The substrate specificity of cyclic AMP-dependent protein kinase: amino acid sequences at the phosphorylation sites of herring protamine (clupeine)

The localization of the cAMP-dependent protein kinase phosphorylation site in the platelet rat protein, rap 1B

Rap 1B is a low molecular weight G protein which is phosphorylated by cAMP-dependent protein kinase. In order to identify the site of phosphorylation by cAMP-dependent protein kinase, purified rap 1B from human platelets was phosphorylated and subjected to limited proteolysis with trypsin. Single digestion fragment containing the phosphorylation site was obtained and purified by reversed-phase HPLC. Sequence analysis of the phosphorylated digestion fragment demonstrated that the sequence of the phosphorylation site was -Lys-Lys-Ser-Ser-. This sequence is near the carboxy terminus and is adjacent to the site of membrane attachment of the protein.

The substrate specificity of protein kinases which phosphorylate the alpha subunit of eukaryotic initiation factor 2

The alpha subunit of eukaryotic protein synthesis initiation factor (eIF-2 alpha) is phosphorylated at a single serine residue (Ser51) by two distinct and well-characterized protein kinase, the haem-controlled repressor (HCR) and the double-stranded RNA-activated inhibitor (dsI). The sequence adjacent to Ser51 is rich in basic residues (Ser51-Arg-Arg-Arg-Ile-Arg) suggesting that they may be important in the substrate specificity of the two kinases, as is the case for several other protein kinases. A number of proteins and synthetic peptides containing clusters of basic residues were tested as substrates for HCR and dsI. Both kinases were able to phosphorylate histones and protamines ar multiple sites as judged by two-dimensional mapping of the tryptic phosphopeptides. These data also showed that the specificities of the two kinases were different from one another and from the specificities of two other protein kinases which recognise basic residues, cAMP-dependent protein kinase and protein kinase C. In histones, HCR phosphorylated only serine residues while dsI phosphorylated serine and threonine. Based on phosphoamino acid analyses and gel filtration of tryptic fragments, dsI was capable of phosphorylating both 'sites' in clupeine Y1 and salmine A1, whereas HCR acted only on the N-terminal cluster of serines in these protamines. The specificities of HCR and dsI were further studied using synthetic peptides with differing configurations of basic residues. Both kinases phosphorylated peptides containing C-terminal clusters of arginines on the 'target' serine residue, provided that they were present at positions +3 and/or +4 relative to Ser51. However, peptides containing only N-terminal basic residues were poor and very poor substrates for dsI and HCR, respectively. These findings are consistent with the disposition of basic residues near the phosphorylation site in eIF-2 alpha and show that the specificities of HCR and dsI differ from other protein kinases whose specificities have been studied.

Effect of limited trypsin digestion on the renal Na+-H+ exchanger and its regulation by cAMP-dependent protein kinase

The Na+-H+ exchanger from solubilized rabbit renal brush border membranes is inhibited by cAMP-dependent protein kinase (PKA) mediated protein phosphorylation. To characterize this inhibitory response and its sensitivity to limited proteolysis, the activity of the transporter was assayed after reconstitution of the proteins into artificial lipid vesicles. Limited trypsin digestion increased the basal rate of proton gradient-stimulated, amiloride-inhibitable sodium uptake in reconstituted proteoliposomes and blocked the inhibitory response to PKA-mediated protein phosphorylation. To determine if the inhibitory response to PKA-mediated protein phosphorylation could be restored to the trypsin-treated solubilized proteins, nontrypsinized solubilized brush border membrane proteins were separated by column chromatography. The addition of small molecular weight polypeptides, fractionated on Superose-12 FPLC (Ve = 0.7), to trypsinized solubilized brush border membrane proteins restored the inhibitory response to PKA-mediated protein phosphorylation. Similarly, the addition of the 0.1 M NaCl fraction from an anion exchange column, Mono Q-FPLC, also restored the inhibitory response to PKA. Both protein fractions contained a common 42-43 kDa protein which was preferentially phosphorylated by PKA. These results indicate that limited trypsin digestion dissociates the activity of the renal Na+-H+ exchanger from its regulation by PKA. It is suggested that trypsin cleaves an inhibitory component of the transporter and that this component is the site of PKA-mediated regulation. Phosphoprotein analysis of fractions that restored PKA regulation raises the possibility that a polypeptide of 42-43 kDa is involved in the inhibition of the renal Na+-H+ exchanger by PKA-mediated protein phosphorylation.

