Optimization of the enzymatic synthesis of O-glycan core 2 structure by use of a genetic algorithm

The enzymatic synthesis of Gal-beta 1,3[GlcNAc-beta 1,6]-GalNAc-alpha 1-OBn (core 2-Bn) using a multi-enzyme system consisting of a beta-galactosidase (EC 3.2.1.23) from bovine testes and a recombinant core 2 beta 1,6-GlcNAc transferase (C2GnT, EC 2.4.1.102) was empirically optimized by the use of a genetic algorithm. After variation of seven relevant parameters and performance of 56 experiments, two local maxima regarding the selection criteria could be found after four generations of optimization. The selectivity of core 2-Bn formation showed values up to 90%.

Olefin self-metathesis as a new entry into xenotransplantation antagonists bearing the Galili antigen

A hexameric disaccharide cluster bearing the terminal Gal alpha related xenotransplantation antigen was constructed using a sequence of ruthenium carbenoid catalyzed olefin self-metathesis of monoallylated tribenzyl pentaerythritol followed, after interconversion of benzyl ethers into para-iodobenzyl ethers, by a single step Sonogashira cross-coupling of six prop-2-ynyl glycosides onto a hexameric aryl iodide scaffold.

3-deoxypentosulose: an alpha-dicarbonyl compound predominating in nonenzymatic browning of oligosaccharides in aqueous solution

The thermal degradation of D-glucose, maltose, and maltotriose in aqueous solution was investigated under caramelization (no glycine) and Maillard (with glycine) conditions. Degradation of the sugar and alpha-dicarbonyls product was monitored. Under both caramelization and Maillard reaction conditions, 3-deoxypentosulose was the predominating alpha-dicarbonyl compound formed from maltose and maltotriose. In the absence of an amino compound, however, 3-deoxypentosulose is formed in much lower concentration. It was concluded that 3-deoxypentosulose is formed by a pathway specific for oligo- and polysaccharides since this alpha-dicarbonyl is formed from the alpha-1-->4 glucans such as maltose and maltotriose but not from glucose. For its formation, a retro Claisen reaction of an enolization product of 1-amino-1,4-dideoxyhexosulose is proposed as the route to its formation. 1-Amino-1,4-dideoxyhexosulose could be formed by vinylogous alpha-elimination from the 2,3-enediol structure after Amadori rearrangement, favored by planar alignment of the bonds between C1 and C4. Subsequent rearrangement by keto-enoltautomerization leads to a 1-imino-3-keto structure. In this structure, attack of a hydroxyl anion, provided by water at neutral pH, could cause a splitting off of the C1. This reaction gives rise to formic acid or formamide and a pentose derivative, which reacts further to give 3-deoxypentosulose.

Determination of the site-specific oligosaccharide distribution of the O-glycans attached to the porcine submaxillary mucin tandem repeat. Further evidence for the modulation of O-glycans side chain structures by peptide sequence

Little is known of the degree that polypeptide sequence and the local environment modulate the structures of O-linked glycans. Toward this understanding, the site-specific mono- (GalNAc-O-), di- (beta-Gal-1,3-alpha-GalNAc-O-), and trisaccharide (alpha-Fuc-1,2-beta-Gal-1,3-alpha-GalNAc-O-) distributions have been determined for 29 of the 31 O-glycosylated Ser/Thr residues in the tandem repeat domains of blood group A-negative porcine submaxillary gland mucin. The glycosylation patterns obtained from three individual animals are in agreement with earlier incomplete determinations on a pooled mucin (Gerken, T. A., Owens, C. L., and Pasumarthy, M. (1997) J. Biol. Chem. 272, 9709-9719; Gerken, T. A., Owens, C. L., and Pasumarthy, M. (1998) J. Biol. Chem. 273, 26580-26588), confirming that the addition of the peptide-linked GalNAc and its substitution by beta-1,3-Gal are sensitive to local peptide sequence in a highly reproducible manner in vivo. The present data further support earlier suggestions of an inverse correlation of the density of hydroxyamino acid residues (and by inference the density of peptide GalNAc) with the extent of substitution of the peptide-linked GalNAc by beta-1,3-Gal. This effect is highly correlated for Ser-linked glycans but not for Thr-linked glycans. A similar correlation is observed with respect to the in vivo peptide GalNAc glycosylation pattern. In contrast, the addition of alpha-1,2-Fuc to beta-Gal shows no apparent correlation with hydroxyamino acid density, although a marked elevation in the fucosylation of Ser-linked glycans compared with Thr-linked glycans is observed. The above effects may represent both steric and conformational factors acting to alter the relative accessibility and activity of the glycosyltransferases toward substrate. These results demonstrate that the porcine submaxillary gland core 1 beta 3-galactosyltransferase and alpha2-fucosyltransferase exhibit unique peptide/glycopeptide sensitivities that may provide mechanisms for the modulation of O-linked side chain structures.

