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PubMed2003

Recognition of arylsulfatase A and B by the UDP-N-acetylglucosamine:lysosomal enzyme N-acetylglucosamine-phosphotransferase.

The critical step for sorting of lysosomal enzymes is the recognition by a Golgi-located phosphotransferase. The topogenic structure common to all lysosomal enzymes essential for this recognition is still not well defined, except that lysine residues seem to play a critical role. Here we have substituted surface-located lysine residues of lysosomal arylsulfatases A and B. In lysosomal arylsulfatase A only substitution of lysine residue 457 caused a reduction of phosphorylation to 33% and increased secretion of the mutant enzyme. In contrast to critical lysines in various other lysosomal enzymes, lysine 457 is not located in an unstructured loop region but in a helix. It is not strictly conserved among six homologous lysosomal sulfatases. Based on three-dimensional structure comparison, lysines 497 and 507 in arylsulfatase B are in a similar position as lysine 457 of arylsulfatase A. Also, the position of oligosaccharide side chains phosphorylated in arylsulfatase A is similar in arylsulfatase B. Despite the high degree of structural homology between these two sulfatases substitution of lysines 497 and 507 in arylsulfatase B has no effect on the sorting and phosphorylation of this sulfatase. Thus, highly homologous lysosomal arylsulfatases A and B did not develop a single conserved phosphotransferase recognition signal, demonstrating the high variability of this signal even in evolutionary closely related enzymes.

Animals↗

PubMedDate not supplied

Iodinated contrast agents. Effect on ATP: creatine N-phosphotransferase isoenzymes in arterial wall.

In the arterial wall, ATP:creatine N-phosphotransferase (E.C.2.7.3.2) is present in the form of its three isoenzymes, MM, MB, and BB, the latter being predominant. Six iodinated contrast agents in routine angiographic use were examined from the point of view of their effects in vitro on the isoenzymes of ATP:creatine N-phosphotransferase from the arterial wall, compared with their effects on the same isoenzymes in other organs. There is a clear inhibitory effect from the contrast agents on all organs, but it is least marked for the arterial wall. Furthermore, nonionic compounds have far less enzyme-inhibitory effect than ionic compounds.

Animals↗

PubMed1981

Adenylic acid: deoxythymidine 5'-phosphotransferase: evidence for the existence of a novel herpes simplex virus-induced enzyme.

BHK (dPyK-) cells infected with herpes simplex virus type 1 (HSV-1) contain a virus-induced deoxythymidine (dThd)-phosphorylating enzyme. This enzyme uses AMP as phosphate donor and is called AMP :deoxythymidine 5'-phosphotransferase (or kinase). The enzyme was purified over 1300-fold and was found to be specific for an AMP substrate. It can thus be distinguished from virus-specific deoxypyrimidine kinase (dPyK). It is shown that the two substrates AMP and dThd participate in the reaction at a 1 : 1 molar ratio; the Km for AMP was 2 X 3 muM and for dThd it was 2 X 1 muM. The mol. wt. of the enzyme was estimated to be between 110 000 (by glycerol gradient centrifugation) and 90 000 (by gel filtration). For optimum activity, the phosphotransferase required an alkaline pH, and 37 degrees C; the activation energy of the reaction was 18 450 cal/mol. The appearance of the enzyme after infection parallels that of viral DNA synthesis-related functions.

Adenosine Monophosphate↗

PubMed1986

Distribution of pyrophosphate:fructose 6-phosphate phosphotransferase in maize leaves.

In leaves of maize (Zea mays) the activity of pyrophosphate:fructose 6-phosphate 1-phosphotransferase (PFP) is much less than that of ATP:fructose 6-phosphate 1-phosphotransferase. A sequential extraction technique was used to study the location of PFP in this tissue. When compared with enzymes known to be restricted to specific locations in maize, the distribution of PFP activity in the sequential extracts indicated that PFP is located predominantly, if not exclusively, in the mesophyll cytoplasm. Although confined to the same site as sucrose synthesis, the level of PFP activity is inadequate to contribute significantly to the gluconeogenic flux from fructose 1,6-bisphosphate to fructose 6-phosphate. The absence of PFP activity from the bundle-sheath demonstrates that this activity is not essential for glycolysis in higher plants.