Isolation and characterization of the gene for Drosophila tyrosine hydroxylase

A Drosophila cDNA homologous to a rat tyrosine hydroxylase (TH) probe has been isolated and sequenced. The deduced amino acid sequence predicts a 57,861 dalton protein with almost 50% identity with rat TH. In vitro transcription of the cDNA followed by in vitro translation yields a single protein species of approximately 58,000 daltons. The in vitro translation product, as well as a protein of the same molecular weight from wild-type Drosophila head protein extracts, is recognized by an antibody made against bovine TH. The presence of TH enzymatic activity in heads was demonstrated. In situ hybridization to polytene chromosomes localized the gene to 65B. The comapping of the mutant pale to this same region, as well as its phenotype, suggests that pale may be a TH mutation.

Partially dephosphorylated phosphopeptide AcSer(P)-Ser(P)-Ser(P) is an excellent substrate for casein kinase-2

The synthetic phosphopeptide AcSer(P)-Ser(P)-Ser(P), reproducing a recurrent feature of casein and other phosphoproteins, once partially dephosphorylated by acid phosphatase, serves as an efficient substrate for casein kinase-2. Previous dephosphorylation beyond 30% hinders subsequent phosphorylation and the entirely dephosphorylated peptide is not a substrate at all. The kinetic constants of the partially dephosphorylated phosphopeptide are much more favourable than those of the synthetic peptides SEEEAA, SSEE and SEE, the latter one being totally inert. Optimal phosphorylation occurs at pH values that ensure complete ionization of the phosphoseryl side chains. These data provide incontrovertible demonstration that phosphoserine can replace carboxylic amino acids as specificity determinant for CK-2, being more effective than glutamic acid itself.

Substrate specificity of Ca2+/CaM-dependent multifunctional protein kinases: comparison of isoenzymes from brain, liver and skeletal muscle

Ca2+/CaM-dependent multifunctional protein kinase isoenzymes from brain, skeletal muscle and liver were compared by their phosphorylation of a number of protein substrates. Under the conditions of assay, the three isoenzymes demonstrated rapid phosphorylation of synapsin I and glycogen synthase. In contrast, rates of phosphorylation of pyruvate kinase and phenylalanine hydroxylase were almost two orders of magnitude slower. Differences in phosphorylation specifically of the latter two substrates was also observed among the three protein kinases. Phosphorylation by Ca2+/CaM-dependent protein kinases was contrasted with cAMP-dependent protein kinase, which phosphorylates these proteins in vitro and in vivo. The potential role of Ca2+/CaM-dependent multifunctional protein kinases in the Ca2+-dependent phosphorylation of these substrates is discussed.

Phosphorylation of protamines by protein kinase C: involvement of sites which are phosphorylated in vivo and are not affected by cAMP-dependent protein kinase

Most fish protamines contain two phosphorylatable sites both of which incorporate phosphate in vivo. Here we show that in two protamines (salmine A1 and clupeine Y1) the site more distant from the N-terminus (residues 20-21) is unaffected by cAMP-dependent protein kinase while it represents the main target for protein kinase C. Such a phosphorylation is typically independent of Ca2+ and phospholipids: responsiveness to these effectors however is conferred by previous fragmentation of protamine with thermolysin. These results suggest that Ca2+, phospholipid-independent phosphorylation of protamine by protein kinase C might have physiological relevance and shed light on the structural basis for the specificity of such an unique process.