Nobiloside, a new neuraminidase inhibitory triterpenoidal saponin from the marine sponge Erylus nobilis

A neuraminidase inhibitor, nobiloside (1), was isolated from the marine sponge Erylus nobilis Thiele, 1903. Its structure was determined as a penasterol trisaccharide. The absolute configurations were determined by NMR and chiral GC analysis. It inhibited neuraminidase from the bacterium Clostridium perfringens with an IC50 value of 0.46 microg/mL.

O-Specific chain structure from the lipopolysaccharide fraction of Pseudomonas reactans: a pathogen of the cultivated mushrooms

An O-specific polysaccharide containing 2-acetamidino-2-deoxy-beta-D-glucopyranose (Glcp2Am), 2,4-diacetamido-2,4,6-trideoxy-beta-D-glucopyranose (QuipNAc4NAc, bacillosamine) and 2,4-di-(N-acetyl-L-alanylamino)-2,4,6-trideoxy-beta-D-glucopyranose (QuipNAlaAc4NAlaAc) was isolated from the phenol-soluble lipopolysaccharide fraction of the mushroom-associated bacterium Pseudomonas reactans. The structure, determined by means of chemical analysis and 1D and 2D NMR spectroscopy, showed a linear trisaccharide-repeating unit, as shown below:-->3)-beta-D-QuipNAlaAc4NAlaAc-(1-->3)-alpha-D-Glcp2Am-(1-->3)-alpha-D-QuipNAc4NAc(1-->To our knowledge, this is the first complete O-chain structure reported for the lipopolysaccharide of a mushroom-associated bacterium.

Complete relaxation and conformational exchange matrix (CORCEMA) analysis of intermolecular saturation transfer effects in reversibly forming ligand-receptor complexes

A couple of recent applications of intermolecular NOE (INOE) experiments as applied to biomolecular systems involve the (i) saturation transfer difference NMR (STD-NMR) method and (ii) the intermolecular cross-saturation NMR (ICS-NMR) experiment. STD-NMR is a promising tool for rapid screening of a large library of compounds to identify bioactive ligands binding to a target protein. Additionally, it is also useful in mapping the binding epitopes presented by a bioactive ligand to its target protein. In this latter application, the STD-NMR technique is essentially similar to the ICS-NMR experiment, which is used to map protein-protein or protein-nucleic acid contact surfaces in complexes. In this work, we present a complete relaxation and conformational exchange matrix (CORCEMA) theory (H. N. B. Moseley et al., J. Magn. Reson. B 108, 243-261 (1995)) applicable for these two closely related experiments. As in our previous work, we show that when exchange is fast on the relaxation rate scale, a simplified CORCEMA theory can be formulated using a generalized average relaxation rate matrix. Its range of validity is established by comparing its predictions with those of the exact CORCEMA theory which is valid for all exchange rates. Using some ideal model systems we have analyzed the factors that influence the ligand proton intensity changes when the resonances from some protons on the receptor protein are saturated. The results show that the intensity changes in the ligand signals in an intermolecular NOE experiment are very much dependent upon: (1) the saturation time, (2) the location of the saturated receptor protons with respect to the ligand protons, (3) the conformation of the ligand-receptor interface, (4) the rotational correlation times for the molecular species, (5) the kinetics of the reversibly forming complex, and (6) the ligand/receptor ratio. As an example of a typical application of the STD-NMR experiment we have also simulated the STD effects for a hypothetical trisaccharide bound to a protein. The CORCEMA theory for INOE and the associated algorithm are useful in a quantitative interpretation of the intensity changes in the ligand in both the STD-NMR and ICS-NMR, provided the identity of the receptor protons experiencing direct RF saturation is known. The formalism presented here is likely to be useful in the design of bioactive ligands to a specific target protein and in the quantitative mapping of binding epitopes and interfaces between molecules in complexes.

