Fluorescence-Polarization-Based Assaying of Lysozyme with Chitooligosaccharide Tracers

Lysozyme is a well-known enzyme found in many biological fluids which plays an important role in the antibacterial protection of humans and animals. Lysozyme assays are used for the diagnosis of a number of diseases and utilized in immunohistochemistry, genetic and cellular engineering studies. The assaying methods are divided into two categories measuring either the concentration of lysozyme as a protein or its activity as an enzyme. While the first category of methods traditionally uses an enzyme-linked immunosorbent assay (ELISA), the methods for the determination of the enzymatic activity of lysozyme use either live bacteria, which is rather inconvenient, or natural peptidoglycans of high heterogeneity and variability, which leads to the low reproducibility of the assay results. In this work, we propose the use of a chemically synthesized substrate of a strictly defined structure to measure in a single experiment both the concentration of lysozyme as a protein and its enzymatic activity by means of the fluorescence polarization (FP) method. Chito-oligosaccharides of different chain lengths were fluorescently labeled and tested leading to the selection of the pentasaccharide as the optimal size tracer and the further optimization of the assay conditions for the accurate (detection limit 0.3 μM) and rapid (<30 min) determination of human lysozyme. The proposed protocol was applied to assay human lysozyme in tear samples and resulted in good correlation with the reference assay. The use of synthetic fluorescently labeled tracer, in contrast to natural peptidoglycan, in FP analysis allows for the development of a reproducible method for the determination of lysozyme activity.

Identification of a new DC-SIGN binding pentamannoside epitope within the complex structure of Candida albicans mannan

The dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN) is an innate immune C-type lectin receptor that recognizes carbohydrate-based pathogen associated with molecular patterns of various bacteria, fungi, viruses and protozoa. Although a range of highly mannosylated glycoproteins have been shown to induce signaling via DC-SIGN, precise structure of the recognized oligosaccharide epitope is still unclear. Using the array of oligosaccharides related to selected fragments of main fungal antigenic polysaccharides we revealed a highly specific pentamannoside ligand of DC-SIGN, consisting of α-(1 → 2)-linked mannose chains with one inner α-(1 → 3)-linked unit. This structural motif is present in Candida albicans cell wall mannan and corresponds to its antigenic factors 4 and 13b. This epitope is not ubiquitous in other yeast species and may account for the species-specific nature of fungal recognition via DC-SIGN. The discovered highly specific oligosaccharide ligands of DC-SIGN are tractable tools for interdisciplinary investigations of mechanisms of fungal innate immunity and anti-Candida defense. Ligand- and receptor-based NMR data demonstrated the pentasaccharide-to-DC-SIGN interaction in solution and enabled the deciphering of the interaction topology.

ASCA-related antibodies in the blood sera of healthy donors and patients with colorectal cancer: characterization with oligosaccharides related to Saccharomyces cerevisiae mannan

Mannans are polysaccharide antigens expressed on the cell wall of different fungal species including Saccharomyces cerevisiae and Candida spp. These fungi are components of the normal intestinal microflora, and the presence of antibodies to fungal antigens is known to reflect the features of the patient's immune system. Thus, titers of IgG and IgA antibodies against Saccharomyces cerevisiae mannan (ASCA) are markers for clinical diagnostics of inflammatory bowel diseases. The complex organization and heterogeneity of cell-wall mannans may reduce the quality and reproducibility of ELISA results due to interference by different antigenic epitopes. In this research, we analyzed the levels of IgG antibodies in the sera of healthy donors and patients with colorectal cancer using an array of synthetic oligosaccharides related to distinct fragments of fungal mannan. This study aimed to establish the influence of oligosaccharide structure on their antigenicity. Variations in the structure of the previously established ASCA epitope (changing type of linkage, chain length, and the presence of branches) significantly modified the ability of ligands to bind to circulating antibodies in blood sera. The study showed that surface presentation density of the ligand critically affects the results of enzyme immunoassay. The transition from natural coating antigens to their corresponding synthetic mimetics with a defined structure opens new opportunities for improving existing ELISA test systems, as well as developing diagnostic kits with new properties.

Stereocontrolled Synthesis and Conformational Analysis of a Series of Disaccharides α,β-d-GlcA-(1→3)-α-L-Fuc

D-Glucuronic acid is a fundamental building block of many biologically important polysaccharides, either in its non-substituted form or bearing a variety of substituents, among them sulfates. We have previously performed a study of the effects of exhaustive sulfation on the conformational behavior of β-gluronopyranosides. Herein, we report an investigation comparing α- and β-derivatives of this monosaccharide within the title disaccharides using NMR and quantum chemistry approaches. It was found that for α-linked disaccharides, the introduction of sulfates did not greatly affect their conformational behavior. However, for β-derivatives, considerable conformational changes were observed. In general, they resemble those that took place for the monosaccharides, except that NOESY experiments and calculations of intra-ring spin-spin coupling constants suggest the presence of a 1S5 conformer along with 3S1 in the fully sulfated disaccharide. During the synthesis of model compounds, hydrogen bond-mediated aglycone delivery was used as an α-directing stereocontrol approach in the glucuronidation reaction.

