Heterologous expression and biological characteristics of UGPases from Lactobacillus acidophilus.

Herein, two genes (LBA0625 and LBA1719) encoding UGPases (UDP-glucose pyrophosphorylase) in Lactobacillus acidophilus (L. acidophilus) were successfully transformed into Escherichia coli BL21 (DE3) to construct recombinant overexpressing strains (E-0625, E-1719) to investigate the biological characteristics of UGPase-0625 and UGPase-1719. The active sites, polysaccharide yield, and anti-freeze-drying stress of L. acidophilus ATCC4356 were also detected. UGPase-0625 and UGPase-1719 belong to the nucleotidyltransferase of stable hydrophilic proteins; contain 300 and 294 amino acids, respectively; and have 20 conserved active sites by prediction. Αlpha-helixes and random coils were the main secondary structures, which constituted the main skeleton of UGPases. The optimal mixture for the high catalytic activity of the two UGPases included 0.5 mM UDP-Glu (uridine diphosphate glucose) and Mg2+ at 37 °C, pH 10.0. By comparing the UGPase activities of the mutant strains with the original recombinant strains, A10, L130, and L263 were determined as the active sites of UGPase-0625 (P < 0.01) and A11, L130, and L263 were determined as the active sites of UGPase-1719 (P < 0.01). In addition, UGPase overexpression could increase the production of polysaccharides and the survival rates of recombinant bacteria after freeze-drying. This is the first study to determine the enzymatic properties, active sites, and structural simulation of UGPases from L. acidophilus, providing in-depth understanding of the biological characteristics of UGPases in lactic acid bacteria.Key points• We detected the biological characteristics of UGPases encoded by LBA0625 and LBA1719.• We identified UGPase-0625 and UGPase-1719 active sites.• UGPase overexpression elevates polysaccharide levels and post-freeze-drying survival.

Bacillus subtilis YngB contributes to wall teichoic acid glucosylation and glycolipid formation during anaerobic growth.

UTP-glucose-1-phosphate uridylyltransferases are enzymes that produce UDP-glucose from UTP and glucose-1-phosphate. In Bacillus subtilis 168, UDP-glucose is required for the decoration of wall teichoic acid (WTA) with glucose residues and the formation of glucolipids. The B. subtilis UGPase GtaB is essential for UDP-glucose production under standard aerobic growth conditions, and gtaB mutants display severe growth and morphological defects. However, bioinformatics predictions indicate that two other UTP-glucose-1-phosphate uridylyltransferases are present in B. subtilis. Here, we investigated the function of one of them named YngB. The crystal structure of YngB revealed that the protein has the typical fold and all necessary active site features of a functional UGPase. Furthermore, UGPase activity could be demonstrated in vitro using UTP and glucose-1-phosphate as substrates. Expression of YngB from a synthetic promoter in a B. subtilis gtaB mutant resulted in the reintroduction of glucose residues on WTA and production of glycolipids, demonstrating that the enzyme can function as UGPase in vivo. When WT and mutant B. subtilis strains were grown under anaerobic conditions, YngB-dependent glycolipid production and glucose decorations on WTA could be detected, revealing that YngB is expressed from its native promoter under anaerobic condition. Based on these findings, along with the structure of the operon containing yngB and the transcription factor thought to be required for its expression, we propose that besides WTA, potentially other cell wall components might be decorated with glucose residues during oxygen-limited growth condition.

Crystal structure of UDP-glucose pyrophosphorylase from Yersinia pestis, a potential therapeutic target against plague.

Yersinia pestis, the causative agent of bubonic plague, is one of the most lethal pathogens in recorded human history. Today, the concern is the possible misuse of Y. pestis as an agent in bioweapons and bioterrorism. Current therapies for the treatment of plague include the use of a small number of antibiotics, but clinical cases of antibiotic resistance have been reported in some areas of the world. Therefore, the discovery of new drugs is required to combat potential Y. pestis infection. Here, the crystal structure of the Y. pestis UDP-glucose pyrophosphorylase (UGP), a metabolic enzyme implicated in the survival of Y. pestis in mouse macrophages, is described at 2.17 Šresolution. The structure provides a foundation that may enable the rational design of inhibitors and open new avenues for the development of antiplague therapeutics.

