Synthesis of Uridine Diphosphate Glucose Pyrophosphorylase during the Development of Dictyostelium discoideum

Screening assay for inhibitors of a recombinant Streptococcus pneumoniae UDP-glucose pyrophosphorylase

The UDP-glucose pyrophosphorylase of Streptococcus pneumoniae (GalU_Spn) is absolutely required for the biosynthesis of capsular polysaccharide, the sine qua non virulence factor of pneumococcus. Since the eukaryotic enzymes are completely unrelated to their prokaryotic counterparts, we propose that the GalU enzyme is a critical target to fight the pneumococcal disease. A recombinant GalU_Spn was overexpressed and purified. An enzymatic assay that is rapid, sensitive and easy to perform was developed. This assay was appropriate for screening chemical libraries for searching GalU inhibitors. This work represents a fundamental step in the exploration of novel antipneumococcal drugs.

Regulation of UDP-glucose pyrophosphorylase isozyme UGP5 associated with cold-sweetening resistance in potatoes

The regulation of UDP-Glc pyrophosphorylase (UGPase) isozyme, UGP5, was investigated in potato tuber. The cDNA for UGP5 was cloned into the bacterial expression vector pET21d and recombinant (RC) enzyme was expressed in E. coli (BL21 star cells). The RC-UGP5 isozyme was purified to near homogeneity using salt precipitation, hydrophobic interaction, and anion-exchange column chromatography. Kinetic analysis revealed that in the synthesis direction, K(m) values for Glc-1-P (0.83 mM) and UTP (0.22 mM) were similar to those observed previously with the mother tuber (MT)-UGP5. In the pyrophosphorolysis direction, the K(m) values for UDP-Glc (0.68 mM) and PPi (0.56 mM) were slightly higher than those observed previously. Maximum reaction velocities (V(max)) for RC-UGP5 were also elevated. Since the molecular mass, charge, and amino acid sequence of the MT- and RC-UGP5 isozymes were identical, it was assumed that altered kinetic constants may be due to an improper folding of RC-UGP5 polypeptide. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) and proteomic analysis demonstrated that the UGP5 isozyme was a single polypeptide with a calculated molecular mass of 51.8kDa consisting of 477 amino acids. Native PAGE and kinetic analysis revealed that this polypeptide was monomeric in nature. Immunoblotting with specific antibodies and LC-MS/MS data indicated that UGP5 did not require any post-translational modification (e.g., phosphorylation, O-glycosylation, oligomerization/de-oligomerization, or the presence of the regulatory 14-3-3 proteins) for its regulation. Additionally, the two closely associated isozymes UGP5 and UGP6 in the cv. Snowden are likely the result of allelic differences of UGPase at a single locus.

Biochemical characterization of the pneumococcal glucose 1-phosphate uridylyltransferase (GalU) essential for capsule biosynthesis

The glucose 1-phosphate uridylyltransferase (GalU) is absolutely required for the biosynthesis of capsular polysaccharide, the sine qua non virulence factor of Streptococcus pneumoniae. The pneumococcal GalU protein was overexpressed in Escherichia coli, and purified. GalU showed a pI of 4.23, and catalyzed the reversible formation of UDP-glucose and pyrophosphate from UTP and glucose 1-phosphate with K(m) values of 0.4 mM: for UDP-glucose, 0.26 mM: for pyrophosphate, 0.19 mM: for glucose 1-phosphate, and 0.24 mM: for UTP. GalU has an optimum pH of 8-8.5, and requires Mg(2+) for activity. Neither ADP-glucose nor TDP-glucose is utilized as substrates in vitro. The purification of GalU represents a fundamental step to provide insights on drug design to control the biosynthesis of the main pneumococcal virulence factor.

Physicochemical and kinetic properties of unique isozymes of UDP-Glc pyrophosphorylase that are associated with resistance to sweetening in cold-stored potato tubers

Isozymes of UGPase with unique catalytic properties were purified from the cold-induced-sweetening (CIS) resistant cultivar Snowden (Solanum tuberosum). Two distinct peaks of UGPase activity were obtained when protein extracts were subjected to anion-exchange chromatography on DEAE-Sephacel. Polypeptides in the first eluted fraction (A-I) were ionically similar to the UGPase isozyme UGP3 previously purified and characterized from the cold-sweetening sensitive cultivar Norchip (Sowokinos et al. 1993, Plant Physiol 101: 1073-1080). Seventy-two percent of the total endogenous UGPase activity in Snowden (cv.) tubers, however, was found in a more basic protein fraction (A-II) that is not found in the Norchip cultivar. This study reports on the physicochemical and kinetic properties of these new polypeptides that demonstrate UGPase activity. The reaction in the direction of UDP-Glc synthesis was specific for the substrates Glc-1-P and UTP and there was an absolute requirement for Mg2+ ions. The catalytic properties of UGP5 were markedly different from UGPase isozymes previously described in terms of (1) affinity for the substrate Glc-1-P, (2) pH optimum, (3) maximum reaction velocity and (4) sensitivity to product inhibition with UDP-Glc. Chi-square analysis of fifty-four genetically diverse potato lines revealed that resistance to CIS was highly correlated with the presence of the A-II isozymes of UGPase. The kinetic properties of these unique forms of UGPase may underlie, in part, a tuber's ability to resist sweetening in the cold.

