Flavonol Biosynthesis Genes and Their Use in Engineering the Plant Antidiabetic Metabolite Montbretin A

The plant metabolite montbretin A (MbA) and its precursor mini-MbA are potential new drugs for treating type 2 diabetes. These complex acylated flavonol glycosides only occur in small amounts in the corms of the ornamental plant montbretia (Crocosmia × crocosmiiflora). Our goal is to metabolically engineer Nicotiana benthamiana using montbretia genes to achieve increased production of mini-MbA and MbA. Two montbretia UDP-dependent glycosyltransferases (UGTs), CcUGT1 and CcUGT2, catalyze the formation of the first two pathway-specific intermediates in MbA biosynthesis, myricetin 3-O-rhamnoside and myricetin 3-O-glucosyl rhamnoside. In previous work, expression of these UGTs in N. benthamiana resulted in small amounts of kaempferol glycosides but not myricetin glycosides, suggesting that myricetin was limiting. Here, we investigated montbretia genes and enzymes of flavonol biosynthesis to enhance myricetin formation in N. benthamiana We characterized two flavanone hydroxylases, a flavonol synthase, a flavonoid 3'-hydroxylase (F3'H), and a flavonoid 3'5'-hydroxylase (F3'5'H). Montbretia flavonol synthase converted dihydromyricetin into myricetin. Unexpectedly, montbretia F3'5'H shared higher sequence relatedness with F3'Hs in the CYP75B subfamily of cytochromes P450 than with those with known F3'5'H activity. Transient expression of combinations of montbretia flavonol biosynthesis genes and a montbretia MYB transcription factor in N. benthamiana resulted in availability of myricetin for MbA biosynthesis. Transient coexpression of montbretia flavonol biosynthesis genes combined with CcUGT1 and CcUGT2 in N. benthamiana resulted in 2 mg g-1 fresh weight of the MbA pathway-specific compound myricetin 3-O-glucosyl rhamnoside. Additional expression of the montbretia acyltransferase CcAT1 led to detectable levels of mini-MbA in N. benthamiana.

Structures and Bioactivities of Six New Triterpene Glycosides, Psolusosides E, F, G, H, H1, and I and the Corrected Structure of Psolusoside B from the Sea Cucumber Psolus fabricii

Seven sulfated triterpene glycosides, psolusosides B (1), E (2), F (3), G (4), H (5), H₁ (6), and I (7), along with earlier known psolusoside A and colochiroside D have been isolated from the sea cucumber Psolus fabricii collected in the Sea of Okhotsk. Herein, the structure of psolusoside B (1), elucidated by us in 1989 as a monosulfated tetraoside, has been revised with application of modern NMR and particularly MS data and proved to be a disulfated tetraoside. The structures of other glycosides were elucidated by 2D NMR spectroscopy and HR-ESI mass-spectrometry. Psolusosides E (2), F (3), and G (4) contain holostane aglycones identical to each other and differ in their sugar compositions and the quantity and position of sulfate groups in linear tetrasaccharide carbohydrate moieties. Psolusosides H (5) and H₁ (6) are characterized by an unusual sulfated trisaccharide carbohydrate moiety with the glucose as the second sugar unit. Psolusoside I (7) has an unprecedented branched tetrasaccharide disulfated carbohydrate moiety with the xylose unit in the second position of the chain. The cytotoxic activities of the compounds 2-7 against several mouse cell lines-ascite form of Ehrlich carcinoma, neuroblastoma Neuro 2A, normal epithelial JB-6 cells, and erythrocytes-were quite different, at that hemolytic effects of the tested compounds were higher than their cytotoxicity against other cells, especially against the ascites of Ehrlich carcinoma. Interestingly, psolusoside G (4) was not cytotoxic against normal JB-6 cells but demonstrated high activity against Neuro 2A cells. The cytotoxic activity against human colorectal adenocarcinoma HT-29 cells and the influence on the colony formation and growth of HT-29 cells of compounds 1-3, 5-7 and psolusoside A was checked. The highest inhibitory activities were demonstrated by psolusosides E (2) and F (3).

