Occurrence of antibodies against chlamydial lipopolysaccharide in human sera as measured by ELISA using an artificial glycoconjugate antigen

An artificial glycoconjugate containing, as a ligand, the deacylated carbohydrate backbone of a recombinant Chlamydia-specific lipopolysaccharide was used as a solid-phase antigen in ELISA to measure antibodies against chlamydial LPS. The specificity and reproducibility of the assay was shown by using a panel of prototype monoclonal antibodies representing the spectrum of antibodies also occurring in patient sera. These mAbs recognized Chlamydia-specific epitopes [alpha 2-->8-linked disaccharide of 3-deoxy-D-manno-octulosonic acid (Kdo) or the trisaccharide alpha Kdo-(2-->8)-alpha Kdo-(2-->4)-alpha Kdo] or those shared between chlamydial and Re-type LPS (alpha Kdo, alpha 2-->4-linked Kdo disaccharide). The assay was used to measure IgG, IgA and IgM antibodies against chlamydial LPS in patients with genital or respiratory tract infections. In comparison to the results obtained with sera from blood donors, it became evident that both types of infection result in significant changes in the profile of LPS antibodies.

Specificity of rabbit antisera against the rough lipopolysaccharide of Salmonella minnesota R4 (chemotype Rd2P-)

Rabbit polyclonal antibodies against the rough mutant lipopolysaccharide (LPS) of Salmonella minnesota R4 (chemotype Rd2P-) were serologically characterized by using R4 LPS, deacylated LPS, dephosphorylated LPS, and synthetic partial structures, including compounds comprising the core region of Rd2P- LPS bound to the beta 1-->6-linked glucosamine disaccharide with two amide-linked 3-hydroxytetradecanoic acid residues or coupled to bovine serum albumin. By using a passive hemolysis assay and an enzyme immunoassay and absorption and inhibition experiments, the antibody specificities present could be determined. One group of antibodies required components of the core oligosaccharide (with or without the side chain 3-deoxy-D-manno-octulosonic acid [Kdo]) and the phosphorylated glucosamine disaccharide of the lipid A moiety for binding. The phosphate-independent antibodies were directed against the core oligosaccharide, recognizing an epitope consisting of one terminal heptose linked to Kdo or to the reducing moiety of the alpha 2-->4-linked Kdo disaccharide. Antibodies requiring the presence of acyl residues and those reacting with a single heptose or Kdo residue were not detected.

Synthesis of glycoconjugates by covalent coupling of O-glycopyranosyl-N-hydroxysuccinimide derivatives of lactose to proteins and lipids and polymerization of their parent acryloyl derivatives into acrylamide polymers

Glycosides of N-hydroxysuccinimide have been synthesized and the succinimide moieties have been opened by amines to give glycolipids or spacer-glycosides. The latter have been coupled to proteins and, after acryloylation, copolymerized into acrylamide polymers. A 13C-NMR study of the stability of the anomeric O-N-C(O) linkage showed the linkage to be stable under conditions used in most biological experiments.

A method for glycoconjugate synthesis

7-Formylheptyl glycosides of 2-acetamido-2-deoxy-beta-D-glucopyranose and O-alpha-L-rhamnopyranosyl-(1-->3)-O-alpha-L-rhamnopyranose were synthesized and were coupled by reductive amination to bovine serum albumin and aminopropyl glass, respectively.

Synthesis of polymeric neoglycoconjugates based on N-substituted polyacrylamides

Several types of polymeric glycoconjugates, N-substituted polyacrylamides, have been synthesized by the reaction of activated polymers with omega-aminoalkylglycosides: (i) (carbohydrate-spacer)n-polyacrylamide, 'pseudopolysaccharides'; (ii) (carbohydrate-spacer)n-phosphatidylethanolaminem-polyacrylamide, neoglycolipids, derivatives of phosphatidylethanolamine; (iii) (carbohydrate-spacer)n-biotin-polyacrylamide, biotinylated probes; (iv) (carbohydrate-spacer)n-polyacrylamide-(macroporous glass), affinity sorbents based on macroporous glass, covalently coated with polyacrylamide. An almost quantitative yield in the conjunction reaction makes it possible to insert in the conjugate a predetermined quantity of the ligand(s). Pseudopolysaccharides proved to be a suitable form of antigen for activation of polystyrene and poly(vinyl chloride) plates (ELISA) and nitrocellulose membranes (dot blot), being advantageous over traditional neoglycoproteins. Polyvalent glycolipids insert well in biological membranes: their physical properties, particularly solubility, can be changed in a desired direction. Biotinylated derivatives were used as probes for detection and analysis of lectins.

