Structural properties of poly C-scleroglucan complexes

Beta-d-glucan-based drug delivery system and its potential application in targeting tumor associated macrophages

Use of polysaccharides as carriers in drug delivery system is a hot topic, especially those with specific recognition of immune cells, enabling them to be applied in targeting delivery system. β-d-glucans are naturally occurring non-digestible polysaccharides with immunomodulatory activities that have attracted increasing attention to serve as therapeutic agents or immune-adjuvants. Being able to be specifically recognized by immune cells like macrophages, β-d-glucans can be developed as promising carriers for targeting delivery with stability, biocompatibility and specificity when applied in immunotherapy. Targeting tumor associated macrophages (TAMs) is an emerging strategy for cancer immunotherapy since it exerts anti-cancer effects based on modulating body immunity in tumor microenvironment (TME). This new strategy does not require high concentration of drugs to kill cancer cells directly and lessen tumor recurrence by creating unique immune memory for malignant cells. In this review, construction strategies of polysaccharide-based drug delivery system of three types of β-d-glucan including non-yeast and yeast β-d-glucans as well as hyper-branched β-d-glucan are discussed with reference to their branching characteristics and conformation. The applications of these β-d-glucans as nano-carrier for drug delivery targeting TAMs are also discussed.

Assembly of single-stranded polydeoxyadenylic acid and β-glucan probed by the sensing platform of graphene oxide based on the fluorescence resonance energy transfer and fluorescence anisotropy

Based on the fluorescence resonance energy transfer (FRET) and fluorescence anisotropy (FA), the present study reported proof-of-principle for a highly sensitive and rapid detection technique that can be precisely utilized for investigating the self-assembly of polydeoxyadenylic acid (poly(dA)) and β-glucan, and the interactions of the poly(dA)-β-glucan complex on the surface of graphene oxide (GO). Due to the noncovalent assembly of fluorescein amidite (FAM)-labeled poly(dA) and GO via π-π stacking, the fluorescence of (FAM)-labeled poly(dA) as a molecular aptamer beacon (MAB) was completely quenched by GO. Conversely, the addition of single-stranded lentinan (s-LNT) resulted in the significant restoration of fluorescence due to the formation of poly(dA)-s-LNT complexes with a stiff rod-like structure, which had a weak affinity to GO and kept the dyes away from GO. However, relatively weak fluorescence restoration was observed by adding another single-stranded curdlan (s-CUR) for positive control, indicative of complex formation with higher binding ability to GO. The fluorescence anisotropy (FA) was also combined to confirm the occurrence with different increments of anisotropy relative to the free poly(dA), which could be conveniently extended for detecting the assembly of other biomolecules with higher sensitivity.

β-1,3-D-glucan schizophyllan/poly(dA) triple-helical complex in dilute solution

A certain length of poly(deoxyadenylic acid) (dA(X)) can form a novel complex with β-1,3-D-glucan schizophyllan (SPG) with a stoichiometric composition of one dA binding two main chain glucoses. We measured dilute solution properties for the complex with light and small-angle X-ray scattering as well as intrinsic viscosity and found that the complex behaves as a semiflexible rod without branching or cross-linking. We analyzed the data with the wormlike cylinder model, and the chain dimensions and the persistence length for the complexes were consistently determined. The chain flexibility was reduced to almost 25% upon complexation for dA/SPG and to 15% for S-dA/SPG, where S-dA denotes the phosphorothioated DNA analogue. The changes in the molar mass per unit length and the diameter indicated that the helix was elongated or stretched along the axis direction upon the complexation.

Characterization of high-molecular-weight nonnative aggregates and aggregation kinetics by size exclusion chromatography with inline multi-angle laser light scattering

Size exclusion chromatography with an inline multi-angle light scattering detector (SEC-MALS) was assessed as a means to characterize and monitor the formation of soluble, high-molecular-weight (HMW) protein aggregates so as to better quantify and model nonnative aggregation kinetics. Assay configuration and robustness were tested with respect to sample preparation, column type, and assay variability. Independent comparison of SEC-MALS with batch light scattering analysis indicates good agreement between the two methods. Weight-average molecular weight (M(w)), radius of gyration (R(g)), apparent polydispersity, and mass fraction monomer (m) together are shown to provide qualitative and quantitative experimental signatures to distinguish high-MW aggregate growth via chain polymerization versus that via aggregate-aggregate condensation. Mechanistic treatment of aggregation kinetics monitored by SEC-MALS is illustrated by data regression using a recently developed Lumry-Eyring Nucleated Polymerization model that explicitly accounts for aggregate nucleation and competing growth via chain- and condensation-polymerization. The combination of time-dependent M(w) and m data are shown to provide a convenient and robust means to separate and quantify characteristic time scales or rate coefficients for concurrent stages of irreversible aggregation. In addition, the scaling of R(g) with M(w) for HMW aggregates provides useful insights into aggregate morphology and mechanisms of aggregate growth.

