Brucella is an animal and human pathogen that expresses several virulence factors required for host cell invasion and intracellular survival. It produces LPS with unusually low toxicity, which hamper the detection of bacteria by the host immune system and thus provides resistance against intracellular antimicrobial mechanisms of the host. By chemical and spectroscopic methods we determined the structure of LPS core and of a non-repetitive oligosaccharide fragment at the reducing end of the O-specific polysaccharide. These data should be useful for understanding biological role of the Brucella LPS.
Brucella; LPS; structure; NMR; MS
•Aqueous 10 μs simulations of N-linked mannosyl cores and sialyl Lewis (sLe) antennae are validated.•Sequence dependent glycosidic linkage and pyranose ring μs motions are implicated in bioactivity.•Stacked pyranoses in sLea and sLex are predicted to be atypically rigid on μs timescales.•In a 25 μs simulation of sLex, all known conformers were sampled within the initial 10 μs of dynamics.•Unbiased 10 μs simulations are proposed as a route to systematic and accurate glycomic 3D-analysis.
The human glycome comprises a vast untapped repository of 3D-structural information that holds the key to glycan recognition and a new era of rationally designed mimetic chemical probes, drugs, and biomaterials. Toward routine prediction of oligosaccharide conformational populations and exchange rates at thermodynamic equilibrium, we apply hardware-accelerated aqueous molecular dynamics to model μs motions in N-glycans that underpin inflammation and immunity. In 10 μs simulations, conformational equilibria of mannosyl cores, sialyl Lewis (sLe) antennae, and constituent sub-sequences agreed with prior refinements (X-ray and NMR). Glycosidic linkage and pyranose ring flexing were affected by branching, linkage position, and secondary structure, implicating sequence dependent motions in glycomic functional diversity. Linkage and ring conformational transitions that have eluded precise quantification by experiment and conventional (ns) simulations were predicted to occur on μs timescales. All rings populated non-chair shapes and the stacked galactose and fucose pyranoses of sLea and sLex were rigidified, suggesting an exploitable 3D-signature of cell adhesion protein binding. Analyses of sLex dynamics over 25 μs revealed that only 10 μs were sufficient to explore all aqueous conformers. This simulation protocol, which yields conformational ensembles that are independent of initial 3D-structure, is proposed as a route to understanding oligosaccharide recognition and structure–activity relationships, toward development of carbohydrate-based novel chemical entities.
Conformation analysis; Glycome; Microsecond timescale; Kinetics; Molecular dynamics; Puckering
O-polysaccharide (OPS) was isolated from purified Burkholderia thailandensis E264 lipopolysaccharide by mild-acid hydrolysis and gel-permeation chromatography. Glycosyl composition and methylation analyses along with 1D and 2D 1H and 13C NMR spectroscopy experiments revealed that the OPS antigen was an unbranched heteropolymer with the following structure:
Collectively, these results suggest that B. thailandensis OPS is structurally more complex than B. pseudomallei OPS and provide evidence of the signal used by B. thailandensis to terminate chain elongation.
Burkholderia thailandensis; Burkholderia pseudomallei; Lipopolysaccharide; O-polysaccharide; NMR; Structure
Two novel N-acetylneuraminic acid derivatives, luciferyl N-acetylneuraminic acid (1) and luciferyl 4,7-di-O-methyl-N-acetylneuraminic acid (2), were designed and synthesized as substrates for the rapid detection of influenza virus neuraminidase. The sensitivity and specificity of the assays with compound 1 or 2 as the substrate for detection of neuraminidases from influenza virus (H1N1 and H5N1) and bacteria (A. ureafaciens and C. perfringens) were evaluated. Compound 1 was sensitive to neuraminidases from both influenza virus and bacteria. Biochemiluminescent assays with this compound with H1N1 and H5N1 neuraminidases were approximately 20- and 16-fold more sensitive, respectively, than the fluorescent method with the commercial substrate 4-MUNANA. In contrast, compound 2 was only sensitive to the neuraminidases from influenza virus, showing approximately 10- and 8-fold greater sensitivity than 4-MUNANA for the detection of H1N1 and H5N1 neuraminidases, respectively. The data showed that compound 2 could be used in assays that detect of influenza viral neuraminidase.
