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At least 127 records · Page 7Linked to original sources
PubMed1996

The first step in sugar transport: crystal structure of the amino terminal domain of enzyme I of the E. coli PEP: sugar phosphotransferase system and a model of the phosphotransfer complex with HPr.

BACKGROUND: The bacterial phosphoenolpyruvate (PEP): sugar phosphotransferase system (PTS) transports exogenous hexose sugars through the membrane and tightly couples transport with phosphoryl transfer from PEP to the sugar via several phosphoprotein intermediates. The phosphate group is first transferred to enzyme I, second to the histidine-containing phosphocarrier protein HPr, and then to one of a number of sugar-specific enzymes II. The structures of several HPrs and enzymes IIA are known. Here we report the structure of the N-terminal half of enzyme I from Escherichia coli (EIN). RESULTS: The crystal structure of EIN (MW approximately 30 kDa) has been determined and refined at 2.5 A resolution. It has two distinct structural subdomains; one contains four alpha helices arranged as two hairpins in a claw-like conformation. The other consists of a beta sandwich containing a three-stranded antiparallel beta sheet and a four-stranded parallel beta sheet, together with three short alpha helices. Plausible models of complexes between EIN and HPr can be made without assuming major structural changes in either protein. CONCLUSIONS: The alpha/beta subdomain of EIN is topologically similar to the phosphohistidine domain of the enzyme pyruvate phosphate dikinase, which is phosphorylated by PEP on a histidyl residue but does not interact with HPr. It is therefore likely that features of this subdomain are important in the autophosphorylation of enzyme I. The helical subdomain of EIN is not found in pyruvate phosphate dikinase; this subdomain is therefore more likely to be involved in phosphoryl transfer to HPr.

Amino Acid Sequence↗
PubMed2006

Structure of phosphorylated enzyme I, the phosphoenolpyruvate:sugar phosphotransferase system sugar translocation signal protein.

Bacterial transport of many sugars, coupled to their phosphorylation, is carried out by the phosphoenolpyruvate (PEP):sugar phosphotransferase system and involves five phosphoryl group transfer reactions. Sugar translocation initiates with the Mg(2+)-dependent phosphorylation of enzyme I (EI) by PEP. Crystals of Escherichia coli EI were obtained by mixing the protein with Mg(2+) and PEP, followed by oxalate, an EI inhibitor. The crystal structure reveals a dimeric protein where each subunit comprises three domains: a domain that binds the partner PEP:sugar phosphotransferase system protein, HPr; a domain that carries the phosphorylated histidine residue, His-189; and a PEP-binding domain. The PEP-binding site is occupied by Mg(2+) and oxalate, and the phosphorylated His-189 is in-line for phosphotransfer to/from the ligand. Thus, the structure represents an enzyme intermediate just after phosphotransfer from PEP and before a conformational transition that brings His-189 approximately P in proximity to the phosphoryl group acceptor, His-15 of HPr. A model of this conformational transition is proposed whereby swiveling around an alpha-helical linker disengages the His domain from the PEP-binding domain. Assuming that HPr binds to the HPr-binding domain as observed by NMR spectroscopy of an EI fragment, a rotation around two linker segments orients the His domain relative to the HPr-binding domain so that His-189 approximately P and His-15 are appropriately stationed for an in-line phosphotransfer reaction.

Binding Sites↗
PubMed2006

Free sugar and sugar alcohol concentrations in human breast milk.

OBJECTIVES: The goal was to determine the free sugars and polyols in human breast milk, both term and preterm, for comparison with formula milks. METHODS: Methodology was developed for the measurement of the free sugars and polyols in breast milk. There were 16 samples collected from women who delivered at term and 17 samples from women delivering preterm. For purposes of comparison, samples were also collected from four commercial formulas for term infants and eight from commercial formulas for preterm infants as well as one sample of cows' milk. All samples were frozen immediately and analyzed by high-performance liquid chromatography techniques. RESULTS: Except for lactose concentrations, no significant differences were detected for all other sugars and polyols between term and preterm breast milk samples. Within breast milk samples, two patterns emerged, with one group containing additional elution peaks for compounds not yet identified. A second group did not contain these compounds. There were a number of significant differences between breast milk and formulas, particularly for inositol, glycerol, glucose, and galactose. All milks contained significant concentrations of mannose. CONCLUSIONS: There are no significant differences among breast milk samples for free sugar and polyol concentrations except lactose. However, some milk contains additional peaks that could be of dietary or genetic origin. Formula milk has relatively high concentrations of glucose and galactose compared with breast milk, suggesting some lactose hydrolysis.