Novel trisaccharide based phospholipids as immunomodulators

A focused library of novel mannosylated glycophospholipids was synthesized employing imidate coupling and H-phosphate phosphorylation methods. All novel glycophospholipids were evaluated for their receptor interactions by molecular docking studies. Docking studies revealed dendritic cell-specific intercellular adhesion molecule-3-grabbing non-integrin (DC-SIGN) specific interaction of the glycophospholipid ligand P4 acts, which was further confirmed by in vitro DC-SIGN expression on monocyte-derived dendritic cells (MoDCs). Further, in vitro and in vivo immunomodulatory activity among the six compounds (P1-P6) examined, compound P4 displayed good immunopotentiation and adjuvant properties as indicated by the induced cytokine expression and enhanced ovalbumin (OVA) specific antibody (IgG) titers. Phosphatidylinositol mannosides (PIMs) analogues in the present study enforced the immunomodulatory properties, truncating parent PIMs or tailor-made of PIMs may bring the novel efficacious molecules, which will be useful in vaccine preparation against different diseases.

Characterization of Electrospray Ionization (ESI) Parameters on In-ESI Hydrogen/Deuterium Exchange of Carbohydrate-Metal Ion Adducts

The conformations of glycans are crucial for their biological functions. In-electrospray ionization (ESI) hydrogen/deuterium exchange-mass spectrometry (HDX-MS) is a promising technique for studying carbohydrate conformations since rapidly exchanging functional groups, e.g., hydroxyls, can be labeled on the timeframe of ESI. However, regular application of in-ESI HDX to characterize carbohydrates requires further analysis of the in-ESI HDX methodology. For instance, in this method, HDX occurs concurrently to the analyte transitioning from solution to gas-phase ions. Therefore, there is a possibility of sampling both gas-phase and solution-phase conformations of the analyte. Herein, we differentiate in-ESI HDX of metal-adducted carbohydrates from gas-phase HDX and illustrate that this method analyzes solvated species. We also systematically examine the effects of ESI parameters, including spray solvent composition, auxiliary gas flow rate, sheath gas flow rate, sample infusion rate, sample concentration, and spray voltage, and discuss their effects on in-ESI HDX. Further, we model the structural changes of a trisaccharide, melezitose, and its intramolecular and intermolecular hydrogen bonding in solvents with different compositions of methanol and water. These molecular dynamic simulations support our experimental results and illustrate how an individual ESI parameter can alter the conformations we sample by in-ESI HDX. In total, this work illustrates how the fundamental processes of ESI alter the magnitude of HDX for carbohydrates and suggest parameters that should be considered and/or optimized prior to performing experiments with this in-ESI HDX technique. Graphical Abstract ᅟ.

Mutagenesis Studies and Structure-function Relationships for GalNAc/Gal-Specific Lectin from the Sea Mussel Crenomytilus grayanus

The GalNAc/Gal-specific lectin from the sea mussel Crenomytilus grayanus (CGL) with anticancer activity represents а novel lectin family with β-trefoil fold. Earlier, the crystal structures of CGL complexes with globotriose, galactose and galactosamine, and mutagenesis studies have revealed that the lectin contained three carbohydrate-binding sites. The ability of CGL to recognize globotriose (Gb3) on the surface of breast cancer cells and bind mucin-type glycoproteins, which are often associated with oncogenic transformation, makes this compound to be perspective as a biosensor for cancer diagnostics. In this study, we describe results on in silico analysis of binding mechanisms of CGL to ligands (galactose, globotriose and mucin) and evaluate the individual contribution of the amino acid residues from carbohydrate-binding sites to CGL activity by site-directed mutagenesis. The alanine substitutions of His37, His129, Glu75, Asp127, His85, Asn27 and Asn119 affect the CGL mucin-binding activity, indicating their importance in the manifestation of lectin activity. It has been found that CGL affinity to ligands depends on their structure, which is determined by the number of hydrogen bonds in the CGL-ligand complexes. The obtained results should be helpful for understanding molecular machinery of CGL functioning and designing a synthetic analog of CGL with enhanced carbohydrate-binding properties.

