Role of a histidine residue in the active site of cyclic AMP-dependent histone kinase

Phosphoenolpyruvate-dependent protein kinase enzyme I of Streptococcus faecalis: purification and properties of the enzyme and characterization of its active center

Enzyme I, the phosphoenolpyruvate:protein phosphotransferase (EC 2.7.3.9), which is part of the bacterial phosphoenolpyruvate- (PEP) dependent phosphotransferase system, has been purified from Streptococcus faecalis by using a large-scale preparation. Size exclusion chromatography revealed a molecular weight of 140 000. On sodium dodecyl sulfate gels, enzyme I gave one band with a molecular weight of 70 000, indicating that enzyme I consists of two identical subunits. The first 59 amino acids of the amino-terminal part of the protein have been sequenced. It showed some similarities with enzyme I of Salmonella typhimurium. The active center of enzyme I has also been determined. After phosphorylation with [32P]PEP, the enzyme was cleaved by using different proteases. Labeled peptides were isolated by high-performance liquid chromatography on a reversed-phase column. The amino acid composition or amino acid sequence of the peptides has been determined. The largest labeled peptide was obtained with Lys-C protease and had the following sequence: -Ala-Phe-Val-Thr-Asp-Ile-Gly- Gly-Arg-Thr-Ser-His*-Ser-Ala-Ile-Met-Ala-Arg-Ser-Leu-Glu-Ile-Pro-Ala- Ile-Val-Gly-Thr-Lys-. It has previously been shown that the phosphoryl group is bound to the N-3 position of a histidyl residue in phosphorylated enzyme I. The single His in position 12 of the above peptide must therefore carry the phosphoryl group.

Physico-chemical principles of cAMP-dependent protein phosphorylation. Catalysis of phosphoryl group transfer to nucleophilic agents

The specificity of pig brain protein kinase towards high- and low-Mr 'analogs' of protein substrate was studied. Solvolysis of the phosphoenzyme intermediate by various nucleophilic agents is shown. The transition state structure of the phosphoryl transfer reaction is discussed.

Mechanistic studies of cAMP-dependent protein kinase action

The details of the process by which protein kinase catalyzes phosphoryl group transfers are beginning to be understood. Early work that explored the primary specificity of cAMP-dependent protein kinase action enabled the synthesis of small peptide substrates for the enzyme. Enzyme-peptide interactions seem simpler to understand than protein-protein interactions, so peptide substrates have been used in most protein kinase studies. In most investigations the kinetics for the phosphorylation of small peptides have been interpreted as being consistent with mechanisms which do not invoke phospho-enzyme intermediates (see, for example, Bolen et al.). Protein kinase has been shown to bind two metal ions in the presence of a nucleotide. Using magnetic resonance techniques the binding of these ions has been utilized to elucidate the conformation of nucleotide and peptide substrates or inhibitors when bound in the enzymic active site. Also, two new peptides with the form Leu-Arg-Arg-Ala-Ser-Y-Gly, where Y was either Pro or (N-methyl)Leu, were synthesized and found not to be substrates, within the limits of detection, for protein kinase. The striking lack of affinity that protein kinase has for such peptides which are unlikely to form a beta 3-6 turn has not been reported before. Our results may indicate that this type of turn is a requirement for protein kinase catalyzed phosphorylation or that these peptides lack the ability to form a particular hydrogen bond with the enzyme. Magnetic resonance techniques have indicated that the distance between the phosphorous in the gamma-phosphoryl group of MgATP and the hydroxyl oxygen of serine in the peptide Leu-Arg-Arg-Ala-Ser-Leu-Gly is 5.3 +/- 0.7 A. This, together with certain kinetic evidence, suggests that the mechanism by which protein kinase catalyzes phosphoryl group transfer has considerable dissociative character. Chemical modifications, including one using a peptide-based affinity label, have identified two residues at or near the active site, lysine-72 and cysteine 199. While neither of these groups has been shown to be catalytically essential, similar studies may help to identify groups that are directly involved in the catalytic process. Finally, a spectrophotometric assay for cAMP-dependent protein kinase has been described. Using this assay the preliminary results of an in-depth study of the pH dependence of protein kinase catalyzed phosphoryl group transfer have been obtained. This study shall aid in the identification of active site residues and should contribute to the elucidation of the enzyme's catalytic mechanism.(ABSTRACT TRUNCATED AT 400 WORDS)