Synthesis of methylphosphorylated oligomannosides structurally related to lipopolysaccharide O-antigens of Klebsiella pneumoniae serotype O3 and their application for detection of specific antibodies in rabbit and human sera

Methylphosphorylated mono-, di- and trimannosides structurally related to the lipopolysaccharide (LPS) O-antigens of Klebsiella pneumoniae of serotype O3 were synthesized and conjugated with a biotin tag. The stereo- and regioselective assembly of target carbohydrate chains was conducted using uniform monosaccharide synthetic blocks. After that, a methylphosphate group was introduced by coupling with a methyl-H-phosphonate reagent followed by oxidation and deprotection to give the target oligosaccharides. The 1H and 13C NMR spectra of the obtained compounds showed a good fit with the spectrum of the corresponding natural polysaccharide. The newly prepared biotinylated oligosaccharides along with the previously reported biotinylated glycoconjugates related to galactan I and galactan II of K. pneumoniae LPS were used for the ELISA detection of antibodies in anti-K. pneumoniae rabbit sera. Anti-O3 serum antibodies specifically recognized the synthesized oligosaccharide ligands with terminal methylphosphomannosyl residues, whereas anti-O1 serum antibodies recognized the oligosaccharide related to K. pneumoniae galactan II. The analysis of human sera from patients with confirmed Klebsiella infection also revealed the presence of antibodies against the synthesized oligosaccharides in clinical cases. Thus, the described compounds together with other Klebsiella related antigenic oligosaccharides could be potentially used as molecular probes for K. pneumoniae serological diagnostics development and strain serotyping.

Biorecognition Layer Based On Biotin-Containing [1]Benzothieno[3,2-b][1]benzothiophene Derivative for Biosensing by Electrolyte-Gated Organic Field-Effect Transistors

Requirements of speed and simplicity in testing stimulate the development of modern biosensors. Electrolyte-gated organic field-effect transistors (EGOFETs) are a promising platform for ultrasensitive, fast, and reliable detection of biological molecules for low-cost, point-of-care bioelectronic sensing. Biosensitivity of the EGOFET devices can be achieved by modification with receptors of one of the electronic active interfaces of the transistor gate or organic semiconductor surface. Functionalization of the latter gives the advantage in the creation of a planar architecture and compact devices for lab-on-chip design. Herein, we propose a universal, fast, and simple technique based on doctor blading and Langmuir-Schaefer methods for functionalization of the semiconducting surface of C₈-BTBT-C₈, allowing the fabrication of a large-scale biorecognition layer based on the novel functional derivative of BTBT-containing biotin fragments as a foundation for further biomodification. The fabricated devices are very efficient and operate stably in phosphate-buffered saline solution with high reproducibility of electrical properties in the EGOFET regime. The development of biorecognition properties of the proposed biolayer is based on the streptavidin-biotin interactions between the consecutive layers and can be used for a wide variety of receptors. As a proof-of-concept, we demonstrate the specific response of the BTBT-based biorecognition layer in EGOFETs to influenza A virus (H7N1 strain). The elaborated approach to biorecognition layer formation is appropriate but not limited to aptamer-based receptor molecules and can be further applied for fabricating several biosensors for various analytes on one substrate and paves the way for "electronic tongue" creation.

Computational and NMR Conformational Analysis of Galactofuranoside Cycles Presented in Bacterial and Fungal Polysaccharide Antigens

Unlike pyranoside cycles which are generally characterized by strictly defined conformational preferences, furanosides are flexible and may adopt a wide range of available conformations. During our previous studies, conformational changes of galactofuranoside cycles upon total sulfation were described computationally, using a simple Hartree–Fock (HF) method, and principal conformers of the 5-membered galactose ring were revealed. However, in the case of more complex disaccharide structures, it was found that this method and the widely applied DFT-B3LYP produced results that deviated from experimental evidence. In this study, other DFT functionals (PBE0 and double hybrid B2PLYP) along with RI-MP2 are employed to study the conformational behavior of the galactofuranoside ring. Reinvestigation of galactofuranosides with a lactic acid substituent at O-3 revealed that changes in the orientation of lactic acid residue at O-3 might induce conformational changes of the furanoside cycle. Such findings are important for further modeling of carbohydrate–protein interaction.

Reinvestigation of Carbohydrate Specificity of EBCA-1 Monoclonal Antibody Used for the Detection of Candida Mannan

Monoclonal antibody EBCA-1 is used in the sandwich immune assay for the detection of circulating Candida mannan in blood sera samples for the diagnosis of invasive candidiasis. To reinvestigate carbohydrate specificity of EBCA-1, a panel of biotinylated oligosaccharides structurally related to distinct fragments of Candida mannan were loaded onto a streptavidin-coated plate to form a glycoarray. Its use demonstrated that EBCA-1 recognizes the trisaccharide β-Man-(1→2)-α-Man-(1→2)-α-Man and not homo-α-(1→2)-linked pentamannoside, as was reported previously.