Preparative route to N-glycolylneuraminic acid phenyl 2-thioglycoside donor and synthesis of Neu5Gc-alpha-(2-->3')-lactosamine 3-aminopropyl glycoside

The spacer-armed trisaccharide, Neu5Gc-alpha-(2-->3')-lactosamine 3-aminopropyl glycoside, was synthesized by regio- and stereoselective sialylation of the suitably protected triol acceptor, 3-trifluoroacetamidopropyl 2-acetamido-3,6-di-O-benzyl-2-deoxy-4-O-(6-O-benzyl-beta-D-galactopyranosyl)-beta-D-glucopyranoside, with the donor methyl [phenyl 5-acetoxyacetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-2-thio-D-glycero-alpha,beta-D-galacto-2-nonulopyranosid]onate. The donor was obtained, in turn, from methyl [phenyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-2-thio-D-glycero-alpha,beta-D-galacto-2-nonulopyranosid]onate by N-tert-butoxycarbonylation of the acetamido group followed by total N- and O-deacetylation, per-O-acetylation, subsequent Boc group removal, and N-acetoxyacetylation.

Characterization of the recognition of blood group B trisaccharide derivatives by the lectin from Marasmius oreades using frontal affinity chromatography-mass spectrometry

A novel lectin from the mushroom Marasmius oreades (MOA) has been shown to bind to human blood group B oligosaccharides [1]. In the present work we examine the binding of a series of analogues of the blood group B-trisaccharide, alphaGal(1-3)[alphaFuc(1-2)]betaGal-OR (1, R = (CH2)8COOMe). MOA was biotinylated and immobilized on a micro column (9.8 microL) for evaluation by Frontal Affinity Chromatography-Mass Spectrometry (FAC-MS) [2]. The trisaccharide 1 was found to be the epitope needed for maximum recognition (Kd = 3.6 microM). A series of synthetic deoxygenated and O-methylated analogues of the B-trisaccharide (R = OMe) were then screened against the lectin, and the key structural elements for binding were determined. OH-4 of the beta-Gal residue and OH-2 of the alpha-Gal residue were found to be critical for recognition. The FAC-MS technique also proved powerful in evaluating mixtures of compounds. Since the solution NMR structure and crystal structure of the B-trisaccharide are known [3], we propose the specific surface of the trisaccharide that is recognized by the lectin.

23Na NMR study of the interaction between hyaluronan and the bications Ca(++), Mg(++) and Cu(++)

The relaxation rate R = pi Delta nu(1/2) of the quadrupolar (23)Na nucleus was measured at pH approximately 7 using a 200 MHz NMR spectrometer with a view to observe the interaction between hyaluronan and its natural counterion Na(+) and the bications Ca(++), Mg(++) and Cu(++). An interpretation of our results, by means of the "entropy of fluctuations" concept of Na(+), is presented. We show that Cu(++) ions are more effective than Ca(++) and Mg(++). A possible model of complexation of Cu(++) in a cage formed by the 1-4 glycosidic bond, the carboxylate side-chain and the acetoamide side-chain is proposed, according to electrostatic potential computations using the ZINDO1 quantum semi empirical method.

