Conformational analysis of aqueous pullulan oligomers: an effective computational approach

A polysaccharide from Lycium barbarum L.: Structure and protective effects against oxidative stress and high-glucose-induced apoptosis in ARPE-19 cells

Lycium barbarum polysaccharides (LBPs) are beneficial for vision; however, relevant research has mainly focused on entire crude polysaccharides, with the basis and exact structure of the polysaccharide rarely explored. In this study, LICP009-3F-2a, a novel polysaccharide from Lycium barbarum L., was separated and then purified using anion-exchange and size-exclusion chromatography. Structural characteristics were investigated using chemical and spectroscopic methods, which revealed that LICP009-3F-2a has an Mw of 13720 Da and is an acidic heteropolysaccharide composed of rhamnose (39.1%), arabinose (7.4%), galactose (22.5%), glucose (8.3%), galacturonic acid (13.7%), and glucuronic acid (4.0%). Linkage and NMR data revealed that LICP009-3F-2a has the following backbone: →2)-α-L-Rha-(1→2,4)-α-L-Rha- (1→4)-α-D-GalAp-(1→3,6)-β-D-Galp-(1→3,6)-β-D-Galp-(1→6)-β-D-Galp-(1→, with three main branches, including: α-L-Araf-(1→5)-α-L-Araf-(1→6)-β-D-Glcp-(1→2,4)-α-L-Rha-(1→, β-D-Glcp-(1→4)-β-D-Glcp-(1→3,6)-β-D-Galp-(1→, and β-D-Galp-(1→3)-β-D-Galp-(1→3,6) -β-D-Galp-(1→. Differential scanning colorimetry and thermogravimetric analysis showed that LICP009-3F-2a is thermally stable, while X-ray diffractometry showed that LICP009-3F-2a has a semi-crystalline structure. In addition, LICP009-3F-2a protects ARPE-19 cells from H₂O₂-induced oxidative damage by regulating the expression of antioxidant SOD1 and CAT enzymes and down-regulating MMP2 expression. Moreover, LICP009-3F-2a promotes the proliferation of ARPE-19 cells in a concentration-dependent manner, and protects ARPE-19 cells from hyperglycemia by inhibiting apoptosis.

Effect of Polysaccharide Conformation on Ultrafiltration Separation Performance

The manifold array of saccharide linkages leads to a great variety of polysaccharide architectures, comprising three conformations in aqueous solution: compact sphere, random coil, and rigid rod. This conformational variation limits the suitability of the commonly applied molecular weight cut-off (MWCO) as selection criteria for polysaccharide ultrafiltration membranes, as it is based on globular marker proteins with narrow M_w and hydrodynamic volume relation. Here we show the effect of conformation on ultrafiltration performance using randomly coiled pullulan and rigid rod-like scleroglucan as model polysaccharides for membrane rejection and molecular weight distribution. Ultrafiltration with a 10 kDa polyethersulfone membrane yielded significant different recoveries for pullulan and scleroglucan showing 1% and 71%, respectively. We found deviations greater than 77-fold between nominal MWCO and apparent M_w of pullulan and scleroglucan, while recovering over 90% polysaccharide with unchanged M_w. We anticipate our work as starting point towards an optimized membrane selection for polysaccharide applications.

Challenges for the modern analytical ultracentrifuge analysis of polysaccharides

This article reviews some of the recent advances in analytical ultracentrifugation and how these advances have impacted--and can impact--on our understanding of the size, shape through conformation modelling, interactions and charge properties of polysaccharides in solution, particularly when used in combination with other solution techniques and also imaging techniques. Specifically we look at (1) polysaccharide polydispersity and simple shape analysis by sedimentation velocity, and in particular using new approaches such as SEDFIT analysis; (2) polysaccharide molecular-weight analysis by sedimentation equilibrium and MSTAR analysis and how this complements analysis of size exclusion chromatography coupled to multi-angle laser light scattering; (3) polysaccharide conformation analysis using traditional procedures such as the Wales-van Holde ratio, power law or 'scaling' relations, more specialised treatments for rigid cylindrical structures, semi-flexible chains and worm-like coils and complications through draining effects; (4) Analysis of polysaccharide interactions and in particular complex formation phenomena, focusing on interesting applications in the areas of mucoadhesion and sedimentation fingerprinting; and (5) the possibilities for macromolecular charge and charge screening measurement.

Hyaluronan chain conformation and dynamics

An overview of the present state of research in the field of hyaluronan chain conformational aspects is presented. The relationship between structure and dynamics are illustrated for a series of hyaluronan oligomers. Conformational characteristics of hyaluronan chains are discussed, together with the dynamic chain patterns, evaluated by using a theoretical approach to diffusive polymer dynamics. The dependence of correlation times and NMR relaxation parameters from the chain dimension are investigated. Topological features and dimensional properties are related to the structural determinants by using classical computational methods of molecular mechanics and Monte Carlo simulation.

Current knowledge on biosynthesis, biological activity, and chemical modification of the exopolysaccharide, pullulan

The article presents an overview of the latest advances in investigations of the biosynthesis, molecular properties, and associated biological activity of pullulan. The literature survey on the pullulan biosynthesis is intended to illustrate how the great variety of environmental conditions as well as variability in strain characteristics influences the metabolic pathways of the pullulan formation and effects structural composition of the biopolymer. Molecular properties of pullulan as alpha-(1-->4)- and alpha-(1-->6)-glucan are discussed in terms of similarities with amylose and dextran structures, and an emphasis is made on the inherent biological activity of pullulan molecules. The author also attempts to summarize the concepts, options, and strategies in chemical modification of the biopolymer and to delineate future prospects in designing new biologically active derivatives.

Determination of structural peculiarities of dexran, pullulan and gamma-irradiated pullulan by Fourier-transform IR spectroscopy

Deconvoluted IR-absorbance spectra of dextran, pullulan and gamma-irradiated pullulan were analyzed in order to find the most specific spectral peculiarities that allow one to obtain information about the structure and conformation of these macromolecules in solvents that exhibit different influences on the system of intra- and intermolecular interactions. The changes in intensity and width of the IR bands at about 1040, 1020 and, in the case of pullulan, also at 996 cm(-1), were related to changes in conformation and short-range interactions of the polysaccharides. Furthermore, certain bands within the 1200-900 cm(-1) region were considered as a characteristic for the type of glycosidic linkage. The results of the FTIR spectroscopy study allowed one to suggest a predominant cleavage of the alpha-(1-->4) linkages upon the radiation-chemical destruction of pullulan.