Animals↗
PubMed2002

Effect of replacing the general energy-coupling proteins of the PEP:sugar phosphotransferase system of Salmonella typhimurium with their fructose-inducible counterparts on utilization of the PTS sugar glucitol.

A strain of Salmonella typhimurium in which the genes encoding the general phosphoenolpyruvate:sugar phosphotransferase system (PTS) proteins HPr and Enzyme I have been deleted, the normally cryptic gene encoding the fructose-inducible Enzyme I (EI* or EI(fructose)) is expressed, and the fructose repressor protein is inactive (fruR or cra mutant) was studied. This strain lacks HPr and EI, but expresses FPr (DTP) and EI(fructose) constitutively. Since FPr and EI(fructose) can substitute for HPr and EI, the strain grew in minimal liquid medium supplemented with the PTS sugars glucose, fructose, N-acetylglucosamine, mannitol or mannose. However, it showed very poor to negligible growth on the PTS sugar glucitol. It also grew very poorly on the non-PTS sugars maltose, melibiose and especially glycerol. Adding cAMP to the medium allowed growth on glucitol, but did not affect growth on glycerol. We suggest that poor phosphorylation of the regulatory molecule Enzyme IIA(glucose) by FPr is responsible for these effects.

Bacterial Proteins↗
PubMed2004

Osmotic and matric potential effects on growth, sugar alcohol and sugar accumulation by Aspergillus section Flavi strains from Argentina.

AIMS: The effect of osmotic and matric potential stress on growth and sugar alcohols (polyols: glycerol, erythritol, arabitol and mannitol) and sugars (trehalose and glucose) accumulation in toxigenic and nontoxigenic colonies of Aspergillus flavus and A. parasiticus was evaluated. METHODS AND RESULTS: Growth of Aspergillus section Flavi with significant reductions at 20 and 30 degrees C was more sensitive to changes in matric potential, between 60 and 100% in the range of -7 to -14 MPa. No significant differences were found between toxigenic and nontoxigenic strains for both species. Total polyol accumulation in unamended maize meal agar medium (-0.75 MPa water potential) was higher at 30 than 20 degrees C. The major change in concentrations of endogenous sugars and total polyols was in matrically amended medium (with PEG 8000) at -7 and -10 MPa. Accumulation of glucose, arabitol, mannitol and erythritol content of A. flavus and A. parasiticus mycelial colonies was greater in normal unstressed maize meal agar medium (-0.75 Mpa) at 20 degrees C. This was modified by solute and matric stress. CONCLUSIONS: The data showed relative sensitivity to osmotic and matric potential, and temperature, and the impact on growth rates, polyol and sugar accumulation in mycelia of A. flavus and A. parasiticus. SIGNIFICANCE AND IMPACT OF THE STUDY: The matric potential effects on growth may be of particular importance for growth and survival in environments with low-matric potential stress. The tolerance of spoilage fungi such as Aspergillus section Flavi to such modifications could increase the potential for spoilage and mycotoxin production in such substrates. This knowledge is important for understanding the relative ecological fitness of these aflatoxigenic species and in the development of prevention strategies for their control.

Argentina↗
PubMed2002

Different sugar kinases are involved in the sugar sensing of Galdieria sulphuraria.

The unicellular acidophilic red alga Galdieria sulphuraria is a facultative heterotroph with a complex uptake system for sugars and polyols, consisting of at least 14 transporters. Upon transfer to heterotrophic conditions, these transporters were induced simultaneously. Once induced, transporters for common hexoses and pentoses are apparently not down-regulated under heterotrophic conditions. Uptake of deoxysugars (FUC/Rha), however, was repressed by substrates metabolized via gluco-, galacto-, glycero-, or hexokinase, whereas substrates phosphorylated by xylulokinase had no effect. This indicates that several sugar kinases play a key role in sugar sensing. In contrast, polyol transporters were repressed only by glucose or its analogs but not by other sugars. This repression does not involve the activity of kinases. Most likely this type of glucose sensing is independent of metabolism and takes place prior to or during uptake. In its natural environment, these two different sensing mechanisms would enable the alga to utilize a mixture of different substrates in a most economic way by repressing dispensible transporters.