Oxidation of the flavonoids galangin and kaempferide by human liver microsomes and CYP1A1, CYP1A2, and CYP2C9

There is very limited information on cytochrome P450 (P450)-mediated oxidative metabolism of dietary flavonoids in humans. In this study, we used human liver microsomes and recombinant P450 isoforms to examine the metabolism of two flavonols, galangin and kaempferide, and one flavone, chrysin. Both galangin and kaempferide, but not chrysin, were oxidized by human liver microsomes to kaempferol, with K(m) values of 9.5 and 17.8 microM, respectively. These oxidations were catalyzed mainly by CYP1A2 but also by CYP2C9. Consistent with these observations, the human liver microsomal metabolism of galangin and kaempferide were inhibited by the P450 inhibitors furafylline and sulfaphenazole. In addition, CYP1A1, although less efficient, was also able to oxidize the two flavonols. Thus, dietary flavonols are likely to undergo oxidative metabolism mainly in the liver but also extrahepatically.

Conformational studies of Lewis X and Lewis A trisaccharides using NMR residual dipolar couplings

The conformations of the histo-blood group carbohydrate antigens Lewis X (Le(x)) and Lewis A (Le(a)) were studied by NMR measurements of one-bond C-H residual dipolar couplings in partially oriented liquid crystal solutions. A strategy for rapid calculation of the difference between theoretical and experimental dipolar couplings of a large number of model structures generated by computer simulations was developed, resulting in an accurate model structure for the compounds. Monte Carlo simulations were used to generate models for the trisaccharides, and orientations of each model were sought that could reproduce the experimental residual dipolar coupling values. For both, Le(a) and Le(x), single low energy models giving excellent agreement with experiment were found, implying a compact rigidly folded conformation for both trisaccharides. The new approach was also applied to the pentasaccharides lacto-N-fucopentaose 2 (LNF-2) and lacto-N-fucopentaose 3 (LNF-3) proving its consistency and robustness. For describing the conformation of tightly folded oligosaccharides, a definition for characterization of ring planes in pyranoside chairs is proposed and applied to the analysis of the relation between the fucose and galactose residues in the epitopes, revealing the structural similarity between them.

Crowding by trisaccharides and the 2:1 cytochrome c-cytochrome c peroxidase complex

Proteins are designed to function under crowded conditions where the solute concentration can reach 400 g/L, but they are almost always studied in dilute solutions. To address this discrepancy, we have undertaken a series of studies to determine the effects of high solute concentrations on the thermodynamics of protein equilibria. Recently, we used isothermal titration calorimetry (ITC) to show that high concentrations of mono-, di-, and tetrasaccharides have a small stabilizing effect on the crystallographically defined cytochrome c binding site on yeast ferricytochrome c peroxidase [Morar, A. S., Wang, X., and Pielak, G. J. (2001) Biochemistry 40, 281-285]. Here, we use this technique to show that trisaccharides increase the apparent thermodynamic binding constants for both cytochrome c binding sites on the peroxidase. Mutagenesis studies confirm that the second site includes Asp 148 on the peroxidase. Binding of both cytochrome c molecules is exothermic. The data are interpreted by assuming either the presence or absence of intersite interactions.

Synthesis of alpha-lactosyl-(1-->3)-L-glycero-alpha-D-manno-heptopyranoside, a partial oligosaccharide structure expressed within the lipooligosaccharide produced by Neisseria gonorrhoeae strain 15253

The glycosyl donor, hepta-O-benzyl-beta-lactosyl trichloroacetimidate (4) was prepared by treating hepta-O-benzyl-lactose with trichloroacetonitrile in the presence of potassium carbonate. The acceptor, methyl 2-O-benzyl-4,6-O-benzylidene-7,8-dideoxy-alpha-D-manno-oct-7-enopyranoside (8) was synthesized by hydrolysis of a 3,4-butane diacetal of methyl L-glycero-alpha-D-manno-oct-enopyranoside and subsequent benzylidenation. Glycosidation of the donor 4 with the acceptor 8 in 1,4-dioxane using Me(3)SiOTf as a promoter for 1 h at room temperature gave methyl (2,3,4,6-tetra-O-benzyl-beta-D-galactopyranosyl)-(1-->4)-(2,3,6-tri-O-benzyl-alpha-D-glucopyranosyl)-(1-->3)-2-O-benzyl-4,6-O-benzylidene-7,8-dideoxy-alpha-D-manno-oct-7-enopyranoside (9) as a major product (59%). The oct-enopyranoside moiety of the trisaccharide 9 was converted to a heptopyranoside (80%) by oxidative cleavage with OsO(4)-NaIO(4) and subsequent reduction. Hydrogenolysis of the resulting trisaccharide and subsequent acetylation gave the peracetate of alpha-lactosyl-(1-->3)-Hep. Deacetylation of the peracetate afforded the title trisaccharide.