Rapid detection; Influenza virus neuraminidase; N-acetylneuraminic acid derivatives; Bioluminescence
Undecaprenyl Pyrophosphate Synthase (UPPS) is a key enzyme that catalyzes the production of bactoprenols, which act as membrane anchors for the assembly of complex bacterial oligosaccharides. One of the major hurdles in understanding the assembly of oligosaccharide assembly is a lack of chemical tools to study this process, since bactoprenols and the resulting isoprenoid-linked oligosaccharides lack handles or chromophores for use in pathway analysis. Here we describe the isolation of a new UPPS from the symbiotic microorganism Bacteroides fragilis, a key species in the human microbiome. The protein was purified to homogeneity and utilized to accept a chromophore containing farnesyl diphosphate analogue as a substrate. The analogue was utilized by the enzyme and resulted in a bactoprenyl diphosphate product with an easy to monitor tag associated with it. Furthermore, the diphosphate is shown to be readily converted to monophosphate using a common molecular biology reagent. This monophosphate product allowed for the investigation of complex oligosaccharide biosynthesis, and was used to probe the activity of glycosyltransferases involved in the well characterized Campylobacter jejuni N-linked protein glycosylation. Novel reagents similar to this will provide key tools for the study of uncharacterized oligosaccharide assemblies, and open the possibility for the development of rapid screening methodology for these biosynthetic systems.
bactoprenol; undecaprenol; undecaprenyl diphosphate synthase; cis-prenyl transferases; Bacteroides fragilis
Oviduct-specific glycoprotein (OVGP1) is a major mucin-like glycoprotein synthesized and secreted exclusively by non-ciliated secretory cells of mammalian oviduct. In vitro functional studies showed that OVGP1 plays important roles during fertilization and early embryo development. We have recently produced recombinant human oviduct-specific glycoprotein (rhOVGP1) in human embryonic kidney 293 (HEK293) cells. The present study was undertaken to characterize the structures and determine the biosynthetic pathways of the N- and O-glycans of rhOVGP1. Treatment of the stable rhOVGP1-expressing HEK293 cells with either GalNAcα-Bn to block O-glycan extension, tunicamycin to block N-glycosylation, or neuraminidase increased the electrophoretic mobility of rhOVGP1. A detailed analysis of O- and N-linked glycans of rhOVGP1 by mass spectrometry showed a broad range of many simple and complex glycan structures. In order to identify the enzymes involved in the glycosylation of rhOVGP1, we assayed glycosyltransferase activities involved in the assembly of O- and N-glycans in HEK293 cells, and compared these to those from the immortalized human oviductal cells (OE-E6/E7). Our results demonstrate that HEK293 and OE-E6/E7 cells exhibit a similar spectrum of glycosyltransferase activities that can synthesize elongated and sialylated O-glycans with core 1 and 2 structures, as well as complex multiantennary N-glycans. It is anticipated that the knowledge gained from the present study will facilitate future studies of the role of the glycans of human OVGP1 in fertilization and early embryo development.
Oviduct; Oviduct-specific glycoprotein; Oviductin; Glycosyltransferases; Glycan structures; HEK293 cells
β-Configured peracetylated sugars are often used as easily accessible glycosyl donors that are typically activated with common Lewis acids such as boron trifluoride or trimethylsilyltriflouromethane sulfonate. Often these glycosylations occur with unsatisfactory yields due to incomplete reactions or extensive byproduct formation, primarily as a result of loss of an additional acetyl group generating partially unprotected glycosides. Here we report a simple glycosylation-reacetylation protocol for the generation of peracetylated β-allylglucoside, -galactoside, - lactoside, and -maltoside with substantially improved reaction yields.
Glycosylation; Allylglycosides; Reacetylation; Acetylated Glycosyl Donors
It is reported that the replacement of the 4- and 6-O-benzyl ethers in 2,3,4,6-tetra-O-benzyl-α,β-mannopyranose by a 4,6-O-benzylidene acetal results in an increased population of the β-anomer at equilibrium in CDCl3 solution. The phenomenon is considered to arise from the lower steric bulk of the benzylidene acetal that, through diminished buttressing interactions, reduces steric interactions normally present in the β-anomer.
