Falch BH, Elgsaeter A, Stokke BT
The Norwegian Biopolymer Laboratory, Department of Physics, Sem Saelands vei 9, The Norwegian University of Science and Technology, NTNU, N-7491 Trondheim, Norway.
Biopolymers. 1999 Oct 15;50(5):496-512. doi: 10.1002/(SICI)1097-0282(19991015)50:5<496::AID-BIP4>3.0.CO;2-7.
The immunologically important (1 --> 6) comb-like branched (1 --> 3)-beta-D-glucans scleroglucan, schizophyllan, lentinan, and others, exist mainly as linear triple-helical structures in aqueous solution. Partial interconversion from linear to circular topology has been reported to take place following conformational transition of the triple-helical structure and subsequent regeneration of the triplex conformation. We here report on experimental data indicating that complete strand separation of the triple-helical structure is required for this interconversion. NaOH or dimethylsulfoxide was used to induce dissociation of the triplex at combinations of concentrations and temperatures shown by calorimetry to yield a conformational transition of the triplex structures. For the alkaline treatment at 55 degrees C, it is found that up to about 30% of the material readily can be converted to the cyclic topology. This fraction increased to about 60% when the subsequent annealing of the scleroglucan in aqueous solution at pH 7 was carried out at 100 degrees C. Further increase of the annealing temperature yielded a smaller relative amount of cyclic species. The data indicate that the lower molecular weight fraction of the molecular weight distributions can be converted selectively to the macrocyclic topology by conditions that do not yield complete strand separation of the whole sample. These findings add to previous reports by providing more details about how the conditions required for the linear triplex to macrocycle interconversion relate to the conformational properties of the triple-helical structure. Copyright 1999 John Wiley & Sons, Inc.
具有免疫重要性的（1→6）梳状支链（1→3）-β-D-葡聚糖，如硬葡聚糖、裂褶菌多糖、香菇多糖等，在水溶液中主要以线性三螺旋结构存在。据报道，在三螺旋结构发生构象转变并随后三链构象再生后，会发生从线性拓扑到环状拓扑的部分相互转化。我们在此报告的实验数据表明，这种相互转化需要三螺旋结构完全链分离。使用氢氧化钠或二甲基亚砜在量热法显示的浓度和温度组合下诱导三链解离，以产生三链结构的构象转变。对于55℃的碱性处理，发现高达约30%的物质很容易转化为环状拓扑结构。当在100℃对硬葡聚糖在pH 7的水溶液中进行后续退火时，这一比例增加到约60%。退火温度的进一步升高导致环状物种的相对量减少。数据表明，分子量分布中较低分子量部分可以通过不会导致整个样品完全链分离的条件选择性地转化为大环拓扑结构。这些发现通过提供更多关于线性三链到大环相互转化所需条件与三螺旋结构构象性质之间关系的细节，补充了先前的报道。版权所有1999约翰威立父子公司。