Ca2+ phospholipid-dependent and independent phosphorylation of synthetic peptide substrates by protein kinase C

Several synthetic peptides reproducing fragments of protamines have been used as model substrates for Ca2+/phospholipid-dependent protein kinase C, tested both in the absence of any effector (basal conditions) and upon activation by either Ca2+ and phosphatidylserine (or diacylglycerol) or limited proteolysis. Only the peptide Arg4-Tyr-Gly-Ser-Arg6-Tyr [Ga(52-65)] shares the unique property of protamines of being readily phosphorylated even under basal conditions. Optimal activity in the absence of effectors is observed with Tris/HCl buffer pH 7.5; Pipes and Hepes are less effective at pH 7.5, and at pH 6.5 basal phosphorylation is reduced. Under the best conditions for basal phosphorylation of Ga(52-65), its derivative with ornithine replaced for arginine and those corresponding to its C-terminal fragments Gly-Ser-Arg6-Tyr [Ga(57-65)] and Gly-Ser-Arg3 [Ga(57-61)], as well as the peptides Pro-Arg5-Ser2-Arg-Pro-Val-Arg [Th(1-12)], Arg4-Tyr-Arg2-Ser-Thr-Val-Ala [Th(13-23)] and Arg2-Leu-Ser2-Leu-Arg-Ala are not significantly affected though all of them, like histones, are more or less readily phosphorylated upon activation of protein kinase C by Ca2+/phosphatidylserine. The peptide Ser2-Arg-Pro-Val-Arg [Th(7-12)] however, corresponding to the C-terminal part of Th(1-12), is not phosphorylated even in the presence of activators. Limited proteolysis can roughly mimic the Ca2+/phosphatidylserine effect inducing however different extents of activation depending on the nature of the peptide substrates. Our results support the following two conclusions. Basal phosphorylation by protein kinase C in the absence of any effector requires peptide substrates whose target residue(s) are included between two extended arginyl blocks and is also dependent on pH and nature of the buffer. Peptides having extended clusters of either arginyl or ornithyl residues on the C-terminal side of serine are also readily phosphorylated, but they need activation of protein kinase by either Ca2+/phosphatidylserine or limited proteolysis. The same is true of peptides having basic residues only on the N-terminal side, or even on both sides but in limited number.

Calmodulin-dependent multifunctional protein kinase. Evidence for isoenzyme forms in mammalian tissues

Calcium/calmodulin-dependent multifunctional protein kinases, extensively purified from rat brain (with apparent molecular mass 640 kDa), rabbit liver (300 kDa) and rabbit skeletal muscle (700 kDa), were analysed for their structural, immunological, and enzymatic properties. The immunological cross-reactivity with affinity-purified polyclonal antibodies to the 50-kDa catalytic subunit of the brain calmodulin-dependent protein kinase confirmed the presence of common antigenic determinants in all subunits of the protein kinases. One-dimensional phosphopeptide patterns, obtained by digestion of the autophosphorylated protein kinases with S. aureus V8 protease, and two-dimensional fingerprints of the 125I-labelled proteins digested with a combination of trypsin and chymotrypsin, revealed a close similarity between the two subunits (51 kDa and 53 kDa) of the liver enzyme. Similar identity was observed between the 56-kDa and/or 58-kDa polypeptides of the skeletal muscle calmodulin-dependent protein kinase. The data suggest that the subunits of the liver and muscle protein kinases may be derived by partial proteolysis or by autophosphorylation. The peptide patterns for the 50-kDa and 60-kDa subunits of the brain enzyme confirmed that the two catalytic subunits represented distinct protein products. The comparison of the phosphopeptide maps and the two-dimensional peptide fingerprints, indicated considerable structural homology among the 50-kDa and 60-kDa subunits of the brain calmodulin-dependent protein kinase and the liver and muscle polypeptides. However, a significant number of unique peptides in the liver 51-kDa subunit, skeletal muscle 56-kDa, and the brain 50-kDa and 60-kDa polypeptides were observed and suggest the existence of isoenzyme forms. All calmodulin-dependent protein kinases rapidly phosphorylated synapsin I with a stoichiometry of 3-5 mol phosphate/mol protein. The two-dimensional separation of phosphopeptides obtained by tryptic/chymotryptic digestion of 32P-labelled synapsin I indicated that the same peptides were phosphorylated by all the calmodulin-dependent protein kinases. Such data represent the first structural and immunological comparison of the liver calmodulin-dependent protein kinase with the enzymes isolated from brain and skeletal muscle. The findings indicate the presence of a family of highly conserved calmodulin-dependent multifunctional protein kinases, with similar structural, immunological and enzymatic properties. The individual catalytic subunits appear to represent the expression of distinct protein products or isoenzymes which are selectively expressed in mammalian tissues.

