-range periodic amino acid sequence of the bifunctional silk/cement protein from larvae of the caddisfly, Stenopsyche marmorata, is discussed in this study. The protein, named the S. marmorata silk protein (Smsp-1), was first purified to electrophoretic homogeneity. The results of Edman-based sequencing of Smsp-1 tryptic digests were consistent with the amino acid sequence deduced from a cDNA clone of the Smsp-1 gene. All undetected amino acids in the Edman-based sequencing were encoded as Ser, suggesting the presence of O-phospho-Ser. (31)P-NMR and an O-phospho-amino acid analysis successfully showed that the O-phospho-Ser residue occurred in a clustered manner, serving a cement function for Smsp-1. Two patterns of non-phosphorylated repeats, -SLGPYGDPRGDXLGPYGG- (X = V, G or D) and -GVGPYGDGLGPYGG-, were enriched in Smsp-1 compared with the O-phospho-Ser cluster, and have fibre-forming functions.

A manual sequence method of peptides and phosphopeptides using 4-(1'-cyanoisoindolyl)phenylisothiocyanate

A method for sequence analysis and identification of phosphoamino acids in peptides based on high performance liquid chromatography (HPLC) is described. The peptides were derivatized with an Edman type reagent, 4-(1'-cyanoisoindolyl)phenylisothiocyanate (CIPIC) and subsequently cleaved to generate stable and fluorescent 4-(1'-cyanoisoindolyl)phenylthiazolinone (CIP-TZ)-amino acids. Several experimental factors that affected derivatization on membranes were examined. Under the optimized conditions, the CIP-TZ derivatives of Try(p), Thr(p) and Ser(p) were obtained and separated from their parent amino acids with baseline resolution using an isocratic elution system. Up to the 4th residue of phosphorylated pentapeptides was successfully identified, whereas phosphoamino acid residues could not be detected by the conventional procedure using phenylisothiocyanate (PITC). The results demonstrated the potential of CIPIC as a derivatization reagent for peptide sequencing and the applicability of the method for the study and identification of phosphoamino acids in peptides.

Liquid chromatographic analysis of phosphoamino acids at femtomole level using chemical derivatization with N-hydroxysuccinimidyl fluorescein-O-acetate

Phosphorylation of amino acid residues in proteins plays a major role in biological systems. In this paper, a reversed-phase high performance liquid chromatographic (HPLC) method based on chemical derivatization has been described for the separation and quantification of phosphoamino acids at femtomole level, using fluorimetric detection (FLD). The protocol involved pre-column derivatization of phosphoamino acids with N-hydroxysuccinimidyl fluorescein-O-acetate (SIFA) and subsequent separation on ZORBAX Eclipse XDB-C8 column. Several experimental factors that influenced derivatization and separation were carefully investigated. The derivatization was performed at 40 degrees C for 40 min in borate buffer (pH 8.5). Under the optimum conditions, phosphoserine (P-Ser), phosphothreonine (P-Thr) and phosphotyrosine (P-Tyr) were satisfactorily separated in 8 min. The detection limits (signal-to-noise ratio=3) for the phosphoamino acids could reach 10-20 fmol, which was the lowest value reported for HPLC methods and comparable to those obtained by capillary electrophoresis with laser-induced fluorescence (CE-LIF) detection methods. The proposed method has been validated and used to characterize the phosphoamino acids in the hydrolyzed phosphorylated protein samples. The results clearly demonstrated the potential of this technique to study phosphoamino acids as well as provided a new analytical methodology that should be applicable to the study of phosphorylation of protein in biological system.

