Conformation-dependent change in antitumor activity of linear and branched (1----3)-beta-D-glucans on the basis of conformational elucidation by carbon-13 nuclear magnetic resonance spectroscopy

Dectin-1 multimerization and signaling depends on fungal β-glucan structure and exposure

Dectin-1A is a C-type lectin innate immunoreceptor that recognizes β-(1,3;1,6)-glucan, a structural component of Candida species cell walls. β-Glucans can adopt solution structures ranging from random coil to insoluble fiber due to tertiary (helical) and quaternary structure. Fungal β-glucans of medium and high molecular weight are highly structured, but low molecular weight glucan is much less structured. Despite similar affinity for Dectin-1, the ability of glucans to induce Dectin-1A-mediated signaling correlates with degree of structure. Glucan denaturation experiments showed that glucan structure determines agonistic potential, but not receptor binding affinity. We explored the impact of glucan structure on molecular aggregation of Dectin-1A. Stimulation with glucan signaling decreased Dectin-1A diffusion coefficient. Fluorescence measurements provided direct evidence of ligation-induced Dectin-1A aggregation, which positively correlated with increasing glucan structure content. In contrast, Dectin-1A is predominantly in a low aggregation state in resting cells. Molecular aggregates formed during interaction with highly structured, agonistic glucans did not exceed relatively small (<15 nm) clusters of a few engaged receptors. Finally, we observed increased molecular aggregation of Dectin-1A at fungal particle contact sites in a manner that positively correlated with the degree of exposed glucan on the particle surface. These results indicate that Dectin-1A senses the solution conformation of β-glucans through their varying ability to drive receptor dimer/oligomer formation and activation of membrane proximal signaling events.

Immunostimulatory effects of a subcritical water extract of Ganoderma

Ganoderma, a medicinal mushroom with various physiological activities, has been extensively investigated regarding its effectiveness. The aim of the present study was to examine the effects of a subcritical water extract of Ganoderma (SWEG) on the immune system. The use of subcritical water with a higher temperature and pressure than hot water allows efficient elution of components from natural products. As an evaluation of the effectiveness of SWEG, a cell proliferation and a cell differentiation test were carried out using A-6 cells, a model of hematopoietic stem cells. Furthermore, an oral administration test in mice was conducted to examine the effects of SWEG on the number and function of immune cells. As a result, SWEG was revealed to promote both self-renewal and differentiation into immune cells such as T cells and natural killer (NK) cells in experiments with A-6 cells. These results were not obtained in experiments using hot water extract of Ganoderma lucidum and Ganoderma sinense. The oral administration test in mice demonstrated that SWEG increased hematopoietic precursor cells, immature B cells, and NK cells in the bone marrow, and T cells in the thymus. In addition, SWEG enhanced the immune functions in the spleen by promoting granzyme B expression and NK cell activity. SWEG was demonstrated to be a food material that acts on HSCs and regulates immunity in vivo.

From Cancer Therapy to Winemaking: The Molecular Structure and Applications of β-Glucans and β-1, 3-Glucanases

β-glucans are a diverse group of polysaccharides composed of β-1,3 or β-(1,3-1,4) linked glucose monomers. They are mainly synthesized by fungi, plants, seaweed and bacteria, where they carry out structural, protective and energy storage roles. Because of their unique physicochemical properties, they have important applications in several industrial, biomedical and biotechnological processes. β-glucans are also major bioactive molecules with marked immunomodulatory and metabolic properties. As such, they have been the focus of many studies attesting to their ability to, among other roles, fight cancer, reduce the risk of cardiovascular diseases and control diabetes. The physicochemical and functional profiles of β-glucans are deeply influenced by their molecular structure. This structure governs β-glucan interaction with multiple β-glucan binding proteins, triggering myriad biological responses. It is then imperative to understand the structural properties of β-glucans to fully reveal their biological roles and potential applications. The deconstruction of β-glucans is a result of β-glucanase activity. In addition to being invaluable tools for the study of β-glucans, these enzymes have applications in numerous biotechnological and industrial processes, both alone and in conjunction with their natural substrates. Here, we review potential applications for β-glucans and β-glucanases, and explore how their functionalities are dictated by their structure.