A synthetic peptide substrate specific for casein kinase II

A synthetic peptide having the sequence Arg-Arg-Arg-Glu-Glu-Thr-Glu-Glu-Glu was found to serve as a convenient substrate for the protein kinase generally referred to as casein kinase II. The enzyme exhibited an apparent Km of 500 microM for the peptide, as compared to an apparent Km of 50 microM for casein. The maximum velocities for phosphorylation of the peptide and of casein were similar. The peptide was not phosphorylated by any of eight other protein kinases, all of which were shown to be active toward their known substrates. The peptide was used to monitor activity during steps in the purification of casein kinase II from bovine liver. These experiments demonstrated that with this peptide it is now possible to obtain specific measurements of casein kinase II activity in crude enzyme preparations.

Complete coding sequence of rat tyrosine hydroxylase mRNA

Several clones specific for tyrosine hydroxylase [tyrosine 3-monooxygenase, L-tyrosine, tetrahydropteridine:oxygen oxidoreductase (3-hydroxylating), EC 1.14.16.2] have been identified from a rat PC12 library by using the previously characterized clone pTH-1. The most complete of these, pTH-51, is 1758 base pairs long and covers most of the length of the mRNA, including the entire coding and 3' untranslated region. The polypeptide has an estimated molecular weight of 55,903 and some of its characteristic features are discussed.

Cyclic AMP-dependent and -independent protein kinases and protein phosphorylation in human promyelocytic leukemia (HL60) cells induced to differentiate by retinoic acid

The human leukemia cell line HL60 which resembles promyelocytes can be induced to differentiate to cells displaying features of the mature myeloid phenotype by a variety of agents including retinoic acid (RA) and agents that elevate intracellular adenosine 3:5 cyclic monophosphate (cyclic AMP) levels, e.g., 8-bromo-cyclic adenosine 3:5 monophosphate (8-Br-cyclic AMP), cholera toxin. Since most, if not all the effects of cyclic AMP, are mediated by adenosine 3:5 cyclic monophosphate-dependent protein kinase (cyclic AMP-dPK), we investigated the role of cyclic AMP-dPK and adenosine 3:5 cyclic monophosphate-independent protein kinase (cyclic AMP-iPK) in the induced differentiation of HL60 cells. Marked stimulation of cyclic AMP-dPK and cyclic AMP-iPK appears to be intimately involved with and specific for HL60 myeloid differentiation as evidenced by: (1) Stimulation of cyclic AMP-dPK and cyclic AMP-iPK early during HL60 myeloid differentiation and prior to phenotypic changes. (2) RA and dimethylformamide (DMF), agents that induce differentiation along the myeloid pathway, cause a marked increase in the type l cytosolic cyclic AMP-dPK and cyclic AMP-iPK (protamine kinase) while no such increases are noted in cells treated with 12-0-tetradecanoyl-phorbol-13-acetate (TPA) which induces differentiation along the monocyte/macrophage pathway. (3) Both native polyacrylamide gel electrophoresis as well as photoaffinity labeling with 8-azido-cyclic AMP demonstrate marked increases in type l cyclic AMP-dPK in the cytosols of cells exposed to agents that induce myeloid differentiation but no increase in TPA-differentiated cells. (4) The appearance and disappearance of specific cyclic AMP-dependent and -independent protein phosphorylations are associated with the induced myeloid differentiated state.

In vitro phosphorylation of a synthetic collagen peptide by cyclic AMP-dependent protein kinase

A synthetic tridecapeptide that corresponds closely to amino acid residues 98 to 110 in chick collagen alpha 1(I) contains several determinants of specificity required for recognition and phosphorylation by the cyclic AMP-dependent protein kinase. The peptide Gly-Leu-Hyp-Gly-Nle-Lys-Gly-His-Arg-Gly-Phe-Ser-Gly was predicted to be a substrate for the cyclic AMP-dependent protein kinase because it contained multiple basic amino acids NH2-terminal to a potentially phosphorylatable seryl residue. When tested as a substrate for the enzyme, the peptide was stoichiometrically phosphorylated. Phosphoserine was identified as the only phosphoamino acid in a partial hydrolysate of the phosphorylated peptide. The peptide and several of its analogs were phosphorylated by the cyclic AMP-dependent protein kinase with Km values from 1 to 6 mM and Vmax values from 1 to 3 mumol of phosphate/min/mg of enzyme. Although the Km of the kinase for the collagen peptide was high, these results confirmed the prediction made from knowledge of the substrate specificity of cyclic AMP-dependent protein kinase. The potential for such a phosphorylation reaction to occur in vivo is discussed.