Enzymatic synthesis of UDP-GlcN by a two step hollow fiber enzyme reactor system

UDP-GlcN was synthesized from GlcN and UTP by a two step hollow fiber enzyme reactor method. In step 1, GlcN was converted to GlcN 6-P and then to GlcN 1-P by hexokinase and phosphoglucomutase, respectively, and UTP was used as the phosphate donor. In step 2, GlcN 1-P was converted to UDP-GlcN by UDP glucose pyrophosphorylase. All the enzymes required for the synthesis of UDP-GlcN were enclosed in hollow fiber bundles which allow for the free diffusion of substrates and products across the membranes to and from the enzymes, allow for the reutilization of the enzymes, and simplify the isolation of the product, UDP-GlcN. We show that both UTP and GlcN 6-P are inhibitors of the yeast UDPG pyrophosphorylase and therefore their concentrations must be regulated to obtain maximum yields of UDP-GlcN. The UDP-GlcN produced can be N-acetylated with [14C]acetic anhydride to produce UDP-[14C]GlcNAc. This method can also be used to synthesize [32P]UDP-GlcN and [32P]UDP-GlcNAc from [alpha-32P]UTP and GlcN 1-P.

Role of nucleotide pyrophosphatase in enflurane-induced reduction of UDP-glucuronic acid concentration in mouse liver

Because hepatic UDP-glucuronic acid levels decrease upon exposure to volatile anesthetics, the present study was designed to determine the mechanism by which enflurane decreases UDP-glucuronic acid in mice by measuring the concentrations of intermediates and the activities of enzymes in the UDP-glucuronic acid pathway. UDP-glucuronic acid concentrations were decreased by 40% in both male and female mice after 10 min of enflurane-induced narcosis. Concentration of UDP-glucose and the activities of diethylstilbestrol UDP-glucuronosyltransferase and UDP-glucose dehydrogenase were not affected by enflurane treatment. In contrast, nucleotide pyrophophatase activity was increased approximately 50% in both sexes. Thus, the decrease in hepatic UDP-glucuronic acid upon exposure of mice to enflurane is probably due to increased degradation by nucleotide pyrophosphatase.

Non-Michaelian kinetics of rabbit muscle uridine diphosphoglucose pyrophosphorylase

The kinetic properties of rabbit muscle uridine diphosphoglucose (UDP-Glc) pyrophosphorylase have been studied, in both directions, with respect to substrate saturation, product inhibition, and cation requirement for activity. The results demonstrate that UDP-Glc pyrophosphorylase is a non-Michaelian enzyme: the synthetic reaction is characterized by a marked inhibition by glucose-1-phosphate (at concentrations higher than 0.3 mM) and by an hyperbolic saturation for UTP. In the reverse reaction, instead, the saturation function for UDP-Glc is hyperbolic and that for inorganic pyrophosphate is sigmoid, with a high Hill coefficient of (nH) 2.5. The study of the metal requirement indicates a distinctive ability of cations to stimulate the reactions of synthesis and degradation of the sugar nucleotide and a different stoichiometry of the metal chelates involved. The reaction mechanism is of the ordered-sequential type and the data of product inhibition allowed the identification of glucose-1-phosphate as the first substrate bound and UDP-Glc as the last product released. The inhibition pattern by UDP-Glc gives evidence for cooperativity also in the binding of this molecule.