A Stable Gold Nanoparticle-Based Vaccine for the Targeted Delivery of Tumor-Associated Glycopeptide Antigens

We have developed a novel antigen delivery system based on polysaccharide-coated gold nanoparticles (AuNPs) targeted to antigen presenting cells (APCs) expressing Dectin-1. AuNPs were synthesized de-novo using yeast-derived β-1,3-glucans (B13G) as the reductant and passivating agent in a microwave-catalyzed procedure yielding highly uniform and serum-stable particles. These were further functionalized with both a peptide and a specific glycosylated form from the tandem repeat sequence of mucin 4 (MUC4), a glycoprotein overexpressed in pancreatic tumors. The glycosylated sequence contained the Thomsen-Friedenreich disaccharide, a pan-carcinoma, Tumor-Associated Carbohydrate Antigen (TACA), which has been a traditional target for antitumor vaccine design. These motifs were prepared with a cathepsin B protease cleavage site (Gly-Phe-Leu-Gly), loaded on the B13G-coated particles and these constructs were examined for Dectin-1 binding, APC processing and presentation in a model in vitro system and for immune responses in mice. We showed that these particles elicit strong in vivo immune responses through the production of both high-titer antibodies and priming of antigen-recognizing T-cells. Further examination showed that a favorable antitumor balance of expressed cytokines was generated, with limited expression of immunosuppressive Il-10. This system is modular in that any range of antigens can be conjugated to our particles and efficiently delivered to APCs expressing Dectin-1.

Preparation and characterization of curdlan with unique single-helical conformation and its assembly with Congo Red

Elucidating the structure-activity relationship of curdlan is hampered by a lack of characterization with unique specific conformations (i.e., single- or triple-helix). In this study, single-helical curdlan is generated in dilute NaOH solutions at 35-50 °C, and characterized with NMR, SAXS, and GPC. The conformational transition from coil to single-helix and the intramolecular hydrogen bond interaction are explored using NMR. It is found that the two aforementioned types of curdlan interact with Congo Red in very different ways. Single-helical curdlan can encapsulate Congo Red to form a stable, supramolecular dye assembly, which is demonstrated by the shortest distance between the H3 of curdlan and the phenyl groups of Congo Red, and also the same self-diffusion coefficients of Congo Red and curdlan. In contrast, random-coil curdlan interacts weakly with Congo Red and cannot enwrap it. This study offers insight into the specific structure-activity relationship of beta-(1,3)-glucans.

Molecular dynamic simulation: Structural insights of multi-stranded curdlan in aqueous solution

In this work, by using molecular dynamic simulation we provide microscale structure information which helps to reveal the molecular mechanisms concerning the multi-chain conformational behavior of short curdlan. Through simulations starting with different conformations of curldan dodecasaccharides, it is found that the right-handed triple helix is thermodynamically the most stable conformation in aqueous solutions, which is well maintained and stabilized by an inter-strand hydrogen bonding network of the C₂ hydroxyls. Unlike any predicted forms, the inter-strand hydrogen bonds exhibit a left-handed double helix pattern with preferred global orientations. Temperature REMD results suggest that the formation of triple helix is temperature sensitive, but the already formed triple helix is not. Investigation of curdlan with numbers of repeating units from 3 to 12 captures a critical value of 6, which in a way elucidates the relationship between the formation of triple helix and the chain length.

3D Structural Insights into β-Glucans and Their Binding Proteins

β(1,3)-glucans are a component of fungal and plant cell walls. The β-glucan of pathogens is recognized as a non-self-component in the host defense system. Long β-glucan chains are capable of forming a triple helix structure, and the tertiary structure may profoundly affect the interaction with β-glucan-binding proteins. Although the atomic details of β-glucan binding and signaling of cognate receptors remain mostly unclear, X-ray crystallography and NMR analyses have revealed some aspects of β-glucan structure and interaction. Here, we will review three-dimensional (3D) structural characteristics of β-glucans and the modes of interaction with β-glucan-binding proteins.

A Cyclic Periodic Wave Function Approach for the Study of Infinitely Periodic Solid-State Systems: II. Application to Helical Polysaccharides

The cyclic periodic wave function (CPWF) approach is applied at the AM1 and PM3 semiempirical levels of approximation to two infinitely periodic polymer systems in the solid state. The two polysaccharides of interest here are (1→3)-β-d-glucan and (1→3)-β-d-xylan. Our calculated results show excellent agreement with the available data for the two polysaccharides and demonstrate that the use of the CPWF approach at the AM1 and PM3 levels of approximation provides a convenient and reliable method for the study of infinitely periodic bonds of two different types: moderately strong O-H···O hydrogen bonding and strong C-O-C covalent bonding.