Autophosphorylation of phosphoglucosamine mutase from Escherichia coli

Phosphoglucosamine mutase (GlmM) catalyzes the formation of glucosamine-1-phosphate from glucosamine-6-phosphate, an essential step in the pathway for UDP-N-acetylglucosamine biosynthesis in bacteria. This enzyme must be phosphorylated to be active and acts according to a ping-pong mechanism involving glucosamine-1, 6-diphosphate as an intermediate (L. Jolly, P. Ferrari, D. Blanot, J. van Heijenoort, F. Fassy, and D. Mengin-Lecreulx, Eur. J. Biochem. 262:202-210, 1999). However, the process by which the initial phosphorylation of the enzyme is achieved in vivo remains unknown. Here we show that the phosphoglucosamine mutase from Escherichia coli autophosphorylates in vitro in the presence of [(32)P]ATP. The same is observed with phosphoglucosamine mutases from other bacterial species, yeast N-acetylglucosamine-phosphate mutase, and rabbit muscle phosphoglucomutase. Labeling of the E. coli GlmM enzyme with [(32)P]ATP requires the presence of a divalent cation, and the label is subsequently lost when the enzyme is incubated with either of its substrates. Analysis of enzyme phosphorylation by high-pressure liquid chromatography and coupled mass spectrometry confirms that only one phosphate has been covalently linked to the enzyme. Only phosphoserine could be detected after acid hydrolysis of the labeled protein, and site-directed mutagenesis of serine residues located in or near the active site identifies the serine residue at position 102 as the site of autophosphorylation of E. coli GlmM.

Protein phosphorylation: technologies for the identification of phosphoamino acids

Protein phosphorylation plays a central role in many biological and biomedical phenomena. In this review, while a brief overview of the occurrence and function of protein phosphorylation is given, the primary focus is on studies related to the detection and analysis of phosphorylation both in vivo and in vitro. We focus on phosphorylation of serine, threonine and tyrosine, the most commonly phosphorylated amino acids in eukaryotes. Technologies such as radiolabelling, antibody recognition, chromatographic methods (HPLC, TLC), electrophoresis, Edman sequencing and mass spectrometry are reviewed. We consider the speed, simplicity and sensitivity of tools for detection and identification of protein phosphorylation, as well as quantitation and site characterisation. The limitations of currently available methods are summarised.

Tyrosine protein kinase assays

Protein kinases form a large family of enzymes that play a major role in a number of live processes. The study of their action is important for the understanding of the transformation mechanisms and of the normal and pathological growth events. The quality of an enzyme assay is often the key point of an enzymatic study. It must be flexible and compatible with various experimental conditions, such as those for the purification process, the screening of inhibitors and the substrate specificity studies. As will be shown in the present review, two categories of substrates, peptidic and proteic, should be distinguished. The use of peptide substrates facilitates the determination of the recognition requirements of the enzyme and of the kinetic effects of even minute variations in their sequence. These linear peptide structures are assumed to mimic a complex interaction between the enzyme and a protein substrate in which distant amino acids in the sequence are vicinal in the folded substrate. Less amenable to a systematic study, but probably more adequate to investigate the natural substrate of a given kinase, are the proteic substrates. Obviously the tools to measure protein kinase activities are not the same in these two cases. The main difficulty in assaying protein kinases is the use of labelled gamma-ATP, mostly at large excess concentration, since the final product of the reaction has to be separated from the non-reacted labelled ATP. In the case of peptide substrates, the difficulty is to separate them from ATP basing on differences of molecular mass. Despite the efforts of many investigators to rely upon differences in solubility, in charges or in "affinity", this separation, which is crucial for the assay, is still an unsolved experimental problem. Chromatographic, as well as electrophoretic assays appeared relatively late in this domain, and more work in assessing new methodologies might bring new breakthroughs in the next few years. Specific, simple and reliable kinase assays are still a major challenge. Their improvement will help to conduct specificity studies, to elucidate complex growth mechanisms in which they are involved and to discover more selective potent inhibitors.

Analysis of the phosphoamino acid content of phosphoproteins

A method has been developed for the analysis of phosphoserine, phosphothreonine and phosphotyrosine in 32P-phosphoprotein hydrolysates. The hydrolysates are treated with dabsyl reagent (28.8 mM) for 10 min at 70 degrees C. After a clean-up using a disposable C18 column, the covalently modified phosphoamino acids are separated on silica TLC aluminum sheets using a one-dimensional solvent system. The method is straightforward and permits the simultaneous analysis of numerous samples. Very clean chromatograms are obtained enabling the unambiguous identification of the well separated dabsylated phosphoamino acids with autoradiography. The phosphoamino acids can be quantified by simply cutting out the relevant spots from the aluminum sheets followed by 32P-quantification using liquid scintillation spectrometry.