Mannopyranosides; 4,6-O-Benzylidene acetal; Anomeric equiliblium; Anomeric effect; Conformational analysis
By the action of D-fructose 1,6-bisphosphate aldolases (FruA) from rabbit muscle and Staphylococcus carnosus, various ketoses were synthesized from glyceraldehydes or other aliphatic aldehydes as acceptors in a one-pot four-enzyme system.
Enzymatic synthesis; aldolase; ketose; FruA; Staphylococcus carnosus
D-Glucose, lactose, maltose, and melibiose were benzoylated with Bz2O–Et3N reagent to give fully benzoylated β products. Under the same conditions, D-mannose produced a mixture where the β-benzoate predominated. Treatment of the foregoing compounds with EtSH at slightly elevated temperature (50– 60 °C) in the presence of BF3·Et2O as a promoter gave the corresponding ethyl 1-thio glycosides in high yields. The α-products predominated in all cases in the anomeric mixtures formed. Individual products of all reactions were isolated by chromatography, they were obtained in analytically pure state, and were fully characterized by 1H and 13C NMR data and physical constants.
β-Selective 1-O-benzoylation; Thioglycosylation; Thioglycosidation
An alternative synthesis of Glc-β-(1→4)-GlcNAc oxazoline was described and its enzymatic reaction with the endo-β-N-acetylglucosaminidase from Arthrobacter protophormiae (Endo-A) was re-investigated. Under normal transglycosylation conditions with a catalytic amount of enzyme, Endo-A showed only marginal activity for transglycosylation with the disaccharide oxazoline, consistent with our previous observations. However, when used in a relatively large quantity, Endo-A could promote the transglycosylation of the disaccharide oxazoline to a GlcNAc-Asn acceptor. In addition to the initial transglycosylation product, a series of large oligosaccharides were also formed due to the tandem transglycosylation to the terminal glucose residues in the intermediate products. In the absence of an external acceptor, Endo-A could polymerize the disaccharide oxazoline to form oligo- and polysaccharides having the -4Glcβ-(1→4)-GlcNAcβ1– repeating units. This is the first example of an endo-β-N-acetylglucosaminidase promoted polymerization of activated oligosaccharide substrates. This enzymatic polymerization may find useful applications for the synthesis of novel artificial polysaccharides.
Transglycosylation; Enzymatic polymerization; Endoglycosidase; Carbohydrate oxazoline derivative; Glycopeptides
An orthogonally protected disaccharide (GlcN(α1→4)Glc) with a β-linked 2′-aminoethyl linker was used to generate a series of sulfated derivatives (sulfoforms), with a 6-O-sulfate on the glucose residue and one or more sulfate esters on the terminal glucosamine. Deprotection and sulfonation steps were performed in solution and in variable order, with isolated yields of 36–54% (85–90% per operation) after HPLC purification. The modular deprotection–sulfonation sequences can be performed with efficient recovery of the polysulfate products, and avoids complications associated with heterogeneous reactivity in solid-phase synthesis.
A novel biopolymer-based antioxidant, chitosan conjugated with gallic acid (chitosan galloylate, chitosan– GA), is proposed. Electron paramagnetic resonance (EPR) demonstrates a wide range of antioxidant activity for chitosan–GA as evidenced from its reactions with oxidizing free radicals, that is, 1,1-diphenyl-2-picryl-hydrazyl (DPPH), horseradish peroxidase (HRP)–H2O2, carbon-centered alkyl radicals, and hydroxyl radicals. The EPR spectrum of the radical formed on chitosan–GA was attributed to the semiquinone radical of the gallate moiety. The stoichiometry and effective concentration (EC50) of the DPPH free radical with chitosan–GA show that the radical scavenging capacity is maintained even after thermal treatment at 100 °C for an hour. Although the degree of substitution of GA on chitosan was about 15%, its antioxidant capacity, that is, the reaction with carbon-centered and hydroxyl radicals, is comparable to that of GA.
