Characterization of the elongating alpha-D-mannosyl phosphate transferase from three species of Leishmania using synthetic acceptor substrate analogues

Leishmania express lipophosphoglycans and proteophosphoglycans that contain Galbeta1-4Manalpha1-P phosphosaccharide repeat structures assembled by the sequential addition of Manalpha1-P and betaGal. The synthetic acceptor substrate Galbeta1-4Manalpha1-P-decenyl and a series of analogues were used to probe Leishmania alpha-D-mannosyl phosphate transferase activity. We show that the activity detected with Galbeta1-4Manalpha1-P-decenyl is the elongating alpha-D-mannosyl phosphate transferase associated with lipophosphoglycan biosynthesis (eMPT(LPG)). Differences in the apparent K(m) values for the donor and acceptor substrates were found using L. major, L. mexicana, and L. donovani promastigote membranes, but total activity correlated with the number of lipophosphoglycan repeats. Further comparisons showed that lesion-derived L. mexicana amastigotes, that do not express lipophosphoglycan, lack eMPT(LPG) and that nondividing L. major metacyclic promastigotes contain 5-fold less eMPT(LPG) activity than dividing procyclic promastigotes. The fine specificity of promastigote eMPT(LPG) activity was determined using 24 synthetic analogues of Galbeta1-4Manalpha1-P-decenyl. The three species gave similar results: the negative charge of the phosphodiester and the C-6 hydroxyl of the alphaMan residue are essential for substrate recognition, the latter most likely acting as a hydrogen bond acceptor. The C-6' hydroxyl of the betaGal residue is required for substrate recognition as well as for catalysis. The rate of Manalpha1-P transfer declines with increasing acceptor substrate chain length. The presence of a monosaccharide substituent at the C-3 position of the terminal betaGal residue abrogates Man-P transfer, showing that chain elongation must precede side chain modification during lipophosphoglycan biosynthesis. In contrast, substitution of the penultimate phosphosaccharide repeat does not abrogate transfer but is slightly stimulatory in L. mexicana and inhibitory in L. major.

Stereocontrolled synthesis of lankanolide from 1,6-anhydro-beta-D-glucopyranose (levoglucosan): 1, synthesis of the C-1/7 and C-8/15 segments

A scheme has been designed for the stereocontrolled synthesis of lankanolide, the aglycon of lankamycin. Synthesis of its C-1/7 and C-8/15 segments has been accomplished starting from 1,6-anhydro-2,4-dideoxy-2,4-di-C-methyl-beta-D-glucopyranose.

An efficient and stereoselective synthesis of beta-D-Arap-(1-->2)-beta-D-Galp-(1-->3)-beta-D-Galp-(1-->4)-alpha-D-Manp, a tetrasaccharide fragment of Leishmania major lipophosphoglycan

A tetrasaccharide fragment of Leishmania major lipophosphoglycan (which seems to be involved in a biological mechanism for the parasite transmission) has been synthesised using the thioglycoside, trichloroacetimidate and halide-exchange glycosylation procedures and step-wise chain elongation strategy.

Analysis of close proximity quenching of phosphorescent metalloporphyrin labels in oligonucleotide structures

Quenching of phosphorescent platinum(II) and palladium(II) coproporphyrin (MeCP) labelled oligonucleotides was investigated. Strong hybridization-specific quenching was observed in duplex DNA structures with a variety of quenchers and with two identical porphyrin labels when in close proximity. Classical resonance energy transfer mechanism was ruled out, since quenching did not correlate with spectral overlaps and lifetime changes were insignificant. Quenching of MeCP by the free quenchers in solution revealed that porphyrin-porphyrin quenching is predominantly static while other dyes quench dynamically. The results suggest that the quenching in DNA duplex proceeds via direct contact.