Carbohydrate Metabolism↗
PubMed1987

Microcalorimetric investigation into the metabolic activity of rat caecal flora in the presence of different sugars and sugar substitutes.

When adapting young rats to different sugar substitutes (sorbitol, PolydextroseR and PalatinitR), effects were seen in the caecal morphology and caecal content e.g. bacterial concentration, which did not occur when adapting rats to sugars (glucose, sucrose). For in vitro studies, anaerobic growth of caecal flora in thioglycollate medium with and without the respective substances was monitored by continuous measurement of heat production, optical density and pH. Additionally, biochemical analyses and light microscopic observations were performed in order to detect differences between adapted and non-adapted flora. In particular the microcalorimetric data furnished valuable information about alterations in bacterial metabolic activity after adaptation to sugars and sugar substitutes, and clearly indicated that all the substances tested influenced the metabolism of caecal flora.

Anaerobiosis↗
PubMed2004

Sol-gel polycondensation of tetraethyl orthosilicate (TEOS) in sugar-based porphyrin organogels: inorganic conversion of a sugar-directed porphyrinic fiber library through sol-gel transcription processes.

Sugar-appended porphyrins (1 a-e) with monosaccharide groups at their periphery have been rationally designed for a new class of gelating reagents. A few of these compounds have the tendancy to form one-dimensional aggregates stable enough to show successful gelation ability for DMF-alcohol mixed solvents. The aggregation mode in the specific columnar super structures has been evaluated in detail by UV-visible spectrometry (UV/Vis), circular dichroism (CD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). All UV-visible spectra of sugar-appended porphyrinic gels obtained from 1 a-c exhibit Soret band absorptions, which shift to lower wavelength and are significantly broadened. This phenomenon indicates that these porphyrin cores strongly interact with each other in an H-aggregate fashion, which drives the generation of a one-dimensional porphyrin-stacking array. The CD spectra of the organogels from 1 a and 1 b, which are in anomers, exhibit an almost symmetric pattern, whereas the gel from 1 c gives a completely different pattern. This implies that the gel fibrils wind themselves in a right- or left-handed fashion; this reflects chirality in the specific molecular structure of the gelators. The results from SEM for the gel fibrils are in good agreement with the CD patterns. The gel fibrils in 1 a possess left-handed helicity, whereas those in 1 b wind themselves right-handedly. Macroscopic helical morphology reflects the microscopic structure well at a molecular level, which gives structural variety of the gel fibrils, which can be defined by the sugar library. Inorganic conversion of the organic helical fibrils by a sol-gel transcription process successfully gives the helical-silica structures, which finely inherit the organic morphology. A striking observation is that a unimolecular porphyrin-stacking array is also transcribed into silica fibers when the optimized sol-gel reaction conditions are selected. A sugar-based organic-fiber library in porphyrinic gels thus provides a variety of inorganic materials through the sol-gel transcription process.

Journal Article↗
PubMed1995

Inhibition of glycosylation by amphomycin and sugar nucleotide analogs PP36 and PP55 indicates that Haloferax volcanii beta-glucosylates both glycoproteins and glycolipids through lipid-linked sugar intermediates: evidence for three novel glycoproteins and a novel sulfated dihexosyl-archaeol glycolipid.