Higher order structure of (1,3)-beta-D-glucans and its influence on their biological activities and complexation abilities

(1,3)-beta-D-Glucans form a group of biologically active biopolymers that exist in different structural organizations depending on the environmental conditions. The biological effect of (1,3)-beta-D-glucans is a core issue stimulating large research efforts of the molecular properties and their consequences for action as biological response modifiers. The fascination for these molecules increased further following the finding of their ability to form complexes of defined geometry with a number of structures, ranging from linear architectures as polymers or carbon nanotubes, to globular structures as gold particles or dye molecules. The fascinating information concerning the relationship between sample treatment history and molecular organization has not yet reached out to all the contributors within the field, resulting in unnecessary apparent inconsistencies in the literature. In addition to environmental conditions, the sample history is known to influence on the precise structural organization of these molecules. The present knowledge related to the structure of native as well as denatured, renatured and annealed (1,3)-beta-D-glucans is reviewed. The influence of their structural organization on the biological activity and complexation abilities is discussed, and some factors hindering progress in the understanding of their biological effects or complexation abilities are pointed out.

Potentiation of histamine release by Microfungal (1-->3)- and (1-->6)-beta-D-glucans

(1-->3)-beta-D-Glucans, a cell wall component in most microfungi, are suggested to play a role in the development of respiratory and general symptoms in organic dust-related diseases. The mechanisms by which they induce these effects are, however, not clear. In the present study, mediator release and its potentiation by the (1-->3)-beta-D-glucan as well as by the (1-->6)-beta-D-glucan found in yeast and other fungi were therefore examined. Blood leucocytes from healthy volunteers and from patients allergic to house dust mite were incubated with (1-->3)-beta-D-glucans with increasing 1,6-branchings: curdlan [a linear (1-->3)-beta-D-glucan], laminarin and scleroglucan, and furthermore with pustulan, a linear (1-->6)-beta-D-glucan. Histamine release was not observed on exposure to the glucans only, but in the presence of anti-immunoglobulin E (IgE) antibody or specific antigens, all the glucans investigated led to an enhancement of the IgE-mediated histamine release. The glucans induced a significant potentiation of the mediator release when present at concentrations in the range of 2-5 x 10(-5) M. These results suggest that (1-->3)-beta-D-glucan as well as (1-->6)-beta-D-glucan aggravates IgE-mediated histamine release. Knowledge concerning the effects of glucans on immune responses may be of importance for understanding and treating inflammatory and allergic diseases.

Instantaneous inclusion of a polynucleotide and hydrophobic guest molecules into a helical core of cationic beta-1,3-glucan polysaccharide

We succeeded in the quantitative and selective introduction of an ammonium cationic group into the C6 position of Curdlan (CUR) by "Click Chemistry", and the obtained cationic Curdlan (CUR-N+) showed good solubility in water. ORD studies suggested that CUR-N+ adopts a single-stranded structure, different from a right-handed, triple-stranded helical structure of beta-1,3-glucan polysaccharides in water. It has been revealed that the polymeric complexes of CUR-N+ with polymeric guest molecules, such as polycytidylic acid (poly(C)), permethyldecasilane (PMDS), and single-walled carbon nanotubes (SWNTs), can be easily obtained by just mixing them in water with sonication. The characterization of the resultant CUR-N+-poly(C) complexes by UV-vis, CD spectroscopic measurements, and AFM and TEM observations revealed that they have stoichiometric, nanosized fibrous structures. From these experimental results as well as our precedent studies (e.g., refs 6 and 23), we propose that the complexation would be driven by the cooperative action of (1) the hydrogen-bonding interaction between the OH group at the C2 position and hydrogen-bonding sites of the cytosine ring (ref 6d), (2) the electrostatic interaction between the ammonium cation and the phosphate anion (ref 23), as well as (3) the background hydrophobic interaction. In addition, the complexed polynucleotide chain showed a strong resistance against enzymatic hydrolysis. Likewise, the dispersion of PMDS and SWNTs in water by CUR-N+ and the fibrous structures of the complexes were confirmed by spectroscopic measurements as well as microscopic observations. These binding properties of CUR-N+, which can proceed spontaneously in water, clearly differ from those of schizophyllan (SPG), which inevitably require a denature-renature process corresponding to a conversion of a triple strand to single strands induced by DMSO or base for inclusion of polymeric guest molecules.