Derivatization of posttranslationally modified amino acids

After a brief overview of posttranslational modifications of protein amino acids, the use of various derivatizing reagents for amino acid analysis is discussed. Derivatization and chromatographic separation of hydroxyproline, methylhistidine, and phosphorylated amino acids are discussed in detail to illustrate some of the strategies that can be applied to the analysis of posttranslationally modified amino acids.

Measurement of picomoles of phosphoamino acids by high-performance liquid chromatography

A reverse-phase, high-performance liquid chromatographic system (HPLC) is described that makes possible optimal resolution and quantitation of picomole levels of phosphoamino acids, both with or without the presence of a large excess of nonphosphorylated amino acids. The assay involves precolumn derivatization of an amino acid mixture with phenyl isothiocyanate (PITC) at room temperature, followed by separation of phosphoamino acids from other amino acids by HPLC. The liquid chromatography was carried out on a C18 reverse-phase column at pH 7.4 and 30 degrees C using gradient elution with eluent A as 157 mM sodium acetate containing 2% acetonitrile and eluent B as 60% acetonitrile in water. A uv absorption at 254 nm is employed for detection of the PITC-derivatized amino acids eluting from the column. Amino acids are eluted with baseline resolution in the following order: phosphoserine, phosphothreonine, aspartic acid, glutamic acid, and phosphotyrosine followed by other amino acids. The sensitivity is in the picomole range, and the separation time, injection to injection, is 36 min. Phosphoserine, phosphothreonine, and phosphotyrosine are resolved within the first 8 min. This procedure enables determination of as low as 5 pmol of nonradioactive phosphoamino acids in a 100-fold excess of amino acids, as is usually present in most phosphoproteins in the natural state. Phosphoamino acids in polypeptides separated by sodium dodecyl sulfate-polyacrylamide electrophoresis and transferred to polyvinylidene difluoride (PVDF) membrane, or protein samples directly blotted on the membrane, can also be analyzed by this procedure after acid hydrolysis of the proteins bound to the PVDF membrane.

The major component of the rat sperm fibrous sheath is a phosphoprotein

The fibrous sheath from rat epididymal sperm was isolated by sequential extraction, first with Triton X-100 and dithiothreitol, and then with 6 M urea and dithiothreitol. The latter extraction procedure solubilized most of the sperm components, leaving the head and the fibrous sheath as the only intact structures. This material was purified by sucrose gradient centrifugation. Electron microscopy confirmed the purity of the isolated material and revealed the characteristic structural features of the fibrous sheath. Polyacrylamide gel electrophoresis (in the presence of sodium dodecyl sulfate) of the fibrillar material, showed a complex polypeptide composition. The polypeptides with molecular weights of 80,000, 24,000, and 11,500 accounted for about 65% of the total protein of the fibrous sheath. Peptide map analyses indicated that the components of molecular weights of 80,000 and 24,000 are unrelated to the polypeptides of similar size of the outer dense fibers. On the other hand, it appears that the fibrous sheath and the outer dense fibers share the polypeptide of 11,500 daltons. The component of 80,000 daltons contains on the average about 3 mol of phosphoserine per mol of polypeptide, indicating that the most abundant polypeptide of the fibrous sheath is a phosphoprotein.

Determination of [32P]phosphoamino acids in protein hydrolysates by isocratic anion-exchange high-performance liquid chromatography