The use of synthetic peptides for defining the specificity of typrosine protein kinases

The tyrosine protein kinases are a large family of enzymes that may be involved in regulating cell growth and differentiation. An important property of these enzymes is their substrate specificity. Defining the specificity of these enzymes will contribute to a greater understanding of their biological functions. Synthetic peptides provide a useful means for studying the specificities of protein kinases. The utility of synthetic peptides for specificity studies is exemplified by the results obtained with the cyclic nucleotide-dependent protein kinases. A large number of synthetic peptides have been tested as substrates for these enzymes. There are three important conclusions from this work. First, in terms of primary sequence, the two cyclic nucleotide-dependent protein kinases both require the presence of a pair of basic residues on the N-terminal side of the phosphorylatable residue. Second, recognition of a specific secondary structure in the substrate is an equally important factor in the substrate specificities of these enzymes. Third, the specificities of the two cyclic nucleotide-dependent protein kinases are remarkably similar in terms of both primary and secondary structure recognition. Sequences at the sites of tyrosine phosphorylation often show the presence of numerous acidic residues on the N-terminal side of the tyrosine. This result led to the suggestion that these acidic residues might be important for the recognition of these sites by the tyrosine protein kinases. Specificity studies using synthetic peptides have provided some experimental verification of this concept. In the case of four tyrosine protein kinases, LSTRA cell tyrosine protein kinase, epidermal growth factor receptor kinase, insulin receptor kinase and pp60gag-yes tyrosine protein kinase, the presence of acidic residues on the N-terminal side of the tyrosine in a synthetic peptide was a favorable determinant. In the case of a fifth member of the tyrosine protein kinase family, namely pp60src kinase, the data are less clear that the presence of acidic residues is involved in substrate recognition. This enzyme readily phosphorylated several peptides that did not have acidic residues on the N-terminal side of the tyrosine. Although there is some indication that the presence of acidic residues on the N-terminal side of the tyrosine is a factor in substrate recognition by several of the tyrosine protein kinases, the changes in kinetic parameters with the various peptide substrates were rather small. In addition, some sites phosphorylated in proteins do not have any acidic residues on the N-terminal side of the phosphorylated tyrosine residue.(ABSTRACT TRUNCATED AT 400 WORDS)

A study with model substrates of the structure of the sites phosphorylated by rat liver casein kinase TS

Two new sites phosphorylated by rat liver cyclic AMP-independent casein kinase TS have been identified in denatured pepsin and soybean antiprotease C-II, exhibiting the sequences: Cys-Ser-Ser(P)-Ile-Asp-Ser and His-Ser3(P)-Asp-Asp-Glu, respectively. Their phosphorylation efficiency has been compared to that of previously identified sites and the effects of chemical modifications in the vicinity of the phosphorylatable residue have been studied. The results obtained support the following conclusions: 1. All sites affected by casein kinase TS conform to the sequence: Ser/Thr-X-Glu/Asp which is also believed to be required by the mammary gland casein kinase. Threonine appears to be less suitable for phosphorylation then serine. The presence of some additional residues on the C-terminal side also appears to be required. 2. X can be either an additional acidic residue or a natural one, but not a basic residue. The contiguity of an acidic cluster to the C-terminal side of the target greatly improves the phosphorylation efficiency. 3. The residues N-terminal to the target one do not seem to be relevant for determining the site recognition by the protein kinase. 4. The predicted secondary structure constantly occurring at the phosphorylation sites is the beta-turn: apparently the bend must include both the target residue and the acidic determinant at the n + 2 position.