Quantifying the binding stoichiometry and affinity of histo-blood group antigen oligosaccharides for human noroviruses

Human noroviruses (HuNoVs) are a major cause of acute gastroenteritis. Many HuNoVs recognize histo-blood group antigens (HBGAs) as cellular receptors or attachment factors for infection. It was recently proposed that HuNoV recognition of HBGAs involves a cooperative, multistep binding mechanism that exploits both known and previously unknown glycan binding sites. In this study, binding measurements, implemented using electrospray ionization mass spectrometry (ESI-MS) were performed on homodimers of the protruding domain (P dimers) of the capsid protein of three HuNoV strains [Saga (GII.4), Vietnam 026 (GII.10) and VA387 (GII.4)] with the ethyl glycoside of the B trisaccharide (α-d-Gal-(1→3)-[α-l-Fuc-(1→2)]-β-d-Gal-OC2H5) and free B type 1 tetrasaccharide (α-d-Gal-(1→3)-[α-l-Fuc-(1→2)]-β-d-Gal-(1→3)-d-GlcNAc) in an effort to confirm the existence of new HBGA binding sites. After correcting the mass spectra for nonspecific interactions that form in ESI droplets as they evaporate to dryness, all three P dimers were found to bind a maximum of two B trisaccharides at the highest concentrations investigated. The apparent affinities measured for stepwise binding of B trisaccharide suggest positive cooperativity. Similar results were obtained for B type 1 tetrasaccharide binding to Saga P dimer. Based on these results, it is proposed that HuNoV P dimers possess only two HBGA binding sites. It is also shown that nonspecific binding corrections applied to mass spectra acquired using energetic ion source conditions that promote in-source dissociation can lead to apparent HuNoV-HBGA oligosaccharide binding stoichiometries and affinities that are artificially high. Finally, evidence that high concentrations of oligosaccharide can induce conformational changes in HuNoV P dimers is presented.

Combining pure shift and J-edited spectroscopies: A strategy for extracting chemical shifts and scalar couplings from highly crowded proton spectra of oligomeric saccharides

We report the application of pure shift and J-edited nuclear magnetic resonance spectroscopies to the structural analysis of a protected maltotrioside synthetic intermediate whose crowded ¹ H spectrum displays highly crowded regions. The analytical strategy is based on the implementation of J-edited and TOCSY experiments whose resolution is optimized by the use of broadband homonuclear decoupling and selective refocusing techniques, to assign and measure chemical shifts and homonuclear scalar couplings with high accuracy. The resulting data show a high level of complementarity, providing a detailed insight into each subunit of this oligomeric saccharide, even for proton sites whose nuclear magnetic resonance signals strongly overlap. This approach allowed for fully assigning proton chemical shifts and extracting 80% of the ³ J_HH couplings that are in excellent agreement with those expected for D-gluco-pyranosyl units in ⁴ C₁ conformations.

Purification, characterization, and functional analysis of a novel 6G&1-FEH mainly hydrolyzing neokestose from asparagus

Asparagus (Asparagus officinalis L.) accumulates inulin- and inulin neoseries-type fructans. Fructose released by the hydrolysis of fructans is an energy source for emerging asparagus spears. Plant fructans are hydrolyzed by fructan exohydrolases (FEHs), whose presence in asparagus has not yet been fully characterized. Here, we describe for the first time the purification and characterization of an FEH from asparagus, and the functional analysis of its gene. The purified enzyme was predicted to exist as a dimer (approximately 130 kDa) consisting of two polypeptides with a molecular mass of approximately 68 kDa. N-terminal sequences of the purified enzyme were matched with the amino acid sequences of aoeh4a and aoeh4b cDNAs isolated from asparagus (cv. Gijnlim and Taihouwase). Native enzymes obtained from asparagus roots and recombinant enzymes produced by Pichia pastoris showed fructan 1-exohydrolase (1-FEH) activity via the hydrolysis of inulin-type fructan. Unlike other 1-FEHs, these enzymes showed minimal hydrolysis of 1-kestose but efficiently hydrolyzed neokestose. Therefore, the enzyme was termed 6G&1-FEH. Gene expression studies in asparagus roots showed that aoeh4 increased during root storage at 2 °C and spear harvesting. These findings suggest that 6G&1-FEH may be involved in fructan hydrolysis in asparagus roots to provide an energy source for emerging asparagus spears.