Arachaebacteria have been recently placed in evolution as a separate kingdom of organisms between procaryotes and eucaryotes. Although these organisms contain both glycolipids and glycoproteins, they possess no Golgi. No biosynthetic work has been published on the complex carbohydrates of these newly reassigned organisms. This report describes preliminary results from one member of this kingdom, Haloferax volcanii, which suggest that all glycosylation proceeds through lipid intermediates. Evidence for novel glycolipid structure was also found during this study. H. volcanii plasma membranes contain all of the enzyme activities for synthesis of N-linked glycoproteins and archaeol-based glycolipids. For glucose transfer, all reactions apparently proceed through glucose-phosphopolyisoprenol using UDP-glucose as primary donor. Incorporation of D-[3H]glucose from UDP-D-[3H]glucose into glycoproteins and glycolipids of H. volcanii was stimulated by addition of C55-polyisoprenol phosphate, but not by C85-105 dolichol phosphate, and was inhibited by amphomycin and two recently described sugar nucleotide analogs, PP36 (5'-[N-(2-decanoylamino-3-hydroxy-3-phenylpropyloxy carbonyl)glycyl]amino]-5'-deoxyuridine) and PP55 (5'-O-[[(2-decanoylamino-3-phenylpropyloxycarbonyl) amino]sulfonyl]uridine). All three inhibitors are reported to block transfer of sugar from UDP-sugars to phosphopolyisoprenols in eucaryotes. However, in H. volcanii these inhibitors apparently block transfer of glucose from polyprenyl intermediates to final glycoproteins and glycolipid products. The sulfodihexosyl archaeol glycolipid fraction was partially characterized by mass spectrometry and was found to contain a previously unreported structure with sulfate on the reducing-end sugar. Four major glycoproteins 190, 105, 56, and 52 kDa and an archaeol-based glycolipid fraction were labeled by amphomycin-sensitive pathways. Photoaffinity labeling of H. volcanii homogenate with 5-azido-[32P]UDP-Glc tagged only one 45-kDa polypeptide which is a probable glucosyl-phosphorylpolyisoprenol synthase. The fact that only one polypeptide band was photoaffinity-labeled indicated that no other transferase utilized UDP-glucose directly in H. volcanii. The salt requirement of the UDP-glucose-dependent pathways suggests that cytoplasmic enzymes function in a high salt environment in H. volcanii. The archaebacterial plasma membrane thus expresses many functions for glycosylation of both glycoproteins and glycolipids, normally found in the endoplasmic reticulum and Golgi of eucaryotes.

Archaea↗
PubMed1998

Stabilization against thermal inactivation promoted by sugars on enzyme structure and function: why is trehalose more effective than other sugars?

Trehalose has been described to act as the best stabilizer of structure and function of several macromolecules. Although other sugars also stabilize macromolecules, none of them are as effective as trehalose. The extraordinary effect of trehalose has been attributed to several of its properties such as making hydrogen bonds with membranes or the ability to modify the solvation layer of proteins. However, the explanations always result in a question: Why is trehalose more effective than other sugars? Here, we show that trehalose has a larger hydrated volume than other related sugars. According to our results, trehalose occupies at least 2.5 times larger volume than sucrose, maltose, glucose, and fructose. We correlate this property with the ability to protect the structure and function of enzymes against thermal inactivation. When the concentrations of all sugars were corrected by the percentage of the occupied volume, they presented the same effectiveness. Our results suggest that because of this larger hydrated volume, trehalose can substitute more water molecules in the solution, and this property is very close to its effectiveness. Finally, these data drive us to conclude that the higher size exclusion effect is responsible for the difference in efficiency of protection against thermal inactivation of enzymes.

Enzyme Activation↗
PubMed2005

The glycolytic genes pfk and pyk from Lactobacillus casei are induced by sugars transported by the phosphoenolpyruvate:sugar phosphotransferase system and repressed by CcpA.

In Lactobacillus casei BL23, phosphofructokinase activity was higher in cells utilizing sugars transported by the phosphoenolpyruvate:sugar phosphotransferase system (PTS). The phosphofructokinase gene (pfk) was cloned from L. casei and shown to be clustered with the gene encoding pyruvate kinase (pyk). pfk and pyk genes are cotranscribed and induced upon growth on sugars transported by the PTS. Contrarily to the model proposed for Lactococcus lactis, where the global catabolite regulator protein (CcpA) is involved in PTS-induced transcription of pfk and pyk, a ccpA mutation resulted in a slight increase in pfk-pyk expression in L. casei. This weak regulation was evidenced by CcpA binding to a region of the pfk-pyk promoter which contained two cre sequences significantly deviated from the consensus. The PTS induction of pfk-pyk seems to be counteracted by the CcpA-mediated repression. Our results suggest that the need to accommodate the levels of pfk-pyk mRNA to the availability of sugars is fulfilled in L. casei by a PTS/CcpA-mediated signal transduction different from L. lactis.

