High-performance liquid chromatography of acid-stable and acid-labile phosphoamino acids

Histidine kinases and two-component signal transduction systems

The phosphorylation of histidine is the first step in many signal transduction cascades in bacteria, yeast and higher plants. The transfer of a very reactive phosphoryl group from phosphorylated histidine kinase to an acceptor is an essential step in many cellular signaling responses.

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.

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.

Properties of poliovirus associated protein kinase

Highly purified virulent poliovirus preparations harbour an endogenous protein kinase. Enzyme activity increases significantly upon purification of infectious virus particles from infected HeLa cells. Enzyme activity is stimulated by divalent cations. The substrate specificity and the degree of stimulation of the kinase are dependent on the nature of the divalent cations included in the assay. The preferred substrates for this kinase are the viral capsid proteins. Exogenously added proteins such as alpha-casein, phosvitin and protamine are also phosphorylated by the kinase. Moreover, these proteins enhance the phosphorylation of viral proteins. In the presence of Mg++ VP 2 and VP 0 are highly phosphorylated, while in the presence of Zn++ only VP 2 and VP 4, but not VP 0 or exogenous proteins are phosphorylated. Poliovirus associated protein kinase exhibits optimal activity at pH 7.9 in the presence of 10 mM Mg++. The Km for ATP is shown to be 40 microM. By testing different nucleotides as phosphate donors a specificity of the phosphorylation reaction for ATP is demonstrated. Phosphoamino acid analysis of hydrolysates of the substrates phosphorylated in the presence of Mg++ by thin layer electrochromatography and HPLC yielded phosphoserine and phosphothreonine from viral capsid proteins while hydrolysates of protamine yield only phosphoserine. Destabilization of the viral capsid, e.g. by preincubation at 42 degrees C for 20 minutes results in a stimulation of kinase activity. Moreover, phosphorylation of the poliovirus capsid proteins itself results in destabilization of the viral capsid. These findings suggest that phosphorylation of the viral coat proteins triggers or enhances the uncoating of poliovirus leading to the release of viral RNA.

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.

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.

A simple and rapid method of quantitative analysis of phosphoamino acids by high-performance liquid chromatography

A high-performance liquid chromatographic system for the separation of nonradiolabeled phosphoamino acids and orthophosphate by ion-pair reverse-phase chromatography has been developed. By the use of low-ionic-strength phthalate buffers at pH 6.3, the phosphoamino acids can be visualized by virtue of this uv-active eluant. The technique is sensitive to 200 pmol of phosphoamino acid and has been shown to be directly applicable to the analysis of isolated phosphoproteins.

Quantitative analysis of lysine analogs and derivatives

Methods for the modification of lysine residues in proteins and the analysis of artificially or naturally modified lysine derivatives by quantitative chromatographic procedures are described. The compilation of results should assist structure-function studies and the analysis of new lysine derivatives.

Synthesis and properties of N-, O-, and S-phospho derivatives of amino acids, peptides, and proteins

The literature on chemical (i.e., nonenzymic) phosphorylation of amino acids, peptides, and proteins is reviewed through 1982. The review covers synthetic methods, chemical reactions, and physical properties, with emphasis on the techniques used for separation and characterization of the products. Synthetic methods are classified by reagent rather than product, and are illustrated by experimental procedures for the most important methods. Chemical reactions are classified into four groups depending on whether the reaction site is the phospho group, the amino group, the carboxyl group, or in the case of serine the hydroxyl group. Physical data are given for all of the known N-, O-, and S-phospho derivatives of the amino acids, peptides, and proteins, within certain limitations, and are discussed in detail in the section on physical properties. Emphasis is given to the techniques used for separation of the products, such as chromatography and electrophoresis, and for characterization of the products, particularly spectroscopy. Medical and other uses of the products are mentioned.

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.

Endogenous protein phosphorylation in rat brain mitochondria: occurrence of a novel ATP-dependent form of the autophosphorylated enzyme succinyl-CoA synthetase

When rat brain mitochondria are incubated with [gamma-32P]ATP, there is a rapid (10 s) phosphorylation of proteins designated E1 and F of M.W. 42,000 and 32,000, respectively. Although [gamma-32P]ATP was the preferred substrate for protein F, a small amount of labeling did occur with [gamma-32P]GTP. Phosphorylation of E1 was absolutely ATP-dependent. On the other hand, a 32,000 M.W. protein from rat liver mitoplasts (mitochondria devoid of an outer membrane) was highly phosphorylated when [gamma-32P]GTP was used but not at all phosphorylated within short time periods with [gamma-32P]ATP. Both the ATP-labeled brain phosphoprotein F and GTP-labeled liver protein migrated to identical positions on high-resolution two-dimensional polyacrylamide gels, and both contained acid-labile phosphoryl groups. Furthermore, both phosphoproteins were identified as the autophosphorylated subunit of succinyl-CoA synthetase (SCS, EC 6.2.1.4) by using antibody directed against purified GTP-dependent porcine SCS. However, immunotitration experiments with anti-porcine SCS revealed that ATP- and GTP-labeled protein F in brain differed in their interactions with antibody, suggesting that in rat brain mitochondria two different forms of the enzyme exist that are immunologically distinct and differ in substrate specificity. When mitochondrial preparations enriched in particular brain cell or subcellular types were examined, an unequal distribution of E1 and the two forms of protein F were observed. A brain subfraction containing neuronal cell body and glial mitochondria (CM) was found to contain E1 and approximately equal amounts of the ATP- and GTP-dependent forms of protein F. Light synaptic mitochondria (SM1) contained ATP-dependent protein F almost exclusively and were depleted in E1. Dense synaptic mitochondria (SM2) are rich in the ATP form of SCS but also contain low amounts of the GTP enzyme.

Characterization of chemical and enzymatic acid-labile phosphorylation of histone H4 using phosphorus-31 nuclear magnetic resonance

Phosphorus-31 nuclear magnetic resonance (31P NMR) is used to investigate acid-labile phosphorylation of histone H4. 31P NMR detects phosphorylated histidine residues in in vitro enzymatically phosphorylated H4. The source of kinase is nuclei from either regenerating rat liver or Walker-256 carcinosarcoma. When regenerating rat liver is the source, 31P NMR spectroscopy on the denatured phosphorylated protein exhibits a resonance at 5.3 ppm relative to an 85% orthophosphoric acid external reference. This peak corresponds well with the chemical shift of standard pi-phosphohistidine scanned under similar conditions. Sodium dodecyl sulfate (NaDodSO4)--polyacrylamide gel electrophoresis confirms acid lability. When the source of kinase is Walker-256 carcinosarcoma, the 31P NMR spectrum contains a resonance at 4.9 ppm which corresponds well with standard tau-phosphohistidine run under the same conditions. Chemical phosphorylation of H4 has been accomplished by using dipotassium phosphoramidate which specifically phosphorylated the imidazole moiety of histidine at neutral pH. NaDodSO4--polyacrylamide gel electrophoresis confirms acid lability, and high-pressure liquid chromatography of protein hydrolysates yields phosphohistidine. 31P NMR of chemically phosphorylated H4 in a structured state reveals two peaks at 4.8 and 7.3 ppm with line widths of 9 and 55 Hz, respectively. These resonances indicate that both histidine residues of H4 (His-18 and His-75) are phosphorylated, the latter relatively immobile and the former relatively free in solution. 31P NMR studies on chemically phosphorylated peptide fragments of H4, namely, H4(1-23) and H4(38-102), confirm this model of H4 structure.