Synthesis and conformational analysis of vicinally branched trisaccharide β-d-Galf-(1 → 2)-[β-d-Galf-(1 → 3)-]-α-Galp from Cryptococcus neoformans galactoxylomannan

The synthesis of a vicinally branched trisaccharide composed of two d-galactofuranoside residues attached viaβ-(1 → 2)- and β-(1 → 3)-linkages to the α-d-galactopyranoside unit has been performed for the first time. The reported trisaccharide represents the galactoxylomannan moiety first described in 2017, which is the capsular polysaccharide of the opportunistic fungal pathogen Cryptococcus neoformans responsible for life-threatening infections in immunocompromised patients. The NMR-data reported here for the synthetic model trisaccharide are in good agreement with the previously assessed structure of galactoxylomannan and are useful for structural analysis of related polysaccharides. The target trisaccharide as well as the constituent disaccharides were analyzed by a combination of computational and NMR methods to demonstrate good convergence of the theoretical and experimental results. The results suggest that the furanoside ring conformation may strongly depend on the aglycon structure. The reported conformational tendencies are important for further analysis of carbohydrate-protein interaction, which is critical for the host response toward C. neoformans infection.

Biotinylated Oligo-α-(1 → 4)-d-galactosamines and Their N-Acetylated Derivatives: α-Stereoselective Synthesis and Immunology Application

Using 3-O-benzoyl-4,6-O-di-tert-butylsilylidene-2-azido-2-deoxy-selenogalactoside, biotinylated oligo-α-(1 → 4)-d-galactosamines comprising from two to six GalN units were prepared for the first time together with their N-acetylated derivatives. The combination of blocking groups used herein provided stereocontrol for the α-stereospecific glycosylation, to show also high efficiency of phenyl 2-azido-2-deoxy-selenogalactosides as glycosyl donors. The obtained glycoconjugates are related to fragments of exopolysaccharide galactosaminogalactan (GG) found in Aspergillus fumigatus, which is the most important airborne human fungal pathogen in industrialized countries. The synthesized glycoconjugates were arrayed on streptavidin-coated plates and used to investigate the GG epitopes recognized by mouse monoclonal antibodies against GG and by human antibodies in the sera of patients with aspergillosis. The obtained data showed that the oligo-α-(1 → 4)-d-galactosamines and their N-acetylated derivatives allowed the first precise analysis of the specificity of the antibody responses to this extremely complex fungal polysaccharide.

Importance of Candida Antigenic Factors: Structure-Driven Immunomodulation Properties of Synthetically Prepared Mannooligosaccharides in RAW264.7 Macrophages

The incidence and prevalence of serious fungal infections is rising, especially in immunosuppressed individuals. Moreover, co-administration of antibiotics and immunosuppressants has driven the emergence of new multidrug-resistant pathogens. The significant increase of multidrug-resistant pathogens, together with their ability to form biofilms, is associated with morbidity and mortality. Research on novel synthetically prepared immunomodulators as potential antifungal immunotherapeutics is of serious interest. Our study demonstrated the immunobiological activity of synthetically prepared biotinylated mannooligosaccharides mimicking Candida antigenic factors using RAW264.7 macrophages. Macrophage exposure to the set of eight structurally different mannooligosaccharides induced a release of Th1, Th2, Th17, and Treg cytokine signature patterns. The observed immune responses were tightly associated with structure, dose, exposure time, and selected signature cytokines. The viability/cytotoxicity of the mannooligosaccharide formulas was assessed based on cell proliferation. The structure-based immunomodulatory activity of the formulas was evaluated with respect to the length, branching and conformation of the various formulas. Glycoconjugate formulas with terminal β-mannosyl-units tended to be more potent in terms of Candida relevant cytokines IL-12 p70, IL-17, GM-CSF, IL-6, and TNFα induction and cell proliferation, and this tendency was associated with structural differences between the studied glycoconjugate formulas. The eight tested mannooligosaccharide conjugates can be considered potential in vitro immunomodulative agents suitable for in vitro Candida diagnostics or prospectively for subcellular anti-Candida vaccine design.

Monoclonal Antibody AP3 Binds Galactomannan Antigens Displayed by the Pathogens Aspergillus flavus, A. fumigatus, and A. parasiticus

Aspergillus fumigatus and A. flavus are the fungal pathogens responsible for most cases of invasive aspergillosis (IA). Early detection of the circulating antigen galactomannan (GM) in serum allows the prompt application of effective antifungal therapy, thus improving the survival rate of IA patients. However, the use of monoclonal antibodies (mAbs) for the diagnosis of IA is often associated with false positives due to cross-reaction with bacterial polysaccharides. More specific antibodies are therefore needed. Here we describe the characterization of the Aspergillus-specific mAb AP3 (IgG1κ), including the precise identification of its corresponding antigen. The antibody was generated using A. parasiticus cell wall fragments and was shown to bind several Aspergillus species. Immunofluorescence microscopy revealed that AP3 binds a cell wall antigen, but immunoprecipitation and enzyme-linked immunosorbent assays showed that the antigen is also secreted into the culture medium. The inability of AP3 to bind the A. fumigatus galactofuranose (Galf )-deficient mutant ΔglfA confirmed that Galf residues are part of the epitope. Several lines of evidence strongly indicated that AP3 recognizes the Galf residues of O-linked glycans on Aspergillus proteins. Glycoarray analysis revealed that AP3 recognizes oligo-[β-D-Galf-1,5] sequences containing four or more residues with longer chains more efficiently. We also showed that AP3 captures GM in serum, suggesting it may be useful as a diagnostic tool for patients with IA.