We have developed a simple method for phosphoamino acid analysis of 32P-labeled phosphoproteins using anion-exchange high-performance liquid chromatography (HPLC). Phosphoproteins undergo partial acid hydrolysis and the resulting hydrolysate is injected directly onto a column. The sample is then isocratically eluted from the column by 35 mM phosphoric acid at pH 3.0 with collected fractions analyzed by Cerenkov counting. Phosphoamino acid identification is accomplished by the comparison of the retention times of 32P-labeled peaks to retention times of phosphoamino acid standards which had been monitored at 206 nm. This method has greater sensitivity and is more reliable than cellulose thin-layer electrophoresis and the results obtained by high-efficiency Cerenkov counting can be evaluated immediately, instead of waiting days or weeks for autoradiographic development of cellulose plates. This HPLC protocol is an improvement over other published HPLC protocols in that there is no need for pre- or post-column derivatization and the free [32P]phosphate elutes long after the phosphoamino acids. Thus sensitivity is increased as there is no interference from the free phosphate. Selection of an HPLC anion-exchange column is critical for this separation. Only two of the four columns that we tested performed well. We present data from several phosphoproteins including calcium-calmodulin dependent protein kinase, the beta-subunit of the insulin receptor, and phosphorylated calmodulin to demonstrate the utility of this procedure.

Analysis of strongly acidic amino acids by the conventional amino acid analyzer: application to determination of protein-bound cysteine and glutathione

A rapid analysis method of strongly acidic amino acids and related compounds by a simple modification of an existing amino acid analyzer is presented. In this method, an anion-exchanger column (2.6 X 150 mm) packed with Hitachi 3013-N resin was developed with 0.2 M citric acid. Complete separation of phosphothreonine, phosphoserine, phosphotyrosine, cysteic acid, homocysteic acid, and glutathionesulfonic acid was achieved within 35 min, with no regeneration of the column being required. Tyrosine-O-sulfate was analyzed by the same column using 2 M sodium acetate buffer, pH 5.5. Performic acid oxidation of a variety of proteins and direct analysis of the products by this system successfully detected cysteine, homocysteine, and/or glutathione bound to proteins through disulfide bonds. This suggest the potential use of the method for analysis of the states of protein thiol groups, especially those of clinically significant mutant proteins where mutation of arginine to cysteine is rather frequently recognized.

A 36 kDa monomeric protein and its complex with a 10 kDa protein both isolated from bovine aorta are calpactin-like proteins that differ in their Ca2+-dependent calmodulin-binding and actin-severing properties

Interaction of plasma membrane with the cytoskeleton involves a large number of proteins, among them a 36 kDa protein that was found to be involved in the interaction with actin filaments. We have isolated a 36 kDa protein from bovine aorta as a monomer and in a complex with a 10 kDa protein. Partial amino acid sequence determinations show that the 36 kDa and 10 kDa proteins isolated from bovine aorta are analogous to or identical with corresponding proteins purified from bovine intestine already described by Kristensen, Saris, Hunter, Hicks, Noonan, Glenney & Tack [(1986) Biochemistry 25, 4497-4503]. We report here that the association of the 10 kDa protein with the 36 kDa protein confers specific calmodulin-binding and actin-severing properties on the complex that are not possessed by the 36 kDa monomer alone. These findings suggest that the protein complex could be involved in thin-filament-related structures or could modulate some Ca2+-regulated events mediated by calmodulin.

Phosphorylation, glycosylation, and proteolytic activity of the 52-kD estrogen-induced protein secreted by MCF7 cells

We have studied the posttranslational modifications of the 52-kD protein, an estrogen-regulated autocrine mitogen secreted by several human breast cancer cells in culture (Westley, B., and H. Rochefort, 1980, Cell, 20:353-362). The secreted 52-kD protein was found to be phosphorylated mostly (94%) on high-mannose N-linked oligosaccharide chains, and mannose-6-phosphate signals were identified. The phosphate signal was totally removed by alkaline phosphatase hydrolysis. The secreted 52-kD protein was partly taken up by MCF7 cells via mannose-6-phosphate receptors and processed into 48- and 34-kD protein moieties as with lysosomal hydrolases. By electron microscopy, immunoperoxidase staining revealed most of the reactive proteins in lysosomes. After complete purification by immunoaffinity chromatography, we identified both the secreted 52-kD protein and its processed cellular forms as aspartic and acidic proteinases specifically inhibited by pepstatin. The 52-kD protease is secreted in breast cancer cells under its inactive proenzyme form, which can be autoactivated at acidic pH with a slight decrease of molecular mass. The enzyme of breast cancer cells, when compared with cathepsin D(s) of normal tissue, was found to be similar in molecular weight, enzymatic activities (inhibitors, substrates, specific activities), and immunoreactivity. However, the 52-kD protein and its cellular processed forms of breast cancer cells were totally sensitive to endo-beta-N-acetylglucosaminidase H (Endo H), whereas several cellular cathepsin D(s) of normal tissue were partially Endo H-resistant. This difference, in addition to others concerning tissue distribution, mitogenic activity and hormonal regulation, strongly suggests that the 52-kD cathepsin D-like enzyme of breast cancer cells is different from previously described cathepsin D(s). The 52-kD estrogen-induced lysosomal proteinase may have important functions in facilitating the mammary cancer cells to proliferate, migrate, and metastasize.

