Sletmoen Marit, Christensen Bjørn E, Stokke Bjørn T
Biophysics and Medical Technology, Department of Physics, The Norwegian University of Science and Technology, NTNU, NO-7491 Trondheim, Norway.
Carbohydr Res. 2005 Apr 11;340(5):971-9. doi: 10.1016/j.carres.2005.01.026.
Comb-like branched (1-->3)-beta-D-glucans dissolve in water as stiff triple-helical structures. Dissociation followed by re-association leads to the formation of a blend of various macromolecular topologies, where the cyclic species make up a significant fraction. In this study, the molecular properties of these nanosized cyclic structures of (1-->3)-beta-D-glucans were probed using a combination of AFM and SEC-MALLS. The cyclic structures were obtained by subjecting linear triple-helical molecules of (1-->3)-beta-D-glucans to a denaturation-renaturation cycle, and the fraction of cyclic structures in the renatured sample was determined by AFM. Samples containing different known fractions of linear and circular molecules were studied by SEC with online multi-angle laser-light scattering and viscometric detectors. The molecular weight and the radius of gyration of the molecules eluting from the SEC column, as well as the concentration and the intrinsic viscosity, were determined simultaneously. By extrapolating the results to a situation of only circular species, the results allowed to determine the linear mass per unit length (M(L)) of not only the linear but also the circular morphologies of the (1-->3)-beta-D-glucans. The values obtained were M(L)=2140+/-180 g mol(-1)nm(-1) for the circular species and 2045+/-80 g mol(-1)nm(-1) for the linear species. This is the first direct determination of the M(L) parameter of the circular topology, and the results indicate that the reassociation of the individual chains yield a triplex structure also for the circular morphology, similar to the initial triple helix.
梳状支化的(1→3)-β-D-葡聚糖以刚性三螺旋结构溶解于水中。解离后再缔合会导致形成各种大分子拓扑结构的混合物，其中环状物种占相当大的比例。在本研究中，使用原子力显微镜（AFM）和尺寸排阻色谱-多角度激光光散射联用技术（SEC-MALLS）相结合的方法对这些(1→3)-β-D-葡聚糖纳米级环状结构的分子性质进行了探究。通过使(1→3)-β-D-葡聚糖的线性三螺旋分子经历变性-复性循环来获得环状结构，并用AFM测定复性样品中环状结构的比例。通过配备在线多角度激光光散射和粘度检测器的SEC对含有不同已知比例线性和环状分子的样品进行了研究。同时测定了从SEC柱中洗脱的分子的分子量、回转半径以及浓度和特性粘度。通过将结果外推到仅存在环状物种的情况，这些结果不仅可以确定(1→3)-β-D-葡聚糖线性形态的单位长度线质量（M(L)），还可以确定其环状形态的单位长度线质量。得到的环状物种的值为M(L)=2140±180 g mol⁻¹nm⁻¹，线性物种的值为2045±80 g mol⁻¹nm⁻¹。这是首次直接测定环状拓扑结构的M(L)参数，结果表明单个链的重新缔合也会为环状形态产生三链结构，类似于初始的三螺旋结构。