Carbohydrate Specificity and Isotypes of Monoclonal and Polyclonal Antibodies to Conjugated Tetrasaccharide, a Synthetic Analogue of Repeating Unit of Capsular Polysaccharide of Streptococcus Pneumoniae Serotype 14

We studied carbohydrate specificity and isotypes of antibodies to BSA-conjugated tetrasaccharide, a repeating unit of the capsular polysaccharide of Streptococcus pneumoniae serotype 14, in mouse polyclonal sera and hybridoma-synthesized products. Natural IgM antibodies to the tetrasaccharide containing epitopes similar to surface carbohydrate structures of mammalian and human cells in low titers were determined in native mouse serum by ELISA using biotinylated tetrasaccharide and synthetic capsular polysaccharide as the solid-phase antigens. Polyclonal sera to the conjugated tetrasaccharide contained IgM and all subclasses of IgG antibodies, which were detected in a higher titer when the biotinylated tetrasaccharide was used as a solid phase antigen compared to synthetic capsular polysaccharide. Monoclonal antibodies to S. pneumoniae serotype 14 tetrasaccharide were identified in an equivalent titer using either biotinylated tetrasaccharide or synthetic capsular polysaccharide. Monoclonal antibodies obtained in vitro belonged to IgM isotype and cross-reacted with secondary full-size IgG antibodies. In the serum of mice inoculated with hybridoma, IgM and IgG2a antibodies recognizing the tetrasaccharide epitope in the structure of synthetic capsular polysaccharide were simultaneously determined.

SYNTHETIC CONJUGATED ANALOGUES OF CAPSULE POLYSACCHARIDES OF PNEUMOCOCCUS - AN INSTRUMENT FOR DETECTION OF POST-VACCINATION ANTIBODIES

Aim. Evaluation of the ability of capsule polysaccharides (CP) of Streptococcus pneumoniae serotype 3 and 14 and their synthetic structure analogues, conjugated with bovine serum albumin (BSA), to detect antibodies in post-vaccination sera of mice. Materials and methods. Oligosaccharides corresponding to one, one and a half and two repeating links of serotype 3 and 14 S. pneumoniae CP were synthesized, their conjugates with BSA were produced by squarate method as well. Ligand content per BSA molecule was controlled by MALDI-TOF spectrometry. Immune sera were obtained after 2 intraperi-toneal administrations to mice of glucoconjugates adsorbed on aluminum hydroxide or 13-valent pneumococcal conjugated vaccine. Determination of levels of post-vaccination class G antibodies and their sub-isotypes was carried out in EIA. Results. Immunization of mice with neoglucoconjugates resulted in formation of predominantly IgGl recognizing serotype 3 and 14 S. pneumoniae CP. IgGl in mice immunized with a 13-valent conjugated vaccine recognized serotype 3 S. pneumoniae CP, but detected serotype 14 S. pneumoniae CP weakly. All the conjugated synthetic oligosaccharides were characterized by a high ability to bind antibodies in blood of mice immunized with the polysaccharide conjugated vaccine. BSA-tetrasaccharide of serotype 3 S. pneumoniae and BSA-tetrasaccharide of serotype 14 S. pneumoniae were characterized by the highest ability to detect IgG 1 against CP. Conclusion. Synthetic oligosaccharides, conjugated with BSA protein-carrier, may be used to develop diagnostic test-systems for determination of antibodies in post-vaccination sera.

[SYNTHETIC CONJUGATED ANALOGUES OF CAPSULE POLYSACCHARIDES OF PNEUMOCOCCUS - AN INSTRUMENT FOR DETECTION OF POST-VACCINATION ANTIBODIES]

AIM

Evaluation ofthe ability of capsule polysaccharides (CP) of Streptococcus pneumoniae serotype 3 and 14 and their synthetic structure analogues, conjugated with bovine serum albumin (BSA), to detect antibodies in post-vaccination sera of mice. Materials andmethods. Oligosaccharides correspond- ing to one, one and a half and two repeating links of serotype 3 and 14 S. pneumoniae CP were synthe- sized, their conjugates with BSA were produced by squarate method as well. Ligand content-per BSA molecule was controlled by MALDI-TOF spectrometry. Immune sera were obtained after 2 intraperi- toneal administrations to mice of glucoconjugates adsorbed on aluminum hydroxide or 13-valent pneumococcal conjugated vaccine. Determination of levels of post-vaccination class G antibodies and their sub-isotypes was carried out in EIA.