Amino Acid Sequence↗
PubMed1994

Noise analysis of ion current through the open and the sugar-induced closed state of the LamB channel of Escherichia coli outer membrane: evaluation of the sugar binding kinetics to the channel interior.

LamB, a sugar-specific channel of Escherichia coli outer membrane was reconstituted into lipid bilayer membranes and the current noise was investigated using fast Fourier transformation. The current noise through the open channels had a rather small spectral density, which was a function of the inverse frequency up to about 100 Hz. The spectral density of the noise of the open LamB channels was a quadratic function of the applied voltage. Its magnitude was not correlated to the number of channels in the lipid bilayer membrane. Upon addition of sugars to the aqueous phase the current decreased in a dose-dependent manner. Simultaneously, the spectral density of the current noise increased drastically, which indicated interaction of the sugars with the binding site inside the channel. The frequency dependence of the spectral density was of Lorentzian type, although the power of its frequency dependence was not identical to -2. Analysis of the power density spectra using a previously proposed simple model (Benz, R., A. Schmid, and G. H. Vos-Scheperkeuter. 1987. J. Membr. Biol. 100: 12-29), allowed the evaluation of the on- and the off-rate constants for the maltopentaose binding to the binding site inside the LamB channels. This means also that the maltopentaose flux through the LamB channel could be estimated by assuming a simple one-site, two-barrier model for the sugar transport from the results of the noise analysis.

Bacterial Outer Membrane Proteins↗
PubMed1986

Study by X-ray diffraction of the geometrical shape of glycoprotein sugar chains in two model glycoconjugates, a liposaccharide and a phospholiposaccharide, having the same sugar chain.

Two amphipatic, model glycoconjugates having the same sugar chain but differing in their hydrophobic component were studied by X-ray diffraction in concentrated water solution and in the dry state. The liposaccharide 2, obtained by linking the NH2-4 group of the asparagine residue of the glycoaminoacid obtained from hen ovotransferrin with the activated carboxylic acid group of palmitic acid exhibited a cubic structure in which the sugar chain adopted a slightly deformed, "T-shaped conformation". The phospholiposaccharide 3, obtained by linking the NH2-4 group of the asparagine residue of the same glycoamino acid with the primary amine group of dipalmitoylphosphatidylethanolamine through a suberyl bridge exhibited a lamellar structure in which the sugar chain adopted a "Y-shaped conformation". Thus, it was possible to induce a conformational change of the hen ovotransferrin sugar chain by changing the "hydrophobic residue" to which it is linked.

Animals↗
PubMed2002

One-step synthesis of non-anomeric sugar isothiocyanates from sugar azides.

Tandem Staudinger-aza-Wittig reaction of primary azidodeoxy sugars with triphenylphosphine-carbon disulfide affords the corresponding primary deoxyisothiocyanato sugars in high yield. No products arising from O --> N acyl migration or formation of dimeric carbodiimides were observed. Interestingly, a polymer-supported triarylphosphine can advantageously replace triphenylphosphine, thus limiting the purification step to a simple filtration process. The reaction also allows the preparation of 5-deoxy-5-isothiocyanato sugars, a hitherto unknown class of compounds, from the corresponding azide precursors. Secondary sugar azides bearing the azido group at an endocyclic carbon atom afforded much lower isothiocyanation yields under these reaction conditions.

Azides↗
PubMed2000

Differences in the contents of total sugars, reducing sugars, starch and sucrose in embryogenic and non-embryogenic calli from Medicago arborea L.

The total sugars, reducing sugars, starch and sucrose in embryogenic and non-embryogenic calli from explants (cotyledons, petioles, hypocotyls and leaves) obtained from Medicago arborea L. seedlings were evaluated. Total sugars were the major components in the calli and no significant differences between embryogenic and non-embryogenic calli were observed. In contrast, important differences between the embryogenic and non-embryogenic calli were observed for reducing sugars, the highest levels being observed in embryogenic calli. The highest starch levels were found in non-embryogenic calli developed in MS medium. During the development of somatic embryogenesis very low starch levels in the callus were found. During the first months of culture, no significant differences in the sucrose content were found between calli that produced embryos and those that did not. The most important differences in sucrose were seen between calli transferred to medium F0, which had the greatest embryogenic capacity, and those transferred to medium F6, which inhibited embryogenesis. In the latter case, an increase in sucrose was observed.