Explicit-solvent molecular dynamics simulations of the polysaccharide schizophyllan in water

Schizophyllan is a beta(1-->3)-D-glucan polysaccharide with beta(1-->6)-branched lateral glucose residues that presents a very stiff triple-helical structure under most experimental conditions. Despite the remarkable stability of this structure (which persists up to 120 degrees C in aqueous solution), schizophyllan undergoes a major change of state around 7 degrees C in water that has been hypothesized to result from an order-disorder transition in the lateral residues. This hypothesis is only supported by indirect experimental evidence and detailed knowledge (at the atomic level) concerning hydrogen-bonding networks, interactions with the solvent molecules, orientational freedom of the lateral residues, and orientational correlations among them is still lacking. In this study explicit-solvent molecular dynamics simulations of a schizophyllan fragment (complemented by simulations of its tetrasaccharide monomer) are performed at three different temperatures (273 K, 350 K, and 450 K) and with two different types of boundary conditions (finite nonperiodic or infinite periodic fragment) as an attempt to provide detailed structural and dynamical information about the triple-helical conformation in solution and the mechanism of the low-temperature transition. These simulations suggest that three important driving forces for the high stability of the triple helix are i), the limited conformational work involved in its formation; ii), the formation of a dense hydrogen-bonding network at its center; and iii), the formation of interchain hydrogen bonds between main-chain and lateral glucose residues. However, these simulations evidence a moderate and continuous variation of the simulated observables upon increasing the temperature, rather than a sharp transition between the two lowest temperatures (that could be associated with the state transition). Although water-mediated hydrogen-bonded association of neighboring lateral residues is observed, this interaction is not strong enough to promote the formation of an ordered state (correlated motions of the lateral residues), even at the lowest temperature considered.

Determination of molecular size and shape of hyperbranched polysaccharide in solution

The chemical structure of a water-soluble polysaccharide, coded as TM3b, extracted from sclerotia of Pleurotus tuber-rigium was analyzed to be a hyperbranched beta-D-glucan with beta-(1-->6), beta-(1-->4), and beta-(1-->3)-linked residues, with degree of branching (DB) of 57.6%. The results from size-exclusion chromatography combined with laser light scattering (SEC-LLS) revealed that the hyperbranched polysaccharide easily aggregated in 0.15 M aqueous NaCl, whereas it dispersed as individual chains in DMSO. The weight-average molecular weight (M(w)), radius of gyration, intrinsic viscosity, and chain density of TM3b in DMSO and in 0.15 M aqueous NaCl were measured with SEC-LLS, LLS, and viscometry. The results indicated that single chains and aggregates with aggregation number of 12 coexisted in the aqueous solution, whereas individual molecules of TM3b occurred in DMSO. In view of the molecular parameters, the aggregates in aqueous solution exhibited more compact chain structure than the individual molecules in DMSO. Furthermore, transmission electron microscopy and atomic force microscopy showed that all of the aggregates and individual molecules exhibited spherical particles in the solutions. This work provided the valuable information of chain conformation and molecular morphology of the hyperbranched polysaccharide in different solvents.

Too many strictures on structure

In a recent Opinion article in Trends in Microbiology, Dmitriev et al. proposed an alternative to the existing model of peptidoglycan structure, in which the cell wall is composed of chains that are perpendicular to the membrane (as opposed to horizontal) and form a scaffold interconnected by peptide branches. However, both this model and the classical model are based on underlying assumptions about pore sizes, composition and structural regularity that deserve careful consideration. Not only do the uncertainties surrounding these basic mechanical questions make it impossible to decide which model of peptidoglycan structure is correct, they also leave open the possibility that the real structure is an amalgam of these or other models that have yet to be described.