Journal Article↗

PubMed1987

Comparison of the Activities and Some Properties of Pyrophosphate and ATP Dependent Fructose-6-Phosphate 1-Phosphotransferases of Phaseolus vulgaris Seeds.

THE DISTRIBUTION OF PYROPHOSPHATE: fructose 6-phosphate phosphotransferase (PFP) and ATP: fructose-6-phosphate 1-phosphotransferase (PFK) was studied in germinating bean (Phaseolus vulgaris cv Top Crop) seeds. In the cotyledons the PFP activity was comparable with that of PFK. However, in the plumule and radicle plus hypocotyl, PFP activity exceeds that of PFK. Approximately 70 to 90%, depending on the stage of germination, of the total PFP and PFK activities were present in the cotyledons. Highest specific activity of both enzymes, however, occurred in the radicle plus hypocotyl (64-90 nanomoles.min.milligram protein). Fractionation studies indicate that 40% of the total PFK activity was associated with the plastids while PFP is apparently confined to the cytoplasm. The cytosolic isozyme of PFK exhibits hyperbolic kinetics with respect to fructose 6-P and ATP with K(m) values of 320 and 46 micromolar, respectively. PFP also exhibits hyperbolic kinetics both in the presence and absence of the activator fructose-2,6-P(2). The activation is caused by lowering the K(m) for fructose 6-P from 18 to 1.1 millimolar and that for pyrophosphate (PPi) from 40 to 25 micromolar, respectively. Levels of fructose 2,6-P(2) and PPi in the seeds are sufficient to activate PFP and thereby enable a glycolytic role for PFP during germination. However, the fructose 6-P content appears to be well below the K(m) of PFP for this compound and would therefore preferentially bind to the catalytic site of PFK, which has a lower K(m) for fructose 6-P. The ATP content appears to be at saturating levels for PFK.

Journal Article↗

PubMed1988

Molecular Comparison of Pyrophosphate- and ATP-Dependent Fructose 6-Phosphate 1-Phosphotransferases from Potato Tuber.

The aim of this work was to compare the molecular properties of pyrophosphate:fructose 6-phosphate 1-phosphotransferase (PFP) and ATP:fructose 6-phosphate 1-phosphotransferase (PFK). Both enzymes were purified to apparent homogeneity from potato tubers (Solanum tuberosum cv Record). Neither PFP nor PFK preparations contained detectable activity of the other enzyme. PFP was composed of two polypeptides of apparent molecular weight 58,000 and 55,700 whereas PFK contained four polypeptides of apparent molecular weight between 46,300 and 53,300. Chemical cleavage of individual PFP and PFK polypeptides gave a different set of fragments for each polypeptide. On Western blots antisera against PFP failed to cross-react with any of the four PFK polypeptides, and antibodies against PFK failed to bind to either of the PFP polypeptides. Antibodies that immunoprecipitate PFP activity had no effect on PFK activity. Conversely, antibodies against the four PFK polypeptides precipitated the activity of PFK, but not that of PFP. This work shows that potato tuber PFP and PFK are composed of distinct, unrelated polypeptides and indicate that interconversion between PFP and PFK is unlikely.

Journal Article↗

PubMed1992

Substrate specificity of pyrophosphate:fructose 6-phosphate 1-phosphotransferase from potato tuber.

The aim of this work was to establish the precise ionic form of the reactants used by pyrophosphate:fructose-6-phosphate phosphotransferase. The enzyme was purified to near-homogeneity from potato (Solanum tuberosum L.) tubers. Changes in enzyme activity when the pH of the assay and the concentration of fructose 6-phosphate, pyrophosphate, and magnesium are varied independently indicate that fructose 6-phosphate(2-) and MgP(2)O(7) (2-) are the reacting species in the glycolytic direction. Analogous experiments with fructose 1,6-bisphosphate, inorganic phosphate, and magnesium demonstrate that the enzyme uses fructose 1,6-bisphosphate(4-), HPO(4) (2-), and Mg(2+) in the gluconeogenic direction. The ionic species used in the glycolytic direction are comparable with those required by bacterial ATP-dependent phosphofructokinase. This is consistent with the proposal that the active site of pyrophosphate:fructose-6-phosphate phosphotransferase in plants is equivalent to that of the bacterial phosphofructokinase (SM Carlisle et al. [1990] J Biol Chem 265: 18366-18371).