Conformational changes in common monosaccharides caused by per-O-sulfation

Polysulfated carbohydrates play an important role in many biological processes because of their ability to bind to various protein receptors such as different growth factors, blood coagulation factors, adhesion lectins etc. Precise information about spatial organization of sulfated derivatives is of high demand for molecular modelling of such interactions as well as for understanding of the mechanism of pyranoside-into-furanoside rearrangement. In this review we summarize the changes recently revealed for the conformations of common pyranosides and furanosides upon total O-sulfation which were studied by means of NMR spectroscopy as well as molecular modelling. It was found that pentoses, being more flexible, undergo complete conformational chair inversion. Meanwhile, for hexoses the situation strongly depends on the monosaccharide configuration. Conformational changes are most pronounced in gluco-compounds though quantum chemical calculations helped to establish that no complete chair inversion occurred. In furanosides distortions of two types were observed: either the ring conformation or the conformation of the side chain changed. The presented data may be used for the analysis of chemical, physical and biological properties of sulfated carbohydrates.

Novel mouse monoclonal antibodies specifically recognizing β-(1→3)-D-glucan antigen

β-(1→3)-D-Glucan is an essential component of the fungal cell wall. Mouse monoclonal antibodies (mAbs) against synthetic nona-β-(1→3)-D-glucoside conjugated with bovine serum albumin (BSA) were generated using hybridoma technology. The affinity constants of two selected mAbs, 3G11 and 5H5, measured by a surface plasmon resonance biosensor assay using biotinylated nona-β-(1→3)-D-glucan as the ligand, were approximately 11 nM and 1.9 nM, respectively. The glycoarray, which included a series of synthetic oligosaccharide derivatives representing β-glucans with different lengths of oligo-β-(1→3)-D-glucoside chains, demonstrated that linear tri-, penta- and nonaglucoside, as well as a β-(1→6)-branched octasaccharide, were recognized by mAb 5H5. By contrast, only linear oligo-β-(1→3)-D-glucoside chains that were not shorter than pentaglucosides (but not the branched octaglucoside) were ligands for mAb 3G11. Immunolabelling indicated that 3G11 and 5H5 interact with both yeasts and filamentous fungi, including species from Aspergillus, Candida, Penicillium genera and Saccharomyces cerevisiae, but not bacteria. Both mAbs could inhibit the germination of Aspergillus fumigatus conidia during the initial hours and demonstrated synergy with the antifungal fluconazole in killing C. albicans in vitro. In addition, mAbs 3G11 and 5H5 demonstrated protective activity in in vivo experiments, suggesting that these β-glucan-specific mAbs could be useful in combinatorial antifungal therapy.

Synthesis of oligosaccharides related to galactomannans from Aspergillus fumigatus and their NMR spectral data

The synthesis of model oligosaccharides related to antigenic galactomannans of the dangerous fungal pathogen Aspergillus fumigatus has been performed employing pyranoside-into-furanoside (PIF) rearrangement and controlled O(5) → O(6) benzoyl migration as key synthetic methods. The prepared compounds along with some previously synthesized oligosaccharides were studied by NMR spectroscopy with the full assignment of ¹H and ¹³C signals and the determination of ¹³C NMR glycosylation effects. The obtained NMR database on ¹³C NMR chemical shifts for oligosaccharides representing galactomannan fragments forms the basis for further structural analysis of galactomannan related polysaccharides by a non-destructive approach based on the calculation of the ¹³C NMR spectra of polysaccharides by additive schemes.

Influence of per-O-sulfation upon the conformational behaviour of common furanosides

The studies on the recently discovered pyranoside-into-furanoside rearrangement have led us to conformational investigations of furanosides upon their total sulfation. Experimental NMR data showed that in some cases drastic changes of the ring conformation occurred while sometimes only the conformation of the exocyclic C4-C5 linkage changed. Herein we describe a combined quantum chemical and NMR conformational investigation of three common monosaccharide furanosides as their propyl glycosides: α-mannose, β-glucose and β-galactose. Full exploration of the furanoside ring by means of ab initio calculations was performed and coupling constants were calculated for each of the low-energy conformers. The results demonstrated preferred trans-orientation of H4-H5 protons in the non-sulfated molecules which changed to gauche-orientation upon sulfation. The effect is less pronounced in the galactosides. For all the studied structures changes in the conformational distribution were revealed by quantum mechanical calculations, that explained the observed changes in intraring coupling constants occurring upon introduction of sulfates.