Comparison of radioiodinated TOC, TOCA and Mtr-TOCA: the effect of carbohydration on the pharmacokinetics

Although somatostatin-based peptide receptor imaging (sst-PRI) and peptide receptor radiotherapy (sst-PRRT) of human endocrine tumours and their metastases has become a valuable method, the experience with radiohalogenated sst-directed peptides has so far been disappointing. To extend the broad spectrum of radiohalogens with suitable radionuclide properties for sst-PRI and PRRT, new strategies in ligand development are required. The major drawbacks to be overcome include fast hepatic uptake, high abdominal background activity and low tumour uptake. Recently we introduced radiolabelled glycated octreotides as a new series of sst-binding radiotracers with excellent physicochemical characteristics. In this study we compared [(125)I]Tyr(3)-octreotide ([(125)I]TOC, ( 1)), [(125)I]Tyr(3)-octreotate ([(125)I]TOCA, ( 2)) and a carbohydrated octreotide derivative, maltotriose-[(125)I]Tyr(3)-octreotate ([(125)I]Mtr-TOCA, ( 3)) to evaluate the effect of single C-terminal oxidation and simultaneous N-terminal carbohydration. The biodistribution was compared in nude mice bearing AR42J tumour xenografts. Compared with ( 1), activity uptake of ( 2) and ( 3) at 1 h was decreased in intestine [36% ( 2), 72% ( 3)], liver [62% ( 2), 79% ( 3)] and kidney [34% ( 2), 41% ( 3)], respectively. Blood clearance was fast for all compounds investigated. Using ( 1) as reference, tumour uptake of ( 2) and ( 3) was 3.8- and 4.3-fold higher at 1 h p.i. At 1 h the tumour-to-blood ratio of ( 3) was 28.2+/-7.3, and the tumour-to-muscle ratio, 147+/-48. Specificity of tumour uptake was demonstrated in AR42J tumour-bearing mice by pretreatment with 0.8 mg TOC/kg 5 min prior to injection of ( 3). In cells transfected with sst1-sst5, the binding profile of I-Mtr-TOCA revealed a very high affinity and selectivity for sst2. In a first scintigraphic [(123)I]Mtr-TOCA study of a patient with a carcinoid of the small intestine with known peritoneal carcinomatosis and a solitary liver metastasis, all tumour tissues, including the liver metastasis, were well defined and clearly visible as soon as 30 min p.i. Based on these encouraging findings we conclude that carbohydration is a powerful strategy for the development of new radiolabelled sst-binding peptides and may represent a general method to improve pharmacokinetics of other peptide radioligands. [(123)I]Mtr-TOCA is a very promising new candidate for sst-directed PRI.