Elucidating paramylon and other carbohydrate metabolism in Euglena gracilis: Kinetic characterization, structure and cellular localization of UDP-glucose pyrophosphorylase.

Many oligo and polysaccharides (including paramylon) are critical in the Euglena gracilis life-cycle and they are synthesized by glycosyl transferases using UDP-glucose as a substrate. Herein, we report the molecular cloning of a gene putatively coding for a UDP-glucose pyrophosphorylase (EgrUDP-GlcPPase) in E. gracilis. After heterologous expression of the gene in Escherichia coli, the recombinant enzyme was characterized structural and functionally. Highly purified EgrUDP-GlcPPase exhibited a monomeric structure, able to catalyze synthesis of UDP-glucose with a Vmax of 3350 U.mg-1. Glucose-1P and UTP were the preferred substrates, although the enzyme also used (with lower catalytic efficiency) TTP, galactose-1P and mannose-1P. Oxidation by hydrogen peroxide inactivated the enzyme, an effect reversed by reduction with dithiothreitol or thioredoxin. The redox process would involve sulfenic acid formation, since no pair of the 7 cysteine residues is close enough in the 3D structure of the protein to form a disulfide bridge. Electrophoresis studies suggest that, after oxidation, the enzyme arranges in many enzymatically inactive structural conformations; which were also detected in vivo. Finally, confocal fluorescence microscopy provided evidence for a cytosolic (mainly in the flagellum) localization of the enzyme.

UDP-glucose pyrophosphorylase: Isolation, purification and characterization from developing thermotolerant wheat (Triticum aestivum) grains.

UDP-glucose pyrophosphorylase (UGPase, EC 2.7.7.9) activity was determined in four different thermotolerant varieties of wheat viz. WH-1021, PBW-373, Raj-3765 and DBW-16. The specific activity of UGPase was found to be highest at 21 days after anthesis (DAA) in the variety WH-1021 which has been developed by Haryana Agricultural University, Hisar (Haryana, India). Hence, crude extract prepared from immature grains (21 days after anthesis) of WH-1021 was used for purification of UGPase using standard protein purification techniques which exploit differences in protein properties viz. ammonium sulphate fractionation (based on solubility differences), DEAE-ion exchange chromatography (based on charge differences) and molecular sieving through Sephadex G-100 gel (based on molecular mass differences). Near homogeneous enzyme preparation with molecular mass of 82 kDa and subunit molecular weight of 39 kDa was obtained. The purified enzyme had thermostability upto 50 °C. Kinetic studies revealed that the enzyme followed Michaelis Menten kinetics with Km value of 0.9 mM and 1.66 mM for UDP and PPi, respectively. Physico-chemical and kinetic characterization suggested that the enzyme UGPase from WH-1021 is a homodimer which has adapted to high temperature stress and that lower availability of substrates and high Km values may be responsible for reduced starch synthesis/grain yield.

In silico Predicted Glucose-1-phosphate Uridylyltransferase (GalU) Inhibitors Block a Key Pathway Required for Listeria Virulence.

Peptidoglycan walls of gram positive bacteria are functionalized by glycopolymers called wall teichoic acid (WTA). In Listeria monocytogenes, multiple enzymes including the glucose-1-phosphate uridylyltransferase (GalU) were identified as mandatory for WTA galactosylation, so that the inhibition of GalU is associated with a significant attenuation of Listeria virulence. Herein, we report on a series of in silico predicted GalU inhibitors identified using structure-based virtual screening and experimentally validated to be effective in blocking the WTA galactosylation pathway in vitro. Several hits such as C04, a pyrimidinyl benzamide, afforded promising experimental potencies. This proof-of-concept study opens new perspectives for the development of potent and selective GalU inhibitors of high interest to attenuate Listeria virulence. It also underscores the high relevance of using molecular modeling for facilitating the identification of bacterial virulence attenuators and more generally antibacterials.

Crystal structure and insights into the oligomeric state of UDP-glucose pyrophosphorylase from sugarcane.