Chitosan; Polysaccharide; Gallic acid (GA); Antioxidant; Electron paramagnetic resonance (EPR)
The hydrolysis of various carbohydrates was investigated under acidic conditions in real time by 1H NMR spectroscopy, with a focus on the polysaccharide inulin. Sucrose was used as a model compound to illustrate the applicability of this technique. The hydrolysis of sucrose was shown to follow pseudo first order kinetics and have an activation energy of 107.0 kJ.mol−1 (s.d. 1.7 kJ.mol−1). Inulin, pullulan and glycogen also all followed pseudo first order kinetics, but had an initiation phase at least partially generated by the protonation of the glycosidic bonds. It was also demonstrated that polysaccharide chain length has an effect on the hydrolysis of inulin. For short chain inulin (DPn 18, s.d. 0.70) the activation energy calculated for the hydrolytic cleavage of glucose was similar to sucrose at 108.5 kJ.mol−1 (std. dev. 0.60). For long chain inulin (DPn 30, s.d. 1.3) the activation energy for the hydrolytic cleavage of glucose was reduced to 80.5 kJ.mol−1 (s.d. 2.3 kJ.mol−1). This anomaly has been attributed to varied conformations for the two different lengths of inulin chain in solution.
Inulin; Polysaccharide hydrolysis; 1H NMR spectroscopy
A simplified method for the preparation of Fmoc-serine and Fmoc-threonine glycosides for use in O-linked glycopeptide synthesis is described. Lewis acids promote glycoside formation, but also promote undesired reactions of the glycoside products. Use of “minimally competent” Lewis acids such as InBr3 promotes the desired activation catalytically, and with greatly reduced side products from sugar peracetates.
Alkyl β-D-xylopyranosides are highly surface active, biodegradable surfactants that can be prepared from hemicelluloses and are of interest for use as pharmaceuticals, detergents, agrochemicals and personal care products. To gain further insights into their structure-property and structure-activity relationships, the present study synthesized a series of hydrocarbon (-C6H13 to -C16H33) and fluorocarbon (-(CH2)2C6F13) alkyl β-D-xylopyranosides in four steps from D-xylose by acylation or benzoylation, bromination, Koenigs-Knorr reaction and hydrolysis, with the benzoyl protecting group giving better yields compared to the acyl group in the Koenigs-Knorr reaction. All alkyl β-D-xylopyranosides formed thermotropic liquid crystals. The phase transition of the solid crystalline phase to a liquid crystalline phase increased linearly with the length of the hydrophobic tail. The clearing points were near constant for alkyl β-D-xylopyranosides with a hydrophobic tail ≥ 8, but occurred at a significantly lower temperature for hexyl β-D-xylopyranoside. Short and long-chain alkyl β-D-xylopyranosides displayed no cytotoxicity at concentration below their aqueous solubility limit. Hydrocarbon and fluorocarbon alkyl β-D-xylopyranosides with intermediate chain length displayed some toxicity at millimolar concentrations due to apoptosis.
Next-generation surfactants; Renewable precursors; Xylose; Structure-activity relationship; Structure-property relationship; Koenigs-Knorr reaction; Liquid crystals; Biocompatibility; Apoptosis; Necrosis
D-Fructose was analysed by NMR spectroscopy and previously unidentified 1H NMR resonances were assigned to the keto and α-pyranose tautomers. The full assignment of shifts for the various fructose tautomers enabled the use of 1H NMR spectroscopy in studies of the mutarotation (5 – 25 °C) and tautomeric composition at equilibrium (5 – 50 °C). The mutarotation of β-pyranose to furanose tautomers in D2O at a concentration of 0.18 M was found to have an activation energy of 62.6 kJ.mol−1. At tautomeric equilibrium (20 °C in D2O) the distribution of the β-pyranose, β-furanose, α-furanose, α-pyranose and the keto tautomers was found to be 68.23%, 22.35%, 6.24%, 2.67% and 0.50%, respectively. This tautomeric composition was not significantly affected by varying concentration between 0.089 and 0.36 M or acidification to pH 3. Upon equilibrating at 6 temperatures between 5 and 50 °C there was a linear relationship between the change in concentration and temperature for all forms.