RESULTS

Immunization of mice with neoglucoconjugates resulted in formation of predominantly IgGl recognizing serotype 3 and 14 S. pneumoniae C. IgG1 in mice immunized with a 13-valent conjugated vaccine recognized serotype 3 S. pneumoniae CP, but detected serotype 14 S. pneumoniae CP weakly. All the conjugated synthetic oligosaccharides were characterized by a high ability to bind antibodies in blood of mice immunized with the polysaccharide conjugated vaccine. BSA-tetrasaccharide of serotype 3 S. pneumoniae and BSA-tetrasaccharide of serotype 14 S.pneumoniae were characterized by the highest ability to detect IgG1 against C.

CONCLUSION

Synthetic oligosaccharides, conjugated with BSA protein-carrier, may be used to develop diagnostic test-systems for determination of antibodies in post-vaccination sera.

Synthesis of biotinylated pentasaccharide structurally related to a fragment of glucomannan from Candida utilis

The polysaccharide mannan is the main surface antigen of the cell wall of Candida fungi, playing an important role in the pathogenesis of diseases caused by these mycopathogens. Mannan has a complex, comb-like structure and includes a variety of structural units, with their combination varying depending on the Candida species and strain. Glucomannan, a polysaccharide from Candida utilis, contains terminal α-d-glucose residues attached to oligomannoside side chains. This paper describes the first synthesis of a pentasaccharide structurally related to C. utilis glucomannan fragment, which is an α-(1→2)-linked tetramannoside terminated at the non-reducing end by an α-d-glucopyranosyl residue. The pentasaccharide was obtained as a 3-aminopropyl glycoside, which made it possible to synthesize also its biotinylated derivative, suitable for various glycobiological studies. The most complicated step in the pentasaccharide synthesis was stereoselective 1,2-cis-glycosylation to attach the α-d-glucopyranosyl residue. This was accomplished using a glucosyl donor specially developed in our laboratory, the protecting groups of which provide the necessary α-stereoselectivity. The target biotinylated pentasaccharide thus obtained will be used in the future as a model antigen for the detection of immunodeterminant epitopes of Candida mannans.

[EPITOPIC SPECIFICITY OF A SYNTHETIC DISACCHARIDE, RECURRING LINK OF CAPSULE POLYSACCHARIDE CHAIN OF SEROTYPE 3 STREPTOCCUS PNEUMONIAE]

AIM

Study epitopic specificity of synthetic disaccharide, recurring link of serotype 3 S. pneumoniae, conjugated with bovine serum albumin (BSA).

MATERIALS AND METHODS

Conjugate of the synthetic disaccharide with BSA was obtained by squarate method. Antigenic activity of the conjugate was studied in competitive EIA. Titers of IgG against capsule polysaccharide of serotype 3 S. pneumoniae were determined in EIA by using sera of mice immunized twice with disaccharide conjugate sorbed onto aluminum hydroxide.

RESULTS

Disaccharide conjugate used as a well-covering antigen (4 µg/well) in EIA was characterized by a high degree of specificity and interacted only with IgG against serotype 3 S. pneumoniae in antimicrobial sera of animals without reacting with antibodies (ABs) against other pneumococcus serotypes (6B, 10A, 19A, 19F, 23F). Disaccharide conjugated with BSA was determined in competitive EIA to inhibit bonding of ABs to disaccharide by 78.8%, bacterial capsule polysaccharide by 56.9%, BSA did not inhibit the sera activity. The study of sera of mice immunized by serotype 3 S. pneumoniae disaccharide conjugate in EIA, where capsule polysaccharide was used as a plate-sorbed antigen, has established the presence of IgG against capsule polysaccharide at a titer of 1:1600.

CONCLUSION

The disaccharide that is a single recurring link of serotype 3 S. pneumoniae contains a key epitope of capsule polysaccharide. The synthetic disaccharide could be used as a component of multivalent conjugated pneumococcal vaccines and for development of diagnostic test-systems.