Nanomedical Relevance of the Intermolecular Interaction Dynamics-Examples from Lysozymes and Insulins

Insulin and lysozyme share the common features of being prone to aggregate and having biomedical importance. Encapsulating lysozyme and insulin in micellar nanoparticles probably would prevent aggregation and facilitate oral drug delivery. Despite the vivid structural knowledge of lysozyme and insulin, the environment-dependent oligomerization (dimer, trimer, and multimer) and associated structural dynamics remain elusive. The knowledge of the intra- and intermolecular interaction profiles has cardinal importance for the design of encapsulation protocols. We have employed various biophysical methods such as NMR spectroscopy, X-ray crystallography, Thioflavin T fluorescence, and atomic force microscopy in conjugation with molecular modeling to improve the understanding of interaction dynamics during homo-oligomerization of lysozyme (human and hen egg) and insulin (porcine, human, and glargine). The results obtained depict the atomistic intra- and intermolecular interaction details of the homo-oligomerization and confirm the propensity to form fibrils. Taken together, the data accumulated and knowledge gained will further facilitate nanoparticle design and production with insulin or lysozyme-related protein encapsulation.

Reinvestigation of carbohydrate specificity of EB-A2 monoclonal antibody used in the immune detection of Aspergillus fumigatus galactomannan

Great progresses have been made in the recent years in the detection of circulating galactofuranose-bearing molecules for the diagnosis of aspergillosis. However, the test used in the clinical practice is hampered by the occurrence of false positives. A glycoarray with dozens of oligosaccharides structurally related to the Aspergillus fumigatus galactomannan has allowed us to reinvestigate the carbohydrate specificity of the EB-A2 monoclonal antibody used in the Platelia^TM Aspergillus sandwich immune assay. We have now demonstrated that the mAb can recognize shorter oligosaccharides than the previously reported tetrasaccharide Galf-β-(1→5)-Galf-β-(1→5)-Galf-β-(1→5)-Galf-β and oligosaccharides which contains alternating β-(1→5)/β-(1→6)-linkages. This result could explain the occurrence of false-positive signals due to the presence of the abovementioned epitopes not only in A. fumigatus galactomannan but also in other bacteria and fungi.

Driving Force of the Pyranoside-into-Furanoside Rearrangement

Ab initio calculations of fully O-sulfated model monosaccharides, including common hexoses (glucose, galactose, fucose, and mannose) and pentoses (arabinose and xylose), were performed to study the energetic properties of the recently discovered pyranoside-into-furanoside (PIF) rearrangement. It was shown that the per-O-sulfated derivatives of furanoside isomers generally had lower energies than the corresponding per-O-sulfated pyranosides, while nonsulfated furanosides were always less favored than nonsulfated pyranosides. Mannose, which is known to be unreactive in PIF rearrangement, was the only exception. The results of the theoretical calculations were confirmed by experimental studies of monosaccharide models and explained the driving force of such unusual ring contraction process as PIF rearrangement. The conclusions of performed investigation can be used for prediction of new substrates applicability for PIF rearrangement.

Synthetic Oligosaccharides Mimicking Fungal Cell Wall Polysaccharides

The cell wall of pathogenic fungi is highly important for the development of fungal infections and is the first cellular component to interact with the host immune system. The fungal cell wall is mainly built up of different polysaccharides representing ligands for pattern recognition receptors (PRRs) on immune cells and antibodies. Purified fungal polysaccharides are not easily available; in addition, they are structurally heterogenic and have wide molecular weight distribution that limits the possibility to use natural polysaccharides to assess the structure of their active determinants. The synthetic oligosaccharides of definite structure representing distinct polysaccharide fragments are indispensable tools for a variety of biological investigations and represent an advantageous alternative to natural polysaccharides. The attachment of a spacer group to these oligosaccharides permits their efficient transformation into immunogenic glycoconjugates as well as their immobilization on plates or microbeads. Herein, we summarize current information on synthetic availability of the variety of oligosaccharides related to main types of fungal cell wall components: galactomannan, α- and β-mannan, α- and β-(1 → 3)-glucan, chitin, chitosan, and others. These data are supplemented with published results of biochemical and immunological applications of synthetic oligosaccharides as molecular probes especially as the components of thematic glycoarrays suitable for characterization of anti-polysaccharide antibodies and cellular lectins or PRRs.

Chemical Synthesis and Application of Biotinylated Oligo-α-(1 → 3)-d-Glucosides To Study the Antibody and Cytokine Response against the Cell Wall α-(1 → 3)-d-Glucan of Aspergillus fumigatus

Biotinylated hepta-, nona- and undeca-α-(1 → 3)-d-glucosides representing long oligosaccharides of α-(1 → 3)-d-glucan, one of the major components of the cell walls of the fungal pathogen Aspergillus fumigatus, were synthesized for the first time via a blockwise strategy. Convergent assembly of the α-(1 → 3)-d-glucan chains was achieved by glycosylation with oligoglucoside derivatives bearing 6- O-benzoyl groups. Those groups are capable of remote α-stereocontrolling participation, making them efficient α-directing tools even in the case of large glycosyl donors. Synthetic biotinylated oligoglucosides (and biotinylated derivatives of previously synthesized tri- and penta-α-(1 → 3)-d-glucosides) loaded on streptavidin microtiter plates were shown to be better recognized by anti-α-(1 → 3)-glucan human polyclonal antibodies and to induce higher cytokine responses upon stimulation of human peripheral blood mononuclear cells than their natural counterpart, α-(1 → 3)-d-glucan, immobilized on a conventional microtiter plate. Attachment of the synthetic oligosaccharides equipped with a hydrophilic spacer via the streptavidin-biotin pair allows better spatial presentation and control of the loading compared to the random sorption of natural α-(1 → 3)-glucan. Increase of oligoglucoside length results in their better recognition and enhancement of cytokine production. Thus, using synthetic α-(1 → 3)-glucan oligosaccharides, we developed an assay for the host immune response that is more sensitive than the assay based on native α-(1 → 3)-glucan.