Simple Approach for De Novo Structural Identification of Mannose Trisaccharides

Oligosaccharides have diverse functions in biological systems. However, the structural determination of oligosaccharides remains difficult and has created a bottleneck in carbohydrate research. In this study, a new approach for the de novo structural determination of underivatized oligosaccharides is demonstrated. A low-energy collision-induced dissociation (CID) of sodium ion adducts was used to facilitate the cleavage of desired chemical bonds during the dissociation. The selection of fragments for the subsequent CID was guided using a procedure that we built from the understanding of the saccharide dissociation mechanism. The linkages, anomeric configurations, and branch locations of oligosaccharides were determined by comparing the CID spectra of oligosaccharide with the fragmentation patterns based on the dissociation mechanism and our specially prepared disaccharide CID spectrum database. The usefulness of this method was demonstrated to determine the structures of several mannose trisaccharides. This method can also be applied in the structural determination of oligosaccharides larger than trisaccharides and containing hexose other than mannose if authentic standards are available. Graphical Abstract.

Galactosylation of the Secondary Cell Wall Polysaccharide of Bacillus anthracis and Its Contribution to Anthrax Pathogenesis

Bacillus anthracis, the causative agent of anthrax disease, elaborates a secondary cell wall polysaccharide (SCWP) that is essential for bacterial growth and cell division. B. anthracis SCWP is comprised of trisaccharide repeats with the structure, [→4)-β-ManNAc-(1→4)-β-GlcNAc(O3-α-Gal)-(1→6)-α-GlcNAc(O3-α-Gal, O4-β-Gal)-(1→]6-12 The genes whose products promote the galactosylation of B. anthracis SCWP are not yet known. We show here that the expression of galE1, encoding a UDP-glucose 4-epimerase necessary for the synthesis of UDP-galactose, is required for B. anthracis SCWP galactosylation. The galE1 mutant assembles surface (S) layer and S layer-associated proteins that associate with ketal-pyruvylated SCWP via their S layer homology domains similarly to wild-type B. anthracis, but the mutant displays a defect in γ-phage murein hydrolase binding to SCWP. Furthermore, deletion of galE1 diminishes the capsulation of B. anthracis with poly-d-γ-glutamic acid (PDGA) and causes a reduction in bacterial virulence. These data suggest that SCWP galactosylation is required for the physiologic assembly of the B. anthracis cell wall envelope and for the pathogenesis of anthrax disease.IMPORTANCE Unlike virulent Bacillus anthracis isolates, B. anthracis strain CDC684 synthesizes secondary cell wall polysaccharide (SCWP) trisaccharide repeats without galactosyl modification, exhibits diminished growth in vitro in broth cultures, and is severely attenuated in an animal model of anthrax. To examine whether SCWP galactosylation is a requirement for anthrax disease, we generated variants of B. anthracis strains Sterne 34F2 and Ames lacking UDP-glucose 4-epimerase by mutating the genes galE1 and galE2 We identified galE1 as necessary for SCWP galactosylation. Deletion of galE1 decreased the poly-d-γ-glutamic acid (PDGA) capsulation of the vegetative form of B. anthracis and increased the bacterial inoculum required to produce lethal disease in mice, indicating that SCWP galactosylation is indeed a determinant of anthrax disease.

Biosynthesis of Neokestose Laurate Catalyzed by Candida antarctica Lipase B and Its Antimicrobial Activity against Food Pathogenic and Spoilage Bacteria

To increase the functionality and broaden the potential application of neokestose, neokestose laurate was biosynthesized using Candida antarctica lipase B as biocatalyst, for which a mixture of 20% DMSO in 2-methyl-2-butanol (v/v) was chosen as the reaction medium. The optimum conditions for biosynthesis were as follows: a molar ratio of vinyl laurate to neokestose of 12, a temperature of 50 °C, molecular sieves of 100 g/L, and enzyme loading of 10 g/L. Under the optimal conditions, the conversion rate was achieved over 80%. The synthesized chemical 6'-O-lauroylneokestose confirmed by nuclear magnetic resonance (NMR) exhibited good emulsification with critical micelle concentration (CMC) of 352 μM and broad antibacterial activity against Gram-positive bacteria such as Staphylococcus aureus, Listeria monocytogenes, Streptococcus mutans, Bacillus subtilis, and Bacillus cereus. Conclusively, 6'-O-lauroylneokestose was evidenced to be a dual-functional agent with emulsification and antibacterial activity, showing promising application potential in the food industry.