Molecular Interactions of β-(1→3)-Glucans with Their Receptors

β-(1→3)-Glucans can be found as structural polysaccharides in cereals, in algae or as exo-polysaccharides secreted on the surfaces of mushrooms or fungi. Research has now established that β-(1→3)-glucans can trigger different immune responses and act as efficient immunostimulating agents. They constitute prevalent sources of carbons for microorganisms after subsequent recognition by digesting enzymes. Nevertheless, mechanisms associated with both roles are not yet clearly understood. This review focuses on the variety of elucidated molecular interactions that involve these natural or synthetic polysaccharides and their receptors, i.e., Dectin-1, CR3, glycolipids, langerin and carbohydrate-binding modules.

NMR study of short β(1-3)-glucans provides insights into the structure and interaction with Dectin-1

β(1-3)-Glucans, abundant in fungi, have the potential to activate the innate immune response against various pathogens. Although part of the action is exerted through the C-type lectin-like receptor Dectin-1, details of the interaction mechanism with respect to glucan chain-length remain unclear. In this study, we investigated a set of short β(1-3)-glucans with varying degree of polymerization (DP); 3, 6, 7, 16, and laminarin (average DP; 25), analyzing the relationship between the structure and interaction with the C-type lectin-like domain (CTLD) of Dectin-1. The interaction of short β(1-3)-glucans (DP6, DP16, and laminarin) with the CTLD of Dectin-1 was systematically analyzed by (1)H-NMR titration as well as by saturation transfer difference (STD)-NMR. The domain interacted weakly with DP6, moderately with DP16 and strongly with laminarin, the latter plausibly forming oligomeric protein-laminarin complexes. To obtain structural insights of short β(1-3)-glucans, the exchange rates of hydroxy protons were analyzed by deuterium induced (13)C-NMR isotope shifts. The hydroxy proton at C4 of laminarin has slower exchange with the solvent than those of DP7 and DP16, suggesting that laminarin has a secondary structure. Diffusion ordered spectroscopy revealed that none of the short β(1-3)-glucans including laminarin forms a double or triple helix in water. Insights into the interaction of the short β(1-3)-glucans with Dectin-1 CTLD provide a basis to understand the molecular mechanisms of β-glucan recognition and cellular activation by Dectin-1.

Structural insights into recognition of triple-helical beta-glucans by an insect fungal receptor

The innate ability to detect pathogens is achieved by pattern recognition receptors, which recognize non-self-components such as β1,3-glucan. β1,3-Glucans form a triple-helical structure stabilized by interchain hydrogen bonds. β1,3-Glucan recognition protein (βGRP)/gram-negative bacteria-binding protein 3 (GNBP3), one of the pattern recognition receptors, binds to long, structured β1,3-glucan to initiate innate immune response. However, binding details and how specificity is achieved in such receptors remain important unresolved issues. We solved the crystal structures of the N-terminal β1,3-glucan recognition domain of βGRP/GNBP3 (βGRP-N) in complex with the β1,3-linked glucose hexamer, laminarihexaose. In the crystals, three structured laminarihexaoses simultaneously interact through six glucose residues (two from each chain) with one βGRP-N. The spatial arrangement of the laminarihexaoses bound to βGRP-N is almost identical to that of a β1,3-glucan triple-helical structure. Therefore, our crystallographic structures together with site-directed mutagenesis data provide a structural basis for the unique recognition by such receptors of the triple-helical structure of β1,3-glucan.

Polysaccharide biological response modifiers

Biological response modifiers (BRMs) are substances which augment immune response. BRMs can be cytokines which are produced endogenously in our body by immune cells or derivatives of bacteria, fungi, brown algae, Aloe vera and photosynthetic plants. Such exogeneous derivatives (exogeneous BRMs) can be nucleic acid (CpG), lipid (lipotechoic acid), protein or polysaccharide in nature. The receptors for these exogeneous BRMs are pattern recognition receptors. The binding of exogeneous BRMs to pattern recognition receptors triggers immune response. Exogenous BRMs have been reported to have anti-viral, anti-bacterial, anti-fungal, anti-parasitic, and anti-tumor activities. Among different exogeneous BRMs, polysaccharide BRMs have the widest occurrence in nature. Some polysaccharide BRMs have been tested for their therapeutic properties in human clinical trials. An overview of current understandings of polysaccharide BRMs is summarized in this review.