D-Fructose; Carbohydrate structural analysis; Mutarotation; Tautomeric equilibrium
O-Specific polysaccharides of Gram-negative bacteria are synthesized by two different mechanisms: polymerization of the pre-formed O-repeating unit or sequential addition of the monosaccharides to the growing polysaccharide chain. In the second case, growth of the polymer can be further subdivided into two groups depending on the presence or absence of a special monosaccharide or non-sugar substituent that terminates the glycan. A family of polymannose O-polysaccharides provides prototypes for the chain terminating process. Polysaccharides of Klebsiella pneumoniae O3, Hafnia alvei PCM 1223, and Escherichia coli O9 have the same penta-mannose repeating unit. E. coli O9a has tetra-mannose repeat and this structure can be produced by mutants of E. coli O9. The mechanism of biosynthesis of H. alvei 1223 O-polysaccharide has not been reported. Here we show that all above polysaccharides contain the same modification at the non-reducing end; presence of a methyl phosphate group at O-3 of α-mannopyranose, that serves as the signal for termination of the chain elongation.
Hafnia; Klebsiella; LPS; methyl phosphate; O-specific polysaccharide
InCl3, InBr3, and In(OTf)3 were tested as promoters in the preparation of glycosides from trichloroacetimidate precursors. A range of protecting groups and of alcohol acceptors were used to determine the versatility of these promoters. Disaccharide formation was demonstrated. In most cases, the In(III) compounds were shown to promote glycosylation better than the widely used promoter BF3•OEt2.
Glycosylation; Trichloroacetimidate; Indium(III) promotion; InBr3; InCl3; In(OTf)3
The presence of a novel coaggregation receptor polysaccharide (RPS) on the dental plaque isolate Streptococcus cristatus LS4 was suggested by this strain’s antigenic and coaggregation properties. Examination of RPS isolated from strain LS4 by a combination of 2-dimensional and pseudo 3-dimensional single quantum heteronuclear NMR methods that included detection of 13C chemical shifts at high resolution revealed the following repeat unit structure: →6)-β-d-Galf-(1→6)-β-d-GalpNAc-(1→3)-α-d-Galp-(1→P→6)-α-d-Galp-(1→3)-β-l-Rhap-(1→4)-β-d-Glcp-(1→ The identification of this polysaccharide as RPS3Gn, a new structural type, was established by the α-D-Galp-containing epitope of RPS serotype 3 and Gn recognition motif (i.e. β-D-GalpNAc (1→3)-α-D-Galp) for coaggregation with other bacteria.
The Candida albicans cell wall provides an architecture that allows for the organism to survive environmental stresses as well as interaction with host tissues. Previous work has focused on growing C. albicans on media such as Sabouraud or YPD at 30 °C. Because C. albicans normally colonizes a host, we hypothesized that cultivation on blood or serum at 37 °C would result in structural changes in cell wall mannan. C. albicans SC5314 was inoculated onto YPD, 5% blood, or 5% serum agar media three successive times at 30 °C and 37 °C, then cultivated overnight at 30 °C in YPD. The mannan was extracted and characterized using 1D and 2D 1H NMR techniques. At 30 °C cells grown in blood and serum contain less acid-stable terminal β-(1→2)-linked D-mannose and α-(1→2)-linked D-mannose-containing side chains, while the acid-labile side chains of mannan grown in blood and serum contain fewer β-Man-(1→2)-α-Man-(1→ side chains. The decrement in acid-stable mannan side chains is greater at 37 °C than at 30 °C. Cells grown on blood at 37 °C show fewer →6)-α-Man-(1→ structural motifs in the acid-stable polymer backbone. The data indicate that C. albicans, grown on media containing host derived components, produces less complex mannan. This is accentuated when the cells are cultured at 37 °C. This study demonstrates that the C. albicans cell wall is a dynamic and adaptive organelle, which alters its structural phenotype in response to growth in host-derived media at physiological temperature.