Enzymatic Synthesis and Structural Characterization of Theanderose through Transfructosylation Reaction Catalyzed by Levansucrase from Bacillus subtilis CECT 39

This work addresses the high-yield and fast enzymatic production of theanderose, a naturally occurring carbohydrate, also known as isomaltosucrose, whose chemical structure determined by NMR is α-d-glucopyranosyl-(1 → 6)-α-d-glucopyranosyl-(1 → 2)-β-d-fructofuranose. The ability of isomaltose to act as an acceptor in the Bacillus subtilis CECT 39 levansucrase-catalyzed transfructosylation reaction to efficiently produce theanderose in the presence of sucrose as a donor is described by using four different sucrose:isomaltose concentration ratios. The maximum theanderose concentration ranged from 122.4 to 130.4 g L^-1, was obtained after only 1 h and at a moderate temperature (37 °C), leading to high productivity (109.7-130.4 g L^-1h^-1) and yield (up to 37.3%) values. The enzymatic synthesis was highly regiospecific, since no other detectable acceptor reaction products were formed. The development of efficient and cost-effective procedures for the biosynthesis of unexplored but appealing oligosaccharides as potential sweeteners, such as theanderose, could help to expand its potential applications which are currently limited by their low availability.

Structural Insights into VLR Fine Specificity for Blood Group Carbohydrates

High-quality reagents to study and detect glycans with high specificity for research and clinical applications are severely lacking. Here, we structurally and functionally characterize several variable lymphocyte receptor (VLR)-based antibodies from lampreys immunized with O erythrocytes that specifically recognize the blood group H-trisaccharide type II antigen. Glycan microarray analysis and biophysical data reveal that these VLRs exhibit greater specificity for H-trisaccharide compared with the plant lectin UEA-1, which is widely used in blood typing. Among these antibodies, O13 exhibits superior specificity for H-trisaccharide, the basis for which is revealed by comparative analysis of high-resolution VLR:glycan crystal structures. Using a structure-guided approach, we designed an O13 mutant with further enhanced specificity for H-trisaccharide. These insights into glycan recognition by VLRs suggest that lampreys can produce highly specific glycan antibodies, and are a valuable resource for the production of next-generation glycan reagents for biological and biomedical research and as diagnostics and therapeutics.

Crystal structure of a family 6 cellobiohydrolase from the basidiomycete Phanerochaete chrysosporium

Cellobiohydrolases belonging to glycoside hydrolase family 6 (CBH II, Cel6A) play key roles in the hydrolysis of crystalline cellulose. CBH II from the white-rot fungus Phanerochaete chrysosporium (PcCel6A) consists of a catalytic domain (CD) and a carbohydrate-binding module connected by a linker peptide, like other known fungal cellobiohydrolases. In the present study, the CD of PcCel6A was crystallized without ligands, and p-nitrophenyl β-D-cellotrioside (pNPG3) was soaked into the crystals. The determined structures of the ligand-free and pNPG3-soaked crystals revealed that binding of cellobiose at substrate subsites +1 and +2 induces a conformational change of the N-terminal and C-terminal loops, switching the tunnel-shaped active site from the open to the closed form.

Interactions between a Heparin Trisaccharide Library and FGF-1 Analyzed by NMR Methods

FGF-1 is a potent mitogen that, by interacting simultaneously with Heparan Sulfate Glycosaminoglycan HSGAG and the extracellular domains of its membrane receptor (FGFR), generates an intracellular signal that finally leads to cell division. The overall structure of the ternary complex Heparin:FGF-1:FGFR has been finally elucidated after some controversy and the interactions within the ternary complex have been deeply described. However, since the structure of the ternary complex was described, not much attention has been given to the molecular basis of the interaction between FGF-1 and the HSGAG. It is known that within the complex, the carbohydrate maintains the same helical structure of free heparin that leads to sulfate groups directed towards opposite directions along the molecular axis. The precise role of single individual interactions remains unclear, as sliding and/or rotating of the saccharide along the binding pocket are possibilities difficult to discard. The HSGAG binding pocket can be subdivided into two regions, the main one can accommodate a trisaccharide, while the other binds a disaccharide. We have studied and analyzed the interaction between FGF-1 and a library of trisaccharides by STD-NMR and selective longitudinal relaxation rates. The library of trisaccharides corresponds to the heparin backbone and it has been designed to interact with the main subsite of the protein.