Secondary structure prediction of fish protamines

The secondary structures of thirteen fish protamines have been predicted by the statistical method of Chou and Fasman as well as by two modifications of it. The occurrence of phosphorylatable residues in predicted beta-turns is discussed. The results are compared with available spectroscopic observations.

Modification and identification of glutamate residues at the arginine-recognition site in the catalytic subunit of adenosine 3' :5'-cyclic monophosphate-dependent protein kinase of rabbit skeletal muscle

It has been proposed that the active centre of cyclic AMP-dependent protein kinase contains an arginine-recognition site, which is considered to be essential for the function of the catalytic subunit of the kinase [Matsuo, Huang & Huang (1978) Biochem. J.173, 441-447]. The catalytic subunit can be inactivated by 3-(3-dimethylaminopropyl)-1-ethylcarbodi-imide and glycine ethyl ester at pH6.5. The enzyme can be protected from inactivation by preincubation with histone, a protein substrate of the enzyme. On the other hand, ATP, which also serves as a protein kinase substrate, does not afford protection. Polyarginine, a competitive inhibitor of protein kinase, which is known from kinetic studies to interact specifically with the arginine-recognition site, partially protects the catalytic subunit from inactivation by 3-(3-dimethylaminopropyl)-1-ethylcarbodi-imide. These results lead to the conclusion that the site of modification by carbodi-imide/glycine ethyl ester is most likely located at the arginine-recognition site of the active centre. A value of 1.7+/-0.2 (mean+/-s.d.) mol of carboxy groups per mol of catalytic subunit has been obtained for the number of essential carboxy groups for the function of protein kinase; a complete chemical modification of these essential carboxy groups results in total loss of catalytic activity. Finally, we have identified the essential carboxy group in the catalytic subunit of cyclic AMP-dependent protein kinase as being derived from glutamate residues. This is achieved by a three-step procedure involving an extensive proteolytic digestion of the [1-(14)C]glycine ethyl ester-modified enzyme and two successive high-voltage electrophoreses of the hydrolysate. It is concluded that 1.7mol of glutamyl carboxy groups per mol of catalytic subunit may be considered a component of the arginine-recognition site in the active centre of cyclic AMP-dependent protein kinase.

Protein kinases of rat liver endoplasmic reticulum. Solubilisation, partial characterisation and comparison with protein kinases of rat liver cytosol

Protein kinase associated with rat liver microsomes was only partly extracted by treatment with 1.5 M KCl. The enzyme was solubilised by Triton X-100 or sodium deoxycholate at the same or slightly higher detergent concentrations than microsomal marker components. The enzyme activity increased 2-3 fold upon solubilisation. Three peaks with protein kinase activity (fractions MI, MII and MIII) were resolved on DEAE-cellulose chromatography. Fraction MIII but not fractions MI or MII was activated by adenosine 3':5'-monophosphate (cyclic AMP). All fractions catalysed the phosphorylation of protamine and histones but not that of casein or phosvitin. Fractions MI and MIII had a similar substrate specificity and phosphorylated histones at a relatively much higher rate than did fraction MII. The isoelectric points were 8.1 for fraction MI, 5.5 for fraction MII and 4.9 for fraction MIII. On incubation of fraction MIII with cyclic AMP it was split into two catalytically active components with pI 8.1 and 7.35. The component with pI 8.1 was predominant and corresponded to fraction MI. Five protein kinase peaks were resolved from rat liver cytosol by DEAE-cellulose chromatography. Three of them (fractions CIa, CIIb and CIII) had the same properties as each of the microsomal kinase fractions. A forth fraction (CIIa) was cyclic-AMP-dependent and had the same substrate specificity as fractions MI and MIII. Its pI was 5.1, and it was split into two components by cyclic AMP (pI 8.1 and 7.35). In binding studies fraction CIIb bound more efficiently to microsomes than fraction CIII, while fractions CIa, CIIa and the microsomal protein kinase fractions did not bind appreciably. When microsomes were treated with trypsin exposed protein kinase was inactivated and the latency of the remaining enzyme increased substantially. Most of fraction MII was inactivated by trypsin while fraction MIII was resistant. The possible orientation of protein kinase fractions MII and MIII in the microsomal membrane is discussed.