Involvement of water in carbohydrate-protein binding

The interactions of trimannosides 1 and 2 with Con A were studied to reveal the effects of displacement of well-ordered water molecules on the thermodynamic parameters of protein-ligand complexation. Trisaccharide 2 is a derivative of 1, in which the hydroxyl at C-2 of the central mannose unit is replaced by a hydroxyethyl moiety. Upon binding, this moiety displaces a conserved water molecule present in the Con A binding site. Structural studies by NMR spectroscopy and MD simulations showed that the two compounds have very similar solution conformational properties. MD simulations of the complexes of Con A with 1 and 2 demonstrated that the hydroxyethyl side chain of 2 can establish the same hydrogen bonds in a low energy conformation with the protein binding site as those mediated by the water molecule in the complex of 1 with Con A. Isothermal titration microcalorimetry (ITC) measurements showed that 2 has a more favorable entropy of binding compared to 1. This term, which was expected, arises from the return of the highly ordered water molecule to bulk solution. The favorable entropy term was, however, offset by a relatively large unfavorable enthalpy term. This observation was rationalized by comparing the extent of hydrogen bond and solvation changes during binding. It is proposed that an indirect interaction through a water molecule will provide a larger number of hydrogen bonds in the complex that have higher occupancies than in bulk solution, thereby stabilizing the complex.

The first polymer-assisted solution-phase synthesis of deoxyglycosides

[reaction--see text] A glycosylation protocol for the synthesis of 2-deoxyglycosides has been developed which is based on the use of polymer-bound reagents. Glycals are transformed into 2-iodoglycosyl acetates using polymer-bound bis(acetoxy)iodate(I) complex (1). Activation of the anomeric center is achieved by employing polymer-bound silyl triflate (2). In the presence of different glycosyl acceptors, 2-deoxy-2-iodoglycosides are generated in very good yields. Furthermore, it is shown that this method can be embedded in multistep sequences toward glycosylated testosterone and rhodinosyl-olivosyl-olivoside.

Carbohydrates and derivatives as potential drug candidates with emphasis on the selectin and linear-B area

Enzymatic carbohydrate synthesis using glycosyltransferases is highly regio- and stereospecific and does not require extensive protecting group designs. Naturally occurring carbohydrates have been prepared by this biomimetic pathway successfully. As more and more transferases are isolated and get cloned and overexpressed, non-natural substrates were probed with these biocatalysts. Key-polar groups and non-essential residues of the substrates have been determined. Consequently, this technique was employed to generate natural and non-natural carbohydrate libraries for pharmaceutical purposes. The synthesis of sialyl-Lewis(a)- and sialyl-Lewis(x) libraries and non-natural Linear-B derivatives applying glycosyltransferases is presented in this article. The respective transferases investigated are alpha(1-3)galactosyltransferase, beta(1-3)galactosyltransferase, beta(1-4)galactosyltransferase, alpha(2-3)sialyltransferase, alpha(1- 3)fucosyltransferase III and alpha(1-3)fucosyltransferase VI. With respect to the natural acceptors, the aglycon part and the N-acetyl group of the glucosamide have been varied. All enzymes tolerate an unexpected wide range of non-natural acceptors, which is not yet exploited in its full scale. In addition, fucosyltransferase III and VI can be employed to convert also non-natural donors with non-natural acceptors at the same time. Thus sialyl- Lewis(a)- and sialyl-Lewis(x)-libraries which differ in three positions compared to the natural tetrasaccharides are generated very efficiently. Also a library of linear-B trisaccharides, a reactive xenoantigen, has been prepared enzymatically. The aglycon part and the natural N-acetyl group of the glucosamine which is part of the acceptor substrate have been altered widely. This convenient methodology is compared with the evolving solid-phase carbohydrate synthesis using conventional chemistry. The potential use of transferases in solid-phase carbohydrate chemistry is discussed together with the possibility to use these biocatalysts to synthesize carbohydrate mimetics. The presented findings may also be useful to design potential glycosyltransferase inhibitors.

Four novel withanolide-type steroids from the leaves of Solanum cilistum

Four novel withanolide-type steroids named cilistols p, pm, p1 and u (1-4, respectively), were isolated from the leaves of Solanum cilistum. The respective structures were characterized by spectroscopic means as follows: cilistol p (1) was (22R,24R,25R,26S)-1-oxo-22,26-epoxy-3alpha,5alpha-cycloergostane-6beta,17alpha, 24,25,26-pentaol 26-O-beta-D-glucopyranoside, cilistol pm (2) corresponded to the 6-O-methyl ether derivative of 1; cilistol p1 (3) was represented as the 24-O-methyl ether of 1, and cilistol u (4) was shown to be the epoxide between C-24 and -25, presumably bearing cilistols p, pm and p1 by ring-opening.