Structure of the LPS O-chain from Fusobacterium nucleatum strain 10953, containing sialic acid

Fusobacterium nucleatum is an anaerobic bacterium found in the human mouth where it causes periodontitis. Recently, it has been gaining attention as a potential causative agent for colorectal cancer and is strongly linked with pregnancy complications including pre-term and still births. Little is known about virulence factors of this organism and thus we have initiated studies to examine the bacterial surface glycochemistry. Consistent with a recent paper suggesting that F. nucleatum strain 10593 can synthesize sialic acid, a staining technique identified sialic acid on the bacterial surface. We isolated lipopolysaccharide from this F. nucleatum strain and performed structural analysis on the O-antigen. Our studies identified a trisaccharide repeating unit of the O-antigen with the following structure: -[→4)-α-Neup5Ac-(2 → 4)-β-d-Galp-(1 → 3)-α-d-FucpNAc4NAc-(1-]- where Ac indicates 4-N-acetylation of ∼30% FucNAc4N residues. The presence of sialic acid as a constituent of the O-antigen is consistent with recent data identifying de novo sialic acid synthesis in this strain.

Glycodendrimer PPI as a Potential Drug in Chronic Lymphocytic Leukaemia. The Influence of Glycodendrimer on Apoptosis in In Vitro B-CLL Cells Defined by Microarrays

BACKGROUND

Chronic lymphocytic leukaemia (CLL) cells are characterized by failures in the apoptosis pathway and increased proliferation, resulting in the progressive accumulation of B-lymphocytes in blood. Despite the wide range of antileukaemic drugs, CLL remains an incurable disease. However, a breakthrough is expected which will allow more effective treatment.

OBJECTIVE

The study investigates the influence of poly(propyleneimine) (PPI) dendrimer with peripheral amino groups, 30% of which were coated with maltotriose (PPI-G4-OS-Mal-III), on CLL cells, and demonstrates that it acts through the induction of the apoptotic mechanism. It is important to note that the dendrimer was used as a drug itself and not as a drug carrier.

METHOD

CLL and normal lymphocytes were treated in vitro with the dendrimer, either alone or in combination with fludarabine (FA). The percentages of apoptotic and necrotic cells, and the protein expression, were checked using a flow cytometer. Gene expression was screened using a two-colour microarray with 60-mer probes.

RESULTS

The results confirm that PPI-G4-OS-Mal-III influences the viability of CLL cells in vitro and does not exert any significant harmful effect on normal lymphocytes. The dendrimer appears to significantly influence gene and protein expression in CLL cells.

CONCLUSION

Since dendrimers can be specifically targeted, they may be very effective in CLL therapy, especially since in vitro PPI-G4-OS-Mal-III has been found to have stronger effect than fludarabine.

Functional dissection of the N-terminal sequence of Clostridium sp. G0005 glucoamylase: identification of components critical for folding the catalytic domain and for constructing the active site structure

Clostridium sp. G0005 glucoamylase (CGA) is composed of a β-sandwich domain (BD), a linker, and a catalytic domain (CD). In the present study, CGA was expressed in Escherichia coli as inclusion bodies when the N-terminal region (39 amino acid residues) of the BD was truncated. To further elucidate the role of the N-terminal region of the BD, we constructed N-terminally truncated proteins (Δ19, Δ24, Δ29, and Δ34) and assessed their solubility and activity. Although all evaluated proteins were soluble, their hydrolytic activities toward maltotriose as a substrate varied: Δ19 and Δ24 were almost as active as CGA, but the activity of Δ29 was substantially lower, and Δ34 exhibited little hydrolytic activity. Subsequent truncation analysis of the N-terminal region sequence between residues 25 and 28 revealed that truncation of less than 26 residues did not affect CGA activity, whereas truncation of 26 or more residues resulted in a substantial loss of activity. Based on further site-directed mutagenesis and N-terminal sequence analysis, we concluded that the 26XaaXaaTrp28 sequence of CGA is important in exhibiting CGA activity. These results suggest that the N-terminal region of the BD in bacterial GAs may function not only in folding the protein into the correct structure but also in constructing a competent active site for catalyzing the hydrolytic reaction.