1-N-glycyl beta-oligosaccharide derivatives as stable intermediates for the formation of glycoconjugate probes

Incubation of reducing sugars in ammonium bicarbonate was found to be a simple procedure for the formation of beta-D-glycosylamines of purified complex oligosaccharides in 70-80% yield. These provide valuable intermediates for the synthesis of a wide range of oligosaccharide probes and derivatives by acylation of the 1-amino function. The 1-amino function showed different rates of reactivity with different reagents. In general, interactions with large ring systems such as the fluorophores dansyl chloride and carboxyfluorescein gave 10-20% yields of products, which consisted of mixtures of both anomeric forms, whereas smaller acylating reagents gave near-quantitative yields of the desired beta-D-derivatives. Steric effects may explain differences in reactivity. N-Chloroacetamido derivatives could be obtained in high yield with retention of the beta-anomeric configuration. Subsequent ammonolysis of the chloroacetamido function afforded the corresponding N-glycyl beta-derivatives. The linker thereby introduced retains the amino function, possesses the useful properties of fixed anomeric configuration, improved stability, and uniform reactivity with a variety of reagents, and is structurally analogous to an asparagine side chain. The potential therefore exists for the generation of oligosaccharide derivatives tailored for different applications.

Glycopeptidolipids--a new class of artificial antigens with carbohydrate determinants. Synthesis of artificial antigen with type-specific oligosaccharide hapten from Neisseria meningitidis group B

Synthetic lipopeptide N-palmitoyltyrosyl-seryl-seryl-asparaginyl-alanine, an analogue of B-mitogenic tripalmitoyl-pentapeptide from Escherichia coli lipoprotein, was coupled with an oligosaccharide hapten from Neisseria meningitidis lipooligosaccharide to give a glycopeptidolipid conjugate--the artificial antigen of a new type processing the type-specific microbial determinant.

2-(Trimethylsilyl)ethyl glycosides. Synthesis of the asialo-GM1-tetrasaccharide, spacer glycoside, and BSA and Sepharose glycoconjugates

The tri and tetra-saccharide glycosides beta-D-GalNAc-(1-4)-beta-D-Gal-(1-4)-beta-D-Glc-1-OTMSEt and beta-D-Gal-(1-3)-beta-D-GalNAc-(1-4)-beta-D-Gal-(1-4)-beta-D-Glc-1-OT MSEt (asialo-GM1) have been synthesized by sequential glycosylations of a suitably protected 2-(trimethylsilyl)ethyl (TMSEt) lactoside with 3,4,6-tri-O-acetyl-2-deoxy-2-phthalimido-beta-D-galactopyranosyl chloride and 2,3,4,6-tetra-O-acetyl-beta-D-galactopyranosyl bromide. The tetrasaccharide glycoside was transformed into the corresponding hemiacetal sugar as well as the 1-chloro sugar. The latter was used for glycosylation of 2-bromoethanol. The resulting glycoside was used to alkylate methyl 3-mercaptopropionate and the resulting spacer glycoside was used for the preparation of the title glycoconjugates.

A synthetic glycoconjugate representing the genus-specific epitope of chlamydial lipopolysaccharide exhibits the same specificity as its natural counterpart