UDP-glucose pyrophosphorylase (UGPase) is found in all organisms and catalyses the formation of UDP-glucose. In sugarcane, UDP-glucose is a branch-point in the carbon channelling into other carbohydrates, such as sucrose and cellulose, which are the major factors for sugarcane productivity. In most plants, UGPase has been described to be enzymatically active in the monomeric form, while in human and yeast, homo-octamers represent the active form of the protein. Here, we present the crystal structure of UGPase from sugarcane (ScUGPase-1) at resolution of 2.0 Å. The crystals of ScUGPase-1 reveal the presence of two molecules in the asymmetric unit and the multi-angle light scattering analysis shows that ScUGPase-1 forms a mixture of species ranging from monomers to larger oligomers in solution, suggesting similarities with the orthologs from yeast and human.

Glucose-1-phosphate uridylyltransferase from Erwinia amylovora: Activity, structure and substrate specificity.

Erwinia amylovora, a Gram-negative plant pathogen, is the causal agent of Fire Blight, a contagious necrotic disease affecting plants belonging to the Rosaceae family, including apple and pear. E. amylovora is highly virulent and capable of rapid dissemination in orchards; effective control methods are still lacking. One of its most important pathogenicity factors is the exopolysaccharide amylovoran. Amylovoran is a branched polymer made by the repetition of units mainly composed of galactose, with some residues of glucose, glucuronic acid and pyruvate. E. amylovora glucose-1-phosphate uridylyltransferase (UDP-glucose pyrophosphorylase, EC 2.7.7.9) has a key role in amylovoran biosynthesis. This enzyme catalyses the production of UDP-glucose from glucose-1-phosphate and UTP, which the epimerase GalE converts into UDP-galactose, the main building block of amylovoran. We determined EaGalU kinetic parameters and substrate specificity with a range of sugar 1-phosphates. At time point 120min the enzyme catalysed conversion of the sugar 1-phosphate into the corresponding UDP-sugar reached 74% for N-acetyl-α-d-glucosamine 1-phosphate, 28% for α-d-galactose 1-phosphate, 0% for α-d-galactosamine 1-phosphate, 100% for α-d-xylose 1-phosphate, 100% for α-d-glucosamine 1-phosphate, 70% for α-d-mannose 1-phosphate, and 0% for α-d-galacturonic acid 1-phosphate. To explain our results we obtained the crystal structure of EaGalU and augmented our study by docking the different sugar 1-phosphates into EaGalU active site, providing both reliable models for substrate binding and enzyme specificity, and a rationale that explains the different activity of EaGalU on the sugar 1-phosphates used. These data demonstrate EaGalU potential as a biocatalyst for biotechnological purposes, as an alternative to the enzyme from Escherichia coli, besides playing an important role in E. amylovora pathogenicity.

Structure of uridine diphosphate N-acetylglucosamine pyrophosphorylase from Entamoeba histolytica.

Uridine diphosphate N-acetylglucosamine pyrophosphorylase (UAP) catalyzes the final step in the synthesis of UDP-GlcNAc, which is involved in cell-wall biogenesis in plants and fungi and in protein glycosylation. Small-molecule inhibitors have been developed against UAP from Trypanosoma brucei that target an allosteric pocket to provide selectivity over the human enzyme. A 1.8 Å resolution crystal structure was determined of UAP from Entamoeba histolytica, an anaerobic parasitic protozoan that causes amoebic dysentery. Although E. histolytica UAP exhibits the same three-domain global architecture as other UAPs, it appears to lack three α-helices at the N-terminus and contains two amino acids in the allosteric pocket that make it appear more like the enzyme from the human host than that from the other parasite T. brucei. Thus, allosteric inhibitors of T. brucei UAP are unlikely to target Entamoeba UAPs.

A quaternary mechanism enables the complex biological functions of octameric human UDP-glucose pyrophosphorylase, a key enzyme in cell metabolism.

In mammals, UDP-glucose pyrophosphorylase (UGP) is the only enzyme capable of activating glucose-1-phosphate (Glc-1-P) to UDP-glucose (UDP-Glc), a metabolite located at the intersection of virtually all metabolic pathways in the mammalian cell. Despite the essential role of its product, the molecular basis of UGP function is poorly understood. Here we report the crystal structure of human UGP in complex with its product UDP-Glc. Beyond providing first insight into the active site architecture, we describe the substrate binding mode and intermolecular interactions in the octameric enzyme that are crucial to its activity. Importantly, the quaternary mechanism identified for human UGP in this study may be common for oligomeric sugar-activating nucleotidyltransferases. Elucidating such mechanisms is essential for understanding nucleotide sugar metabolism and opens the perspective for the development of drugs that specifically inhibit simpler organized nucleotidyltransferases in pathogens.