Synthesis and Evaluation of QS-21-Based Immunoadjuvants with a Terminal-Functionalized Side Chain Incorporated in the West Wing Trisaccharide

Three QS-21-based vaccine adjuvant candidates with a terminal-functionalized side chain incorporated in the west wing trisaccharide have been synthesized. The terminal polar functional group serves to increase the solubility of these analogues in water. Two of the synthetic analogues have been shown to have adjuvant activity comparable to that of GPI-0100. The stand-alone adjuvant activity of the new synthetic analogues again confirmed that it is a feasible way to develop new saponin-based vaccine adjuvants through derivatizing at the west wing branched trisaccharide domain. Inclusion of an additional polar functional group such as a carboxyl group (as in 3x) or a monosaccharide (as in 4x and 5x) is sufficient to increase the water solubility of the corresponding synthetic analogues to a level comparable to that of GPI-0100 and suitable for immunological studies and clinical application. The structure of the incorporated side chain has a significant impact on the adjuvant activity in terms of the magnitude and nature of the host's responses.

Highly efficient recovery of xylobiose from xylooligosaccharides using a simulated moving bed method

Xylobiose (X2), which is currently available from xylooligosaccharides (XOS), has been reported to have outstanding prebiotic function and to be highly suitable for application in food industries. This has sparked an interest in the economical production of X2 of high purity (> 99%) in food and prebiotic industries. To address such issue, we developed a highly-efficient chromatographic method for the recovery of X2 from XOS with high purity and high recovery. As a first step for this work, an eligible adsorbent for a large-scale separation between X2 and other XOS components was selected. For the selected adsorbent, a single-column experiment was carried out to determine the intrinsic parameters of all the XOS components, which were then used in the optimal design of the continuous X2-recovery process based on a simulated moving bed (SMB) chromatographic method. Finally, the performance of the designed X2-recovery SMB process was verified by the relevant SMB experiments, which confirmed that the developed process in this study could recover X2 from XOS with the purity of 99.5% and the recovery of 92.3% on a continuous-separation mode. The results of this study will be useful in enabling the economical production of high-purity X2 on a large scale.

Novel Combination of Prebiotics Galacto-Oligosaccharides and Inulin-Inhibited Aberrant Crypt Foci Formation and Biomarkers of Colon Cancer in Wistar Rats

The selectivity and beneficial effects of prebiotics are mainly dependent on composition and glycosidic linkage among monosaccharide units. This is the first study to use prebiotic galacto-oligosaccharides (GOS) that contains β-1,6 and β-1,3 glycosidic linkages and the novel combination of GOS and inulin in cancer prevention. The objective of the present study is to explore the role of novel GOS and inulin against various biomarkers of colorectal cancer (CRC) and the incidence of aberrant crypt foci (ACF) in a 1,2-dimethyl hydrazine dihydrochloride (DMH)-induced rodent model. Prebiotic treatments of combined GOS and inulin (57 mg each), as well as individual doses (GOS: 76-151 mg; inulin 114 mg), were given to DMH-treated animals for 16 weeks. Our data reveal the significant preventive effect of the GOS and inulin combination against the development of CRC. It was observed that inhibition of ACF formation (55.8%) was significantly (p ≤ 0.05) higher using the GOS and inulin combination than GOS (41.4%) and inulin (51.2%) treatments alone. This combination also rendered better results on short-chain fatty acids (SCFA) and bacterial enzymatic activities. Dose-dependent effects of prebiotic treatments were also observed on cecum and fecal bacterial enzymes and on SCFA. Thus, this study demonstrated that novel combination of GOS and inulin exhibited stronger preventive activity than their individual treatments alone, and can be a promising strategy for CRC chemoprevention.