The tetrasaccharide 3-deoxy-alpha-D-manno-2-octulosonic acid (alpha-KDO) (2----8)-alpha-KDO(2----4)-alpha-KDO(2----6)-beta GlcNAc, a partial structure of chlamydial lipopolysaccharide (LPS) representing a genus-specific epitope, was synthesized and covalently linked to bovine serum albumin, resulting in an artificial glycoconjugate antigen. Mice were immunized with the glycoconjugate to prepare chlamydia-specific monoclonal antibodies. They were selected with chlamydia-specific LPS antigens and the structurally and antigenically related Re-type LPS of a Salmonella minnesota rough mutant. Characterization of the selected antibodies was by (i) hemagglutination of sheep erythrocytes coated with recombinant chlamydia-specific LPS, (ii) inhibition by synthetic polyacrylamide derivatives containing the genus-specific epitope or partial structures thereof, (iii) enzyme immunoassay with recombinant LPS and synthetic bovine serum albumin glycoconjugates as solid-phase antigens, (iv) immunofluorescence of L929 monolayers infected with Chlamydia psittaci or C. trachomatis, and (v) Western immunoblots with glycoconjugates and LPS as the antigen. Two groups of monoclonal antibodies were obtained; the monoclonal antibodies in one group cross-reacted with chlamydial and Re-type LPS, but those of the other group were chlamydia specific. Among the latter, KDO trisaccharide-specific antibodies that had the same epitope specificity as antibodies obtained after immunization with chlamydial elementary bodies were identified; however, they exhibited a more than 100-fold higher affinity. In addition, antibodies that bound preferentially to the 2.8-linked KDO disaccharide were detected, although with lower affinity. The data show that the artificial glycoconjugate antigen is similar to its natural counterpart.

Synthesis of lysine-containing fragments of the Proteus mirabilis O27 O-specific polysaccharide and neoglycoconjugates therefrom

Amide-linked lysine mono- and di-uronic acid fragments of the O-specific polysaccharide from P. mirabilis O27 have been synthesised. N epsilon-Boc-L-lysine tert-butyl ester was condensed with 2-azidoethyl glycosides of glucuronic acid and beta-D-GlcpNAc-(1----3)-beta-D-GlcpA. Transformation of the products into 2-acrylamidoethyl glycosides, followed by deprotection using trifluoroacetic acid, gave the target monomers that were converted into high-molecular-weight copolymer-type neoglycoconjugates.

Glycoconjugates of opioid peptides. Synthesis and biological activity of [Leu5]enkephalin related glycoconjugates with amide type of linkage

Three N-glycoconjugates of the general formula H-Tyr-Gly-Gly-Phe-Leu-NH-R (R = carbohydrate residue) were synthesized in order to determine the influence of some carbohydrate molecules (6-amino-6-deoxy-D-glucopyranose, 2-amino-2-deoxy-D-glucopyranose, beta-D-glucopyranosylamine) on the biological activity, conformation, and stability of the opioid pentapeptide [Leu5]enkephalin. For the preparation of this compound different methods of peptide synthesis (active ester and mixed anhydride) were investigated. In comparison with [Leu5]enkephalin, all three N-glycoconjugates showed higher potency in the guinea pig ileum assay and lower potency in the mouse vas deferens assay, indicating a decrease in delta opioid receptor selectivity.

Synthesis of carbohydrate-amino acid conjugates related to the capsular antigen K54 from Escherichia coli O6:K54:H10 and artificial antigens therefrom

The disaccharides alpha-L-Rhap-(1----3)-beta-D-GlcpA and beta-D-GlcpA-(1----3)-alpha-L-Rhap bearing amide-linked L-serine or L-threonine, which represent the repeating unit(s) of the capsular polysaccharide from E. coli O6:K54:H10, have been synthesised. O-tert-Butyl-protected amino acid tert-butyl esters were condensed with the corresponding biouronic acid as the 2-acrylamidoethyl or 2-azidoethyl glycosides. The azido function was replaced by the acrylamido group by catalytic hydrogenation followed by N-acryloylation. The tert-butyl groups were removed by treatment with trifluoroacetic acid to give the target monomers which were copolymerised with acrylamide to give neoglycoconjugates that are potentially useful for immunochemical studies.

Synthesis of neoglycoconjugates using oligosaccharide transferring activity of ceramide glycanase

