Yui T, Goto K, Kawano Y, Ogawa K
Faculty of Engineering, Miyazaki University, Japan.
Biosci Biotechnol Biochem. 2000 Jan;64(1):52-60. doi: 10.1271/bbb.64.52.
A systematic search for possible regular helical structures of a highly branching (1-->3)-alpha-D-glucan was done using the n-h mapping technique, combined with MM3-generated relaxed-residue energy map calculations with respect to the conformations of the backbone glycosidic linkages. The alpha-D-glucan, consisting of a (1-->3)-alpha-linked backbone with alpha-D-glucose side residues attaching to an O6 atom of every second backbone residue, was considered as a model polysaccharide of a branching part of the glucan produced by oral bacteria, which was known to be related to dental plaque formation and to contribute to dental caries. The potential energy surfaces of the trisaccharide repeating unit of the branching alpha-D-glucan indicated that (1-->6)-alpha-linked side residues did not appear to interfere significantly with the backbone stereochemistry, probably due to a further separation of the three-bond-linked side residue compared with an ordinary two-bond-linked residue. Based on the n-h maps of the branching alpha-D-glucan, the side residues, when involved in a complete helix, mostly contributed additional stabilizations to particular helical structures. It was found by checking the typical helix models that formation of hydrogen bonds involving side residues was probably a major cause of the stabilization. This hydrogen bonding was expected to increase insolubility for the glucan chain--a typical, physical property observed for the bacterial alpha-D-glucan--by introducing its backbone stereochemistry as an additional stiff feature.
使用n-h映射技术，并结合MM3生成的关于主链糖苷键构象的松弛残基能量图计算，对高度分支的(1→3)-α-D-葡聚糖可能的规则螺旋结构进行了系统搜索。由(1→3)-α-连接的主链和连接到每隔一个主链残基的O6原子上的α-D-葡萄糖侧链残基组成的α-D-葡聚糖，被视为口腔细菌产生的葡聚糖分支部分的模型多糖，已知其与牙菌斑形成有关并导致龋齿。分支α-D-葡聚糖三糖重复单元的势能面表明，(1→6)-α-连接的侧链残基似乎不会对主链立体化学产生显著干扰，这可能是由于与普通的双键连接残基相比，三键连接的侧链残基进一步分离。基于分支α-D-葡聚糖的n-h图，侧链残基在参与完整螺旋时，大多对特定的螺旋结构有额外的稳定作用。通过检查典型的螺旋模型发现，涉及侧链残基的氢键形成可能是稳定的主要原因。预计这种氢键作用会通过引入主链立体化学作为额外的刚性特征，增加葡聚糖链的不溶性——这是细菌α-D-葡聚糖观察到的典型物理性质。