Synthesis of part structures of Cryptococcus neoformans serotype C capsular polysaccharide

Cryptococcus neoformans is a fungal pathogen that can cause life-threatening infections in immunocompromised patients. The development of a vaccine based on the capsular polysaccharide of C. neoformans is still an open challenge due to the heterogeneity of the capsular polysaccharide and the difficulty of identifying protective epitopes. Therefore, construction of structurally defined part structures of the C. neoformans GXM capsule is in great demand. Herein is presented the synthesis of a 3-O-naphthalenylmethyl protected trisaccharide thioglycoside building block which is present in C. neoformans serotype C polysaccharide. Its property as a donor in a glycosylation reaction with a model acceptor has been evaluated together with its behaviour as an acceptor following removal of the temporary protecting group. The heavily branched hexasaccharide was obtained in good yields and excellent α-selectivity. The frame shifted octasaccharide structural triad motif for serotype C was also prepared following the same building block strategy. For the first time this structural motif, which is the most substituted amongst the four C. neoformans serotypes, was prepared. Three synthesized C. neoformans serotype C fragments of varying size, from penta-up to octasaccharide, were deprotected and will be included in unique glycoarrays to further investigate the possibility to develop a synthetic vaccine against this pathogen.

Aqueous Glycosylation of Unprotected Sucrose Employing Glycosyl Fluorides in the Presence of Calcium Ion and Trimethylamine

We report a synthetic glycosylation reaction between sucrosyl acceptors and glycosyl fluoride donors to yield the derived trisaccharides. This reaction proceeds at room temperature in an aqueous solvent mixture. Calcium salts and a tertiary amine base promote the reaction with high site-selectivity for either the 3'-position or 1'-position of the fructofuranoside unit. Because nonenzymatic aqueous oligosaccharide syntheses are underdeveloped, mechanistic studies were carried out in order to identify the origin of the selectivity, which we hypothesized was related to the structure of the hydroxyl group array in sucrose. The solution conformation of various monodeoxysucrose analogs revealed the co-operative nature of the hydroxyl groups in mediating both this aqueous glycosyl bond-forming reaction and the site-selectivity at the same time.

A biotechnological process efficiently co-produces two high value-added products, glucose and xylooligosaccharides, from sugarcane bagasse

In this study, a co-production of two high value-added products, glucose and xylooligosaccharides (XOS), was investigated by utilizing sugarcane bagasse (SB) within a multi-product bio-refinery framework optimized by Box-Behnken design-based response surface methodology. The developed process resulted in a maximum cellulose conversion of xylan-removed SB, 98.69±1.30%, and a maximum extracted SB xylan conversion into XOS (xylobiose and xylotriose) of 57.36±0.79% that was the highest SB xylan conversion reported in the literature, employing cellulase from Penicillium oxalicum EU2106 and recombinant endo-β-1,4-xylanase in Pichia pastoris. Consequently, a mass balance analysis showed that the maximum yields of glucose and XOS were 34.43±0.32g and 5.96±0.09 g per 100 g raw SB. Overall, this described process may be a preferred option for the comprehensive utilization of SB.

Structural characterisation of human galectin-4 N-terminal carbohydrate recognition domain in complex with glycerol, lactose, 3'-sulfo-lactose, and 2'-fucosyllactose

Galectin-4 is a tandem-repeat galectin with two distinct carbohydrate recognition domains (CRD). Galectin-4 is expressed mainly in the alimentary tract and is proposed to function as a lipid raft and adherens junction stabilizer by its glycan cross-linking capacity. Galectin-4 plays divergent roles in cancer and inflammatory conditions, either promoting or inhibiting each disease progression, depending on the specific pathological condition. The study of galectin-4's ligand-binding profile may help decipher its roles under specific conditions. Here we present the X-ray structures of human galectin-4 N-terminal CRD (galectin-4N) bound to different saccharide ligands. Galectin-4's overall fold and its core interactions to lactose are similar to other galectin CRDs. Galectin-4N recognises the sulfate cap of 3'-sulfated glycans by a weak interaction through Arg45 and two water-mediated hydrogen bonds via Trp84 and Asn49. When galectin-4N interacts with the H-antigen mimic, 2'-fucosyllactose, an interaction is formed between the ring oxygen of fucose and Arg45. The extended binding site of galectin-4N may not be well suited to the A/B-antigen determinants, α-GalNAc/α-Gal, specifically due to clashes with residue Phe47. Overall, galectin-4N favours sulfated glycans whilst galectin-4C prefers blood group determinants. However, the two CRDs of galectin-4 can, to a less extent, recognise each other's ligands.