Abstract
This review describes examples of the structural characterization of sugar chains in solutions or gels at the nano level using small-angle X-ray scattering (SAXS). The review initially focuses on carrageenan, a sulfate-containing electrolytic polysaccharide, aqueous solutions of which undergo gelation when cooled. The gelation process is based on the formation of double helix structures as crosslinking regions. The association state of the various sugar chains can be determined by SAXS. On the basis of SAXS results, it was demonstrated that a 3% solution of κ-carrageenan, with potassium ion as the counter cation, yields gels by initial double helix formation and the subsequent association of 2 double helices. In contrast, the gelation of ι-carrageenan, which contains a greater number of sulfate groups, was due solely to the formation of double helices. In the second example, the SAXS observation on the structural association between regioselectively desulfated heparin and fibroblast growth factor (FGF) is described. The SAXS results indicated that the sulfate group at the 2-O position in the iduronic acid moiety of heparin was essential for aggregation with FGF. It is suggested that the nature of this structural association influences physiological activity. Finally, the SAXS data from a cyclic sugar chain, which has a characteristic profile that differs from the linear chain structure, is presented, and its inclusion structure is described.