Structural basis for the substrate specificity of the feruloyl esterase domain of the cellulosomal xylanase Z from Clostridium thermocellum

Feruloyl esterases function in the cleavage of ferulic acid's bonds to arabinoxylan and pectin where the ferulic acid moieties cross-link the layers of polysaccharide chains within hemicellulose. This work presents the crystal structure of FAE_XynZ, the domain of Clostridium thermocellum's cellulosomal xylanase Z that displays feruloyl esterase activity. The structure was obtained via multiple isomorphous replacement with anomalous scattering (MIRAS) using three heavy atom derivatives and refined against X-ray diffraction data of up to 1.75 A resolution. The R-value of the final model was 0.187 (R(free) = 0.21). FAE_XynZ displays an eight-stranded alpha/beta-fold with the characteristic "catalytic triad" at the heart of the active site. To define the substrate specificity determinants of the enzyme, the crystal structures of FAE_XynZ and the inactive FAE_XynZ(S172A) mutant were determined in complexes with the feruloyl-arabinoxylans FAXX and FAX(3), respectively. In the complex crystals, the ferulic acid moieties are clearly recognizable and allowed identification of the hydrophobic binding pocket. The carbohydrate part of both substrates is not visible in either structure. The location of the putative carbohydrate binding-pocket was inferred based on the location and orientation of the adjacent ferulic acid molecule. Five of the six residues lining the pocket were found to be conserved in FAE A from Orpinomyces sp., which further supports the proposed role of these amino acids.

A monoclonal antibody recognizing the 3-deoxy-D-manno-oct-2-ulosonic acid (Kdo) trisaccharide alphaKdo(2-->4)alphaKdo(2-->4)alphaKdo of Chlamydophila psittaci 6BC lipopolysaccharide

A monoclonal antibody (mAb) S45-18 was generated against a synthetic neoglycoconjugate containing the trisaccharide alphaKdo(2-->4)alphaKdo(2-->4)alphaKdo (Kdo, 3-deoxy-D-manno-oct-2-ulopyranosonic acid) which represents a structure of the lipopolysaccharide (LPS) from Chlamydophila psittaci 6BC. The antibody was characterized by binding and inhibition assays in ELISA using: (i) the immunizing antigen and chemically synthesized derivatives thereof; (ii) chlamydial elementary bodies (EB); and (iii) LPS of Chl. psittaci 6BC and Chlamydia trachomatis L2. The specificity was determined in comparison to that of mAb S25-23 recognizing the alphaKdo(2-->8)alphaKdo(2-->4)alphaKdo trisaccharide which represents an epitope shared by all species of the family. MAb S45-18 bound to an epitope of the structure alphaKdo(2-->4)alphaKdo(2-->4)alphaKdo, with lower reactivity with the (2-->8)-(2-->4)-linked analog. Using chlamydial EB or LPS, mAb S45-18 bound preferentially to LPS and EB of Chl. psittaci. Therefore, Chl. psittaci LPS contains, in addition to the known genus-specific epitope, a species-specific epitope.

Oligosaccharide synthesis with glycosyl phosphate and dithiophosphate triesters as glycosylating agents

Described is an efficient one-pot synthesis of alpha- and beta-glycosyl phosphate and dithiophosphate triesters from glycals via 1,2-anhydrosugars. Glycosyl phosphates function as versatile glycosylating agents for the synthesis of beta-glucosidic, beta-galactosidic, alpha-fucosidic, alpha-mannosidic, beta-glucuronic acid, and beta-glucosamine linkages upon activation with trimethylsilyl trifluoromethanesulfonate (TMSOTf). In addition to serving as efficient donors for O-glycosylations, glycosyl phosphates are effective in the preparation of S-glycosides and C-glycosides. Furthermore, the acid-catalyzed coupling of glycosyl phosphates with silylated acceptors is also discussed. Glycosyl dithiophosphates are synthesized and are also used as glycosyl donors. This alternate method offers compatibility with acceptors containing glycals to form beta-glycosides. To minimize protecting group manipulations, orthogonal and regioselective glycosylation strategies with glycosyl phosphates are reported. An orthogonal glycosylation method involving the activation of a glycosyl phosphate donor in the presence of a thioglycoside acceptor is described, as is an acceptor-mediated regioselective glycosylation strategy. Additionally, a unique glycosylation strategy exploiting the difference in reactivity of alpha- and beta-glycosyl phosphates is disclosed. The procedures outlined here provide the basis for the assembly of complex oligosaccharides in solution and by automated solid-phase synthesis with glycosyl phosphate building blocks exclusively or in concert with other donors.