The autophosphorylation reaction in the mechanism of activation of pig brain cyclic AMP-dependent protein kinase

Autophosphorylation of cyclic AMP-dependent protein kinase (ATP: protein phosphotransferase, EC 2.7.1.37) was shown to occur via an intramolecular mechanism: the regulatory subunit undergoes phosphorylation only within the holoenzyme. The phospho form of the catalytic subunit has the capacity to phosphorylate the regulatory subunit. The phosphotransferase reaction and the reaction of autophosphorylation were found to proceed with the involvement of the same active site. The activation constant of phospho- and dephosphoprotein kinase under the influence of cyclic AMP and the dissociation constant of the cyclic AMP complex with phospho- and dephospho forms of the holoenzyme were estimated. Autophosphorylation was demonstrated to lead to almost complete dissociation of the holoenzyme under the influence of cyclic AMP. Circular dichroism spectra of the phosphorylated and non-phosphorylated forms of protein kinase were studied. The relative content of the secondary structure elements in proteins was estimated and conformational changes were detected in the enzyme upon its interaction with cycli AMP. The anti-conformation of the cyclic nucleotide fixed in the complex with the phospho form of the regulatory subunit is suggested.

Studies on the mechanism of action of the histone kinase dependent on adenosine 3',5'-monophosphate. Interaction of ATP with the catalytic subunit of the pig-brain enzyme: application of the quenched-flow technique

A significant release of inorganic phosphate from ATP in the presence of the cAMP-dependent pig-brain histone kinase was detected. The high degree of homogeneity of the enzyme preparations used, identity of Michaelis constants (Km for ATP = 12 microM), the close values of cAMP activation constants (48 nM and 51 nM) for the phosphotransferase and ATPase activities, respectively, are all evidence that ATP decomposition is catalysed by the histone kinase under study. The ATPase activity observed supports the ping-pong bi-bi mechanism established earlier for the phosphotransferase reaction and can be regarded as due to decomposition of the phosphoryl enzyme. The transient and steady-state phases of the ATP hydrolysis were studied. The simplest reaction pathway can be described in terms of a three-step mechanism. The close values of the rate constant for the elementary stages of the ATPase reaction obtained in the nucleophile competition study and by computer simulation of the quenched-flow kinetics give further support for the mechanism proposed. The phosphoryl enzyme decomposition was shown to be a rate-limiting step under the experimental conditions used (pH 7.8-8.0).

Studies on the mechanism of action of histone kinase dependent on adenosine 3':5'-monophosphate. Evidence for involvement of histidine and lysine residues in the phosphotransferase reaction

The reaction of the phosphate residue transfer catalysed by histone kinase dependent on adenosine 3':5'-monophosphate (cyclic AMP) was studied. The phosphotransferase reaction was shown to obey the mechanism of ping-pong bi-bi type. After incubation of the catalytic subunit of histone kinase with [gamma-32P]ATP the incorporation of one mole of [32P]phosphage per mole of protein was observed. The tryptic [32P]phosphohistidine-containing peptide was isolated and its N-terminus and amino acid composition were determined. The 2',3'-dialdehyde derivative of ATP (oATP) was used as the affinity label for the catalytic subunit of cyclic-AMP-dependent histone kinase. The inhibitor formed an alidmine bond with epsilon-amino group of the lysine residue of the active site and was irreversibly bound to the enzyme after reduction by sodium borohydride with concurrent irreversible inactivation of the enzyme. After inactivation, about one mole of 14C-labelled inhibitor was incorporated per mole of the enzyme. ATP effectively protected the catalytic subunit of histone kinase against inactivation by oATP. Tryptic digestion of the enzyme-inhibitor complex led to the isolation of the 14C-labelled peptide of the active site of histone kinase. Basing on these results, the role of histidine and lysine residues in the active site of the catalytic subunit of histone kinase was suggested.