Structural observation of complexes of FGF-2 and regioselectively desulfated heparin in aqueous solutions.

In order to clarify the mechanism of interaction between FGF-2 and heparin, the association structures between human FGF-2 and different kinds of regioselectively desulfated heparins were observed by small angle X-ray scattering. In the FGF-2-native heparin complex, the global FGF-2 molecules appeared to attach along heparin chain as strained unilaterally. The complexes with the 6-O-, or N-desulfated heparin seemed to have randomly associated structure as compared with above system. On the other hand, 2-O-desulfated heparin did not indicate the aggregation with FGF-2, indicating that the sulfate groups at O-2 of iduronate residues in heparin is most essential for association with FGF-2. These structural characteristics will be deeply related with signal transduction in the association with FGF-2 receptor.

Effect of the carbohydrate side-chain on the conformation of a glycoconjugate polystyrene in aqueous solution.

An oligomaltose-carrying polystyrene "glycoconjugate polystyrene" was synthesized by the homopolymerization of 4-vinylbenzylamine oligomaltonic amides, derived from maltose, maltotriose, maltopentaose, and maltoheptaose. The resultant amphiphilic glycoconjugate polystyrenes were dissolved in 0.1 M aqueous urea, and their structures characterized by small-angle X-ray scattering and molecular modeling. "Glycoconjugate polystyrene" was found to behave as a "molecular bottle brush", composed of a large pseudo-helical polystyrene backbone and carbohydrate brushes. A large pseudo-helical polystyrene backbone is formed by a random sequence of TT, TG, and/or TTGG. The results indicate that the cross-section of a backbone chain with smaller oligosaccharide side-chains is obliged to expand more than that with longer side-chains. Even with rigid hydrophilic pendant oligosaccharide chains, the larger pseudo-helix of the main chain could orient the side-chains so as to envelop the hydrophobic backbone in aqueous solution. Thus the conformation of the main chain is determined not only by the chemical nature of an oligosaccharide chain but also by its length.

Small-angle X-ray scattering and rheological characterization of alginate gels. 3. Alginic acid gels.

Alginic acid gels were studied by small-angle X-ray scattering and rheology to elucidate the influence of alginate chemical composition and molecular weight on the gel elasticity and molecular structure. The alginic acid gels were prepared by homogeneous pH reduction throughout the sample. Three alginates with different chemical composition and sequence, and two to three different molecular weights of each sample were examined. Three alginate samples with fractions of guluronic acid residues of 0.39 (LoG), 0.50 (InG), and 0.68 (HiG), covering the range of commercially available alginates, were employed. The excess scattering intensity I of the alginic acid gels was about 1 order of magnitude larger and exhibited a stronger curvature toward low q compared to ionically cross-linked alginate. The I(q) were decomposed into two components by assuming that the alginic acid gel is composed of aggregated multiple junctions and single chains. Time-resolved experiments showed a large increase in the average size of aggregates and their weight fraction within the first 2 h after onset of gelling, which also coincides with the most pronounced rheological changes. At equilibrium, little or no effect of molecular weight was observed, whereas at comparable molecular weights, an increased scattering intensity with increasing content of guluronic acid residues was recorded, probably because of a larger apparent molecular mass of domains. The results suggest a quasi-ordered junction zone is formed in the initial stage, followed by subsequent assembling of such zones, forming domains in the order of 50 A. The average length of the initial junction zones, being governed by the relative fraction of stabilizing G-blocks and destabilizing alternating (MG) blocks, determines the density of the final random aggregates. Hence, high-G alginates give alginic acid gels of a higher aggregate density compared to domains composed of loosely packed shorter junction zones in InG or LoG system.