Ceramide glycanase (CGase) isolated from the leech Macrobdella decora was found to transfer the oligosaccharide en bloc from various glycosphingolipids to suitable acceptors. For example, CGase transferred the intact II3NeuAcGgOse4 from GM1 to 4-phenyl-1-butanol, 1,8-octanediol and various 1-alkanols having a chain length of six or more carbons. Among various 1-alkanols, 1-octanol was found to be the best acceptor. In an incubation mixture of 50 microliters containing 30 nmol of GM1, 50 micrograms of sodium cholate, 20 microliters of 1-octanol, and 0.1 unit of CGase, the ratio between hydrolysis and transglycosylation was approximately 3:1. Negative fast atom bombardment-mass spectral analysis of the enzymatically synthesized octyl-II3NeuAcGgOse4 showed a mass ion at m/z 1109.7 for the parent ion, consistent with its expected mass. NMR analysis of the enzymatically synthesized octyl-II3NeuAcGgOse4 showed that the Glc residue is linked to the octanol through a beta-linkage. Vicinal coupling constants of the ring protons of the sugar residues indicate that their pyranose ring geometries are not affected by the transferase activity. CGase also transferred the oligosaccharide from GM1 to CF3CO-NH(CH2)5CH2OH, (CH3)3CO-CO-NH(CH2)5CH2OH, (HOCH2)3C-NHCO-(CH2)4-COOMe, CH2 = CH-(CH2)7CH2OH and 1,2:3,4-di-O-isopropylidene-D-galactopyranose. The oligosaccharide transferring reaction carried out by CGase should become useful for the synthesis of neoglycoconjugates to study the biological functions expressed by glycan chains in glycosphingolipids.

Antibodies directed against the thiomannose moiety of a glycoconjugate of 2-imino-2-methoxyethyl 1-thio-alpha-D-mannopyranoside and bovine serum albumin

Anti-thiomannose antibodies were induced in rabbits immunized with a glycoconjugate of 2-imino-2-methoxyethyl 1-thio-alpha-D-mannopyranoside (Man-S) and bovine serum albumin (BSA). Also anti-BSA antibodies directed against the BSA moiety of the glycoconjugate were detected in low concentrations in the immune serum. However, antibodies against the combinatorial epitope of the hapten group and the carrier protein were not detected. The anti-thiomannose and the anti-BSA antibodies were isolated in pure forms by affinity chromatography on Sepharose 4B-bearing thiomannosyl-BSA ligands or BSA ligands. The anti-thiomannose antibodies constituted the major fraction of the antibodies, and these antibodies were isolated in pure form for the first time. The specificity of the thiomannose antibodies was established from data of experiments of periodate oxidation, perpropionic acid oxidation, hapten inhibition, and agar diffusion, Isoelectrofocusing showed that the anti-thiomannose antibody preparation consisted of at least six isomeric proteins, all of which exhibited antibody activity against the glycoconjugate of thiomannose and BSA.

Synthesis of glycoconjugates derived from various lipopolysaccharides of the Vibrionaceae family

Conjugation of simple ketoses (such as 3-deoxy-D-manno-2-octulosonic acid and N-acetylneuraminic acid) and of various O-specific polysaccharides (from Aeromonas hydrophila and Aeromonas salmonicida) to the bifunctional spacer 1,6-hexanediamine, was achieved by reductive amination. The saccharide--1-(6-amino)-hexane alkyamines obtained were converted into the corresponding isothiocyanate derivatives and coupled to the free epsilon-amino group of lysine residues of the protein carrier bovine serum albumin. In similar manner, the aldehyde group introduced by selective periodate oxidation into the partially O-deacylated lipopolysaccharide of Vibrio anguillarum was conjugated to 1,6-hexanediamine, converted into the corresponding isothiocyanate and covalently attached to bovine serum albumin.

Stereoselective O-glycosylation of trans-4-hydroxy-L-proline derivatives promoted by silver zeolite

Trans-4-hydroxy-L-proline has been converted to four imino- and carboxyl-blocked derivatives which are suitable for the synthesis of 4-O-glycosyl conjugates. Reaction of these derivatives with 2,3,5-tri-O-benzyl-alpha-L-arabinofuranosyl chloride in the presence of a silver zeolite promoter yielded the blocked beta-furanosyl amino-acid conjugates. Deprotection gave trans-4-(beta-L-arabinofuranosyloxy)-L-proline which was characterised as its crystalline isopropyl ester. 13C-NMR Data are presented for the compounds described.

The role of organic synthesis in glycoconjugate research: selected examples

Chemical synthesis of various oligosaccharides allowed the determination of structural requirements for specific interaction between heparin and anti-thrombin III. The synthesis of a sialylated tetrasaccharide, subunit of the human blood group Cad determinant, is also reported.