Structure and Function of Prokaryotic UDP-Glucose Pyrophosphorylase, A Drug Target Candidate.

UDP-glucose is an essential metabolite for a variety of processes in the cell physiology in all organisms. In prokaryotes, it is involved in the synthesis of trehalose, an osmoprotectant, in galactose utilization via the Leloir pathway and it plays a key role in the synthesis of the components of the bacterial envelope, particularly the lipopolysaccharide and the capsule, which represent necessary virulence factors of many bacterial pathogens. UDP-glucose is synthesized in bacteria by the prokaryotic UDP-glucose pyrophosphorylase (UGP, EC 2.7.7.9), an enzyme belonging to the family of sugar:nucleotidyl transferases. Despite the ubiquitous distribution of UGP activity in all domains of life, prokaryotic UGPs are evolutionarily unrelated to their eukaryotic counterparts. Taken together, these features make of bacterial UGP an attractive target candidate for the discovery and development of new generation antibiotics. This review summarizes the current knowledge on structure and function of bacterial UGPs, underlying their potential as drug target candidates.

Oligomerization, membrane association, and in vivo phosphorylation of sugarcane UDP-glucose pyrophosphorylase.

Sugarcane is a monocot plant that accumulates sucrose to levels of up to 50% of dry weight in the stalk. The mechanisms that are involved in sucrose accumulation in sugarcane are not well understood, and little is known with regard to factors that control the extent of sucrose storage in the stalks. UDP-glucose pyrophosphorylase (UGPase; EC 2.7.7.9) is an enzyme that produces UDP-glucose, a key precursor for sucrose metabolism and cell wall biosynthesis. The objective of this work was to gain insights into the ScUGPase-1 expression pattern and regulatory mechanisms that control protein activity. ScUGPase-1 expression was negatively correlated with the sucrose content in the internodes during development, and only slight differences in the expression patterns were observed between two cultivars that differ in sucrose content. The intracellular localization of ScUGPase-1 indicated partial membrane association of this soluble protein in both the leaves and internodes. Using a phospho-specific antibody, we observed that ScUGPase-1 was phosphorylated in vivo at the Ser-419 site in the soluble and membrane fractions from the leaves but not from the internodes. The purified recombinant enzyme was kinetically characterized in the direction of UDP-glucose formation, and the enzyme activity was affected by redox modification. Preincubation with H2O2 strongly inhibited this activity, which could be reversed by DTT. Small angle x-ray scattering analysis indicated that the dimer interface is located at the C terminus and provided the first structural model of the dimer of sugarcane UGPase in solution.

Expression, purification, crystallization and preliminary X-ray analysis of glucose-1-phosphate uridylyltransferase (GalU) from Erwinia amylovora.

Glucose-1-phosphate uridylyltransferase from Erwinia amylovora CFPB1430 was expressed as a His-tag fusion protein in Escherichia coli. After tag removal, the purified protein was crystallized from 100 mM Tris pH 8.5, 2 M ammonium sulfate, 5% ethylene glycol. Diffraction data sets were collected to a maximum resolution of 2.46 Šusing synchrotron radiation. The crystals belonged to the hexagonal space group P62, with unit-cell parameters a = 80.67, b = 80.67, c = 169.18. The structure was solved by molecular replacement using the structure of the E. coli enzyme as a search model.

Analysis of enzyme activities.

The evaluation of enzyme activities, especially their capacities, represents an important step towards the modelling of biochemical pathways in living organisms. The implementation of microplate technology enables the determination of up to >50 enzymes in relatively large numbers of samples and in various biological materials. Most of these enzymes are involved in central metabolism and several pathways are entirely covered. Direct or indirect assays can be used, as well as highly sensitive assays, depending on the abundance of the enzymes under study. To exemplify such methods, protocols for UDP-glucose pyrophosphorylase (E.C. 2.7.7.9) operating in real time and for pyrophosphate:fructose-6-phosphate 1-phosphotransferase (E.C. 2.7.1.90) are presented.