Journal Article↗

PubMed1984

Function of anti-Streptococcus mutans antibodies: anti-ribosomal antibodies inhibit acid production, growth, and glucose phosphotransferase activity.

Antibodies induced in sera and saliva of rats and rabbits immunized with ribosomal preparations from Streptococcus mutans 6715 inhibited transport of glucose by the phosphotransferase system by greater than 60%, acid production from sucrose by greater than 95%, and growth of the homologous S. mutans by greater than 59%. Inhibition of growth and acid production by immune sera and saliva were abrogated by prior adsorption with S. mutans 6715 whole cells, glucosyltransferase, lipoteichoic acid, or alpha 1-6 or alpha 1-3 dextran. These results indicate that antibodies induced to an S. mutans ribosomal preparation react with cell surface determinants and suggest that the antibodies inhibit sucrose-induced acid formation and growth of virulent S. mutans by neutralizing the glucose-phosphotransferase system.

Animals↗

PubMed2000

Simultaneous stable expression of neomycin phosphotransferase and green fluorescence protein genes in Trypanosoma cruzi.

The ribosomal RNA (rRNA) gene promoter was used to construct plasmid vectors that simultaneously express multiple exogenous genes in Trypanosoma cruzi. Vector pBSPANEO expresses neomycin phosphotransferase, and pPAGFPAN expresses both green fluorescent protein and neomycin phosphotransferase from a single promoter. Both vectors require the presence of the rRNA promoter for stable transfection; epimastigotes transfected with pPAGFPAN strongly fluoresced due to green fluorescent protein expression. Intact plasmids were rescued from the T. cruzi-transfected population after >8 mo of culture, indicating stable replication of these vectors. Vectors were integrated into the rRNA locus by homologous recombination and into other loci, presumably by illegitimate recombination. Parasites bearing tandem concatamers of plasmids were also found among the transfectants. Transfectants expressing green fluorescent protein showed a bright green fluorescence distributed throughout the cell. Fluorescence was also detected in amastigotes after infection of mammalian cells with transfected parasites, indicating that the rRNA promoter can drive efficient expression of these reporter genes in multiple life-cycle stages of the parasite. Expression of the heterologous genes was detected after passage in mice or in the insect vector. These vectors will be useful for the genetic dissection of T. cruzi biology and pathogenesis.

Animals↗

PubMed1999

Developing a snapshot of the ATP binding domain(s) of aminoglycoside phosphotransferases.

The aminoglycoside (AG) 3'-phosphotransferases [APH(3')s] are an important class of modifying enzymes which confer high-level resistance to those AGs actively modified by the enzymes. They catalyze the transfer of the terminal phosphate from ATP to the drug, thus preventing the AG s action at the 70S ribosome. These enzymes, which utilize ATP as a co-substrate, appear from amino acid alignments to be part of a much larger superfamily of kinases and ATP-binding proteins. Structure-function analyses have been initiated in our laboratory for APH(3')-II, whose gene was derived from transposon Tn5. Site-directed mutagenesis of the cloned APH(3')-II gene was used to genetically examine the residues in two highly-conserved motifs proposed to participate in ATP binding. Several of these residues, in fact, were shown to affect the enzyme s affinity for ATP. We have also initiated studies using photoaffinity labelling of APH(3')-II with the ATP analogs, 8-azido-ATP and 2-azido-ATP. We have shown that 8-N3ATP and 2-N3ATP can be substituted for ATP in the APH(3')-II catalyzed phosphorylation of kanamycin; such findings indicate that the interaction of these photoaffinity analogs of ATP with APH(3')-II is biologically relevant. One of the best-characterized of the APH(3') enzymes is APH(3')-IIIa, the first of the group whose structure has been analyzed by x- ray crystallography. Several studies have demonstrated that this enzyme functions by a Theorell-Chance mechanism. Moreover, the architecture of the enzyme, crystallized in the presence of ADP has revealed residues in the ATP-binding pocket which are likely to play important roles in catalysis. Once the results from biochemical analyses can be correlated with those from mutagenesis studies and x-ray crystallography, a clearer picture of the active site will be provided for an important class of AG-modifying enzymes and phosphotransferases. This picture will also allow a better understanding of these enzymes within the greater context of kinases and nucleotide-binding proteins.