Separation and quantitative analysis of O-linked phosphoamino acids by isocratic high-performance liquid chromatography of the 9-fluorenylmethyl chloroformate derivatives

Phosphoamino acids derivatized with 9-fluorenylmethyl chloroformate were separated on an anion-exchange column (Partisil 10 SAX) at pH 3.90 using an isocratic elution with 10.0 mM potassium phosphate, 1.0% tetrahydrofuran, and 55% methanol. Phosphoamino acids were eluted with baseline resolution in the following order: phosphotyrosine, phosphothreonine, and phosphoserine. Each phosphoamino acid was separated from its parent amino acid, dicarboxylic amino acids, sugaramine phosphates, as well as the other common amino acids. The turn-around time from injection to injection was 35 min. The linearity for all three O-linked phosphoamino acids extended from 0.5-1000 pmol and has been shown to be directly applicable to the analysis of isolated phosphoproteins.

Changes in the activity of the maturation-promoting factor during meiotic maturation and following activation of amphibian and starfish oocytes: their correlations with protein phosphorylation

Changes in the extent of protein phosphorylation and their possible correlation with changes in the activity of maturation-promoting (MPF) factor were investigated throughout meiotic maturation and following activation of amphibian and starfish oocytes. Despite several exceptions in the pattern of phosphorylation of individual proteins, high and low levels of protein phosphorylation were found to be correlated with high and low levels of MPF activity. Both the extent of protein phosphorylation and MPF activity were found to drop upon parthenogenetic activation and to cycle synchronously thereafter in the amphibian. In contrast no drop in MPF activity or in the extent of protein phosphorylation was observed following activation of starfish oocytes with ionophore A23187. This suggests that changes of protein phosphorylation and of MPF activity are rather related to the progression of the cell cycle than directly to Ca2+-dependent activation reaction. In amphibians global protein kinase activity in homogenates was found to drop with MPF activity following activation. Changes in the ratio of threonine vs serine phosphorylation were also investigated during the course of meiotic maturation and activation in both amphibian and starfish oocytes: changes in the activity of MPF were found to be better correlated with changes in threonine than serine phosphorylation.

Properties of a membrane-bound tyrosine kinase phosphorylating the cytosolic fragment of the red cell membrane band 3 protein

Band 3 protein of human erythrocyte membrane is phosphorylated on a tyrosine residue located near the NH2 terminal by an endogenous tyrosine kinase activity (Dekowski, S., Rybicki, A. and Drickamer, K. (1983) J. Biol. Chem. 258, 2750-2753). A tyrosine kinase phosphorylating the band 3 protein in situ has been extracted from ghosts by non-ionic detergent and partially characterized (Phan-Dinh-Tuy, F., Henry, J. and Kahn, A. (1985) Biochem. Biophys. Res. Commun. 126, 304-312). We have studied the properties of the tyrosine kinase activity which remains bound to the ghosts after detergent extraction using the 43 kDa fragment of protein 3 as substrate. This activity, solubilized from the detergent-resistant material at 0.25 M NaCl and concentrated by phosphocellulose and tyrosine-agarose chromatographies, remains linked to high molecular weight complexes. It is specific for tyrosine. Assayed with the purified 43 kDa fragment it requires the presence of Mn2+ which cannot be replaced by Mg2+. Its affinity for 43 kDa fragment is very high with a Km of 3.3 microM. ATP acts as a phosphoryl donor with a Km of 0.55 microM. The tyrosine kinase activity was not modified by insulin, DMSO, phorbol ester and epidermal growth factor, vanadate and xanthine derivatives. Polyamines spermidine and the polylysine are inhibitors in the presence of Mn2+ but not in the presence of Mg2+. Heparin is a competitive inhibitor of ATP. 2,3-Diphosphoglycerate is an inhibitor at physiological concentrations (Ki = 2 mM). Purified red cell actin is not phosphorylated by the tyrosine kinase. These properties distinguish the red cell membrane-bound tyrosine kinase from other tyrosine kinases extracted from normal cells.