Identification and characterization of UDP-glucose pyrophosphorylase in cyanobacteria Anabaena sp. PCC 7120.

Exopolysaccharides produced by photosynthetic cyanobacteria have received considerable attention in recent years for their potential applications in the production of renewable biofuels. Particularly, cyanobacterial cellulose is one of the most promising products because it is extracellularly secreted as a non-crystalline form, which can be easily harvested from the media and converted into glucose units. In cyanobacteria, the production of UDP-glucose, the cellulose precursor, is a key step in the cellulose synthesis pathway. UDP-glucose is synthesized from UTP and glucose-1-phosphate (Glc-1P) by UDP-glucose pyrophosphorylase (UGPase), but this pathway in cyanobacteria has not been well characterized. Therefore, to elucidate the overall cellulose biosynthesis pathway in cyanobacteria, we studied the putative UGPase All3274 and seven other putative NDP-sugar pyrophosphorylases (NSPases), All4645, Alr2825, Alr4491, Alr0188, Alr3400, Alr2361, and Alr3921 of Anabaena sp. PCC 7120. Assays using the purified recombinant proteins revealed that All3274 exhibited UGPase activity, All4645, Alr2825, Alr4491, Alr0188, and Alr3921 exhibited pyrophosphorylase activities on ADP-glucose, CDP-glucose, dTDP-glucose, GDP-mannose, and UDP-N-acetylglucosamine, respectively. Further characterization of All3274 revealed that the kcat for UDP-glucose formation was one or two orders lower than those of other known UGPases. The activity and dimerization tendency of All3274 increased at higher enzyme concentrations, implying catalytic activation by dimerization. However, most interestingly, All3274 dimerization was inhibited by UTP and Glc-1P, but not by UDP-glucose. This study presents the first in vitro characterization of a cyanobacterial UGPase, and provides insights into biotechnological attempts to utilize the photosynthetic production of cellulose from cyanobacteria.

A Chimeric UDP-glucose pyrophosphorylase produced by protein engineering exhibits sensitivity to allosteric regulators.

In bacteria, glycogen or oligosaccharide accumulation involves glucose-1-phosphate partitioning into either ADP-glucose (ADP-Glc) or UDP-Glc. Their respective synthesis is catalyzed by allosterically regulated ADP-Glc pyrophosphorylase (EC 2.7.7.27, ADP-Glc PPase) or unregulated UDP-Glc PPase (EC 2.7.7.9). In this work, we characterized the UDP-Glc PPase from Streptococcus mutans. In addition, we constructed a chimeric protein by cutting the C-terminal domain of the ADP-Glc PPase from Escherichia coli and pasting it to the entire S. mutans UDP-Glc PPase. Both proteins were fully active as UDP-Glc PPases and their kinetic parameters were measured. The chimeric enzyme had a slightly higher affinity for substrates than the native S. mutans UDP-Glc PPase, but the maximal activity was four times lower. Interestingly, the chimeric protein was sensitive to regulation by pyruvate, 3-phosphoglyceric acid and fructose-1,6-bis-phosphate, which are known to be effectors of ADP-Glc PPases from different sources. The three compounds activated the chimeric enzyme up to three-fold, and increased the affinity for substrates. This chimeric protein is the first reported UDP-Glc PPase with allosteric regulatory properties. In addition, this is a pioneer work dealing with a chimeric enzyme constructed as a hybrid of two pyrophosphorylases with different specificity toward nucleoside-diphospho-glucose and our results turn to be relevant for a deeper understanding of the evolution of allosterism in this family of enzymes.

Octamerization is essential for enzymatic function of human UDP-glucose pyrophosphorylase.