Mannan; NMR; Growth conditions
Synthesis of amphiphilic oligosaccharides is problematic because traditional methods for separating and purifying oligosaccharides, including sulfated oligosaccharides, are generally not applicable to working with amphiphilic sugars. We report here RPIP-LC and LC-MS methods that enable the synthesis, separation, and characterization of amphiphilic N-arylacyl O-sulfonated aminoglycosides, which are being pursued as small-molecule glycosaminoglycan mimics. The methods described in this work for separating and characterizing these amphiphilic saccharides are further applied to a number of uses: monitoring the progression of sulfonation reactions with analytical RP-HPLC, characterizing sulfate content for individual molecules with ESI-MS, determining the degree of sulfation for products having mixed degrees of sulfation with HPLC and LC-MS, and purifying products with benchtop C18 column chromatography. We believe the methods described here will be broadly applicable to enabling the synthesis, separation and characterization of amphiphilic, sulfated and phosphorylated oligosaccharides and other types of molecules substituted to varying degrees with both anionic and hydrophobic groups.
Biomimetic synthesis; Aliphatic oligosaccharide; Mass spectrometry; Reversed-phase ion-pairing; Sulfation; Electrospray ionization
The conformational behavior of a series of linear and cyclic oligo-(1→6)-β-D-glucosamines and their N-acetylated derivatives, which are related to fragments of natural poly-N-acetylglucosamine, was studied by theoretical molecular modeling and experimental determination of transglycosidic vicinal coupling constants 3JC,H and 3JH,H. Molecular dynamics simulations were performed under several types of conditions varying in the consideration of ionization of amino groups, solvent effect and temperature. Neural network clustering and asphericity calculations were performed on the basis of molecular dynamics data. It was shown that disaccharide fragments in the studied linear oligosaccharides were not rigid, and tended to have several conformers, thus determining the overall twisted shape with helical elements. In addition, it was found that the behavior of C5–C6 bond depended significantly upon the simulation conditions. The cyclic di-, tri-, and tetrasaccharides mostly had symmetrical ring-shaped conformations. The larger cycles tended to adopt more complicated shapes, and the conformational behavior of their disaccharide fragments was close to that in the linear oligosaccharides.
Cyclic oligosaccharides; Glucosamine; Conformation analysis; MM3; SASA; Transglycosidic coupling constants
We report the efficient O-glycosidation of glycosyl bromides with therapeutically relevant acceptors facilitated by silver N-heterocyclic carbene (Ag-NHC) complexes. A set of four Ag-NHC complexes was synthesized and evaluated as promoters for glycosidation reactions. Two new bis-Ag-NHC complexes derived from ionic liquids 1-benzyl-3-methyl-1H-imidazolium chloride and 1-(2-methoxyethyl)-3-methyl-1H-imidazolium chloride were found to efficiently promote glycosidation, whereas known mono-Ag complexes of 1,3-bis(2,4,6-trimethylphenyl)imidazolium chloride and 1,3-bis(2,6-di-isopropylphenyl)imidazolium chloride failed to facilitate the reaction. The structures of the promoters were established by X-ray crystallography, and these complexes were employed in the glycosidation of different glycosyl bromide donors with biologically valuable acceptors, such as estrone, estradiol, and various flavones. The products were obtained in yields considered good to excellent, and all reactions were highly selective for the β isomer regardless of neighboring group effects.
O-glycosidation; Silver N-heterocyclic carbene complex; Carbohydrates
Ozone is known to add across and cleave carbon–carbon double bonds. Ozonolysis is widely used for the preparation of pharmaceuticals, for bleaching substances and for killing microorganisms in air and water sources. Some polysaccharides and oligosaccharides, such as those prepared using chemical or enzymatic β-elimination, contain a site of unsaturation. We examined ozonolysis of low-molecular-weight heparins (LMWHs), enoxaparin and logiparin, and heparosan oligo- and polysaccharide for the removal of the nonreducing terminal unsaturated uronate residue. 1D 1H NMR showed that these ozone-treated polysaccharides retained the same structure as the starting polysaccharide, except that the C4–C5 double bond in the nonreducing end unsaturated uronate had been removed. The anticoagulant activity of the resulting product from enoxaparin and logiparin was comparable to that of the starting material. These results demonstrate that ozonolysis is an important tool for the removal of unsaturated uronate residues from LMWHs and heparosan without modification of the core polysaccharide structure or diminution of anticoagulant activity. This reaction also has potential applications in the chemoenzymatic synthesis of bioengineered heparin from Escherichia coli-derived K5 heparosan.
heparosan; low-molecular-weight heparin; ozone; beta elimination; unsaturated uronic acid