Novel mouse monoclonal antibodies specifically recognize Aspergillus fumigatus galactomannan

A panel of specific monoclonal antibodies (mAbs) against synthetic pentasaccharide β-D-Galf-(1→5)-[β-D-Galf-(1→5)]₃-α-D-Manp, structurally related to Aspergillus fumigatus galactomannan, was generated using mice immunized with synthetic pentasaccharide-BSA conjugate and by hybridoma technology. Two selected mAbs, 7B8 and 8G4, could bind with the initial pentasaccharide with affinity constants of approximately 5.3 nM and 6.4 nM, respectively, based on surface plasmon resonance-based biosensor assay. The glycoarray, built from a series of synthetic oligosaccharide derivatives representing different galactomannan fragments, demonstrated that mAb 8G4 could effectively recognize the parental pentasaccharide while mAb 7B8 recognizes its constituting trisaccharide parts. Immunofluorescence studies showed that both 7B8 and 8G4 could stain A. fumigatus cells in culture efficiently, but not the mutant strain lacking galactomannan. In addition, confocal microscopy demonstrated that Candida albicans, Bifidobacterium longum, Lactobacillus plantarum, and numerous gram-positive and gram-negative bacteria were not labeled by mAbs 7B8 and 8G4. The generated mAbs can be considered promising for the development of a new specific enzyme-linked assay for detection of A. fumigatus, which is highly demanded for medical and environmental controls.

Immunobiological Activity of Synthetically Prepared Immunodominant Galactomannosides Structurally Mimicking Aspergillus Galactomannan

The study is oriented at the in vitro evaluation of the immunobiological activity and efficacy of synthetically prepared isomeric pentasaccharides representing fragments of Aspergillus fumigatus cell-wall galactomannan and containing β-(1→5)-linked tetragalactofuranoside chain attached to O-6 (GM-1) or O-3 (GM-2) of a spacer-armed mannopyranoside residue. These compounds were studied as biotinylated conjugates which both demonstrated immunomodulatory activities on the RAW 264.7 cell line murine macrophages as in vitro innate immunity cell model. Immunobiological studies revealed time- and concentration-dependent efficient immunomodulation. The proliferation of RAW 264.7 macrophages was induced at higher concentration (100 µg/mL) of studied glycoconjugates and longer exposure (48 h), with more pronounced efficacy for GM-1. The increase of proliferation followed the previous increase of IL-2 production. The cytokine profile of the macrophages treated with the glycoconjugates was predominantly pro-inflammatory Th1 type with significant increase of TNFα, IL-6, and IL-12 release for both glycoconjugates. The RAW 264.7 macrophages production of free radicals was not significantly affected by glycoconjugates stimulation. The phagocytic activity of RAW 264.7 cells was reduced following GM-1 treatment and was significantly increased after 24 h stimulation with GM-2, contrary to 48 h stimulation. Moreover, the synthetically prepared galactomannoside derivatives have been evaluated as efficient serodiagnostic antigens recognized by specific Ig isotypes, and significant presence of specific IgM antibodies in serum of patients suffering from vulvovaginitis was observed.

Expression and biochemical characterization and substrate specificity of the fucoidanase from Formosa algae

A gene that encodes fucoidanase ffa2 in the marine bacterium Formosa algae strain KMM 3553T was cloned, and the protein (FFA2) was produced in Escherichia coli. Recombinant fucoidanase FFA2 was purified, and the biochemical properties of this enzyme were studied. The amino acid sequence of FFA2 showed 57% identity with known fucoidanase FcnA from Mariniflexile fucanivorans. The mass of the gene product FFA2 is 101.2 kDa (918 amino acid residues). Sequence analysis has revealed that fucoidanase FFA2 belongs to the GH107 (CAZy) family. Detailed substrate specificity was studied by using fucoidans from brown seaweeds as well as synthetic fucooligosaccharide with distinct structures. Fucoidanase FFA2 catalyzes the cleavage of (1→4)-α-glycosidic bonds in the fucoidan from Fucus evanescens within a structural fragment (→3)-α-l-Fucp2S-(1→4)-α-l-Fucp2S-(1→)n but not in a fragment (→3)-α-l-Fucp2S,4S-(1→4)-α-l-Fucp2S-(1→)n. Using synthetic di-, tetra- and octasaccharides built up of the alternative (1→4)- and (1→3)-linked α-l-Fucp2S units, the difference in substrate specificity and in the rate of enzymatic selectivity was investigated. Nonsulfated and persulfated synthetic oligosaccharides were not transformed by the enzyme. Therefore, FFA2 was specified as poly[(1→4)-α-l-fucoside-2-sulfate] glycanohydrolase. This enzyme could be used for the modification of natural fucoidans to obtain more regular and easier characterized derivatives useful for research and practical applications.