Natural and modified (1-->3)-beta-D-glucans in health promotion and disease alleviation

A number of polysaccharides with beta-glycosidic linkage are widespread in nature in a variety of sources. All have a common structure and the (1-->3)-beta-D-glucan backbone is essential. They have attracted attention over the years because of their bioactive and medicinal properties. In many cases their functional role is a mystery, in others it is well established. Because of their insoluble chemical nature, particulate (1-->3)-beta-D-glucans are not suitable for many medical applications. Various methods of changing or modifying the beta-D-glucan chemical structure and transforming it to a soluble form have been published. The beta-D-glucan bioactive properties can be affected positively or negatively by such modifications. This review examines beta-glucan sources in nature, health effects and structure-activity relationships. It presents the current state of beta-D-glucan solubilization methods and discusses their effectiveness and application possibilities for the future.

Protein/Polysaccharide Cogel Formation Based on Gelatin and Chemically Modified Schizophyllan

In the work, aldehyde groups were quantitatively introduced into schizophyllan (SPG) side chains through periodate oxidation. The periodate-oxidized SPG (POSPG) forms an elastic gel with gelatin. The cogel formation is based on the Schiff-base reaction between the amino groups of gelatin chains and the aldehyde groups of POSPG chains. The POSPG/gelatin cogel has an elastomeric character with a very small value of loss tangent. The gelation kinetics and gel properties were discussed as a function of POSPG concentration, gelatin concentration, oxidation degree, temperature, and pH. This method can be used to design a large variety of cogels between SPG and proteins.

Observation of a partially opened triple-helix conformation in 1-->3-beta-glucan by fluorescence resonance energy transfer spectroscopy

This study used fluorescence resonance energy transfer (FRET) spectroscopy as an indirect method to investigate the effect of NaOH treatment on the conformation of a triple-helix (1-->3)-beta-D-glucan and then evaluated the effect of conformation on biological activity. Previous studies have suggested that treatment of the triple-helix glucans with NaOH produces single-helix conformers. FRET spectra of the triple-helix glucan, laminarin, doubly labeled with 1-aminopyrene as donor probe and fluorescein-5-isothiocyanate as acceptor probe attached at the reducing end, showed that a partially opened triple-helix conformer was formed on treatment with NaOH. Increasing degrees of strand opening was associated with increasing concentrations of NaOH. Based on these observations we propose that a partially opened triple-helix rather than a single helix, is formed by treating the triple-helix glucans with NaOH. After neutralizing the NaOH, changes in FRET indicated that the partially opened conformer gradually reverts to the triple-helix over 8 days. Laminarian was stabilized at different degrees of partial opening and its biological activity examined using the Limulus amebocyte lysate assay and nitric oxide production by alveolar macrophage. Both Limulus amebocyte lysate activity and nitric oxide production were related to the degree of opening of the triple-helix. Partially open conformers were more biologically active than the intact triple-helix.

Immunotoxicity of soluble beta-glucans induced by indomethacin treatment

(1 --> 3)-Beta-D-Glucan (beta-glucan) is a biological response modifier that regulates host immune response. However, the side effects of this drug have not been extensively examined. In this study, we found that the combination of a beta-glucan and a nonsteroidal anti-inflammatory drug, indomethacin, induced lethal toxicity in mice. Lethal toxicity of orally administered indomethacin (multiple administration to ICR mice; once a day for 2 weeks) was 0/8 (2.5 mg kg(-1)) and 5/8 (5 mg kg(-1)) (death/total) over 2 weeks. The toxicity was enhanced to 3/8 and 8/8 in mice treated with a clinical beta-glucan preparation, sonifilan (250 microg/mouse, single i.p. administration on day 0). A similar effect was observed for other beta-glucans, including SSG, grifolan, zymosan A and zymocel. Enhanced lethal toxicity resulted from a single p.o. administration of indomethacin on day 5 to day 9 after multiple beta-glucans administration. Interferon-gamma, interleukin-6 and colony stimulating factor concentrations in sera of indomethacin/beta-glucan-treated mice were significantly elevated. These results strongly suggest that indomethacin/beta-glucan treatment induces lethality in mice by maladjusting the cytokine network.