Adenosine Triphosphate↗

PubMed1999

Aminoglycoside phosphotransferases: proteins, structure, and mechanism.

Aminoglycoside antibiotics constitute an important class of clinically useful drugs which are imperiled by the emergence of resistant organisms. Aminoglycoside resistance in the clinics is primarily due to the presence of modifying enzymes which N-acetylate, O-adenylate or O-phosphorylate the antibiotics. The latter family of enzymes are termed the aminoglycoside phosphotransferases or kinases and are the subject of this review. There are seven classes of aminoglycoside phosphotransferases (APH(3'), APH(2''), APH(3'off'), APH(6), APH(9), APH(4), APH(7'')) and many isozymes in each class, and although there is very little overall general sequence homology among these enzymes, certain signature residues and sequences are common. The recent determination of the three-dimensional structure of the broad spectrum aminoglycoside kinase APH(3')-IIIa complexed with the product ADP, in addition to mechanistic and mutagenic studies on this and related enzymes, has added a great deal to our understanding of this class of antibiotic resistance enzyme. In particular, the revelation of structural and mechanistic similarities between APHs and Ser/Thr and Tyr kinases has set the stage for future inhibition studies which could prove important in reversing aminoglycoside resistance.

Aminoglycosides↗

PubMedDate not supplied

[Dependence of aminoglycoside 3'-phosphotransferase VIII activity on protein serine/threonine kinases in Streptomyces rimosus].

In Streptomyces rimosus, selection with aminoglycoside kanamycin triggers "silent" aminoglycoside 3'-phosphotransferase (aph) VIII gene. Expression of aphVIII was accompanied by amplification of a chromosomal DNA fragment, which contained aphVIII. Earlier, S. rimosus aphVIII gene was isolated, sequenced, and deduced APHVIII protein sequence was reported. Using in vitro labeling and immunoprecipitation with anti-APHVIII antibody, we demonstrate that one of the abundant proteins phosphorylated by endogenous protein kinases (PKs) in extracts of S. rimosus strain S683 is APHVIII. Phosphoamino acid assay has shown phosphorylation of two seryl residues in APH molecule. The amount of phosphate incorporated into APHVIII in the presence of Ca2+ was 1.84-fold as much as that detected without Ca2+. As shown by in the gel self-phosphorylation and in the substrate-containing gel phosphorylation analyses, two serine PKs with molecular masses of 74 kDa and 55 kDa were active against APHVIII. The 55-kDa PK showed a clear Ca2+ and calmodulin dependency in activity. The specific kanamycin phosphotransferase activity of exhaustedly phosphorylated APHVIII was 3.72-fold as much as that detected in the preparation of nonphosphorylated enzyme. These results suggest involvement of PKs under study in the modulation of APHVIII aminoglycoside phosphorylating activity and in the generation of kanamycin resistance in S. rimosus.

Calcium↗

PubMed1986

Glycoprotein phosphorylation in simple eucaryotic organisms. Identification of UDP-GlcNAc:glycoprotein N-acetylglucosamine-1-phosphotransferase activity and analysis of substrate specificity.

UDP-N-acetylglucosamine:glycoprotein N-acetylglucosamine-1-phosphotransferase activity has been identified in both Acanthamoeba castellani and Dictyostelium discoideum. Each of these activities exhibits a different in vitro specificity toward various purified glycoproteins. The N-acetylglucosaminyl-phosphotransferase of A. castellani is very similar to the mammalian enzyme in that it phosphorylates the lysosomal enzymes cathepsin D and uteroferrin much more efficiently than nonlysosomal glycoproteins and appears to recognize a determinant on the protein portion of these good acceptors. In contrast the D. discoideum enzyme cannot utilize cathepsin D as a good substrate and, although it phosphorylates uteroferrin efficiently, it does not recognize the protein portion of this acceptor. The oligosaccharide of uteroferrin appears to assume a different conformation than the oligosaccharides of other glycoproteins and glycopeptides, as evidenced by its enhanced sensitivity to mannosidase digestion. This conformation, presumably induced by some interaction with the underlying protein, may be responsible for the specific phosphorylation of uteroferrin by the N-acetylglucosaminylphosphotransferase of D. discoideum.