Recent advances in the synthesis of fungal antigenic oligosaccharides

The driving force for the constant improvement and development of new synthetic methodologies in carbohydrate chemistry is a growing demand for biologically important oligosaccharide ligands and neoglycoconjugates thereof for numerous biochemical investigations such as cell-to-pathogen interactions, immune response, cell adhesion, etc. Here we report our syntheses of the spacer-armed antigenic oligosaccharides related to three groups of the polysaccharides of the fungal cell-wall including α- and β-mannan, α- and β-glucan and galactomannan chains, which include new rationally designed synthetic blocks, efficient solutions for the stereoselective construction of glycoside bonds, and novel strategy for preparation of furanoside-containing oligosaccharides based on recently discovered pyranoside-into-furanoside (PIF) rearrangement.

The Use of Pyranoside-into-Furanoside Rearrangement and Controlled O(5) → O(6) Benzoyl Migration as the Basis of a Synthetic Strategy To Assemble (1→5)- and (1→6)-Linked Galactofuranosyl Chains

A new pyranoside-into-furanoside (PIF) rearrangement of selectively protected galactopyranosides, followed by controlled O(5) → O(6) benzoate migration, gives either 5-OH or 6-OH products. It has been applied for the synthesis of four oligosaccharides related to the galactomannan from Aspergillus fumigatus. The assembly of target oligosaccharides containing both (1→5) and (1→6) linkages between galactofuranosyl residues was performed by applying terminal mannoside and digalactofuranoside blocks, forming a versatile approach toward fungal and bacterial carbohydrate antigens containing both 5-O- and 6-O-substituted galactofuranoside residues.

The synthesis of heterosaccharides related to the fucoidan from Chordaria flagelliformis bearing an α-L-fucofuranosyl unit

Sulfated polysaccharides, fucoidans, from brown algae are built up mainly of α-L-fucopyranosyl units and form a group of natural biopolymers with a wide spectrum of biological activities. Systematic synthesis of oligosaccharides representing fucoidans' fragments gives molecular probes for detecting pharmacophores within fucoidan polysaccharide chains. Recently, it was discovered that the fucoidan from brown seaweed Chordaria flagelliformis contains not only α-L-fucopyranosyl units but also α-L-fucofuranosyl ones. To establish the influence of the unusual α-L-fucofuranose residue on the biological activity and conformational properties of fucoidans, the synthesis of selectively O-sulfated pentasaccharides, which represent the main repeating unit of the fucoidan from C. flagelliformis, was performed. The features of the synthesis were the use of the pyranoside-into-furanoside rearrangement to prepare the fucofuranoside precursor and remote stereocontrolling participation of O-acyl groups to manage stereoselective α-bond formation in glycosylation reactions.

Convergent synthesis of isomeric heterosaccharides related to the fragments of galactomannan from Aspergillus fumigatus

Aspergillus fumigatus is a very common fungus with high pathogenic potential for immunosuppressed hospital patients. A. fumigatus galactomannan, being the part of its cell wall, is considered as a promising candidate for vaccine and diagnostic test-systems. In this article we report the convergent synthesis of pentasaccharide fragments of the galactomannan containing the β-(1→5)-linked galactofuranoside chain attached to O-3 or O-6 of a spacer-armed mannopyranoside residue. The synthesis of selectively protected galactofuranoside precursors has been performed using recently developed pyranoside-into-furanoside (PIF) rearrangement. For assembling the target galactomannan structures the [1 + 2 + 2]-scheme was applied. This strategy was shown to be highly efficient and can easily be extended to the synthesis of longer fragments of thegalactomannan.

Pyranoside-into-furanoside rearrangement: new reaction in carbohydrate chemistry and its application in oligosaccharide synthesis

Great interest in natural furanoside-containing compounds has challenged the development of preparative methods for their synthesis. Herein a novel reaction in carbohydrate chemistry, namely a pyranoside-into-furanoside (PIF) rearrangement permitting the transformation of selectively O-substituted pyranosides into the corresponding furanosides is reported. The discovered process includes acid-promoted sulfation accompanied by rearrangement of the pyranoside ring into a furanoside ring followed by solvolytic O-desulfation. This process, which has no analogy in organic chemistry, was shown to be a very useful tool for the synthesis of furanoside-containing complex oligosaccharides, which was demonstrated by synthesizing disaccharide derivatives α-D-Galp-(1→3)-β-D-Galf-OPr, 3-O-s-lactyl-β-D-Galf-(1→3)-β-D-Glcp-OPr, and α-L-Fucf-(1→4)-β-D-GlcpA-OPr related to polysaccharides from the bacteria Klebsiella pneumoniae and Enterococcus faecalis and the brown seaweed Chordaria flagelliformis.

