title: Molecular dynamics studies of side chain effect on the beta-1,3-D-glucan triple helix in aqueous solution.
abstract: beta-1,3-D-glucans have been isolated from fungi as right-handed 6(1) triple helices. They are categorized by the side chains bound to the main triple helix through beta-(1-->6)-D-glycosyl linkage. Indeed, since a glucose-based side chain is water soluble, the presence and frequency of glucose-based side chains give rise to significant variation in the physical properties of the glucan family. Curdlan has no side chains and self-assembles to form an water-insoluble triple helical structure, while schizophyllan, which has a 1,6-D-glucose side chain on every third glucose unit along the main chain, is completely water soluble. A thermal fluctuation in the optical rotatory dispersion is observed for the side chain, indicating probable co-operative interaction between the side chains and water molecules. This paper documents molecular dynamics simulations in aqueous solution for three models of the beta-1,3-D-glucan series: curdlan (no side chain), schizophyllan (a beta-(1-->6)-D-glycosyl side-chain at every third position), and a hypothetical triple helix with a side chain at every sixth main-chain glucose unit. A decrease was observed in the helical pitch as the population of the side chain increased. Two types of hydrogen bonding via water molecules, the side chain/main chain and the side chain/side chain hydrogen bonding, play an important role in determination of the triple helix conformation. The formation of a one-dimensional cavity of diameter about 3.5 A was observed in the schizophyllan triple helix, while curdlan showed no such cavity. The side chain/side chain hydrogen bonding in schizophyllan and the hypothetical beta-1,3-D-glucan triple helix could cause the tilt of the main-chain glucose residues to the helix.
authors.affiliation: Department of Chemical Processes and Environments, Faculty of Environmental Engineering, The University of Kitakyushu, 1-1 Hibikino, Wakamatsu-ku, Kitakyushu, Fukuoka 808-0135, Japan.
authors.forename: Tadashi
authors.initials: T
authors.lastname: Okobira
authors.forename: Kentaro
authors.initials: K
authors.lastname: Miyoshi
authors.forename: Kazuya
authors.initials: K
authors.lastname: Uezu
authors.forename: Kazuo
authors.initials: K
authors.lastname: Sakurai
authors.forename: Seiji
authors.initials: S
authors.lastname: Shinkai
mesh_terms: D002240:Carbohydrate Sequence; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D011509:Proteoglycans; D012566:Sizofiran / Q000737:chemistry*; D012996:Solutions; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*; D047071:beta-Glucans / Q000737:chemistry*
chemical_list: D011509:Proteoglycans; D012996:Solutions; D047071:beta-Glucans; D014867:Water; C010770:polysaccharide-K; C038459:curdlan; D012566:Sizofiran