Acid Phosphatase↗

PubMedDate not supplied

[Pyrophosphate-dependent D-fructose-6-phosphate-phosphotransferase in Rhodospirillaceae (author's transl)].

A pyrophosphate-dependent fructose-6-phosphate phosphotransferase from the photosynthetic bacterium Rhodospirillum rubrum was partially purified and characterized in respect to kinetic and regulatory properties. The enzyme had a molecular weight of about 95 000 dalton and required Mg2+-ions for catalysis and maintenance of activity. The phosphotransferase was specific for fructose-6-phosphate (F-6-P) and inorganic pyrophosphate (PP) as substrates of the fructose-1,6-bisphosphate-forming reaction (forward reaction). In the phosphate (Pi)-dependent back reaction, the preferred substrate was fructose-1,6-bisphosphate (FBP). At optimal pH (7.2 for the forward, and 8.6 for the back reaction) the back reaction had a slightly higher Vmax than the forward reaction. The substrate-saturation curves of the enzyme were all hyperbolic with intersecting kinetic pattern. The Km-values (in mM) at saturating MgCl2-concentration were: 0.38 (F-6-P); 0.25 (PP); 0.02 (FBP) and 0.82 (Pi). The forward reaction was inhibited by ADP. The inhibition by ADP (Ki = 0.18 mM) was of the mixed type in respect to F-6-P, but independent of the PP-concentration. The inhibition by AMP (Ki = 0.017 mM) was of a more complex type, because AMP not only decreased the Vmax of the F-6-P- or PP-saturation curve, but also increased the Hill-coefficient from nH = 1 to nH = 2.5 of the F-6-P-saturation curve. The inhibition of the back reaction by the two adenylates was less pronounced. ATP (at 2.5 mM), like citrate, inhibited the back reaction only at low MgCl2 concentration (1 mM) indicating that the inhibitory effect was due to the chelation of Mg2+. Out of 5 other species of the Rhodospirillaceae tested, the PP-dependent phosphofructokinase was only shown to present in Rhodopseudomonas gelatinosa.

Kinetics↗

PubMed1997

[Determination of the nucleotide sequence of the silent aminoglycoside phosphotransferase gene in Streptomyces rimosus P3].

The nucleotide sequence BgIII-Pstl of the DNA fragment containing the aph gene cloned from Streptomyces rimosus P3 not producing aminoglycoside antibiotics was determined. The aph gene was shown to encode neomycin phosphotransferase differing by the substrate specificity from the enzyme encoded by the aph genes from the organisms producing aminoglycoside antibiotics. Comparison of the cloned aph VIII gene and its product with the aph genes and their products from the antibiotic-producing actinomycetes and clinical microbial strains permitted to consider it as a representative of the third group genes which are likely widely distributed in soil microorganisms not producing aminoglycoside antibiotics. The gene length was 777 nucleotide pairs at the average GC content of 67 per cent. Comparison of the nucleotide and protein sequences of the S.rimosus gene with those of the genes cloned from the aminoglycoside-producing organisms (S.fradiae and Micromonospora chalcea) revealed high homology in the 3'-end region of the genes. However, the homology percentage by DNA for the S.rimosus gene was lower than that for the genes from the other organisms on their comparison with each other: 56-67 and 82-86 per cent respectively. Comparison of the profiles of the protein hydrophilic properties revealed differences in the region of the first 110 amino acids of the gene under the investigation. The amino acid sequence contained all the highly conservative regions characteristics of aminoglycoside phosphotransferases but had several amino acid substitutes detected for the first time including those in the region responsible for the antibiotic binding.

Amino Acid Sequence↗

PubMed2001

Mechanism-based inhibition of enzyme I of the Escherichia coli phosphotransferase system. Cysteine 502 is an essential residue.

