title: Microfibrillar structure of PGG-glucan in aqueous solution as triple-helix aggregates by small angle x-ray scattering.
abstract: The conformation of polysaccharide PGG-Glucan, isolated from yeast cell walls, in aqueous solution was investigated by small angle x-ray scattering (SAXS) and multidetector gel permeation chromatography coupled with postcolumn delivery (GPC/PCD) techniques in comparison with scleroglucan. It was shown that both polysaccharides exhibit a rigid rod-like conformation in aqueous solution by SAXS experiments. The mass per unit length (M/L) and radius (R) of rod cross section of PGG-Glucan were measured to be 6300 daltons/nm and 1.89 nm, while those of scleroglucan are 2300 and 0.83, respectively. Utilizing a GPC/light scattering technique, the average aggregation number of PGG-Glucan is 9, while that of scleroglucan is around 3. From the comparison of the M/L and R of the respective rod cross sections as well as their aggregation number data, it is concluded that PGG-Glucan is composed of triple helices, which tend to aggregate as triplets in solution, whereas scleroglucan is composed of a single triple helix. The aggregation number distribution of PGG-Glucan was found to range from 1 to about 25 determined by GPC/PCD. From the observation of a Debye-Scherrer ring type of peak in the macroscopic scattering cross section of PGG-Glucan by SAXS, the existence of a small amount of ordered clusters of PGG-Glucan can be deduced. The "lattice parameter" of these ordered fasces-like clusters is consistent with the radius of the individual triple-helical rods forming a microfibrillar superstructure. These results indicate that higher aggregated forms of PGG-Glucan containing up to 8 triple helices behave as ordered fasces-like clusters. We conclude that PGG-Glucan is triple-helix aggregates formed by rigid rods stacking together side by side. We propose a molecular structural model for PGG-Glucan conformations.
authors.affiliation: Institut fur Feskorperforschung, Forschungszentrum Juelich GmbH, D-52425 Juelich, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Gawronski
authors.forename: J T
authors.initials: JT
authors.lastname: Park
authors.forename: A S
authors.initials: AS
authors.lastname: Magee
authors.forename: H
authors.initials: H
authors.lastname: Conrad
mesh_terms: D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D002850:Chromatography, Gel / Q000379:methods; D005936:Glucans / Q000737:chemistry*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D012542:Scattering, Radiation; D012996:Solutions; D014867:Water; D047071:beta-Glucans
chemical_list: D005936:Glucans; D012996:Solutions; D047071:beta-Glucans; C069894:poly-1-6-glucopyranosyl-1-3-glucopyranose glucan; D014867:Water; C045938:scleroglucan