Journal Article↗
PubMed1968

Control of amino sugar metabolism in Escherichia coli and isolation of mutants unable to degrade amino sugars.

1. Growth of Escherichia coli on glucosamine results in an induction of glucosamine 6-phosphate deaminase [2-amino-2-deoxy-d-glucose 6-phosphate ketol-isomerase (deaminating), EC 5.3.1.10] and a repression of glucosamine 6-phosphate synthetase (l-glutamine-d-fructose 6-phosphate aminotransferase, EC 2.6.1.16); glucose abolishes these control effects. 2. Growth of E. coli on N-acetylglucosamine results in an induction of N-acetylglucosamine 6-phosphate deacetylase and glucosamine 6-phosphate deaminase, and in a repression of glucosamine 6-phosphate synthetase; glucose diminishes these control effects. 3. The synthesis of amino sugar kinases (EC 2.7.1.8 and 2.7.1.9) is unaffected by growth on amino sugars. 4. Glucosamine 6-phosphate synthetase is inhibited by glucosamine 6-phosphate. 5. Mutants of E. coli that are unable to grow on N-acetylglucosamine have been isolated, and lack either N-acetylglucosamine 6-phosphate deacetylase (deacetylaseless) or glucosamine 6-phosphate deaminase (deaminaseless). Deacetylaseless mutants can grow on glucosamine but deaminaseless mutants cannot. 6. After growth on glucose, deacetylaseless mutants have a repressed glucosamine 6-phosphate synthetase and a super-induced glucosamine 6-phosphate deaminase; this may be related to an intracellular accumulation of acetylamino sugar that also occurs under these conditions. In one mutant the acetylamino sugar was shown to be partly as N-acetylglucosamine 6-phosphate. Deaminaseless mutants have no abnormal control effects after growth on glucose. 7. Addition of N-acetylglucosamine or glucosamine to cultures of a deaminaseless mutant caused inhibition of growth. Addition of N-acetylglucosamine to cultures of a deacetylaseless mutant caused lysis, and secondary mutants were isolated that did not lyse; most of these secondary mutants had lost glucosamine 6-phosphate deaminase and an uptake mechanism for N-acetylglucosamine. 8. Similar amounts of (14)C were incorporated from [1-(14)C]-glucosamine by cells of mutants and wild-type growing on broth. Cells of wild-type and a deaminaseless mutant incorporated (14)C from N-acetyl[1-(14)C]glucosamine more efficiently than from N[1-(14)C]-acetylglucosamine, incorporation from the latter being further decreased by acetate; cells of a deacetylaseless mutant showed a poor incorporation of both types of labelled N-acetylglucosamine.

Bacteriolysis↗
PubMed1980

[Self-control of blood sugar with a new blood sugar test strip (author's transl)].

Blood sugar self-control was assessed in 20 in-patients using a new blood sugar test strip, Haemo-Glukotest 20--800. Comparative estimations of 445 strip tests with values obtained by the hexokinase method showed good correlations particularly in the low range below the renal threshold. Nearly 70% of measurements were assessed correctly in this range. Mean deviations of test strip results from the corresponding laboratory value were 0.61 to 0.89 mmol/l (11--16 mg/dl). Haemo-Glukotest 20--800 is thus well suited for blood glucose self-control particularly in the range below the renal threshold. In a survey most patients estimated the importance of blood sugar to be more than that of urinary sugar.

Activities of Daily Living↗
PubMed1987

Sugar and sugar substitutes. Comparisons and indications.

Public confusion and concern about the use of sugar and sugar substitutes are widespread. Physicians must be prepared to answer patients' inquiries about these substances. Some population groups should avoid certain sugar substitutes. In particular, pregnant women and young children should avoid saccharin, and phenylketonuric homozygous persons should avoid aspartame. In a varied, balanced diet, the use of aspartame and saccharin is one safe way for the general population to enjoy sweet foods with fewer calories and less cariogenic potential. Sugar substitutes may be helpful in dietary compliance for overweight and diabetic patients.

Animals↗