Fucoidans as a platform for new anticoagulant drugs discovery

Anionic fucose-containing polysaccharides (fucoidans of brown seaweeds, sulfated fucans and fucosylated chondroitin sulfates of invertebrates) are attracting a rapidly growing research interest due to different types of their biological activity discovered in recent years. In particular, algal fucoidans are characterized by large structural variations depending on the species used for their isolation and by the lack of structural regularity due to random distribution of both carbohydrate and non-carbohydrate substituents along the polymer chains. These features make it difficult to find distinct correlations between structural elements and biological properties of polysaccharides. Nevertheless, there is expectation that systematic structural and biochemical studies of fucoidans will form a basis for the development of new drugs. Herewith we summarize our recent results on the influence of fucoidan structure on blood coagulation.

Influence of fucoidans on hemostatic system

Three structurally different fucoidans from the brown seaweeds Saccharina latissima (SL), Fucus vesiculosus (FV), and Cladosiphon okamuranus (CO), two chemically modified fucoidans with a higher degree of sulfation (SL-S, CO-S), and a synthetic totally sulfated octasaccharide (OS), related to fucoidans, were assessed on anticoagulant and antithrombotic activities in different in vitro experiments. The effects were shown to depend on the structural features of the compounds tested. Native fucoidan SL with a degree of sulfation (DS) of 1.3 was found to be the most active sample, fucoidan FV (DS 0.9) demonstrated moderate activity, while the polysaccharide CO (DS 0.4) was inactive in all performed experiments, even at high concentrations. Additional introduction of sulfate groups into fucoidan SL slightly decreased the anticoagulant effect of SL-S, while sulfation of CO, giving rise to the preparation CO-S, increased the activity dramatically. The high level of anticoagulant activity of polysaccharides SL, SL-S, and CO-S was explained by their ability to form ternary complexes with ATIII-Xa and ATIII-IIa, as well as to bind directly to thrombin. Synthetic per-O-sulfated octasaccharide OS showed moderate anticoagulant effect, determined mainly by the interaction of OS with the factor Xa in the presence of ATIII. Comparable tendencies were observed in the antithrombotic properties of the compounds tested.

Molecular cloning of a xylosyltransferase that transfers the second xylose to O-glucosylated epidermal growth factor repeats of notch

The extracellular domain of Notch contains epidermal growth factor (EGF) repeats that are extensively modified with different O-linked glycans. O-Fucosylation is essential for receptor function, and elongation with N-acetylglucosamine, catalyzed by members of the Fringe family, modulates Notch activity. Only recently, genes encoding enzymes involved in the O-glucosylation pathway have been cloned. In the Drosophila mutant rumi, characterized by a mutation in the protein O-glucosyltransferase, Notch signaling is impaired in a temperature-dependent manner, and a mouse knock-out leads to embryonic lethality. We have previously identified two human genes, GXYLT1 and GXYLT2, encoding glucoside xylosyltransferases responsible for the transfer of xylose to O-linked glucose. The identity of the enzyme further elongating the glycan to generate the final trisaccharide xylose-xylose-glucose, however, remained unknown. Here, we describe that the human gene C3ORF21 encodes a UDP-xylose:α-xyloside α1,3-xylosyltransferase, acting on xylose-α1,3-glucoseβ1-containing acceptor structures. We have, therefore, renamed it XXYLT1 (xyloside xylosyltransferase 1). XXYLT1 cannot act on a synthetic acceptor containing an α-linked xylose alone, but requires the presence of the underlying glucose. Activity on Notch EGF repeats was proven by in vitro xylosylation of a mouse Notch1 fragment recombinantly produced in Sf9 insect cells, a bacterially expressed EGF repeat from mouse Notch2 modified in vitro by Rumi and Gxylt2 and in vivo by co-expression of the enzyme with the Notch1 fragment. The enzyme was shown to be a typical type II membrane-bound glycosyltransferase localized in the endoplasmic reticulum.

Identification of glycosyltransferase 8 family members as xylosyltransferases acting on O-glucosylated notch epidermal growth factor repeats

The epidermal growth factor repeats of the Notch receptor are extensively glycosylated with three different O-glycans. O-Fucosylation and elongation by the glycosyltransferase Fringe have been well studied and shown to be essential for proper Notch signaling. In contrast, biosynthesis of O-glucose and O-N-acetylglucosamine is less well understood. Recently, the isolation of the Drosophila mutant rumi has shown that absence of O-glucose impairs Notch function. O-Glucose is further extended by two contiguous alpha1,3-linked xylose residues. We have identified two enzymes of the human glycosyltransferase 8 family, now named GXYLT1 and GXYLT2 (glucoside xylosyltransferase), as UDP-d-xylose:beta-d-glucoside alpha1,3-d-xylosyltransferases adding the first xylose. The enzymes are specific for beta-glucose-terminating acceptors and UDP-xylose as donor substrate. Generation of the alpha1,3-linkage was confirmed by nuclear magnetic resonance. Activity on a natural acceptor could be shown by in vitro xylosylation of a Notch fragment expressed in a UDP-xylose-deficient cell line and in vivo by co-expression of the enzymes and the Notch fragment in insect cells followed by mass spectrometric analysis of peptide fragments.