Four phosphoenolpyruvate (PEP) derivatives, carrying reactive or activable chemical functions in each of the three chemical regions of PEP, were assayed as alternative substrates of enzyme I (EI) of the Escherichia coli PEP:glucose phosphotransferase system. The Z- and E-isomers of 3-chlorophosphoenolpyruvate (3-Cl-PEP) were substrates, presenting K(m) values of 0.08 and 0.12 mm, respectively, very similar to the K(m) of 0.14 mm measured for PEP, and k(cat) of 40 and 4 min(-1), compared with 2,200 min(-1), for PEP. The low catalytic efficiency of these substrates permits the study of activity at in vivo EI concentrations. Z-Cl-PEP was a competitive inhibitor of PEP with a K(I) of 0.4 mm. E-Cl-PEP was not an inhibitor. Compounds 3 and 4, obtained by modification of the carboxylic and phosphate groups of PEP, were neither substrates nor inhibitors of EI, highlighting the importance of these functionalities for recognition by EI. Z-Cl-PEP is a suicide inhibitor. About 10-50 turnovers sufficed to inactivate EI completely. Such a property can be exploited to reveal and quantitate phosphoryl transfer from EI to other proteins at in vivo concentrations. Inactivation was saturatable in Z-Cl-PEP, with an apparent K(m)(inact) of 0.2-0.4 mm. The rate of inactivation increased with the concentration of EI, indicating a preferential or exclusive reaction with the dimeric form of EI. E-Cl-PEP inactivates EI much more slowly, and unlike PEP, it did not protect against inactivation by Z-Cl-PEP. This and the ineffectiveness of E-Cl-PEP as a competitive inhibitor have been related to the presence of two EI active species. Cys-502 of EI was identified by mass spectrometry as the reacting residue. The C502A EI mutant showed less than 0.06% wild-type activity. Sequence alignments and comparisons of x-ray structures of different PEP-utilizing enzymes indicate that Cys-502 might serve as a proton donor during catalysis.

Amino Acid Sequence↗

PubMed2003

Effect of enzyme I of the bacterial phosphoenolpyruvate : sugar phosphotransferase system (PTS) on virulence in a murine model.

The phosphoenolpyruvate : sugar phosphotransferase system (PTS) catalyses translocation with concomitant phosphorylation of sugars and hexitols and it regulates metabolism in response to the availability of carbohydrates. The PTS forms an interface between energy and signal transduction and its inhibition is likely to have pleiotropic effects. It is present in about one-third of bacteria with fully sequenced genomes, including many common pathogens, but does not occur in eukaryotes. Enzyme I (ptsI) is the first component of the divergent protein phosphorylation cascade. ptsI deletions were constructed in Salmonella typhimurium, Staphylococcus aureus and Haemophilus influenzae and virulence of the mutants was characterized in an intraperitoneal mouse model. The log(attenuation) values were 2.3, 1.4 and 0.9 for the Sal. typhimurium, Sta. aureus and H. influenzae ptsI mutants, respectively. The degree of attenuation is correlated with the complexity of the respective PTS, which comprises approximately 40 components in Sal. typhimurium, but only 5 in H. influenzae.

Animals↗

PubMed1991

Sugar transport by the bacterial phosphotransferase system. Structural and thermodynamic domains of enzyme I of Salmonella typhimurium.

Enzyme I, the first in the sequence of phosphocarrier proteins of the bacterial phosphoenolpyruvate:glycose phosphotransferase system, is a potential critical point for regulating sugar uptake. The thermal stability of Enzyme I was studied by high sensitivity differential scanning calorimetry. At pH 7.5, thermal unfolding of the protein exhibits two peaks with maxima (Tm) at 47.6 and 55.1 degrees C, indicating that the protein comprises two cooperative unfolding structures. Interaction between the two domains is markedly dependent on pH within the range 6.5-8.5. At pH 7.5, catalytic activity was unaffected by heating through the first transition but was lost by heating through the second. Cleavage of Enzyme I (63.5 kDa) by trypsin, chymotrypsin, or Staphylococcus aureus V8 protease yields a 30-kDa fragment, EI-N, containing the NH2 terminus and the active site, His-189. Protease and differential scanning calorimetry experiments show that EI-N is the structural domain corresponding to the cooperative region in the intact enzyme that unfolds at the higher Tm. EI-N catalyzes one activity of Enzyme I; it accepts a phosphoryl group from phosphohistidine-containing phosphocarrier protein but cannot be phosphorylated by phospho-Enzyme I or phosphoenolpyruvate. The phosphoryl transfer between EI-N and the histidine-containing phosphocarrier protein is reversible. Portions of the Salmonella typhimurium ptsI DNA sequence are known; the complete sequence is presented here and compared to Escherichia coli ptsI.

Base Sequence↗