Separation and characterization of two UTP-utilizing hexose phosphate uridylyltransferases from Entamoeba histolytica

Two UTP-utilizing uridylyltransferases which react with both glucose 1-phosphate and galactose 1-phosphate were isolated from cell-free extracts of Entamoeba histolytica. The more specific of these enzymes, glucose-1-phosphate uridylyltransferase, acts preferentially on glucose 1-phosphate, having a maximum velocity 20-fold greater with this substrate than with galactose 1-phosphate. It was purified 200 fold with a 25% yield and has a molecular weight of 45 000. This enzyme requires a reducing agent for stability. The less specific transferase reacts with both hexose phosphates, having a maximum velocity of 1.35 times greater with galactose 1-phosphate. It was purified 1000 fold with a 20% yield, and has a molecular weight of 40 000. The common Leloir enzyme, UDP glucose-hexose-1-phosphate uridylytransferase (EC 2.7.7.12), was not found in this organism. To avoid confusion with the Leloir enzyme our experience suggests that the less specific enzyme, which is presently referred to in the literature as galactose-1-phosphate uridylyltransferase (EC 2.7.7.10), should be named UTP:hexose-1-phosphate uridylyltransferase (EC 2.7.7.?). The more specific enzyme (EC 2.7.7.9) should be more clearly named UTP:glucose-1-phosphate uridylyltransferase.

Myxospore coat synthesis in Myxococcus xanthus: in vivo incorporation of acetate and glycine

Myxospore coat synthesis in Myxococcus xanthus was studied by incorporation of [(14)C]acetate into intermediates in the biosynthesis of coat polysaccharide and into acid-insoluble material during vegetative growth and after glycerol induction of myxospores. During short labeling periods at 27 degrees C, the radioactivity was shown to be located primarily in N-acetyl groups rather than sugar moieties. Two hours after glycerol induction, the pools of N-acetylglucosamine 6-phosphate and uridine 5'-diphosphate-N-acetylgalactosamine (UDPGalNAc) plus uridine 5'-diphosphate-N-glucosamine increased about twofold and were labeled at twice the rate measured for vegetative cells. The increased rate of synthesis of UDPGalNAc and its precursors could be correlated with increased enzyme activities measured in vitro. Controlled acid hydrolysis revealed that the galactosamine portion of the myxospore coat was N-acetylated. After glycerol induction, the incorporation of acetate into acid-insoluble material increased threefold. This enhanced incorporation was sensitive to neither penicillin nor d-cycloserine. In contrast, bacitracin inhibited the incorporation of [(14)C]acetate into acid-insoluble material more effectively 2 h after myxospore induction than during vegetative growth. Chloramphenicol added to cells 90 min after induction blocked further increase in the rate of [(14)C]acetate incorporation. Since the myxospore coat contains glycine, polymer synthesis was also measured by chloramphenicol-insensitive [(14)C]glycine incorporation into acid-insoluble material. Although protein synthesis decreased after glycerol induction, glycine incorporation increased. Two hours after induction, glycine incorporation was only 75% inhibited by chloramphenicol and rifampin. The chloramphenicol-insensitive rate of incorporation of [(14)C]glycine increased during the first hour after myxospore induction and reached a peak rate after 2 to 3 h. The chloramphenicol-resistant incorporation of [(14)C]glycine was resistant to penicillin but sensitive to bacitracin.

[Presence of a pathway for biosynthesis of UDP-glucose in the Golgi apparatus of rat hepatocytes]

Glucokinase, phosphoglucomutase and glucose-1-phosphate uridylyltransferase are the three enzymes involved in a microsomic pathway for the synthesis of UDP glucose. Evidence is given, in this paper, for the localization of these three enzymes in a Golgi-rich fraction of rat liver. This fraction is prepared, from smooth microsomes, by the means of a discontinuous four-step sucrose gradient. Three of the lighter fractions (d = 1.08-1.13) are enriched in the Golgi markers (galactosyltransferase, sialytransferase and thiamin pyrophosphatase), especially the one with density 1.13. The three enzymes we are interested in are enriched in the two upper hands (d 1.08-1.11), which display an activity for the biosynthesis of UDP-glucose from glucose equivalent to the one obtained in a crude microsomic preparation, and which are not contaminated by other subcellular components.

Changes in morphogenesis and developmental enzyme levels in Dictyostelium discoideum after gamma irradiation

Changes in the levels of specific activity of two enzymes believed to be involved in developmental regulation were observed after irradiating differentiating cells of Dictyostelium discoideum. Stimulation of the levels of specific activity of alkaline phosphatase occured after irradiation at the beginning of development and at the end of the aggregation period, but not after irradiation at the beginning of aggregation. A stimulation in UDP-glucose pyrophosphorylase specific activity was also observed, but to a lesser extent and only after irradiation at the end of aggregation. Dose-dependent delays in the appearance of peaks of specific activity were noted. The delay per unit dose was less when irradiation took place at the beginning of development as opposed to the beginning or end of the aggregation period. Radiation-induced delays in progression through visible developmental stages were almost identical to delays in enzyme appearance. Other radiation effects on morphogenesis included the induction of a migratory slug phase.