Thermal decomposition of a gaseous multiprotein complex studied by blackbody infrared radiative dissociation. Investigating the origin of the asymmetric dissociation behavior

The blackbody infrared radiative dissociation technique was used to study the thermal decomposition of the gaseous B5 pentamer of the Shiga-like toxin I and its complexes with the Pk trisaccharide and a decavalent Pk-based oligosaccharide ligand (STARFISH, S). Dissociation of the protonated pentamer, (B5 + nH)n+ triple bond B5n+ where n = 11-14, proceeds almost exclusively by the loss of a single subunit (B) with a disproportionately large fraction (30-50%) of the parent ion charge. The degree of charge enrichment of the leaving subunit increases with increasing parent ion charge state. For n = 12-14, a distribution of product ion charge states is observed. The yields of the complementary pairs of product ions are sensitive to the reaction temperature, with higher temperatures favoring greater charge enrichment of the leaving subunit for +13 and +14, and the opposite effect for +12. These results indicate that some of the protons are rapidly exchanged between subunits in the gas phase. Dissociation of B5(14+) x S proceeds exclusively by the loss of one subunit, although the ligand increases the stability of the complex and also reduces the degree of charge enrichment in the ejected monomer. For B5(12+)(Pk)1-3, the loss of neutral Pk competes with loss of a subunit at low temperatures. Linear Arrhenius plots were obtained from the temperature-dependent dissociation rate constants measured for the loss of B from B5n+ and B514+ x S. The magnitude of the Arrhenius parameters is highly dependent on the charge state of the pentamer: Ea = 35 kcal/mol and A = 1,019 s(-1) (+14), 46 kcal/mol and 1,023 S(-1) (+13), 50 kcal/mol and 1026 s(-1) (+12), and 80 kcal/mol and 10(39) (+11). The Ea and A for B5(14+) x S are 59 kcal/mol and 10(30) s(-1), respectively. The reaction pathways leading to greater charge enrichment of the subunit lost from the B5(14+) and B5(13+) ions correspond to higher energy processes, however, these pathways are kinetically preferred at higher temperatures due to their large A factors. A simple electrostatic model, whereby charge enrichment leads to Coulombic repulsion-induced denaturation of the subunits and disruption of the intersubunit interactions, provides an explanation for the magnitude of the Arrhenius parameters and the origin of the asymmetric dissociation behavior of the complexes.

The trimannosyl cores of N-glycans are important for the procoagulant protease-inhibitory activity of urinary protein C inhibitor

We investigated the relationship between the procoagulant protease-inhibitory activity and the N-glycan structures in urinary protein C inhibitor (uPCI) by sequential exoglycosidase digestions based on the N-glycan structures elucidated in this report. uPCI was glycosylated on the three potential N-glycosylation sites, asparagines 230, 243 and 319 (N230, N243 and N319) in the molecule and had four biantennary complex type sugar chains. The inhibitory activities of uPCI toward thrombin and plasma kallikrein were little changed by the sequential removal of N-acetylneuraminic acid and galactose residues from the termini and N-acetylglucosamine residues from the branches of the N-glycans. However, the inhibitory activities were markedly decreased by further removing alpha-mannose residues from the trimannosyl cores of the N-glycans. These results suggest that the trimannosyl cores of N-glycans are important for uPCI to inhibit the procoagulant protease.