Proposal of a new hydrogen-bonding form to maintain curdlan triple helix.
Curdlan and other beta-1,3-D-glucans form right-handed triple helices, and it has been believed that the intermolecular H-bond is present at the center of the helix to maintain the structure. In this H-bond model, three secondary OH groups form an inequilateral hexagonal shape perpendicular to the helix axis. This hexagonal form seems to be characteristic for beta-1,3-D-glucans and is widely accepted. We carried out MOPAC and ab initio calculations for the curdlan helix, and we propose a new intermolecular H-bonding model. In our model, the H-bonds are formed between the O2-atoms on different x-y planes along the curdlan helix, hence the H-bonds are not perpendicular to the helix axis. The new H-bonds are connected along the helix, traversing three curdlan chains to make a left-handed helix. Therefore, the H-bonding array leads to a reverse helix of the main chain. According to our MOPAC calculation, this model is more stable than the previous one. We believe that the continuous H-bonding array is stabilized by cooperative phenomena in the polymeric system.
Miyoshi
Kentaro
K
Department of Chemical Processes and Environments, Faculty of Environmental Engineering, The University of Kitakyushu, 1-1 Hibikino Wakamatsu-ku, Kitakyushu, Fukuoka 808-0135, Japan.
Uezu
Kazuya
K
Sakurai
Kazuo
K
Shinkai
Seiji
S
D002236:Carbohydrate Conformation; D006860:Hydrogen Bonding; D017433:Protein Structure, Secondary / Q000502:physiology; D047071:beta-Glucans / Q000737:chemistry* / Q000378:metabolism*
D047071:beta-Glucans; C038459:curdlan