Molecular Dynamics Studies of Side Chain Effect on the b-1,3-d-Glucan Triple Helix in Aqueous Solution

• Published in: Biomacromolecules 2008-02, Vol.9 (3), p.783-788
• Main Authors: Okobira, Tadashi, Miyoshi, Kentaro, Uezu, Kazuya, Sakurai, Kazuo, Shinkai, Seiji
• Format: Article
• Language: English
• ISSN: 1525-7797
• DOI: 10.1021/bm700511d

*b-1,3-d-Glucans have been isolated from fungi as right-handed 61 triple helices. They are categorized by the side chains bound to the main triple helix through *b-(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 *b-1,3-d-glucan series: curdlan (no side chain), schizophyllan (a *b-(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 *b-1,3-d-glucan triple helix could cause the tilt of the main-chain glucose residues to the helix.