Bovine serum brevin. Purification by hydrophobic chromatography and properties

Brevin, an actin-severing protein present in serum from numerous mammals, has been purified to homogeneity from bovine serum, using hydrophobic chromatography as the last purification step. The physicochemical parameters of brevin have been established and some of them studied in the absence and presence of Ca2+. Brevin exhibits an apparent Stokes radius, Rs, of 3.4 nm, an intrinsic sedimentation coefficient S degrees 20, W, of 4.8 S and 4.4 S in the absence and presence of Ca2+ respectively, indicative of calcium-induced conformational change. The native molecular mass of brevin was found to be 68 kDa and the hydrodynamic data suggest that the protein is an asymmetric molecule. Sedimentation equilibrium studies demonstrated that Ca2+ affects the shape (asymmetry) of brevin without altering its molecular mass. Limited tryptic and chymotryptic digestion of brevin distinguishes the Ca2+-induced conformation from the EGTA one. No change in the electrophoretic migration of brevin was seen upon Ca2+ addition. Several isoforms were detected by two-dimensional gel electrophoresis. Brevin increases the rate of nucleation of actin but decreases the rate of elongation of the filaments and the steady-state viscosity of F-actin in substoichiometric amounts, as measured by viscometric assays under high shear conditions. Electron microscopic examination documents these effects. Brevin produces shorter actin filaments and binds to the 'barbed' end of filaments to which monomers add preferentially during elongation, as demonstrated by indirect immunogold staining of antibodies against brevin. Filament elongation occurs only at the slowly growing end. An enzyme-linked immunosorbent assay was developed and used to detect and quantify brevin and related proteins in extracts of different bovine cells and tissues. Liver and smooth muscles were found to contain the highest amounts of the severing protein.

Rapid separation of phosphoamino acids including the phosphohistidines by isocratic high-performance liquid chromatography of the orthophthalaldehyde derivatives

Amino acids were derivatized with orthophthalaldehyde and separated by high-performance liquid chromatography on a polymer-based reverse-phase column (Hamilton PRP-1) at pH 7.2 using isocratic elution with 14.3 mM sodium phosphate, 1.1% tetrahydrofuran, 6.6% acetonitrile. Phosphorylated amino acids were eluted with baseline resolution in the following order: 1-phosphohistidine, phosphoserine, 3-phosphohistidine, phosphotyrosine, phosphothreonine, and phosphoarginine. Each of the phosphoamino acids was separated from its parent amino acid but aspartate and glutamate eluted in the same region as the phosphoamino acids. The sensitivity is in the picomole range and the separation time, injection to injection, is 15 min. The linearity for phosphothreonine extends at least from 30 pmol to 30 nmol. Quantitation by radioactivity is good for each of the phosphoamino acids except in the case of [1-32P]phosphohistidine, which coelutes with inorganic phosphate.

Preparation and characterization of bovine aortic actin

A functional vascular smooth-muscle actin from bovine aorta was purified to homogeneity by an original method and was able to polymerize. Aortic actin is composed of two major isoforms and at least two minor ones. This actin was not phosphorylated by either cyclic AMP-dependent protein kinase or C kinase. The physical properties of aortic actin were found to be very similar to those of skeletal-muscle actin, except for amino acid composition (three tryptophan residues instead of four). The aortic actin and skeletal-muscle actin differ in the extent of activation of the Mg-dependent ATPase of skeletal-muscle myosin.