Uridine diphosphate-glucose pyrophosphorylase (UGP) occupies a central position in carbohydrate metabolism in all kingdoms of life, since its product uridine diphosphate-glucose (UDP-glucose) is essential in a number of anabolic and catabolic pathways and is a precursor for other sugar nucleotides. Its significance as a virulence factor in protists and bacteria has given momentum to the search for species-specific inhibitors. These attempts are, however, hampered by high structural conservation of the active site architecture. A feature that discriminates UGPs of different species is the quaternary organization. While UGPs in protists are monomers, di- and tetrameric forms exist in bacteria, and crystal structures obtained for the enzyme from yeast and human identified octameric UGPs. These octamers are formed by contacts between highly conserved amino acids in the C-terminal ß-helix. Still under debate is the question whether octamerization is required for the functionality of the human enzyme. Here, we used single amino acid replacements in the C-terminal ß-helix to interrogate the impact of highly conserved residues on octamer formation and functional activity of human UGP (hUGP). Replacements were guided by the sequence of Arabidopsis thaliana UGP, known to be active as a monomer. Correlating the data obtained in blue native PAGE, size exclusion chromatography and enzymatic activity testing, we prove that the octamer is the active enzyme form. This new insight into structure-function relationships in hUGP does not only improve the understanding of the catalysis of this important enzyme, but in addition broadens the basis for studies aimed at designing drugs that selectively inhibit UGPs from pathogens.

Influence of controlled pH on the activity of UDPG-pyrophosphorylase in Aureobasidium pullulans.

UDPG-pyrophosphorylase is the key enzyme involved in pullulan biosynthesis and pullulan production by Aureobasidium pullulans. In this study, effect of controlled pH on fermentation time, pullulan production, biomass, and UDPG-pyrophosphorylase activity was investigated. Pullulan yield increased to reach a maximum within 4 days, and maximum UDPG-pyrophosphorylase activity was observed at day 3, while the biomass continued to increase until the end of the experimental period. The A. pullulans isolated from sea mud grew well at relatively low pH. UDPG-pyrophosphorylase activity was affected by the controlled pH and reached a maximum at pH 5.5. Results indicated that UDPG-pyrophosphorylase activity was highly correlated with controlled pH and pullulan biosynthesis rate.

Substrate kinetics and substrate effects on the quaternary structure of barley UDP-glucose pyrophosphorylase.

UDP-Glc pyrophosphorylase (UGPase) is an essential enzyme responsible for production of UDP-Glc, which is used in hundreds of glycosylation reactions involving addition of Glc to a variety of compounds. In this study, barley UGPase was characterized with respect to effects of its substrates on activity and quaternary structure of the protein. Its K(m) values with Glc-1-P and UTP were 0.33 and 0.25 mM, respectively. Besides using Glc-1-P as a substrate, the enzyme had also considerable activity with Gal-1-P; however, the K(m) for Gal-1-P was very high (>10 mM), rendering this reaction unlikely under physiological conditions. UGPase had a relatively broad pH optimum of 6.5-8.5, regardless of the direction of reaction. The enzyme equilibrium constant was 0.4, suggesting slight preference for the Glc-1-P synthesis direction of the reaction. The quaternary structure of the enzyme, studied by Gas-phase Electrophoretic Mobility Macromolecule Analysis (GEMMA), was affected by addition of either single or both substrates in either direction of the reaction, resulting in a shift from UGPase dimers toward monomers, the active form of the enzyme. The substrate-induced changes in quaternary structure of the enzyme may have a regulatory role to assure maximal activity. Kinetics and factors affecting the oligomerization status of UGPase are discussed.

The crystal structure of human UDP-glucose pyrophosphorylase reveals a latch effect that influences enzymatic activity.

UGPase (UDP-glucose pyrophosphorylase) is highly conserved among eukaryotes. UGPase reversibly catalyses the formation of UDP-glucose and is critical in carbohydrate metabolism. Previous studies have mainly focused on the UGPases from plants, fungi and parasites, and indicate that the regulatory mechanisms responsible for the enzyme activity vary among different organisms. In the present study, the crystal structure of hUGPase (human UGPase) was determined and shown to form octamers through end-to-end and side-by-side interactions. The observed latch loop in hUGPase differs distinctly from yUGPase (yeast UGPase), which could explain why hUGPase and yUGPase possess different enzymatic activities. Mutagenesis studies showed that both dissociation of octamers and mutations of the latch loop can significantly affect the UGPase activity. Moreover, this latch effect is also evolutionarily meaningful in UGPase from different species.